ANIMA WG                                                  T. Eckert, Ed.
Internet-Draft                                             Futurewei USA
Intended status: Standards Track                       M. Behringer, Ed.
Expires: August 6, 2020
                                                            S. Bjarnason
                                                          Arbor Networks
                                                        February 3, 2020

                    An Autonomic Control Plane (ACP)


   Autonomic functions need a control plane to communicate, which
   depends on some addressing and routing.  This Autonomic Management
   and Control Plane should ideally be self-managing, and as independent
   as possible of configuration.  This document defines such a plane and
   calls it the "Autonomic Control Plane", with the primary use as a
   control plane for autonomic functions.  It also serves as a "virtual
   out-of-band channel" for Operations Administration and Management
   (OAM) communications over a network that provides automatically
   configured hop-by-hop authenticated and encrypted communications via
   automatically configured IPv6 even when the network is not
   configured, or misconfigured.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on August 6, 2020.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents

   1.  Introduction (Informative)  . . . . . . . . . . . . . . . . .   5
     1.1.  Applicability and Scope . . . . . . . . . . . . . . . . .   8
   2.  Acronyms and Terminology (Informative)  . . . . . . . . . . .   9
   3.  Use Cases for an Autonomic Control Plane (Informative)  . . .  15
     3.1.  An Infrastructure for Autonomic Functions . . . . . . . .  15
     3.2.  Secure Bootstrap over a not configured Network  . . . . .  15
     3.3.  Data-Plane Independent Permanent Reachability . . . . . .  16
   4.  Requirements (Informative)  . . . . . . . . . . . . . . . . .  17
   5.  Overview (Informative)  . . . . . . . . . . . . . . . . . . .  18
   6.  Self-Creation of an Autonomic Control Plane (ACP) (Normative)  20
     6.1.  ACP Domain, Certificate and Network . . . . . . . . . . .  20
       6.1.1.  ACP Certificates  . . . . . . . . . . . . . . . . . .  21
       6.1.2.  ACP Certificate ACP Domain Information Field  . . . .  23
       6.1.3.  ACP domain membership check . . . . . . . . . . . . .  27
       6.1.4.  Trust Points and Trust Anchors  . . . . . . . . . . .  29
       6.1.5.  Certificate and Trust Point Maintenance . . . . . . .  30  GRASP objective for EST server  . . . . . . . . .  31  Renewal . . . . . . . . . . . . . . . . . . . . .  32  Certificate Revocation Lists (CRLs) . . . . . . .  32  Lifetimes . . . . . . . . . . . . . . . . . . . .  33  Re-enrollment . . . . . . . . . . . . . . . . . .  33  Failing Certificates  . . . . . . . . . . . . . .  35
     6.2.  ACP Adjacency Table . . . . . . . . . . . . . . . . . . .  35
     6.3.  Neighbor Discovery with DULL GRASP  . . . . . . . . . . .  36
     6.4.  Candidate ACP Neighbor Selection  . . . . . . . . . . . .  39
     6.5.  Channel Selection . . . . . . . . . . . . . . . . . . . .  39
     6.6.  Candidate ACP Neighbor verification . . . . . . . . . . .  43
     6.7.  Security Association (Secure Channel) protocols . . . . .  43
       6.7.1.  ACP via IPsec . . . . . . . . . . . . . . . . . . . .  44  Native IPsec  . . . . . . . . . . . . . . . . . .  44  IPsec with GRE encapsulation  . . . . . . . . . .  47
       6.7.2.  ACP via DTLS  . . . . . . . . . . . . . . . . . . . .  48
       6.7.3.  ACP Secure Channel Requirements . . . . . . . . . . .  48
     6.8.  GRASP in the ACP  . . . . . . . . . . . . . . . . . . . .  49
       6.8.1.  GRASP as a core service of the ACP  . . . . . . . . .  49
       6.8.2.  ACP as the Security and Transport substrate for GRASP  50

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  Discussion  . . . . . . . . . . . . . . . . . . .  52
     6.9.  Context Separation  . . . . . . . . . . . . . . . . . . .  53
     6.10. Addressing inside the ACP . . . . . . . . . . . . . . . .  54
       6.10.1.  Fundamental Concepts of Autonomic Addressing . . . .  54
       6.10.2.  The ACP Addressing Base Scheme . . . . . . . . . . .  56
       6.10.3.  ACP Zone Addressing Sub-Scheme . . . . . . . . . . .  57  Usage of the Zone-ID Field . . . . . . . . . . .  59
       6.10.4.  ACP Manual Addressing Sub-Scheme . . . . . . . . . .  60
       6.10.5.  ACP Vlong Addressing Sub-Scheme  . . . . . . . . . .  61
       6.10.6.  Other ACP Addressing Sub-Schemes . . . . . . . . . .  62
       6.10.7.  ACP Registrars . . . . . . . . . . . . . . . . . . .  62  Use of BRSKI or other Mechanism/Protocols  . . .  63  Unique Address/Prefix allocation . . . . . . . .  63  Addressing Sub-Scheme Policies . . . . . . . . .  64  Address/Prefix Persistence . . . . . . . . . . .  65  Further Details  . . . . . . . . . . . . . . . .  65
     6.11. Routing in the ACP  . . . . . . . . . . . . . . . . . . .  65
       6.11.1.  RPL Profile  . . . . . . . . . . . . . . . . . . . .  66  Overview . . . . . . . . . . . . . . . . . . . .  66  RPL Instances  . . . . . . . . . . . . . . . . .  68  Storing vs. Non-Storing Mode . . . . . . . . . .  68  DAO Policy . . . . . . . . . . . . . . . . . . .  68  Path Metric  . . . . . . . . . . . . . . . . . .  68  Objective Function . . . . . . . . . . . . . . .  68  DODAG Repair . . . . . . . . . . . . . . . . . .  68  Multicast  . . . . . . . . . . . . . . . . . . .  69  Security . . . . . . . . . . . . . . . . . . . .  69 P2P communications . . . . . . . . . . . . . . .  69 IPv6 address configuration . . . . . . . . . . .  69 Administrative parameters  . . . . . . . . . . .  69 RPL Data-Plane artifacts . . . . . . . . . . . .  70 Unknown Destinations . . . . . . . . . . . . . .  70
     6.12. General ACP Considerations  . . . . . . . . . . . . . . .  70
       6.12.1.  Performance  . . . . . . . . . . . . . . . . . . . .  70
       6.12.2.  Addressing of Secure Channels  . . . . . . . . . . .  71
       6.12.3.  MTU  . . . . . . . . . . . . . . . . . . . . . . . .  71
       6.12.4.  Multiple links between nodes . . . . . . . . . . . .  72
       6.12.5.  ACP interfaces . . . . . . . . . . . . . . . . . . .  72
   7.  ACP support on L2 switches/ports (Normative)  . . . . . . . .  75
     7.1.  Why (Benefits of ACP on L2 switches)  . . . . . . . . . .  75
     7.2.  How (per L2 port DULL GRASP)  . . . . . . . . . . . . . .  76
   8.  Support for Non-ACP Components (Normative)  . . . . . . . . .  78
     8.1.  ACP Connect . . . . . . . . . . . . . . . . . . . . . . .  78
       8.1.1.  Non-ACP Controller / NMS system . . . . . . . . . . .  78
       8.1.2.  Software Components . . . . . . . . . . . . . . . . .  80
       8.1.3.  Auto Configuration  . . . . . . . . . . . . . . . . .  81
       8.1.4.  Combined ACP/Data-Plane Interface (VRF Select)  . . .  82
       8.1.5.  Use of GRASP  . . . . . . . . . . . . . . . . . . . .  83

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     8.2.  ACP through Non-ACP L3 Clouds (Remote ACP neighbors)  . .  84
       8.2.1.  Configured Remote ACP neighbor  . . . . . . . . . . .  84
       8.2.2.  Tunneled Remote ACP Neighbor  . . . . . . . . . . . .  86
       8.2.3.  Summary . . . . . . . . . . . . . . . . . . . . . . .  86
   9.  Benefits (Informative)  . . . . . . . . . . . . . . . . . . .  86
     9.1.  Self-Healing Properties . . . . . . . . . . . . . . . . .  86
     9.2.  Self-Protection Properties  . . . . . . . . . . . . . . .  88
       9.2.1.  From the outside  . . . . . . . . . . . . . . . . . .  88
       9.2.2.  From the inside . . . . . . . . . . . . . . . . . . .  89
     9.3.  The Administrator View  . . . . . . . . . . . . . . . . .  89
   10. ACP Operations (Informative)  . . . . . . . . . . . . . . . .  90
     10.1.  ACP (and BRSKI) Diagnostics  . . . . . . . . . . . . . .  91
     10.2.  ACP Registrars . . . . . . . . . . . . . . . . . . . . .  95
       10.2.1.  Registrar interactions . . . . . . . . . . . . . . .  95
       10.2.2.  Registrar Parameter  . . . . . . . . . . . . . . . .  96
       10.2.3.  Certificate renewal and limitations  . . . . . . . .  97
       10.2.4.  ACP Registrars with sub-CA . . . . . . . . . . . . .  98
       10.2.5.  Centralized Policy Control . . . . . . . . . . . . .  98
     10.3.  Enabling and disabling ACP/ANI . . . . . . . . . . . . .  99
       10.3.1.  Filtering for non-ACP/ANI packets  . . . . . . . . .  99
       10.3.2.  Admin Down State . . . . . . . . . . . . . . . . . . 100  Security . . . . . . . . . . . . . . . . . . . . 101  Fast state propagation and Diagnostics . . . . . 101  Low Level Link Diagnostics . . . . . . . . . . . 102  Power Consumption Issues . . . . . . . . . . . . 102
       10.3.3.  Interface level ACP/ANI enable . . . . . . . . . . . 103
       10.3.4.  Which interfaces to auto-enable? . . . . . . . . . . 103
       10.3.5.  Node Level ACP/ANI enable  . . . . . . . . . . . . . 104  Brownfield nodes . . . . . . . . . . . . . . . . 105  Greenfield nodes . . . . . . . . . . . . . . . . 105
       10.3.6.  Undoing ANI/ACP enable . . . . . . . . . . . . . . . 106
       10.3.7.  Summary  . . . . . . . . . . . . . . . . . . . . . . 106
     10.4.  Configuration and the ACP (summary)  . . . . . . . . . . 107
   11. Security Considerations . . . . . . . . . . . . . . . . . . . 108
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 111
   13. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . 111
   14. Change log [RFC Editor: Please remove]  . . . . . . . . . . . 112
     14.1.  Summary of changes since entering IESG review  . . . . . 112
       14.1.1.  Reviews (while in IESG review status) / status . . . 112
       14.1.2.  BRSKI / ACP registrar related enhancements . . . . . 113
       14.1.3.  Normative enhancements since start of IESG review  . 113
       14.1.4.  Explanatory enhancements since start of IESG review  114
     14.2.  draft-ietf-anima-autonomic-control-plane-22  . . . . . . 115
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . . 117
     15.1.  Normative References . . . . . . . . . . . . . . . . . . 117
     15.2.  Informative References . . . . . . . . . . . . . . . . . 120
     15.3.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 127
   Appendix A.  Background and Futures (Informative) . . . . . . . . 127

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     A.1.  ACP Address Space Schemes . . . . . . . . . . . . . . . . 127
     A.2.  BRSKI Bootstrap (ANI) . . . . . . . . . . . . . . . . . . 128
     A.3.  ACP Neighbor discovery protocol selection . . . . . . . . 129
       A.3.1.  LLDP  . . . . . . . . . . . . . . . . . . . . . . . . 129
       A.3.2.  mDNS and L2 support . . . . . . . . . . . . . . . . . 129
       A.3.3.  Why DULL GRASP  . . . . . . . . . . . . . . . . . . . 130
     A.4.  Choice of routing protocol (RPL)  . . . . . . . . . . . . 130
     A.5.  ACP Information Distribution and multicast  . . . . . . . 131
     A.6.  Extending ACP channel negotiation (via GRASP) . . . . . . 132
     A.7.  CAs, domains and routing subdomains . . . . . . . . . . . 134
     A.8.  Intent for the ACP  . . . . . . . . . . . . . . . . . . . 135
     A.9.  Adopting ACP concepts for other environments  . . . . . . 136
     A.10. Further (future) options  . . . . . . . . . . . . . . . . 138
       A.10.1.  Auto-aggregation of routes . . . . . . . . . . . . . 138
       A.10.2.  More options for avoiding IPv6 Data-Plane dependency 138
       A.10.3.  ACP APIs and operational models (YANG) . . . . . . . 139
       A.10.4.  RPL enhancements . . . . . . . . . . . . . . . . . . 139
       A.10.5.  Role assignments . . . . . . . . . . . . . . . . . . 140
       A.10.6.  Autonomic L3 transit . . . . . . . . . . . . . . . . 141
       A.10.7.  Diagnostics  . . . . . . . . . . . . . . . . . . . . 141
       A.10.8.  Avoiding and dealing with compromised ACP nodes  . . 142
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . 143

1.  Introduction (Informative)

   Autonomic Networking is a concept of self-management: Autonomic
   functions self-configure, and negotiate parameters and settings
   across the network.  [RFC7575] defines the fundamental ideas and
   design goals of Autonomic Networking.  A gap analysis of Autonomic
   Networking is given in [RFC7576].  The reference architecture for
   Autonomic Networking in the IETF is specified in the document

   Autonomic functions need an autonomically built communications
   infrastructure.  This infrastructure needs to be secure, resilient
   and re-usable by all autonomic functions.  Section 5 of [RFC7575]
   introduces that infrastructure and calls it the Autonomic Control
   Plane (ACP).  More descriptively it would be the "Autonomic
   communications infrastructure for Management and Control".  For
   naming consistency with that prior document, this document continues
   to use the name ACP though.

   Today, the management and control plane of networks typically uses a
   routing and forwarding table which is dependent on correct
   configuration and routing.  Misconfigurations or routing problems can
   disrupt management and control channels.  Traditionally, an out-of-
   band network has been used to avoid or allow recovery from such
   problems, or personnel are sent on site to access devices through

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   out-of-band management ports (also called craft ports, serial
   console, management ethernet port).  However, both options are

   In increasingly automated networks either centralized management
   systems or distributed autonomic service agents in the network
   require a control plane which is independent of the configuration of
   the network they manage, to avoid impacting their own operations
   through the configuration actions they take.

   This document describes a modular design for a self-forming, self-
   managing and self-protecting Autonomic Control Plane (ACP), which is
   a virtual in-band network designed to be as independent as possible
   of configuration, addressing and routing problems.  The details how
   this is achieved are described in Section 6.  The ACP is designed to
   remain operational even in the presence of configuration errors,
   addressing or routing issues, or where policy could inadvertently
   affect connectivity of both data packets or control packets.

   This document uses the term "Data-Plane" to refer to anything in the
   network nodes that is not the ACP, and therefore considered to be
   dependent on (mis-)configuration.  This Data-Plane includes both the
   traditional forwarding-plane, as well as any pre-existing control-
   plane, such as routing protocols that establish routing tables for
   the forwarding plane.

   The Autonomic Control Plane serves several purposes at the same time:

   1.  Autonomic functions communicate over the ACP.  The ACP therefore
       directly supports Autonomic Networking functions, as described in
       [I-D.ietf-anima-reference-model].  For example, Generic Autonomic
       Signaling Protocol (GRASP - [I-D.ietf-anima-grasp]) runs securely
       inside the ACP and depends on the ACP as its "security and
       transport substrate".

   2.  A controller or network management system can use it to securely
       bootstrap network devices in remote locations, even if the (Data-
       Plane) network in between is not yet configured; no Data-Plane
       dependent bootstrap configuration is required.  An example of
       such a secure bootstrap process is described in

   3.  An operator can use it to log into remote devices, even if the
       network is misconfigured or not configured.

   This document describes these purposes as use cases for the ACP in
   Section 3, it defines the requirements in Section 4.  Section 5 gives
   an overview how the ACP is constructed.

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   The normative part of this document starts with Section 6, where the
   ACP is specified.  Section 7 defines normative how to support ACP on
   L2 switches.  Section 8 explains normative how non-ACP nodes and
   networks can be integrated.

   The remaining sections are non-normative: Section 9 reviews benefits
   of the ACP (after all the details have been defined), Section 10
   provides operational recommendations, Appendix A provides additional
   explanations and describes additional details or future standard or
   propriety extensions that were considered not to be appropriate for
   standardization in this document but were considered important to
   document.  There are no dependencies against Appendix A to build a
   complete working and interoperable ACP according to this document.

   The ACP provides secure IPv6 connectivity, therefore it can be used
   not only as the secure connectivity for self-management as required
   for the ACP in [RFC7575], but it can also be used as the secure
   connectivity for traditional (centralized) management.  The ACP can
   be implemented and operated without any other components of autonomic
   networks, except for the GRASP protocol.  ACP relies on per-link DULL
   GRASP (see Section 6.3) to autodiscover ACP neighbors, and includes
   the ACP GRASP instance to provide service discovery for clients of
   the ACP (see Section 6.8) including for its own maintenance of ACP

   The document "Using Autonomic Control Plane for Stable Connectivity
   of Network OAM" [RFC8368] describes how the ACP alone can be used to
   provide secure and stable connectivity for autonomic and non-
   autonomic Operations Administration and Management (OAM)
   applications.  That document also explains how existing management
   solutions can leverage the ACP in parallel with traditional
   management models, when to use the ACP and how to integrate with
   potentially IPv4 only OAM backends.

   Combining ACP with Bootstrapping Remote Secure Key Infrastructures
   (BRSKI), see [I-D.ietf-anima-bootstrapping-keyinfra]) results in the
   "Autonomic Network Infrastructure" as defined in
   [I-D.ietf-anima-reference-model], which provides autonomic
   connectivity (from ACP) with secure zero-touch (automated) bootstrap
   from BRSKI.  The ANI itself does not constitute an Autonomic Network,
   but it allows the building of more or less autonomic networks on top
   of it - using either centralized, Software Defined Networking-
   (SDN-)style (see [RFC7426]) automation or distributed automation via
   Autonomic Service Agents (ASA) / Autonomic Functions (AF) - or a
   mixture of both.  See [I-D.ietf-anima-reference-model] for more

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1.1.  Applicability and Scope

   Please see the following Terminology section (Section 2) for
   explanations of terms used in this section.

   The design of the ACP as defined in this document is considered to be
   applicable to all types of "professionally managed" networks: Service
   Provider, Local Area Network (LAN), Metro(politan networks), Wide
   Area Network (WAN), Enterprise Information Technology (IT) and
   ->"Operational Technology" () (OT) networks.  The ACP can operate
   equally on layer 3 equipment and on layer 2 equipment such as bridges
   (see Section 7).  The hop-by-hop authentication and confidentiality
   mechanism used by the ACP is defined to be negotiable, therefore it
   can be extended to environments with different protocol preferences.
   The minimum implementation requirements in this document attempt to
   achieve maximum interoperability by requiring support for multiple
   options depending on the type of device: IPsec, see [RFC4301], and
   datagram Transport Layer Security version 1.2 (DTLS), see [RFC6347]).

   The implementation footprint of the ACP consists of Public Key
   Infrastructure (PKI) code for the ACP certificate, the GRASP
   protocol, UDP, TCP and TLS (for security and reliability of GRASP),
   the ACP secure channel protocol used (such as IPsec or DTLS), and an
   instance of IPv6 packet forwarding and routing via the Routing
   Protocol for Low-power and Lossy Networks (RPL), see [RFC6550], that
   is separate from routing and forwarding for the Data-Plane (user

   The ACP uses only IPv6 to avoid complexity of dual-stack ACP
   operations (IPv6/IPv4).  Nevertheless, it can without any changes be
   integrated into even otherwise IPv4-only network devices.  The Data-
   Plane itself would not need to change, it could continue to be IPv4
   only.  For such IPv4 only devices, the IPv6 protocol itself would be
   additional implementation footprint only used for the ACP.

   The protocol choices of the ACP are primarily based on wide use and
   support in networks and devices, well understood security properties
   and required scalability.  The ACP design is an attempt to produce
   the lowest risk combination of existing technologies and protocols to
   build a widely applicable operational network management solution:

   RPL was chosen because it requires a smaller routing table footprint
   in large networks compared to other routing protocols with an
   autonomically configured single area.  The deployment experience of
   large scale Internet of Things (IoT) networks serves as the basis for
   wide deployment experience with RPL.  The profile chosen for RPL in
   the ACP does not leverage any RPL specific forwarding plane features

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   (IPv6 extension headers), making its implementation a pure control
   plane software requirement.

   GRASP is the only completely novel protocol used in the ACP, and this
   choice was necessary because there is no existing suitable protocol
   to provide the necessary functions to the ACP, so GRASP was developed
   to fill that gap.

   The ACP design can be applicable to (cpu, memory) constrained devices
   and (bitrate, reliability) constrained networks, but this document
   does not attempt to define the most constrained type of devices or
   networks to which the ACP is applicable.  RPL and DTLS for ACP secure
   channels are two protocol choices already making ACP more applicable
   to constrained environments.  Support for constrained devices in this
   specification is opportunistic, but not complete, because the
   reliable transport for GRASP (see Section 6.8.2) only specifies TCP/
   TLS).  See Appendix A.9 for discussions about how future standards or
   proprietary extensions/variations of the ACP could better meet
   different expectations from those on which the current design is
   based including supporting constrained devices better.

2.  Acronyms and Terminology (Informative)

   [RFC Editor: WG/IETF/IESG review of the terms below asked for
   references between these terms when they refer to each other.  The
   only option I could fin RFC/XML to point to a hanging text acronym
   definition that also displays the actual term is the format="title"
   version, which leads to references such as '->"ACP domain
   certificate" ()'.  I found no reasonable way to eliminate the
   trailing '()' generated by this type of cross references.  Can you
   please take care of removing these artefacts during editing (after
   conversion to nroff ?).  I also created a ticket to ask for an
   xml2rfc enhancement to avoid this in the future:

   [RFC Editor: Question: Is it possible to change the first occurrences
   of [RFCxxxx] references to "rfcxxx title" [RFCxxxx]? the XML2RFC
   format does not seem to offer such a format, but I did not want to
   duplicate 50 first references - one reference for title mentioning
   and one for RFC number.]

   In the rest of the document we will refer to systems using the ACP as
   "nodes".  Typically such a node is a physical (network equipment)
   device, but it can equally be some virtualized system.  Therefore, we
   do not refer to them as devices unless the context specifically calls
   for a physical system.

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   This document introduces or uses the following terms (sorted
   alphabetically).  Terms introduced are explained on first use, so
   this list is for reference only.

   ACP:  "Autonomic Control Plane".  The Autonomic Function as defined
      in this document.  It provides secure zero-touch (automated)
      transitive (network wide) IPv6 connectivity for all nodes in the
      same ACP domain as well as a GRASP instance running across this
      ACP IPv6 connectivity.  The ACP is primarily meant to be used as a
      component of the ANI to enable Autonomic Networks but it can
      equally be used in simple ANI networks (with no other Autonomic
      Functions) or completely by itself.

   ACP address:  An IPv6 address assigned to the ACP node.  It is stored
      in the domain information field of the ->"ACP domain certificate"

   ACP address range/set:  The ACP address may imply a range or set of
      addresses that the node can assign for different purposes.  This
      address range/set is derived by the node from the format of the
      ACP address called the "addressing sub-scheme".

   ACP connect interface:  An interface on an ACP node providing access
      to the ACP for non ACP capable nodes without using an ACP secure
      channel.  See Section 8.1.1.

   ACP domain:  The ACP domain is the set of nodes with ->"ACP domain
      certificates" that allow them to authenticate each other as
      members of the ACP domain.  See also Section 6.1.3.

   ACP (ANI/AN) Domain Certificate:  A [RFC5280] certificate (LDevID)
      carrying the domain information field which is used by the ACP to
      learn its address in the ACP and to derive and cryptographically
      assert its membership in the ACP domain.

   domain information (field):  An rfc822Name information element (e.g.,
      field) in the domain certificate in which the ACP relevant
      information is encoded: the domain name and the ACP address.

   ACP Loopback interface:  The Loopback interface in the ACP Virtual
      Routing and Forwarding (VRF) that has the ACP address assigned to

   ACP network:  The ACP network constitutes all the nodes that have
      access to the ACP.  It is the set of active and transitively
      connected nodes of an ACP domain plus all nodes that get access to
      the ACP of that domain via ACP edge nodes.

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   ACP (ULA) prefix(es):  The /48 IPv6 address prefixes used across the
      ACP.  In the normal/simple case, the ACP has one ULA prefix, see
      Section 6.10.  The ACP routing table may include multiple ULA
      prefixes if the "rsub" option is used to create addresses from
      more than one ULA prefix.  See Section 6.1.2.  The ACP may also
      include non-ULA prefixes if those are configured on ACP connect
      interfaces.  See Section 8.1.1.

   ACP secure channel:  A cryptographically authenticated and encrypted
      data connection established between (normally) adjacent ACP nodes
      to carry traffic of the ACP VRF securely and isolated from Data-
      Plane traffic in-band over the same link/path as the Data-Plane.

   ACP secure channel protocol:  The protocol used to build an ACP
      secure channel, e.g., Internet Key Exchange Protocol version 2
      (IKEv2) with IPsec or Datagram Transport Layer Security (DTLS).

   ACP virtual interface:  An interface in the ACP VRF mapped to one or
      more ACP secure channels.  See Section 6.12.5.

   AN "Autonomic Network": A network according to
      [I-D.ietf-anima-reference-model].  Its main components are ANI,
      Autonomic Functions and Intent.

   (AN) Domain Name:  An FQDN (Fully Qualified Domain Name) in the
      domain information field of the Domain Certificate.  See
      Section 6.1.2.

   ANI (nodes/network):  "Autonomic Network Infrastructure".  The ANI is
      the infrastructure to enable Autonomic Networks.  It includes ACP,
      BRSKI and GRASP.  Every Autonomic Network includes the ANI, but
      not every ANI network needs to include autonomic functions beyond
      the ANI (nor Intent).  An ANI network without further autonomic
      functions can for example support secure zero-touch (automated)
      bootstrap and stable connectivity for SDN networks - see

   ANIMA:  "Autonomic Networking Integrated Model and Approach".  ACP,
      BRSKI and GRASP are products of the IETF ANIMA working group.

   ASA:  "Autonomic Service Agent".  Autonomic software modules running
      on an ANI device.  The components making up the ANI (BRSKI, ACP,
      GRASP) are also described as ASAs.

   Autonomic Function:  A function/service in an Autonomic Network (AN)
      composed of one or more ASA across one or more ANI nodes.

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   BRSKI:  "Bootstrapping Remote Secure Key Infrastructures"
      ([I-D.ietf-anima-bootstrapping-keyinfra].  A protocol extending
      EST to enable secure zero-touch bootstrap in conjunction with ACP.
      ANI nodes use ACP, BRSKI and GRASP.

   Data-Plane:  The counterpoint to the ACP VRF in an ACP node: all
      routing and forwarding in the node other than the ACP VRF.  In a
      simple ACP or ANI node, the Data-Plane is typically provisioned by
      means other than autonomically, for example manually (including
      across the ACP) or via SDN controllers.  In a fully Autonomic
      Network node, the Data-Plane is managed autonomically via
      Autonomic Functions and Intent.  Note that other (non-ANIMA) RFCs
      use the Data-Plane to refer to what is better called the
      forwarding plane.  This is not the way the term is used in this

   device:  A physical system, or physical node.

   Enrollment:  The process where a node presents identification (for
      example through keying material such as the private key of an
      IDevID) to a network and acquires a network specific identity uch
      as an LDevID and trust anchors such as Certificate Authority (CA)

   EST:  "Enrollment over Secure Transport" ([RFC7030]).  IETF standard-
      track protocol for enrollment of a node with an LDevID.  BRSKI is
      based on EST.

   GRASP:  "Generic Autonomic Signaling Protocol".  An extensible
      signaling protocol required by the ACP for ACP neighbor discovery.

      The ACP also provides the "security and transport substrate" for
      the "ACP instance of GRASP".  This instance of GRASP runs across
      the ACP secure channels to support BRSKI and other NOC/OAM or
      Autonomic Functions.  See [I-D.ietf-anima-grasp].

   IDevID:  An "Initial Device IDentity" X.509 certificate installed by
      the vendor on new equipment.  Contains information that
      establishes the identity of the node in the context of its vendor/
      manufacturer such as device model/type and serial number.  See
      [AR8021].  IDevID cannot be used for the ACP because they are not
      provisioned by the owner of the network, so they can not directly
      indicate an ACP domain they belong to.

   in-band (management):  The type of management used predominantly in
      IP based networks, not leveraging an ->"out-of-band network" ().
      In in-band management, access to the managed equipment depends on
      the configuration of this equipment itself: interface, addressing,

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      forwarding, routing, policy, security, management.  This
      dependency makes in-band management fragile because the
      configuration actions performed may break in-band management
      connectivity.  Breakage can not only be unintentional, it can
      simply be an unavoidable side effect of being unable to create
      configuration schemes where in-band management connectivity
      configuration is unaffected by Data-Plane configuration.  See also
      ->"(virtual) out-of-band network" ().

   Intent:  Policy language of an autonomic network according to

   Loopback interface:  The conventional name for an internal IP
      interface to which addresses may be assigned, but which transmits
      no external traffic.

   LDevID:  A "Local Device IDentity" is an X.509 certificate installed
      during "enrollment".  The Domain Certificate used by the ACP is an
      LDevID.  See [AR8021].

   MIC:  "Manufacturer Installed Certificate".  This is another word to
      describe an IDevID in referenced materials.  This term is not used
      in this document.

   native interface:  Interfaces existing on a node without
      configuration of the already running node.  On physical nodes
      these are usually physical interfaces.  On virtual nodes their

   node:  A system, e.g., supporting the ACP according to this document.
      Can be virtual or physical.  Physical nodes are called devices.

   Node-ID:  The identifier of an ACP node inside that ACP.  It is the
      last 64 (see Section 6.10.3) or 78-bits (see Section 6.10.5) of
      the ACP address.

   Operational Technology (OT):  "
      Operational_Technology" [1]: "The hardware and software dedicated
      to detecting or causing changes in physical processes through
      direct monitoring and/or control of physical devices such as
      valves, pumps, etc.".  OT networks are today in most cases well
      separated from Information Technology (IT) networks.

   (virtual) out-of-band network:  An out-of-band network is a secondary
      network used to manage a primary network.  The equipment of the
      primary network is connected to the out-of-band network via
      dedicated management ports on the primary network equipment.
      Serial (console) management ports were historically most common,

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      higher end network equipment now also has ethernet ports dedicated
      only for management.  An out-of-band network provides management
      access to the primary network independent of the configuration
      state of the primary network.  One of the goals of the ACP is to
      provide this benefit of out-of-band networks virtually on the
      primary network equipment.  The ACP VRF acts as a virtual out of
      band network device providing configuration independent management
      access.  The ACP secure channels are the virtual links of the ACP
      virtual out-of-band network, meant to be operating independent of
      the configuration of the primary network.  See also ->"in-band
      (management)" ().

   RPL:  "IPv6 Routing Protocol for Low-Power and Lossy Networks".  The
      routing protocol used in the ACP.  See [RFC6550].

   MASA (service):  "Manufacturer Authorized Signing Authority".  A
      vendor/manufacturer or delegated cloud service on the Internet
      used as part of the BRSKI protocol.

   (ACP/ANI/BRSKI) Registrar:  An ACP registrar is an entity (software
      and/or person) that is orchestrating the enrollment of ACP nodes
      with the ACP domain certificate.  ANI nodes use BRSKI, so ANI
      registrars are also called BRSKI registrars.  For non-ANI ACP
      nodes, the registrar mechanisms are undefined by this document.
      See Section 6.10.7.  Renewal and other maintenance (such as
      revocation) of ACP domain certificates may be performed by other
      entities than registrars.  EST must be supported for ACP domain
      certificate renewal (see Section 6.1.5).  BRSKI is an extension of
      EST, so ANI/BRSKI registrars can easily support ACP domain
      certificate renewal in addition to initial enrollment.

   sUDI:  "secured Unique Device Identifier".  This is another word to
      describe an IDevID in referenced material.  This term is not used
      in this document.

   UDI:  "Unique Device Identifier".  In the context of this document
      unsecured identity information of a node typically consisting of
      at least device model/type and serial number, often in a vendor
      specific format.  See sUDI and LDevID.

   ULA: (Global ID prefix)  A "Unique Local Address" (ULA) is an IPv6
      address in the block fc00::/7, defined in [RFC4193].  It is the
      approximate IPv6 counterpart of the IPv4 private address
      ([RFC1918]).  The ULA Global ID prefix are the first 48-bits of a
      ULA address.  In this document it is abbreviated as "ULA prefix".

   (ACP) VRF:  The ACP is modeled in this document as a "Virtual Routing
      and Forwarding" instance (VRF).  This means that it is based on a

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      "virtual router" consisting of a separate IPv6 forwarding table to
      which the ACP virtual interfaces are attached and an associated
      IPv6 routing table separate from the Data-Plane.  Unlike the VRFs
      on MPLS/VPN-PE ([RFC4364]) or LISP XTR ([RFC6830]), the ACP VRF
      does not have any special "core facing" functionality or routing/
      mapping protocols shared across multiple VRFs.  In vendor products
      a VRF such as the ACP-VRF may also be referred to as a so called

   (ACP) Zone:  An ACP zone is a set of ACP nodes using the same zone
      field value in their ACP address according to Section 6.10.3.
      Zones are a mechanism to support structured addressing of ACP
      addresses within the same /48-bit ULA prefix.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119],[RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Use Cases for an Autonomic Control Plane (Informative)

   This section summarizes the use cases that are intended to be
   supported by an ACP.  To understand how these are derived from and
   relate to the larger set of use cases for autonomic networks, please
   refer to [RFC8316].

3.1.  An Infrastructure for Autonomic Functions

   Autonomic Functions need a stable infrastructure to run on, and all
   autonomic functions should use the same infrastructure to minimize
   the complexity of the network.  In this way, there is only need for a
   single discovery mechanism, a single security mechanism, and single
   instances of other processes that distributed functions require.

3.2.  Secure Bootstrap over a not configured Network

   Today, bootstrapping a new node typically requires all nodes between
   a controlling node such as an SDN controller ("Software Defined
   Networking", see [RFC7426]) and the new node to be completely and
   correctly addressed, configured and secured.  Bootstrapping and
   configuration of a network happens in rings around the controller -
   configuring each ring of devices before the next one can be
   bootstrapped.  Without console access (for example through an out-of-
   band network) it is not possible today to make devices securely
   reachable before having configured the entire network leading up to

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   With the ACP, secure bootstrap of new devices and whole new networks
   can happen without requiring any configuration of unconfigured
   devices along the path: As long as all devices along the path support
   ACP and a zero-touch bootstrap mechanism such as BRSKI, the ACP
   across a whole network of unconfigured devices can be brought up
   without operator/provisioning intervention.  The ACP also provides
   additional security for any bootstrap mechanism, because it can
   provide encrypted discovery (via ACP GRASP) of registrars or other
   bootstrap servers by bootstrap proxies connecting to nodes that are
   to be bootstrapped and the ACP encryption hides the identities of the
   communicating entities (pledge and registrar), making it more
   difficult to learn which network node might be attackable.  The ACP
   domain certificate can also be used to end-to-end encrypt the
   bootstrap communication between such proxies and server.  Note that
   bootstrapping here includes not only the first step that can be
   provided by BRSKI (secure keys), but also later stages where
   configuration is bootstrapped.

3.3.  Data-Plane Independent Permanent Reachability

   Today, most critical control plane protocols and network management
   protocols are using the Data-Plane of the network.  This leads to
   often undesirable dependencies between control and management plane
   on one side and the Data-Plane on the other: Only if the forwarding
   and control plane of the Data-Plane are configured correctly, will
   the Data-Plane and the management plane work as expected.

   Data-Plane connectivity can be affected by errors and faults, for
   example misconfigurations that make AAA (Authentication,
   Authorization and Accounting) servers unreachable or can lock an
   administrator out of a device; routing or addressing issues can make
   a device unreachable; shutting down interfaces over which a current
   management session is running can lock an admin irreversibly out of
   the device.  Traditionally only out-of-band access can help recover
   from such issues (such as serial console or ethernet management

   Data-Plane dependencies also affect applications in a Network
   Operations Center (NOC) such as SDN controller applications: Certain
   network changes are today hard to implement, because the change
   itself may affect reachability of the devices.  Examples are address
   or mask changes, routing changes, or security policies.  Today such
   changes require precise hop-by-hop planning.

   Note that specific control plane functions for the Data-Plane often
   want to depend on forwarding of their packets via the Data-Plane:
   Aliveness and routing protocol signaling packets across the Data-
   Plane to verify reachability across the Data-Plane, using IPv4

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   signaling packets for IPv4 routing vs. IPv6 signaling packets for
   IPv6 routing.

   Assuming appropriate implementation (see Section 6.12.2 for more
   details), the ACP provides reachability that is independent of the
   Data-Plane.  This allows the control plane and management plane to
   operate more robustly:

   o  For management plane protocols, the ACP provides the functionality
      of a Virtual out-of-band (VooB) channel, by providing connectivity
      to all nodes regardless of their Data-Plane configuration, routing
      and forwarding tables.

   o  For control plane protocols, the ACP allows their operation even
      when the Data-Plane is temporarily faulty, or during transitional
      events, such as routing changes, which may affect the control
      plane at least temporarily.  This is specifically important for
      autonomic service agents, which could affect Data-Plane

   The document "Using Autonomic Control Plane for Stable Connectivity
   of Network OAM" [RFC8368] explains this use case for the ACP in
   significantly more detail and explains how the ACP can be used in
   practical network operations.

4.  Requirements (Informative)

   The following requirements were identified for the design of the ACP
   based on the above use-cases (Section 3).  These requirements are
   informative.  The ACP as specified in the normative parts of this
   document is meeting or exceeding these use-case requirements:

   ACP1:  The ACP should provide robust connectivity: As far as
          possible, it should be independent of configured addressing,
          configuration and routing.  Requirements 2 and 3 build on this
          requirement, but also have value on their own.

   ACP2:  The ACP must have a separate address space from the Data-
          Plane.  Reason: traceability, debug-ability, separation from
          Data-Plane, infrastructure security (filtering based on known
          address space).

   ACP3:  The ACP must use autonomically managed address space.  Reason:
          easy bootstrap and setup ("autonomic"); robustness (admin
          cannot break network easily).  This document suggests using
          ULA addressing for this purpose ("Unique Local Address", see

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   ACP4:  The ACP must be generic, that is it must be usable by all the
          functions and protocols of the ANI.  Clients of the ACP must
          not be tied to a particular application or transport protocol.

   ACP5:  The ACP must provide security: Messages coming through the ACP
          must be authenticated to be from a trusted node, and should
          (very strong should) be encrypted.

   Explanation for ACP4: In a fully autonomic network (AN), newly
   written ASA could potentially all communicate exclusively via GRASP
   with each other, and if that was assumed to be the only requirement
   against the ACP, it would not need to provide IPv6 layer connectivity
   between nodes, but only GRASP connectivity.  Nevertheless, because
   ACP also intends to support non-AN networks, it is crucial to support
   IPv6 layer connectivity across the ACP to support any transport and
   application layer protocols.

   The ACP operates hop-by-hop, because this interaction can be built on
   IPv6 link local addressing, which is autonomic, and has no dependency
   on configuration (requirement 1).  It may be necessary to have ACP
   connectivity across non-ACP nodes, for example to link ACP nodes over
   the general Internet.  This is possible, but introduces a dependency
   against stable/resilient routing over the non-ACP hops (see
   Section 8.2).

5.  Overview (Informative)

   The Autonomic Control Plane is constructed in the following way (for
   details, see Section 6):

   1.  An ACP node creates a Virtual Routing and Forwarding (VRF)
       instance, or a similar virtual context.

   2.  It determines, following a policy, a candidate peer list.  This
       is the list of nodes to which it should establish an Autonomic
       Control Plane.  Default policy is: To all link-layer adjacent
       nodes supporting ACP.

   3.  For each node in the candidate peer list, it authenticates that
       node (according to Section 6.1.3) and negotiates a mutually
       acceptable channel type.

   4.  For each node in the candidate peer list, it then establishes a
       secure tunnel of the negotiated channel type.  The resulting
       tunnels are then placed into the previously set up VRF.  This
       creates an overlay network with hop-by-hop tunnels.

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   5.  Inside the ACP VRF, each node assigns its ULA IPv6 address to a
       Loopback interface assigned to the ACP VRF.

   6.  Each node runs a lightweight routing protocol, to announce
       reachability of the virtual addresses inside the ACP (see
       Section 6.12.5).


   o  Non-ACP NMS ("Network Management Systems") or SDN controllers have
      to be explicitly configured for connection into the ACP.

   o  Connecting over non-ACP Layer-3 clouds requires explicit
      configuration.  See Section 8.2.

   o  None of the above operations (except explicit configured ones) are
      reflected in the configuration of the node.

   The following figure illustrates the ACP.

             ACP node 1                          ACP node 2
          ...................               ...................
   secure .                 .   secure      .                 .  secure
   channel:  +-----------+  :   channel     :  +-----------+  : channel
   ..--------| ACP VRF   |---------------------| ACP VRF   |---------..
          : / \         / \   <--routing-->   / \         / \ :
          : \ /         \ /                   \ /         \ / :
   ..--------| Loopback  |---------------------| Loopback  |---------..
          :  | interface |  :               :  | interface |  :
          :  +-----------+  :               :  +-----------+  :
          :                 :               :                 :
          :   Data-Plane    :...............:   Data-Plane    :
          :                 :    link       :                 :
          :.................:               :.................:

                   Figure 1: ACP VRF and secure channels

   The resulting overlay network is normally based exclusively on hop-
   by-hop tunnels.  This is because addressing used on links is IPv6
   link local addressing, which does not require any prior set-up.  In
   this way the ACP can be built even if there is no configuration on
   the node, or if the Data-Plane has issues such as addressing or
   routing problems.

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6.  Self-Creation of an Autonomic Control Plane (ACP) (Normative)

   This section describes the components and steps to set up an
   Autonomic Control Plane (ACP), and highlights the key properties
   which make it "indestructible" against many inadvertent changes to
   the Data-Plane, for example caused by misconfigurations.

   An ACP node can be a router, switch, controller, NMS host, or any
   other IP capable node.  Initially, it must have its ACP domain
   certificate, as well as an (empty) ACP Adjacency Table (described in
   Section 6.2).  It then can start to discover ACP neighbors and build
   the ACP.  This is described step by step in the following sections:

6.1.  ACP Domain, Certificate and Network

   The ACP relies on group security.  An ACP domain is a group of nodes
   that trust each other to participate in ACP operations such as
   creating ACP secure channels in an autonomous peer-to-peer fashion
   between ACP domain members via protocols such as IPsec.  To establish
   trust, each ACP member requires keying material: An ACP node MUST
   have a certificate (LDevID) and a Trust Anchor (TA) consisting of a
   certificate (chain) used to sign the LDevID of all ACP domain
   members.  The LDevID is used to cryptographically authenticate the
   membership of its owner node in the ACP domain to other ACP domain
   members.  The TA is used to authenticate the ACP domain membership of
   other nodes (see Section 6.1.3).

   Manual keying via shared secrets is not usable for an ACP domain
   because it would require a single shared secret across all current
   and future ACP domain members to meet the expectation of autonomous,
   peer-to-peer establishment of ACP secure channels between any ACP
   domain members.  Such a single shared secret would be an inacceptable
   security weakness.  Asymmetric keying material (public keys) without
   certificates does not provide the mechanisms to authenticate ACP
   domain membership in an autonomous, peer-to-peer fashion for current
   and future ACP domain members.

   The LDevID is called the ACP domain certificate, the TA is the
   Certificate Authority (CA) of the ACP domain.

   The ACP does not mandate specific mechanisms by which this keying
   material is provisioned into the ACP node.  It only requires the
   certificate to comply with Section 6.1.1, specifically the Domain
   information field as specified in Section 6.1.2 in its domain
   certificate as well as those of candidate ACP peers.  See
   Appendix A.2 for more information about enrollment or provisioning

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   This document uses the term ACP in many places where the Autonomic
   Networking reference documents [RFC7575] and
   [I-D.ietf-anima-reference-model] use the word autonomic.  This is
   done because those reference documents consider (only) fully
   autonomic networks and nodes, but support of ACP does not require
   support for other components of autonomic networks except for relying
   on GRASP and providing security and transport for GRASP.  Therefore
   the word autonomic might be misleading to operators interested in
   only the ACP.

   [RFC7575] defines the term "Autonomic Domain" as a collection of
   autonomic nodes.  ACP nodes do not need to be fully autonomic, but
   when they are, then the ACP domain is an autonomic domain.  Likewise,
   [I-D.ietf-anima-reference-model] defines the term "Domain
   Certificate" as the certificate used in an autonomic domain.  The ACP
   domain certificate is that domain certificate when ACP nodes are
   (fully) autonomic nodes.  Finally, this document uses the term ACP
   network to refer to the network created by active ACP nodes in an ACP
   domain.  The ACP network itself can extend beyond ACP nodes through
   the mechanisms described in Section 8.1.

6.1.1.  ACP Certificates

   ACP domain certificates MUST be [RFC5280] compliant X.509

   ACP nodes MUST support RSA and Elliptic Curve (ECC) public keys in
   ACP certificates.  ACP certificates wth ECC keys MUST indicate to be
   Elliptic Curve Diffie-Hellman capable (ECDH) if X.509 v3 keyUsage and
   extendedKeyUsage are included in the certificate.

   ACP nodes MUST support Certificates RSA keys with no less than 2048
   bit key length and ECC keys with NIST P-256, P-384 and P-521 key
   length (and curve) or better.  ACP nodes MUST support SHA-256, SHA-
   384, SHA-512 or better signatures for ACP certificates with RSA key
   and the same RSA signatures plus ECDSA signatures for ACP
   certificates with ECC key.

   The ACP certificate SHOULD use an RSA key and an RSA signature when
   the ACP certificate is intended to be used not only for ACP
   authentication but also for other purposes.  The ACP certificate MAY
   use an ECC key and an ECDSA signature if the ACP certificate is only
   used for ACP and ANI authentication and authorization.

   Any secure channel protocols used for the ACP as specified in this
   document or extensions of this document MUST therefore support
   authentication (e.g.:signing) starting with these type of
   certificates.  See [RFC4492] for more information.

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   The reason for these choices are as follows: As of 2020, RSA is still
   more widely used than ECC, therefore the MUST for RSA.  ECC offers
   equivalent security at (logarithmically) shorter key lengths (see
   [RFC4492]).  This can be beneficial especially in the presence of
   constrained bandwidth or constrained nodes in an ACP/ANI network.
   Some ACP functions such as GRASP peer-2-peer across the ACP require
   end-to-end/any-to-any authentication/authorization, therefore ECC can
   only reliably be used in the ACP when it MUST be supported on all ACP
   nodes.  RSA signatures are mandatory to be supported also for ECC
   certificates because CAs themselves may not support ECC yet.

   For further certificate details, ACP certificates may follow the
   recommendations from [CABFORUM].

   The ACP domain certificate SHOULD be used for any authentication
   between nodes with ACP domain certificates (ACP nodes and NOC nodes)
   where the required authorization condition is ACP domain membership,
   such as ACP node to NOC/OAM end-to-end security and ASA to ASA end-
   to-end security.  Section 6.1.3 defines this "ACP domain membership
   check".  The uses of this check that are standardized in this
   document are for the establishment of hop-by-hop ACP secure channels
   (Section 6.6) and for ACP GRASP (Section 6.8.2) end-to-end via TLS

   The ACP domain membership check requires a minimum amount of elements
   in a certificate as described in Section 6.1.3.  All elements are
   [RFC5280] compliant.  The identity of a node in the ACP is carried
   via the ACP Domain Information Field as defined in Section 6.1.2
   which is encoded as an rfc822Name field.

   Any other field of the ACP domain certificate is to be populated as
   required by [RFC5280] or desired by the operator of the ACP domain
   ACP registrars/CA and required by other purposes that the ACP domain
   certificate is intended to be used for.

   For diagnostic and other operational purposes, it is beneficial to
   copy the device identifying fields of the node's IDevID into the ACP
   domain certificate, such as the "serialNumber" (see
   [I-D.ietf-anima-bootstrapping-keyinfra] section 2.3.1).  Inclusion of
   this information makes it easier to potentially attack the node
   though, for example by learning the device model, which may help to
   select a fitting subset of attacks.  Neighboring attackers can
   retrieve the certificate through an otherwise unsuccessful initiation
   of a secure channel association.

   Note that there is no intention to constrain authorization within the
   ACP or autonomic networks using the ACP to just the ACP domain
   membership check as defined in this document.  It can be extended or

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   modified with future requirements.  Such future authorizations can
   use and require additional elements in certificates or policies or
   even additional certificates.  For an example, see Appendix A.10.5.

6.1.2.  ACP Certificate ACP Domain Information Field

   Information about the domain MUST be encoded in the domain
   certificate in a subjectAltName / rfc822Name field according to the
   following ABNF ([RFC5234]) definition:

   [RFC Editor: Please substitute SELF in all occurrences of rfcSELF in
   this document with the RFC number assigned to this document and
   remove this comment line]

     domain-information = local-part "@" acp-domain-name
     local-part = key [ "+" local-info ]
     key = "rfcSELF"
     local-info = [ acp-address ] [ "+" rsub extensions ]
     acp-address = 32HEXDIG | 0 ; HEXDIG as of RFC5234 section B.1
     rsub = [ <subdomain> ] ; <subdomain> as of RFC1034, section 3.5
     acp-domain-name = ; <domain> ; as of RFC 1034, section 3.5
     extensions = *( "+" extension )
     extension = ; future standard definition.
                 ; Must fit RFC5322 simple dot-atom format.

     routing-subdomain = [ rsub " ." ] acp-domain-name

       given an ACP address   of fd89:b714:f3db:0:200:0:6400:0000
       and an ACP domain-name of
       and an rsub extenstion of area51.research

     then this results in:
     domain-information = rfcSELF+FD89B714F3DB00000200000064000000
     acp-domain-name    =
     routing-subdomain  =

                Figure 2: ACP Domain Information Field ABNF

   domain-information is the encoded information that is put into the
   ACP domain certificates subjectAltName / rfc822Name field. routing-
   subdomain is a string that can be constructed from the domain-
   information, and it is used in the hash-creation of the ULA (see
   below).  The requirements and sementics of the parts of this
   information are explained in the following paragraphs:

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   Nodes complying with this specification MUST be able to receive their
   ACP address through the domain certificate, in which case their own
   ACP domain certificate MUST have the 32HEXDIG "acp-address" field.
   Nodes complying with this specification MUST also be able to
   authenticate nodes as ACP domain members or ACP secure channel peers
   when they have a 0-value acp-address field and as ACP domain members
   (but not as ACP secure channel peers) when they have an empty acp-
   address field.  See Section 6.1.3.

   "acp-domain-name" is used to indicate the ACP Domain across which all
   ACP nodes trust each other and are willing to build ACP channels to
   each other.  See Section 6.1.3.  Acp-domain-name SHOULD be the FQDN
   of a DNS domain owned by the operator assigning the certificate.
   This is a simple method to ensure that the domain is globally unique
   and collision of ACP addresses would therefore only happen due to ULA
   hash collisions (see Section 6.10.2).  If the operator does not own
   any FQDN, it should choose a string (in FQDN format) that it intends
   to be equally unique.

   To keep the encoding simple, there is no consideration for
   internationalized acp-domain-names.  The ACP domain information is
   not intended for enduser consumption, and there is no protection
   against someone not owning a domain name to simpy choose it.
   Instead, it only serves as a hash seed for the ULA and for
   diagnostics to the operator.  Therefore, any operator owning only an
   internationalized domain name should be able to pick an equivalently
   unique 7-bit ASCII acp-domain-name string representing the
   internationalized domain name.

   "routing-subdomain" is a heuristic that allows a Registrar to
   consistently generate a unique 48-bit ULA prefix for ACP addresses.
   The presence of the "rsub" component allows to a single ACP domain to
   employ multiple /48 ULA prefixes.  See Appendix A.7 for example use-

   The optional "extensions" field is used for future standardized
   extensions to this specification.  It MUST be ignored if present and
   not understood.

   Formatting notes:

   o  "rsub" needs to be in the "local-part": If the format just had
      routing-subdomain as the domain part of the domain-information,
      rsub and acp-domain-name could not be separated from each other.
      It also makes domain-information a valid e-mail target across all

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   o  "acp-address" cannot use standard IPv6 address formats because it
      must match the simple dot-atom format of [RFC5322].  The character
      ":" is not allowed in that format.

   o  If "acp-address" is empty, and "rsub" is empty too, the "local-
      part" will have the format "rfcSELF++extension(s)".  The two plus
      characters are necessary so the node can unambiguously parse that
      both "acp-address" and "rsub" are empty.

   o  The maximum size of "domain-information" is 254 characters and the
      maximum size of local-part is 64 characters according to [RFC5280]
      that is referring to [RFC2821] (superseded by [RFC5321]).

   The subjectAltName / rfc822Name encoding of the ACP domain name and
   ACP address is used for the following reasons:

   Rfc822name encoding for the ACP domain information was choosen for
   the following reasons.

   o  The ACP domain information field is the identifier of a node's
      ACP.  It includes the the necessary components to identify a nodes
      ACP both from within the ACP as well as from the outside of the

   o  For manual and/or automated diagnostics and backend management of
      devices and ACPs, it is necessary to have an easily human readible
      and software parsed standard, single string representation of the
      ACP domain information.  For example, inventory or other backend
      systems can always identify an entity by one unique string field
      but not by a combination of multiple fields, which would be
      necessary if there was no single string representation.

   o  If the encoding of the ACP domain information into the ACP domains
      certificate was not that of such a string, it would be necessary
      to define a second standard encoding to provide this format
      (standard string encoding).

   o  Rfc822 addresses have become standard identifiers of entities in
      many systems, including the majority of user identification in web
      or mobile applications, where in many cases, e-mail is not even
      part of the service for which an rfc822 address is used as an
      entities identifier.  In single-sign-on systems for example,
      <local-part>@<domain> is instead used to indicate a <domain> with
      which authentication and authorization of <local-part> is
      performend without any other use of RFC822 than its address format
      (e.g.: no rfc822 formatted message exchanges).

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   o  Encoding the ACP nodes identity/name in the format of an
      rfc822address is therefore following common practices for how
      rfc822 addresses are used in other contexts.  It also very well
      matches the format of rfc822 address structure <local-
      part>@<domain> because the ACP domain information does logically
      also consist of a <domain> identifying the ACP, and a <local-part>
      identifying a nodes ACP.

   o  subjectAltName / rfc822Name is the standard, mandatory to
      implement certificate attribute to encode the certificate subjects
      rfc822 address and can be the only subjects name.


   o  It should be possible to use the ACP domain certificate as an
      LDevID on the system for other uses beside the ACP.  Therefore,
      the information element required for the ACP should be encoded so
      that it minimizes the possibility of creating incompatibilities
      with such other uses.  The subjectName for example is for example
      often used as an entity identifier in non-ACP uses.

   o  The element should not require additional ASN.1 en/decoding,
      because libraries to access certificate information especially for
      embedded devices may not support extended ASN.1 decoding beyond
      predefined, manadatory fields. subjectAltName / rfc822Name is such
      a mandatory predefined field. subjectAlName / otherName for
      example is not.

   o  Encoding of the ACP domain information as a human readable string
      in a manadatory certificate field also has the benefit that it can
      be diagnosed/decoded in any pre-existing certificate diagnostic

   o  The element required for the ACP should not be misinterpreted by
      any other uses of the LDevID.  If the element used for the ACP is
      interpreted by other components than the ACP, the impact should be
      benign.  By using fully rfc822address compliant encoding, the
      benign side effect of non-ACP software using the ACP rfc822address
      would be emails sent to the mailbox identified by the
      rfc822address.  If it is desired to receive such emails, suitable
      email software may also support assigning all rfc822addresses for
      an ACP domain to a single mailbox rfcSELF@<domain>.  This is
      possible when "+" (which follows rfcSELF) is supported by the Mail
      User Agent as a separator between mail subscriber and sub-mailbox.

   See section of [RFC5280] for details on the subjectAltName

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6.1.3.  ACP domain membership check

   The following points constitute the ACP domain membership check of a
   candidate peer via its certificate:

   1:   The peer certificate is valid (lifetime).

   2:   The peer has proved ownership of the private key associated with
      the certificate's public key.  This check is performed by the
      security association protocol used, for example [RFC7296], section

   3:   The peer's certificate passes certificate path validation as
      defined in [RFC5280], section 6 against one of the Trust Anchors
      associated with the ACP node's ACP domain certificate (see
      Section 6.1.4 below).

   4:   If the node certificate indicates a Certificate Revocation List
      (CRL) Distribution Point (CDP) ([RFC5280], section or
      Online Certificate Status Protocol (OCSP) responder ([RFC5280],
      section, then the peer's certificate must be valid
      according to those criteria: An OCSP check for the peer's
      certificate across the ACP must succeed or the peer certificate
      must not be listed in the CRL retrieved from the CDP.  This rule
      has to be skipped for ACP secure channel peer authentication when
      the node has no ACP or non-ACP connectivity to retrieve current
      CRL or access an OCSP responder (and the security association
      protocol itself has also no way to communicate CRL or OCSP check).

   5:   The peer's certificate has a syntactically valid ACP domain
      information field (encoded as subjectAltName / rfc822Name) and the
      acp-domain-name in that peer's domain information field is the
      same as in this ACP node's certificate (lowercase normalized).

   Note: When an ACP node learns later via OCSP/CRL that an ACP peer's
   certificate for which rule 4 had to be skipped during ACP secure
   channel establishment is invalid, then the ACP secure channel to that
   peer SHOULD be closed even if this peer is the only connectivity to
   access CRL/OCSP.  The ACP secure channel connection MUST be retried
   periodically to support the case that the neighbor aquires a new,
   valid certificate.

   When checking a candidate peer's certificate for the purpose of
   establishing an ACP secure channel, one additional check is

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   6:   The candidate peer certificate's ACP domain information field
      has a non-empty acp-address field (either 32HEXDIG or 0, according
      to Figure 2).

   Technically, ACP secure channels can only be built with nodes that
   have an acp-address.  Rule 6 ensures that this is taken into account
   during ACP domain membership check.

   Nodes with an empty acp-address field can only use their ACP domain
   certificate for non-ACP-secure channel authentication purposes.  This
   includes for example NMS type nodes permitted to communicate into the
   ACP via ACP connect (Section 8.1)

   The special value 0 in an ACP certificates acp-address field is used
   for nodes that can and should determine their ACP address through
   other mechanisms than learning it through the acp-address field in
   their ACP domain certificate.  These ACP nodes are permitted to
   establish ACP secure channels.  Mechanisms for those nodes to
   determine their ACP address are outside the scope of this
   specification, but this option is defined here so that any ACP nodes
   can build ACP secure channels to them according to Rule 6.

   In summary:

      Steps 1...4 constitute standard certificate validity verification
      and private key authentication as defined by [RFC5280] and
      security association protocols (such as IKEv2 [RFC7296] when
      leveraging certificates.

      Steps 1...4 do not include verification of any pre-existing form
      of non-public-key-only based identity elements of a certificate
      such as a web servers domain name prefix often encoded in
      certificate common name.  Steps 5 and 6 are the equivalent steps.

      Step 4 Constitutes standard CRL/OCSP checks refined for the case
      of missing connectivity and limited functionality security
      association protocols.

      Step 5 Checks for the presence of an ACP identity for the peer.

      Steps 1...5 authorize to build any secure connection between
      members of the same ACP domain except for ACP secure channels.

      Step 6 is the additional verification of the presence of an ACP

      Steps 1...6 authorize to build an ACP secure channel.

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   For brevity, the remainder of this document refers to this process
   only as authentication instead of as authentication and

6.1.4.  Trust Points and Trust Anchors

   ACP nodes need Trust Point (TP) certificates to perform certificate
   path validation as required by Section 6.1.3, rule 3.  Trust Point(s)
   must be provisioned to an ACP node (together with its ACP domain
   certificate) by an ACP Registrar during initial enrolment of a
   candidate ACP node.  ACP nodes MUST also support renewal of TPs via
   EST as described below in Section 6.1.5.

   Trust Point is the term used in this document for a certificate
   authority (CA) and its associated set of certificates.  Multiple
   certificates are required for a CA to deal with CA certificate
   renewals as explained in Section 4.4 of CMP ([RFC4210]).

   A certificate path is a chain of certificates starting at the ACP
   certificate (leaf/end-entity) followed by zero or more intermediate
   Trust Point or sub-CA certificates and ending with a self-signed
   certificate of a so called root-CA or Trust Anchor.  Certificate path
   validation authenticates that the ACP certificate is signed by a
   Trust Anchor, directly or indirectly via one or more intermediate
   Trust Points.

   Note that different ACP nodes may have different Trust Points and
   even different Trust Anchors in their certificate path, as long as
   the set of Trust Points for all ACP node includes the same set of
   Trust Anchors (usually 1), and each ACP nodes set of Trust Anchors
   includes the intermediate Trust Points for its own ACP domain
   certificate.  The protocols through which ACP domain membership check
   rules 1-4 are performed therefore need to support the exchange not
   only of the ACP nodes certificates, but also their intermediate Trust

   ACP nodes MUST support for the ACP domain membership check the
   certificate path validation with 0 or 1 intermediate Trust Points.
   They SHOULD support 2 intermediate Trust Points and two Trust Anchors
   (to permit migration to different root-CAs).

   Trust Points for ACP domain certificates must be trusted to sign
   certificates with valid ACP domain information fields only for
   trusted ACP registrars of that domain.  This can be achieved by using
   Trust Anchors private to the owner of the ACP domain or potentially
   through appropriate contractual agreements between the involved
   parties.  Public CA without such obligations and guarantees can not
   be used.

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   A single owner can operate multiple independent ACP domains from the
   same set of private trust anchors (CAs) when the ACP Registrars are
   trusted not to permit certificates with incorrect ACP information
   fields to be signed, such as ACP information with a wrong acp-domain
   field.  In this case, CAs can be completely unaware of ACP specifics,
   so that it should be possible to use any existing CA software.  When
   ACP Registrars are not to be trusted, the correctness of the ACP
   domain information field for the candidate ACP node has to be
   verified by the CA signing the ACP domain certificate.

6.1.5.  Certificate and Trust Point Maintenance

   ACP nodes MUST support renewal of their Certificate and Trust Points
   (TP) via EST ("Enrollment over Secure Transport", see [RFC7030]) and
   MAY support other mechanisms.  An ACP network MUST have at least one
   ACP node supporting EST server functionality across the ACP so that
   EST renewal is useable.

   ACP nodes SHOULD be able to remember the EST server from which they
   last renewed their ACP domain certificate and SHOULD provide the
   ability for this remembered EST server to also be set by the ACP
   Registrar (see Section 6.10.7) that initially enrolled the ACP device
   with its ACP domain certificate.  When BRSKI (see
   [I-D.ietf-anima-bootstrapping-keyinfra]) is used, the ACP address of
   the BRSKI registrar from the BRSKI TLS connection SHOULD be
   remembered and used for the next renewal via EST if that registrar
   also announces itself as an EST server via GRASP (see next section)
   on its ACP address.

   The EST server MUST present a certificate that is passing ACP domain
   membership check in its TLS connection setup (Section 6.1.3, rules
   1..5, not rule 6 as this is not for an ACP secure channel setup).
   The EST server certificate MUST also contain the id-kp-cmcRA
   [RFC6402] extended key usage extension and the EST client must check
   its presence.

   The additional check against the id-kp-cmcRA extended key usage
   extension field ensures that clients do not fall prey to an illicit
   EST server.  While such illicit EST servers should not be able to
   support certificate signing requests (as they are not able to elicit
   a signing response from a valid CA), such an illicit EST server would
   be able to provide faked CA certificates to EST clients that need to
   renew their CA certificates when they expire.

   Note that EST servers supporting multiple ACP domains will need to
   have for each of these ACP domains a separate certificate and respond
   on a different transport address (IPv6 address and/or TCP port), but
   this is easily automated on the EST server as long as the CA does not

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   restrict registrars to request certificates with the id-kp-cmcRA
   extended usage extension for themselves.  GRASP objective for EST server

   ACP nodes that are EST servers MUST announce their service via GRASP
   in the ACP through M_FLOOD messages.  See [I-D.ietf-anima-grasp],
   section 2.8.11 for the definition of this message type:


        [M_FLOOD, 12340815, h'fd89b714f3db0000200000064000001', 210000,
            ["SRV.est", 4, 255 ],
                 h'fd89b714f3db0000200000064000001', TCP, 443]

                      Figure 3: GRASP SRV.est example

   The formal definition of the objective in Concise data definition
   language (CDDL) (see [I-D.ietf-cbor-cddl]) is as follows:

    flood-message = [M_FLOOD, session-id, initiator, ttl,
                     +[objective, (locator-option / [])]]
                                 ; see example above and explanation
                                 ; below for initiator and ttl

    objective = ["SRV.est", objective-flags, loop-count,

    objective-flags = sync-only  ; as in GRASP spec
    sync-only       = 4          ; M_FLOOD only requires synchronization
    loop-count      = 255        ; recommended as there is no mechanism
                                 ; to discover network diameter.
    objective-value = any        ; reserved for future extensions

                    Figure 4: GRASP SRV.est definition

   The objective name "SRV.est" indicates that the objective is an
   [RFC7030] compliant EST server because "est" is an [RFC6335]
   registered service name for [RFC7030].  Objective-value MUST be
   ignored if present.  Backward compatible extensions to [RFC7030] MAY
   be indicated through objective-value.  Non [RFC7030] compatible
   certificate renewal options MUST use a different objective-name.
   Non-recognized objective-values (or parts thereof if it is a
   structure partially understood) MUST be ignored.

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   The M_FLOOD message MUST be sent periodically.  The default SHOULD be
   60 seconds, the value SHOULD be operator configurable but SHOULD be
   not smaller than 60 seconds.  The frequency of sending MUST be such
   that the aggregate amount of periodic M_FLOODs from all flooding
   sources cause only negligible traffic across the ACP.  The time-to-
   live (ttl) parameter SHOULD be 3.5 times the period so that up to
   three consecutive messages can be dropped before considering an
   announcement expired.  In the example above, the ttl is 210000 msec,
   3.5 times 60 seconds.  When a service announcer using these
   parameters unexpectedly dies immediately after sending the M_FLOOD,
   receivers would consider it expired 210 seconds later.  When a
   receiver tries to connect to this dead service before this timeout,
   it will experience a failing connection and use that as an indication
   that the service instance is dead and select another instance of the
   same service instead (from another GRASP announcement).  Renewal

   When performing renewal, the node SHOULD attempt to connect to the
   remembered EST server.  If that fails, it SHOULD attempt to connect
   to an EST server learned via GRASP.  The server with which
   certificate renewal succeeds SHOULD be remembered for the next

   Remembering the last renewal server and preferring it provides
   stickiness which can help diagnostics.  It also provides some
   protection against off-path compromised ACP members announcing bogus
   information into GRASP.

   Renewal of certificates SHOULD start after less than 50% of the
   domain certificate lifetime so that network operations has ample time
   to investigate and resolve any problems that causes a node to not
   renew its domain certificate in time - and to allow prolonged periods
   of running parts of a network disconnected from any CA.  Certificate Revocation Lists (CRLs)

   The ACP node SHOULD support Certificate Revocation Lists (CRL) via
   HTTP from one or more CRL Distribution Points (CDPs).  The CDP(s)
   MUST be indicated in the Domain Certificate when used.  If the CDP
   URL uses an IPv6 address (ULA address when using the addressing rules
   specified in this document), the ACP node will connect to the CDP via
   the ACP.  If the CDP uses a domain name, the ACP node will connect to
   the CDP via the Data-Plane.

   It is common to use domain names for CDP(s), but there is no
   requirement for the ACP to support DNS.  Any DNS lookup in the Data-
   Plane is not only a possible security issue, but it would also not

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   indicate whether the resolved address is meant to be reachable across
   the ACP.  Therefore, the use of an IPv6 address versus the use of a
   DNS name doubles as an indicator whether or not to reach the CDP via
   the ACP.

   A CDP can be reachable across the ACP either by running it on a node
   with ACP or by connecting its node via an ACP connect interface (see
   Section 8.1).  The CDP SHOULD use an ACP domain certificate for its
   HTTPs connections.  The connecting ACP node SHOULD verify that the
   CDP certificate used during the HTTPs connection has the same ACP
   address as indicated in the CDP URL of the node's ACP domain
   certificate if the CDP URL uses an IPv6 address.  Lifetimes

   Certificate lifetime may be set to shorter lifetimes than customary
   (1 year) because certificate renewal is fully automated via ACP and
   EST.  The primary limiting factor for shorter certificate lifetimes
   is load on the EST server(s) and CA.  It is therefore recommended
   that ACP domain certificates are managed via a CA chain where the
   assigning CA has enough performance to manage short lived
   certificates.  See also Section 10.2.4 for discussion about an
   example setup achieving this.  See also [I-D.ietf-acme-star].

   When certificate lifetimes are sufficiently short, such as few hours,
   certificate revocation may not be necessary, allowing to simplify the
   overall certificate maintenance infrastructure.

   See Appendix A.2 for further optimizations of certificate maintenance
   when BRSKI can be used ("Bootstrapping Remote Secure Key
   Infrastructures", see [I-D.ietf-anima-bootstrapping-keyinfra]).  Re-enrollment

   An ACP node may determine that its ACP domain certificate has
   expired, for example because the ACP node was powered down or
   disconnected longer than its certificate lifetime.  In this case, the
   ACP node SHOULD convert to a role of a re-enrolling candidate ACP

   In this role, the node does maintain the trust anchor and certificate
   chain associated with its ACP domain certificate exclusively for the
   purpose of re-enrollment, and attempts (or waits) to get re-enrolled
   with a new ACP certificate.  The details depend on the mechanisms/
   protocols used by the ACP registrars.

   Please refer to Section 6.10.7 and
   [I-D.ietf-anima-bootstrapping-keyinfra] for explanations about ACP

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   registrars and vouchers as used in the following text.  When ACP is
   intended to be used without BRSKI, the details about BRSKI and
   vouchers in the following text can be skipped.

   When BRSKI is used (i.e.: on ACP nodes that are ANI nodes), the re-
   enrolling candidate ACP node would attempt to enroll like a candidate
   ACP node (BRSKI pledge), but instead of using the ACP nodes IDevID,
   it SHOULD first attempt to use its ACP domain certificate in the
   BRSKI TLS authentication.  The BRSKI registrar MAY honor this
   certificate beyond its expiration date purely for the purpose of re-
   enrollment.  Using the ACP node's domain certificate allows the BRSKI
   registrar to learn that node's ACP domain information field, so that
   the BRSKI registrar can re-assign the same ACP address information to
   the ACP node in the new ACP domain certificate.

   If the BRSKI registrar denies the use of the old ACP domain
   certificate, the re-enrolling candidate ACP node MUST re-attempt re-
   enrollment using its IDevID as defined in BRSKI during the TLS
   connection setup.

   Both when the BRSKI connection is attempted with the old ACP domain
   certificate or the IDevID, the re-enrolling candidate ACP node SHOULD
   authenticate the BRSKI registrar during TLS connection setup based on
   its existing trust anchor/certificate chain information associated
   with its old ACP certificate.  The re-enrolling candidate ACP node
   SHOULD only fall back to requesting a voucher from the BRSKI
   registrar when this authentication fails during TLS connection setup.

   When other mechanisms than BRSKI are used for ACP domain certificate
   enrollment, the principles of the re-enrolling candidate ACP node are
   the same.  The re-enrolling candidate ACP node attempts to
   authenticate any ACP registrar peers during re-enrollment protocol/
   mechanisms via its existing certificate chain/trust anchor and
   provides its existing ACP domain certificate and other identification
   (such as the IDevID) as necessary to the registrar.

   Maintaining existing trust anchor information is especially important
   when enrollment mechanisms are used that unlike BRSKI do not leverage
   a voucher mechanism to authenticate the ACP registrar and where
   therefore the injection of certificate failures could otherwise make
   the ACP node easily attackable remotely.

   When using BRSKI or other protocol/mechanisms supporting vouchers,
   maintaining existing trust anchor information allows for re-
   enrollment of expired ACP certificates to be more lightweight,
   especially in environments where repeated acquisition of vouchers
   during the lifetime of ACP nodes may be operationally expensive or
   otherwise undesirable.

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   An ACP domain certificate is called failing in this document, if/when
   the ACP node to which the certificate was issued can determine that
   it was revoked (or explicitly not renewed), or in the absence of such
   explicit local diagnostics, when the ACP node fails to connect to
   other ACP nodes in the same ACP domain using its ACP certificate.
   For connection failures to determine the ACP domain certificate as
   the culprit, the peer should pass the domain membership check
   (Section 6.1.3) and other reasons for the connection failure can be
   excluded because of the connection error diagnostics.

   This type of failure can happen during setup/refresh of a secure ACP
   channel connections or any other use of the ACP domain certificate,
   such as for the TLS connection to an EST server for the renewal of
   the ACP domain certificate.

   Example reasons for failing certificates that the ACP node can only
   discover through connection failure are that the domain certificate
   or any of its signing certificates could have been revoked or may
   have expired, but the ACP node cannot self-diagnose this condition
   directly.  Revocation information or clock synchronization may only
   be available across the ACP, but the ACP node cannot build ACP secure
   channels because ACP peers reject the ACP node's domain certificate.

   ACP nodes SHOULD support the option to determines whether its ACP
   certificate is failing, and when it does, put itself into the role of
   a re-enrolling candidate ACP node as explained above

6.2.  ACP Adjacency Table

   To know to which nodes to establish an ACP channel, every ACP node
   maintains an adjacency table.  The adjacency table contains
   information about adjacent ACP nodes, at a minimum: Node-ID
   (identifier of the node inside the ACP, see Section 6.10.3 and
   Section 6.10.5), interface on which neighbor was discovered (by GRASP
   as explained below), link-local IPv6 address of neighbor on that
   interface, certificate (including domain information field).  An ACP
   node MUST maintain this adjacency table.  This table is used to
   determine to which neighbor an ACP connection is established.

   Where the next ACP node is not directly adjacent (i.e., not on a link
   connected to this node), the information in the adjacency table can
   be supplemented by configuration.  For example, the Node-ID and IP
   address could be configured.  See Section 8.2.

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   The adjacency table MAY contain information about the validity and
   trust of the adjacent ACP node's certificate.  However, subsequent
   steps MUST always start with the ACP domain membership check against
   the peer (see Section 6.1.3).

   The adjacency table contains information about adjacent ACP nodes in
   general, independently of their domain and trust status.  The next
   step determines to which of those ACP nodes an ACP connection should
   be established.

6.3.  Neighbor Discovery with DULL GRASP

   [RFC Editor: GRASP draft is in RFC editor queue, waiting for
   dependencies, including ACP.  Please ensure that references to I-
   D.ietf-anima-grasp that include section number references (throughout
   this document) will be updated in case any last-minute changes in
   GRASP would make those section references change.

   Discovery Unsolicited Link-Local (DULL) GRASP is a limited subset of
   GRASP intended to operate across an insecure link-local scope.  See
   section 2.5.2 of [I-D.ietf-anima-grasp] for its formal definition.
   The ACP uses one instance of DULL GRASP for every L2 interface of the
   ACP node to discover link level adjacent candidate ACP neighbors.
   Unless modified by policy as noted earlier (Section 5 bullet point
   2.), native interfaces (e.g., physical interfaces on physical nodes)
   SHOULD be initialized automatically to a state in which ACP discovery
   can be performed and any native interfaces with ACP neighbors can
   then be brought into the ACP even if the interface is otherwise not
   configured.  Reception of packets on such otherwise not configured
   interfaces MUST be limited so that at first only IPv6 StateLess
   Address Auto Configuration (SLAAC - [RFC4862]) and DULL GRASP work
   and then only the following ACP secure channel setup packets - but
   not any other unnecessary traffic (e.g., no other link-local IPv6
   transport stack responders for example).

   Note that the use of the IPv6 link-local multicast address
   (ALL_GRASP_NEIGHBORS) implies the need to use Multicast Listener
   Discovery Version 2 (MLDv2, see [RFC3810]) to announce the desire to
   receive packets for that address.  Otherwise DULL GRASP could fail to
   operate correctly in the presence of MLD snooping, non-ACP enabled L2
   switches - because those would stop forwarding DULL GRASP packets.
   Switches not supporting MLD snooping simply need to operate as pure
   L2 bridges for IPv6 multicast packets for DULL GRASP to work.

   ACP discovery SHOULD NOT be enabled by default on non-native
   interfaces.  In particular, ACP discovery MUST NOT run inside the ACP
   across ACP virtual interfaces.  See Section 10.3 for further, non-
   normative suggestions on how to enable/disable ACP at node and

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   interface level.  See Section 8.2.2 for more details about tunnels
   (typical non-native interfaces).  See Section 7 for how ACP should be
   extended on devices operating (also) as L2 bridges.

   Note: If an ACP node also implements BRSKI to enroll its ACP domain
   certificate (see Appendix A.2 for a summary), then the above
   considerations also apply to GRASP discovery for BRSKI.  Each DULL
   instance of GRASP set up for ACP is then also used for the discovery
   of a bootstrap proxy via BRSKI when the node does not have a domain
   certificate.  Discovery of ACP neighbors happens only when the node
   does have the certificate.  The node therefore never needs to
   discover both a bootstrap proxy and ACP neighbor at the same time.

   An ACP node announces itself to potential ACP peers by use of the
   "AN_ACP" objective.  This is a synchronization objective intended to
   be flooded on a single link using the GRASP Flood Synchronization
   (M_FLOOD) message.  In accordance with the design of the Flood
   message, a locator consisting of a specific link-local IP address, IP
   protocol number and port number will be distributed with the flooded
   objective.  An example of the message is informally:

         [M_FLOOD, 12340815, h'fe80000000000000c0011001FEEF0000, 210000,
             ["AN_ACP", 4, 1, "IKEv2" ],
                  h'fe80000000000000c0011001FEEF0000, UDP, 15000]
             ["AN_ACP", 4, 1, "DTLS" ],
                  h'fe80000000000000c0011001FEEF0000, UDP, 17000]

                      Figure 5: GRASP AN_ACP example

   The formal CDDL definition is:

           flood-message = [M_FLOOD, session-id, initiator, ttl,
                            +[objective, (locator-option / [])]]

           objective = ["AN_ACP", objective-flags, loop-count,

           objective-flags = sync-only ; as in the GRASP specification
           sync-only =  4    ; M_FLOOD only requires synchronization
           loop-count = 1    ; limit to link-local operation
           objective-value = method
           method = "IKEv2" / "DTLS"  ; or future standard methods

                     Figure 6: GRASP AN_ACP definition

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   The objective-flags field is set to indicate synchronization.

   The loop-count is fixed at 1 since this is a link-local operation.

   In the above example the RECOMMENDED period of sending of the
   objective is 60 seconds.  The indicated ttl of 210000 msec means that
   the objective would be cached by ACP nodes even when two out of three
   messages are dropped in transit.

   The session-id is a random number used for loop prevention
   (distinguishing a message from a prior instance of the same message).
   In DULL this field is irrelevant but must still be set according to
   the GRASP specification.

   The originator MUST be the IPv6 link local address of the originating
   ACP node on the sending interface.

   The 'objective-value' parameter is a string indicating the protocol
   available at the specified or implied locator.  It must be a protocol
   supported by the node to negotiate a secure channel.  IKEv2 as shown
   above is the protocol used to negotiate an IPsec secure channel.

   The locator-option is optional and only required when the secure
   channel protocol is not offered at a well-defined port number, or if
   there is no well-defined port number.

   "IKEv2" is the abbreviation for "Internet Key Exchange protocol
   version 2".  It is the main protocol used by the Internet IP security
   architecture (IPsec).  We therefore use the term "IKEv2" and not
   "IPsec" in the GRASP definitions and example above.  "IKEv2" has a
   well-defined port number 500, but in the above example, the candidate
   ACP neighbor is offering ACP secure channel negotiation via IKEv2 on
   port 15000 (for the sake of creating a non-standard example).

   "DTLS" indicates datagram Transport Layer Security version 1.2.
   There is no default UDP port, it must always be locally assigned by
   the node.  See Section 6.7.2.

   If a locator is included, it MUST be an O_IPv6_LOCATOR, and the IPv6
   address MUST be the same as the initiator address (these are DULL
   requirements to minimize third party DoS attacks).

   The secure channel methods defined in this document use the
   objective-values of "IKEv2" and "DTLS".  There is no distinction
   between IKEv2 native and GRE-IKEv2 because this is purely negotiated
   via IKEv2.

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   A node that supports more than one secure channel protocol method
   needs to flood multiple versions of the "AN_ACP" objective so that
   each method can be accompanied by its own locator-option.  This can
   use a single GRASP M_FLOOD message as shown in Figure 5.

   Note that a node serving both as an ACP node and BRSKI Join Proxy may
   choose to distribute the "AN_ACP" objective and the respective BRSKI
   in the same M_FLOOD message, since GRASP allows multiple objectives
   in one message.  This may be impractical though if ACP and BRSKI
   operations are implemented via separate software modules / ASAs.

   The result of the discovery is the IPv6 link-local address of the
   neighbor as well as its supported secure channel protocols (and non-
   standard port they are running on).  It is stored in the ACP
   Adjacency Table (see Section 6.2), which then drives the further
   building of the ACP to that neighbor.

   Note that the DULL GRASP objective described does intentionally not
   include ACP nodes ACP domain certificate even though this would be
   useful for diagnostics and to simplify the security exchange in ACP
   secure channel security association protocols (see Section 6.7).  The
   reason is that DULL GRASP messages are periodically multicasted
   across IPv6 subnets and full certificates could easily lead to
   fragmented IPv6 DULL GRASP multicast packets due to the size of a
   certificate.  This would be highly undesirable.

6.4.  Candidate ACP Neighbor Selection

   An ACP node must determine to which other ACP nodes in the adjacency
   table it should build an ACP connection.  This is based on the
   information in the ACP Adjacency table.

   The ACP is established exclusively between nodes in the same domain.
   This includes all routing subdomains.  Appendix A.7 explains how ACP
   connections across multiple routing subdomains are special.

   The result of the candidate ACP neighbor selection process is a list
   of adjacent or configured autonomic neighbors to which an ACP channel
   should be established.  The next step begins that channel

6.5.  Channel Selection

   To avoid attacks, initial discovery of candidate ACP peers cannot
   include any non-protected negotiation.  To avoid re-inventing and
   validating security association mechanisms, the next step after
   discovering the address of a candidate neighbor can only be to try

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   first to establish a security association with that neighbor using a
   well-known security association method.

   From the use-cases it seems clear that not all type of ACP nodes can
   or need to connect directly to each other or are able to support or
   prefer all possible mechanisms.  For example, code space limited IoT
   devices may only support DTLS because that code exists already on
   them for end-to-end security, but low-end in-ceiling L2 switches may
   only want to support Media Access Control Security (MacSec, see
   802.1AE ([MACSEC]) because that is also supported in their chips.
   Only a flexible gateway device may need to support both of these
   mechanisms and potentially more.  Note that MacSec is not required by
   any profiles of the ACP in this specification but just mentioned as a
   likely next interesting secure channel protocol.

   To support extensible secure channel protocol selection without a
   single common MTI protocol, ACP nodes must try all the ACP secure
   channel protocols it supports and that are feasible because the
   candidate ACP neighbor also announced them via its AN_ACP GRASP
   parameters (these are called the "feasible" ACP secure channel

   To ensure that the selection of the secure channel protocols always
   succeeds in a predictable fashion without blocking, the following
   rules apply:

   o  An ACP node may choose to attempt to initiate the different
      feasible ACP secure channel protocols it supports according to its
      local policies sequentially or in parallel, but it MUST support
      acting as a responder to all of them in parallel.

   o  Once the first secure channel protocol succeeds, the two peers
      know each other's certificates because they must be used by all
      secure channel protocols for mutual authentication.  The node with
      the lower Node-ID in the ACP address of its ACP domain certificate
      becomes Bob, the one with the higher Node-ID in the certificate
      Alice.  A peer with an empty ACP address field in its ACP domain
      certificate becomes Bob (this specification does not define such
      peers, only the interoperability with them).

   o  Bob becomes passive, he does not attempt to further initiate ACP
      secure channel protocols with Alice and does not consider it to be
      an error when Alice closes secure channels.  Alice becomes the
      active party, continues to attempt setting up secure channel
      protocols with Bob until she arrives at the best one from her view
      that also works with Bob.

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   For example, originally Bob could have been the initiator of one ACP
   secure channel protocol that Bob prefers and the security association
   succeeded.  The roles of Bob and Alice are then assigned and the
   connection setup is completed.  The protocol could for example be
   IPsec via IKEv2 ("IP security", see [RFC4301] and "Internet Key
   Exchange protocol version 2", see [RFC7296].  It is now up to Alice
   to decide how to proceed.  Even if the IPsec connection from Bob
   succeeded, Alice might prefer another secure protocol over IPsec
   (e.g., FOOBAR), and try to set that up with Bob.  If that preference
   of Alice succeeds, she would close the IPsec connection.  If no
   better protocol attempt succeeds, she would keep the IPsec

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   The following sequence of steps show this example in more detail:

   [1]    Node 1 sends GRASP AN_ACP message to announce itself

   [2]    Node 2 sends GRASP AN_ACP message to announce itself

   [3]    Node 2 receives [1] from Node 1

   [4:C1] Because of [3], Node 2 starts as initiator on its
          preferred secure channel protocol towards Node 1.
          Connection C1.

   [5]    Node 1 receives [2] from Node 2

   [6:C2] Because of [5], Node 1 starts as initiator on its
          preferred secure channel protocol towards Node 2.
          Connection C2.

   [7:C1] Node1 and Node2 have authenticated each others
          certificate on connection C1 as valid ACP peers.

   [8:C1] Node 1 certificate has lower ACP Node-ID than  Node2,
          therefore Node 1 considers itself Bob and Node 2 Alice
          on connection C1. Connection setup C1 is completed.

   [9]    Node 1 (Bob)) refrains from attempting any further secure
          channel connections to Node 2 (Alice) as learned from [2]
          because it knows from [8:C1] that it is Bob relative
          to Node 1.

   [10:C2] Node1 and Node2 have authenticated each others
          certificate on connection C2 (like [7:C1]).

   [11:C2] Node 1 certificate has lower ACP Node-ID than Node2,
           therefore Node 1 considers itself Bob and Node 2 Alice
           on connection C1, but they also identify that C2 is to the
           same mutual peer as their C1, so this has no further impact.

   [12:C2] Node 1 (Alice) closes C1. Because of [8:C1], Node 2 (Bob)
           expected this.

   [13]    Node 1 (Alice) and Node 2 (Bob) start data transfer across
           C2, which makes it become a secure channel for the ACP.

                Figure 7: Secure Channel sequence of steps

   All this negotiation is in the context of an "L2 interface".  Alice
   and Bob will build ACP connections to each other on every "L2

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   interface" that they both connect to.  An autonomic node MUST NOT
   assume that neighbors with the same L2 or link-local IPv6 addresses
   on different L2 interfaces are the same node.  This can only be
   determined after examining the certificate after a successful
   security association attempt.

6.6.  Candidate ACP Neighbor verification

   Independent of the security association protocol chosen, candidate
   ACP neighbors need to be authenticated based on their domain
   certificate.  This implies that any secure channel protocol MUST
   support certificate based authentication that can support the ACP
   domain membership check as defined in Section 6.1.3.  If it fails,
   the connection attempt is aborted and an error logged.  Attempts to
   reconnect MUST be throttled.  The RECOMMENDED default is exponential
   base 2 backoff with a minimum delay of 10 seconds and a maximum delay
   of 640 seconds.

6.7.  Security Association (Secure Channel) protocols

   Due to Channel Selection (Section 6.5), ACP can support an evolving
   set of security association protocols.  These protocols only need to
   be used to establish secure channels with L2 adjacent ACP neighbors
   and only optionally (where needed) across non-ACP capable L3 network
   (see Section 8.2).  Therefore, there is architecturally no need for
   any network wide mandatory to implement (MTI) security association
   protocols.  Instead, ACP nodes only need to implement those protocols
   required to be supported by their neighbors.  See Section 6.7.3 for
   an example of this.

   The authentication of peers in any security association protocol MUST
   use the ACP domain certificate according to Section 6.1.3.  Because
   auto-discovery of candidate ACP neighbors via GRASP (see Section 6.3)
   as specified in this document does not communicate the neighbors ACP
   domain certificate, and ACP nodes may not (yet) have any other
   network connectivity to retrieve certificates, any security
   association protocol MUST use a mechanism to communicate the
   certificate directly instead of relying on a referential mechanism
   such as communicating only a hash and/or URL for the certificate.

   Any security association protocol MUST provide Forward Secrecy
   (whether inherently or as part of a profile of the security
   association protocol).

   The degree of security required on every hop of an ACP network needs
   to be consistent across the network so that there is no designated
   "weakest link" because it is that "weakest link" that would otherwise
   become the designated point of attack.  When the secure channel

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   protection on one link is compromised, it can be used to send/receive
   packets across the whole ACP network.  This principle does not imply
   that the requirements against ACP security association protocols have
   to be the same across all subnets in an ACP network:

   o  Underlying L2 mechanisms such as strong encrypted radio
      technologies or [MACSEC] may offer equivalent encryption and the
      ACP security association protocol may only be required to
      authenticate ACP domain membership of a peer and/or derive a key
      for the L2 mechanism.  Mechanisms to auto-discover and associate
      ACP peers leveraging such underlying L2 security are possible and
      desirable to avoid duplication of encryption, but none are
      specified in this document.

   o  Strong physical security of a link may stand in where
      cryptographic security is infeasible.  As there is no secure
      mechanism to automatically discover strong physical security
      solely between two peers, it can only be used with explicit
      configuration and that configuration too could become an attack
      vector.  This document therefore only specifies with ACP connect
      (Figure 15) one explicitly configured mechanism without any secure
      channel association protocol - for the case where both the link
      and the nodes attached to it have strong physical security.

   The following sub-sections define the security association protocols
   that are considered to be important and feasible to specify in this

6.7.1.  ACP via IPsec

   An ACP node announces its ability to support IPsec, negotiated via
   IKEv2, as the ACP secure channel protocol using the "IKEv2"
   objective-value in the "AN_ACP" GRASP objective.

   The ACP usage of IPsec and IKEv2 mandates a narrow profile of the
   current standards-track usage guidance for IPsec [RFC8221] and IKEv2
   [RFC8247].  This profile provides for stringent security properties
   and can exclude deprecated/legacy algorithms because there is no need
   for interoperability with legacy equipment for ACP secure channels.
   Any such backward compatibility would lead only to increased attack
   surface and implementation complexity, for no benefit.  Native IPsec

   To run ACP via IPsec natively, no further IANA assignments/
   definitions are required.

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   An ACP node that is supporting native IPsec MUST use IPsec in tunnel
   mode, negotiated via IKEv2, and with IPv6 payload (e.g., ESP Next
   Header of 41).  It MUST use local and peer link-local IPv6 addresses
   for encapsulation.  Manual keying MUST NOT be used, see Section 6.1.

   IPsec tunnel mode is required because the ACP will route/forward
   packets received from any other ACP node across the ACP secure
   channels, and not only its own generated ACP packets.  With IPsec
   transport mode, it would only be possible to send packets originated
   by the ACP node itself.  RFC8221 (IPsec/ESP)

   ACP IPsec implementations MUST comply with [RFC8221] (and its
   updates), with the following modifications to simplify hardware
   accelerated ACP IPsec implementation requirements by eliminating
   requirements for legacy or cryptographically weak options.

   ACP MUST NOT use any NULL encryption option due to the
   confidentiality of ACP payload that may not be encrypted by itself
   when carrying legacy management protocol traffics as well as hop-by-
   hop GRASP, which is designed to rely on the ACP for confidentiality
   of hop-by-hop distributed information.  Therefore, IPsec MUST support
   ESP and MUST NOT use AH.  For ESP, ENCR_NULL MUST NOT be used for ACP
   secure channels.

   Only ENCR_AES_GCM_16 is REQUIRED as an encryption algorithm for ACP
   secure channels with ESP.

   If an ACP node can perform ENCR_AES_CBC, ENCR_AES_CCM_8 at higher
   performance than ENCR_AES_GCM_16 or ENCR_CHACHA20_POLY1305 at equal
   or higher performance than ENCR_AES_GCM_16 then that ACP node SHOULD
   support such an encryption algorithm and prefer it in the IKEv2
   negotiation if its performance is higher than that of
   ENCR_AES_GCM_16.  Otherwise there are no normative requirements
   against either of these options.  These requirements are overriding
   the MUST/SHOULD/SHOULD requirements of [RFC8221] for these three
   algorithms for the following reasons:

   o  There is no unconditional requirement against ENCR_AES_CBC because

      *  ENCR_AES_GCM_16 is assumed to be feasible with less cost/higher
         higher performance in modern devices hardware accelerated
         implementations compared to ENCR-AES_CBC.

      *  AES-GCM is an authenticated encryption with associated data
         (AEAD) cipher mode, so no ESP authentication algorithm

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         requirement is needed (unless further encryption algorithms are
         supported), further simplifying ACP IPsec implementations.

      *  there is no requirement to interoperate with legacy equipment
         in ACP secure channels, so a single MTI encryption algorithm
         for IPsec in ACP secure channels is sufficient for

   o  There is no unconditional requirement against ENCR_AES_CCM_8
      because it is currently not likely that it would be preferrable in
      ACP secure channels for more constrained IoT devices over options
      such as DTLS.  In [RFC8221] this algorithm is more desirable,
      because of solutions relying only on IPsec without such non-IPsec

   o  There is no unconditional requirement against
      ENCR_CHACHA20_POLY1305 because there is currently no mechanism in
      the ACP to migrate all secure channels in an ACP domain to a
      different preferred encryption algorithm in the case of future
      discovered crypto weaknesses of AES.  Once such mechanisms are
      defined, ENCR_CHACHA20_POLY1305 would be a good encryption
      algorithm, but due to the transitive traffic through ACP secure
      channels only when this does not result in an unexpected drop in

   When using AES for encryption, keys less than 256 bits MUST NOT be
   used, and 256-bit keys MUST be supported.

   Once there are updates to [RFC8221], these should accordingly be
   reflected in updates to these ACP requirements, for example if
   ENCR_AES_GCM_16 was to be superceeded in the future.  RFC847 (IKEv2)

   IKEv2 for ACP secure channels MUST support the requirements of
   [RFC8247] (as necessary to support the above described modified
   [RFC8221] requirements for IPsec via ESP).  Because IKEv2 for ACP
   secure channels is sufficient to be implemented in control plane
   software as opposed to ESP (which may need to be implemented in
   accelerated forwarding plane for sufficient performance), there are
   no restrictions on the requirements of [RFC8247] for ACP secure
   channels.  Instead, the following paragraphs describe additional or
   stricter requirements necessary for the authentication of ACP secure
   channels in IKEv2 via ACP domain certificates.

   IKEv2 Diffie-Hellman key exchange group 19 (256-bit random ECP) MUST
   be supported (in addition to 2048-bit MODP).  ECC provides a similar

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   security level to finite-field (MODP) key exchange with a shorter key
   length, so is generally preferred absent other considerations.

   IKEv2 authentication MUST use the ACP domain certificates.  The
   Certificate Encoding "PKCS #7 wrapped X.509 certificate" (1) MUST be
   supported (see [IKEV2IANA] for this and other IANA IKEv2 parameter
   names used in this text).  If certificate chains are used, all
   intermediate certificates up to, but not including the locally
   provisioned trust anchor certificate must be signaled.

   A certificate payload with the ACP certificate MUST be included
   during IKEv2 authentication to support the ACP domain membership
   check as described in Section 6.1.3, because it is using additional
   elements of the ACP certificates.  ACP peers are expected to have the
   same set of Trust Anchors (TA), so a certificate path MUST only be
   included in the signaled payload when the path contains intermediate
   certificates not in the TA set, such as sub-CAs (see Section 6.10.7).

   In IKEv2, ACP nodes are identified by their ACP address.  The
   ID_IPv6_ADDR IKEv2 identification payload MUST be used and MUST
   convey the ACP address.  If the peer's ACP domain certificate
   includes an ACP address in the ACP domain information field (not "0"
   or empty), the address in the IKEv2 identification payload must match
   it.  See Section 6.1.3 for more information about "0" or empty ACP
   address fields in the ACP domain information field.

   IKEv2 authentication MUST use authentication method 14 ("Digital
   Signature") for ACP certificates; this authentication method can be
   used with both RSA and ECDSA certificates, as indicated by a PKIX-
   style OID.

   The Digital Signature hash SHA2-512 MUST be supported (in addition to
   SHA2-256).  IPsec with GRE encapsulation

   In network devices it is often more common to implement high
   performance virtual interfaces on top of GRE encapsulation than on
   top of a "native" IPsec association (without any other encapsulation
   than those defined by IPsec).  On those devices it may be beneficial
   to run the ACP secure channel on top of GRE protected by the IPsec

   To run ACP via GRE/IPsec, no further IANA assignments/definitions are

   The requirements for ESP/IPsec/IKEv2 are the same as for native IPsec
   (see Section except that IPsec transport mode and next

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   protocol GRE (47) are to be negotiated.  Tunnel mode is not required
   because of GRE.

   If IKEv2 initiator and responder support IPsec over GRE, it has to be
   preferred over native IPsec.  The ACP IPv6 traffic has to be carried
   across GRE according to [RFC7676].

6.7.2.  ACP via DTLS

   We define the use of ACP via DTLS in the assumption that it is likely
   the first transport encryption supported in some classes of
   constrained devices.

   An ACP node announces its ability to support DTLS (as described here)
   as an ACP secure channel protocol in GRASP through the "DTLS"
   objective-value in the "AN_ACP" objective.

   To run ACP via UDP and DTLS v1.2 [RFC6347] a locally assigned UDP
   port is used that is announced as a parameter in the GRASP AN_ACP
   objective to candidate neighbors.

   All ACP nodes supporting DTLS as a secure channel protocol MUST
   adhere to the DTLS implementation recommendations and security
   considerations of BCP 195 [RFC7525] except with respect to the DTLS
   version.  ACP nodes supporting DTLS MUST implement only DTLS 1.2 or
   later.  For example, implementing DTLS-1.3 ([I-D.ietf-tls-dtls13]) is
   also an option.

   There is no additional session setup or other security association
   besides this simple DTLS setup.  As soon as the DTLS session is
   functional, the ACP peers will exchange ACP IPv6 packets as the
   payload of the DTLS transport connection.  Any DTLS defined security
   association mechanisms such as re-keying are used as they would be
   for any transport application relying solely on DTLS.

6.7.3.  ACP Secure Channel Requirements

   As explained in the beginning of Section 6.5, there is no single
   secure channel mechanism mandated for all ACP nodes.  Instead, this
   section defines two ACP profiles (baseline and constrained) for ACP
   nodes that do introduce such requirements.

   A baseline ACP node MUST support IPsec natively and MAY support IPsec
   via GRE.  A constrained ACP node that cannot support IPsec MUST
   support DTLS.  An ACP node connecting an area of constrained ACP
   nodes with an area of baseline ACP nodes must therefore support IPsec
   and DTLS and supports therefore the baseline and constrained profile.

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   Explanation: Not all type of ACP nodes can or need to connect
   directly to each other or are able to support or prefer all possible
   secure channel mechanisms.  For example, code space limited IoT
   devices may only support DTLS because that code exists already on
   them for end-to-end security, but high-end core routers may not want
   to support DTLS because they can perform IPsec in accelerated
   hardware but would need to support DTLS in an underpowered CPU
   forwarding path shared with critical control plane operations.  This
   is not a deployment issue for a single ACP across these type of nodes
   as long as there are also appropriate gateway ACP nodes that support
   sufficiently many secure channel mechanisms to allow interconnecting
   areas of ACP nodes with a more constrained set of secure channel
   protocols.  On the edge between IoT areas and high-end core networks,
   general-purpose routers that act as those gateways and that can
   support a variety of secure channel protocols is the norm already.

   ACP nodes need to specify in documentation the set of secure ACP
   mechanisms they support and should declare which profile they support
   according to above requirements.

   An ACP secure channel MUST immediately be terminated when the
   lifetime of any certificate in the chain used to authenticate the
   neighbor expires or becomes revoked.  Note that this is not standard
   behavior in secure channel protocols such as IPsec because the
   certificate authentication only influences the setup of the secure
   channel in these protocols.

6.8.  GRASP in the ACP

6.8.1.  GRASP as a core service of the ACP

   The ACP MUST run an instance of GRASP inside of it.  It is a key part
   of the ACP services.  The function in GRASP that makes it fundamental
   as a service of the ACP is the ability to provide ACP wide service
   discovery (using objectives in GRASP).

   ACP provides IP unicast routing via the RPL routing protocol (see
   Section 6.11).

   The ACP does not use IP multicast routing nor does it provide generic
   IP multicast services (the handling of GRASP link-local multicast
   messages is explained in Section 6.8.2).  Instead, the ACP provides
   service discovery via the objective discovery/announcement and
   negotiation mechanisms of the ACP GRASP instance (services are a form
   of objectives).  These mechanisms use hop-by-hop reliable flooding of
   GRASP messages for both service discovery (GRASP M_DISCOVERY
   messages) and service announcement (GRASP M_FLOOD messages).

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   See Appendix A.5 for discussion about this design choice of the ACP.

6.8.2.  ACP as the Security and Transport substrate for GRASP

   In the terminology of GRASP ([I-D.ietf-anima-grasp]), the ACP is the
   security and transport substrate for the GRASP instance run inside
   the ACP ("ACP GRASP").

   This means that the ACP is responsible for ensuring that this
   instance of GRASP is only sending messages across the ACP GRASP
   virtual interfaces.  Whenever the ACP adds or deletes such an
   interface because of new ACP secure channels or loss thereof, the ACP
   needs to indicate this to the ACP instance of GRASP.  The ACP exists
   also in the absence of any active ACP neighbors.  It is created when
   the node has a domain certificate, and continues to exist even if all
   of its neighbors cease operation.

   In this case ASAs using GRASP running on the same node would still
   need to be able to discover each other's objectives.  When the ACP
   does not exist, ASAs leveraging the ACP instance of GRASP via APIs
   MUST still be able to operate, and MUST be able to understand that
   there is no ACP and that therefore the ACP instance of GRASP cannot

   The way ACP acts as the security and transport substrate for GRASP is
   visualized in the following picture:

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       .                                                             .
       .         /-GRASP-flooding-\         ACP GRASP instance       .
       .        /                  \                                 A
       .    GRASP      GRASP      GRASP                              C
       .  link-local   unicast  link-local                           P
       .   multicast  messages   multicast                           .
       .   messages      |       messages                            .
       .      |          |          |                                .
       .      v          v          v    ACP security and transport  .
       .      |          |          |    substrate for GRASP         .
       .      |          |          |                                .
       .      |       ACP GRASP     |       - ACP GRASP              A
       .      |       Loopback      |         Loopback interface     C
       .      |       interface     |       - ACP-cert auth          P
       .      |         TLS         |                                .
       .   ACP GRASP     |       ACP GRASP  - ACP GRASP virtual      .
       .   subnet1       |       subnet2      virtual interfaces     .
       .     TCP         |         TCP                               .
       .      |          |          |                                .
       .      |          |          |   ^^^ Users of ACP (GRASP/ASA) .
       .      |          |          |   ACP interfaces/addressing    .
       .      |          |          |                                .
       .      |          |          |                                A
       .      | ACP-Loopback Interf.|      <- ACP Loopback interface C
       .      |      ACP-address    |       - address (global ULA)   P
       .    subnet1      |        subnet2  <- ACP virtual interfaces .
       .  link-local     |      link-local  - link-local addresses   .
       .      |          |          |   ACP VRF                      .
       .      |     RPL-routing     | virtual routing and forwarding .
       .      |   /IP-Forwarding\   |                                A
       .      |  /               \  |                                C
       .  ACP IPv6 packets   ACP IPv6 packets                        P
       .      |/                   \|                                .
       .    IPsec/DTLS        IPsec/DTLS  - ACP-cert auth            .
                |                   |   Data-Plane
                |                   |
                |                   |     - ACP secure channel
            link-local        link-local  - encapsulation addresses
              subnet1            subnet2  - Data-Plane interfaces
                |                   |
             ACP-Nbr1            ACP-Nbr2

        Figure 8: ACP as security and transport substrate for GRASP

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   GRASP unicast messages inside the ACP always use the ACP address.
   Link-local addresses from the ACP VRF must not be used inside
   objectives.  GRASP unicast messages inside the ACP are transported
   via TLS according to [RFC7525] execept that only TLS version 1.2
   ([RFC5246]) or higher MUST be used - because there is no need for
   backward compatibility in the new use-case of ACP.  Mutual
   authentication MUST use the ACP domain membership check defined in
   (Section 6.1.3).

   GRASP link-local multicast messages are targeted for a specific ACP
   virtual interface (as defined Section 6.12.5) but are sent by the ACP
   into an ACP GRASP virtual interface that is constructed from the TCP
   connection(s) to the IPv6 link-local neighbor address(es) on the
   underlying ACP virtual interface.  If the ACP GRASP virtual interface
   has two or more neighbors, the GRASP link-local multicast messages
   are replicated to all neighbor TCP connections.

   TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 and MUST NOT offer options
   with less than 256bit AES or less than SHA384.  TLS for GRASP MUST
   also include the "Supported Elliptic Curves" extension, it MUST
   support support the NIST P-256 (secp256r1) and P-384 (secp384r1(24))
   curves [RFC4492].  In addition, GRASP TLS clients SHOULD send an
   ec_point_formats extension with a single element, "uncompressed".
   For further interoperability recommendations, GRASP TLS
   implementations SHOULD follow [RFC7525].

   TCP and TLS connections for GRASP in the ACP use the IANA assigned
   TCP port for GRASP (7107).  Effectively the transport stack is
   expected to be TLS for connections from/to the ACP address (e.g.,
   global scope address(es)) and TCP for connections from/to link-local
   addresses on the ACP virtual interfaces.  The latter ones are only
   used for flooding of GRASP messages.  Discussion

   TCP encapsulation for GRASP M_DISCOVERY and M_FLOOD link local
   messages is used because these messages are flooded across
   potentially many hops to all ACP nodes and a single link with even
   temporary packet loss issues (e.g., WiFi/Powerline link) can reduce
   the probability for loss free transmission so much that applications
   would want to increase the frequency with which they send these
   messages.  Such shorter periodic retransmission of datagrams would
   result in more traffic and processing overhead in the ACP than the
   hop-by-hop reliable retransmission mechanism by TCP and duplicate
   elimination by GRASP.

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   TLS is mandated for GRASP non-link-local unicast because the ACP
   secure channel mandatory authentication and encryption protects only
   against attacks from the outside but not against attacks from the
   inside: Compromised ACP members that have (not yet) been detected and
   removed (e.g., via domain certificate revocation / expiry).

   If GRASP peer connections were to use just TCP, compromised ACP
   members could simply eavesdrop passively on GRASP peer connections
   for whom they are on-path ("Man In The Middle" - MITM) or intercept
   and modify them.  With TLS, it is not possible to completely
   eliminate problems with compromised ACP members, but attacks are a
   lot more complex:

   Eavesdropping/spoofing by a compromised ACP node is still possible
   because in the model of the ACP and GRASP, the provider and consumer
   of an objective have initially no unique information (such as an
   identity) about the other side which would allow them to distinguish
   a benevolent from a compromised peer.  The compromised ACP node would
   simply announce the objective as well, potentially filter the
   original objective in GRASP when it is a MITM and act as an
   application level proxy.  This of course requires that the
   compromised ACP node understand the semantics of the GRASP
   negotiation to an extent that allows it to proxy it without being
   detected, but in an ACP environment this is quite likely public
   knowledge or even standardized.

   The GRASP TLS connections are run the same as any other ACP traffic
   through the ACP secure channels.  This leads to double
   authentication/encryption, which has the following benefits:

   o  Secure channel methods such as IPsec may provide protection
      against additional attacks, for example reset-attacks.

   o  The secure channel method may leverage hardware acceleration and
      there may be little or no gain in eliminating it.

   o  There is no different security model for ACP GRASP from other ACP
      traffic.  Instead, there is just another layer of protection
      against certain attacks from the inside which is important due to
      the role of GRASP in the ACP.

6.9.  Context Separation

   The ACP is in a separate context from the normal Data-Plane of the
   node.  This context includes the ACP channels' IPv6 forwarding and
   routing as well as any required higher layer ACP functions.

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   In classical network system, a dedicated so called Virtual routing
   and forwarding instance (VRF) is one logical implementation option
   for the ACP.  If possible by the systems software architecture,
   separation options that minimize shared components are preferred,
   such as a logical container or virtual machine instance.  The context
   for the ACP needs to be established automatically during bootstrap of
   a node.  As much as possible it should be protected from being
   modified unintentionally by ("Data-Plane") configuration.

   Context separation improves security, because the ACP is not
   reachable from the Data-Plane routing or forwarding table(s).  Also,
   configuration errors from the Data-Plane setup do not affect the ACP.

6.10.  Addressing inside the ACP

   The channels explained above typically only establish communication
   between two adjacent nodes.  In order for communication to happen
   across multiple hops, the autonomic control plane requires ACP
   network wide valid addresses and routing.  Each ACP node must create
   a Loopback interface with an ACP network wide unique address inside
   the ACP context (as explained in in Section 6.9).  This address may
   be used also in other virtual contexts.

   With the algorithm introduced here, all ACP nodes in the same routing
   subdomain have the same /48 ULA prefix.  Conversely, ULA global IDs
   from different domains are unlikely to clash, such that two ACP
   networks can be merged, as long as the policy allows that merge.  See
   also Section 9.1 for a discussion on merging domains.

   Links inside the ACP only use link-local IPv6 addressing, such that
   each node's ACP only requires one routable virtual address.

6.10.1.  Fundamental Concepts of Autonomic Addressing

   o  Usage: Autonomic addresses are exclusively used for self-
      management functions inside a trusted domain.  They are not used
      for user traffic.  Communications with entities outside the
      trusted domain use another address space, for example normally
      managed routable address space (called "Data-Plane" in this

   o  Separation: Autonomic address space is used separately from user
      address space and other address realms.  This supports the
      robustness requirement.

   o  Loopback-only: Only ACP Loopback interfaces (and potentially those
      configured for "ACP connect", see Section 8.1) carry routable
      address(es); all other interfaces (called ACP virtual interfaces)

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      only use IPv6 link local addresses.  The usage of IPv6 link local
      addressing is discussed in [RFC7404].

   o  Use-ULA: For Loopback interfaces of ACP nodes, we use Unique Local
      Addresses (ULA), as defined in [RFC4193] with L=1 (as defined in
      section 3.1 of [RFC4193]).  Note that the random hash for ACP
      Loopback addresses uses the definition in Section 6.10.2 and not
      the one of [RFC4193] section 3.2.2.

   o  No external connectivity: They do not provide access to the
      Internet.  If a node requires further reaching connectivity, it
      should use another, traditionally managed address scheme in

   o  Addresses in the ACP are permanent, and do not support temporary
      addresses as defined in [RFC4941].

   o  Addresses in the ACP are not considered sensitive on privacy
      grounds because ACP nodes are not expected to be end-user host.
      All ACP nodes are in one (potentially federated) administrative
      domain.  They are assumed to be to be candidate hosts of ACP
      traffic amongst each other or transit thereof.  There are no
      transit nodes less privileged to know about the identity of other
      hosts in the ACP.  Therefore, ACP addresses do not need to be
      pseudo-random as discussed in [RFC7721].  Because they are not
      propagated to untrusted (non ACP) nodes and stay within a domain
      (of trust), we also consider them not to be subject to scanning

   The ACP is based exclusively on IPv6 addressing, for a variety of

   o  Simplicity, reliability and scale: If other network layer
      protocols were supported, each would have to have its own set of
      security associations, routing table and process, etc.

   o  Autonomic functions do not require IPv4: Autonomic functions and
      autonomic service agents are new concepts.  They can be
      exclusively built on IPv6 from day one.  There is no need for
      backward compatibility.

   o  OAM protocols do not require IPv4: The ACP may carry OAM
      protocols.  All relevant protocols (SNMP, TFTP, SSH, SCP, Radius,
      Diameter, ...) are available in IPv6.  See also [RFC8368] for how
      ACP could be made to interoperate with IPv4 only OAM.

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6.10.2.  The ACP Addressing Base Scheme

   The Base ULA addressing scheme for ACP nodes has the following

     8      40                     2                     78
   |fd| hash(routing-subdomain) | Type |     (sub-scheme)             |

                   Figure 9: ACP Addressing Base Scheme

   The first 48-bits follow the ULA scheme, as defined in [RFC4193], to
   which a type field is added:

   o  "fd" identifies a locally defined ULA address.

   o  The 40-bits ULA "global ID" (term from [RFC4193]) for ACP
      addresses carried in the domain information field of domain
      certificates are the first 40-bits of the SHA256 hash of the
      routing subdomain from the same domain information field.  In the
      example of Section 6.1.2, the routing subdomain is
      "" and the 40-bits ULA "global ID"

   o  When creating a new routing-subdomain for an existing autonomic
      network, it MUST be ensured, that rsub is selected so the
      resulting hash of the routing-subdomain does not collide with the
      hash of any pre-existing routing-subdomains of the autonomic
      network.  This ensures that ACP addresses created by registrars
      for different routing subdomains do not collide with each others.

   o  To allow for extensibility, the fact that the ULA "global ID" is a
      hash of the routing subdomain SHOULD NOT be assumed by any ACP
      node during normal operations.  The hash function is only executed
      during the creation of the certificate.  If BRSKI is used then the
      BRSKI registrar will create the domain information field in
      response to the EST Certificate Signing Request (CSR) Attribute
      Request message by the pledge.

   o  Establishing connectivity between different ACP (different acp-
      domain-name) is outside the scope of this specification.  If it is
      being done through future extensions, then the rsub of all
      routing-subdomains across those autonomic networks need to be
      selected so the resulting routing-subdomain hashes do not collide.
      For example a large cooperation with its own private Trust Anchor
      may want to create different autonomic networks that initially
      should not be able to connect but where the option to do so should

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      be kept open.  When taking this future possibility into account,
      it is easy to always select rsub so that no collisions happen.

   o  Type: This field allows different address sub-schemes.  This
      addresses the "upgradability" requirement.  Assignment of types
      for this field will be maintained by IANA.

   The sub-scheme may imply a range or set of addresses assigned to the
   node, this is called the ACP address range/set and explained in each

   Please refer to Section 6.10.7 and Appendix A.1 for further
   explanations why the following Sub-Addressing schemes are used and
   why multiple are necessary.

   The following summarizes the addressing schemes:

   | type | Z   | name           | F-bit | V-bit size |
   | 0x00 | 0   | ACP Zone       | N/A   | 1 bit      |
   | 0x00 | 1   | ACP Manual     | N/A   | 1 bit      |
   | 0x01 | N/A | VLong-ASA      | 0     | 8-bits     |
   | 0x01 | N/A | VLong-ACP-edge | 1     | 16-bits    |

                       Figure 10: Addressing schemes

6.10.3.  ACP Zone Addressing Sub-Scheme

   The sub-scheme defined here is defined by the Type value 00b (zero)
   in the base scheme and 0 in the Z bit.

                    64                             64
   |  (base scheme)  | Z | Zone-ID ||           Node-ID               |
   |                 |   |         || Registrar-ID |   Node-Number| V |
            50         1     13            48           15          1

                 Figure 11: ACP Zone Addressing Sub-Scheme

   The fields are defined as follows:

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   o  Zone-ID: If set to all zero bits: The Node-ID bits are used as an
      identifier (as opposed to a locator).  This results in a non-
      hierarchical, flat addressing scheme.  Any other value indicates a
      zone.  See Section on how this field is used in detail.

   o  Z: MUST be 0.

   o  Node-ID: A unique value for each node.

   The 64-bit Node-ID is derived and composed as follows:

   o  Registrar-ID (48-bit): A number unique inside the domain that
      identifies the ACP registrar which assigned the Node-ID to the
      node.  A MAC address of the ACP registrar can be used for this

   o  Node-Number: A number which is unique for a given ACP registrar,
      to identify the node.  This can be a sequentially assigned number.

   o  V (1-bit): Virtualization bit: 0: Indicates the ACP itself ("ACP
      node base system); 1: Indicates the optional "host" context on the
      ACP node (see below).

   In the ACP Zone Addressing Sub-Scheme, the ACP address in the
   certificate has Zone-ID and V fields as all zero bits.  The ACP
   address set includes addresses with any Zone-ID value and any V

   The "Node-ID" itself is unique in a domain (i.e., the Zone-ID is not
   required for uniqueness).  Therefore, a node can be addressed either
   as part of a flat hierarchy (Zone-ID = 0), or with an aggregation
   scheme (any other Zone-ID).  An address with Zone-ID = 0 is an
   identifier, with a Zone-ID !=0 it is a locator.  See Section
   for more details.

   The Virtual bit in this sub-scheme allows the easy addition of the
   ACP as a component to existing systems without causing problems in
   the port number space between the services in the ACP and the
   existing system.  V:0 is the ACP router (autonomic node base system),
   V:1 is the host with pre-existing transport endpoints on it that
   could collide with the transport endpoints used by the ACP router.
   The ACP host could for example have a p2p virtual interface with the
   V:0 address as its router into the ACP.  Depending on the software
   design of ASAs, which is outside the scope of this specification,
   they may use the V:0 or V:1 address.

   The location of the V bit(s) at the end of the address allows the
   announcement of a single prefix for each ACP node.  For example, in a

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   network with 20,000 ACP nodes, this avoid 20,000 additional routes in
   the routing table.  Usage of the Zone-ID Field

   The Zone-ID allows for the introduction of route prefixes in the
   addressing scheme.

   Zone-ID = 0 is the default addressing scheme in an ACP domain.  Every
   ACP node with a Zone Addressing Sub-Scheme address MUST respond to
   its ACP address with Zone-ID = 0.  Used on its own this leads to a
   non-hierarchical address scheme, which is suitable for networks up to
   a certain size.  Zone-ID = 0 addresses act as identifiers for the
   nodes, and aggregation of these address in the ACP routing table is
   not possible.

   If aggregation is required, the 13-bit Zone-ID value allows for up to
   8191 zones.  The allocation of Zone-ID's may either happen
   automatically through a to-be-defined algorithm; or it could be
   configured and maintained explicitly.

   If a node learns (see Appendix A.10.1) that it is part of a zone, it
   MUST also respond to its ACP address with that Zone-ID.  In this case
   the ACP Loopback is configured with two ACP addresses: One for Zone-
   ID = 0 and one for the assigned Zone-ID.  This method allows for a
   smooth transition between a flat addressing scheme and a hierarchical

   A node knowing it is in a zone MUST use that Zone-ID != 0 address in
   GRASP locator fields.  This eliminates the use of the identifier
   address (Zone-ID = 0) in forwarding and the need for network wide
   reachability of those non-aggregable identifier addresses.  Zone-ID
   != 0 addresses are assumed to be aggregable in routing/forwarding
   based on how they are allocated in the ACP topology.

   Note: The Zone-ID is one method to introduce structure or hierarchy
   into the ACP.  Another way is the use of the routing subdomain field
   in the ACP that leads to multiple /48 Global IDs within an ACP

   Note: Zones and Zone-ID as defined here are not related to [RFC4007]
   zones or zone_id.  ACP zone addresses are not scoped (reachable only
   from within an RFC4007 zone) but reachable across the whole ACP.  An
   RFC4007 zone_id is a zone index that has only local significance on a
   node, whereas an ACP Zone-ID is an identifier for an ACP zone that is
   unique across that ACP.

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6.10.4.  ACP Manual Addressing Sub-Scheme

   The sub-scheme defined here is defined by the Type value 00b (zero)
   in the base scheme and 1 in the Z bit.

                   64                             64
   |    (base scheme)    | Z | Subnet-ID||     Interface Identifier    |
            50             1    13

                Figure 12: ACP Manual Addressing Sub-Scheme

   The fields are defined as follows:

   o  Subnet-ID: Configured subnet identifier.

   o  Z: MUST be 1.

   o  Interface Identifier.

   This sub-scheme is meant for "manual" allocation to subnets where the
   other addressing schemes cannot be used.  The primary use case is for
   assignment to ACP connect subnets (see Section 8.1.1).

   "Manual" means that allocations of the Subnet-ID need to be done
   today with pre-existing, non-autonomic mechanisms.  Every subnet that
   uses this addressing sub-scheme needs to use a unique Subnet-ID
   (unless some anycast setup is done).

   The Z bit field was added to distinguish Zone addressing and manual
   addressing sub-schemes without requiring one more bit in the base
   scheme and therefore allowing for the Vlong scheme (described below)
   to have one more bit available.

   Manual addressing sub-scheme addresses SHOULD NOT be used in ACP
   domain certificates.  Any node capable to build ACP secure channels
   and permitted by Registrar policy to participate in building ACP
   secure channels SHOULD receive an ACP address (prefix) from one of
   the other ACP addressing sub-schemes.  Nodes not capable (or
   permitted) to participate in ACP secure channels can connect to the
   ACP via ACP connect interfaces of ACP edge nodes (see Section 8.1),
   without setting up an ACP secure channel.  Their ACP domain
   certificate MUST include an empty acp-address to indicate that their
   ACP domain certificate is only usable for non- ACP secure channel

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   authentication, such as end-to-end transport connections across the
   ACP or Data-Plane.

   Address management of ACP connect subnets is done using traditional
   assignment methods and existing IPv6 protocols.  See Section 8.1.3
   for details.

6.10.5.  ACP Vlong Addressing Sub-Scheme

   The sub-scheme defined here is defined by the Type value 01b (one) in
   the base scheme.

             50                              78
   |    (base scheme)    ||           Node-ID                      |
   |                     || Registrar-ID |F| Node-Number|        V |
             50                46         1   23/15          8/16

                Figure 13: ACP Vlong Addressing Sub-Scheme

   This addressing scheme foregoes the Zone-ID field to allow for
   larger, flatter routed networks (e.g., as in IoT) with 8421376 Node-
   Numbers (2^23+2^15).  It also allows for up to 2^16 (i.e. 65536)
   different virtualized addresses within a node, which could be used to
   address individual software components in an ACP node.

   The fields are the same as in the Zone-ID sub-scheme with the
   following refinements:

   o  F: format bit.  This bit determines the format of the subsequent

   o  V: Virtualization bit: this is a field that is either 8 or 16
      bits.  For F=0, it is 8 bits, for F=1 it is 16 bits.  The V bits
      are assigned by the ACP node.  In the ACP certificate's ACP
      address Section 6.1.2, the V-bits are always set to 0.

   o  Registrar-ID: To maximize Node-Number and V, the Registrar-ID is
      reduced to 46-bits.  This still permits the use of the MAC address
      of an ACP registrar by removing the V and U bits from the 48-bits
      of a MAC address (those two bits are never unique, so they cannot
      be used to distinguish MAC addresses).

   o  The Node-Number is unique to each ACP node.  There are two formats
      for the Node-Number.  When F=0, the node-number is 23 bits, for

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      F=1 it is 15 bits.  Each format of node-number is considered to be
      in a unique number space.

   The F=0 bit format addresses are intended to be used for "general
   purpose" ACP nodes that would potentially have a limited number (<
   256) of clients (ASA/Autonomic Functions or legacy services) of the
   ACP that require separate V(irtual) addresses.

   The F=1 bit Node-Numbers are intended for ACP nodes that are ACP edge
   nodes (see Section 8.1.1) or that have a large number of clients
   requiring separate V(irtual) addresses.  For example large SDN
   controllers with container modular software architecture (see
   Section 8.1.2).

   In the Vlong addressing sub-scheme, the ACP address in the
   certificate has all V field bits as zero.  The ACP address set for
   the node includes any V value.

6.10.6.  Other ACP Addressing Sub-Schemes

   Before further addressing sub-schemes are defined, experience with
   the schemes defined here should be collected.  The schemes defined in
   this document have been devised to allow hopefully sufficiently
   flexible setup of ACPs for a variety of situation.  These reasons
   also lead to the fairly liberal use of address space: The Zone
   Addressing Sub-Scheme is intended to enable optimized routing in
   large networks by reserving bits for Zone-ID's.  The Vlong addressing
   sub-scheme enables the allocation of 8/16-bit of addresses inside
   individual ACP nodes.  Both address spaces allow distributed,
   uncoordinated allocation of node addresses by reserving bits for the
   registrar-ID field in the address.

   IANA is asked need to assign a new "type" for each new addressing
   sub-scheme.  With the current allocations, only 2 more schemes are
   possible, so the last addressing scheme MUST provide further
   extensions (e.g., by reserving bits from it for further extensions).

6.10.7.  ACP Registrars

   ACP registrars are responsible to enroll candidate ACP nodes with ACP
   domain certificates and associated trust point(s).  They are also
   responsible that an ACP domain information field is included in the
   ACP domain certificate carrying the ACP domain name and the ACP nodes
   ACP address prefix.  This address prefix is intended to persist
   unchanged through the lifetime of the ACP node.

   Because of the ACP addressing sub-schemes, an ACP domain can have
   multiple distributed ACP registrars that do not need to coordinate

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   for address assignment.  ACP registrars can also be sub-CAs, in which
   case they can also assign ACP domain certificates without
   dependencies against a (shared) root-CA (except during renewals of
   their own certificates).

   ACP registrars are PKI registration authorities (RA) enhanced with
   the handling of the ACP domain certificate specific fields.  They
   request certificates for ACP nodes from a Certificate Authority
   through any appropriate mechanism (out of scope in this document, but
   required to be BRSKI for ANI registrars).  Only nodes that are
   trusted to be compliant with the requirements against registrar
   described in this section must be given the necessary credentials to
   perform this RA function, such as credentials for the BRSKI
   connection to the CA for ANI registrars.  Use of BRSKI or other Mechanism/Protocols

   Any protocols or mechanisms may be used as ACP registrars, as long as
   the resulting ACP certificate and trust anchors allow to perform the
   ACP domain membership described in Section 6.1.3 with other ACP
   domain members, and meet the ACP addressing requirements for its ACP
   domain information field as described further below in this section.

   An ACP registrar could be a person deciding whether to enroll a
   candidate ACP node and then orchestrating the enrollment of the ACP
   certificate and associated trust anchor, using command line or web
   based commands on the candidate ACP node and trust anchor to generate
   and sign the ACP domain certificate and configure certificate and
   trust anchors onto the node.

   The only currently defined protocol for ACP registrars is BRSKI
   ([I-D.ietf-anima-bootstrapping-keyinfra]).  When BRSKI is used, the
   ACP nodes are called ANI nodes, and the ACP registrars are called
   BRSKI or ANI registrars.  The BRSKI specification does not define the
   handling of the ACP domain information field because the rules do not
   depend on BRSKI but apply equally to any protocols/mechanisms an ACP
   registrar may use.  Unique Address/Prefix allocation

   ACP registrars MUST NOT allocate ACP address prefixes to ACP nodes
   via the ACP domain information field that would collide with the ACP
   address prefixes of other ACP nodes in the same ACP domain.  This
   includes both prefixes allocated by the same ACP registrar to
   different ACP nodes as well as prefixes allocated by other ACP
   registrars for the same ACP domain.

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   For this purpose, an ACP registrar MUST have one or more unique
   46-bit identifiers called Registrar-IDs used to allocate ACP address
   prefixes.  The lower 46-bits of a EUI-48 MAC addresses are globally
   unique 46 bit identifiers, so ACP registrars with known unique EUI-48
   MAC addresses can use these as Registrar-IDs.  Registrar-IDs do not
   need to be globally unique but only unique across the set of ACP
   registrars for an ACP domain, so other means to assign unique
   Registrar-IDs to ACP registrars can be used, such as configuration on
   the ACP registrars.

   When the candidate ACP device (called Pledge in BRSKI) is to be
   enrolled into an ACP domain, the ACP registrar needs to allocate a
   unique ACP address to the node and ensure that the ACP certificate
   gets a domain information field (Section 6.1.2) with the appropriate
   information - ACP domain-name, ACP-address, and so on.  If the ACP
   registrar uses BRSKI, it signals the ACP domain information field to
   the Pledge via the EST /csrattrs command (see
   [I-D.ietf-anima-bootstrapping-keyinfra], section 5.9.2 - "EST CSR

   [RFC Editor: please update reference to section 5.9.2 accordingly
   with latest BRSKI draft at time of publishing, or RFC]  Addressing Sub-Scheme Policies

   The ACP registrar selects for the candidate ACP node a unique address
   prefix from an appropriate ACP addressing sub-scheme, either a zone
   addressing sub-scheme prefix (see Section 6.10.3), or a Vlong
   addressing sub-scheme prefix (see Section 6.10.5).  The assigned ACP
   address prefix encoded in the domain information field of the ACP
   domain certificate indicates to the ACP node its ACP address
   information.  The sub-addressing scheme indicates the prefix length:
   /127 for zone address sub-scheme, /120 or /112 for Vlong address sub-
   scheme.  The first address of the prefix is the ACP address.  All
   other addresses in the prefix are for other uses by the ACP node as
   described in the zone and Vlong addressing sub scheme sections.  The
   ACP address prefix itself is then signaled by the ACP node into the
   ACP routing protocol (see Section 6.11) to establish IPv6
   reachability across the ACP.

   The choice of addressing sub-scheme and prefix-length in the Vlong
   address sub-scheme is subject to ACP registrar policy.  It could be
   an ACP domain wide policy, or a per ACP node or per ACP node type
   policy.  For example, in BRSKI, the ACP registrar is aware of the
   IDevID of the candidate ACP node, which contains a "serialNnumber"
   that is typically indicating the node's vendor and device type and
   can be used to drive a policy selecting an appropriate addressing
   sub-scheme for the (class of) node(s).

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   ACP registrars SHOULD default to allocate ACP zone sub-address scheme
   addresses with Zone-ID 0.  Allocation and use of zone sub-addresses
   with Zone-ID != 0 is outside the scope of this specification because
   it would need to go along with rules for extending ACP routing to
   multiple zones, which is outside the scope of this specification.

   ACP registrars that can use the IDevID of a candidate ACP device
   SHOULD be able to choose the zone vs. Vlong sub-address scheme for
   ACP nodes based on the "serialNumber" of the IDevID, for example by
   the PID (Product Identifier) part which identifies the product type,
   or the complete "serialNumber".

   In a simple allocation scheme, an ACP registrar remembers
   persistently across reboots its currently used Registrar-ID and for
   each addressing scheme (zone with Zone-ID 0, Vlong with /112, Vlong
   with /120), the next Node-Number available for allocation and
   increases it during successful enrollment to an ACP node.  In this
   simple allocation scheme, the ACP registrar would not recycle ACP
   address prefixes from no longer used ACP nodes.  Address/Prefix Persistence

   When an ACP domain certificate is renewed or rekeyed via EST or other
   mechanisms, the ACP address/prefix in the ACP domain information
   field MUST be maintained unless security issues or violations of the
   unique address assignment requirements exist or are suspected by the
   ACP registrar.

   ACP address information SHOULD be maintained even when the renewing/
   rekeying ACP registrar is not the same as the one that enrolled the
   prior ACP certificate.  See Section 10.2.4 for an example.

   ACP address information SHOULD also be maintained even after an ACP
   certificate did expire or failed.  See Section and
   Section  Further Details

   Section 10.2 discusses further informative details of ACP registrars:
   What interactions registrars need, what parameters they require,
   certificate renewal and limitations, use of sub-CAs on registrars and
   centralized policy control.

6.11.  Routing in the ACP

   Once ULA address are set up all autonomic entities should run a
   routing protocol within the autonomic control plane context.  This
   routing protocol distributes the ULA created in the previous section

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   for reachability.  The use of the autonomic control plane specific
   context eliminates the probable clash with Data-Plane routing tables
   and also secures the ACP from interference from the configuration
   mismatch or incorrect routing updates.

   The establishment of the routing plane and its parameters are
   automatic and strictly within the confines of the autonomic control
   plane.  Therefore, no explicit configuration is required.

   All routing updates are automatically secured in transit as the
   channels of the ACP are encrypted, and this routing runs only inside
   the ACP.

   The routing protocol inside the ACP is RPL ([RFC6550]).  See
   Appendix A.4 for more details on the choice of RPL.

   RPL adjacencies are set up across all ACP channels in the same domain
   including all its routing subdomains.  See Appendix A.7 for more

6.11.1.  RPL Profile

   The following is a description of the RPL profile that ACP nodes need
   to support by default.  The format of this section is derived from
   draft-ietf-roll-applicability-template.  Overview

   The choosen RPL profile is one that expects a fairly reliable network
   with reasonably fast links so that RPL convergence will be triggered
   immediately upon recognition of link failure/recovery.

   The profile is also designed to not require any RPL Data-Plane
   artifacts (such as defined in [RFC6553]).  This is largely driven by
   the desire to avoid introducing the required Hop-by-Hop headers into
   the ACP forwarding plane, especially to support devices with silicon
   forwarding planes that cannot support insertion/removal of these
   headers in silicon or hop-by-hop forwarding based on them.  Note:
   Insertion/removal of headers by a (potentially silicon based) ACP
   node would be be necessary when senders/receivers of ACP packets are
   legacy NOC devices connected via ACP connect (see Section 8.1.1 to
   the ACP.  Their connectivity can be handled in RPL as non-RPL-aware
   leafs (or "Internet") according to the Data-Plane architecture
   explained in [I-D.ietf-roll-useofrplinfo].

   To avoid Data-Plane artefacts, the profile uses a simple destination
   prefix based routing/forwarding table.  To achieve this, the profiles
   uses only one RPL instanceID.  This single instanceID can contain

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   only one Destination Oriented Directed Acyclic Graph (DODAG), and the
   routing/forwarding table can therefore only calculate a single class
   of service ("best effort towards the primary NOC/root") and cannot
   create optimized routing paths to accomplish latency or energy goals
   between any two nodes.

   Consider a network that has multiple NOCs in different locations.
   Only one NOC will become the DODAG root.  Traffic to and from other
   NOCs has to be sent through the DODAG (shortest path tree) rooted in
   the primary NOC.  Depending on topology, this can be an annoyance
   from a latency point of view or from minimizing network path
   resources, but this is deemed to be acceptable given how ACP traffic
   is "only" network management/control traffic.

   Using a single instanceID/DODAG does not introduce a single point of
   failure, as the DODAG will reconfigure itself when it detects data-
   plane forwarding failures including choosing a different root when
   the primary one fails.  See Appendix A.10.4 for more details.

   The benefit of this profile, especially compared to other IGPs is
   that it does not calculate routes for node reachable through the same
   interface as the DODAG root.  This RPL profile can therefore scale to
   much larger number of ACP nodes in the same amount of compute and
   memory than other routing protocols.  Especially on nodes that are
   leafs of the topology or those close to those leafs.

   The lack of RPL Packet Information (RPI, the IPv6 header for RPL
   defined by [RFC6553]), means that the Data-Plane will have no rank
   value that can be used to detect loops.  As a result, traffic may
   loop until the time-to-live (TTL) of the packet reaches zero.  This
   is the same behavior as that of other IGPs that do not have the Data-
   Plane options of RPL.

   Since links in the ACP are assumed to be mostly reliable (or have
   link layer protection against loss) and because there is no stretch
   according to Section, loops caused by RPL routing packet
   loss should be exceedingly rare.

   There are a variety of mechanisms possible in RPL to further avoid
   temporary loops: DODAG Information Objects (DIOs) SHOULD be sent
   2...3 times to inform children when losing the last parent.  The
   technique in [RFC6550] section  (Detaching) SHOULD be
   favored over that in section, (Poisoning) because it allows
   local connectivity.  Nodes SHOULD select more than one parent, at
   least 3 if possible, and send Destination Advertisement Objects
   (DAO)s to all of them in parallel.

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   Additionally, failed ACP tunnels can be quickly discovered trough the
   secure channel protocol mechanisms such as IKEv2 Dead Peer Detection.
   This can function as a replacement for a Low-power and Lossy
   Networks' (LLN's) Expected Transmission Count (ETX) feature that is
   not used in this profile.  A failure of an ACP tunnel should
   imediately signal the RPL control plane to pick a different parent.  RPL Instances

   Single RPL instance.  Default RPLInstanceID = 0.  Storing vs. Non-Storing Mode

   RPL Mode of Operations (MOP): MUST support mode 2 - "Storing Mode of
   Operations with no multicast support".  Implementations MAY support
   mode 3 ("... with multicast support" as that is a superset of mode
   2).  Note: Root indicates mode in DIO flow.  DAO Policy

   Proactive, aggressive DAO state maintenance:

   o  Use K-flag in unsolicited DAO indicating change from previous
      information (to require DAO-ACK).

   o  Retry such DAO DAO-RETRIES(3) times with DAO- ACK_TIME_OUT(256ms)
      in between.  Path Metric

   Hopcount.  Objective Function

   Objective Function (OF): Use OF0 [RFC6552].  No use of metric

   rank_factor: Derived from link speed: <= 100Mbps:

   Global Repair: we assume stable links and ranks (metrics), so no need
   to periodically rebuild DODAG.  DODAG version only incremented under
   catastrophic events (e.g., administrative action).

   Local Repair: As soon as link breakage is detected, send No-Path DAO
   for all the targets that were reachable only via this link.  As soon

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   as link repair is detected, validate if this link provides you a
   better parent.  If so, compute your new rank, and send new DIO that
   advertises your new rank.  Then send a DAO with a new path sequence
   about yourself.

   stretch_rank: none provided ("not stretched").

   Data Path Validation: Not used.

   Trickle: Not used.  Multicast

   Not used yet but possible because of the selected mode of operations.  Security

   [RFC6550] security not used, substituted by ACP security.

   Because the ACP links already include provisions for confidentiality
   and integrity protection, their usage at the RPL layer would be
   redundant, and so RPL security is not used.  P2P communications

   Not used.  IPv6 address configuration

   Every ACP node (RPL node) announces an IPv6 prefix covering the
   address(es) used in the ACP node.  The prefix length depends on the
   chosen addressing sub-scheme of the ACP address provisioned into the
   certificate of the ACP node, e.g., /127 for Zone Addressing Sub-
   Scheme or /112 or /120 for Vlong addressing sub-scheme.  See
   Section 6.10 for more details.

   Every ACP node MUST install a black hole (aka null) route for
   whatever ACP address space that it advertises (i.e.: the /96 or
   /127).  This is avoid routing loops for addresses that an ACP node
   has not (yet) used.  Administrative parameters

   Administrative Preference ([RFC6550], 3.2.6 - to become root):
   Indicated in DODAGPreference field of DIO message.

   o  Explicit configured "root": 0b100

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   o  ACP registrar (Default): 0b011

   o  ACP-connect (non-registrar): 0b010

   o  Default: 0b001.  RPL Data-Plane artifacts

   RPI (RPL Packet Information [RFC6553]): Not used as there is only a
   single instance, and data path validation is not being used.

   SRH (RPL Source Routing - RFC6552): Not used.  Storing mode is being
   used.  Unknown Destinations

   Because RPL minimizes the size of the routing and forwarding table,
   prefixes reachable through the same interface as the RPL root are not
   known on every ACP node.  Therefore traffic to unknown destination
   addresses can only be discovered at the RPL root.  The RPL root
   SHOULD have attach safe mechanisms to operationally discover and log
   such packets.

   As this requirement raises additional data plane requirements, it
   does not apply to nodes where the administrative parameter to become
   root (Section can always only be 0b001, e.g.: the node
   does not support explicit configuration to be root, or to be ACP
   registrar or to have ACP-connect functionality.  If an ACP network is
   degraded to the point where there are no nodes that could be
   configured roots, ACP registrars or ACP-connect nodes, traffic to
   unknown destinations could not be diagnosed, but in the absence of
   any intelligent nodes supporting other than 0b001 administrative
   preference, there is likely also no diagnostic function possible.

6.12.  General ACP Considerations

   Since channels are by default established between adjacent neighbors,
   the resulting overlay network does hop-by-hop encryption.  Each node
   decrypts incoming traffic from the ACP, and encrypts outgoing traffic
   to its neighbors in the ACP.  Routing is discussed in Section 6.11.

6.12.1.  Performance

   There are no performance requirements against ACP implementations
   defined in this document because the performance requirements depend
   on the intended use case.  It is expected that full autonomic node
   with a wide range of ASA can require high forwarding plane
   performance in the ACP, for example for telemetry.  Implementations

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   of ACP to solely support traditional/SDN style use cases can benefit
   from ACP at lower performance, especially if the ACP is used only for
   critical operations, e.g., when the Data-Plane is not available.  The
   design of the ACP as specified in this document is intended to
   support a wide range of performance options: It is intended to allow
   software-only implementations at potentially low performance, but can
   also support high performance options.  See [RFC8368] for more

6.12.2.  Addressing of Secure Channels

   In order to be independent of the Data-Plane (routing and addressing)
   the GRASP discovered (autonomic) ACP secure channels use IPv6 link
   local addresses between adjacent neighbors.  Note: Section 8.2
   specifies extensions in which secure channels are configured tunnels
   operating over the Data-Plane, so those secure channels cannot be
   independent of the Data-Plane.

   To avoid that Data-Plane configuration can impact the operations of
   the IPv6 (link-local) interface/address used for ACP channels,
   appropriate implementation considerations are required.  If the IPv6
   interface/link-local address is shared with the Data-Plane it needs
   to be impossible to unconfigure/disable it through configuration.
   Instead of sharing the IPv6 interface/link-local address, a separate
   (virtual) interface with a separate IPv6 link-local address can be
   used.  For example, the ACP interface could be run over a separate
   MAC address of an underlying L2 (Ethernet) interface.  For more
   details and options, see Appendix A.10.2.

   Note that other (non-ideal) implementation choices may introduce
   additional undesired dependencies against the Data-Plane.  For
   example shared code and configuration of the secure channel protocols
   (IPsec / DTLS).

6.12.3.  MTU

   The MTU for ACP secure channels must be derived locally from the
   underlying link MTU minus the secure channel encapsulation overhead.

   ACP secure Channel protocols do not need to perform MTU discovery
   because they are built across L2 adjacencies - the MTU on both sides
   connecting to the L2 connection are assumed to be consistent.
   Extensions to ACP where the ACP is for example tunneled need to
   consider how to guarantee MTU consistency.  This is an issue of
   tunnels, not an issue of running the ACP across a tunnel.  Transport
   stacks running across ACP can perform normal PMTUD (Path MTU
   Discovery).  Because the ACP is meant to be prioritize reliability
   over performance, they MAY opt to only expect IPv6 minimum MTU (1280)

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   to avoid running into PMTUD implementation bugs or underlying link
   MTU mismatch problems.

6.12.4.  Multiple links between nodes

   If two nodes are connected via several links, the ACP SHOULD be
   established across every link, but it is possible to establish the
   ACP only on a sub-set of links.  Having an ACP channel on every link
   has a number of advantages, for example it allows for a faster
   failover in case of link failure, and it reflects the physical
   topology more closely.  Using a subset of links (for example, a
   single link), reduces resource consumption on the node, because state
   needs to be kept per ACP channel.  The negotiation scheme explained
   in Section 6.5 allows Alice (the node with the higher ACP address) to
   drop all but the desired ACP channels to Bob - and Bob will not re-
   try to build these secure channels from his side unless Alice shows
   up with a previously unknown GRASP announcement (e.g., on a different
   link or with a different address announced in GRASP).

6.12.5.  ACP interfaces

   The ACP VRF has conceptually two type of interfaces: The "ACP
   Loopback interface(s)" to which the ACP ULA address(es) are assigned
   and the "ACP virtual interfaces" that are mapped to the ACP secure

   The term "Loopback interface" was introduced initially to refer to an
   internal interface on a node that would allow IP traffic between
   transport endpoints on the node in the absence or failure of any or
   all external interfaces, see [RFC4291] section 2.5.3.

   Even though Loopback interfaces were originally designed to hold only
   Loopback addresses not reachable from outside the node, these
   interfaces are also commonly used today to hold addresses reachable
   from the outside.  They are meant to be reachable independent of any
   external interface being operational, and therefore to be more
   resilient.  These addresses on Loopback interfaces can be thought of
   as "node addresses" instead of "interface addresses", and that is
   what ACP address(es) are.  This construct makes it therefore possible
   to address ACP nodes with a well-defined set of addresses independent
   of the number of external interfaces.

   For these reason, the ACP (ULA) address(es) are assigned to Loopback

   Any type of ACP secure channels to another ACP node can be mapped to
   ACP virtual interfaces in following ways.  This is independent of the

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   chosen secure channel protocol (IPsec, DTLS or other future protocol
   - standards or non-standards):

   ACP point-to-point virtual interface:

   Each ACP secure channel is mapped into a separate point-to-point ACP
   virtual interface.  If a physical subnet has more than two ACP
   capable nodes (in the same domain), this implementation approach will
   lead to a full mesh of ACP virtual interfaces between them.

   ACP multi-access virtual interface:

   In a more advanced implementation approach, the ACP will construct a
   single multi-access ACP virtual interface for all ACP secure channels
   to ACP capable nodes reachable across the same underlying (physical)
   subnet.  IPv6 link-local multicast packets sent into an ACP multi-
   access virtual interface are replicated to every ACP secure channel
   mapped into the ACP multicast-access virtual interface.  IPv6 unicast
   packets sent into an ACP multi-access virtual interface are sent to
   the ACP secure channel that belongs to the ACP neighbor that is the
   next-hop in the ACP forwarding table entry used to reach the packets
   destination address.

   There is no requirement for all ACP nodes on the same multi-access
   subnet to use the same type of ACP virtual interface.  This is purely
   a node local decision.

   ACP nodes MUST perform standard IPv6 operations across ACP virtual
   interfaces including SLAAC (Stateless Address Auto-Configuration) -
   [RFC4862]) to assign their IPv6 link local address on the ACP virtual
   interface and ND (Neighbor Discovery - [RFC4861]) to discover which
   IPv6 link-local neighbor address belongs to which ACP secure channel
   mapped to the ACP virtual interface.  This is independent of whether
   the ACP virtual interface is point-to-point or multi-access.

   "Optimistic Duplicate Address Detection (DAD)" according to [RFC4429]
   is RECOMMENDED because the likelihood for duplicates between ACP
   nodes is highly improbable as long as the address can be formed from
   a globally unique local assigned identifier (e.g., EUI-48/EUI-64, see

   ACP nodes MAY reduce the amount of link-local IPv6 multicast packets
   from ND by learning the IPv6 link-local neighbor address to ACP
   secure channel mapping from other messages such as the source address
   of IPv6 link-local multicast RPL messages - and therefore forego the
   need to send Neighbor Solicitation messages.

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   The ACP virtual interface IPv6 link local address can be derived from
   any appropriate local mechanism such as node local EUI-48 or EUI-64
   ("EUI" stands for "Extended Unique Identifier").  It MUST NOT depend
   on something that is attackable from the Data-Plane such as the IPv6
   link-local address of the underlying physical interface, which can be
   attacked by SLAAC, or parameters of the secure channel encapsulation
   header that may not be protected by the secure channel mechanism.

   The link-layer address of an ACP virtual interface is the address
   used for the underlying interface across which the secure tunnels are
   built, typically Ethernet addresses.  Because unicast IPv6 packets
   sent to an ACP virtual interface are not sent to a link-layer
   destination address but rather an ACP secure channel, the link-layer
   address fields SHOULD be ignored on reception and instead the ACP
   secure channel from which the message was received should be

   Multi-access ACP virtual interfaces are preferable implementations
   when the underlying interface is a (broadcast) multi-access subnet
   because they do reflect the presence of the underlying multi-access
   subnet into the virtual interfaces of the ACP.  This makes it for
   example simpler to build services with topology awareness inside the
   ACP VRF in the same way as they could have been built running
   natively on the multi-access interfaces.

   Consider also the impact of point-to-point vs. multi-access virtual
   interface on the efficiency of flooding via link local multicasted

   Assume a LAN with three ACP neighbors, Alice, Bob and Carol.  Alice's
   ACP GRASP wants to send a link-local GRASP multicast message to Bob
   and Carol.  If Alice's ACP emulates the LAN as one point-to-point
   virtual interface to Bob and one to Carol, The sending applications
   itself will send two copies, if Alice's ACP emulates a LAN, GRASP
   will send one packet and the ACP will replicate it.  The result is
   the same.  The difference happens when Bob and Carol receive their
   packet.  If they use ACP point-to-point virtual interfaces, their
   GRASP instance would forward the packet from Alice to each other as
   part of the GRASP flooding procedure.  These packets are unnecessary
   and would be discarded by GRASP on receipt as duplicates (by use of
   the GRASP Session ID).  If Bob and Carol's ACP would emulate a multi-
   access virtual interface, then this would not happen, because GRASPs
   flooding procedure does not replicate back packets to the interface
   that they were received from.

   Note that link-local GRASP multicast messages are not sent directly
   as IPv6 link-local multicast UDP messages into ACP virtual
   interfaces, but instead into ACP GRASP virtual interfaces, that are

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   layered on top of ACP virtual interfaces to add TCP reliability to
   link-local multicast GRASP messages.  Nevertheless, these ACP GRASP
   virtual interfaces perform the same replication of message and,
   therefore, result in the same impact on flooding.  See Section 6.8.2
   for more details.

   RPL does support operations and correct routing table construction
   across non-broadcast multi-access (NBMA) subnets.  This is common
   when using many radio technologies.  When such NBMA subnets are used,
   they MUST NOT be represented as ACP multi-access virtual interfaces
   because the replication of IPv6 link-local multicast messages will
   not reach all NBMA subnet neighbors.  In result, GRASP message
   flooding would fail.  Instead, each ACP secure channel across such an
   interface MUST be represented as a ACP point-to-point virtual
   interface.  See also Appendix A.10.4.

   Care must also be taken when creating multi-access ACP virtual
   interfaces across ACP secure channels between ACP nodes in different
   domains or routing subdomains.  If for example future inter-domain
   ACP policies are defined as "peer-to-peer" policies, it is easier to
   create ACP point-to-point virtual interfaces for these inter-domain
   secure channels.

7.  ACP support on L2 switches/ports (Normative)

7.1.  Why (Benefits of ACP on L2 switches)

       ANrtr1 ------ ANswitch1 --- ANswitch2 ------- ANrtr2
                 .../   \                   \  ...
       ANrtrM ------     \                   ------- ANrtrN
                          ANswitchM ...

                 Figure 14: Topology with L2 ACP switches

   Consider a large L2 LAN with ANrtr1...ANrtrN connected via some
   topology of L2 switches.  Examples include large enterprise campus
   networks with an L2 core, IoT networks or broadband aggregation
   networks which often have even a multi-level L2 switched topology.

   If the discovery protocol used for the ACP is operating at the subnet
   level, every ACP router will see all other ACP routers on the LAN as
   neighbors and a full mesh of ACP channels will be built.  If some or
   all of the AN switches are autonomic with the same discovery
   protocol, then the full mesh would include those switches as well.

   A full mesh of ACP connections can create fundamental scale
   challenges.  The number of security associations of the secure

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   channel protocols will likely not scale arbitrarily, especially when
   they leverage platform accelerated encryption/decryption.  Likewise,
   any other ACP operations (such as routing) needs to scale to the
   number of direct ACP neighbors.  An ACP router with just 4 physical
   interfaces might be deployed into a LAN with hundreds of neighbors
   connected via switches.  Introducing such a new unpredictable scaling
   factor requirement makes it harder to support the ACP on arbitrary
   platforms and in arbitrary deployments.

   Predictable scaling requirements for ACP neighbors can most easily be
   achieved if in topologies such as these, ACP capable L2 switches can
   ensure that discovery messages terminate on them so that neighboring
   ACP routers and switches will only find the physically connected ACP
   L2 switches as their candidate ACP neighbors.  With such a discovery
   mechanism in place, the ACP and its security associations will only
   need to scale to the number of physical interfaces instead of a
   potentially much larger number of "LAN-connected" neighbors.  And the
   ACP topology will follow directly the physical topology, something
   which can then also be leveraged in management operations or by ASAs.

   In the example above, consider ANswitch1 and ANswitchM are ACP
   capable, and ANswitch2 is not ACP capable.  The desired ACP topology
   is that ANrtr1 and ANrtrM only have an ACP connection to ANswitch1,
   and that ANswitch1, ANrtr2, ANrtrN have a full mesh of ACP connection
   amongst each other.  ANswitch1 also has an ACP connection with
   ANswitchM and ANswitchM has ACP connections to anything else behind

7.2.  How (per L2 port DULL GRASP)

   To support ACP on L2 switches or L2 switched ports of an L3 device,
   it is necessary to make those L2 ports look like L3 interfaces for
   the ACP implementation.  This primarily involves the creation of a
   separate DULL GRASP instance/domain on every such L2 port.  Because
   GRASP has a dedicated link-local IPv6 multicast address
   (ALL_GRASP_NEIGHBORS), it is sufficient that all packets for this
   address are being extracted at the port level and passed to that DULL
   GRASP instance.  Likewise the IPv6 link-local multicast packets sent
   by that DULL GRASP instance need to be sent only towards the L2 port
   for this DULL GRASP instance.

   If the device with L2 ports is supporting per L2 port ACP DULL GRASP
   as well as MLD snooping ([RFC4541]), then MLD snooping must be
   changed to never forward packets for ALL_GRASP_NEIGHBORS because that
   would cause the problem that per L2 port ACP DULL GRASP is meant to
   overcome (forwarding DULL GRASP packets across L2 ports).

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   The rest of ACP operations can operate in the same way as in L3
   devices: Assume for example that the device is an L3/L2 hybrid device
   where L3 interfaces are assigned to VLANs and each VLAN has
   potentially multiple ports.  DULL GRASP is run as described
   individually on each L2 port.  When it discovers a candidate ACP
   neighbor, it passes its IPv6 link-local address and supported secure
   channel protocols to the ACP secure channel negotiation that can be
   bound to the L3 (VLAN) interface.  It will simply use link-local IPv6
   multicast packets to the candidate ACP neighbor.  Once a secure
   channel is established to such a neighbor, the virtual interface to
   which this secure channel is mapped should then actually be the L2
   port and not the L3 interface to best map the actual physical
   topology into the ACP virtual interfaces.  See Section 6.12.5 for
   more details about how to map secure channels into ACP virtual
   interfaces.  Note that a single L2 port can still have multiple ACP
   neighbors if it connect for example to multiple ACP neighbors via a
   non-ACP enabled switch.  The per L2 port ACP virtual interface can
   therefore still be a multi-access virtual LAN.

   For example, in the above picture, ANswitch1 would run separate DULL
   GRASP instances on its ports to ANrtr1, ANswitch2 and ANswitchI, even
   though all those three ports may be in the data plane in the same
   (V)LAN and perform L2 switching between these ports, ANswitch1 would
   perform ACP L3 routing between them.

   The description in the previous paragraph was specifically meant to
   illustrate that on hybrid L3/L2 devices that are common in
   enterprise, IoT and broadband aggregation, there is only the GRASP
   packet extraction (by Ethernet address) and GRASP link-local
   multicast per L2-port packet injection that has to consider L2 ports
   at the hardware forwarding level.  The remaining operations are
   purely ACP control plane and setup of secure channels across the L3
   interface.  This hopefully makes support for per-L2 port ACP on those
   hybrid devices easy.

   This L2/L3 optimized approach is subject to "address stealing", e.g.,
   where a device on one port uses addresses of a device on another
   port.  This is a generic issue in L2 LANs and switches often already
   have some form of "port security" to prohibit this.  They rely on NDP
   or DHCP learning of which port/MAC-address and IPv6 address belong
   together and block duplicates.  This type of function needs to be
   enabled to prohibit DoS attacks.  Likewise the GRASP DULL instance
   needs to ensure that the IPv6 address in the locator-option matches
   the source IPv6 address of the DULL GRASP packet.

   In devices without such a mix of L2 port/interfaces and L3 interfaces
   (to terminate any transport layer connections), implementation
   details will differ.  Logically most simply every L2 port is

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   considered and used as a separate L3 subnet for all ACP operations.
   The fact that the ACP only requires IPv6 link-local unicast and
   multicast should make support for it on any type of L2 devices as
   simple as possible.

   A generic issue with ACP in L2 switched networks is the interaction
   with the Spanning Tree Protocol.  Without further L2 enhancements,
   the ACP would run only across the active STP topology and the ACP
   would be interrupted and re-converge with STP changes.  Ideally, ACP
   peering should be built also across ports that are blocked in STP so
   that the ACP does not depend on STP and can continue to run
   unaffected across STP topology changes, where re-convergence can be
   quite slow.  The above described simple implementation options are
   not sufficient to achieve this.

8.  Support for Non-ACP Components (Normative)

8.1.  ACP Connect

8.1.1.  Non-ACP Controller / NMS system

   The Autonomic Control Plane can be used by management systems, such
   as controllers or network management system (NMS) hosts (henceforth
   called simply "NMS hosts"), to connect to devices (or other type of
   nodes) through it.  For this, an NMS host must have access to the
   ACP.  The ACP is a self-protecting overlay network, which allows by
   default access only to trusted, autonomic systems.  Therefore, a
   traditional, non-ACP NMS system does not have access to the ACP by
   default, such as any other external node.

   If the NMS host is not autonomic, i.e., it does not support autonomic
   negotiation of the ACP, then it can be brought into the ACP by
   explicit configuration.  To support connections to adjacent non-ACP
   nodes, an ACP node must support "ACP connect" (sometimes also called
   "autonomic connect"):

   "ACP connect" is an interface level configured workaround for
   connection of trusted non-ACP nodes to the ACP.  The ACP node on
   which ACP connect is configured is called an "ACP edge node".  With
   ACP connect, the ACP is accessible from those non-ACP nodes (such as
   NOC systems) on such an interface without those non-ACP nodes having
   to support any ACP discovery or ACP channel setup.  This is also
   called "native" access to the ACP because to those (NOC) systems the
   interface looks like a normal network interface (without any

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                                   Data-Plane "native" (no ACP)
  +--------+       +----------------+       .         +-------------+
  | ACP    |       |ACP Edge Node   |       .         |             |
  | Node   |       |                |       v         |             |
  |        |-------|...[ACP VRF]....+-----------------|             |+
  |        |   ^   |.               |                 | NOC Device  ||
  |        |   .   | .[Data-Plane]..+-----------------| "NMS hosts" ||
  |        |   .   |  [          ]  | .          ^    |             ||
  +--------+   .   +----------------+  .         .    +-------------+|
               .                        .        .     +-------------+
               .                        .        .
            Data-Plane "native"         .     ACP "native" (unencrypted)
          + ACP auto-negotiated         .    "ACP connect subnet"
            and encrypted               .
                                        ACP connect interface
                                        e.g., "VRF ACP native" (config)

                          Figure 15: ACP connect

   ACP connect has security consequences: All systems and processes
   connected via ACP connect have access to all ACP nodes on the entire
   ACP, without further authentication.  Thus, the ACP connect interface
   and (NOC) systems connected to it must be physically controlled/
   secured.  For this reason the mechanisms described here do explicitly
   not include options to allow for a non-ACP router to be connected
   across an ACP connect interface and addresses behind such a router
   routed inside the ACP.

   An ACP connect interface provides exclusively access to only the ACP.
   This is likely insufficient for many NMS hosts.  Instead, they would
   require a second "Data-Plane" interface outside the ACP for
   connections between the NMS host and administrators, or Internet
   based services, or for direct access to the Data-Plane.  The document
   "Using Autonomic Control Plane for Stable Connectivity of Network
   OAM" [RFC8368] explains in more detail how the ACP can be integrated
   in a mixed NOC environment.

   An ACP connect interface SHOULD use an IPv6 address/prefix from the
   ACP Manual Addressing Sub-Scheme (Section 6.10.4), letting the
   operator configure for example only the Subnet-ID and having the node
   automatically assign the remaining part of the prefix/address.  It
   SHOULD NOT use a prefix that is also routed outside the ACP so that
   the addresses clearly indicate whether it is used inside the ACP or

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   The prefix of ACP connect subnets MUST be distributed by the ACP edge
   node into the ACP routing protocol (RPL).  The NMS hosts MUST connect
   to prefixes in the ACP routing table via its ACP connect interface.
   In the simple case where the ACP uses only one ULA prefix and all ACP
   connect subnets have prefixes covered by that ULA prefix, NMS hosts
   can rely on [RFC6724] to determine longest match prefix routes
   towards its different interfaces, ACP and data-plane.  With RFC6724,
   The NMS host will select the ACP connect interface for all addresses
   in the ACP because any ACP destination address is longest matched by
   the address on the ACP connect interface.  If the NMS hosts ACP
   connect interface uses another prefix or if the ACP uses multiple ULA
   prefixes, then the NMS hosts require (static) routes towards the ACP
   interface for these prefixes.

   When an ACP Edge node receives a packet from an ACP connect
   interface, the ACP Edge node MUST only forward the packet into the
   ACP if the packet has an IPv6 source address from that interface.
   This is sometimes called "RPF filtering".  This MAY be changed
   through administrative measures.

   To limit the security impact of ACP connect, nodes supporting it
   SHOULD implement a security mechanism to allow configuration/use of
   ACP connect interfaces only on nodes explicitly targeted to be
   deployed with it (those in physically secure locations such as a
   NOC).  For example, the registrar could disable the ability to enable
   ACP connect on devices during enrollment and that property could only
   be changed through re-enrollment.  See also Appendix A.10.5.

8.1.2.  Software Components

   The ACP connect mechanism be only be used to connect physically
   external systems (NMS hosts) to the ACP but also other applications,
   containers or virtual machines.  In fact, one possible way to
   eliminate the security issue of the external ACP connect interface is
   to collocate an ACP edge node and an NMS host by making one a virtual
   machine or container inside the other; and therefore converting the
   unprotected external ACP subnet into an internal virtual subnet in a
   single device.  This would ultimately result in a fully ACP enabled
   NMS host with minimum impact to the NMS hosts software architecture.
   This approach is not limited to NMS hosts but could equally be
   applied to devices consisting of one or more VNF (virtual network
   functions): An internal virtual subnet connecting out-of-band
   management interfaces of the VNFs to an ACP edge router VNF.

   The core requirement is that the software components need to have a
   network stack that permits access to the ACP and optionally also the
   Data-Plane.  Like in the physical setup for NMS hosts this can be
   realized via two internal virtual subnets.  One that is connecting to

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   the ACP (which could be a container or virtual machine by itself),
   and one (or more) connecting into the Data-Plane.

   This "internal" use of ACP connect approach should not considered to
   be a "workaround" because in this case it is possible to build a
   correct security model: It is not necessary to rely on unprovable
   external physical security mechanisms as in the case of external NMS
   hosts.  Instead, the orchestration of the ACP, the virtual subnets
   and the software components can be done by trusted software that
   could be considered to be part of the ANI (or even an extended ACP).
   This software component is responsible for ensuring that only trusted
   software components will get access to that virtual subnet and that
   only even more trusted software components will get access to both
   the ACP virtual subnet and the Data-Plane (because those ACP users
   could leak traffic between ACP and Data-Plane).  This trust could be
   established for example through cryptographic means such as signed
   software packages.

8.1.3.  Auto Configuration

   ACP edge nodes, NMS hosts and software components that as described
   in the previous section are meant to be composed via virtual
   interfaces SHOULD support on the ACP connect subnet StateLess Address
   Autoconfiguration (SLAAC - [RFC4862]) and route auto configuration
   according to [RFC4191].

   The ACP edge node acts as the router on the ACP connect subnet,
   providing the (auto-)configured prefix for the ACP connect subnet to
   NMS hosts and/or software components.  The ACP edge node uses route
   prefix option of RFC4191 to announce the default route (::/) with a
   lifetime of 0 and aggregated prefixes for routes in the ACP routing
   table with normal lifetimes.  This will ensure that the ACP edge node
   does not become a default router, but that the NMS hosts and software
   components will route the prefixes used in the ACP to the ACP edge

   Aggregated prefix means that the ACP edge node needs to only announce
   the /48 ULA prefixes used in the ACP but none of the actual /64
   (Manual Addressing Sub-Scheme), /127 (ACP Zone Addressing Sub-
   Scheme), /112 or /120 (Vlong Addressing Sub-Scheme) routes of actual
   ACP nodes.  If ACP interfaces are configured with non ULA prefixes,
   then those prefixes cannot be aggregated without further configured
   policy on the ACP edge node.  This explains the above recommendation
   to use ACP ULA prefix covered prefixes for ACP connect interfaces:
   They allow for a shorter list of prefixes to be signaled via RFC4191
   to NMS hosts and software components.

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   The ACP edge nodes that have a Vlong ACP address MAY allocate a
   subset of their /112 or /120 address prefix to ACP connect
   interface(s) to eliminate the need to non-autonomically configure/
   provision the address prefixes for such ACP connect interfaces.

8.1.4.  Combined ACP/Data-Plane Interface (VRF Select)

                        Combined ACP and Data-Plane interface
     +--------+       +--------------------+    .   +--------------+
     | ACP    |       |ACP Edge No         |    .   | NMS Host(s)  |
     | Node   |       |                    |    .   | / Software   |
     |        |       |  [ACP  ].          |    .   |              |+
     |        |       | .[VRF  ] .[VRF   ] |    v   | "ACP address"||
     |        +-------+.         .[Select].+--------+ "Date Plane  ||
     |        |   ^   | .[Data ].          |        |  Address(es)"||
     |        |   .   |  [Plane]           |        |              ||
     |        |   .   |  [     ]           |        +--------------+|
     +--------+   .   +--------------------+         +--------------+
           Data-Plane "native" and + ACP auto-negotiated/encrypted

                           Figure 16: VRF select

   Using two physical and/or virtual subnets (and therefore interfaces)
   into NMS Hosts (as per Section 8.1.1) or Software (as per
   Section 8.1.2) may be seen as additional complexity, for example with
   legacy NMS Hosts that support only one IP interface.

   To provide a single subnet into both ACP and Data-Plane, the ACP Edge
   node needs to de-multiplex packets from NMS hosts into ACP VRF and
   Data-Plane.  This is sometimes called "VRF select".  If the ACP VRF
   has no overlapping IPv6 addresses with the Data-Plane (it should have
   no overlapping addresses), then this function can use the IPv6
   Destination address.  The problem is Source Address Selection on the
   NMS Host(s) according to RFC6724.

   Consider the simple case: The ACP uses only one ULA prefix, the ACP
   IPv6 prefix for the Combined ACP and Data-Plane interface is covered
   by that ULA prefix.  The ACP edge node announces both the ACP IPv6
   prefix and one (or more) prefixes for the Data-Plane.  Without
   further policy configurations on the NMS Host(s), it may select its
   ACP address as a source address for Data-Plane ULA destinations
   because of Rule 8 of RFC6724.  The ACP edge node can pass on the
   packet to the Data-Plane, but the ACP source address should not be
   used for Data-Plane traffic, and return traffic may fail.

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   If the ACP carries multiple ULA prefixes or non-ULA ACP connect
   prefixes, then the correct source address selection becomes even more

   With separate ACP connect and Data-Plane subnets and RFC4191 prefix
   announcements that are to be routed across the ACP connect interface,
   RFC6724 source address selection Rule 5 (use address of outgoing
   interface) will be used, so that above problems do not occur, even in
   more complex cases of multiple ULA and non-ULA prefixes in the ACP
   routing table.

   To achieve the same behavior with a Combined ACP and Data-Plane
   interface, the ACP Edge Node needs to behave as two separate routers
   on the interface: One link-local IPv6 address/router for its ACP
   reachability, and one link-local IPv6 address/router for its Data-
   Plane reachability.  The Router Advertisements for both are as
   described above (Section 8.1.3): For the ACP, the ACP prefix is
   announced together with RFC4191 option for the prefixes routed across
   the ACP and lifetime=0 to disqualify this next-hop as a default
   router.  For the Data-Plane, the Data-Plane prefix(es) are announced
   together with whatever dafault router parameters are used for the

   In result, RFC6724 source address selection Rule 5.5 may result in
   the same correct source address selection behavior of NMS hosts
   without further configuration on it as the separate ACP connect and
   Data-Plane interfaces.  As described in the text for Rule 5.5, this
   is only a MAY, because IPv6 hosts are not required to track next-hop
   information.  If an NMS Host does not do this, then separate ACP
   connect and Data-Plane interfaces are the preferable method of
   attachment.  Hosts implementing [RFC8028] should (instead of may)
   implement [RFC6724] Rule 5.5, so it is preferred for hosts to support

   ACP edge nodes MAY support the Combined ACP and Data-Plane interface.

8.1.5.  Use of GRASP

   GRASP can and should be possible to use across ACP connect
   interfaces, especially in the architectural correct solution when it
   is used as a mechanism to connect Software (e.g., ASA or legacy NMS
   applications) to the ACP.

   Given how the ACP is the security and transport substrate for GRASP,
   the requirements for devices connected via ACP connect is that those
   are equivalently (if not better) secured against attacks and run only
   software that is equally (if not better) protected, known (or

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   trusted) not to be malicious and accordingly designed to isolate
   access to the ACP against external equipment.

   The difference in security is that cryptographic security of the ACP
   secure channel is replaced by required physical security of the
   network connection between an ACP edge node and the NMS or other host
   reachable via the ACP connect interface.  Node integrity too is
   expected to be easier because the ACP connect node, the ACP connect
   link and the nodes connecting to it must be in a contiguous secure
   location, hence assuming there can be no physical attack against the

   When using "Combined ACP and Data-Plane Interfaces", care must be
   taken that only GRASP messages intended for the ACP GRASP domain
   received from Software or NMS Hosts are forwarded by ACP edge nodes.
   Currently there is no definition for a GRASP security and transport
   substrate beside the ACP, so there is no definition how such
   Software/NMS Host could participate in two separate GRASP Domains
   across the same subnet (ACP and Data-Plane domains).  At current it
   is assumed that all GRASP packets on a Combined ACP and Data-Plane
   interface belong to the GRASP ACP Domain.  They must all use the ACP
   IPv6 addresses of the Software/NMS Hosts.  The link-local IPv6
   addresses of Software/NMS Hosts (used for GRASP M_DISCOVERY and
   M_FLOOD messages) are also assumed to belong to the ACP address

8.2.  ACP through Non-ACP L3 Clouds (Remote ACP neighbors)

   Not all nodes in a network may support the ACP.  If non-ACP Layer-2
   devices are between ACP nodes, the ACP will work across it since it
   is IP based.  However, the autonomic discovery of ACP neighbors via
   DULL GRASP is only intended to work across L2 connections, so it is
   not sufficient to autonomically create ACP connections across non-ACP
   Layer-3 devices.

8.2.1.  Configured Remote ACP neighbor

   On the ACP node, remote ACP neighbors are configured explicitly.  The
   parameters of such a "connection" are described in the following

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     connection = [ method , local-addr, remote-addr, ?pmtu ]
     method   = [ "IKEv2" , ?port ]
     method //= [ "DTLS",    port ]
     local-addr  = [ address , ?vrf  ]
     remote-addr = [ address ]
     address = ("any" | ipv4-address | ipv6-address )
     vrf = tstr ; Name of a VRF on this node with local-address

              Figure 17: Parameters for remote ACP neighbors

   Explicit configuration of a remote-peer according to this ABNF
   provides all the information to build a secure channel without
   requiring a tunnel to that peer and running DULL GRASP inside of it.

   The configuration includes the parameters otherwise signaled via DULL
   GRASP: local address, remote (peer) locator and method.  The
   differences over DULL GRASP local neighbor discovery and secure
   channel creation are as follows:

   o  The local and remote address can be IPv4 or IPv6 and are typically
      global scope addresses.

   o  The VRF across which the connection is built (and in which local-
      addr exists) can to be specified.  If vrf is not specified, it is
      the default VRF on the node.  In DULL GRASP the VRF is implied by
      the interface across which DULL GRASP operates.

   o  If local address is "any", the local address used when initiating
      a secure channel connection is decided by source address selection
      ([RFC6724] for IPv6).  As a responder, the connection listens on
      all addresses of the node in the selected VRF.

   o  Configuration of port is only required for methods where no
      defaults exist (e.g., "DTLS").

   o  If remote address is "any", the connection is only a responder.
      It is a "hub" that can be used by multiple remote peers to connect
      simultaneously - without having to know or configure their
      addresses.  Example: Hub site for remote "spoke" sites reachable
      over the Internet.

   o  Pmtu should be configurable to overcome issues/limitations of Path
      MTU Discovery (PMTUD).

   o  IKEv2/IPsec to remote peers should support the optional NAT
      Traversal (NAT-T) procedures.

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8.2.2.  Tunneled Remote ACP Neighbor

   An IPinIP, GRE or other form of pre-existing tunnel is configured
   between two remote ACP peers and the virtual interfaces representing
   the tunnel are configured for "ACP enable".  This will enable IPv6
   link local addresses and DULL on this tunnel.  In result, the tunnel
   is used for normal "L2 adjacent" candidate ACP neighbor discovery
   with DULL and secure channel setup procedures described in this

   Tunneled Remote ACP Neighbor requires two encapsulations: the
   configured tunnel and the secure channel inside of that tunnel.  This
   makes it in general less desirable than Configured Remote ACP
   Neighbor.  Benefits of tunnels are that it may be easier to implement
   because there is no change to the ACP functionality - just running it
   over a virtual (tunnel) interface instead of only native interfaces.
   The tunnel itself may also provide PMTUD while the secure channel
   method may not.  Or the tunnel mechanism is permitted/possible
   through some firewall while the secure channel method may not.

8.2.3.  Summary

   Configured/Tunneled Remote ACP neighbors are less "indestructible"
   than L2 adjacent ACP neighbors based on link local addressing, since
   they depend on more correct Data-Plane operations, such as routing
   and global addressing.

   Nevertheless, these options may be crucial to incrementally deploy
   the ACP, especially if it is meant to connect islands across the
   Internet.  Implementations SHOULD support at least Tunneled Remote
   ACP Neighbors via GRE tunnels - which is likely the most common
   router-to-router tunneling protocol in use today.

9.  Benefits (Informative)

9.1.  Self-Healing Properties

   The ACP is self-healing:

   o  New neighbors will automatically join the ACP after successful
      validation and will become reachable using their unique ULA
      address across the ACP.

   o  When any changes happen in the topology, the routing protocol used
      in the ACP will automatically adapt to the changes and will
      continue to provide reachability to all nodes.

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   o  The ACP tracks the validity of peer certificates and tears down
      ACP secure channels when a peer certificate has expired.  When
      short-lived certificates with lifetimes in the order of OCSP/CRL
      refresh times are used, then this allows for removal of invalid
      peers (whose certificate was not renewed) at similar speeds as
      when using OCSP/CRL.  The same benefit can be achieved when using
      CRL/OCSP, periodically refreshing the revocation information and
      also tearing down ACP secure channels when the peer's (long-lived)
      certificate is revoked.  There is no requirement against ACP
      implementations to require this enhancement though to keep the
      mandatory implementations simpler.

   The ACP can also sustain network partitions and mergers.  Practically
   all ACP operations are link local, where a network partition has no
   impact.  Nodes authenticate each other using the domain certificates
   to establish the ACP locally.  Addressing inside the ACP remains
   unchanged, and the routing protocol inside both parts of the ACP will
   lead to two working (although partitioned) ACPs.

   There are few central dependencies: A certificate revocation list
   (CRL) may not be available during a network partition; a suitable
   policy to not immediately disconnect neighbors when no CRL is
   available can address this issue.  Also, an ACP registrar or
   Certificate Authority might not be available during a partition.
   This may delay renewal of certificates that are to expire in the
   future, and it may prevent the enrollment of new nodes during the

   Highly resilient ACP designs can be built by using ACP registrars
   with embedded sub-CA, as outlined in Section 10.2.4.  As long as a
   partition is left with one or more of such ACP registrars, it can
   continue to enroll new candidate ACP nodes as long as the ACP
   registrar's sub-CA certificate does not expire.  Because the ACP
   addressing relies on unique Registrar-IDs, a later re-merge of
   partitions will also not cause problems with ACP addresses assigned
   during partitioning.

   After a network partition, a re-merge will just establish the
   previous status, certificates can be renewed, the CRL is available,
   and new nodes can be enrolled everywhere.  Since all nodes use the
   same trust anchor(s), a re-merge will be smooth.

   Merging two networks with different trust anchors requires the ACP
   nodes to trust the union of Trust Anchors.  As long as the routing-
   subdomain hashes are different, the addressing will not overlap,
   which only happens in the unlikely event of a 40-bit hash collision
   in SHA256 (see Section 6.10).  Note that the complete mechanisms to
   merge networks is out of scope of this specification.

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   It is also highly desirable for implementation of the ACP to be able
   to run it over interfaces that are administratively down.  If this is
   not feasible, then it might instead be possible to request explicit
   operator override upon administrative actions that would
   administratively bring down an interface across which the ACP is
   running.  Especially if bringing down the ACP is known to disconnect
   the operator from the node.  For example any such down administrative
   action could perform a dependency check to see if the transport
   connection across which this action is performed is affected by the
   down action (with default RPL routing used, packet forwarding will be
   symmetric, so this is actually possible to check).

9.2.  Self-Protection Properties

9.2.1.  From the outside

   As explained in Section 6, the ACP is based on secure channels built
   between nodes that have mutually authenticated each other with their
   domain certificates.  The channels themselves are protected using
   standard encryption technologies such as DTLS or IPsec which provide
   additional authentication during channel establishment, data
   integrity and data confidentiality protection of data inside the ACP
   and in addition, provide replay protection.

   An attacker will not be able to join the ACP unless having a valid
   domain certificate, also packet injection and sniffing traffic will
   not be possible due to the security provided by the encryption

   The ACP also serves as protection (through authentication and
   encryption) for protocols relevant to OAM that may not have secured
   protocol stack options or where implementation or deployment of those
   options fail on some vendor/product/customer limitations.  This
   includes protocols such as SNMP ([RFC3411]), NTP ([RFC5905]), PTP
   ([IEEE-1588-2008]), DNS ([RFC1886]), DHCPv6 ([RFC3315]), syslog
   ([RFC3164]), Radius ([RFC2865]), Diameter ([RFC6733]), TACACS
   ([RFC1492]), IPFIX ([RFC7011]), Netflow ([RFC3954]) - just to name a
   few.  Protection via the ACP secure hop-by-hop channels for these
   protocols is meant to be only a stopgap though: The ultimate goal is
   for these and other protocols to use end-to-end encryption utilizing
   the domain certificate and rely on the ACP secure channels primarily
   for zero-touch reliable connectivity, but not primarily for security.

   The remaining attack vector would be to attack the underlying ACP
   protocols themselves, either via directed attacks or by denial-of-
   service attacks.  However, as the ACP is built using link-local IPv6
   addresses, remote attacks from the data-plane are impossible as long
   as the data-plane has no facilities to remotely sent IPv6 link-local

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   packets.  The only exception are ACP connected interfaces which
   require higher physical protection.  The ULA addresses are only
   reachable inside the ACP context, therefore, unreachable from the
   Data-Plane.  Also, the ACP protocols should be implemented to be
   attack resistant and not consume unnecessary resources even while
   under attack.

9.2.2.  From the inside

   The security model of the ACP is based on trusting all members of the
   group of nodes that receive an ACP domain certificate for the same
   domain.  Attacks from the inside by a compromised group member are
   therefore the biggest challenge.

   Group members must be protected against attackers so that there is no
   easy way to compromise them, or use them as a proxy for attacking
   other devices across the ACP.  For example, management plane
   functions (transport ports) should only be reachable from the ACP but
   not the Data-Plane.  Especially for those management plane functions
   that have no good protection by themselves because they do not have
   secure end-to-end transport and to whom ACP not only provides
   automatic reliable connectivity but also protection against attacks.
   Protection across all potential attack vectors is typically easier to
   do in devices whose software is designed from the ground up with
   security in mind than with legacy software based systems where the
   ACP is added on as another feature.

   As explained above, traffic across the ACP SHOULD still be end-to-end
   encrypted whenever possible.  This includes traffic such as GRASP,
   EST and BRSKI inside the ACP.  This minimizes man in the middle
   attacks by compromised ACP group members.  Such attackers cannot
   eavesdrop or modify communications, they can just filter them (which
   is unavoidable by any means).

   See Appendix A.10.8 for further considerations how to avoid and deal
   with compromised nodes.

9.3.  The Administrator View

   An ACP is self-forming, self-managing and self-protecting, therefore
   has minimal dependencies on the administrator of the network.
   Specifically, since it is (intended to be) independent of
   configuration, there is only limited scope for configuration errors
   on the ACP itself.  The administrator may have the option to enable
   or disable the entire approach, but detailed configuration is not
   possible.  This means that the ACP must not be reflected in the
   running configuration of nodes, except a possible on/off switch (and
   even that is undesirable).

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   While configuration (except for Section 8 and Section 10.2) is not
   possible, an administrator must have full visibility of the ACP and
   all its parameters, to be able to do trouble-shooting.  Therefore, an
   ACP must support all show and debug options, as for any other network
   function.  Specifically, a network management system or controller
   must be able to discover the ACP, and monitor its health.  This
   visibility of ACP operations must clearly be separated from
   visibility of Data-Plane so automated systems will never have to deal
   with ACP aspects unless they explicitly desire to do so.

   Since an ACP is self-protecting, a node not supporting the ACP, or
   without a valid domain certificate cannot connect to it.  This means
   that by default a traditional controller or network management system
   cannot connect to an ACP.  See Section 8.1.1 for more details on how
   to connect an NMS host into the ACP.

10.  ACP Operations (Informative)

   The following sections document important operational aspects of the
   ACP.  They are not normative because they do not impact the
   interoperability between components of the ACP, but they include
   recommendations/requirements for the internal operational model
   beneficial or necessary to achieve the desired use-case benefits of
   the ACP (see Section 3).

   o  Section 10.1 describes recommended operator diagnostics
      capabilities of ACP nodes.  The have been derived from diagnostic
      of a commercially available ACP implementation.

   o  Section 10.2 describes high level how an ACP registrar needs to
      work, what its configuration parameters are and specific issues
      impacting the choices of deployment design due to renewal and
      revocation issues.  It describes a model where ACP Registrars have
      their own sub-CA to provide the most distributed deployment option
      for ACP Registrars, and it describes considerations for
      centralized policy control of ACP Registrar operations.

   o  Section 10.3 describes suggested ACP node behavior and operational
      interfaces (configuration options) to manage the ACP in so-called
      greenfield devices (previously unconfigured) and brownfield
      devices (preconfigured).

   The recommendations and suggestions of this chapter were derived from
   operational experience gained with a commercially available pre-
   standard ACP implementation.

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10.1.  ACP (and BRSKI) Diagnostics

   Even though ACP and ANI in general are taking out many manual
   configuration mistakes through their automation, it is important to
   provide good diagnostics for them.

   The basic diagnostics is support of (yang) data models representing
   the complete (auto-)configuration and operational state of all
   components: BRSKI, GRASP, ACP and the infrastructure used by them:
   TLS/DTLS, IPsec, certificates, trust anchors, time, VRF and so on.
   While necessary, this is not sufficient:

   Simply representing the state of components does not allow operators
   to quickly take action - unless they do understand how to interpret
   the data, and that can mean a requirement for deep understanding of
   all components and how they interact in the ACP/ANI.

   Diagnostic supports should help to quickly answer the questions
   operators are expected to ask, such as "is the ACP working
   correctly?", or "why is there no ACP connection to a known
   neighboring node?"

   In current network management approaches, the logic to answer these
   questions is most often built as centralized diagnostics software
   that leverages the above mentioned data models.  While this approach
   is feasible for components utilizing the ANI, it is not sufficient to
   diagnose the ANI itself:

   o  Developing the logic to identify common issues requires
      operational experience with the components of the ANI.  Letting
      each management system define its own analysis is inefficient.

   o  When the ANI is not operating correctly, it may not be possible to
      run diagnostics from remote because of missing connectivity.  The
      ANI should therefore have diagnostic capabilities available
      locally on the nodes themselves.

   o  Certain operations are difficult or impossible to monitor in real-
      time, such as initial bootstrap issues in a network location where
      no capabilities exist to attach local diagnostics.  Therefore it
      is important to also define means of capturing (logging)
      diagnostics locally for later retrieval.  Ideally, these captures
      are also non-volatile so that they can survive extended power-off
      conditions - for example when a device that fails to be brought up
      zero-touch is being sent back for diagnostics at a more
      appropriate location.

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   The most simple form of diagnostics answering questions such as the
   above is to represent the relevant information sequentially in
   dependency order, so that the first non-expected/non-operational item
   is the most likely root cause.  Or just log/highlight that item.  For

   Q: Is ACP operational to accept neighbor connections:

   o  Check if any potentially necessary configuration to make ACP/ANI
      operational are correct (see Section 10.3 for a discussion of such

   o  Does the system time look reasonable, or could it be the default
      system time after clock chip battery failure (certificate checks
      depend on reasonable notion of time).

   o  Does the node have keying material - domain certificate, trust

   o  If no keying material and ANI is supported/enabled, check the
      state of BRSKI (not detailed in this example).

   o  Check the validity of the domain certificate:

      *  Does the certificate validate against the trust anchor?

      *  Has it been revoked?

      *  Was the last scheduled attempt to retrieve a CRL successful
         (e.g., do we know that our CRL information is up to date).

      *  Is the certificate valid: validity start time in the past,
         expiration time in the future?

      *  Does the certificate have a correctly formatted ACP domain
         information field?

   o  Was the ACP VRF successfully created?

   o  Is ACP enabled on one or more interfaces that are up and running?

   If all this looks good, the ACP should be running locally "fine" -
   but we did not check any ACP neighbor relationships.

   Question: why does the node not create a working ACP connection to a
   neighbor on an interface?

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   o  Is the interface physically up?  Does it have an IPv6 link-local

   o  Is it enabled for ACP?

   o  Do we successfully send DULL GRASP messages to the interface (link
      layer errors)?

   o  Do we receive DULL GRASP messages on the interface?  If not, some
      intervening L2 equipment performing bad MLD snooping could have
      caused problems.  Provide e.g., diagnostics of the MLD querier
      IPv6 and MAC address.

   o  Do we see the ACP objective in any DULL GRASP message from that
      interface?  Diagnose the supported secure channel methods.

   o  Do we know the MAC address of the neighbor with the ACP objective?
      If not, diagnose SLAAC/ND state.

   o  When did we last attempt to build an ACP secure channel to the

   o  If it failed, why:

      *  Did the neighbor close the connection on us or did we close the
         connection on it because the domain certificate membership

      *  If the neighbor closed the connection on us, provide any error
         diagnostics from the secure channel protocol.

      *  If we failed the attempt, display our local reason:

         +  There was no common secure channel protocol supported by the
            two neighbors (this could not happen on nodes supporting
            this specification because it mandates common support for

         +  The ACP domain certificate membership check (Section 6.1.3)

            -  The neighbor's certificate does not have the required
               trust anchor.  Provide diagnostics which trust anchor it
               has (can identify whom the device belongs to).

            -  The neighbor's certificate does not have the same domain
               (or no domain at all).  Diagnose domain-name and
               potentially other cert info.

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            -  The neighbor's certificate has been revoked or could not
               be authenticated by OCSP.

            -  The neighbor's certificate has expired - or is not yet

      *  Any other connection issues in e.g., IKEv2 / IPsec, DTLS?.

   Question: Is the ACP operating correctly across its secure channels?

   o  Are there one or more active ACP neighbors with secure channels?

   o  Is the RPL routing protocol for the ACP running?

   o  Is there a default route to the root in the ACP routing table?

   o  Is there for each direct ACP neighbor not reachable over the ACP
      virtual interface to the root a route in the ACP routing table?

   o  Is ACP GRASP running?

   o  Is at least one SRV.est objective cached (to support certificate

   o  Is there at least one BRSKI registrar objective cached (in case
      BRSKI is supported)

   o  Is BRSKI proxy operating normally on all interfaces where ACP is

   o  ...

   These lists are not necessarily complete, but illustrate the
   principle and show that there are variety of issues ranging from
   normal operational causes (a neighbor in another ACP domain) over
   problems in the credentials management (certificate lifetimes),
   explicit security actions (revocation) or unexpected connectivity
   issues (intervening L2 equipment).

   The items so far are illustrating how the ANI operations can be
   diagnosed with passive observation of the operational state of its
   components including historic/cached/counted events.  This is not
   necessary sufficient to provide good enough diagnostics overall:

   The components of ACP and BRSKI are designed with security in mind
   but they do not attempt to provide diagnostics for building the
   network itself.  Consider two examples:

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   1.  BRSKI does not allow for a neighboring device to identify the
       pledges certificate (IDevID).  Only the selected BRSKI registrar
       can do this, but it may be difficult to disseminate information
       about undesired pledges from those BRSKI registrars to locations/
       nodes where information about those pledges is desired.

   2.  The Link Layer Discovery Protocol (LLDP, [LLDP]) disseminates
       information about nodes to their immediate neighbors, such as
       node model/type/software and interface name/number of the
       connection.  This information is often helpful or even necessary
       in network diagnostics.  It can equally considered to be too
       insecure to make this information available unprotected to all
       possible neighbors.

   An "interested adjacent party" can always determine the IDevID of a
   BRSKI pledge by behaving like a BRSKI proxy/registrar.  Therefore the
   IDevID of a BRSKI pledge is not meant to be protected - it just has
   to be queried and is not signaled unsolicited (as it would be in
   LLDP) so that other observers on the same subnet can determine who is
   an "interested adjacent party".

10.2.  ACP Registrars

   As described in Section 6.10.7, the ACP addressing mechanism is
   designed to enable lightweight, distributed and uncoordinated ACP
   registrars that are providing ACP address prefixes to candidate ACP
   nodes by enrolling them with an ACP domain certificate into an ACP
   domain via any appropriate mechanism/protocol, automated or not.

   This section discusses informatively more details and options for ACP

10.2.1.  Registrar interactions

   This section summarizes and discusses the interactions with other
   entities required by an ACP registrar.

   In a simple instance of an ACP network, no central NOC component
   beside a trust anchor (root CA) is required.  One or more
   uncoordinated acting ACP registrar can be set up, performing the
   following interactions:

   To orchestrate enrolling a candidate ACP node autonomically, the ACP
   registrar can rely on the ACP and use Proxies to reach the candidate
   ACP node, therefore allowing minimum pre-existing (auto-)configured
   network services on the candidate ACP node.  BRSKI defines the BRSKI
   proxy, a design that can be adopted for various protocols that

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   Pledges/candidate ACP nodes could want to use, for example BRSKI over
   CoAP (Constrained Application Protocol), or proxying of Netconf.

   To reach a trust anchor unaware of the ACP, the ACP registrar would
   use the Data-Plane.  ACP and Data-Plane in an ACP registrar could
   (and by default should be) completely isolated from each other at the
   network level.  Only applications such as the ACP registrar would
   need the ability for their transport stacks to access both.

   In non-autonomic enrollment options, the Data-Plane between a ACP
   registrar and the candidate ACP node needs to be configured first.
   This includes the ACP registrar and the candidate ACP node.  Then any
   appropriate set of protocols can be used between ACP registrar and
   candidate ACP node to discover the other side, and then connect and
   enroll (configure) the candidate ACP node with an ACP domain
   certificate.  Netconf ZeroTouch ([I-D.ietf-netconf-zerotouch]) is an
   example protocol that could be used for this.  BRSKI using optional
   discovery mechanisms is equally a possibility for candidate ACP nodes
   attempting to be enrolled across non-ACP networks, such as the

   When candidate ACP nodes have secure bootstrap, such as BRSKI
   Pledges, they will not trust to be configured/enrolled across the
   network, unless being presented with a voucher (see [RFC8366])
   authorizing the network to take possession of the node.  An ACP
   registrar will then need a method to retrieve such a voucher, either
   offline, or online from a MASA (Manufacturer Authorized Signing
   Authority).  BRSKI and Netconf ZeroTouch are two protocols that
   include capabilities to present the voucher to the candidate ACP

   An ACP registrar could operate EST for ACP certificate renewal and/or
   act as a CRL Distribution point.  A node performing these services
   does not need to support performing (initial) enrollment, but it does
   require the same above described connectivity as an ACP registrar:
   via the ACP to ACP nodes and via the Data-Plane to the trust anchor
   and other sources of CRL information.

10.2.2.  Registrar Parameter

   The interactions of an ACP registrar outlined Section 6.10.7 and
   Section 10.2.1 above depend on the following parameters:

      A URL to the trust anchor (root CA) and credentials so that the
      ACP registrar can let the trust anchor sign candidate ACP member

      The ACP domain-name.

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      The Registrar-ID to use.  This could default to a MAC address of
      the ACP registrar.

      For recovery, the next-useable Node-IDs for zone (Zone-ID=0) sub-
      addressing scheme, for Vlong /112 and for Vlong /1120 sub-
      addressing scheme.  These IDs would only need to be provisioned
      after recovering from a crash.  Some other mechanism would be
      required to remember these IDs in a backup location or to recover
      them from the set of currently known ACP nodes.

      Policies if candidate ACP nodes should receive a domain
      certificate or not, for example based on the devices IDevID as in
      BRSKI.  The ACP registrar may have a whitelist or blacklist of
      devices "serialNumbers" from their IDevID.

      Policies what type of address prefix to assign to a candidate ACP
      devices, based on likely the same information.

      For BRSKI or other mechanisms using vouchers: Parameters to
      determine how to retrieve vouchers for specific type of secure
      bootstrap candidate ACP nodes (such as MASA URLs), unless this
      information is automatically learned such as from the IDevID of
      candidate ACP nodes (as defined in BRSKI).

10.2.3.  Certificate renewal and limitations

   When an ACP node renews/rekeys its certificate, it may end up doing
   so via a different registrar (e.g., EST server) than the one it
   originally received its ACP domain certificate from, for example
   because that original ACP registrar is gone.  The ACP registrar
   through which the renewal/rekeying is performed would by default
   trust the ACP domain information from the ACP nodes current ACP
   domain certificate and maintain this information so that the ACP node
   maintains its ACP address prefix.  In EST renewal/rekeying, the ACP
   nodes current ACP domain certificate is signaled during the TLS

   This simple scenario has two limitations:

   1.  The ACP registrars cannot directly assign certificates to nodes
       and therefore needs an "online" connection to the trust anchor
       (root CA).

   2.  Recovery from a compromised ACP registrar is difficult.  When an
       ACP registrar is compromised, it can insert for example
       conflicting ACP domain information and create thereby an attack
       against other ACP nodes through the ACP routing protocol.

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   Even when such a malicious ACP registrar is detected, resolving the
   problem may be difficult because it would require identifying all the
   wrong ACP domain certificates assigned via the ACP registrar after it
   was compromised.  And without additional centralized tracking of
   assigned certificates there is no way to do this.

10.2.4.  ACP Registrars with sub-CA

   In situations, where either of the above two limitations are an
   issue, ACP registrars could also be sub-CAs.  This removes the need
   for connectivity to a root-CA whenever an ACP node is enrolled, and
   reduces the need for connectivity of such an ACP registrar to a root-
   CA to only those times when it needs to renew its own certificate.
   The ACP registrar would also now use its own (sub-CA) certificate to
   enroll and sign the ACP nodes certificates, and therefore it is only
   necessary to revoke a compromised ACP registrars sub-CA certificate.
   Alternatively one can let it expire and not renew it, when the
   certificate of the sub-CA is appropriately short-lived.

   As the ACP domain membership check verifies a peer ACP node's ACP
   domain certificate trust chain, it will also verify the signing
   certificate which is the compromised/revoked sub-CA certificate.
   Therefore ACP domain membership for an ACP node enrolled from a
   compromised and discovered ACP registrar will fail.

   ACP nodes enrolled by a compromised ACP registrar would automatically
   fail to establish ACP channels and ACP domain certificate renewal via
   EST and therefore revert to their role as a candidate ACP members and
   attempt to get a new ACP domain certificate from an ACP registrar -
   for example, via BRSKI.  In result, ACP registrars that have an
   associated sub-CA makes isolating and resolving issues with
   compromised registrars easier.

   Note that ACP registrars with sub-CA functionality also can control
   the lifetime of ACP domain certificates easier and therefore also be
   used as a tool to introduce short lived certificates and not rely on
   CRL, whereas the certificates for the sub-CAs themselves could be
   longer lived and subject to CRL.

10.2.5.  Centralized Policy Control

   When using multiple, uncoordinated ACP registrars, several advanced
   operations are potentially more complex than with a single, resilient
   policy control backend, for example including but not limited to:

      Which candidate ACP node is permitted or not permitted into an ACP
      domain.  This may not be a decision to be taken upfront, so that a
      per-"serialNumber" policy can be loaded into every ACP registrar.

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      Instead, it may better be decided in real-time including
      potentially a human decision in a NOC.

      Tracking of all enrolled ACP nodes and their certificate
      information.  For example in support of revoking individual ACP
      nodes certificates.

      More flexible policies what type of address prefix or even what
      specific address prefix to assign to a candidate ACP node.

   These and other operations could be introduced more easily by
   introducing a centralized Policy Management System (PMS) and
   modifying ACP registrar behavior so that it queries the PMS for any
   policy decision occurring during the candidate ACP node enrollment
   process and/or the ACP node certificate renewal process.  For
   example, which ACP address prefix to assign.  Likewise the ACP
   registrar would report any relevant state change information to the
   PMS as well, for example when a certificate was successfully enrolled
   onto a candidate ACP node.

10.3.  Enabling and disabling ACP/ANI

   Both ACP and BRSKI require interfaces to be operational enough to
   support sending/receiving their packets.  In node types where
   interfaces are by default (e.g., without operator configuration)
   enabled, such as most L2 switches, this would be less of a change in
   behavior than in most L3 devices (e.g.: routers), where interfaces
   are by default disabled.  In almost all network devices it is common
   though for configuration to change interfaces to a physically
   disabled state and that would break the ACP.

   In this section, we discuss a suggested operational model to enable/
   disable interfaces and nodes for ACP/ANI in a way that minimizes the
   risk of operator action to break the ACP in this way, and that also
   minimizes operator surprise when ACP/ANI becomes supported in node

10.3.1.  Filtering for non-ACP/ANI packets

   Whenever this document refers to enabling an interface for ACP (or
   BRSKI), it only requires to permit the interface to send/receive
   packets necessary to operate ACP (or BRSKI) - but not any other Data-
   Plane packets.  Unless the Data-Plane is explicitly configured/
   enabled, all packets not required for ACP/BRSKI should be filtered on
   input and output:

   Both BRSKI and ACP require link-local only IPv6 operations on
   interfaces and DULL GRASP.  IPv6 link-local operations means the

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   minimum signaling to auto-assign an IPv6 link-local address and talk
   to neighbors via their link-local address: SLAAC (Stateless Address
   Auto-Configuration - [RFC4862]) and ND (Neighbor Discovery -
   [RFC4861]).  When the device is a BRSKI pledge, it may also require
   TCP/TLS connections to BRSKI proxies on the interface.  When the
   device has keying material, and the ACP is running, it requires DULL
   GRASP packets and packets necessary for the secure-channel mechanism
   it supports, e.g., IKEv2 and IPsec ESP packets or DTLS packets to the
   IPv6 link-local address of an ACP neighbor on the interface.  It also
   requires TCP/TLS packets for its BRSKI proxy functionality, if it
   does support BRSKI.

10.3.2.  Admin Down State

   Interfaces on most network equipment have at least two states: "up"
   and "down".  These may have product specific names.  "down" for
   example could be called "shutdown" and "up" could be called "no
   shutdown".  The "down" state disables all interface operations down
   to the physical level.  The "up" state enables the interface enough
   for all possible L2/L3 services to operate on top of it and it may
   also auto-enable some subset of them.  More commonly, the operations
   of various L2/L3 services is controlled via additional node-wide or
   interface level options, but they all become only active when the
   interface is not "down".  Therefore an easy way to ensure that all
   L2/L3 operations on an interface are inactive is to put the interface
   into "down" state.  The fact that this also physically shuts down the
   interface is in many cases just a side effect, but it may be
   important in other cases (see below, Section

   To provide ACP/ANI resilience against operators configuring
   interfaces to "down" state, this document recommends to separate the
   "down" state of interfaces into an "admin down" state where the
   physical layer is kept running and ACP/ANI can use the interface and
   a "physical down" state.  Any existing "down" configurations would
   map to "admin down".  In "admin down", any existing L2/L3 services of
   the Data-Plane should see no difference to "physical down" state.  To
   ensure that no Data-Plane packets could be sent/received, packet
   filtering could be established automatically as described above in
   Section 10.3.1.

   As necessary (see discussion below) new configuration options could
   be introduced to issue "physical down".  The options should be
   provided with additional checks to minimize the risk of issuing them
   in a way that breaks the ACP without automatic restoration.  For
   example they could be denied to be issued from a control connection
   (netconf/ssh) that goes across the interface itself ("do not
   disconnect yourself").  Or they could be performed only temporary and
   only be made permanent with additional later reconfirmation.

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   In the following sub-sections important aspects to the introduction
   of "admin down" state are discussed.  Security

   Interfaces are physically brought down (or left in default down
   state) as a form of security.  "Admin down" state as described above
   provides also a high level of security because it only permits ACP/
   ANI operations which are both well secured.  Ultimately, it is
   subject to security review for the deployment whether "admin down" is
   a feasible replacement for "physical down".

   The need to trust the security of ACP/ANI operations needs to be
   weighed against the operational benefits of permitting this: Consider
   the typical example of a CPE (customer premises equipment) with no
   on-site network expert.  User ports are in physical down state unless
   explicitly configured not to be.  In a misconfiguration situation,
   the uplink connection is incorrectly plugged into such as user port.
   The device is disconnected from the network and therefore no
   diagnostics from the network side is possible anymore.
   Alternatively, all ports default to "admin down".  The ACP (but not
   the Data-Plane) would still automatically form.  Diagnostics from the
   network side is possible and operator reaction could include to
   either make this port the operational uplink port or to instruct re-
   cabling.  Security wise, only ACP/ANI could be attacked, all other
   functions are filtered on interfaces in "admin down" state.  Fast state propagation and Diagnostics

   "Physical down" state propagates on many interface types (e.g.,
   Ethernet) to the other side.  This can trigger fast L2/L3 protocol
   reaction on the other side and "admin down" would not have the same
   (fast) result.

   Bringing interfaces to "physical down" state is to the best of our
   knowledge always a result of operator action, but today, never the
   result of (autonomic) L2/L3 services running on the nodes.  Therefore
   one option is to change the operator action to not rely on link-state
   propagation anymore.  This may not be possible when both sides are
   under different operator control, but in that case it is unlikely
   that the ACP is running across the link and actually putting the
   interface into "physical down" state may still be a good option.

   Ideally, fast physical state propagation is replaced by fast software
   driven state propagation.  For example a DULL GRASP "admin-state"
   objective could be used to auto configure a Bidirectional Forwarding
   Protocol (BFD, [RFC5880]) session between the two sides of the link
   that would be used to propagate the "up" vs. admin down state.

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   Triggering physical down state may also be used as a mean of
   diagnosing cabling in the absence of easier methods.  It is more
   complex than automated neighbor diagnostics because it requires
   coordinated remote access to both (likely) sides of a link to
   determine whether up/down toggling will cause the same reaction on
   the remote side.

   See Section 10.1 for a discussion about how LLDP and/or diagnostics
   via GRASP could be used to provide neighbor diagnostics, and
   therefore hopefully eliminating the need for "physical down" for
   neighbor diagnostics - as long as both neighbors support ACP/ANI.  Low Level Link Diagnostics

   "Physical down" is performed to diagnose low-level interface behavior
   when higher layer services (e.g., IPv6) are not working.  Especially
   Ethernet links are subject to a wide variety of possible wrong
   configuration/cablings if they do not support automatic selection of
   variable parameters such as speed (10/100/1000 Mbps), crossover
   (Auto-MDIX) and connector (fiber, copper - when interfaces have
   multiple but can only enable one at a time).  The need for low level
   link diagnostic can therefore be minimized by using fully auto
   configuring links.

   In addition to "Physical down", low level diagnostics of Ethernet or
   other interfaces also involve the creation of other states on
   interfaces, such as physical Loopback (internal and/or external) or
   bringing down all packet transmissions for reflection/cable-length
   measurements.  Any of these options would disrupt ACP as well.

   In cases where such low-level diagnostics of an operational link is
   desired but where the link could be a single point of failure for the
   ACP, ASA on both nodes of the link could perform a negotiated
   diagnostics that automatically terminates in a predetermined manner
   without dependence on external input ensuring the link will become
   operational again.  Power Consumption Issues

   Power consumption of "physical down" interfaces, may be significantly
   lower than those in "admin down" state, for example on long-range
   fiber interfaces.  Bringing up interfaces, for example to probe
   reachability, may also consume additional power.  This can make these
   type of interfaces inappropriate to operate purely for the ACP when
   they are not currently needed for the Data-Plane.

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10.3.3.  Interface level ACP/ANI enable

   The interface level configuration option "ACP enable" enables ACP
   operations on an interface, starting with ACP neighbor discovery via
   DULL GRAP.  The interface level configuration option "ANI enable" on
   nodes supporting BRSKI and ACP starts with BRSKI pledge operations
   when there is no domain certificate on the node.  On ACP/BRSKI nodes,
   "ACP enable" may not need to be supported, but only "ANI enable".
   Unless overridden by global configuration options (see later), "ACP/
   ANI enable" will result in "down" state on an interface to behave as
   "admin down".

10.3.4.  Which interfaces to auto-enable?

   (Section 6.3) requires that "ACP enable" is automatically set on
   native interfaces, but not on non-native interfaces (reminder: a
   native interface is one that exists without operator configuration
   action such as physical interfaces in physical devices).

   Ideally, ACP enable is set automatically on all interfaces that
   provide access to additional connectivity that allows to reach more
   nodes of the ACP domain.  The best set of interfaces necessary to
   achieve this is not possible to determine automatically.  Native
   interfaces are the best automatic approximation.

   Consider an ACP domain of ACP nodes transitively connected via native
   interfaces.  A Data-Plane tunnel between two of these nodes that are
   non-adjacent is created and "ACP enable" is set for that tunnel.  ACP
   RPL sees this tunnel as just as a single hop.  Routes in the ACP
   would use this hop as an attractive path element to connect regions
   adjacent to the tunnel nodes.  In result, the actual hop-by-hop paths
   used by traffic in the ACP can become worse.  In addition, correct
   forwarding in the ACP now depends on correct Data-Plane forwarding
   config including QoS, filtering and other security on the Data-Plane
   path across which this tunnel runs.  This is the main issue why "ACP/
   ANI enable" should not be set automatically on non-native interfaces.

   If the tunnel would connect two previously disjoint ACP regions, then
   it likely would be useful for the ACP.  A Data-Plane tunnel could
   also run across nodes without ACP and provide additional connectivity
   for an already connected ACP network.  The benefit of this additional
   ACP redundancy has to be weighed against the problems of relying on
   the Data-Plane.  If a tunnel connects two separate ACP regions: how
   many tunnels should be created to connect these ACP regions reliably
   enough?  Between which nodes?  These are all standard tunneled
   network design questions not specific to the ACP, and there are no
   generic fully automated answers.

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   Instead of automatically setting "ACP enable" on these type of
   interfaces, the decision needs to be based on the use purpose of the
   non-native interface and "ACP enable" needs to be set in conjunction
   with the mechanism through which the non-native interface is created/

   In addition to explicit setting of "ACP/ANI enable", non-native
   interfaces also need to support configuration of the ACP RPL cost of
   the link - to avoid the problems of attracting too much traffic to
   the link as described above.

   Even native interfaces may not be able to automatically perform BRSKI
   or ACP because they may require additional operator input to become
   operational.  Example include DSL interfaces requiring PPPoE
   credentials or mobile interfaces requiring credentials from a SIM
   card.  Whatever mechanism is used to provide the necessary config to
   the device to enable the interface can also be expanded to decide on
   whether or not to set "ACP/ANI enable".

   The goal of automatically setting "ACP/ANI enable" on interfaces
   (native or not) is to eliminate unnecessary "touches" to the node to
   make its operation as much as possible "zero-touch" with respect to
   ACP/ANI.  If there are "unavoidable touches" such a creating/
   configuring a non-native interface or provisioning credentials for a
   native interface, then "ACP/ANI enable" should be added as an option
   to that "touch".  If a wrong "touch" is easily fixed (not creating
   another high-cost touch), then the default should be not to enable
   ANI/ACP, and if it is potentially expensive or slow to fix (e.g.,
   parameters on SIM card shipped to remote location), then the default
   should be to enable ACP/ANI.

10.3.5.  Node Level ACP/ANI enable

   A node level command "ACP/ANI enable [up-if-only]" enables ACP or ANI
   on the node (ANI = ACP + BRSKI).  Without this command set, any
   interface level "ACP/ANI enable" is ignored.  Once set, ACP/ANI will
   operate an interface where "ACP/ANI enable" is set.  Setting of
   interface level "ACP/ANI enable" is either automatic (default) or
   explicit through operator action as described in the previous

   If the option "up-if-only" is selected, the behavior of "down"
   interfaces is unchanged, and ACP/ANI will only operate on interfaces
   where "ACP/ANI enable" is set and that are "up".  When it is not set,
   then "down" state of interfaces with "ACP/ANI enable" is modified to
   behave as "admin down".

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   A "brownfield" node is one that already has a configured Data-Plane.

   Executing global "ACP/ANI enable [up-if-only]" on each node is the
   only command necessary to create an ACP across a network of
   brownfield nodes once all the nodes have a domain certificate.  When
   BRSKI is used ("ANI enable"), provisioning of the certificates only
   requires set-up of a single BRSKI registrar node which could also
   implement a CA for the network.  This is the most simple way to
   introduce ACP/ANI into existing (== brownfield) networks.

   The need to explicitly enable ACP/ANI is especially important in
   brownfield nodes because otherwise software updates may introduce
   support for ACP/ANI: Automatic enablement of ACP/ANI in networks
   where the operator does not only not want ACP/ANI but where the
   operator likely never even heard of it could be quite irritating to
   the operator.  Especially when "down" behavior is changed to "admin

   Automatically setting "ANI enable" on brownfield nodes where the
   operator is unaware of BRSKI and MASA operations could also be an
   unlikely but then critical security issue.  If an attacker could
   impersonate the operator and register as the operator at the MASA or
   otherwise get hold of vouchers and can get enough physical access to
   the network so pledges would register to an attacking registrar, then
   the attacker could gain access to the network through the ACP that
   the attacker then has access to.

   In networks where the operator explicitly wants to enable the ANI
   this could not happen, because the operator would create a BRSKI
   registrar that would discover attack attempts, and the operator would
   be setting up his registrar with the MASA.  Nodes requiring
   "ownership vouchers" would not be subject to that attack.  See
   [I-D.ietf-anima-bootstrapping-keyinfra] for more details.  Note that
   a global "ACP enable" alone is not subject to these type of attacks,
   because it always depends on some other mechanism first to provision
   domain certificates into the device.  Greenfield nodes

   A "greenfield" node is one that did not have any prior configuration.

   For greenfield nodes, only "ANI enable" is relevant.  If another
   mechanism than BRSKI is used to (zero-touch) bootstrap a node, then
   it is up to that mechanism to provision domain certificates and to
   set global "ACP enable" as desired.

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   Nodes supporting full ANI functionality set "ANI enable"
   automatically when they decide that they are greenfield, e.g., that
   they are powering on from factory condition.  They will then put all
   native interfaces into "admin down" state and start to perform BRSKI
   pledge functionality - and once a domain certificate is enrolled they
   automatically enable ACP.

   Attempts for BRSKI pledge operations in greenfield state should
   terminate automatically when another method of configuring the node
   is used.  Methods that indicate some form of physical possession of
   the device such as configuration via the serial console port could
   lead to immediate termination of BRSKI, while other parallel auto
   configuration methods subject to remote attacks might lead to BRSKI
   termination only after they were successful.  Details of this may
   vary widely over different type of nodes.  When BRSKI pledge
   operation terminates, this will automatically unset "ANI enable" and
   should terminate any temporarily needed state on the device to
   perform BRSKI - DULL GRASP, BRSKI pledge and any IPv6 configuration
   on interfaces.

10.3.6.  Undoing ANI/ACP enable

   Disabling ANI/ACP by undoing "ACP/ANI enable" is a risk for the
   reliable operations of the ACP if it can be executed by mistake or
   unauthorized.  This behavior could be influenced through some
   additional (future) property in the certificate (e.g., in the domain
   information extension field): In an ANI deployment intended for
   convenience, disabling it could be allowed without further
   constraints.  In an ANI deployment considered to be critical more
   checks would be required.  One very controlled option would be to not
   permit these commands unless the domain certificate has been revoked
   or is denied renewal.  Configuring this option would be a parameter
   on the BRSKI registrar(s).  As long as the node did not receive a
   domain certificate, undoing "ANI/ACP enable" should not have any
   additional constraints.

10.3.7.  Summary

   Node-wide "ACP/ANI enable [up-if-only]" commands enable the operation
   of ACP/ANI.  This is only auto-enabled on ANI greenfield devices,
   otherwise it must be configured explicitly.

   If the option "up-if-only" is not selected, interfaces enabled for
   ACP/ANI interpret "down" state as "admin down" and not "physical
   down".  In "admin-down" all non-ACP/ANI packets are filtered, but the
   physical layer is kept running to permit ACP/ANI to operate.

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   (New) commands that result in physical interruption ("physical down",
   "loopback") of ACP/ANI enabled interfaces should be built to protect
   continuance or reestablishment of ACP as much as possible.

   Interface level "ACP/ANI enable" control per-interface operations.
   It is enabled by default on native interfaces and has to be
   configured explicitly on other interfaces.

   Disabling "ACP/ANI enable" global and per-interface should have
   additional checks to minimize undesired breakage of ACP.  The degree
   of control could be a domain wide parameter in the domain

10.4.  Configuration and the ACP (summary)

   There is no desirable configuration for the ACP.  Instead, all
   parameters that need to be configured in support of the ACP are
   limitations of the solution, but they are only needed in cases where
   not all components are made autonomic.  Whereever this is necessary,
   it relies on pre-existing mechanisms for configuration such as CLI or
   YANG ([RFC7950]) data models.

   The most important examples of such configuration include:

   o  When ACP nodes do not support an autonomic way to receive an ACP
      domain certificate, for example BRSKI, then such certificate needs
      to be configured via some pre-existing mechanisms outside the
      scope of this specification.  Today, router have typically a
      variety of mechanisms to do this.

   o  Certificate maintenance requires PKI functions.  Discovery of
      these functions across the ACP is automated (see Section 6.1.5),
      but their configuration is not.

   o  When non-ACP capable nodes such as pre-existing NMS need to be
      physically connected to the ACP, the ACP node to which they attach
      needs to be configured with ACP-connect according to Section 8.1.
      It is also possible to use that single physical connection to
      connect both to ACP and the data-plane of the network as explained
      in Section 8.1.4.

   o  When devices are not autonomically bootstrapped, explicit
      configuration to enable the ACP needs to be applied.  See
      Section 10.3.

   o  When the ACP needs to be extended across interfacess other than
      L2, the ACP as defined in this document can not autodiscover

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      candidate neighbors automatically.  Remote neighbors need to be
      configured, see Section 8.2.

   Once the ACP is operating, any further configuration for the data-
   plane can be configured more reliably across the ACP itself because
   the ACP provides addressing and connectivity (routing) independent of
   the data-plane itself.  For this, the configuration methods simply
   need to also allow to operate across the ACP VRF - netconf, ssh or
   any other method.

   The ACP also provides additional security through its hop-by-hop
   encryption for any such configuration operations: Some legacy
   configuration methods (SNMP, TFTP, HTTP) may not use end-to-end
   encryption, and most of the end-to-end secured configuration methods
   still allow for easy passive observation along the path about
   configuration taking place (transport flows, port numbers, IP

   The ACP can and should equally be used as the transport to configure
   any of the aforemention non-automic components of the ACP, but in
   that case, the same caution needs to be exercised as with data-plane
   configuration without ACP: Misconfiguration may cause the configuring
   entity to be disconnected from the node it configures - for example
   when incorrectly unconfiguring a remote ACP neighbor through which
   the configured ACP node is reached.

11.  Security Considerations

   After seeding an ACP by configuring at least one ACP registrar with
   routing-subdomain and a CA, an ACP is self-protecting and there is no
   need to apply configuration to make it secure (typically the ACP
   Registrar doubles as EST server for certificate renewal).  Its
   security therefore does not depend on configuration.  This does not
   include workarounds for non-autonomic components as explained in
   Section 8.  See Section 9.2 for details of how the ACP protects
   itself against attacks from the outside and to a more limited degree
   from the inside as well.

   However, the security of the ACP depends on a number of other

   o  The usage of domain certificates depends on a valid supporting PKI
      infrastructure.  If the chain of trust of this PKI infrastructure
      is compromised, the security of the ACP is also compromised.  This
      is typically under the control of the network administrator.

   o  Every ACP registrar is criticial infrastructure that needs to be
      hardened against attacks, similar to a CA.  A malicious registrar

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      can enroll enemy plegdes to an ACP network or break ACP routing by
      duplicate ACP address assignment to pledges via their ACP domain

   o  Security can be compromised by implementation errors (bugs), as in
      all products.

   There is no prevention of source-address spoofing inside the ACP.
   This implies that if an attacker gains access to the ACP, it can
   spoof all addresses inside the ACP and fake messages from any other

   The ACP is designed to enable automation of current network
   management and future autonomic peer-to-peer/distributed network
   automation.  Any ACP member can send ACP IPv6 packet to other ACP
   members and announce via ACP GRASP services to all ACP members
   without depenency against centralized components.

   The ACP relies on peer-to-peer authentication and authorization using
   ACP certificates.  This security model is necessary to enable the
   autonomic ad-hoc any-to-any connectivity between ACP nodes.  It
   provides infrastructure protection through hop by hop authentication
   and encryption - without relying on third parties.  For any services
   where this complete autonomic peer-to-peer group security model is
   appropriate, the ACP domain certificate can also be used unchanged.
   For example for any type of data-plane routing protocol security.

   This ACP security model is designed primarily to protect against
   attack from the outside, but not against attacks from the inside.  To
   protect against spoofing attacks from compromised on-path ACP nodes,
   end-to-end encryption inside the ACP is used by new ACP signaling:
   GRASP across the ACP using TLS.  The same is expected from any non-
   legacy services/protocols using the ACP.  Because no group-keys are
   used, there is no risk for impacted nodes to access end-to-end
   encrypted traffic from other ACP nodes.

   Attacks from impacted ACP nodes against the ACP are more difficult
   than against the data-plane because of the autoconfiguration of the
   ACP and the absence of configuration options that could be abused
   that allow to change/break ACP behavior.  This is excluding
   configuration for workaround in support of non-autonomic components.

   Mitigation against compromised ACP members is possible through
   standard automated certificate management mechanisms including
   revocation and non-renewal of short-lived certificates.  In this
   version of the specification, there are no further optimization of
   these mechanisms defined for the ACP (but see Appendix A.10.8).

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   Higher layer service built using ACP domain certificates should not
   solely rely on undifferentiated group security when another model is
   more appropriate/more secure.  For example central network
   configuration relies on a security model where only few especially
   trusted nodes are allowed to configure the data-plane of network
   nodes (CLIL, Netconf).  This can be done through ACP domain
   certificates by differentiating them and introduce roles.  See
   Appendix A.10.5.

   Fundamentally, security depends on avoiding operator and network
   operations automation mistakes, implementation and architecture.
   Autonomic approaches such as the ACP largely eliminate operator
   mistakes and make it easier to recover from network operations
   mistakes.  Implementation and architectural mistakes are still
   possible, as in all networking technologies.

   Many details of ACP are designed with security in mind and discussed
   elsewhere in the document:

   IPv6 addresses used by nodes in the ACP are covered as part of the
   node's domain certificate as described in Section 6.1.2.  This allows
   even verification of ownership of a peer's IPv6 address when using a
   connection authenticated with the domain certificate.

   The ACP acts as a security (and transport) substrate for GRASP inside
   the ACP such that GRASP is not only protected by attacks from the
   outside, but also by attacks from compromised inside attackers - by
   relying not only on hop-by-hop security of ACP secure channels, but
   adding end-to-end security for those GRASP messages.  See
   Section 6.8.2.

   ACP provides for secure, resilient zero-touch discovery of EST
   servers for certificate renewal.  See Section 6.1.5.

   ACP provides extensible, auto-configuring hop-by-hop protection of
   the ACP infrastructure via the negotiation of hop-by-hop secure
   channel protocols.  See Section 6.5.

   The ACP is designed to minimize attacks from the outside by
   minimizing its dependency against any non-ACP (Data-Plane)
   operations/configuration on a node.  See also Section 6.12.2.

   In combination with BRSKI, ACP enables a resilient, fully zero-touch
   network solution for short-lived certificates that can be renewed or
   re-enrolled even after unintentional expiry (e.g., because of
   interrupted connectivity).  See Appendix A.2.

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   Because ACP secure channels can be long lived, but certificates used
   may be short lived, secure channels, for example built via IPsec need
   to be terminated when peer certificates expire.  See Section 6.7.3.

   The ACP is designed to minimize attacks from the outside by
   minimizing its dependency against any non-ACP (Data-Plane)
   operations/configuration on a node.  See also Section 6.12.2.

12.  IANA Considerations

   This document defines the "Autonomic Control Plane".

   The IANA is requested to register the value "AN_ACP" (without quotes)
   to the GRASP Objectives Names Table in the GRASP Parameter Registry.
   The specification for this value is this document, Section 6.3.

   The IANA is requested to register the value "SRV.est" (without
   quotes) to the GRASP Objectives Names Table in the GRASP Parameter
   Registry.  The specification for this value is this document,
   Section 6.1.5.

   Explanation: This document chooses the initially strange looking
   format "SRV.<service-name>" because these objective names would be in
   line with potential future simplification of the GRASP objective
   registry.  Today, every name in the GRASP objective registry needs to
   be explicitly allocated with IANA.  In the future, this type of
   objective names could considered to be automatically registered in
   that registry for the same service for which <service-name> is
   registered according to [RFC6335].  This explanation is solely
   informational and has no impact on the requested registration.

   The IANA is requested to create an ACP Parameter Registry with
   currently one registry table - the "ACP Address Type" table.

   "ACP Address Type" Table.  The value in this table are numeric values
   0...3 paired with a name (string).  Future values MUST be assigned
   using the Standards Action policy defined by [RFC8126].  The
   following initial values are assigned by this document:

   0: ACP Zone Addressing Sub-Scheme (ACP RFC Figure 11) / ACP Manual
   Addressing Sub-Scheme (ACP RFC Section 6.10.4)
   1: ACP Vlong Addressing Sub-Scheme (ACP RFC Section 6.10.5)

13.  Acknowledgements

   This work originated from an Autonomic Networking project at Cisco
   Systems, which started in early 2010.  Many people contributed to
   this project and the idea of the Autonomic Control Plane, amongst

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   which (in alphabetical order): Ignas Bagdonas, Parag Bhide, Balaji
   BL, Alex Clemm, Yves Hertoghs, Bruno Klauser, Max Pritikin, Michael
   Richardson, Ravi Kumar Vadapalli.

   Special thanks to Brian Carpenter, Elwyn Davies, Joel Halpern and
   Sheng Jiang for their thorough reviews and to Pascal Thubert and
   Michael Richardson to provide the details for the recommendations of
   the use of RPL in the ACP.

   Thanks to Valery Smyslov for review of the IPsec and IKEv2
   configuration parameters.

   Further input, review or suggestions were received from: Rene Struik,
   Brian Carpenter, Benoit Claise, William Atwood and Yongkang Zhang.

14.  Change log [RFC Editor: Please remove]

14.1.  Summary of changes since entering IESG review

   This text replaces the prior changelog with a summary to provide
   guidance for further IESG review.

   Please see revision -21 for the individual changelogs of prior
   versions .

14.1.1.  Reviews (while in IESG review status) / status

   This document entered IESG review with version -13.  It has since
   seen the following reviews:

   IESG: Original owner/Yes: Terry Manderson (INT).

   IESG: No Objection: Deborah Brungard (RTG), Alissa Cooper (GEN),
   Warren Kumari (OPS), Mirja Kuehlewind (TSV), Alexey Melnikov (ART),
   Adam Roach (ART).

   IESG: No Objection, not counted anymore as they have left IESG: Ben
   Campbell (ART), Spencer Dawkins (TSV).

   IESG: Open DISCUSS hopefully resolved by this version: Eric Rescorla
   (SEC, left IESG), Benjamin Kaduk (SEC).

   Other: Michael Richardson (WG), Brian Carpenter (WG), Pascal Thubert
   (WG), Frank Xialiang (WG), Elwyn Davies (GEN), Joel Halpern (RTGdir),
   Yongkang Zhang (WG), William Atwood (WG).

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14.1.2.  BRSKI / ACP registrar related enhancements

   Only after ACP entered IESG review did it become clear that the in-
   progress BRSKI document would not provide all the explanations needed
   for ACP registrars as expected earlier by ACP authors.  Instead,
   BRSKI will only specify a subset of required ACP behavior related to
   certificate handling and registrar.  There, it became clear that the
   ACP draft should specify generic ACP registrar behavior independent
   of BRSKI so ACP could be implemented with or without BRSKI and any
   manual/proprietary or future standardized BRSKI alternatives (for
   example via NetConf) would understand the requirements for ACP
   registrars and its certificate handling.

   This lead to additional text about ACP registrars in the ACP

   1.  Defined relationship ACP / ANI (ANI = ACP + BRSKI).

   6.1.4 (new) Overview of trust points and trust anchors required for
   ACP. Added explanations/requirements for Re-enrolment.

   6.10.7 Normative requirements for ACP registrars (BRSKI or not).

   10.2 Operational expectations against ACP registrars (BRSKI or not).

14.1.3.  Normative enhancements since start of IESG review

   In addition to above ACP registrar / BRSKI related enhancements there
   is a range of minor normative (also explanatory) enhancements since
   the start of IESG review:

   6.1.1 Hex digits in ACP domain information field now upper-case (no
   specific reason except that both options are equally good, but
   capitalized ones are used in rfc5234). Added explanations about CRLs. Added explanations of behavior under failing certificates.

   6.1.2 Allow ACP adddress '0' in ACP domain information field:
   presence of address indicates permission to build ACP secure channel
   to node, 0 indicates that the address of the node is assigned by
   (future) other means than certificate.  Non-autonomic nodes have no
   address at all (that was in -13), and can only connect via ACP
   connect interfaces to ACP.

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   6.1.3 Distinction of real ACP nodes (with address) and those with
   domain certificate without address added as a new rule to ACP domain
   membership check.

   6.6 Added throttling of secure-channel setup attempts. Removed requirement to handle unknown destination ACP
   traffic in low-end nodes that would never be RPL roots.

   6.12.5 Added recommendation to use IPv6 DAD.

   6.1.1,, 6.7.2, 6.7.3, 6.8.2 Various refined additional
   certificate, secure channel protocol (IPsec/IKEv2 and DTLS) and ACP
   GRASP TLS protocol parameter requirements to ensure interoperating
   implementations (from SEC-AD review).

14.1.4.  Explanatory enhancements since start of IESG review

   Beyond the functional enhancements from the previous two sections,
   the mayority of changes since -13 are additional explanations from
   review feedback, textual nits and restructuring - with no functional
   requirement additions/changes.

   1.1 Added "applicability and scope" section with summarized

   2.Added in-band vs. out-of-band management definitions.

   6.1.2 (was 6.1.1) expanded explanations of reasoning for elements of
   the ACP domain information field.

   6.1.3 refined explanations of ACP domain membership check and
   justifications for it.

   6.5 Elaborated step-by-step secure channel setup.

   6.10 Additional explanations for addressing modes, additional table
   of addressing formats (thanks MichaelR).

   6.10.5 introduced 'F' bit position as a better visual representation
   in the Vlong address space. extensive overhaul to improve readability of use of RPL
   (from IESG feedback of non-routing/RPL experts).

   6.12.2 Added caution about unconfiguring data-plane IPv6 addresses
   and impact to ACP (limitation of current ACP design, and pointint to
   more details in 10.2).

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   10.4 New explanations / summary of configurations for ACP (aka: all
   config is undesirable and only required for integrating with non-
   autonomic components, primarily ACP-connect and Registrars).

   11.  Textually enhanced / better structured security considerations
   section after IESG security review.

   A. (new) Moved all explanations and discussions about futures from
   section 10 into this new appendix.  This text should not be removed
   because it captures a lot of repeated asked questions in WG and
   during reviews and from users, and also captures ideas for some
   likely important followup work.  But none of this is relevant to
   implementing (section 6) and operating (section 10) the ACP.

14.2.  draft-ietf-anima-autonomic-control-plane-22

   Ben Kaduk review of -21:

   RFC822 encoding of ACP domain information:

   6.1.2 rewrote text for explaining / justifying use of rfc822name as
   identifier for node CP in certificate (was discussed in thread, but
   badly written in prior versions).

   6.1.2 Changed EBNF syntax to use "+" after rfcSELF because that is
   the known primary name to extensions separator in many email systems
   ("." was wrong in prior versions).

   6.1.2 Rewrote/improved explanations for use of rfc822name field to
   explain better why it is PKIX compliant and the right thing to do.

   Crypto parameters for IPsec:

   6.1 - Added explanation of why manual keying for ACP is not feasible
   for ACP.  Surprisingly, that text did not exist.  Referred to by
   IPsec text (6.7.1), but here is the right place to describe the

   6.1.2 - Small textual refinement referring to requirements to
   authenticate peers (for the special cases of empty or '0' ACP address
   in ACP domain information field.

   6.3 - To better justify Bens proposed change of secure channel
   protocol being IPsec vs. GRASP objective being IKEv2, better
   explained how protocol indicated in GRASP objective-value is name of
   protocol used to negotiate secure channel, use example of IKEv2 to
   negotiate IPsec.

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   6.7.1 - refinemenet similar to 6.3.

   - moved new paragraph from Bens pull request up from to 6.7.1
   as it equally applies to GRE encapped IPsec (looks nicer one level

   - created subsections (IPsec/ESP) / (IKEv2) to
   clearer distinguish between these two requirements blocks.

   - Refined the text in these two sections to hopefully be a good
   answer to Valery's concern of not randomnly mocking with existing
   requirements docs (rfc8247 / rfc8221). - IPsec/ESP requirements section:

   - MUST support rfc8221 mandatory EXCEPT for the superceeding
   requirements in this section.  Previously, this was not quite clear
   from the text.

   - Hopefully persuasive explanations about the requirements levels for
   ENCR_CHACHA20_POLY1305: Restructured text for why not ENCR_AES_CBC
   (was in prior version, just not well structured), added new
   expanations for ENCR_AES_CCM_8 and ENCR_CHACHA20_POLY130.

   - In simple terms, requirements for ENCR_AES_CBC, ENCR_AES_CCM_8,
   ENCR_CHACHACHA are SHOULD when they are implementable with rqual or
   faster performancce than ENCR_AES_GCM_16.

   - Removed text about "additional rfc8221" reqiurements MAY be used.
   Now the logic is that all other requirements apply.  Hopefully we
   have written enough so that we prohibited downgrades. - RFC8247 requirements:

   - Added mandate to support rfc8247, added explanation that there is
   no "stripping down" requirement, just additional stronger
   requirements to mandate correct use of ACP certificartes during

   - refined text on identifying ACP by IPv6 address to be clearer:
   Identifying in the context of IKEv2 and cases for '0' in ACP domain

   - removed last two paragraphs about relationship to rfc8247, as his
   is now written in first paragraph of the section.

   End of Ben Kaduk review related fixes.

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   Forgot to update example of ACP domain information to use capitalized
   hex-digits as required by HEXDIGIT used.

   Added reference to RFC8316 (AN use-cases) to beginning of section 3
   (ACP use cases).

   Small Enhanced IPsec parameters description / requirements fixes
   (from Michael Richardson).

15.  References

15.1.  Normative References

              Bormann, C., Carpenter, B., and B. Liu, "A Generic
              Autonomic Signaling Protocol (GRASP)", draft-ietf-anima-
              grasp-15 (work in progress), July 2017.

              Birkholz, H., Vigano, C., and C. Bormann, "Concise data
              definition language (CDDL): a notational convention to
              express CBOR and JSON data structures", draft-ietf-cbor-
              cddl-08 (work in progress), March 2019.

              IANA, "Internet Key Exchange Version 2 (IKEv2)
              Parameters", <

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,

   [RFC3810]  Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
              Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
              DOI 10.17487/RFC3810, June 2004,

   [RFC4106]  Viega, J. and D. McGrew, "The Use of Galois/Counter Mode
              (GCM) in IPsec Encapsulating Security Payload (ESP)",
              RFC 4106, DOI 10.17487/RFC4106, June 2005,

   [RFC4191]  Draves, R. and D. Thaler, "Default Router Preferences and
              More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191,
              November 2005, <>.

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   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
              Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <>.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
              December 2005, <>.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007,

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862,
              DOI 10.17487/RFC4862, September 2007,

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,

   [RFC5322]  Resnick, P., Ed., "Internet Message Format", RFC 5322,
              DOI 10.17487/RFC5322, October 2008,

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <>.

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   [RFC6550]  Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
              Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
              JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
              Low-Power and Lossy Networks", RFC 6550,
              DOI 10.17487/RFC6550, March 2012,

   [RFC6552]  Thubert, P., Ed., "Objective Function Zero for the Routing
              Protocol for Low-Power and Lossy Networks (RPL)",
              RFC 6552, DOI 10.17487/RFC6552, March 2012,

   [RFC6553]  Hui, J. and JP. Vasseur, "The Routing Protocol for Low-
              Power and Lossy Networks (RPL) Option for Carrying RPL
              Information in Data-Plane Datagrams", RFC 6553,
              DOI 10.17487/RFC6553, March 2012,

   [RFC7030]  Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
              "Enrollment over Secure Transport", RFC 7030,
              DOI 10.17487/RFC7030, October 2013,

   [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
              Kivinen, "Internet Key Exchange Protocol Version 2
              (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
              2014, <>.

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <>.

   [RFC7676]  Pignataro, C., Bonica, R., and S. Krishnan, "IPv6 Support
              for Generic Routing Encapsulation (GRE)", RFC 7676,
              DOI 10.17487/RFC7676, October 2015,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

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   [RFC8221]  Wouters, P., Migault, D., Mattsson, J., Nir, Y., and T.
              Kivinen, "Cryptographic Algorithm Implementation
              Requirements and Usage Guidance for Encapsulating Security
              Payload (ESP) and Authentication Header (AH)", RFC 8221,
              DOI 10.17487/RFC8221, October 2017,

   [RFC8247]  Nir, Y., Kivinen, T., Wouters, P., and D. Migault,
              "Algorithm Implementation Requirements and Usage Guidance
              for the Internet Key Exchange Protocol Version 2 (IKEv2)",
              RFC 8247, DOI 10.17487/RFC8247, September 2017,

15.2.  Informative References

   [AR8021]   Group, W. -. H. L. L. P. W., "IEEE Standard for Local and
              metropolitan area networks - Secure Device Identity",
              December 2009, <

              CA/Browser Forum, "Certificate Contents for Baseline SSL",
              Nov 2019, <

              Eckert, T., "Autoconfiguration of NOC services in ACP
              networks via GRASP", draft-eckert-anima-noc-autoconfig-00
              (work in progress), July 2018.

              Sheffer, Y., Lopez, D., Dios, O., Pastor, A., and T.
              Fossati, "Support for Short-Term, Automatically-Renewed
              (STAR) Certificates in Automated Certificate Management
              Environment (ACME)", draft-ietf-acme-star-11 (work in
              progress), October 2019.

              Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
              and K. Watsen, "Bootstrapping Remote Secure Key
              Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping-
              keyinfra-34 (work in progress), January 2020.

              Jiang, S., Du, Z., Carpenter, B., and Q. Sun, "Autonomic
              IPv6 Edge Prefix Management in Large-scale Networks",
              draft-ietf-anima-prefix-management-07 (work in progress),
              December 2017.

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              Behringer, M., Carpenter, B., Eckert, T., Ciavaglia, L.,
              and J. Nobre, "A Reference Model for Autonomic
              Networking", draft-ietf-anima-reference-model-10 (work in
              progress), November 2018.

              Watsen, K., Abrahamsson, M., and I. Farrer, "Secure Zero
              Touch Provisioning (SZTP)", draft-ietf-netconf-
              zerotouch-29 (work in progress), January 2019.

              Richardson, M., "ROLL Applicability Statement Template",
              draft-ietf-roll-applicability-template-09 (work in
              progress), May 2016.

              Robles, I., Richardson, M., and P. Thubert, "Using RPI
              Option Type, Routing Header for Source Routes and IPv6-in-
              IPv6 encapsulation in the RPL Data Plane", draft-ietf-
              roll-useofrplinfo-34 (work in progress), January 2020.

              Rescorla, E., Tschofenig, H., and N. Modadugu, "The
              Datagram Transport Layer Security (DTLS) Protocol Version
              1.3", draft-ietf-tls-dtls13-34 (work in progress),
              November 2019.

              IEEE, "IEEE Standard for a Precision Clock Synchronization
              Protocol for Networked Measurement and Control Systems",
              December 2008, <

              Group, W. -. H. L. L. P. W., "IEEE Standard for Local and
              Metropolitan Area Networks: Port-Based Network Access
              Control", February 2010,

   [LLDP]     Group, W. -. H. L. L. P. W., "IEEE Standard for Local and
              Metropolitan Area Networks: Station and Media Access
              Control Connectivity Discovery", June 2016,

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   [MACSEC]   Group, W. -. H. L. L. P. W., "IEEE Standard for Local and
              Metropolitan Area Networks: Media Access Control (MAC)
              Security", June 2006,

   [RFC1112]  Deering, S., "Host extensions for IP multicasting", STD 5,
              RFC 1112, DOI 10.17487/RFC1112, August 1989,

   [RFC1492]  Finseth, C., "An Access Control Protocol, Sometimes Called
              TACACS", RFC 1492, DOI 10.17487/RFC1492, July 1993,

   [RFC1886]  Thomson, S. and C. Huitema, "DNS Extensions to support IP
              version 6", RFC 1886, DOI 10.17487/RFC1886, December 1995,

   [RFC1918]  Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
              and E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996,

   [RFC2315]  Kaliski, B., "PKCS #7: Cryptographic Message Syntax
              Version 1.5", RFC 2315, DOI 10.17487/RFC2315, March 1998,

   [RFC2821]  Klensin, J., Ed., "Simple Mail Transfer Protocol",
              RFC 2821, DOI 10.17487/RFC2821, April 2001,

   [RFC2865]  Rigney, C., Willens, S., Rubens, A., and W. Simpson,
              "Remote Authentication Dial In User Service (RADIUS)",
              RFC 2865, DOI 10.17487/RFC2865, June 2000,

   [RFC3164]  Lonvick, C., "The BSD Syslog Protocol", RFC 3164,
              DOI 10.17487/RFC3164, August 2001,

   [RFC3315]  Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
              C., and M. Carney, "Dynamic Host Configuration Protocol
              for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
              2003, <>.

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   [RFC3411]  Harrington, D., Presuhn, R., and B. Wijnen, "An
              Architecture for Describing Simple Network Management
              Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
              DOI 10.17487/RFC3411, December 2002,

   [RFC3954]  Claise, B., Ed., "Cisco Systems NetFlow Services Export
              Version 9", RFC 3954, DOI 10.17487/RFC3954, October 2004,

   [RFC4007]  Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and
              B. Zill, "IPv6 Scoped Address Architecture", RFC 4007,
              DOI 10.17487/RFC4007, March 2005,

   [RFC4210]  Adams, C., Farrell, S., Kause, T., and T. Mononen,
              "Internet X.509 Public Key Infrastructure Certificate
              Management Protocol (CMP)", RFC 4210,
              DOI 10.17487/RFC4210, September 2005,

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <>.

   [RFC4429]  Moore, N., "Optimistic Duplicate Address Detection (DAD)
              for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006,

   [RFC4492]  Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
              Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
              for Transport Layer Security (TLS)", RFC 4492,
              DOI 10.17487/RFC4492, May 2006,

   [RFC4541]  Christensen, M., Kimball, K., and F. Solensky,
              "Considerations for Internet Group Management Protocol
              (IGMP) and Multicast Listener Discovery (MLD) Snooping
              Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006,

   [RFC4604]  Holbrook, H., Cain, B., and B. Haberman, "Using Internet
              Group Management Protocol Version 3 (IGMPv3) and Multicast
              Listener Discovery Protocol Version 2 (MLDv2) for Source-
              Specific Multicast", RFC 4604, DOI 10.17487/RFC4604,
              August 2006, <>.

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   [RFC4607]  Holbrook, H. and B. Cain, "Source-Specific Multicast for
              IP", RFC 4607, DOI 10.17487/RFC4607, August 2006,

   [RFC4610]  Farinacci, D. and Y. Cai, "Anycast-RP Using Protocol
              Independent Multicast (PIM)", RFC 4610,
              DOI 10.17487/RFC4610, August 2006,

   [RFC4941]  Narten, T., Draves, R., and S. Krishnan, "Privacy
              Extensions for Stateless Address Autoconfiguration in
              IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,

   [RFC5321]  Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
              DOI 10.17487/RFC5321, October 2008,

   [RFC5790]  Liu, H., Cao, W., and H. Asaeda, "Lightweight Internet
              Group Management Protocol Version 3 (IGMPv3) and Multicast
              Listener Discovery Version 2 (MLDv2) Protocols", RFC 5790,
              DOI 10.17487/RFC5790, February 2010,

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,

   [RFC5905]  Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
              "Network Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,

   [RFC6335]  Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
              Cheshire, "Internet Assigned Numbers Authority (IANA)
              Procedures for the Management of the Service Name and
              Transport Protocol Port Number Registry", BCP 165,
              RFC 6335, DOI 10.17487/RFC6335, August 2011,

   [RFC6402]  Schaad, J., "Certificate Management over CMS (CMC)
              Updates", RFC 6402, DOI 10.17487/RFC6402, November 2011,

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   [RFC6724]  Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown,
              "Default Address Selection for Internet Protocol Version 6
              (IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012,

   [RFC6733]  Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn,
              Ed., "Diameter Base Protocol", RFC 6733,
              DOI 10.17487/RFC6733, October 2012,

   [RFC6762]  Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
              DOI 10.17487/RFC6762, February 2013,

   [RFC6763]  Cheshire, S. and M. Krochmal, "DNS-Based Service
              Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,

   [RFC6830]  Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
              Locator/ID Separation Protocol (LISP)", RFC 6830,
              DOI 10.17487/RFC6830, January 2013,

   [RFC7011]  Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
              "Specification of the IP Flow Information Export (IPFIX)
              Protocol for the Exchange of Flow Information", STD 77,
              RFC 7011, DOI 10.17487/RFC7011, September 2013,

   [RFC7404]  Behringer, M. and E. Vyncke, "Using Only Link-Local
              Addressing inside an IPv6 Network", RFC 7404,
              DOI 10.17487/RFC7404, November 2014,

   [RFC7426]  Haleplidis, E., Ed., Pentikousis, K., Ed., Denazis, S.,
              Hadi Salim, J., Meyer, D., and O. Koufopavlou, "Software-
              Defined Networking (SDN): Layers and Architecture
              Terminology", RFC 7426, DOI 10.17487/RFC7426, January
              2015, <>.

   [RFC7575]  Behringer, M., Pritikin, M., Bjarnason, S., Clemm, A.,
              Carpenter, B., Jiang, S., and L. Ciavaglia, "Autonomic
              Networking: Definitions and Design Goals", RFC 7575,
              DOI 10.17487/RFC7575, June 2015,

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   [RFC7576]  Jiang, S., Carpenter, B., and M. Behringer, "General Gap
              Analysis for Autonomic Networking", RFC 7576,
              DOI 10.17487/RFC7576, June 2015,

   [RFC7721]  Cooper, A., Gont, F., and D. Thaler, "Security and Privacy
              Considerations for IPv6 Address Generation Mechanisms",
              RFC 7721, DOI 10.17487/RFC7721, March 2016,

   [RFC7761]  Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
              Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
              Multicast - Sparse Mode (PIM-SM): Protocol Specification
              (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
              2016, <>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,

   [RFC8028]  Baker, F. and B. Carpenter, "First-Hop Router Selection by
              Hosts in a Multi-Prefix Network", RFC 8028,
              DOI 10.17487/RFC8028, November 2016,

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,

   [RFC8316]  Nobre, J., Granville, L., Clemm, A., and A. Gonzalez
              Prieto, "Autonomic Networking Use Case for Distributed
              Detection of Service Level Agreement (SLA) Violations",
              RFC 8316, DOI 10.17487/RFC8316, February 2018,

   [RFC8366]  Watsen, K., Richardson, M., Pritikin, M., and T. Eckert,
              "A Voucher Artifact for Bootstrapping Protocols",
              RFC 8366, DOI 10.17487/RFC8366, May 2018,

   [RFC8368]  Eckert, T., Ed. and M. Behringer, "Using an Autonomic
              Control Plane for Stable Connectivity of Network
              Operations, Administration, and Maintenance (OAM)",
              RFC 8368, DOI 10.17487/RFC8368, May 2018,

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15.3.  URIs



Appendix A.  Background and Futures (Informative)

   The following sections discuss additional background information
   about aspects of the normative parts of this document or associated
   mechanisms such as BRSKI (such as why specific choices were made by
   the ACP) and they provide discussion about possible future variations
   of the ACP.

A.1.  ACP Address Space Schemes

   This document defines the Zone, Vlong and Manual sub address schemes
   primarily to support address prefix assignment via distributed,
   potentially uncoordinated ACP registrars as defined in
   Section 6.10.7.  This costs 48/46-bit identifier so that these ACP
   registrar can assign non-conflicting address prefixes.  This design
   does not leave enough bits to simultaneously support a large number
   of nodes (Node-ID) plus a large prefix of local addresses for every
   node plus a large enough set of bits to identify a routing Zone.  In
   result, Zone, Vlong 8/16 attempt to support all features, but in via
   separate prefixes.

   In networks that always expect to rely on a centralized PMS as
   described above (Section 10.2.5), the 48/46-bits for the Registrar-ID
   could be saved.  Such variations of the ACP addressing mechanisms
   could be introduced through future work in different ways.  If the
   prefix rfcSELF in the ACP information field was changed, incompatible
   ACP variations could be created where every design aspect of the ACP
   could be changed.  Including all addressing choices.  If instead a
   new addressing sub-type would be defined, it could be a backward
   compatible extension of this ACP specification.  Information such as
   the size of a zone-prefix and the length of the prefix assigned to
   the ACP node itself could be encoded via the extension field of the
   ACP domain information.

   Note that an explicitly defined "Manual" addressing sub-scheme is
   always beneficial to provide an easy way for ACP nodes to prohibit
   incorrect manual configuration of any non-"Manual" ACP address spaces
   and therefore ensure that "Manual" operations will never impact
   correct routing for any non-"Manual" ACP addresses assigned via ACP
   domain certificates.

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A.2.  BRSKI Bootstrap (ANI)

   [I-D.ietf-anima-bootstrapping-keyinfra] (BRSKI) describes how nodes
   with an IDevID certificate can securely and zero-touch enroll with a
   domain certificate (LDevID) to support the ACP.  BRSKI also leverages
   the ACP to enable zero-touch bootstrap of new nodes across networks
   without any configuration requirements across the transit nodes
   (e.g., no DHCP/DNS forwarding/server setup).  This includes otherwise
   not configured networks as described in Section 3.2.  Therefore BRSKI
   in conjunction with ACP provides for a secure and zero-touch
   management solution for complete networks.  Nodes supporting such an
   infrastructure (BRSKI and ACP) are called ANI nodes (Autonomic
   Networking Infrastructure), see [I-D.ietf-anima-reference-model].
   Nodes that do not support an IDevID but only an (insecure) vendor
   specific Unique Device Identifier (UDI) or nodes whose manufacturer
   does not support a MASA could use some future security reduced
   version of BRSKI.

   When BRSKI is used to provision a domain certificate (which is called
   enrollment), the BRSKI registrar (acting as an enhanced EST server)
   must include the subjectAltName / rfc822Name encoded ACP address and
   domain name to the enrolling node (called pledge) via its response to
   the pledges EST CSR Attribute request that is mandatory in BRSKI.

   The Certificate Authority in an ACP network must not change the
   subjectAltName / rfc822Name in the certificate.  The ACP nodes can
   therefore find their ACP address and domain using this field in the
   domain certificate, both for themselves, as well as for other nodes.

   The use of BRSKI in conjunction with the ACP can also help to further
   simplify maintenance and renewal of domain certificates.  Instead of
   relying on CRL, the lifetime of certificates can be made extremely
   small, for example in the order of hours.  When a node fails to
   connect to the ACP within its certificate lifetime, it cannot connect
   to the ACP to renew its certificate across it (using just EST), but
   it can still renew its certificate as an "enrolled/expired pledge"
   via the BRSKI bootstrap proxy.  This requires only that the BRSKI
   registrar honors expired domain certificates and that the pledge
   attempts to perform TLS authentication for BRSKI bootstrap using its
   expired domain certificate before falling back to attempting to use
   its IDevID for BRSKI.  This mechanism could also render CRLs
   unnecessary because the BRSKI registrar in conjunction with the CA
   would not renew revoked certificates - only a "Do-not-renew" list
   would be necessary on BRSKI registrars/CA.

   In the absence of BRSKI or less secure variants thereof, provisioning
   of certificates may involve one or more touches or non-standardized
   automation.  Node vendors usually support provisioning of

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   certificates into nodes via PKCS#7 (see [RFC2315]) and may support
   this provisioning through vendor specific models via Netconf
   ([RFC6241]).  If such nodes also support Netconf Zero-Touch
   ([I-D.ietf-netconf-zerotouch]) then this can be combined to zero-
   touch provisioning of domain certificates into nodes.  Unless there
   are equivalent integration of Netconf connections across the ACP as
   there is in BRSKI, this combination would not support zero-touch
   bootstrap across a not configured network though.

A.3.  ACP Neighbor discovery protocol selection

   This section discusses why GRASP DULL was chosen as the discovery
   protocol for L2 adjacent candidate ACP neighbors.  The contenders
   considered where GRASP, mDNS or LLDP.

A.3.1.  LLDP

   LLDP and Cisco's earlier Cisco Discovery Protocol (CDP) are example
   of L2 discovery protocols that terminate their messages on L2 ports.
   If those protocols would be chosen for ACP neighbor discovery, ACP
   neighbor discovery would therefore also terminate on L2 ports.  This
   would prevent ACP construction over non-ACP capable but LLDP or CDP
   enabled L2 switches.  LLDP has extensions using different MAC
   addresses and this could have been an option for ACP discovery as
   well, but the additional required IEEE standardization and definition
   of a profile for such a modified instance of LLDP seemed to be more
   work than the benefit of "reusing the existing protocol" LLDP for
   this very simple purpose.

A.3.2.  mDNS and L2 support

   Multicast DNNS (mDNS) [RFC6762] with DNS Service Discovery (DNS-SD)
   Resource Records (RRs) as defined in [RFC6763] is a key contender as
   an ACP discovery protocol. because it relies on link-local IP
   multicast, it does operates at the subnet level, and is also found in
   L2 switches.  The authors of this document are not aware of mDNS
   implementation that terminate their mDNS messages on L2 ports instead
   of the subnet level.  If mDNS was used as the ACP discovery mechanism
   on an ACP capable (L3)/L2 switch as outlined in Section 7, then this
   would be necessary to implement.  It is likely that termination of
   mDNS messages could only be applied to all mDNS messages from such a
   port, which would then make it necessary to software forward any non-
   ACP related mDNS messages to maintain prior non-ACP mDNS
   functionality.  Adding support for ACP into such L2 switches with
   mDNS could therefore create regression problems for prior mDNS
   functionality on those nodes.  With low performance of software
   forwarding in many L2 switches, this could also make the ACP risky to
   support on such L2 switches.

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A.3.3.  Why DULL GRASP

   LLDP was not considered because of the above mentioned issues. mDNS
   was not selected because of the above L2 mDNS considerations and
   because of the following additional points:

   If mDNS was not already existing in a node, it would be more work to
   implement than DULL GRASP, and if an existing implementation of mDNS
   was used, it would likely be more code space than a separate
   implementation of DULL GRASP or a shared implementation of DULL GRASP
   and GRASP in the ACP.

A.4.  Choice of routing protocol (RPL)

   This section motivates why RPL - "IPv6 Routing Protocol for Low-Power
   and Lossy Networks ([RFC6550] was chosen as the default (and in this
   specification only) routing protocol for the ACP.  The choice and
   above explained profile was derived from a pre-standard
   implementation of ACP that was successfully deployed in operational

   Requirements for routing in the ACP are:

   o  Self-management: The ACP must build automatically, without human
      intervention.  Therefore routing protocol must also work
      completely automatically.  RPL is a simple, self-managing
      protocol, which does not require zones or areas; it is also self-
      configuring, since configuration is carried as part of the
      protocol (see Section 6.7.6 of [RFC6550]).

   o  Scale: The ACP builds over an entire domain, which could be a
      large enterprise or service provider network.  The routing
      protocol must therefore support domains of 100,000 nodes or more,
      ideally without the need for zoning or separation into areas.  RPL
      has this scale property.  This is based on extensive use of
      default routing.

   o  Low resource consumption: The ACP supports traditional network
      infrastructure, thus runs in addition to traditional protocols.
      The ACP, and specifically the routing protocol must have low
      resource consumption both in terms of memory and CPU requirements.
      Specifically, at edge nodes, where memory and CPU are scarce,
      consumption should be minimal.  RPL builds a destination-oriented
      directed acyclic graph (DODAG), where the main resource
      consumption is at the root of the DODAG.  The closer to the edge
      of the network, the less state needs to be maintained.  This
      adapts nicely to the typical network design.  Also, all changes
      below a common parent node are kept below that parent node.

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   o  Support for unstructured address space: In the Autonomic
      Networking Infrastructure, node addresses are identifiers, and may
      not be assigned in a topological way.  Also, nodes may move
      topologically, without changing their address.  Therefore, the
      routing protocol must support completely unstructured address
      space.  RPL is specifically made for mobile ad-hoc networks, with
      no assumptions on topologically aligned addressing.

   o  Modularity: To keep the initial implementation small, yet allow
      later for more complex methods, it is highly desirable that the
      routing protocol has a simple base functionality, but can import
      new functional modules if needed.  RPL has this property with the
      concept of "objective function", which is a plugin to modify
      routing behavior.

   o  Extensibility: Since the Autonomic Networking Infrastructure is a
      new concept, it is likely that changes in the way of operation
      will happen over time.  RPL allows for new objective functions to
      be introduced later, which allow changes to the way the routing
      protocol creates the DAGs.

   o  Multi-topology support: It may become necessary in the future to
      support more than one DODAG for different purposes, using
      different objective functions.  RPL allow for the creation of
      several parallel DODAGs, should this be required.  This could be
      used to create different topologies to reach different roots.

   o  No need for path optimization: RPL does not necessarily compute
      the optimal path between any two nodes.  However, the ACP does not
      require this today, since it carries mainly non-delay-sensitive
      feedback loops.  It is possible that different optimization
      schemes become necessary in the future, but RPL can be expanded
      (see point "Extensibility" above).

A.5.  ACP Information Distribution and multicast

   IP multicast is not used by the ACP because the ANI (Autonomic
   Networking Infrastructure) itself does not require IP multicast but
   only service announcement/discovery.  Using IP multicast for that
   would have made it necessary to develop a zero-touch auto configuring
   solution for ASM (Any Source Multicast - the original form of IP
   multicast defined in [RFC1112]), which would be quite complex and
   difficult to justify.  One aspect of complexity where no attempt at a
   solution has been described in IETF documents is the automatic-
   selection of routers that should be PIM Sparse Mode (PIM-SM)
   Rendezvous Points (RPs) (see [RFC7761]).  The other aspects of
   complexity are the implementation of MLD ([RFC4604]), PIM-SM and
   Anycast-RP (see [RFC4610]).  If those implementations already exist

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   in a product, then they would be very likely tied to accelerated
   forwarding which consumes hardware resources, and that in return is
   difficult to justify as a cost of performing only service discovery.

   Some future ASA may need high performance in-network data
   replication.  That is the case when the use of IP multicast is
   justified.  Such an ASA can then use service discovery from ACP
   GRASP, and then they do not need ASM but only SSM (Source Specific
   Multicast, see [RFC4607]) for the IP multicast replication.  SSM
   itself can simply be enabled in the Data-Plane (or even in an update
   to the ACP) without any other configuration than just enabling it on
   all nodes and only requires a simpler version of MLD (see [RFC5790]).

   LSP (Link State Protocol) based IGP routing protocols typically have
   a mechanism to flood information, and such a mechanism could be used
   to flood GRASP objectives by defining them to be information of that
   IGP.  This would be a possible optimization in future variations of
   the ACP that do use an LSP routing protocol.  Note though that such a
   mechanism would not work easily for GRASP M_DISCOVERY messages which
   are intelligently (constrained) flooded not across the whole ACP, but
   only up to a node where a responder is found.  We do expect that many
   future services in ASA will have only few consuming ASA, and for
   those cases, M_DISCOVERY is the more efficient method than flooding
   across the whole domain.

   Because the ACP uses RPL, one desirable future extension is to use
   RPLs existing notion of loop-free distribution trees (DODAG) to make
   GRASPs flooding more efficient both for M_FLOOD and M_DISCOVERY) See
   Section 6.12.5 how this will be specifically beneficial when using
   NBMA interfaces.  This is not currently specified in this document
   because it is not quite clear yet what exactly the implications are
   to make GRASP flooding depend on RPL DODAG convergence and how
   difficult it would be to let GRASP flooding access the DODAG

A.6.  Extending ACP channel negotiation (via GRASP)

   [RFC Editor: This section to be removed before RFC.

   [This section kept for informational purposes up until the last draft
   version as that would be the version that readers interested in the
   changelog would also go to to revisit it.]

   The mechanism described in the normative part of this document to
   support multiple different ACP secure channel protocols without a
   single network wide MTI protocol is important to allow extending
   secure ACP channel protocols beyond what is specified in this

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   document, but it will run into problem if it would be used for
   multiple protocols:

   The need to potentially have multiple of these security associations
   even temporarily run in parallel to determine which of them works
   best does not support the most lightweight implementation options.

   The simple policy of letting one side (Alice) decide what is best may
   not lead to the mutual best result.

   The two limitations can easier be solved if the solution was more
   modular and as few as possible initial secure channel negotiation
   protocols would be used, and these protocols would then take on the
   responsibility to support more flexible objectives to negotiate the
   mutually preferred ACP security channel protocol.

   IKEv2 is the IETF standard protocol to negotiate network security
   associations.  It is meant to be extensible, but it is unclear
   whether it would be feasible to extend IKEv2 to support possible
   future requirements for ACP secure channel negotiation:

   Consider the simple case where the use of native IPsec vs. IPsec via
   GRE is to be negotiated and the objective is the maximum throughput.
   Both sides would indicate some agreed upon performance metric and the
   preferred encapsulation is the one with the higher performance of the
   slower side.  IKEv2 does not support negotiation with this objective.

   Consider DTLS and some form of MacSec are to be added as negotiation
   options - and the performance objective should work across all IPsec,
   DTLS and MacSec options.  In the case of MacSEC, the negotiation
   would also need to determine a key for the peering.  It is unclear if
   it would be even appropriate to consider extending the scope of
   negotiation in IKEv2 to those cases.  Even if feasible to define, it
   is unclear if implementations of IKEv2 would be eager to adopt those
   type of extension given the long cycles of security testing that
   necessarily goes along with core security protocols such as IKEv2

   A more modular alternative to extending IKEv2 could be to layer a
   modular negotiation mechanism on top of the multitude of existing or
   possible future secure channel protocols.  For this, GRASP over TLS
   could be considered as a first ACP secure channel negotiation
   protocol.  The following are initial considerations for such an
   approach.  A full specification is subject to a separate document:

   To explicitly allow negotiation of the ACP channel protocol, GRASP
   over a TLS connection using the GRASP_LISTEN_PORT and the node's and
   peer's link-local IPv6 address is used.  When Alice and Bob support

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   GRASP negotiation, they do prefer it over any other non-explicitly
   negotiated security association protocol and should wait trying any
   non-negotiated ACP channel protocol until after it is clear that
   GRASP/TLS will not work to the peer.

   When Alice and Bob successfully establish the GRASP/TSL session, they
   will negotiate the channel mechanism to use using objectives such as
   performance and perceived quality of the security.  After agreeing on
   a channel mechanism, Alice and Bob start the selected Channel
   protocol.  Once the secure channel protocol is successfully running,
   the GRASP/TLS connection can be kept alive or timed out as long as
   the selected channel protocol has a secure association between Alice
   and Bob.  When it terminates, it needs to be re-negotiated via GRASP/


   o  Negotiation of a channel type may require IANA assignments of code

   o  TLS is subject to reset attacks, which IKEv2 is not.  Normally,
      ACP connections (as specified in this document) will be over link-
      local addresses so the attack surface for this one issue in TCP
      should be reduced (note that this may not be true when ACP is
      tunneled as described in Section 8.2.2.

   o  GRASP packets received inside a TLS connection established for
      GRASP/TLS ACP negotiation are assigned to a separate GRASP domain
      unique to that TLS connection.

A.7.  CAs, domains and routing subdomains

   There is a wide range of setting up different ACP solution by
   appropriately using CAs and the domain and rsub elements in the
   domain information field of the domain certificate.  We summarize
   these options here as they have been explained in different parts of
   the document in before and discuss possible and desirable extensions:

   An ACP domain is the set of all ACP nodes using certificates from one
   or more Trust Anchors (TA) (typically one CA) using the same domain
   field.  GRASP inside the ACP is run across all transitively connected
   ACP nodes in a domain.

   The rsub element in the domain information field permits the use of
   addresses from different ULA prefixes.  One use case is to create
   multiple physical networks that initially may be separated with one
   ACP domain but different routing subdomains, so that all nodes can
   mutual trust their ACP domain certificates (not depending on rsub)

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   and so that they could connect later together into a contiguous ACP

   One instance of such a use case is an ACP for regions interconnected
   via a non-ACP enabled core, for example due to the absence of product
   support for ACP on the core nodes.  ACP connect configurations as
   defined in this document can be used to extend and interconnect those
   ACP islands to the NOC and merge them into a single ACP when later
   that product support gap is closed.

   Note that RPL scales very well.  It is not necessary to use multiple
   routing subdomains to scale ACP domains in a way it would be possible
   if other routing protocols where used.  They exist only as options
   for the above mentioned reasons.

   If different ACP domains are to be created that should not allow to
   connect to each other by default, these ACP domains simply need to
   have different domain elements in the domain information field.
   These domain elements can be arbitrary, including subdomains of one
   another: Domains "" and "" are
   separate domains if both are domain elements in the domain
   information element of certificates.

   It is not necessary to have a separate CA for different ACP domains:
   an operator can use a single CA to sign certificates for multiple ACP
   domains that are not allowed to connect to each other because the
   checks for ACP adjacencies includes comparison of the domain part.

   If multiple independent networks choose the same domain name but had
   their own CA, these would not form a single ACP domain because of CA
   mismatch.  Therefore there is no problem in choosing domain names
   that are potentially also used by others.  Nevertheless it is highly
   recommended to use domain names that one can have high probability to
   be unique.  It is recommended to use domain names that start with a
   DNS domain names owned by the assigning organization and unique
   within it.  For example "" if you own "".

A.8.  Intent for the ACP

   Intent is the architecture component of autonomic networks according
   to [I-D.ietf-anima-reference-model] that allows operators to issue
   policies to the network.  Its applicability for use is quite flexible
   and freeform, with potential applications including policies flooded
   across ACP GRASP and interpreted on every ACP node.

   One concern for future definitions of Intent solutions is the problem
   of circular dependencies when expressing Intent policies about the
   ACP itself.

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   For example, Intent could indicate the desire to build an ACP across
   all domains that have a common parent domain (without relying on the
   rsub/routing-subdomain solution defined in this document).  For
   example ACP nodes with domain "", "",
   "" and "" should all establish
   one single ACP.

   If each domain has its own source of Intent, then the Intent would
   simply have to allow adding the peer domains trust anchors (CA) and
   domain names to the ACP domain membership check (Section 6.1.3) so
   that nodes from those other domains are accepted as ACP peers.

   If this Intent was to be originated only from one domain, it could
   likely not be made to work because the other domains will not build
   any ACP connection amongst each other, whether they use the same or
   different CA due to the ACP domain membership check.

   If the domains use the same CA one could change the ACP setup to
   permit for the ACP to be established between two ACP nodes with
   different acp-domain-names, but only for the purpose of disseminating
   limited information, such as Intent, but not to set up full ACP
   connectivity, specifically not RPL routing and passing of arbitrary
   GRASP information.  Unless the Intent policies permit this to happen
   across domain boundaries.

   This type of approach where the ACP first allows Intent to operate
   and only then sets up the rest of ACP connectivity based on Intent
   policy could also be used to enable Intent policies that would limit
   functionality across the ACP inside a domain, as long as no policy
   would disturb the distribution of Intent.  For example to limit
   reachability across the ACP to certain type of nodes or locations of

A.9.  Adopting ACP concepts for other environments

   The ACP as specified in this document is very explicit about the
   choice of options to allow interoperable implementations.  The
   choices made may not be the best for all environments, but the
   concepts used by the ACP can be used to build derived solutions:

   The ACP specifies the use of ULA and deriving its prefix from the
   domain name so that no address allocation is required to deploy the
   ACP.  The ACP will equally work not using ULA but any other /48 IPv6
   prefix.  This prefix could simply be a configuration of the ACP
   registrars (for example when using BRSKI) to enroll the domain
   certificates - instead of the ACP registrar deriving the /48 ULA
   prefix from the AN domain name.

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   Some solutions may already have an auto-addressing scheme, for
   example derived from existing unique device identifiers (e.g., MAC
   addresses).  In those cases it may not be desirable to assign
   addresses to devices via the ACP address information field in the way
   described in this document.  The certificate may simply serve to
   identify the ACP domain, and the address field could be empty/unused.
   The only fix required in the remaining way the ACP operate is to
   define another element in the domain certificate for the two peers to
   decide who is Alice and who is Bob during secure channel building.
   Note though that future work may leverage the acp address to
   authenticate "ownership" of the address by the device.  If the
   address used by a device is derived from some pre-existing permanent
   local ID (such as MAC address), then it would be useful to store that
   address in the certificate using the format of the access address
   information field or in a similar way.

   The ACP is defined as a separate VRF because it intends to support
   well managed networks with a wide variety of configurations.
   Therefore, reliable, configuration-indestructible connectivity cannot
   be achieved from the Data-Plane itself.  In solutions where all
   transit connectivity impacting functions are fully automated
   (including security), indestructible and resilient, it would be
   possible to eliminate the need for the ACP to be a separate VRF.
   Consider the most simple example system in which there is no separate
   Data-Plane, but the ACP is the Data-Plane.  Add BRSKI, and it becomes
   a fully autonomic network - except that it does not support automatic
   addressing for user equipment.  This gap can then be closed for
   example by adding a solution derived from

   TCP/TLS as the protocols to provide reliability and security to GRASP
   in the ACP may not be the preferred choice in constrained networks.
   For example, CoAP/DTLS (Constrained Application Protocol) may be
   preferred where they are already used, allowing to reduce the
   additional code space footprint for the ACP on those devices.  Hop-
   by-hop reliability for ACP GRASP messages could be made to support
   protocols like DTLS by adding the same type of negotiation as defined
   in this document for ACP secure channel protocol negotiation.  End-
   to-end GRASP connections can be made to select their transport
   protocol in future extensions of the ACP meant to better support
   constrained devices by indicating the supported transport protocols
   (e.g.: TLS/DTLS) via GRASP parameters of the GRASP objective through
   which the transport endpoint is discovered.

   The routing protocol chosen by the ACP design (RPL) does explicitly
   not optimize for shortest paths and fastest convergence.  Variations
   of the ACP may want to use a different routing protocol or introduce
   more advanced RPL profiles.

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   Variations such as what routing protocol to use, or whether to
   instantiate an ACP in a VRF or (as suggested above) as the actual
   Data-Plane, can be automatically chosen in implementations built to
   support multiple options by deriving them from future parameters in
   the certificate.  Parameters in certificates should be limited to
   those that would not need to be changed more often than certificates
   would need to be updated anyhow; Or by ensuring that these parameters
   can be provisioned before the variation of an ACP is activated in a
   node.  Using BRSKI, this could be done for example as additional
   follow-up signaling directly after the certificate enrollment, still
   leveraging the BRSKI TLS connection and therefore not introducing any
   additional connectivity requirements.

   Last but not least, secure channel protocols including their
   encapsulations are easily added to ACP solutions.  ACP hop-by-hop
   network layer secure channels could also be replaced by end-to-end
   security plus other means for infrastructure protection.  Any future
   network OAM should always use end-to-end security anyhow and can
   leverage the domain certificates and is therefore not dependent on
   security to be provided for by ACP secure channels.

A.10.  Further (future) options

A.10.1.  Auto-aggregation of routes

   Routing in the ACP according to this specification only leverages the
   standard RPL mechanism of route optimization, e.g. keeping only
   routes that are not towards the RPL root.  This is known to scale to
   networks with 20,000 or more nodes.  There is no auto-aggregation of
   routes for /48 ULA prefixes (when using rsub in the domain
   information field) and/or Zone-ID based prefixes.

   Automatic assignment of Zone-ID and auto-aggregation of routes could
   be achieved for example by configuring zone-boundaries, announcing
   via GRASP into the zones the zone parameters (zone-ID and /48 ULA
   prefix) and auto-aggegating routes on the zone-boundaries.  Nodes
   would assign their Zone-ID and potentially even /48 prefix based on
   the GRASP announcements.

A.10.2.  More options for avoiding IPv6 Data-Plane dependency

   As described in Section 6.12.2, the ACP depends on the Data-Plane to
   establish IPv6 link-local addressing on interfaces.  Using a separate
   MAC address for the ACP allows to fully isolate the ACP from the
   data-plane in a way that is compatible with this specification.  It
   is also an ideal option when using Single-root input/output
   virtualization (SR-IOV - see
   root_input/output_virtualization [2]) in an implementation to isolate

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   the ACP because different SR-IOV interfaces use different MAC

   When additional MAC address(es) are not available, separation of the
   ACP could be done at different demux points.  The same subnet
   interface could have a separate IPv6 interface for the ACP and Data-
   Plane and therefore separate link-local addresses for both, where the
   ACP interface is non-configurable on the Data-Plane.  This too would
   be compatible with this specification and not impact

   An option that would require additional specification is to use a
   different Ethertype from 0x86DD (IPv6) to encapsulate IPv6 packets
   for the ACP.  This would be a similar approach as used for IP
   authentication packets in [IEEE-802.1X] which use the Extensible
   Authentication Protocol over Local Area Network (EAPoL) ethertype

   Note that in the case of ANI nodes, all the above considerations
   equally apply to the encapsulation of BRSKI packets including GRASP
   used for BRSKI.

A.10.3.  ACP APIs and operational models (YANG)

   Future work should define YANG ([RFC7950]) data model and/or node
   internal APIs to monitor and manage the ACP.

   Support for the ACP Adjacency Table (Section 6.2) and ACP GRASP need
   to be included into such model/API.

A.10.4.  RPL enhancements

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      ..... USA ......              ..... Europe ......

           NOC1                           NOC2
            |                              |
            |            metric 100        |
          ACP1 --------------------------- ACP2  .
            |                              |     . WAN
            | metric 10          metric 20 |     . Core
            |                              |     .
          ACP3 --------------------------- ACP4  .
            |            metric 100        |
            |                              |     .
            |                              |     . Sites
          ACP10                           ACP11  .

                            Figure 18: Dual NOC

   The profile for RPL specified in this document builds only one
   spanning-tree path set to a root (NOC).  In the presence of multiple
   NOCs, routing toward the non-root NOCs may be suboptimal.  Figure 18
   shows an extreme example.  Assuming that node ACP1 becomes the RPL
   root, traffic between ACP11 and NOC2 will pass through
   ACP4-ACP3-ACP1-ACP2 instead of ACP4-ACP2 because the RPL calculated
   DODAG/routes are shortest paths towards the RPL root.

   To overcome these limitations, extensions/modifications to the RPL
   profile can provide optimality for multiple NOCs.  This requires
   utilizing Data-Plane artifact including IPinIP encap/decap on ACP
   routers and processing of IPv6 RPI headers.  Alternatively, (Src,Dst)
   routing table entries could be used.

   Flooding of ACP GRASP messages can be further constrained and
   therefore optimized by flooding only via links that are part of the

A.10.5.  Role assignments

   ACP connect is an explicit mechanism to "leak" ACP traffic explicitly
   (for example in a NOC).  It is therefore also a possible security gap
   when it is easy to enable ACP connect on arbitrary compromised ACP

   One simple solution is to define an extension in the ACP certificates
   ACP information field indicating the permission for ACP connect to be
   configured on that ACP node.  This could similarly be done to decide
   whether a node is permitted to be a registrar or not.

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   Tying the permitted "roles" of an ACP node to the ACP domain
   certificate provides fairly strong protection against
   misconfiguration, but is still subject to code modifications.

   Another interesting role to assign to certificates is that of a NOC
   node.  This would allow to limit certain type of connections such as
   OAM TLS connections to only NOC initiator or responders.

A.10.6.  Autonomic L3 transit

   In this specification, the ACP can only establish autonomic
   connectivity across L2 hops and only explicitly configured options to
   tunnel across L3.  Future work should specify mechanisms to
   automatically tunnel ACP across L3 networks.  A hub&spoke option
   would allow to tunnel across the Internet to a cloud or central
   instance of the ACP, a peer-to-peer tunneling mechanism could tunnel
   ACP islands across an L3VPN infrastructure.

A.10.7.  Diagnostics

   Section 10.1 describes diagnostics options that can be done without
   changing the external, interoperability affecting characteristics of
   ACP implementations.

   Even better diagnostics of ACP operations is possible with additional
   signaling extensions, such as:

   1.  Consider if LLDP should be a recommended functionality for ANI
       devices to improve diagnostics, and if so, which information
       elements it should signal (noting that such information is
       conveyed in an insecure manner).  Includes potentially new
       information elements.

   2.  In alternative to LLDP, A DULL GRASP diagnostics objective could
       be defined to carry these information elements.

   3.  The IDevID of BRSKI pledges should be included in the selected
       insecure diagnostics option.  This may be undesirable when
       exposure of device information is seen as too much of a security
       issue (ability to deduce possible attack vectors from device
       model for example).

   4.  A richer set of diagnostics information should be made available
       via the secured ACP channels, using either single-hop GRASP or
       network wide "topology discovery" mechanisms.

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A.10.8.  Avoiding and dealing with compromised ACP nodes

   Compromised ACP nodes pose the biggest risk to the operations of the
   network.  The most common type of compromise is leakage of
   credentials to manage/configure the device and the application of
   malicious configuration including the change of access credentials,
   but not the change of software.  Most of todays networking equipment
   should have secure boot/software infrastructure anyhow, so attacks
   that introduce malicious software should be a lot harder.

   The most important aspect of security design against these type of
   attacks is to eliminate password based configuration access methods
   and instead rely on certificate based credentials handed out only to
   nodes where it is clear that the private keys can not leak.  This
   limits unexpected propagation of credentials.

   If password based credentials to configure devices still need to be
   supported, they must not be locally configurable, but only be
   remotely provisioned or verified (through protocols like Radius or
   Diameter), and there must be no local configuration permitting to
   change these authentication mechanisms, but ideally they should be
   autoconfiguring across the ACP.  See

   Without physical access to the compromised device, attackers with
   access to configuration should not be able to break the ACP
   connectivity, even when they can break or otherwise manipulate
   (spoof) the data-plane connectivity through configuration.  To
   achieve this, it is necessary to avoid providing configuration
   options for the ACP, such as enabling/disabling it on interfaces.
   For example there could be an ACP configuration that locks down the
   current ACP config unless factory reseet is done.

   With such means, the valid administration has the best chances to
   maintain access to ACP nodes, discover malicious configuration though
   ongoing configuration tracking from central locations for example,
   and to react accordingly.

   The primary reaction is withdrawal/change of credentials, terminate
   malicious existing management sessions and fixing the configuration.
   Ensuring that management sessions using invalidated credentials are
   terminated automatically without recourse will likely require new

   Only when these steps are not feasible would it be necessary to
   revoke or expire the ACP domain certificate credentials and consider
   the node kicked off the network - until the situation can be further
   rectified, likely requiring direct physical access to the node.

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   Without extensions, compromised ACP nodes can only be removed from
   the ACP at the speed of CRL/OCSP information refresh or expiry (and
   non-removal) of short lived certificates.  Future extensions to the
   ACP could for example use GRASP flooding distribution of triggered
   updates of CRL/OCSP or explicit removal indication of the compromised
   nodes domain certificate.

Authors' Addresses

   Toerless Eckert (editor)
   Futurewei Technologies Inc. USA
   2330 Central Expy
   Santa Clara  95050


   Michael H. Behringer (editor)


   Steinthor Bjarnason
   Arbor Networks
   2727 South State Street, Suite 200
   Ann Arbor  MI 48104
   United States


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