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An Autonomic Control Plane (ACP)

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 8994.
Authors Michael H. Behringer , Toerless Eckert , Steinthor Bjarnason
Last updated 2017-08-02
Replaces draft-behringer-anima-autonomic-control-plane
RFC stream Internet Engineering Task Force (IETF)
Additional resources Mailing list discussion
Stream WG state WG Document
Document shepherd Sheng Jiang
IESG IESG state Became RFC 8994 (Proposed Standard)
Consensus boilerplate Yes
Telechat date (None)
Responsible AD (None)
Send notices to "Sheng Jiang" <>
ANIMA WG                                               M. Behringer, Ed.
Updates: 4291,4193 (if approved)                          T. Eckert, Ed.
Intended status: Standards Track                                  Huawei
Expires: February 3, 2018                                   S. Bjarnason
                                                          Arbor Networks
                                                          August 2, 2017

                    An Autonomic Control Plane (ACP)


   Autonomic functions need a control plane to communicate, which
   depends on some addressing and routing.  This Autonomic Control Plane
   should ideally be self-managing, and as independent as possible of
   configuration.  This document defines an "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 OAM communications
   over a network that is not configured, or mis-configured.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on February 3, 2018.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents

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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Use Cases for an Autonomic Control Plane  . . . . . . . . . .   8
     3.1.  An Infrastructure for Autonomic Functions . . . . . . . .   8
     3.2.  Secure Bootstrap over an Unconfigured Network . . . . . .   8
     3.3.  Data Plane Independent Permanent Reachability . . . . . .   9
   4.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .  10
   5.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .  10
   6.  Self-Creation of an Autonomic Control Plane (ACP) (Normative)  12
     6.1.  Domain Certificate  . . . . . . . . . . . . . . . . . . .  12
       6.1.1.  ACP information . . . . . . . . . . . . . . . . . . .  12
       6.1.2.  Maintenance . . . . . . . . . . . . . . . . . . . . .  14
     6.2.  AN Adjacency Table  . . . . . . . . . . . . . . . . . . .  16
     6.3.  Neighbor Discovery with DULL GRASP  . . . . . . . . . . .  17
     6.4.  Candidate ACP Neighbor Selection  . . . . . . . . . . . .  19
     6.5.  Channel Selection . . . . . . . . . . . . . . . . . . . .  20
     6.6.  Candidate ACP Neighbor certificate verification . . . . .  21
     6.7.  Security Association protocols  . . . . . . . . . . . . .  22
       6.7.1.  ACP via IKEv2 . . . . . . . . . . . . . . . . . . . .  22
       6.7.2.  ACP via dTLS  . . . . . . . . . . . . . . . . . . . .  23
       6.7.3.  ACP Secure Channel Requirements . . . . . . . . . . .  23
     6.8.  GRASP in the ACP  . . . . . . . . . . . . . . . . . . . .  24
       6.8.1.  GRASP as a core service of the ACP  . . . . . . . . .  24
       6.8.2.  ACP as the Security and Transport substrate for GRASP  24
     6.9.  Context Separation  . . . . . . . . . . . . . . . . . . .  25
     6.10. Addressing inside the ACP . . . . . . . . . . . . . . . .  25
       6.10.1.  Fundamental Concepts of Autonomic Addressing . . . .  26
       6.10.2.  The ACP Addressing Base Scheme . . . . . . . . . . .  27
       6.10.3.  ACP Zone Addressing Sub-Scheme . . . . . . . . . . .  27
       6.10.4.  ACP Manual Addressing Sub-Scheme . . . . . . . . . .  30
       6.10.5.  ACP Vlong Addressing Sub-Scheme  . . . . . . . . . .  31
       6.10.6.  Other ACP Addressing Sub-Schemes . . . . . . . . . .  32
     6.11. Routing in the ACP  . . . . . . . . . . . . . . . . . . .  32
       6.11.1.  RPL Profile  . . . . . . . . . . . . . . . . . . . .  32
     6.12. General ACP Considerations  . . . . . . . . . . . . . . .  36
       6.12.1.  Addressing of Secure Channels in the data plane  . .  36
       6.12.2.  MTU  . . . . . . . . . . . . . . . . . . . . . . . .  36
       6.12.3.  Multiple links between nodes . . . . . . . . . . . .  37
       6.12.4.  ACP interfaces . . . . . . . . . . . . . . . . . . .  37
   7.  ACP support on L2 switches/ports (Normative)  . . . . . . . .  38

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     7.1.  Why . . . . . . . . . . . . . . . . . . . . . . . . . . .  39
     7.2.  How (per L2 port DULL GRASP)  . . . . . . . . . . . . . .  40
   8.  Support for Non-Autonomic Components (Normative)  . . . . . .  41
     8.1.  ACP Connect . . . . . . . . . . . . . . . . . . . . . . .  41
       8.1.1.  Non-Autonomic Controller / NMS system . . . . . . . .  41
       8.1.2.  Software Components . . . . . . . . . . . . . . . . .  44
       8.1.3.  Auto Configuration  . . . . . . . . . . . . . . . . .  45
       8.1.4.  Combined ACP and Data Data Plane Interface (VRF
               Select) . . . . . . . . . . . . . . . . . . . . . . .  45
       8.1.5.  Use of GRASP  . . . . . . . . . . . . . . . . . . . .  47
     8.2.  ACP through Non-Autonomic L3 Clouds (Remote ACP
           neighbors)  . . . . . . . . . . . . . . . . . . . . . . .  48
       8.2.1.  Configured Remote ACP neighbor  . . . . . . . . . . .  48
       8.2.2.  Tunneled Remote ACP Neighbor  . . . . . . . . . . . .  49
       8.2.3.  Summary . . . . . . . . . . . . . . . . . . . . . . .  50
   9.  Benefits (Informative)  . . . . . . . . . . . . . . . . . . .  50
     9.1.  Self-Healing Properties . . . . . . . . . . . . . . . . .  50
     9.2.  Self-Protection Properties  . . . . . . . . . . . . . . .  51
       9.2.1.  From the outside  . . . . . . . . . . . . . . . . . .  51
       9.2.2.  From the inside . . . . . . . . . . . . . . . . . . .  52
     9.3.  The Administrator View  . . . . . . . . . . . . . . . . .  53
   10. Further Considerations (Informative)  . . . . . . . . . . . .  53
     10.1.  Domain Certificate provisioning / enrollment . . . . . .  53
     10.2.  ACP Neighbor discovery protocol selection  . . . . . . .  55
       10.2.1.  LLDP . . . . . . . . . . . . . . . . . . . . . . . .  55
       10.2.2.  mDNS and L2 support  . . . . . . . . . . . . . . . .  55
       10.2.3.  Why DULL GRASP . . . . . . . . . . . . . . . . . . .  55
     10.3.  Choice of routing protocol (RPL) . . . . . . . . . . . .  56
     10.4.  Extending ACP channel negotiation (via GRASP)  . . . . .  57
     10.5.  CAs, domains and routing subdomains  . . . . . . . . . .  59
   11. RFC4291/RFC4193 Updates Considerations  . . . . . . . . . . .  61
   12. Security Considerations . . . . . . . . . . . . . . . . . . .  63
   13. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  63
   14. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  63
   15. Change log [RFC Editor: Please remove]  . . . . . . . . . . .  64
     15.1.  Initial version  . . . . . . . . . . . . . . . . . . . .  64
     15.2.  draft-behringer-anima-autonomic-control-plane-00 . . . .  64
     15.3.  draft-behringer-anima-autonomic-control-plane-01 . . . .  64
     15.4.  draft-behringer-anima-autonomic-control-plane-02 . . . .  64
     15.5.  draft-behringer-anima-autonomic-control-plane-03 . . . .  65
     15.6.  draft-ietf-anima-autonomic-control-plane-00  . . . . . .  65
     15.7.  draft-ietf-anima-autonomic-control-plane-01  . . . . . .  65
     15.8.  draft-ietf-anima-autonomic-control-plane-02  . . . . . .  66
     15.9.  draft-ietf-anima-autonomic-control-plane-03  . . . . . .  66
     15.10. draft-ietf-anima-autonomic-control-plane-04  . . . . . .  66
     15.11. draft-ietf-anima-autonomic-control-plane-05  . . . . . .  67
     15.12. draft-ietf-anima-autonomic-control-plane-06  . . . . . .  67
     15.13. draft-ietf-anima-autonomic-control-plane-07  . . . . . .  68

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     15.14. draft-ietf-anima-autonomic-control-plane-08  . . . . . .  69
     15.15. draft-ietf-anima-autonomic-control-plane-09  . . . . . .  71
   16. References  . . . . . . . . . . . . . . . . . . . . . . . . .  73
     16.1.  Normative References . . . . . . . . . . . . . . . . . .  73
     16.2.  Informative References . . . . . . . . . . . . . . . . .  74
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  76

1.  Introduction

   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 currently being defined in the
   document [I-D.ietf-anima-reference-model]

   Autonomic functions need a stable and robust infrastructure to
   communicate on.  This infrastructure should be as robust as possible,
   and it should be re-usable by all autonomic functions.[RFC7575] calls
   it the "Autonomic Control Plane".  This document defines the
   Autonomic Control Plane.

   Today, the management and control plane of networks typically runs in
   the global routing table, which is dependent on correct configuration
   and routing.  Misconfigurations or routing problems can therefore
   disrupt management and control channels.  Traditionally, an out of
   band network has been used to recover from such problems, or
   personnel is sent on site to access devices through console ports
   (craft ports).  However, both options are operationally expensive.

   In increasingly automated networks either controllers or distributed
   autonomic service agents in the network require a control plane which
   is independent of the network they manage, to avoid impacting their
   own operations.

   This document describes options for a self-forming, self-managing and
   self-protecting "Autonomic Control Plane" (ACP) which is inband on
   the network, yet as independent as possible of configuration,
   addressing and routing problems (for details how this achieved, see
   Section 6).  It therefore remains operational even in the presence of
   configuration errors, addressing or routing issues, or where policy
   could inadvertently affect control plane connectivity.  The Autonomic
   Control Plane serves several purposes at the same time:

   o  Autonomic functions communicate over the ACP.  The ACP therefore
      supports directly Autonomic Networking functions, as described in
      [I-D.ietf-anima-reference-model].  For example, GRASP

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      [I-D.ietf-anima-grasp] runs securely inside the ACP and depends on
      the ACP as its "security substrate".

   o  An operator can use it to log into remote devices, even if the
      data plane is misconfigured or unconfigured.

   o  A controller or network management system can use it to securely
      bootstrap network devices in remote locations, even if the 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

   This document describes some use cases for the ACP in Section 3, it
   defines the requirements in Section 4, Section 5 gives an overview
   how an Autonomic Control Plane is constructed, and in Section 6 the
   detailed process is explained.Section 8 explains how non-autonomic
   nodes and networks can be integrated, and Section 6.7 the first
   channel types for the ACP.

   The document "Autonomic Network Stable Connectivity"
   [I-D.ietf-anima-stable-connectivity] describes how the ACP can be
   used to provide stable connectivity for OAM applications.  It also
   explains on how existing management solutions can leverage the ACP in
   parallel with traditional management models, when to use the ACP
   versus the data plane, how to integrate IPv4 based management, etc.

2.  Terminology

   This document uses the following terms (sorted alphabetically):

   ACP  "Autonomic Control Plane".  The Autonomic Function defined in
      this document.  It provides secure zero-touch network wide IPv6
      connectivity between devices supporting it.  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 ULA address assigned to the ACP device.  It is
      stored in the ACP information field of an ACP devices LDevID.

   ACP connect  A physical interface on an ACP device providing access
      to the ACP for non ACP capable devices.  See Section 8.1.1.

   ACP device  A device supporting the ACP according to this document.

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   ACP information (field)  An rfc822Name information element (eg:
      field) in the Domain Certificate in which the ACP relevant
      information is encoded: the AN Domain Name and the ACP address.

   ACP (loopback) interface  The loopback interface in the ACP VRF that
      hosts the ACP address.

   ACP (ULA) prefix(es)  The prefixes routed 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 6.1.1.  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 virtual subinterface/tunnel established hop-by-
      hop between adjacent ACP devices to carry traffic of the ACP VRF
      separated from Data Plane traffic inband over the same links as
      the Data Plane.

   ACP secure channel protocol  The protocol used to build an ACP secure
      channel, eg: IKEv2/IPsec or dTLS.

   ACP virtual interface  An interface in the ACP VRF mapped to one or
      more ACP secure channels.  See Section 6.12.4.

   ACP VRF  The ACP is modelled in this document as a "Virtual Routing
      and Forwarding" (VRF) component in a network device.

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

   AN Domain Name  An FQDN (Fully Qualified Domain Name) identifying an
      Autonomic Network.  It is stored in the ACP information field of
      an ANI devices LDevID.  See Section 6.1.1.

   ANI (device/network)  "Autonomic Network Infrastructure".  A device
      with ANI supports ACP, BRSKI and GRASP.  The ANI is the
      infrastructure to enable autonomic functions.  An ANI network or
      device is a most basic Autonomic Network or device: it does not
      need to have ASAs other than the ones implementing ACP, BRSKI and
      GRASP nor Intent support.  A simple ANI network (without further
      autonomic functions) can for example support secure zero touch
      bootstrap and stble connectivity for SDN networks - see

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   ANIMA  "Autonomic Networking Integrated Model and Approach".  ACP,
      BRSKI and GRASP are work products of ANIMA.

   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 Devices.

   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 devices use ACP and BRSKI.

   Data Plane  The counterpoint to the ACP in an ACP device: all VRFs
      other than the ACP.  In a simple ACP or ANI device, the Data Plane
      is typically provisioned non-autonomic, for example manually
      (including across the ACP) or via SDN controllers.  In a full
      Autonomic Network Device, the Data Plane is managed autonomically
      via Autonomic Functions and Intent.

   Domain Certificate  An LDevID with an information element defined in
      this document used by the ACP to derive and cryptographically
      assert its membership in an autonomic domain.

   enrollment  The process where a device presents identification (for
      example through keying material such as the private key of an
      IDevID) to a network and acquires a network specific identity and
      trust anchor such as an LDevID.

   EST  "Enrollment over Secure Transport" ([RFC7030]).  IETF standard
      protocol for enrollment of a device 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" which is run inside the ACP to support
      BRSKI and other future Autonomic Functions.  See

   IDevID  An "Initial Device IDentity" X.509 certificate installed by
      the vendor on new equipment.  Contains information that
      establishes the identity of the device in the context of its
      vendor/manufacturer such as device model/type and serial number.

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   LDevID  A "Local Device IDentity" X.509 certificate installed during
      an "enrollment".  The ACP depends on a Domain Certificate which is
      an LDevID.

   MIC  "Manufacturer Installed Certificate".  Another word not used in
      this document to describe an IDevID.

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

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

   sUDI  "secured Unique Device Identifier".  Another term not used in
      this document to refer to an IDevID.

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

   ULA  "Unique Local Address".  The IPv6 equivalent to RFC1918 IPv4
      addresses.  ACP addresses are ULA.

3.  Use Cases for an Autonomic Control Plane

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 minimise
   the complexity of the network.  This way, there is only need for a
   single discovery mechanism, a single security mechanism, and other
   processes that distributed functions require.

3.2.  Secure Bootstrap over an Unconfigured Network

   Today, bootstrapping a new device typically requires all devices
   between a controlling node (such as an SDN controller) and the new
   device to be completely and correctly addressed, configured and
   secured.  Therefore, bootstrapping a network happens in layers around
   the controller.  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 between.

   With the ACP, secure bootstrap of new devices can happen without
   requiring any configuration on the network.  A new device can
   automatically be bootstrapped in a secure fashion and be deployed

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   with a domain certificate.  This does not require any configuration
   on intermediate nodes, because they can communicate through the ACP.

3.3.  Data Plane Independent Permanent Reachability

   Today, most critical control plane protocols and network management
   protocols are running in the data plane (global routing table) of the
   network.  This leads to undesirable dependencies between control and
   management plane on one side and the data plane on the other: Only if
   the data plane is operational, will the other planes work as

   Data plane connectivity can be affected by errors and faults, for
   example certain AAA misconfigurations 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 console access can help recover from such issues.

   Data plane dependencies also affect NOC/SDN controller applications:
   Certain network changes are today hard to operate, 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.

   The ACP provides reachability that is largely independent of the data
   plane, which allows 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 devices regardless of their configuration or
      global routing table.

   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 "Autonomic Network Stable Connectivity"
   [I-D.ietf-anima-stable-connectivity] explains the use cases for the
   ACP in significantly more detail and explains how the ACP can be used
   in practical network operations.

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4.  Requirements

   The Autonomic Control Plane has the following 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, security (can block easily at edge).

   ACP3:  The ACP MUST use autonomically managed address space.  Reason:
          easy bootstrap and setup ("autonomic"); robustness (admin
          can't mess things up so easily).  This document suggests to
          use ULA addressing for this purpose.

   ACP4:  The ACP MUST be generic.  Usable by all the functions and
          protocols of the AN infrastructure.  It MUST NOT be tied to a
          particular 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.

   The default mode of operation of the ACP is 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 over non-autonomic
   nodes, for example to link autonomic nodes over the general Internet.
   This is possible, but then has a dependency on routing over the non-
   autonomic hops (see Section 8.2).

5.  Overview

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

   1.  An autonomic 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 adjacent nodes in the
       same domain.

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   3.  For each node in the candidate peer list, it authenticates that
       node and negotiates a mutually acceptable channel type.

   4.  It then establishes a secure tunnel of the negotiated channel
       type.  These tunnels are placed into the previously set up VRF.
       This creates an overlay network with hop-by-hop tunnels.

   5.  Inside the ACP VRF, each node sets up a virtual (loopback)
       interface with its ULA IPv6 address.

   6.  Each node runs a lightweight routing protocol, to announce
       reachability of the virtual addresses inside the ACP.


   o  Non-autonomic NMS systems or controllers have to be manually
      connected into the ACP.

   o  Connecting over non-autonomic Layer-3 clouds initially requires a
      tunnel between autonomic nodes.

   o  None of the above operations (except manual ones) is reflected in
      the configuration of the device.

   The following figure illustrates the ACP.

           autonomic node 1                  autonomic node 2
          ...................               ...................
   secure .                 .   secure      .                 .  secure
   tunnel :  +-----------+  :   tunnel      :  +-----------+  :  tunnel
   ..--------| ACP VRF   |---------------------| ACP VRF   |---------..
          : / \         / \   <--routing-->   / \         / \ :
          : \ /         \ /                   \ /         \ / :
   ..--------|  virtual  |---------------------|  virtual  |---------..
          :  | interface |  :               :  | interface |  :
          :  +-----------+  :               :  +-----------+  :
          :                 :               :                 :
          :   data plane    :...............:   data plane    :
          :                 :    link       :                 :
          :.................:               :.................:

                                 Figure 1

   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.  This
   way the ACP can be built even if there is no configuration on the

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   devices, or if the data plane has issues such as addressing or
   routing problems.

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

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

   An ACP device can be a router, switch, controller, NMS host, or any
   other IP device.  Initially, it must have a globally unique domain
   certificate (LDevID), as well as an adjacency table.  It then can
   start to discover ACP neighbors and build the ACP.  This is described
   step by step in the following sections:

6.1.  Domain Certificate

   To establish an ACP securely, an ACP device MUST have a globally
   unique domain certificate (LDevID), with which it can
   cryptographically assert its membership in the domain as well as the
   CA certificate chain used to sign the LDevID.  This CA certificate
   chain is used to verify the LDevID of candidate ACP peers (see
   Section 6.6).  The ACP does not mandate specific mechanism by which
   this certificate information is provisioned onto the ACP device, it
   only requires the following ACP specific information field in its
   LDevID as well as the LDevIDs of candidate ACP peers.  See
   Section 10.1 for more information about enrollment or provisioning

6.1.1.  ACP information

   The domain certificate (LDevID) of an autonomic node MUST contain ACP
   specific information, specifically the domain name, the address of
   the device in the ACP with the Zone-ID set to zero ("ACP address").
   This information MUST be encoded in the LDevID in the subjectAltName
   / rfc822Name field in the following way:




   The acp-address MUST be specified as a string of 32 hex characters
   with only lower letters a-f and numbers 0-9 so that the local part of

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   the address can matches the simple dot-atom format of [RFC5322] (":"
   are not allowed in that format).

   <domain> is used to indicate the Autonomic Domain across which all
   ACP nodes trust each other and are willing to build ACP channel with
   each other.  See Section 6.6.  It SHOULD be the FQDN of a domain
   owned by the operator assigning the certificate.  This is a simple
   method to ensure that the domain name is globally unique and
   collision of ACP addresses would therefore only happen due to ULA
   hash collisions.  If the operator does not own any FQDN, it should
   choose am FQDN format string that intends to be equally unique.

   {<rsub>.}<domain> is the autonomic "routing subdomain" that is used
   used in addressing to calculate the hash used in the creation of the
   ACP address of the device.  As the name implies, every routing
   subdomain is also a separate routing subdomain. <rsub> is optional
   and should only used when its impacts are understood.  The domain
   without any leading rsub field is also just another routing

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

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

   o  There are a wide range of pre-existing protocols/services where
      authentication with LDevID is desirable.  Enrolling and
      maintaining separate LDevIDs for each of these protocols/services
      is often undesirable overhead.  Therefore, the information element
      required for the ACP in the domain certificate should be encoded
      in a way that minimizes the possibility of creating
      incompatibilites with such other uses beside the authentication
      for the ACP.

   o  The elements in the LDevID required for the ACP should not cause
      incompatibilities with any pre-existing ASN.1 software potentially
      in use in those other pre-existing SW systems.  This eliminates
      the use of novel information elements because those require
      extensions to those pre-existing ASN.1 parsers.

   o  subjectAltname / rfc822Name is a pre-existing element that must be
      supported by all existing ASN.1 parsers for LDevID.

   o  The elements in the LDevID required for the ACP should also not be
      misinterpreted by any pre-existing protocol/service that might use
      the LDevID.  If the elements used for the ACP are interpreted by
      other protocols/services, then the impact should be benign.

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   o  Using an IP address format encoding could result in non-benign
      misinterpretation of the ACP information, for example other
      protocol/services unaware of the ACP could try to do something
      with the ACP address that would fail to work correctly.  For
      example, the address could be interpreted to be an address of the
      device in a VRF other than the ACP VRF.

   o  At minimum, both the AN domain name and the non-domain name
      derived part of the ACP address need to be encoded in one or more
      appropriate fields of the certificate, so there are not many
      alternatives with pre-existing fields where the only possible
      conflicts would likely be beneficial.

   o  rfc822Name encoding is quite flexible.  We choose to encode the
      full ACP address AND the domain name with sub part into a single
      rfc822Name information element it, so that it is easier to
      examine/use the encoded "ACP information (field)".

   o  The format of the rfc822Name is choosen so that an operator can
      set up a mailbox called   anima.acp@<domain> that would receive
      emails sent towards the rfc822Name of any AN device inside a
      domain.  This is possible because components behind a plus symbol
      are considered part of a single mailbox.  In other words, it is
      not necessary to set up a separate mailbox for every autonomic
      devices ACP information field, but only one for the whole domain.

   o  In result, if any unexpected use of the ACP addressing information
      in a certificate happens, it is benign and detectable: it would be
      mail to that mailbox.

   See section of [RFC5280] for details on the subjectAltName

6.1.2.  Maintenance

   The ACP network MUST have one or more nodes that support EST server
   ([RFC7030] functionality (eg: as an ASA) through which ACP nodes can
   renew their domain certificate.  The ACP address of at least one such
   EST server SHOULD have been enrolled/provisioned into the ACP device
   during initial installation of the domain certificate.

   EST servers MUST announce their service via GRASP in the ACP through
   M_FLOOD messages:

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        [M_FLOOD, 12340815, h'fda379a6f6ee0000200000064000001', 180000,
            ["AN_join_registrar", SYNCH-FLAG, 255, "EST-TLS"],
                 h'fda379a6f6ee0000200000064000001', TCP, 80]

   The formal CDDL definition is:

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

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

       objective-flags = SYNCH-FLAG ; as in GRASP spec
       loop-count      = 255        ; mandatory maximum
       objective-value = text       ; name of the (list of) of supported
                                    ; protocols: "EST-TLS" for RFC7030.

   The M_FLOOD message MUST be sent periodically.  The period is subject
   to network administrator policy (EST server configuration).  It must
   be so low that the aggregate amount of periodic M_FLOODs from all EST
   servers causes negligible traffic across the ACP.

   In the above (recommended) example the period could be 60 seconds and
   the indicated ttl of 180000 msec means that the objective would
   continuously be cached by ACP devices even when two out of three
   messages are dropped in transit (which is unlikely because GRASP hop-
   by-hop forwarding is realiable).

   The locator-option indicates the ACP transport address for the EST
   server.  The loop-count MUST be sete to 255.  When an ACP node
   receives the M_FLOOD, it will have been reduced by the number of hops
   from the EST server.

   When it is time for domain certificate reneal, the ACP device MUST
   attempt to connect to the EST server(s) learned via GRASP starting
   with the one that has the highest remaining loop-count (closest one).
   If certificate renewal does not succeed, the device MUST attempt to
   use the EST server(s) learned during initial provisioning/enrollment
   of the certificate.  After successful renewal of the domain
   certificate, the ACP address from the certificate of the EST server
   (as learned during the TLS handshake) is added to the top of the list
   or provisioned/configured EST-server(s).

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   This logic of selecting an EST server for renewal is choosen to allow
   for distributed EST servers to be used effectively but to also allow
   fallback to the most reliably learned EST server - those that
   performed already successful enrollment in before.  A compromised
   (non EST-server) ACP device for example can filter or fake GRASP
   announcements, but it can not successfully renew a certificate and
   can only prohibit traffic to a valid EST server when it is on the
   path between the ACP device and the EST server.

   The ACP device MUST support Certificate Revocation Lists via HTTPs
   from one or more Certificate Distribution Points.  These CDPs MUST be
   indicated in the Domain Certificate when used.  If the CDP URL uses
   an IPv6 ULA, the ACP device will try to reach it via the ACP.  In
   that case the ACP address in the domain certificate of the CDP as
   learned by the ACP device during the HTTPs TLS handshake MUST match
   that ULA address in the HTTPs URL.

   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 cause a device to not
   renew its domain certificate in time - and to allow prolonged periods
   of running parts of a network disconnected from any CA.

   Certificate lifetime should be set to be as short as feasible.  Given
   how certificate renewal is fully automated via ACP and EST, the
   primarily imiting factor for shorter certificate lifetimes (than the
   typical one year) 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 peformance to manage short
   lived certificates.

   See Section 10.1 for further optimizationss of certificate
   optimizations when BRSKI can be used.

6.2.  AN Adjacency Table

   To know to which nodes to establish an ACP channel, every autonomic
   node maintains an adjacency table.  The adjacency table contains
   information about adjacent autonomic nodes, at a minimum: node-ID, IP
   address, domain, certificate.  An autonomic device MUST maintain this
   adjacency table up to date.  This table is used to determine to which
   neighbor an ACP connection is established.

   Where the next autonomic device is not directly adjacent, the
   information in the adjacency table can be supplemented by
   configuration.  For example, the node-ID and IP address could be

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   The adjacency table MAY contain information about the validity and
   trust of the adjacent autonomic node's certificate.  However,
   subsequent steps MUST always start with authenticating the peer.

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

6.3.  Neighbor Discovery with DULL GRASP

   Because of the the considerations in Section 10.2, the ACP uses DULL
   (Discovery Unsolicited Link-Local) insecure instances of GRASP for
   discovery of ACP neighbors.  See section of
   [I-D.ietf-anima-grasp]  for its formal definition.

   The ACP uses one instance of DULL GRASP for every physical L2 subnet
   of the ACP device to discovery physically adjacent candidate ACP
   neighbors.  Ideally, all physical interfaces SHOULD be brought up
   enough so that ACP discovery can be performed and any physically
   connected 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 unconfigure interfaces MUST be limited so
   that at first only IPv6 link-local address assignment (SLAAC) and
   DULL GRASP works and then only the following ACP secure channel setup
   packets - but not any other unnecessary traffic (eg: no other link-
   local IPv6 transport stack responders for example).

   ACP discovery MUST NOT be enabled by default on any non-physical
   interfaces.  In particular, ACP discovery MUST NOT run inside the
   ACP.  See Section 8.2.2 how to enable and use ACP with auto-discovery
   across configured tunnels.

   See Section 7 for how ACP should be extended on L3/L2 devices.

   Note: If an ACP device also implements BRSKI (see Section 10.1) then
   the above considerations also apply to 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 device does not
   have a domain certificate.  Discovery of ACP neighbors happens only
   when the device does have the certificate.  The device therefore
   never needs to discover both a bootstrap proxy and ACP neighbor at
   the same time.

   An autonomic 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

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   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, 1,
              ["AN_ACP", SYNCH-FLAG, 1, "IKEv2"],
                   h'fe80000000000000c0011001FEEF0000, UDP, 15000]

   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 = ; as in the GRASP specification
           loop-count = 1    ; limit to link-local operation
           objective-value = text ; name of the (list of) secure
                                  ; channel negotiation protocol(s)

   The objective-flags field is set to indicate synchronization.

   The ttl and loop-count are fixed at 1 since this is a link-local

   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
   autonomic node on the sending interface.

   The 'objective-value' parameter is (normally) a string indicating the
   secure channel protocol available at the specified or implied

   The locator 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.  For example, "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).

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   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.

   A node that supports more than one secure channel protocol needs to
   flood multiple versions of the "AN_ACP" objective, each accompanied
   by its own locator.  This can be in a single GRASP M_FLOOD message.

   If multiple secure channel protocols are supported that all are run
   on well-defined ports, then they can be announced via a single AN_ACP
   objective using a list of string names as the objective value without
   a following locator-option.

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

   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 AN Adjacency
   Table, see Section 6.2 which then drives the further building of the
   ACP to that neighbor.

6.4.  Candidate ACP Neighbor Selection

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

   The ACP is by default established exclusively between nodes in the
   same domain.  This includes all routing subdomains.Section 10.5
   explains how ACP connections across routing subdomains are special.

   Future extensions to this document including Intent can change this
   default behaviour.  Examples include:

   o  Build the ACP across all domains that have a common parent domain.
      For example ACP nodes with domain "", nodes of
      "", "", "" and
      "" could all establish one single ACP.

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   o  ACP connections across domains with different CA (certificate
      authorities) could establish a common ACP by installing the
      alternate domains' CA into the trusted anchor store.  This is an
      executive management action that could easily be accomplished
      through the control channel created by the ACP.

   Since Intent is transported over the ACP, the first ACP connection a
   node establishes is always following the default behaviour.  See
   Section 10.5 for more details.

   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 can not
   include any non-protected negotiation.  To avoid re-inventing and
   validating security association mechanisms, the next step after
   discoving the address of a candidate neighbor can only be to try
   first to establish a security association with that neighbor using a
   well-known security association method.

   At this time in the lifecycle of autonomic devices, it is unclear
   whether it is feasible to even decide on a single MTI (mandatory to
   implement) security association protocol across all autonomic

   From the use-cases it seems clear that not all type of autonomic
   devices 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 use-cases), but low-end in-
   ceiling L2 switches may only want to support MacSec because that is
   also supported in HW, and only a more flexible gateway device may
   need to support both of these mechanisms and potentially more.

   To support extensible secure channel protocol selection without a
   single common MTI protocol, autonomic devices 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:

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   An autonomic device may choose to attempt initiate the different
   feasible ACP secure channel protocol 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.

   Once the first secure channel protocol succeeds, the two peers know
   each others certificates (because that must be used by all secure
   channel protocols for mutual authentication.  The device with the
   lower Device-ID in the ACP address becomes Bob, the one with the
   higher Device-ID in the certificate Alice.

   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.

   For example, originally Bob could have been the initiator of one ACP
   secure channel protocol that Bob preferred and the security
   association succeeded.  The roles of Bob abd Alice are then assigned.
   At this stage, the protocol may not even have completed negotiating a
   common security profile.  The protocol could for example have been
   IPsec.  It is not up to Alice to devide how to proceed.  Even if the
   IPsec connecting determined a working profile with Bob, Alice might
   prefer some other secure protocol (eg: dTLS) and try to set that up
   with Bob. If that succeeds, she would close the IPsec connection.  If
   no better protocol attempt succeeds, she would keep the IPsec

   All this negotiation is in the context of an "L2 interface".  Alice
   and Bob will build ACP connections to each other on every "L2
   interface" that they both connect to.  An autonomic device must not
   assume that neighbors with the same L2 or link-local IPv6 addresses
   on different L2 interfaces are the ame devices.  This can only be
   determined after examining the certificate after a successful
   security association attempt.

6.6.  Candidate ACP Neighbor certificate verification

   Independent of the security association protocol choosen, candidate
   ACP neighbors need to be authenticated based on their autonomic
   domain certificate.  This implies that any security association
   protocol MUST support certificate based authentication that can
   support the following verification steps:

   o  The certificate is valid as proven by the security associations
      protocol exchanges.

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   o  The peers certificate is signed by the same CA as the devices
      domain certificate.

   o  If the device certificates indicate a CDP or OCSP then the peer's
      certificate must be valid occording to those criteria. eg: OCSP
      check across the ACP or not listed in the CRL.

   o  The peers certificate has a valid ACP information field
      (subjectAltName / rfc822Name) and the domain name in that peers
      ACP information field is the same as in the devices certificate.
      Note that future Intent rules may modify this for example in
      support of subdomains.  See Section 10.5.

   If the peers certificate fails any of these checks, the connection
   attempt is aborted and an error logged (with throttling).

6.7.  Security Association protocols

   The following sections define the security association protocols that
   we consider to be important and feasible to specify in this document:

6.7.1.  ACP via IKEv2

   An autonomic device announces its ability to support IKEv2 as the ACP
   secure channel protcol in GRASP as "IKEv2".  Native IPsec

   To run ACP via IPsec transport mode, no further IANA assignments/
   definitions are required.  All autonomic devices supporting IPsec
   MUST support IPsec security setup via IKEv2, transport mode
   encapsulation via the device and peer link-local IPv6 addresses,
   AES256 encryption and SHA256 hash.

   In terms of IKEv2, this means the initiator will offer to support
   IPsec transport mode with next protocol equal 41 (IPv6).  IPsec with GRE encapsulation

   In network devices it is often easier to provide virtual interfaces
   on top of GRE encapsulation than natively on top of a simple IPsec
   association.  On those devices it may be necessary to run the ACP
   secure channel on top of a GRE connection protected by the IPsec
   association.  The requirements for the IPsec association are the same
   as in the native IPsec case, but instead of directly carrying the ACP
   IPv6 packets, the payload is an ACP IPv6 packet inside GRE/IPv6.  The
   mandatory security profile is the same as for native IPsec: peer
   link-local IPv6 addresses, AES256 encryption, SHA256 hash.

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   In terms of IKEv2 negotiation, this means the initiator must offer to
   support IPsec transport mode with next protocol equal to GRE (47),
   followed by 41 (IPv6) (because native IPsec is required to be
   supported, see below).

   If IKEv2 initiator and responder support GRE, it will be selected.
   The version of GRE to be used must the 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 code basis supported in some classes
   of constrained devices.

   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 autonomic devices supporting
   ACP via dTLS MUST support AES256 encryption and not permit weaker
   crypto options.

   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

   A baseline autonomic device MUST support IPsec natively and MAY
   support IPsec via GRE.  A constrained autonomic device MUST support
   dTLS.  Autonomic edge device connecting constrained areas with
   baseline areas MUST therefore support IPsec and dTLS.

   Autonomic devices need to specify in documentation the set of secure
   ACP mechanisms they suppport.

   ACP secure channel MUST imediately be terminated when the lifetime of
   any certificate in the chain used to authenticate the neighbor
   expires or becomes revoked.  Note that is 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.

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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.  They function in GRASP that makes it
   fundamental as a service is the ability for ACP wide service
   discovery (called objectives in GRASP).  In most other solution
   designs such distributed discovery does not exist at all or it was
   added as an afterthought and relied upon inconsistently resulting in
   diminished self configuration capabilities.  of prior solutions.

   The ACP does not provide generic IP multicast services, but only IP
   unicast which is realized via the RPL routing protocol (described
   below) and objective discovery and negotiation realized via the ACP
   instance of GRASP.  We consider this to be a more lightweight,
   modular and easier to extend approach than trying to put service
   announcement and discovery onto some autoconfigured network wide IP
   multicast layer (for which so far there is no good definition) or
   embed it into some IGP flooding mechanism (which makes it less
   modular and agile to improve upon).

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.

   This means that the ACP is responsible to ensure that this instance
   of GRASP is only using the ACP 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 device has a domain certificate.
   In this case ASAs using GRASP running on the same device would still
   need to be able to discover each others 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 can not
   provide services.

   GRASP inside the ACP uses link-local UDP IPv6 multicast across the
   ACP virtual interfaces for GRASP neighbor discovery and IPv6 over TLS
   across the ACP virtual interfaces for any of its unicast messages.
   TLS is TLS 1.2 ([RFC5246]) with AES256 encryption and SHA256.
   Authentication is via the the domain certificates on both sides.

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   TLS is mandated for GRASP 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 (eg: via domain
   certificate revocation / expiry).

   Eavesdropping/spoofing by a compromised ACP device is possible
   because the provider and consumer of an objective have no unique
   information about the other side that would allow them to distinguish
   a benevolent from a compromised peer.  The compromised ACP device
   would simply announce the objective as well, potentially filter the
   original objective in GRASP when it is a Man In The Middle (MITM) and
   act as an application level proxy.  This of course requires that the
   compromised ACP node understand the semantic of the GRASP negotiation
   to an extend that allows it to proxy it without being detected.

6.9.  Context Separation

   The ACP is in a separate context from the normal data plane of the
   device.  This context includes the ACP channels IPv6 forwarding and
   routing as well as any required higher layer ACP functions.

   In classical network device platforms, a dedicated so called "Virtual
   routing and forwarding instance" (VRF) is one logical implementation
   option for the ACP.  If possible by the platform SW 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 device.  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 global routing table.  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 internal
   network wide valid addresses and routing.  Each autonomic node must
   create a virtual interface with a network wide unique address inside
   the ACP context mentioned in Section 6.9.  This address may be used
   also in other virtual contexts.

   With the algorithm introduced here, all ACP devices in the same
   subdomain have the same /48 prefix.  Conversely, global IDs from
   different domains are unlikely to clash, such that two networks can

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   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 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 loopback interfaces of autonomic nodes carry
      routable address(es); all other interfaces exclusively use IPv6
      link local for autonomic functions.  The usage of IPv6 link local
      addressing is discussed in [RFC7404].

   o  Use-ULA: For loopback interfaces of autonomic nodes, we use Unique
      Local Addresses (ULA), as specified in [RFC4193].  An alternative
      scheme was discussed, using assigned ULA addressing.  The
      consensus was to use ULA-random [[RFC4193] with L=1], because it
      was deemed to be sufficient.

   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].

   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

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      exclusively built on IPv6 from day one.  There is no need for
      backward compatibility.

   o  OAM protocols no not require IPv4: The ACP may carry OAM
      protocols.  All relevant protocols (SNMP, TFTP, SSH, SCP, Radius,
      Diameter, ...) are available in IPv6.

6.10.2.  The ACP Addressing Base Scheme

   The Base ULA addressing scheme for autonomic nodes has the following

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

                   Figure 2: 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 ULA "global ID" is set here to be a hash of the subdomain
      name, which results in a pseudo-random 40 bit value.  It is
      calculated as the first 40 bits of the SHA256 hash of the
      subdomain name, in the example of Section 6.1.1

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

   o  Type: This field allows different address sub-schemes in the
      future.  The goal is to start with a single sub-schemes, but to
      allow for extensions later if and when required.  This addresses
      the "upgradability" requirement.  Assignment of types for this
      field should be maintained by IANA.

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.

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

                 Figure 3: ACP Zone Addressing Sub-Scheme

   The fields are defined as follows:

   o  Zone-ID: If set to all zero bits: The Device-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 Section on how this field is used in

   o  Z: MUST be 0.

   o  Device-ID: A unique value for each device.

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

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

   o  Device-Number (Device-Number): A number which is unique for a
      given registrar, to identify the device.  This can be a
      sequentially assigned number.

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

   When referring to the Device-ID of an ACP device overall, the V
   bit(s) is/are always "0".  This is also the address used in the ACP
   information in the domain certificate.  The V bit(s) identify the
   bits the device can assign itself.  The Device knows how many bits
   those are from the addressing sub-scheme (see below for a Sub-Scheme
   with more than one V-bit).

   The "Device-ID" itself is unique in a domain (i.e., the Zone-ID is
   not required for uniqueness).  Therefore, a device can be addressed
   either as part of a flat hierarchy (zone ID = 0), or with an
   aggregation scheme (any other zone ID).  A address with zone-ID = 0

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   is an identifier, with another zone-ID as a locator.  See
   Section for a description of the zone bits.

   The Virtual bit in this sub-scheme allows to easily add 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 (autonomous 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 virtual p2p interface with the V:0 address as its
   router into the ACP.  Depending on the SW design of ASA (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 to
   announce a single prefix for each autonomic node.  For example, in a
   network with 20,000 ACP devices, this avoid 20,000 additional routes
   in the routing table.  Usage of the Zone Field

   The "Zone-ID" allows for the introduction of structure in the
   addressing scheme.

   Zone = zero is the default addressing scheme in an autonomic domain.
   Every autonomic node MUST respond to its ACP address with zone=0.
   Used on its own this leads to a non-hierarchical address scheme,
   which is suitable for networks up to a certain size.  In this case,
   the addresses primarily act as identifiers for the nodes, and
   aggregation is not possible.

   If aggregation is required, the 13 bit value allows for up to 8192
   zones.  The allocation of zone numbers may either happen
   automatically through a to-be-defined algorithm; or it could be
   configured and maintained manually.

   If a device learns through an autonomic method or through
   configuration that it is part of a zone, it MUST also respond to its
   ACP address with that zone number.  In this case the ACP loopback is
   configured with two ACP addresses: One for zone 0 and one for the
   assigned zone.  This method allows for a smooth transition between a
   flat addressing scheme and an hierarchical one.

   (Theoretically, the 13 bits for the Zone-ID would allow also for two
   levels of zones, introducing a sub-hierarchy.  We do not think this
   is required at this point, but a new type could be used in the future
   to support such a scheme.)

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   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 different /40 ULA prefixes within an
   autonomic domain.  This gives followup work two options to consider.

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.

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

                Figure 4: 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 can not 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).  Future work may define
   mechanisms for auto-coordination between ACP devices and auto-
   allocation of Subnet-IDs between them.

   The Z field is following the Subnet-ID field so that future work
   could allocate/coordinate both Zone-ID and Subnet-ID consistently and
   use an integrated aggregateable routing approach across them.  Z=0
   (Zone sub-scheme) would then be used for network wide unique,
   registrar assigned (and certificate protected) Device-IDs primarily
   for ACP devices while Z=1 would be used for device-level assigned
   Interface Identifiers primarily for non-ACP-devices.

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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)    ||                Device-ID               |
   |                     || Registrar-ID | Device-Number|        V |
                               46             33/17          8/16

                 Figure 5: ACP Vlong Addressing Sub-Scheme

   This addressing scheme foregoes the Zone field to allow for larger,
   flatter routed networks (eg: as in IoT) with more than 2^32 Device-
   Numbers.  It also allows for up to 2^16 - 65536 different virtualized
   adddresses, which could be used to address individual software
   components in an ACP device.

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

   o  V: Virtualization bit: Values 0 and 1 as in Zone sub-scheme,
      further values use via definition in followup work.

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

   o  If the first bit of the "Device-Number" is "1", then the Device
      number is 17 bit long and the V field is 16 bit long.  Otherwise
      the Device-Number is 33 bit long and the V field is 8 bit long.
      "0" bit Device-Numbers are intended to be used for "general
      purpose" ACP devices that would potentially have a limited number
      (< 256) of internal users of the ACP that require separate
      V(irtual) addresses. "1" bit Device-Numbers are intended for ACP
      devices that are ACP edge devices (see Section 8.1.1) or that have
      a large number of internal ACP users requiring separate V(irtual)
      addresses.  For example large SDN controllers with container
      modular software architecture (see Section 8.1.2).

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6.10.6.  Other ACP Addressing Sub-Schemes

   Other ACP addressing sub-schemes can be defined if and when required.
   IANA would need to assign a new "type" for each new addressing sub-
   scheme.  With the current allocations, 5 more schemes are possible
   without further reducing the number of bits in a future scheme.

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
   for reachability.  The use of the autonomic control plane specific
   context eliminates the probable clash with the global routing table
   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 manual configuration is required.

   All routing updates are automatically secured in transit as the
   channels of the autonomic control plane are by default secured, and
   this routing runs only inside the ACP.

   The routing protocol inside the ACP is RPL ([RFC6550]).  See
   Section 10.3 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 Section 10.5 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.  Summary

   In summary, the profile chosen for RPL is one that expects a fairly
   reliable network reasonable fast links so that RPL convergence will
   be triggered immediately upon recognition of link failure/recovery.

   The key limitation of the chosen profile is that it is designed to
   not require any dataplane artifacts (such as [RFC6553]).  While the
   senders/receivers of ACP packets can be legacy NOC devices connected
   via "ACP connect" (see Section 8.1.1 to the ACP, their connectivity

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   can be handled as non-RPL-aware leafs (or "Internet") accoding to the
   dataplane architecture explained in [I-D.ietf-roll-useofrplinfo].
   This non-artifact profile is largely driven by the desire to avoid
   introducing the required Hop-by-Hop headers into the ACP VRF control
   plane.  Many devices will have their VRF forwarding code designed
   into silicon.

   In this profile choice, RPL has no dataplane artifacts.  A simple
   destination prefix based upon the routing table is used.  A
   consequence of supporting only a single instanceID (containing one
   DODAG), the ACP will only accomodate only a single class of routing
   table and can not create optimized routing paths to accomplish
   latency or energy goals.

   Consider a network that has multiple NOCs in different locations.
   Only one NOC will become the DODAG root.  Other NOCs will have to
   send traffic through the DODAG (tree) rooted in the primary NOC.
   Depending on topology, this can be an annoyance from a latency point
   of view, but it does not represent a single point of failure, as the
   DODAG can reconfigure itself when it detects data plane forwarding

   The lack of a RPI (the header defined by [RFC6553]), means that the
   dataplane will have no rank value that can be used to detect loops.
   As a result, traffic may loop until the TTL of the packet reaches
   zero.  This the same behavior as that of other IGPs that do not have
   the data plane options as RPPL.  There are a variety of heuristics
   that can be used to signal from the data plane to the RPL control
   plane that a new route is needed.

   Additionally, failed ACP tunnels will be detected by IKEv2 Dead Peer
   Detection (which can function as a replacement for an LLN's ETX).  A
   failure of an ACP tunnel should signal the RPL control plane to pick
   a different parent.

   Future Extensions to this 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.  A
   decision for the preferred technology would have to be done when such
   extension is defined.  RPL Instances

   Single RPL instance.  Default RPLInstanceID = 0.

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   RPL Mode of Operations (MOP): mode 3 "Storing Mode of Operations with
   multicast support".  Implementations should support also other modes.
   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 (eg: administrative action).

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

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

   [RFC6550] security not used, substituted by ACP security.  P2P communications

   Not used.  IPv6 address configuration

   Every ACP device (RPL node) announces an IPv6 prefix covering the
   address(es) used internally in the ACP device.  The prefix length
   depends on the choosen addressing sub-scheme of the ACP address
   provisioned into the certificate of the ACP device, eg: /127 for Zone
   addressing sub-scheme or /112 or /120 for Vlong addressing sub-
   scheme.  See Section 6.10 for more details.

   Every ACP device MUST install a blackhole (aka null route) 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 ([RFC6552], 3.2.6 - to become root):
   Indicated in DODAGPreference field of DIO message.

   o  Explicit configured "root": 0b100

   o  Registrar (Default): 0b011

   o  AN-connect (non registrar): 0b010

   o  Default: 0b001.  RPL Dataplane 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

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   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 device.  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.

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.  Addressing of Secure Channels in the data plane

   In order to be independent of the Data Plane configuration of global
   IPv6 subnet addresses (that may not exist when the ACP is brought
   up), Link-local secure channels MUST use IPv6 link local addresses
   between adjacent neighbors.  The fully autonomic mechanisms in this
   document only specify these link-local secure channels.Section 8.2
   specify extensions in which secure channels are tunnels, then this
   requirement does not apply.

   The Link-local secure channels specified in this document therefore
   depend on basic IPv6 link-local functionality to be auto-enabled by
   the ACP and prohibiting the Data Plane from disabling it.  The ACP
   also depends on being able to operate the secure channel protocol
   (eg: IPsec / dTLS) across IPv6 link-local addresses, something that
   may be an uncommon profile.  Functionaly, these are the only
   interactions with the Data Plane that the ACP needs to have.

   To mitigate these interactions with the Data Plane, extensions to
   this document may specify additional layer 2 or layer encapsulations
   for ACP secure channels as well as other protocols to auto-discover
   peer endpoints for such encapsulations (eg: tunneling across L3 or
   use of L2 only encapsulations).

6.12.2.  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.

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   Extensions to ACP where the ACP is for example tunneled need to
   consider how to guarantee MTU consistency.  This is a standard issue
   with tunneling, not specific to running the ACP across it.  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)
   to avoid running into PMTUD implementation bugs or underlying link
   MTU mismatch problems.

6.12.3.  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 devices, 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 (eg: on a
   different link or with a different address announced in GRASP).

6.12.4.  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 channels.

   The term loopback interface is commonly referred to internal pseudo
   interfaces through which the device can only reach itself.  In
   network devices these interfaces are used to hold addresses used by
   the transport stack of the system when an address should be reliable
   reachable in the presence of arbitrary link failures.  As long as
   addresses on a loopback interface are routeable in the routing
   protocol used, they will be reachable as long as there is at least
   one working network path.  This is opposed to routeable address
   assigned to an externally connected interface.  That address will
   become unreachable when that interface goes down.  For this reason,
   the ACP (ULA) address(es) are assigned to loopback type interface.

   ACP secure channels, eg: IPsec, dTLS or other future security
   associations with neighboring ACP devices can be mapped to ACP
   virtual interfaces in different ways: In one case, every 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

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   (in the same domain), this implementation approach will lead to a
   full mesh of ACP virtual interfaces between them.  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 physical subnet.  The multi-access
   ACP virtual interace needs to replicate link-local IPv6 multicast
   packets sent into the interface towards all ACP secure channels
   mapped into it.  There is no need for all ACP capable nodes on the
   same physical multi-access subnet to agree on a common implementation
   approach.  This is purely a node local decision.

   Multi-access ACP virtual interfaces are preferrable because they do
   reflect the presence of a multi-access physical networks 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 habe been built running natively on the multi-
   access interfaces.  One example is the efficiency of flooding of
   GRASP messages.  Assume such a LAN with three ACP neighbors, Alice
   Bob and Carol.  Alice sends a GRASP link-local multicast message to
   Bob and Carol.  If Alices ACP emulates the LAN as one point-to-point
   interface to Bob and one to Carol, GRASP itself will send two copies,
   if Alices 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 point-to-point
   ACP virtual interfaces, their GRASP instance would forward the packet
   from Alice to each other as part of the GRASP flooding procedure.
   These packets are of course redundant (unnecessary) and would be
   discarded by GRASP on receipt as duplicates.  If Bob and Charlies ACP
   would emulate a LAN, then this would not happen, because GRASPs
   flooding procedure does not send bac packets to the interface they
   where received from.

   For this reason, the ACP SHOULD map ACP secure channels on multi-
   access LANs into multi-access ACP virtual interfaces.

   Care must be taken when creating multi-access ACP virtual interfaces
   across ACP secure channels between ACP devices in different domains
   or routing subdomains.  The policies to be negotiated may be
   described as peer-to-peer policies in which case it is easier to
   create point-to-point ACP virtual interfaces for these secure

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

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7.1.  Why

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

                                 Figure 6

   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 AN router will see all other AN 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 like this can creates fundamental
   scale challenges.  The number of security associations of the secure
   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 neigbors.  An AN router with just 4 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 like these, AN capable L2 switches can
   ensure that discovery messages terminate on them so that neighboring
   AN routers and switches will only find the physically connected AN 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 AN
   capable, and ANswitch2 is not AN capable.  The desired ACP topology
   is therefore that ANrtr1 and ANrtrM only have an ACP connetion to
   ANswitch1, and that ANswitch1, ANrtr2, ANrtrN have a full mesh of ACP
   connection amongst each other.  ANswitch1 also has an ACP connection

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   with ANswitchM and ANswitchM has ACP connections to anything else
   behind it.

7.2.  How (per L2 port DULL GRASP)

   To support ACP on L2 switches or L2 switches ports of an L3 device,
   it is necessary to 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 IPv6 link-local multicast address, it is
   sufficient that all ethernet 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.

   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 6.12.4 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
   threfore 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 perfom 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

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   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", eg:
   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
   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, but the need to support secure channel protocols
   may be a limiting factor to supporting ACP on such devices.  Future
   options such as 802.1ae could improve that situation.

   A generic issue with ACP in L2 switched networks is the interaction
   with the Spanning Tree Protocol.  Ideally, the ACP 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 reconvergence can be quite slow).  The above described
   simple implementation options are not sufficient for this.  Instead
   they would simply have the ACP run across the active STP topology and
   therefore the ACP would equally be interrupted and reconverge with
   STP changes.

   L3/L2 devices SHOULD support per-L2 port ACP.

8.  Support for Non-Autonomic Components (Normative)

8.1.  ACP Connect

8.1.1.  Non-Autonomic 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 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-autonomic

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   NMS system does not have access to the ACP by default, just like any
   other external device.

   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-
   autonomic nodes, an autonomic node with ACP must support "ACP
   connect" (sometimes also connect "autonomic connect"):

   "ACP connect" is a function on an autonomic device that is called an
   "ACP edge device".  With "ACP connect", interfaces on the device can
   be configured to be put into the ACP VRF.  The ACP is then accessible
   to other (NOC) systems on such an interface without those systems
   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

                                   data-plane "native" (no ACP)
  +--------+       +----------------+       .         +-------------+
  | ACP    |       |ACP Edge Device |       .         |             |
  | Device |       |                |       v         |             |
  |        |-------|...[ACP VRF]....+-----------------|             |+
  |        |   ^   |.               |                 | NOC Device  ||
  |        |   .   | .[Data Plane]..+-----------------| "NMS hosts" ||
  |        |   .   |  [   VRF    ]  | .          ^    |             ||
  +--------+   .   +----------------+  .         .    +-------------+|
               .                        .        .     +-------------+
               .                        .        .
            data-plane "native"         .     ACP "native" (unencrypted)
          + ACP auto-negotiated         .    "ACP connect subnet"
            and encrypted               .
                                        ACP connect interface
                                        eg: "vrf ACP native" (config)

                           Figure 7: ACP connect

   ACP connect has security consequences: All systems and processes
   connected via ACP connect have access to all autonomic 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.

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   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
   "Autonomic Network Stable Connectivity"
   [I-D.ietf-anima-stable-connectivity] explains in more detail how the
   ACP can be integrated in a mixed NOC environment.

   The ACP connect interface must be (auto-)configured with an IPv6
   address prefix.  Is prefix SHOULD be covered by one of the (ULA)
   prefix(es) used in the ACP.  If using non-autonomic configuration, it
   SHOULD use the ACP Manual Addressing Sub-Scheme (Section 6.10.4).  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

   The prefix of ACP connect subnets MUST be distributed by the ACP edge
   device 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 usesonly one ULA prefix
   and all ACP connect subnets have prefixes covered by that ULA prefix,
   NMS hosts can rely on [RFC6724] - The NMS host will select the ACP
   connect interface because any ACP destination address is best 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

   ACP Edge Device MUST only forward IPv6 packets received from an ACP
   connect interface into the ACP that has an IPv6 address from the ACP
   prefix assigned to this interface (sometimes called "RPF filtering").
   This MAY be changed through administrative measures.

   To limit the security impact of ACP connect, devices supporting it
   SHOULD implement a security mechanism to allow configuration/use of
   ACP connect interfaces only on devices explicitly targeted to be
   deployed with it (such as those physically secure locations like a
   NOC).  For example, the certificate of such devices could include an
   extension required to permit configuration of ACP connect interfaces.
   This prohibits that a random ACP device with easy physical access
   that is not meant to run ACP connect could start leaking the ACP when
   it becomes compromised and the intruder configures ACP connect on it.
   The full workflow including the mechanism by which a registrar would
   select which device to give such a certificate to is subject to
   future work.

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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 device 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 autonomic 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

   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
   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 to ensure 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 signed
   software packages.  The specification of these mechanisms is subject
   to future work.

   Note that ASA (Autonomic Software Agents) could also be software
   components as described in this section, but further details of ASAs
   are subject to future work.

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8.1.3.  Auto Configuration

   ACP edge devices, NMS hosts and software components that as describd
   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 autoconfiguration
   according to [RFC4191].

   The ACP edge device 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 device 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
   device 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 device.

   Aggregated prefix means that the ACP edge device needs to only
   announce the /48 ULA prefixes used in the ACP but none of the actual
   /64 (Manual Addressing Sub-Scheme), /127 (Zone Addressing Sub-
   Scheme), /112 or /120 (Vlong Addressing Sub-Scheme) routes of actual
   ACP devices.  If ACP interfaces are configured with non ULA prefixes,
   then those prefixes can not be aggreged without further configured
   policy on the ACP edge device.  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 signalled
   via RFC4191 to NMS hosts and software components.

   The ACP edge devices 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.  See
   Section 11 for considerations how this updates the IPv6 address
   architecture and ULA specification.

8.1.4.  Combined ACP and Data Data Plane Interface (VRF Select)

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                        Combined ACP and Data Plane interface
     +--------+       +--------------------+    .   +--------------+
     | ACP    |       |ACP Edge Device     |    .   | NMS Host(s)  |
     | Device |       |                    |    .   | / Software   |
     |        |       |  [ACP  ].          |    .   |              |+
     |        |       | .[VRF  ] .[VRF   ] |    v   | "ACP address"||
     |        +-------+.         .[Select].+--------+ "Date Plane  ||
     |        |   ^   | .[Data ].          |        |  Address(es)"||
     |        |   .   |  [Plane]           |        |              ||
     |        |   .   |  [VRF  ]           |        +--------------+|
     +--------+   .   +--------------------+         +--------------+
           data-plane "native" and + ACP auto-negotiated/encrypted

                           Figure 8: 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
   device needs to demultiplex packets from NMS hosts into ACP VRF and
   Data Plane VRF.  This is sometimes called "VRF select".  If the ACP
   VRF has no overlapping IPv6 addresses with the Data Plane (as it
   should), 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 device 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 device 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.

   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

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   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 Device 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
   Data Plane.

   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 preferrable method of

   ACP edge devices MAY support the Combined ACP and Data Plane

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 (eg: ASA or legacy NMS
   applications) to the ACP.  Given how the ACP is the security and
   transport substrate for GRASP, the trustworthyness of devices/
   software allowed to participate in the ACP GRASP domain is one of the
   main reasons why the ACP section describes no solution with non-ACP
   routers participating in the ACP routing table.

   ACP connect interfaces can be dealt with in the GRASP ACP domain like
   any other ACP interface assuming that any physical ACP connect
   interface is physically protected from attacks and that the connected
   Software or NMS Hosts are equally trusted as that on other ACP
   devices.  ACP edge devices SHOULD have options to filter GRASP
   messages in and out of ACP connect interfaces (permit/deny) and MAY
   have more fine-grained filtering (eg: based on IPv6 address of
   originator or objective).

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   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
   devices.  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 therefore assumed that all GRASP packets on a Combined
   ACP and Data Plane interface belong to the GRASP ACP Domain.  They
   must therefore 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 space.

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

   Not all devices 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 neigbhors 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 autonomic device remote ACP neighbors are configured as

       remote-peer = [ local-address, method, remote-address ]
       local-address  = ip-address
       remote-address = transport-address
       transport-address =
          [ (ip-address | pattern) ?( , protocol ?(, port)) (, pmtu) ]
       ip-address = (ipv4-address | ipv6-address )
       method = "IKEv2" / "dTLS" / ..
       pattern = some IP address set

   For each candidate configured remote ACP neighbor, the secure channel
   protocol "method" is configured with its expected local IP address
   and remote transport endpoint (transport protocol and port number for
   the remote transport endpoint are usually not necessary to configure
   if defaults for the secure channel protocol method exist.

   This is the same information that would be communicated via DULL for
   L2 adjacent candidate ACP neighbors.  DULL is not used because the
   remote IP address would need to be configured anyhow and if the
   remote transport address would not be configured but learned via DULL
   then this would create a third party attack vector.

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   The secure channel method leverages the configuration to filter
   incoming connection requests by the remote IP address.  This is
   suplemental security.  The primary security is via the mutual domain
   certificate based authentication of the secure channel protocol.

   On a hub device, the remote IP address may be set to some pattern
   instead of explicit IP addresses.  In this case, the device does not
   attempt to initiate secure channel connections but only acts as their
   responder.  This allows for simple hub&spoke setups for the ACP where
   some method (subject to further specification) provisions the
   transport-address of hubs into spokes and hubs accept connections
   from any spokes.  The typical use case for this are spokes connecting
   via the Internet to hubs.  For example, this would be simple
   extension to BRSKI to allow zero-touch security across the Internet.

   Unlike adjacent ACP neighbor connections, configured remote ACP
   neighbor connections can also be across IPv4.  Not all (future)
   secure channel methods may support running IPv6 (as used in the ACP
   across the secure channel connection) over IPv4 encapsulation.

   Unless the secure channel method supports PMTUD, it needs to be set
   up with minimum MTU or the path mtu (pmtu) should be configured.

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 to "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 physical
   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

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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.

   Future work could envisage an option where the edge devices of the L3
   cloud is configured to automatically forward ACP discovery messages
   to the right exit point.  This optimisation is not considered in this

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 devices.

   o  If an existing device gets revoked, it will automatically be
      denied access to the ACP as its domain certificate will be
      validated against a Certificate Revocation List during
      authentication.  Since the revocation check is only done at the
      establishment of a new security association, existing ones are not
      automatically torn down.  If an immediate disconnect is required,
      existing sessions to a freshly revoked device can be re-set.

   The ACP can also sustain network partitions and mergers.  Practically
   all ACP operations are link local, where a network partition has no
   impact.  Devices 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.

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   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, a 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 enrolment of new devices during the partition.

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

   Merging two networks with different trust anchors requires the trust
   anchors to mutually trust each other (for example, by cross-signing).
   As long as the domain names are different, the addressing will not
   overlap (see Section 6.10).

   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 whicht the ACP is
   running.  Especially if bringing down the ACP is known to disconnect
   the operator from the device.  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 devices that have mutually authenticated each other with
   their domain certificates.  The channels themselves are protected
   using standard encryption technologies like 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 therefore 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 protocol.

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   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 fails on some vendor/product/customer limitations.  This
   includes protocols such as SNMP, NTP/PTP, DNS, DHCP, syslog,
   Radius/Diameter/Tacacs, IPFIX/Netflow - 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 AN
   protocols themselves, either via directed attacks or by denial-of-
   service attacks.  However, as the ACP is built using link-local IPv6
   address, remote attacks are impossible.  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

9.2.2.  From the inside

   The security model of the ACP is based on trusting all members of the
   group of devices that do 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 overall the secured so that there are no easy way
   to compromise them, such as data plane accessible privilege level
   with simple passwords.  This is a lot easier to do in devices whose
   software is designed from the ground up with security in mind than
   with legacy software based system where ACP is added on as another

   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 can not
   eavesdrop or modify communications, they can just filter them (which
   is unavoidable by any means).

   Further security can be achieved by constraining communication
   patterns inside the ACP, for example through roles that could be
   encoded into the domain certificates.  This is subject for future

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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 independent of configuration, there is no
   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 devices, except a
   possible on/off switch.

   While configuration 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 aspect unless they explicitly desire to
   do so.

   Since an ACP is self-protecting, a device 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.  Further Considerations (Informative)

   The following sections cover topics that are beyond the primary cope
   of this document (eg: bootstrap), that explain decisions made in this
   document (eg: choice of GRASP) or that explain desirable extensions
   to the behavior of the ACP that are not far enough worked out to be
   already standardized in this document.

10.1.  Domain Certificate provisioning / enrollment

   [I-D.ietf-anima-bootstrapping-keyinfra] (BRSKI) describes how devices
   with an IDevID certificate can securely and zero-touch enroll with a
   domain certificate to support the ACP.  BRSKI also leverages the ACP
   to enable zero touch bootstrap of new devices across networks without
   any configuration requirements across the transit devices (eg: no
   DHCP/DS forwarding/server setup).  This includes otherwise
   unconfigured 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.  Devices supporting such
   an infrastructure (BRSKI and ACP) are called ANI devices (Autonomic
   Networking Infrstructure), see [I-D.ietf-anima-reference-model].

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   Devices that do not support an IDevID but only an (insecure) vendor
   specific Unique Device Identifier (UDI) or devices 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 registrar (acting as an EST server) MUST include the
   subjectAltName / rfc822Name encoded ACP address and domain name to
   the enrolling device (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 this, and
   create the respective 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 device fails to
   connect to the ACP within its certificate lifetime, it can not
   connect to the ACP to renew its certificate across it, but it can
   still renew its certificate as an "enrolled/expired pledge" via the
   BRSKI bootstrap proxy.  This requires only that the enhanced EST
   server that is part of BRSKI honors expired domain certificates and
   that the pledge first attempts to perform TLS authentication for
   BRSKI bootstrap with its expired domain certificate - and only
   reverts to its IDevID when this fails.  This mechanism also replaces
   CRLs because the EST server (in conunction with the CA) would not
   renew revoked certficates - but in this scheme only the EST-server
   need to know which certificate was revoked.

   In the absence of BRSKI or less secure variants thereof, provisioning
   of certificates may involve one or more touches or non-standardized
   automation.  Device vendors usually support provisioning of
   certificates into devices via PKCS#7 (see [RFC2315]) and may support
   this provisioning through vendor specific models via Netconf
   ([RFC6241]).  If such devices also support Netconf Zerotouch
   ([I-D.ietf-netconf-zerotouch]) then this can be combined to zero-
   touch provisioning of domain certificates into devices.  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 an unconfigured network though.

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10.2.  ACP Neighbor discovery protocol selection

   This section discusses why GRASP DULL was choosen as the discovery
   protocol for L2 adjacent candidate ACP neighbors.  The contenders
   considered where GRASP, mDNS or LLDP.

10.2.1.  LLDP

   LLDP (and Cisco's similar 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

10.2.2.  mDNS and L2 support

   mDNS [RFC6762] with DNS-SD RRs (Resource Records) 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 devices.  With low
   performance of software forwarding in many L2 switches, this could
   also make the ACP risky to support on such L2 switches.

10.2.3.  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 device, 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

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   implementation of DULL GRASP or a shared implementation of DULL GRASP
   and GRASP in the ACP.

10.3.  Choice of routing protocol (RPL)

   This Appendix explains 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.  RPL also has other scalability improvements,
      such as selecting only a subset of peers instead of all possible
      ones, and trickle support for information synchronisation.

   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.

   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

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      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 behaviour.

   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 optimisation: 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 optimisation
      schemes become necessary in the future, but RPL can be expanded
      (see point "Extensibility" above).

10.4.  Extending ACP channel negotiation (via GRASP)

   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
   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

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   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 802.1AE (MacSEC) are to be added as
   negotiation options - and the performance objective should work
   across all IPsec, dDTLS and 802.1AE 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 implementations.

   A more modular alternative to extending IKEv2 could be to layer a
   modular negotiation mechanism on top of the multitide 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 devices and
   peers link-local IPv6 address is used.  When Alice and Bob support
   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

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   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.

10.5.  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 ACP
   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 devices using certificates from
   the same CA using the same domain field.  GRASP inside the ACP is run
   across all transitively connected ACP devices in a domain.

   The rsub element in the ACP information field primarily allows to use
   addresses from different ULA prefixes.  One use case is to create
   multiple networks that initially may be separated, but where it
   should be possible to connect them without further extensions to ACP
   when necessary.

   Another use case for routing subdomains is as the starting point for
   structuring routing inside an ACP.  For example, different routing
   subdomains could run different routing protocols or different
   instances of RPL and auto-aggregation / distribution of routes could
   be done across inter routing subdomain ACP channels based on
   negotiation (eg: via GRASP).  This is subject for further work.

   RPL scales very well.  It is not necessary to use multiple routing
   subdomains to scale autonomic domains in a way it would be possible
   if other routing protocols where used.  They exist only as options
   for the above mentioned reasons.

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   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 ACP 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 ACP information
   element of certificates.

   It is not necessary to have a sparate 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 "".

   Future extensions, primarily through intent can create more flexible
   options how to build ACP domains.

   Intent could modify the ACP connection check to permit connections
   between different domains.

   If different domains use the same CA one would change the ACP setup
   to permit for the ACP to be established between the two ACP devices,
   but no routing nor ACP GRASP to be built across this adjacency.  The
   main difference over routing subdomains is to not permit for the ACP
   GRASP instance to be build across the adjacency.  Instead, one would
   only build a point to point GRASP instance between those peers to
   negotiate what type of exchanges are desired across that connection.
   This would include routing negotiation, how much GRASP information to
   transit and what data-plane forwarding should be done.  This approach
   could also allow for for Intent to only be injected into the network
   from one side and propagate via this GRASP connection.

   If different domains have different CAs, they should start to trust
   each other by intent injected into both domains that would add the
   other domains CA as a trust point during the ACP connection setup -
   and then following up with the previous point of inter-domain
   connections across domains with the same CA (eg: GRASP negotiation).

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11.  RFC4291/RFC4193 Updates Considerations

   This document may be considered to be updating the IPv6 addressing
   architecture ([RFC4291]) and/or the Unique Local IPv6 Unicast
   addresses ([RFC4193]) depending on how strict specific statements in
   those specs are to be interpreted.  This section summarized and
   explains the necessity and benefits of these changes.  The normative
   parts of this document cover the actual updates.

   ACP addresses (Section 6.10) are used by network devices supporting
   the ACP.  They are assigned during bootstrap of the device or initial
   provisioning of the ACP.  They are encoded in the Domain Certificate
   of the device and are primarily used internally within the network
   device.  In that role they can be thought of as loopback addresses.

   Each ACP domain assigns ACP addresses from one or more ULA prefixes.
   Within an ACP network, addresses are assigned by nodes called
   registrars.  A unique Registrar-ID(entifier) is used in ACP addresses
   to allow multiple registrars to assign addresses autonomously and
   uncoordinated from each other.  Typically these Registrar-IDs are
   derived from the IEEE 802 48-bit MAC addresses of registrars.

   In the ACP Zone Addressing Sub-Scheme (Section 6.10.3), the registrar
   assigns a unique 15 bit value to an ACP device.  The ACP address has
   a 64-bit Device-ID(entifier) composed of the 48-bit Registrar-ID, the
   registrar assigned 15-bit Device-Number and 1 V(irtualization) bit
   that allows for an ACP device to have two addresses.

   The 64-bit Device-Identifier in the ACP Zone Addressing Sub-Scheme
   matches the 64 bit Interface Identifier (IID) address part as
   specified in RFC4291 section 2.5.1.  IIDs are unique across ACP
   devices, but all ACP devices with the same ULA prefix that use the
   ACP Zone Addressing Sub-Scheme will share the same subnet prefix
   (according to the definition of that term in RFC4291).  Each ACP
   device injects a /127 route into the ACP routing table to cover its
   two assigned addresses (V(irtual) bit being 0 or 1).  This approach
   is used because these ACP addresses are identifiers and not locators.
   The ACP device can connect anywhere in the autonomic domain without
   having to change its addresses.  A lightweight, highly scaleable
   routing protocol (RPL) is used to allow for large scale ACP networks.

   It is possible, that this scheme constitutes an update to RFC4191
   because the same 64 bit subnet prefix is used across many ACP
   devices.  The ACP Zone addressing Sub-Scheme is very similar to the
   common operational practices of assigning /128 loopback addresses to
   network devices from the same /48 or /64 subnet prefix.

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   In the ACP Vlong Addressing Sub-Scheme (Section 6.10.5), the address
   elements are the same as described for the Zone Addressing Sub-
   Scheme, but the V field is expanded from 1 bit to 8 or 16 bits.  The
   ACP device with ACP Vlong addressing therefore injects /120 or /112
   prefixes into the ACP routing table to cover its internal addresses.

   The goal for the 8 or 16-bit addresses available to an ACP device in
   this scheme is to assign them as required to software components,
   which in autonomic networking are called ASA (Autonomic Service
   Agents).  It could equally be used for existing software components
   such as VNFs (Virtual Networking Functions).  The ACP interface would
   then be the out-of-band management interface of such a VNF software
   component.  It should especially be possible to use these software
   components in a variety of contexts to allow standardized modular
   system composition: Native applications (in some VRF context if
   available), containers, virtual machines or other future ones.  To
   modularily compose a system with containers and virtual machines and
   avoid problems such as port space collision or NAT, it is necessary
   not only to assign separate addresses to those contexts, but also to
   use the notion of virtual interfaces between these contexts to
   compose the system.

   In practical terms, the ACP should be enabled to create from its /8
   or /16 prefix one or more device internal virtual subnets and to
   start software components connected to those virtual subnets.
   Ideally, these software components should be able to autoconfigure
   their addresses on these virtual interfaces.  Future work has to
   determine whether this address autoconfiguration for the virtual
   interface is best done with DHCPv6, if SLAAC should be recommended
   for these /8 or /16 virtual interfaces, or if some additional
   standardized method would be required.

   In the ACP Vlong Addressing scheme, the Device-ID does not match the
   RFC4291/RFC4193 64 bith length for the Interface Identifier, so this
   addressing Sub-Scheme in the ACP is an update to both standards.

   This document also specifies the workaround solution of exposing the
   ACP on physical interfaces in support of adoption by existing
   hardware and software solutions.  A NOC based NMS host could for
   example be configured with a second physical interface connecting to
   an ACP device that exposes the ACP to that NMS host (called ACP edge
   device).  The desired evolution of this workaround is that those two
   functions would merge into a single device, for example by making the
   ACP router a container/virtual machine inside the NMS host or vice
   versa.  The addressing for those physical interfaces allows for
   manually configured address prefixes but it could be fully autonomous
   if it could leverage the Vlong addressing format.  That would result

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   in a non /64 IID boundary on those external interfaces (but instead
   in /112 or /120 subnet prefixes).

   Note that both in the internal as well as the workaround external use
   of ACP addresses, all ACP addresses are meant to be used exclusively
   by components that are part of network control and OAM, but not for
   network users such as normal hosts.  This implies that for example no
   requirements for privacy addressing have been identified for ACP

12.  Security Considerations

   An ACP is self-protecting and there is no need to apply configuration
   to make it secure.  Its security therefore does not depend on

   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  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

   Fundamentally, security depends on correct operation, implementation
   and architecture.  Autonomic approaches such as the ACP largely
   eliminate the dependency on correct operation; implementation and
   architectural mistakes are still possible, as in all networking

13.  IANA Considerations

14.  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
   which (in alphabetical order): Ignas Bagdonas, Parag Bhide, Balaji
   BL, Alex Clemm, Yves Hertoghs, Bruno Klauser, Max Pritikin, Michael
   Richardson, Ravi Kumar Vadapalli.

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   Special thanks to Pascal Thubert and Michael Richardson to provide
   the details for the recommendations of the use of RPL in the ACP

   Further input and suggestions were received from: Rene Struik, Brian
   Carpenter, Benoit Claise.

15.  Change log [RFC Editor: Please remove]

15.1.  Initial version

   First version of this document: draft-behringer-autonomic-control-

15.2.  draft-behringer-anima-autonomic-control-plane-00

   Initial version of the anima document; only minor edits.

15.3.  draft-behringer-anima-autonomic-control-plane-01

   o  Clarified that the ACP should be based on, and support only IPv6.

   o  Clarified in intro that ACP is for both, between devices, as well
      as for access from a central entity, such as an NMS.

   o  Added a section on how to connect an NMS system.

   o  Clarified the hop-by-hop crypto nature of the ACP.

   o  Added several references to GDNP as a candidate protocol.

   o  Added a discussion on network split and merge.  Although, this
      should probably go into the certificate management story longer

15.4.  draft-behringer-anima-autonomic-control-plane-02

   Addresses (numerous) comments from Brian Carpenter.  See mailing list
   for details.  The most important changes are:

   o  Introduced a new section "overview", to ease the understanding of
      the approach.

   o  Merged the previous "problem statement" and "use case" sections
      into a mostly re-written "use cases" section, since they were

   o  Clarified the relationship with draft-ietf-anima-stable-

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15.5.  draft-behringer-anima-autonomic-control-plane-03

   o  Took out requirement for IPv6 --> that's in the reference doc.

   o  Added requirement section.

   o  Changed focus: more focus on autonomic functions, not only virtual
      out of band.  This goes a bit throughout the document, starting
      with a changed abstract and intro.

15.6.  draft-ietf-anima-autonomic-control-plane-00

   No changes; re-submitted as WG document.

15.7.  draft-ietf-anima-autonomic-control-plane-01

   o  Added some paragraphs in addressing section on "why IPv6 only", to
      reflect the discussion on the list.

   o  Moved the data-plane ACP out of the main document, into an
      appendix.  The focus is now the virtually separated ACP, since it
      has significant advantages, and isn't much harder to do.

   o  Changed the self-creation algorithm: Part of the initial steps go
      into the reference document.  This document now assumes an
      adjacency table, and domain certificate.  How those get onto the
      device is outside scope for this document.

   o  Created a new section 6 "workarounds for non-autonomic nodes", and
      put the previous controller section (5.9) into this new section.
      Now, section 5 is "autonomic only", and section 6 explains what to
      do with non-autonomic stuff.  Much cleaner now.

   o  Added an appendix explaining the choice of RPL as a routing

   o  Formalised the creation process a bit more.  Now, we create a
      "candidate peer list" from the adjacency table, and form the ACP
      with those candidates.  Also it explains now better that policy
      (Intent) can influence the peer selection. (section 4 and 5)

   o  Introduce a section for the capability negotiation protocol
      (section 7).  This needs to be worked out in more detail.  This
      will likely be based on GRASP.

   o  Introduce a new parameter: ACP tunnel type.  And defines it in the
      IANA considerations section.  Suggest GRE protected with IPSec
      transport mode as the default tunnel type.

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   o  Updated links, lots of small edits.

15.8.  draft-ietf-anima-autonomic-control-plane-02

   o  Added explicitly text for the ACP channel negotiation.

   o  Merged draft-behringer-anima-autonomic-addressing-02 into this
      document, as suggested by WG chairs.

15.9.  draft-ietf-anima-autonomic-control-plane-03

   o  Changed Neighbor discovery protocol from GRASP to mDNS.  Bootstrap
      protocol team decided to go with mDNS to discover bootstrap proxy,
      and ACP should be consistent with this.  Reasons to go with mDNS
      in bootstrap were a) Bootstrap should be reuseable also outside of
      full anima solutions and introduce as few as possible new
      elements. mDNS was considered well-known and very-likely even pre-
      existing in low-end devices (IoT). b) Using GRASP both for the
      insecure neighbor discovery and secure ACP operatations raises the
      risk of introducing security issues through implementation issues/
      non-isolation between those two instances of GRASP.

   o  Shortened the section on GRASP instances, because with mDNS being
      used for discovery, there is no insecure GRASP session any longer,
      simplifying the GRASP considerations.

   o  Added certificate requirements for ANIMA in section 5.1.1,
      specifically how the ANIMA information is encoded in

   o  Deleted the appendix on "ACP without separation", as originally
      planned, and the paragraph in the main text referring to it.

   o  Deleted one sub-addressing scheme, focusing on a single scheme

   o  Included information on how ANIMA information must be encoded in
      the domain certificate in section "preconditions".

   o  Editorial changes, updated draft references, etc.

15.10.  draft-ietf-anima-autonomic-control-plane-04

   Changed discovery of ACP neighbor back from mDNS to GRASP after
   revisiting the L2 problem.  Described problem in discovery section
   itself to justify.  Added text to explain how ACP discovery relates
   to BRSKY (bootstrap) discovery and pointed to Michael Richardsons
   draft detailing it.  Removed appendix section that contained the

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   original explanations why GRASP would be useful (current text is
   meant to be better).

15.11.  draft-ietf-anima-autonomic-control-plane-05

   o  Section 5.3 (candidate ACP neighbor selection): Add that Intent
      can override only AFTER an initial default ACP establishment.

   o  Section 6.10.1 (addressing): State that addresses in the ACP are
      permanent, and do not support temporary addresses as defined in

   o  Modified Section 6.3 to point to the GRASP objective defined in
      draft-carpenter-anima-ani-objectives. (and added that reference)

   o  Section 6.10.2: changed from MD5 for calculating the first 40 bits
      to SHA256; reason is MD5 should not be used any more.

   o  Added address sub-scheme to the IANA section.

   o  Made the routing section more prescriptive.

   o  Clarified in Section 8.1.1 the ACP Connect port, and defined that
      term "ACP Connect".

   o  Section 8.2: Added some thoughts (from mcr) on how traversing a L3
      cloud could be automated.

   o  Added a CRL check in Section 6.7.

   o  Added a note on the possibility of source-address spoofing into
      the security considerations section.

   o  Other editoral changes, including those proposed by Michael
      Richardson on 30 Nov 2016 (see ANIMA list).

15.12.  draft-ietf-anima-autonomic-control-plane-06

   o  Added proposed RPL profile.

   o  detailed dTLS profile - dTLS with any additional negotiation/
      signaling channel.

   o  Fixed up text for ACP/GRE encap.  Removed text claiming its
      incompatible with non-GRE IPsec and detailled it.

   o  Added text to suggest admin down interfaces should still run ACP.

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15.13.  draft-ietf-anima-autonomic-control-plane-07

   o  Changed author association.

   o  Improved ACP connect setion (after confusion about term came up in
      the stable connectivity draft review).  Added picture, defined
      complete terminology.

   o  Moved ACP channel negotiation from normative section to appendix
      because it can in the timeline of this document not be fully
      specified to be implementable.  Aka: work for future document.
      That work would also need to include analysing IKEv2 and describin
      the difference of a proposed GRASP/TLS solution to it.

   o  Removed IANA request to allocate registry for GRASP/TLS.  This
      would come with future draft (see above).

   o  Gave the name "ACP information field" to the field in the
      certificate carrying the ACP address and domain name.

   o  Changed the rules for mutual authentication of certificates to
      rely on the domain in the ACP information field of the certificate
      instead of the OU in the certificate.  Also renewed the text
      pointing out that the ACP information field in the certificate is
      meant to be in a form that it does not disturb other uses of the
      certificate.  As long as the ACP expected to rely on a common OU
      across all certificates in a domain, this was not really true:
      Other uses of the certificates might require different OUs for
      different areas/type of devices.  With the rules in this draft
      version, the ACP authentication does not rely on any other fields
      in the certificate.

   o  Added an extension field to the ACP information field so that in
      the future additional fields like a subdomain could be inserted.
      An example using such a subdomain field was added to the pre-
      existing text suggesting sub-domains.  This approach is necessary
      so that there can be a single (main) domain in the ACP information
      field, because that is used for mutual authentication of the
      certificate.  Also clarified that only the register(s) SHOULD/MUST
      use that the ACP address was generated from the domain name - so
      that we can easier extend change this in extensions.

   o  Took the text for the GRASP discovery of ACP neighbors from Brians
      grasp-ani-objectives draft.  Alas, that draft was behind the
      latest GRASP draft, so i had to overhaul.  The mayor change is to
      describe in the ACP draft the whole format of the M_FLOOD message
      (and not only the actual objective).  This should make it a lot
      easier to read (without having to go back and forth to the GRASP

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      RFC/draft).  It was also necessary because the locator in the
      M_FLOOD messages has an important role and its not coded inside
      the objective.  The specification of how to format the M_FLOOD
      message shuold now be complete, the text may be some duplicate
      with the DULL specificateion in GRASP, but no contradiction.

   o  One of the main outcomes of reworking the GRASP section was the
      notion that GRASP announces both the candidate peers IPv6 link
      local address but also the support ACP security protocol including
      the port it is running on.  In the past we shied away from using
      this information because it is not secured, but i think the
      additional attack vectors possible by using this information are
      negligible: If an attacker on an L2 subnet can fake another
      devices GRASP message then it can already provide a similar amount
      of attack by purely faking the link-local address.

   o  Removed the section on discovery and BRSKI.  This can be revived
      in the BRSKI document, but it seems mood given how we did remove
      mDNS from the latest BRSKI document (aka: this section discussed
      discrepancies between GRASP and mDNS discovery which should not
      exist anymore with latest BRSKI.

   o  Tried to resolve the EDNOTE about CRL vs. OCSP by pointing out we
      do not specify which one is to be used but that the ACP should be
      used to reach the URL included in the certificate to get to the
      CRL storage or OCSP server.

   o  Changed ACP via IPsec to ACP via IKEv2 and restructured the
      sections to make IPsec native and IPsec via GRE subsections.

   o  No need for any assigned dTLS port if ACP is run across dTLS
      because it is signalled via GRASP.

15.14.  draft-ietf-anima-autonomic-control-plane-08

   Modified mentioning of BRSKI to make it consistent with current
   (07/2017) target for BRSKI: MASA and IDevID are mandatory.  Devices
   with only insecure UDI would need a security reduced variant of
   BRSKI.  Also added mentioning of Netconf Zerotouch.  Made BRSKI non-
   normative for ACP because wrt.  ACP it is just one option how the
   domain certificate can be provisioned.  Instead, BRSKI is mandatory
   when a device implements ANI which is ACP+BRSKI.

   Enhanced text for ACP across tunnels to decribe two options: one
   across configured tunnels (GRE, IPinIP etc) a more efficient one via
   directed DULL.

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   Moved decription of BRSKI to appendex to emphasize that BRSKI is not
   a (normative) dependency of GRASP, enhanced text to indicate other
   options how Domain Certificates can be provisioned.

   Added terminology section.

   Separated references into normative and non-normative.

   Enhanced section about ACP via "tunnels".  Defined an option to run
   ACP secure channel without an outer tunnel, discussed PMTU, benefits
   of tunneling, potential of using this with BRSKI, made ACP via GREP a
   SHOULD requirement.

   Moved appendix sections up before IANA section because there where
   concerns about appendices to be to far on the bottom to be read.
   Added (Informative) / (Normative) to section titles to clarify which
   sections are informative and which are normative

   Moved explanation of ACP with L2 from precondition to separate
   section before workarounds, made it instructive enough to explain how
   to implement ACP on L2 ports for L3/L2 switches and made this part of
   normative requirement (L2/L3 switches SHOULD support this).

   Rewrote section "GRASP in the ACP" to define GRASP in ACP as
   mandatory (and why), and define the ACP as security and transport
   substrate to GRASP in ACP.  And how it works.

   Enhanced "self-protection" properties section: protect legacy
   management protocols.  Security in ACP is for protection from outside
   and those legacy protocols.  Otherwise need end-to-end encryption
   also inside ACP, eg: with domain certificate.

   Enhanced initial domain certificate section to include requirements
   for maintenance (renewal/revocation) of certificates.  Added
   explanation to BRSKI informative section how to handle very short
   lived certificates (renewal via BRSKI with expired cert).

   Modified the encoding of the ACP address to better fit RFC822 simple
   local-parts (":" as required by RFC5952 are not permitted in simple
   dot-atoms according to RFC5322.  Removed reference to RFC5952 as its
   now not needed anymore.

   Introduced a sub-domain field in the ACP information in the
   certificate to allow defining such subdomains with depending on
   future Intent definitions.  It also makes it clear what the "main
   domain" is.  Scheme is called "routing subdomain" to have a unique

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   Added V8 (now called Vlong) addressing sub-scheme according to
   suggestion from mcr in his mail from 30 Nov 2016
   nZpEphrTqDCBdzsKMpaIn2gsIzI).  Also modified the explanation of the
   single V bit in the first sub-scheme now renamed to Zone sub-scheme
   to distinguish it.

15.15.  draft-ietf-anima-autonomic-control-plane-09

   Added reference to RFC4191 and explained how it should be used on ACP
   edge routers to allow autoconfiguration of routing by NMS hosts.
   This came after review of stable connectivity draft where ACP connect
   is being referred to.

   V8 addressing Sub-Scheme was modified to allow not only /8 device-
   local address space but also /16.  This was in response to the
   possible need to have maybe as much as 2^12 local addresses for
   future encaps in BRSKI like IPinIP.  It also would allow fully
   autonomic address assignment for ACP connect interfaces from this
   local address space (on an ACP edge device), subject to approval of
   the implied update to rfc4291/rfc4193 (IID length).  Changed name to
   Vlong addressing sub-scheme.

   Added text in response to Brian Carpenters review of draft-ietf-
   anima-stable-connectivity-04.  The stable connectivity draft was
   vaguely describing ACP connect behavior that is better standardized
   in this ACP draft:

   o  Added new ACP "Manual" addressing sub-scheme with /64 subnets for
      use with ACP connect interfaces.  Being covered by the ACP ULA
      prefix, these subnets do not require additional routing entries
      for NMS hosts.  They also are fully 64-bit IID length compliant
      and therefore not subject to 4191bis considerations.  And they
      avoid that operators manually assign prefixes from the ACP ULA
      prefixes that might later be assigned autonomiously.

   o  ACP connect auto-configuration: Defined that ACP edge devices, NMS
      hosts should use RFC4191 to automatically learn ACP prefixes.
      This is especially necessary when the ACP uses multiple ULA
      prefixes (via eg: the rsub domain certificate option), or if ACP
      connect subinterfaces use manually configured prefixes NOT covered
      by the ACP ULA prefixes.

   o  Explained how rfc6724 is (only) sufficient when the NMS host has a
      separate ACP connect and data plane interface.  But not when there
      is a single interface.

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   o  Added a separate subsection to talk about "software" instead of
      "NMS hosts" connecting to the ACP via the "ACP connect" method.
      The reason is to point out that the "ACP connect" method is not
      only a workaround (for NMS hosts), but an actual desirable long
      term architectural component to modularily build software (eg: ASA
      or OAM for VNF) into ACP devices.

   o  Added a section to define how to run ACP connect across the same
      interface as the Data Plane.  This turns out to be quite
      challenging because we only want to rely on existing standards for
      the network stack in the NMS host/software and only define what
      features the ACP edge device needs.

   o  Added section about use of GRASP over ACP connect.

   o  Added text to indicate packet processing/filtering for security:
      filter incorrect packets arriving on ACP connect interfaces,
      diagnose on RPL root packets to incorrect destination address (not
      in ACP connect section, but because of it).

   o  Reaffirm security goal of ACP: Do not permit non-ACP routers into
      ACP routing domain.

   Made this ACP document be an update to RFC4291 and RFC4193.  At the
   core, some of the ACP addressing sub-schemes do effectively not use
   64-bit IIDs as required by RFC4191 and debated in rfc4191bis.  During
   6man in prague, it was suggested that all documents that do not do
   this should be classified as such updates.  Add a rather long section
   that summarizes the relevant parts of ACP addressing and usage and.
   Aka: This section is meant to be the primary review section for
   readers interested in these changes (eg: 6man WG.).

   Added changes from Michael Richardsons review
   anima-wg/autonomic-control-plane/pull/3/commits, textual and:

   o  ACP discovery inside ACP is bad *doh*!.

   o  Better CA trust and revocation sentences.

   o  More details about RPL behavior in ACP.

   o  blackhole route to avoid loops in RPL.

   Added requirement to terminate ACP channels upon cert expiry/

   Added fixes from 08-mcr-review-reply.txt (on github):

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   o  AN Domain Names are FQDNs.

   o  Fixed bit length of schemes, numerical writing of bits (00b/01b).

   o  Lets use US american english.

16.  References

16.1.  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.

   [RFC4191]  Draves, R. and D. Thaler, "Default Router Preferences and
              More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191,
              November 2005, <>.

   [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, <>.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862,
              DOI 10.17487/RFC4862, September 2007,

   [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,

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   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <>.

   [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,

   [RFC7030]  Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
              "Enrollment over Secure Transport", RFC 7030,
              DOI 10.17487/RFC7030, October 2013,

   [RFC7676]  Pignataro, C., Bonica, R., and S. Krishnan, "IPv6 Support
              for Generic Routing Encapsulation (GRE)", RFC 7676,
              DOI 10.17487/RFC7676, October 2015,

16.2.  Informative References

              Pritikin, M., Richardson, M., Behringer, M., Bjarnason,
              S., and K. Watsen, "Bootstrapping Remote Secure Key
              Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping-
              keyinfra-07 (work in progress), July 2017.

              Behringer, M., Carpenter, B., Eckert, T., Ciavaglia, L.,
              Pierre, P., Liu, B., Nobre, J., and J. Strassner, "A
              Reference Model for Autonomic Networking", draft-ietf-
              anima-reference-model-04 (work in progress), July 2017.

              Eckert, T. and M. Behringer, "Using Autonomic Control
              Plane for Stable Connectivity of Network OAM", draft-ietf-
              anima-stable-connectivity-04 (work in progress), July

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              Watsen, K., Abrahamsson, M., and I. Farrer, "Zero Touch
              Provisioning for NETCONF or RESTCONF based Management",
              draft-ietf-netconf-zerotouch-14 (work in progress), June

              Robles, I., Richardson, M., and P. Thubert, "When to use
              RFC 6553, 6554 and IPv6-in-IPv6", draft-ietf-roll-
              useofrplinfo-16 (work in progress), July 2017.

   [RFC2315]  Kaliski, B., "PKCS #7: Cryptographic Message Syntax
              Version 1.5", RFC 2315, DOI 10.17487/RFC2315, March 1998,

   [RFC4941]  Narten, T., Draves, R., and S. Krishnan, "Privacy
              Extensions for Stateless Address Autoconfiguration in
              IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,

   [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,

   [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,

   [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,

   [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,

   [RFC7404]  Behringer, M. and E. Vyncke, "Using Only Link-Local
              Addressing inside an IPv6 Network", RFC 7404,
              DOI 10.17487/RFC7404, November 2014,

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Internet-Draft      An Autonomic Control Plane (ACP)         August 2017

   [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,

   [RFC7576]  Jiang, S., Carpenter, B., and M. Behringer, "General Gap
              Analysis for Autonomic Networking", RFC 7576,
              DOI 10.17487/RFC7576, June 2015,

Authors' Addresses

   Michael H. Behringer (editor)


   Toerless Eckert (editor)
   Futurewei Technologies Inc.
   2330 Central Expy
   Santa Clara  95050


   Steinthor Bjarnason
   Arbor Networks
   2727 South State Street, Suite 200
   Ann Arbor  MI 48104
   United States


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