ANIMA WG T. Eckert, Ed.
Internet-Draft Huawei
Intended status: Standards Track M. Behringer, Ed.
Expires: February 8, 2019
S. Bjarnason
Arbor Networks
August 07, 2018
An Autonomic Control Plane (ACP)
draft-ietf-anima-autonomic-control-plane-17
Abstract
Autonomic functions need a control plane to communicate, which
depends on some addressing and routing. This Autonomic Management
and Control Plane should ideally be self-managing, and as independent
as possible of configuration. This document defines such a plane and
calls it the "Autonomic Control Plane", with the primary use as a
control plane for autonomic functions. It also serves as a "virtual
out-of-band channel" for Operations Administration and Management
(OAM) communications over a network that is secure and reliable even
when the network is not configured, or misconfigured.
Status of This Memo
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This Internet-Draft will expire on February 8, 2019.
Copyright Notice
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction (Informative) . . . . . . . . . . . . . . . . . 5
1.1. Applicability and Scope . . . . . . . . . . . . . . . . . 8
2. Acronyms and Terminology (Informative) . . . . . . . . . . . 9
3. Use Cases for an Autonomic Control Plane (Informative) . . . 15
3.1. An Infrastructure for Autonomic Functions . . . . . . . . 15
3.2. Secure Bootstrap over a not configured Network . . . . . 15
3.3. Data-Plane Independent Permanent Reachability . . . . . . 16
4. Requirements (Informative) . . . . . . . . . . . . . . . . . 17
5. Overview (Informative) . . . . . . . . . . . . . . . . . . . 18
6. Self-Creation of an Autonomic Control Plane (ACP) (Normative) 19
6.1. ACP Domain, Certificate and Network . . . . . . . . . . . 20
6.1.1. Certificate Domain Information Field . . . . . . . . 21
6.1.2. ACP domain membership check . . . . . . . . . . . . . 23
6.1.3. Certificate Maintenance . . . . . . . . . . . . . . . 24
6.1.3.1. GRASP objective for EST server . . . . . . . . . 25
6.1.3.2. Renewal . . . . . . . . . . . . . . . . . . . . . 26
6.1.3.3. Certificate Revocation Lists (CRLs) . . . . . . . 26
6.1.3.4. Lifetimes . . . . . . . . . . . . . . . . . . . . 27
6.1.3.5. Re-enrollment . . . . . . . . . . . . . . . . . . 27
6.1.3.6. Failing Certificates . . . . . . . . . . . . . . 29
6.2. ACP Adjacency Table . . . . . . . . . . . . . . . . . . . 29
6.3. Neighbor Discovery with DULL GRASP . . . . . . . . . . . 30
6.4. Candidate ACP Neighbor Selection . . . . . . . . . . . . 33
6.5. Channel Selection . . . . . . . . . . . . . . . . . . . . 34
6.6. Candidate ACP Neighbor verification . . . . . . . . . . . 35
6.7. Security Association protocols . . . . . . . . . . . . . 35
6.7.1. ACP via IKEv2 . . . . . . . . . . . . . . . . . . . . 35
6.7.1.1. Native IPsec . . . . . . . . . . . . . . . . . . 36
6.7.1.2. IPsec with GRE encapsulation . . . . . . . . . . 36
6.7.2. ACP via DTLS . . . . . . . . . . . . . . . . . . . . 37
6.7.3. ACP Secure Channel Requirements . . . . . . . . . . . 37
6.8. GRASP in the ACP . . . . . . . . . . . . . . . . . . . . 38
6.8.1. GRASP as a core service of the ACP . . . . . . . . . 38
6.8.2. ACP as the Security and Transport substrate for GRASP 38
6.8.2.1. Discussion . . . . . . . . . . . . . . . . . . . 40
6.9. Context Separation . . . . . . . . . . . . . . . . . . . 41
6.10. Addressing inside the ACP . . . . . . . . . . . . . . . . 42
6.10.1. Fundamental Concepts of Autonomic Addressing . . . . 42
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6.10.2. The ACP Addressing Base Scheme . . . . . . . . . . . 43
6.10.3. ACP Zone Addressing Sub-Scheme . . . . . . . . . . . 44
6.10.3.1. Usage of the Zone-ID Field . . . . . . . . . . . 46
6.10.4. ACP Manual Addressing Sub-Scheme . . . . . . . . . . 47
6.10.5. ACP Vlong Addressing Sub-Scheme . . . . . . . . . . 48
6.10.6. Other ACP Addressing Sub-Schemes . . . . . . . . . . 49
6.10.7. ACP Registrars . . . . . . . . . . . . . . . . . . . 49
6.10.7.1. Use of BRSKI or other Mechanism/Protocols . . . 49
6.10.7.2. Unique Address/Prefix allocation . . . . . . . . 50
6.10.7.3. Addressing Sub-Scheme Policies . . . . . . . . . 51
6.10.7.4. Address/Prefix Persistence . . . . . . . . . . . 52
6.10.7.5. Further Details . . . . . . . . . . . . . . . . 52
6.11. Routing in the ACP . . . . . . . . . . . . . . . . . . . 52
6.11.1. RPL Profile . . . . . . . . . . . . . . . . . . . . 53
6.11.1.1. Summary . . . . . . . . . . . . . . . . . . . . 53
6.11.1.2. RPL Instances . . . . . . . . . . . . . . . . . 54
6.11.1.3. Storing vs. Non-Storing Mode . . . . . . . . . . 54
6.11.1.4. DAO Policy . . . . . . . . . . . . . . . . . . . 54
6.11.1.5. Path Metric . . . . . . . . . . . . . . . . . . 54
6.11.1.6. Objective Function . . . . . . . . . . . . . . . 54
6.11.1.7. DODAG Repair . . . . . . . . . . . . . . . . . . 55
6.11.1.8. Multicast . . . . . . . . . . . . . . . . . . . 55
6.11.1.9. Security . . . . . . . . . . . . . . . . . . . . 55
6.11.1.10. P2P communications . . . . . . . . . . . . . . . 55
6.11.1.11. IPv6 address configuration . . . . . . . . . . . 55
6.11.1.12. Administrative parameters . . . . . . . . . . . 56
6.11.1.13. RPL Data-Plane artifacts . . . . . . . . . . . . 56
6.11.1.14. Unknown Destinations . . . . . . . . . . . . . . 56
6.12. General ACP Considerations . . . . . . . . . . . . . . . 56
6.12.1. Performance . . . . . . . . . . . . . . . . . . . . 56
6.12.2. Addressing of Secure Channels . . . . . . . . . . . 57
6.12.3. MTU . . . . . . . . . . . . . . . . . . . . . . . . 57
6.12.4. Multiple links between nodes . . . . . . . . . . . . 58
6.12.5. ACP interfaces . . . . . . . . . . . . . . . . . . . 58
7. ACP support on L2 switches/ports (Normative) . . . . . . . . 61
7.1. Why . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
7.2. How (per L2 port DULL GRASP) . . . . . . . . . . . . . . 62
8. Support for Non-ACP Components (Normative) . . . . . . . . . 64
8.1. ACP Connect . . . . . . . . . . . . . . . . . . . . . . . 64
8.1.1. Non-ACP Controller / NMS system . . . . . . . . . . . 64
8.1.2. Software Components . . . . . . . . . . . . . . . . . 66
8.1.3. Auto Configuration . . . . . . . . . . . . . . . . . 67
8.1.4. Combined ACP/Data-Plane Interface (VRF Select) . . . 68
8.1.5. Use of GRASP . . . . . . . . . . . . . . . . . . . . 69
8.2. ACP through Non-ACP L3 Clouds (Remote ACP neighbors) . . 70
8.2.1. Configured Remote ACP neighbor . . . . . . . . . . . 70
8.2.2. Tunneled Remote ACP Neighbor . . . . . . . . . . . . 71
8.2.3. Summary . . . . . . . . . . . . . . . . . . . . . . . 72
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9. Benefits (Informative) . . . . . . . . . . . . . . . . . . . 72
9.1. Self-Healing Properties . . . . . . . . . . . . . . . . . 72
9.2. Self-Protection Properties . . . . . . . . . . . . . . . 73
9.2.1. From the outside . . . . . . . . . . . . . . . . . . 73
9.2.2. From the inside . . . . . . . . . . . . . . . . . . . 74
9.3. The Administrator View . . . . . . . . . . . . . . . . . 75
10. ACP Operations (Informative) . . . . . . . . . . . . . . . . 75
10.1. ACP (and BRSKI) Diagnostics . . . . . . . . . . . . . . 76
10.2. ACP Registrars . . . . . . . . . . . . . . . . . . . . . 80
10.2.1. Registrar interactions . . . . . . . . . . . . . . . 81
10.2.2. Registrar Parameter . . . . . . . . . . . . . . . . 82
10.2.3. Certificate renewal and limitations . . . . . . . . 83
10.2.4. ACP Registrars with sub-CA . . . . . . . . . . . . . 83
10.2.5. Centralized Policy Control . . . . . . . . . . . . . 84
10.3. Enabling and disabling ACP/ANI . . . . . . . . . . . . . 85
10.3.1. Filtering for non-ACP/ANI packets . . . . . . . . . 85
10.3.2. Admin Down State . . . . . . . . . . . . . . . . . . 85
10.3.2.1. Security . . . . . . . . . . . . . . . . . . . . 86
10.3.2.2. Fast state propagation and Diagnostics . . . . . 87
10.3.2.3. Low Level Link Diagnostics . . . . . . . . . . . 87
10.3.2.4. Power Consumption Issues . . . . . . . . . . . . 88
10.3.3. Interface level ACP/ANI enable . . . . . . . . . . . 88
10.3.4. Which interfaces to auto-enable? . . . . . . . . . . 88
10.3.5. Node Level ACP/ANI enable . . . . . . . . . . . . . 90
10.3.5.1. Brownfield nodes . . . . . . . . . . . . . . . . 90
10.3.5.2. Greenfield nodes . . . . . . . . . . . . . . . . 91
10.3.6. Undoing ANI/ACP enable . . . . . . . . . . . . . . . 91
10.3.7. Summary . . . . . . . . . . . . . . . . . . . . . . 92
11. Security Considerations . . . . . . . . . . . . . . . . . . . 92
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 94
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 94
14. Change log [RFC Editor: Please remove] . . . . . . . . . . . 95
14.1. Initial version . . . . . . . . . . . . . . . . . . . . 95
14.2. draft-behringer-anima-autonomic-control-plane-00 . . . . 95
14.3. draft-behringer-anima-autonomic-control-plane-01 . . . . 95
14.4. draft-behringer-anima-autonomic-control-plane-02 . . . . 95
14.5. draft-behringer-anima-autonomic-control-plane-03 . . . . 95
14.6. draft-ietf-anima-autonomic-control-plane-00 . . . . . . 96
14.7. draft-ietf-anima-autonomic-control-plane-01 . . . . . . 96
14.8. draft-ietf-anima-autonomic-control-plane-02 . . . . . . 97
14.9. draft-ietf-anima-autonomic-control-plane-03 . . . . . . 97
14.10. draft-ietf-anima-autonomic-control-plane-04 . . . . . . 97
14.11. draft-ietf-anima-autonomic-control-plane-05 . . . . . . 98
14.12. draft-ietf-anima-autonomic-control-plane-06 . . . . . . 98
14.13. draft-ietf-anima-autonomic-control-plane-07 . . . . . . 99
14.14. draft-ietf-anima-autonomic-control-plane-08 . . . . . . 100
14.15. draft-ietf-anima-autonomic-control-plane-09 . . . . . . 102
14.16. draft-ietf-anima-autonomic-control-plane-10 . . . . . . 104
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14.17. draft-ietf-anima-autonomic-control-plane-11 . . . . . . 106
14.18. draft-ietf-anima-autonomic-control-plane-12 . . . . . . 106
14.19. draft-ietf-anima-autonomic-control-plane-13 . . . . . . 107
14.20. draft-ietf-anima-autonomic-control-plane-14 . . . . . . 109
14.21. draft-ietf-anima-autonomic-control-plane-15 . . . . . . 113
14.22. draft-ietf-anima-autonomic-control-plane-16 . . . . . . 114
14.23. draft-ietf-anima-autonomic-control-plane-17 . . . . . . 114
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 116
15.1. Normative References . . . . . . . . . . . . . . . . . . 116
15.2. Informative References . . . . . . . . . . . . . . . . . 119
15.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 123
Appendix A. Background and Futures (Informative) . . . . . . . . 123
A.1. ACP Address Space Schemes . . . . . . . . . . . . . . . . 124
A.2. BRSKI Bootstrap (ANI) . . . . . . . . . . . . . . . . . . 124
A.3. ACP Neighbor discovery protocol selection . . . . . . . . 126
A.3.1. LLDP . . . . . . . . . . . . . . . . . . . . . . . . 126
A.3.2. mDNS and L2 support . . . . . . . . . . . . . . . . . 126
A.3.3. Why DULL GRASP . . . . . . . . . . . . . . . . . . . 126
A.4. Choice of routing protocol (RPL) . . . . . . . . . . . . 127
A.5. ACP Information Distribution and multicast . . . . . . . 128
A.6. Extending ACP channel negotiation (via GRASP) . . . . . . 129
A.7. CAs, domains and routing subdomains . . . . . . . . . . . 131
A.8. Intent for the ACP . . . . . . . . . . . . . . . . . . . 132
A.9. Adopting ACP concepts for other environments . . . . . . 133
A.10. Further options / futures . . . . . . . . . . . . . . . . 135
A.10.1. Auto-aggregation of routes . . . . . . . . . . . . . 135
A.10.2. More options for avoiding IPv6 Data-Plane dependency 135
A.10.3. ACP APIs and operational models (YANG) . . . . . . . 136
A.10.4. RPL enhancements . . . . . . . . . . . . . . . . . . 136
A.10.5. Role assignments . . . . . . . . . . . . . . . . . . 137
A.10.6. Autonomic L3 transit . . . . . . . . . . . . . . . . 137
A.10.7. Diagnostics . . . . . . . . . . . . . . . . . . . . 137
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 138
1. Introduction (Informative)
Autonomic Networking is a concept of self-management: Autonomic
functions self-configure, and negotiate parameters and settings
across the network. [RFC7575] defines the fundamental ideas and
design goals of Autonomic Networking. A gap analysis of Autonomic
Networking is given in [RFC7576]. The reference architecture for
Autonomic Networking in the IETF is specified in the document
[I-D.ietf-anima-reference-model].
Autonomic functions need an autonomically built communications
infrastructure. This infrastructure needs to be secure, resilient
and re-usable by all autonomic functions. Section 5 of [RFC7575]
introduces that infrastructure and calls it the Autonomic Control
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Plane (ACP). More descriptively it would be the "Autonomic
communications infrastructure for Management and Control". For
naming consistency with that prior document, this document continues
to use the name ACP though.
Today, the management and control plane of networks typically uses a
routing and forwarding table which is dependent on correct
configuration and routing. Misconfigurations or routing problems can
therefore disrupt management and control channels. Traditionally, an
out-of-band network has been used to avoid or allow recovery from
such problems, or personnel are sent on site to access devices
through out-of-band management ports (also called craft ports, serial
console, management ethernet port). However, both options are
expensive.
In increasingly automated networks either centralized management
systems or distributed autonomic service agents in the network
require a control plane which is independent of the configuration of
the network they manage, to avoid impacting their own operations
through the configuration actions they take.
This document describes a modular design for a self-forming, self-
managing and self-protecting Autonomic Control Plane (ACP), which is
a virtual in-band network designed to be as independent as possible
of configuration, addressing and routing problems. The details how
this are achieved as described in Section 6. The ACP is designed to
remain operational even in the presence of configuration errors,
addressing or routing issues, or where policy could inadvertently
affect connectivity of both data packets or control packets.
This document uses the term "Data-Plane" to refer to anything in the
network nodes that is not the ACP, and therefore considered to be
dependent on (mis-)configuration. This Data-Plane includes both the
traditional forwarding-plane, as well as any pre-existing control-
plane, such as routing protocols that establish routing tables for
the forwarding plane.
The Autonomic Control Plane serves several purposes at the same time:
1. Autonomic functions communicate over the ACP. The ACP therefore
directly supports Autonomic Networking functions, as described in
[I-D.ietf-anima-reference-model]. For example, Generic Autonomic
Signaling Protocol (GRASP - [I-D.ietf-anima-grasp]) runs securely
inside the ACP and depends on the ACP as its "security and
transport substrate".
2. A controller or network management system can use it to securely
bootstrap network devices in remote locations, even if the (Data-
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Plane) network in between is not yet configured; no Data-Plane
dependent bootstrap configuration is required. An example of
such a secure bootstrap process is described in
[I-D.ietf-anima-bootstrapping-keyinfra].
3. An operator can use it to log into remote devices, even if the
network is misconfigured or not configured.
This document describes these purposes as use cases for the ACP in
Section 3, it defines the requirements in Section 4. Section 5 gives
an overview how the ACP is constructed.
The normative part of this document starts with Section 6, where the
the ACP is specified. Section 7 defines normative how to support ACP
on L2 switches. Section 8 explains normative how non-ACP nodes and
networks can be integrated.
The remaining sections are non-normative: Section 9 reviews benefits
of the ACP (after all the details have been defined), Section 10
provides operational recommendations, Appendix A provides additional
explanations and describes additional details or future standard or
propriety extensions that were considered not to be appropriate for
standardization in this document but were considered important to
document. There are no dependencies against Appendix A to build a
complete working and interoperable ACP according to this document.
The ACP provides secure IPv6 connectivity, therefore it can not only
be used as the secure connectivity for self-management as required
for the ACP in [RFC7575], but it can also be used as the secure
connectivity for traditional (centralized) management. The ACP can
be implemented and operated without any other components of autonomic
networks, except for the GRASP protocol which it leverages.
The document "Using Autonomic Control Plane for Stable Connectivity
of Network OAM" [RFC8368] describes how the ACP alone can be used to
provide secure and stable connectivity for autonomic and non-
autonomic Operations Administration and Management (OAM)
applications. That document also explains how existing management
solutions can leverage the ACP in parallel with traditional
management models, when to use the ACP and how to integrate with
potentially IPv4 only OAM backends.
Combining ACP with Bootstrapping Remote Secure Key Infrastructures
(BRSKI), see [I-D.ietf-anima-bootstrapping-keyinfra]) results in the
"Autonomic Network Infrastructure" as defined in
[I-D.ietf-anima-reference-model], which provides autonomic
connectivity (from ACP) with fully secure zero-touch (automated)
bootstrap from BRSKI. The ANI itself does not constitute an
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Autonomic Network, but it allows the building of more or less
autonomic networks on top of it - using either centralized, Software
Defined Networking- (SDN-)style (see [RFC7426]) automation or
distributed automation via Autonomic Service Agents (ASA) / Autonomic
Functions (AF) - or a mixture of both. See
[I-D.ietf-anima-reference-model] for more information.
1.1. Applicability and Scope
Please see the following Terminology section (Section 2) for
explanations of terms used in this section.
The design of the ACP as defined in this document is considered to be
applicable to all types of "professionally managed" networks: Service
Provider, Local Area Network (LAN), Metro(politan networks), Wide
Area Network (WAN), Enterprise Information Technology (IT) and
->"Operational Technology" () (OT) networks. The ACP can operate
equally on layer 3 equipment and on layer 2 equipment such a bridges
(see Section 7). The encryption mechanism used by the ACP is defined
to be negotiable, therefore it can be extended to environments with
different encryption protocol preferences. The minimum
implementation requirements in this document attempt to achieve
maximum interoperability by requiring support for few options: IP
security (IPsec), see [RFC4301]) and datagram Transport Layer
Security version 1.2 (DTLS), see [RFC6347]), depending on type of
device.
The implementation footprint of the ACP consists of Public Key
Infrastructure (PKI) code for the ACP certificate, the GRASP
protocol, UDP, TCP and TLS (for security and reliability of GRASP),
the ACP secure channel protocol used (such as IPsec or DTLS), and an
instance of IPv6 packet forwarding and routing via the Routing
Protocol for Low-power and Lossy Networks (RPL), see [RFC6550], that
is separate from routing and forwarding for the Data-Plane (user
traffic).
The ACP uses only IPv6 to avoid complexity of dual-stack ACP
operations (IPv6/IPv4). Nevertheless, it can without any changes be
integrated into even otherwise IPv4-only network devices. The Data-
Plane itself would not need to change, it could continue to be IPv4
only. For such IPv4 only devices, the IPv6 protocol itself would be
additional implementation footprint only used for the ACP.
The protocol choices of the ACP are primarily based on wide use and
support in networks and devices, well understood security properties
and required scalability. The ACP design is an attempt to produce
the lowest risk combination of existing technologies and protocols to
build a widely applicable operational network management solution:
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RPL was chosen because it requires a smaller routing table footprint
in large networks compared to other routing protocols with an
autonomically configured single area. The deployment experience of
large scale Internet of Things (IoT) networks serves as the basis for
wide deployment experience with RPL. The profile chosen for RPL in
the ACP does not not leverage any RPL specific forwarding plane
features (IPv6 extension headers), making its implementation a pure
control plane software requirement.
GRASP is the only completely novel protocol used in the ACP, and this
choice was necessary because there is no existing suitable protocol
to provide the necessary functions to the ACP, so GRASP was developed
to fill that gap.
The ACP design can be applicable to (cpu, memory) constrained devices
and (bitrate, reliability) constrained networks, but this document
does not attempt to define the most constrained type of devices or
networks to which the ACP is applicable. RPL and DTLS are two
protocol choices already making ACP more applicable to constrained
environments. See Appendix A.9 for discussions about how future
standards or proprietary extensions/variations variations of the ACP
could better meet different expectations from those on which the
current design is based.
2. Acronyms and Terminology (Informative)
[RFC Editor: WG/IETF/IESG review of the terms below asked for
references betwen these terms when they refer to each other. The
only option in RFC/XML i found to point to a hanging text acronym
definition that also displays the actual term is the format="title"
version, which leads to references such as '->"ACP domain
certificate" ()'. I found no reasonable way to eliminate the
trailing '()' generated by this type of cross references. Can you
please take care of removing these artefacts during editing (after
conversion to nroff ?). Also created ticket to ask for xml2rfc
enhancement to avoid this in the future:
https://trac.tools.ietf.org/tools/xml2rfc/trac/ticket/347.
[RFC Editor: Question: Is it possible to change the first occurences
of [RFCxxxx] references to "rfcxxx title" [RFCxxxx]? the XML2RFC
format does not seem to offer such a format, but i did not want to
duplicate 50 first references to be duplicate - one reference for
title mentioning and one for RFC number.]
In the rest of the document we will refer to systems using the ACP as
"nodes". Typically such a node is a physical (network equipment)
device, but it can equally be some virtualized system. Therefore, we
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do not refer to them as devices unless the context specifically calls
for a physical system.
This document introduces or uses the following terms (sorted
alphabetically). Terms introduced are explained on first use, so
this list is for reference only.
ACP: "Autonomic Control Plane". The Autonomic Function as defined
in this document. It provides secure zero-touch (automated)
transitive (network wide) IPv6 connectivity for all nodes in the
same ACP domain as well as a GRASP instance running across this
ACP IPv6 connectivity. The ACP is primarily meant to be used as a
component of the ANI to enable Autonomic Networks but it can
equally be used in simple ANI networks (with no other Autonomic
Functions) or completely by itself.
ACP address: An IPv6 address assigned to the ACP node. It is stored
in the domain information field of the ->"ACP domain certificate"
().
ACP address range/set: The ACP address may imply a range or set of
addresses that the node can assign for different purposes. This
address range/set is derived by the node from the format of the
ACP address called the "addressing sub-scheme".
ACP connect interface: An interface on an ACP node providing access
to the ACP for non ACP capable nodes without using an ACP secure
channel. See Section 8.1.1.
ACP domain: The ACP domain is the set of nodes with ->"ACP domain
certificates" that allow them to authenticate each other as
members of the ACP domain. See also Section 6.1.2.
ACP (ANI/AN) Domain Certificate: A provisioned [RFC5280] certificate
(LDevID) carrying the domain information field which is used by
the ACP to learn its address in the ACP and to derive and
cryptographically assert its membership in the ACP domain.
domain information (field): An rfc822Name information element (e.g.,
field) in the domain certificate in which the ACP relevant
information is encoded: the domain name and the ACP address.
ACP Loopback interface: The Loopback interface in the ACP Virtual
Routing and Forwarding (VRF) that has the ACP address assigned to
it.
ACP network: The ACP network constitutes all the nodes that have
access to the ACP. It is the set of active and transitively
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connected nodes of an ACP domain plus all nodes that get access to
the ACP of that domain via ACP edge nodes.
ACP (ULA) prefix(es): The /48 IPv6 address prefixes used across the
ACP. In the normal/simple case, the ACP has one ULA prefix, see
Section 6.10. The ACP routing table may include multiple ULA
prefixes if the "rsub" option is used to create addresses from
more than one ULA prefix. See Section 6.1.1. 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 cryptographically authenticated and encrypted
data connection established between (normally) adjacent ACP nodes
to carry traffic of the ACP VRF secure and isolated from Data-
Plane traffic in-band over the same link/path as the Data-Plane.
ACP secure channel protocol: The protocol used to build an ACP
secure channel, e.g., Internet Key Exchange Protocol version 2
(IKEv2) with IPsec or Datagram Transport Layer Security (DTLS).
ACP virtual interface: An interface in the ACP VRF mapped to one or
more ACP secure channels. See Section 6.12.5.
AN "Autonomic Network": A network according to
[I-D.ietf-anima-reference-model]. Its main components are ANI,
Autonomic Functions and Intent.
(AN) Domain Name: An FQDN (Fully Qualified Domain Name) in the
domain information field of the Domain Certificate. See
Section 6.1.1.
ANI (nodes/network): "Autonomic Network Infrastructure". The ANI is
the infrastructure to enable Autonomic Networks. It includes ACP,
BRSKI and GRASP. Every Autonomic Network includes the ANI, but
not every ANI network needs to include autonomic functions beyond
the ANI (nor Intent). An ANI network without further autonomic
functions can for example support secure zero-touch (automated)
bootstrap and stable connectivity for SDN networks - see
[RFC8368].
ANIMA: "Autonomic Networking Integrated Model and Approach". ACP,
BRSKI and GRASP are products of the IETF ANIMA working group.
ASA: "Autonomic Service Agent". Autonomic software modules running
on an ANI device. The components making up the ANI (BRSKI, ACP,
GRASP) are also described as ASAs.
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Autonomic Function: A function/service in an Autonomic Network (AN)
composed of one or more ASA across one or more ANI nodes.
BRSKI: "Bootstrapping Remote Secure Key Infrastructures"
([I-D.ietf-anima-bootstrapping-keyinfra]. A protocol extending
EST to enable secure zero-touch bootstrap in conjunction with ACP.
ANI nodes use ACP, BRSKI and GRASP.
Data-Plane: The counterpoint to the ACP VRF in an ACP node: all
routing and forwarding in the node other than the ACP VRF. In a
simple ACP or ANI node, the Data-Plane is typically provisioned by
means other than autonomically, for example manually (including
across the ACP) or via SDN controllers. In a fully Autonomic
Network node, the Data-Plane is managed autonomically via
Autonomic Functions and Intent. Note that other (non-ANIMA) RFC
use the Data-Plane to refer to what is better called the
forwarding plane. This is not the way the term is used in this
document!
device: A physical system, or physical node.
Enrollment: The process where a node presents identification (for
example through keying material such as the private key of an
IDevID) to a network and acquires a network specific identity and
trust anchor such as an LDevID.
EST: "Enrollment over Secure Transport" ([RFC7030]). IETF standard
protocol for enrollment of a node with an LDevID. BRSKI is based
on EST.
GRASP: "Generic Autonomic Signaling Protocol". An extensible
signaling protocol required by the ACP for ACP neighbor discovery.
The ACP also provides the "security and transport substrate" for
the "ACP instance of GRASP". This instance of GRASP runs across
the ACP secure channels to support BRSKI and other NOC/OAM or
Autonomic Functions. See [I-D.ietf-anima-grasp].
IDevID: An "Initial Device IDentity" X.509 certificate installed by
the vendor on new equipment. Contains information that
establishes the identity of the node in the context of its vendor/
manufacturer such as device model/type and serial number. See
[AR8021]. IDevID can not be used for the ACP because they are not
provisioned by the owner of the network, so they can not directly
indicate an ACP domain they belong to.
in-band (management): The type of management used predominantly in
IP based networks, not leveraging an ->"out-of-band network" ().
In in-band management, access to the managed equipment depends on
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the configuration of this equipment itself: interface, addressing,
forwarding, routing, policy, security, management. This
dependency makes in-band management fragile because the
configuration actions performed may break in-band management
connectivity. Breakage can not only be unintentional, it can
simply be an unavoidable side effect of being unable to create
configuration schemes where in-band management connectivity
configuration is unaffected by Data-Plane configuration. See also
->"(virtual) out-of-band network" ().
Intent: Policy language of an autonomic network according to
[I-D.ietf-anima-reference-model].
Loopback interface: The conventional name for an internal IP
interface to which addresses may be assigned, but which transmits
no external traffic.
LDevID: A "Local Device IDentity" is an X.509 certificate installed
during "enrollment". The Domain Certificate used by the ACP is an
LDevID. See [AR8021].
MIC: "Manufacturer Installed Certificate". Another word not used in
this document to describe an IDevID.
native interface: Interfaces existing on a node without
configuration of the already running node. On physical nodes
these are usually physical interfaces. On virtual nodes their
equivalent.
node: A system, e.g., supporting the ACP according to this document.
Can be virtual or physical. Physical nodes are called devices.
Node-ID: The identifier of an ACP node inside that ACP. It is the
last 64 (see Section 6.10.3) or 78 bits (see Section 6.10.5) of
the ACP address.
Operational Technology (OT): "https://en.wikipedia.org/wiki/
Operational_Technology" [1]: "The hardware and software dedicated
to detecting or causing changes in physical processes through
direct monitoring and/or control of physical devices such as
valves, pumps, etc". OT networks are today in most cases well
separated from Information Technology (IT) networks.
(virtual) out-of-band network: An out-of-band network is a secondary
network used to manage a primary network. The equipment of the
primary network is connected to the out-of-band network via
dedicated management ports on the primary network equipment.
Serial (console) management ports were historically most common,
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higher end network equipment now also has ethernet ports dedicated
only for management. An out-of-band network provides management
access to the primary network independent of the configuration
state of the primary network. One of the goals of the ACP is to
provide this benefit of out-of-band networks virtually on the
primary network equipment. The ACP VRF acts as a virtual out of
band network device providing configuration independent management
access. The ACP secure channels are the virtual links of the ACP
virtual out-of-band network, meant to be operating independent of
the configuration of the primary network. See also ->"in-band
(management)" ().
RPL: "IPv6 Routing Protocol for Low-Power and Lossy Networks". The
routing protocol used in the ACP. See [RFC6550].
MASA (service): "Manufacturer Authorized Signing Authority". A
vendor/manufacturer or delegated cloud service on the Internet
used as part of the BRSKI protocol.
(ACP/ANI/BRSKI) Registrar: An ACP registrar is an entity (software
and/or person) that is orchestrating the enrollment of ACP nodes
with the ACP domain certificate. ANI nodes use BRSKI, so ANI
registrars are also called BRSKI registrars. For non-ANI ACP
nodes, the registrar mechanisms are undefined by this document.
See Section 6.10.7. Renewal and other maintenance (such as
revocation) of ACP domain certificates may be performed by other
entities than registrars. EST must be supported for ACP domain
certificate renewal (see Section 6.1.3). BRSKI is an extension of
EST, so ANI/BRSKI registrars can easily support ACP domain
certificate renewal in addition to initial enrollment.
sUDI: "secured Unique Device Identifier". 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 node typically consisting of
at least device model/type and serial number, often in a vendor
specific format. See sUDI and LDevID.
ULA: (Global ID prefix) A "Unique Local Address" (ULA) is an IPv6
address in the block fc00::/7, defined in [RFC4193]. It is the
approximate IPv6 counterpart of the IPv4 private address
([RFC1918]). The ULA Global ID prefix are the first 48 bits of a
ULA address. In this document it is abbreviated as "ULA prefix".
(ACP) VRF: The ACP is modeled in this document as a "Virtual Routing
and Forwarding" instance (VRF). This means that it is based on a
"virtual router" consisting of a separate IPv6 forwarding table to
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which the ACP virtual interfaces are attached and an associated
IPv6 routing table separate from the Data-Plane. Unlike the VRFs
on MPLS/VPN-PE ([RFC4364]) or LISP XTR ([RFC6830]), the ACP VRF
does not have any special "core facing" functionality or routing/
mapping protocols shared across multiple VRFs. In vendor products
a VRF such as the ACP-VRF may also be referred to as a so called
VRF-lite.
(ACP) Zone: An ACP zone is a set of ACP nodes using the same zone
field value in their ACP address according to Section 6.10.3.
Zones are a mechanism to support structured addressing of ACP
addresses within the same /48 bit ULA prefix.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119],[RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Use Cases for an Autonomic Control Plane (Informative)
3.1. An Infrastructure for Autonomic Functions
Autonomic Functions need a stable infrastructure to run on, and all
autonomic functions should use the same infrastructure to minimize
the complexity of the network. In this way, there is only need for a
single discovery mechanism, a single security mechanism, and single
instances of other processes that distributed functions require.
3.2. Secure Bootstrap over a not configured Network
Today, bootstrapping a new node typically requires all nodes between
a controlling node such as an SDN controller ("Software Defined
Networking", see [RFC7426]) and the new node to be completely and
correctly addressed, configured and secured. Bootstrapping and
configuration of a network happens in rings around the controller -
configuring each ring of devices before the next one can be
bootstrapped. Without console access (for example through an out-of-
band network) it is not possible today to make devices securely
reachable before having configured the entire network leading up to
them.
With the ACP, secure bootstrap of new devices and whole new networks
can happen without requiring any configuration of unconfigured
devices along the path: As long as all devices along the path support
ACP and a zero-touch bootstrap mechanism such as BRSKI, the ACP
across a whole network of unconfigured devices can be brought up
without operator/provisioning intervention. The ACP also provides
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additional security for any bootstrap mechanism, because it encrypts
the traffic along the path hop-by-hop.
3.3. Data-Plane Independent Permanent Reachability
Today, most critical control plane protocols and network management
protocols are using the Data-Plane of the network. This leads to
often undesirable dependencies between control and management plane
on one side and the Data-Plane on the other: Only if the forwarding
and control plane of the Data-Plane are configured correctly, will
the Data-Plane and the management plane work as expected.
Data-Plane connectivity can be affected by errors and faults, for
example misconfigurations that make AAA (Authentication,
Authorization and Accounting) servers unreachable or can lock an
administrator out of a device; routing or addressing issues can make
a device unreachable; shutting down interfaces over which a current
management session is running can lock an admin irreversibly out of
the device. Traditionally only out-of-band access can help recover
from such issues (such as serial console or ethernet management
port).
Data-Plane dependencies also affect applications in a Network
Operations Center (NOC) such as SDN controller applications: Certain
network changes are today hard to implement, because the change
itself may affect reachability of the devices. Examples are address
or mask changes, routing changes, or security policies. Today such
changes require precise hop-by-hop planning.
Note that specific control plane functions for the Data-Plane often
want to depend on forwarding of their packets via the Data-Plane:
Aliveness and routing protocol signaling packets across the Data-
Plane to verify reachability across the Data-Plane, using IPv4
signaling packets for IPv4 routing vs. IPv6 signaling packets for
IPv6 routing.
Assuming appropriate implementation (see Section 6.12.2 for more
details), the ACP provides reachability that is independent of the
Data-Plane. This allows the control plane and management plane to
operate more robustly:
o For management plane protocols, the ACP provides the functionality
of a Virtual out-of-band (VooB) channel, by providing connectivity
to all nodes regardless of their Data-Plane configuration, routing
and forwarding tables.
o For control plane protocols, the ACP allows their operation even
when the Data-Plane is temporarily faulty, or during transitional
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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
connectivity.
The document "Using Autonomic Control Plane for Stable Connectivity
of Network OAM" [RFC8368] explains this use case for the ACP in
significantly more detail and explains how the ACP can be used in
practical network operations.
4. Requirements (Informative)
The following requirements where identified as the basis for the
design of the ACP based on the above use-cases (Section 3). These
requirements are informative for this specification because they
(merely) represent the use-case requirements. The keywords are
therefore highlighted to be different from RFC2119. The ACP as
specified in the normative parts of this document is meeting or
exceeding these use-case requirements:
ACP1: The ACP _SHOULD_ provide robust connectivity: As far as
possible, it should be independent of configured addressing,
configuration and routing. Requirements 2 and 3 build on this
requirement, but also have value on their own.
ACP2: The ACP _MUST_ have a separate address space from the Data-
Plane. Reason: traceability, debug-ability, separation from
Data-Plane, infrastructure security (filtering based on known
address space).
ACP3: The ACP _MUST_ use autonomically managed address space.
Reason: easy bootstrap and setup ("autonomic"); robustness
(admin can't mess things up so easily). This document
suggests using ULA addressing for this purpose ("Unique Local
Address", see [RFC4193]).
ACP4: The ACP _MUST_ be generic, that is it MUST be usable by all
the functions and protocols of the ANI. Clients of the ACP
MUST NOT be tied to a particular application or transport
protocol.
ACP5: The ACP _MUST_ provide security: Messages coming through the
ACP MUST be authenticated to be from a trusted node, and
SHOULD (very strong SHOULD) be encrypted.
Explanation for ACP4: In a fully autonomic network (AN), newly
written ASA could potentially all communicate exclusively via GRASP
with each other, and if that was assumed to be the only requirement
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against the ACP, it would not need to provide IPv6 layer connectivity
between nodes, but only GRASP connectivity. Nevertheless, because
ACP also intends to support non-AN networks, it it is crucial to
support IPv6 layer connectivity across the ACP to support any
transport and application layer protocols.
The ACP operates hop-by-hop, because this interaction can be built on
IPv6 link local addressing, which is autonomic, and has no dependency
on configuration (requirement 1). It may be necessary to have ACP
connectivity across non-ACP nodes, for example to link ACP nodes over
the general Internet. This is possible, but introduces a dependency
against stable/resilient routing over the non-ACP hops (see
Section 8.2).
5. Overview (Informative)
The Autonomic Control Plane is constructed in the following way (for
details, see Section 6):
1. An ACP node creates a Virtual Routing and Forwarding (VRF)
instance, or a similar virtual context.
2. It determines, following a policy, a candidate peer list. This
is the list of nodes to which it should establish an Autonomic
Control Plane. Default policy is: To all link-layer adjacent
nodes supporting ACP.
3. For each node in the candidate peer list, it authenticates that
node and negotiates a mutually acceptable channel type.
4. For each node in the candidate peer list, it then establishes a
secure tunnel of the negotiated type. The resulting tunnels are
then placed into the previously set up VRF. This creates an
overlay network with hop-by-hop tunnels.
5. Inside the ACP VRF, each node assigns its ULA IPv6 address to a
Loopback interface assigned to the ACP VRF.
6. Each node runs a lightweight routing protocol, to announce
reachability of the virtual addresses inside the ACP (see
Section 6.12.5).
Note:
o Non-autonomic NMS ("Network Management Systems") or SDN
controllers have to be explicitly configured for connection into
the ACP.
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o Connecting over non-ACP Layer-3 clouds requires explicit
configuration. See Section 8.2.
o None of the above operations (except explicit configured ones) are
reflected in the configuration of the node.
The following figure illustrates the ACP.
ACP node 1 ACP node 2
................... ...................
secure . . secure . . secure
channel: +-----------+ : channel : +-----------+ : channel
..--------| ACP VRF |---------------------| ACP VRF |---------..
: / \ / \ <--routing--> / \ / \ :
: \ / \ / \ / \ / :
..--------| Loopback |---------------------| Loopback |---------..
: | interface | : : | interface | :
: +-----------+ : : +-----------+ :
: : : :
: Data-Plane :...............: Data-Plane :
: : link : :
:.................: :.................:
Figure 1: ACP VRF and secure channels
The resulting overlay network is normally based exclusively on hop-
by-hop tunnels. This is because addressing used on links is IPv6
link local addressing, which does not require any prior set-up. In
this way the ACP can be built even if there is no configuration on
the node, or if the Data-Plane has issues such as addressing or
routing problems.
6. Self-Creation of an Autonomic Control Plane (ACP) (Normative)
This section describes the components and steps to set up an
Autonomic Control Plane (ACP), and highlights the key properties
which make it "indestructible" against many inadvertent changes to
the Data-Plane, for example caused by misconfigurations.
An ACP node can be a router, switch, controller, NMS host, or any
other IP capable node. Initially, it must have its ACP domain
certificate, as well as an (empty) ACP Adjacency Table (described in
Section 6.2). It then can start to discover ACP neighbors and build
the ACP. This is described step by step in the following sections:
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6.1. ACP Domain, Certificate and Network
The ACP relies on group security. An ACP domain is a group of nodes
that trust each other to participate in ACP operations. To establish
trust, each ACP member requires keying material: An ACP node MUST
have a certificate (LDevID) and a Trust Anchor (TA) consisting of a
certificate (chain) used to sign the LDevID of all ACP domain
members. The LDevID is used to cryptographically authenticate the
membership of its owner node in the ACP domain to other ACP domain
members, the TA is used to authenticate the ACP domain membership of
other nodes (see Section 6.1.2).
The LDevID is called the ACP domain certificate, the TA is the
Certificate Authority (CA) of the ACP domain.
The ACP does not mandate specific mechanisms by which this keying
material is provisioned into the ACP node, it only requires the
Domain information field as specified in Section 6.1.1 in its domain
certificate as well as those of candidate ACP peers. See
Appendix A.2 for more information about enrollment or provisioning
options.
This document uses the term ACP in many places where the Autonomic
Networking reference documents [RFC7575] and
[I-D.ietf-anima-reference-model] use the word autonomic. This is
done because those reference documents consider (only) fully
autonomic networks and nodes, but support of ACP does not require
support for other components of autonomic networks. Therefore the
word autonomic might be misleading to operators interested in only
the ACP.
[RFC7575] defines the term "Autonomic Domain" as a collection of
autonomic nodes. ACP nodes do not need to be fully autonomic, but
when they are, then the ACP domain is an autonomic domain. Likewise,
[I-D.ietf-anima-reference-model] defines the term "Domain
Certificate" as the certificate used in an autonomic domain. The ACP
domain certificate is that domain certificate when ACP nodes are
(fully) autonomic nodes. Finally, this document uses the term ACP
network to refer to the network created by active ACP nodes in an ACP
domain. The ACP network itself can extend beyond ACP nodes through
the mechanisms described in Section 8.1.
The ACP domain certificate SHOULD be used for any authentication
between nodes with ACP domain certificates (ACP nodes and NOC nodes)
where the required condition is ACP domain membership, such as ACP
node to NOC/OAM end-to-en security and ASA to ASA end-to-end
security. Section 6.1.2 defines this "ACP domain membership check".
The uses of this check that are standardized in this document are for
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the establishment of ACP secure channels (Section 6.6) and for ACP
GRASP (Section 6.8.2).
6.1.1. Certificate Domain Information Field
Information about the domain MUST be encoded in the domain
certificate in a subjectAltName / rfc822Name field according to the
following ABNF definition ([RFC5234]):
[RFC Editor: Please substitute SELF in all occurences of rfcSELF in
this document with the RFC number assigned to this document and
remove this comment line]
domain-information = local-part "@" acp-domain-name
local-part = key [ "." local-info ]
key = "rfcSELF"
local-info = [ acp-address ] [ "+" rsub extensions ]
acp-address = 32hex-dig | 0
hex-dig = DIGIT / "a" / "b" / "c" / "d" / "e" / "f"
rsub = [ <subdomain> ] ; <subdomain> as of RFC1034, section 3.5
routing-subdomain = [ rsub " ." ] acp-domain-name
acp-domain-name = ; <domain> ; as of RFC 1034, section 3.5
extensions = *( "+" extension )
extension = ; future standard definition.
; Must fit RFC5322 simple dot-atom format.
Example:
domain-information = rfcSELF+fd89b714f3db00000200000064000000
+area51.research@acp.example.com
acp-domain-name = acp.example.com
routing-subdomain = area51.research.acp.example.com
Figure 2: ACP Domain Information Field ABNF
Nodes complying with this specification MUST be able to receive their
ACP address through the domain certificate, in which case their own
ACP domain certificate MUST have the 32hex-dig "acp-address" field.
Nodes complying with this specification MUST also be able to
authenticate nodes as ACP domain members / ACP secure channel peers
when they have an empty or 0-value acp-address field. See
Section 6.1.2.
"acp-domain-name" is used to indicate the ACP Domain across which all
ACP nodes trust each other and are willing to build ACP channels to
each other. See Section 6.1.2. Acp-domain-name SHOULD be the FQDN
of a DNS domain owned by the operator assigning the certificate.
This is a simple method to ensure that the domain is globally unique
and collision of ACP addresses would therefore only happen due to ULA
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hash collisions. If the operator does not own any FQDN, it should
choose a string (in FQDN format) that it intends to be equally
unique.
"routing-subdomain" is the autonomic subdomain composed of "rsub" and
"acp-domain-name". "rsub" is optional. When not present, "routing-
subdomain" is the same as "acp-domain-name". "routing-subdomain"
determines the /48 ULA prefix for ACP addresses. "rsub" therefore
allows to use multiple /48 ULA prefixes in an ACP domain. See
Appendix A.7 for example use-cases.
The optional "extensions" field is used for future standardized
extensions to this specification. It MUST be ignored if present and
not understood.
Formatting notes:
o "rsub" needs to be in the "local-part": If the format just had
routing-subdomain as the domain part of the domain-information,
rsub and acp-domain-name could not be separated from each other.
It also makes acp-domain-name a valid e-mail target across all
routing-subdomains.
o "acp-address" cannot use standard IPv6 address formats because it
must match the simple dot-atom format of [RFC5322]. The character
":" is not allowed in that format.
o If "acp-address" is empty, and "rsub" is empty too, the "local-
part" will have the format "rfcSELF + + extension(s)". The two
plus characters are necessary so the node can unambiguously parse
that both "acp-address" and "rsub" are empty.
o The maximum size of "domain-information" is 254 characters and the
maximum size of node-info is 64 characters according to [RFC5280]
that is referring to [RFC2821] (superseded by [RFC5321]).
The subjectAltName / rfc822Name encoding of the ACP domain name and
ACP address is used for the following reasons:
o It should be possible to share the LDevID with other uses beside
the ACP. Therefore, the information element required for the ACP
should be encoded so that it minimizes the possibility of creating
incompatibilities with such other uses.
o The information for the ACP should not cause incompatibilities
with any pre-existing ASN.1 software. This eliminates the
introduction of a novel information element because that could
require extensions to such pre-existing ASN.1 parsers.
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o subjectAltName / rfc822Name is a pre-existing element that must be
supported by all existing ASN.1 parsers for LDevID.
o The element required for the ACP should not be misinterpreted by
any other uses of the LDevID. If the element used for the ACP is
interpreted by other uses, the impact should be benign.
o Using an IP address format encoding could result in non-benign
misinterpretation of the domain information field; other uses
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 node which does not belong
to 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. The ACP information field
encodes the full ACP address AND the domain name with rsub part,
so that it is easier to examine/use the "domain information
field".
o The format of the rfc822Name is chosen so that an operator can set
up a mailbox called rfcSELF@<domain> that would receive emails
sent towards the rfc822Name of any node inside a domain. This is
possible because in many modern mail systems, components behind a
"+" character are considered part of a single mailbox. In other
words, it is not necessary to set up a separate mailbox for every
ACP node, 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 4.2.1.6 of [RFC5280] for details on the subjectAltName
field.
6.1.2. ACP domain membership check
The following points constitute the ACP domain membership check of a
candidate peer certificate, independent of the protocol used:
1: The peer certificate is valid (lifetime).
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2: The peer has proved ownership of the private key associated with
the certifictes public key.
3: The peer's certificate is signed by one of the trust anchors
associated with the ACP domain certificate.
4: If the node certificate indicates a Certificate Revocation List
(CRL) Distribution Point (CDP) ([RFC5280], section 4.2.1.13) or
Online Certificate Status Protocol (OCSP) responder ([RFC5280],
section 4.2.2.1), then the peer's certificate must be valid
according to those criteria: An OCSP check for the peer's
certificate across the ACP must succeed or the peer certificate
must not be listed in the CRL retrieved from the CDP.
5: The peer's certificate has a syntactically valid ACP domain
information field (encoded as subjectAltName / rfc822Name) and the
acp-domain-name in that peer's domain information field is the
same as in this ACP node's certificate.
Only when checking a candidate peer's certificate for the purpose of
establishing an ACP secure channel, one additional check is
performed:
6: The candidate peer certificate's ACP domain information field
has a non-empty acp-address field (either 32hex-dig or 0,
according to Figure 2).
Rule 6: for the establishment of ACP secure channels ensures that
they will only be built between nodes which indicate through the acp-
address in their ACP domain certificate indicate ability and
permission by the Registrar to participate in ACP secure-channels.
Nodes without an empty acp-adress field can only use it for non-ACP-
secure channel authentication purposes. The special value 0 in an
ACP certificates acp-address field is used for nodes that can and
should determine their ACP address through other mechanisms than
learning it through their ACP domain certificate, but which are still
permitted to establish ACP secure channels. Mechanisms for those
nodes to determine their ACP address are outside the scope of this
specification.
6.1.3. Certificate Maintenance
ACP nodes MUST support certificate renewal via EST ("Enrollment over
Secure Transport", see [RFC7030]) and MAY support other mechanisms.
An ACP network MUST have at least one ACP node supporting EST server
functionality across the ACP so that EST renewal is useable.
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ACP nodes SHOULD be able to remember the EST server from which they
last renewed their ACP domain certificate and SHOULD provide the
ability for this remembered EST server to also be set by the ACP
Registrar (see Section 6.10.7) that initially enrolled the ACP device
with its ACP domain certificate. When BRSKI (see
[I-D.ietf-anima-bootstrapping-keyinfra]) is used, the ACP address of
the BRSKI registrar from the BRSKI TLS connection SHOULD be
remembered and used for the next renewal via EST if that registrar
also announces itself as an EST server via GRASP (see next section)
on its ACP address.
6.1.3.1. GRASP objective for EST server
ACP nodes that are EST servers MUST announce their service via GRASP
in the ACP through M_FLOOD messages. See [I-D.ietf-anima-grasp],
section 2.8.11 for the definition of this message type:
Example:
[M_FLOOD, 12340815, h'fd89b714f3db0000200000064000001', 210000,
["SRV.est", 4, 255 ],
[O_IPv6_LOCATOR,
h'fd89b714f3db0000200000064000001', TCP, 80]
]
Figure 3: GRASP SRV.est example
The formal definition of the objective in Concise data definition
language (CDDL) (see [I-D.ietf-cbor-cddl]) is as follows:
flood-message = [M_FLOOD, session-id, initiator, ttl,
+[objective, (locator-option / [])]]
objective = ["SRV.est", objective-flags, loop-count,
objective-value]
objective-flags = sync-only ; as in GRASP spec
sync-only = 4 ; M_FLOOD only requires synchronization
loop-count = 255 ; recommended
objective-value = any ; Not used (yet)
Figure 4: GRASP SRV.est definition
The objective value "SRV.est" indicates that the objective is an
[RFC7030] compliant EST server because "est" is an [RFC6335]
registered service name for [RFC7030]. Objective-value MUST be
ignored if present. Backward compatible extensions to [RFC7030] MAY
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be indicated through objective-value. Non [RFC7030] compatible
certificate renewal options MUST use a different objective-name.
The M_FLOOD message MUST be sent periodically. The default SHOULD be
60 seconds, the value SHOULD be operator configurable but SHOULD be
not smaller than 60 seconds. The frequency of sending MUST be such
that the aggregate amount of periodic M_FLOODs from all flooding
sources causes only negligible traffic across the ACP. The time-to-
live (ttl) parameter SHOULD be 3.5 times the period so that up to
three consecutive messages can be dropped before considering an
announcement expired. In the example above, the ttl is 210000 msec,
3.5 times 60 seconds. When a service announcer using these
parameters unexpectedly dies immediately after sending the M_FLOOD,
receivers would consider it expired 210 seconds later. When a
receiver tries to connect to this dead service before this timeout,
it will experience a failing connection and use that as an indication
that the service is dead and select another instance of the same
service instead.
6.1.3.2. Renewal
When performing renewal, the node SHOULD attempt to connect to the
remembered EST server. If that fails, it SHOULD attempt to connect
to an EST server learned via GRASP. The server with which
certificate renewal succeeds SHOULD be remembered for the next
renewal.
Remembering the last renewal server and preferring it provides
stickiness which can help diagnostics. It also provides some
protection against off-path compromised ACP members announcing bogus
information into GRASP.
Renewal of certificates SHOULD start after less than 50% of the
domain certificate lifetime so that network operations has ample time
to investigate and resolve any problems that causes a node to not
renew its domain certificate in time - and to allow prolonged periods
of running parts of a network disconnected from any CA.
6.1.3.3. Certificate Revocation Lists (CRLs)
The ACP node SHOULD support Certificate Revocation Lists (CRL) via
HTTPs from one or more CRL Distribution Points (CDPs). The CDP(s)
MUST be indicated in the Domain Certificate when used. If the CDP
URL uses an IPv6 address (ULA address when using the addressing rules
specified in this document), the ACP node will connect to the CDP via
the ACP. If the CDP URL uses an IPv6 address (ULA address when using
the addressing rules specified in this document), the ACP node will
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connect to the CDP via the ACP. If the CDP uses a domain name, the
ACP node will connect to the CDP via the Data-Plane.
It is common to use domain names for CDP(s), but there is no
requirement for the ACP to support DNS. Any DNS lookup in the Data-
Plane is not only a possible security issue, but it would also not
indicate whether the resolved address is meant to be reachable across
the ACP. Therefore, the use of an IPv6 address versus the use of a
DNS name doubles as an indicator whether or not to reach the CDP via
the ACP.
A CDP can be reachable across the ACP either by running it on a node
with ACP or by connecting its node via an ACP connect interface (see
Section 8.1). The CDP SHOULD use an ACP domain certificate for its
HTTPs connections. The connecting ACP node SHOULD verify that the
CDP certificate used during the HTTPs connection has the same ACP
address as indicated in the CDP URL of the nodes ACP domain
certificate
6.1.3.4. Lifetimes
Certificate lifetime may be set to shorter lifetimes than customary
(1 year) because certificate renewal is fully automated via ACP and
EST. The primary limiting factor for shorter certificate lifetimes
is load on the EST server(s) and CA. It is therefore recommended
that ACP domain certificates are managed via a CA chain where the
assigning CA has enough performance to manage short lived
certificates. See also Section 10.2.4 for discussion about an
example setup achieving this.
When certificate lifetimes are sufficiently short, such as few hours,
certificate revocation may not be necessary, allowing to simplify the
overall certificate maintenance infrastructure.
See Appendix A.2 for further optimizations of certificate maintenance
when BRSKI can be used ("Bootstrapping Remote Secure Key
Infrastructures", see [I-D.ietf-anima-bootstrapping-keyinfra]).
6.1.3.5. Re-enrollment
An ACP node may determine that its ACP domain certificate has
expired, for example because the ACP node was powered down or
disconnected longer than its certificate lifetime. In this case, the
ACP node SHOULD convert to a role of a re-enrolling candidate ACP
node.
In this role, the node does maintain the trust anchor and certificate
chain associated with its ACP domain certificate exclusively for the
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purpose of re-enrollment, and attempts (or waits) to get re-enrolled
with a new ACP certificate. The details depend on the mechanisms/
protocols used by the ACP registrars.
Please refer to Section 6.10.7 for explanations about ACP registrars
and vouchers as used in the following text.
When BRSKI is used (aka: on ACP nodes that are ANI nodes), the re-
enrolling candidate ACP node would attempt to enroll like a candidate
ACP node (BRSKI pledge), but instead of using the ACP nodes IDevID,
it SHOULD first attempt to use its ACP domain certificate in the
BRSKI TLS authentication. The BRSKI registrar MAY honor this
certificate beyond its expiration date purely for the purpose of re-
enrollment. Using the ACP node's domain certificate allows the BRSKI
registrar to learn that nodes ACP domain information field, so that
the BRSKI registrar can re-assign the same ACP address information to
the ACP node in the new ACP domain certificate.
If the BRSKI registrar denies the use of the old ACP domain
certificate, the re-enrolling candidate ACP node MUST re-attempt re-
enrollment using its IDevID as defined in BRSKI during the TLS
connection setup.
Both when the BRSKI connection is attempted with the old ACP domain
certificate or the IDevID, the re-enrolling candidate ACP node SHOULD
authenticate the BRSKI registrar during TLS connection setup based on
its existing trust anchor/certificate chain information associated
with its old ACP certificate. The re-enrolling candidate ACP node
SHOULD only request a voucher from the BRSKI registrar when this
authentication fails during TLS connection setup.
When other mechanisms than BRSKI are used for ACP domain certificate
enrollment, the principles of the re-enrolling candidate ACP node are
the same. The re-enrolling candidate ACP node attempts to
authenticate any ACP registrar peers during re-enrollment protocol/
mechanisms via its existing certificate chain/trust anchor and
provides its existing ACP domain certificate and other identification
(such as the IDevID) as necessary to the registrar.
Maintaining existing trust anchor information is especially important
when enrollment mechanisms are used that unlike BRSKI do not leverage
a voucher mechanism to authenticate the ACP registrar and where
therefore the injection of certificate failures could otherwise make
the ACP node easily attackable remotely.
When using BRSKI or other protocol/mechanisms supporting vouchers,
maintaining existing trust anchor information allows for re-
enrollment of expired ACP certificates to be more lightweight,
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especially in environments where repeated acquisition of vouchers
during the lifetime of ACP nodes may be operationally expensive or
otherwise undesirable.
6.1.3.6. Failing Certificates
An ACP domain certificate is called failing in this document, if/when
the ACP node can determine that it was revoked (or explicitly not
renewed), or in the absence of such explicit local diagnostics, when
the ACP node fails to connect to other ACP nodes in the same ACP
domain using its ACP certificate. For connection failures to
determine the ACP domain certificate as the culprit, the peer should
pass the domain membership check (Section 6.1.2) and other reasons
for the connection failure can be excluded because of the connection
error diagnostics.
This type of failure can happen during setup/refresh of a secure ACP
channel connections or any other use of the ACP domain certificate,
such as for the TLS connection to an EST server for the renewal of
the ACP domain certificate.
Example reasons for failing certificates that the ACP node can only
discover through connection failure are that the domain certificate
or any of its signing certificates could have been revoked or may
have expired, but the ACP node can not self-diagnose this condition
directly. Revocation information or clock synchronization may only
be available across the ACP, but the ACP node can not build ACP
secure channels because ACP peers reject the ACP node's domain
certificate.
ACP nodes SHOULD support the option to determines whether its ACP
certificate is failing, and when it does, put itself into the role of
a re-enrolling candidate ACP node as explained above
(Section 6.1.3.5).
6.2. ACP Adjacency Table
To know to which nodes to establish an ACP channel, every ACP node
maintains an adjacency table. The adjacency table contains
information about adjacent ACP nodes, at a minimum: Node-ID
(identifier of the node inside the ACP, see Section 6.10.3 and
Section 6.10.5), interface on which neighbor was discovered (by GRASP
as explained below), link-local IPv6 address of neighbor on that
interface, certificate (including domain information field). An ACP
node MUST maintain this adjacency table up to date. This table is
used to determine to which neighbor an ACP connection is established.
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Where the next ACP node is not directly adjacent (i.e., not on a link
connected to this node), the information in the adjacency table can
be supplemented by configuration. For example, the Node-ID and IP
address could be configured.
The adjacency table MAY contain information about the validity and
trust of the adjacent ACP node's certificate. However, subsequent
steps MUST always start with authenticating the peer.
The adjacency table contains information about adjacent ACP nodes in
general, independently of their domain and trust status. The next
step determines to which of those ACP nodes an ACP connection should
be established.
6.3. Neighbor Discovery with DULL GRASP
[RFC Editor: GRASP draft is in RFC editor queue, waiting for
dependencies, including ACP. Please ensure that references to I-
D.ietf-anima-grasp that include section number references (throughout
this document) will be updated in case any last-minute changes in
GRASP would make those section references change.
DULL GRASP is a limited subset of GRASP intended to operate across an
insecure link-local scope. See section 2.5.2 of
[I-D.ietf-anima-grasp] for its formal definition. The ACP uses one
instance of DULL GRASP for every L2 interface of the ACP node to
discover link level adjacent candidate ACP neighbors. Unless
modified by policy as noted earlier (Section 5 bullet point 2.),
native interfaces (e.g., physical interfaces on physical nodes)
SHOULD be initialized automatically to a state in which ACP discovery
can be performed and any native interfaces with ACP neighbors can
then be brought into the ACP even if the interface is otherwise not
configured. Reception of packets on such otherwise not configured
interfaces MUST be limited so that at first only IPv6 StateLess
Address Auto Configuration (SLAAC - [RFC4862]) and DULL GRASP work
and then only the following ACP secure channel setup packets - but
not any other unnecessary traffic (e.g., no other link-local IPv6
transport stack responders for example).
Note that the use of the IPv6 link-local multicast address
(ALL_GRASP_NEIGHBORS) implies the need to use Multicast Listener
Discovery Version 2 (MLDv2, see [RFC3810]) to announce the desire to
receive packets for that address. Otherwise DULL GRASP could fail to
operate correctly in the presence of MLD snooping, non-ACP enabled L2
switches - because those would stop forwarding DULL GRASP packets.
Switches not supporting MLD snooping simply need to operate as pure
L2 bridges for IPv6 multicast packets for DULL GRASP to work.
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ACP discovery SHOULD NOT be enabled by default on non-native
interfaces. In particular, ACP discovery MUST NOT run inside the ACP
across ACP virtual interfaces. See Section 10.3 for further, non-
normative suggestions on how to enable/disable ACP at node and
interface level. See Section 8.2.2 for more details about tunnels
(typical non-native interfaces). See Section 7 for how ACP should be
extended on devices operating (also) as L2 bridges.
Note: If an ACP node also implements BRSKI to enroll its ACP domain
certificate (see Appendix A.2 for a summary), then the above
considerations also apply to GRASP discovery for BRSKI. Each DULL
instance of GRASP set up for ACP is then also used for the discovery
of a bootstrap proxy via BRSKI when the node does not have a domain
certificate. Discovery of ACP neighbors happens only when the node
does have the certificate. The node therefore never needs to
discover both a bootstrap proxy and ACP neighbor at the same time.
An ACP node announces itself to potential ACP peers by use of the
"AN_ACP" objective. This is a synchronization objective intended to
be flooded on a single link using the GRASP Flood Synchronization
(M_FLOOD) message. In accordance with the design of the Flood
message, a locator consisting of a specific link-local IP address, IP
protocol number and port number will be distributed with the flooded
objective. An example of the message is informally:
[M_FLOOD, 12340815, h'fe80000000000000c0011001FEEF0000, 210000,
["AN_ACP", 4, 1, "IKEv2" ],
[O_IPv6_LOCATOR,
h'fe80000000000000c0011001FEEF0000, UDP, 15000]
["AN_ACP", 4, 1, "DTLS" ],
[O_IPv6_LOCATOR,
h'fe80000000000000c0011001FEEF0000, UDP, 17000]
]
Figure 5: GRASP AN_ACP example
The formal CDDL definition is:
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flood-message = [M_FLOOD, session-id, initiator, ttl,
+[objective, (locator-option / [])]]
objective = ["AN_ACP", objective-flags, loop-count,
objective-value]
objective-flags = sync-only ; as in the GRASP specification
sync-only = 4 ; M_FLOOD only requires synchronization
loop-count = 1 ; limit to link-local operation
objective-value = method
method = "IKEv2" / "DTLS" ; or future standard methods
Figure 6: GRASP AN_ACP definition
The objective-flags field is set to indicate synchronization.
The loop-count is fixed at 1 since this is a link-local operation.
In the above example the RECOMMENDED period of sending of the
objective is 60 seconds. The indicated ttl of 210000 msec means that
the objective would be cached by ACP nodes even when two out of three
messages are dropped in transit.
The session-id is a random number used for loop prevention
(distinguishing a message from a prior instance of the same message).
In DULL this field is irrelevant but must still be set according to
the GRASP specification.
The originator MUST be the IPv6 link local address of the originating
ACP node on the sending interface.
The 'objective-value' parameter is a string indicating the secure
channel protocol available at the specified or implied locator.
The locator-option is optional and only required when the secure
channel protocol is not offered at a well-defined port number, or if
there is no well-defined port number.
"IKEv2" is the abbreviation for "Internet Key Exchange protocol
version 2", as defined in [RFC7296]. It is the main protocol used by
the Internet IP security architecture (IPsec). We therefore use the
term "IKEv2" and not "IPsec" in the GRASP definitions and example
above. "IKEv2" has a well-defined port number 500, but in the above
example, the candidate ACP neighbor is offering ACP secure channel
negotiation via IKEv2 on port 15000 (for the sake of creating a non-
standard example).
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"DTLS" indicates datagram Transport Layer Security version 1.2.
There is no default UDP port, it must always be locally assigned by
the node. See Section 6.7.2.
If a locator is included, it MUST be an O_IPv6_LOCATOR, and the IPv6
address MUST be the same as the initiator address (these are DULL
requirements to minimize third party DoS attacks).
The secure channel methods defined in this document use the objective
values of "IKEv2" and "DTLS". There is no distinction between IKEv2
native and GRE-IKEv2 because this is purely negotiated via IKEv2.
A node that supports more than one secure channel protocol method
needs to flood multiple versions of the "AN_ACP" objective so that
each method can be accompanied by its own locator-option. This can
use a single GRASP M_FLOOD message as shown in Figure 5.
Note that a node serving both as an ACP node and BRSKI Join Proxy may
choose to distribute the "AN_ACP" objective and the respective BRSKI
in the same M_FLOOD message, since GRASP allows multiple objectives
in one message. This may be impractical though if ACP and BRSKI
operations are implemented via separate software modules / ASAs.
The result of the discovery is the IPv6 link-local address of the
neighbor as well as its supported secure channel protocols (and non-
standard port they are running on). It is stored in the ACP
Adjacency Table, see Section 6.2 which then drives the further
building of the ACP to that neighbor.
6.4. Candidate ACP Neighbor Selection
An ACP node must determine to which other ACP nodes in the adjacency
table it should build an ACP connection. This is based on the
information in the ACP Adjacency table.
The ACP is established exclusively between nodes in the same domain.
This includes all routing subdomains. Appendix A.7 explains how ACP
connections across multiple routing subdomains are special.
The result of the candidate ACP neighbor selection process is a list
of adjacent or configured autonomic neighbors to which an ACP channel
should be established. The next step begins that channel
establishment.
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6.5. Channel Selection
To avoid attacks, initial discovery of candidate ACP peers cannot
include any non-protected negotiation. To avoid re-inventing and
validating security association mechanisms, the next step after
discovering the address of a candidate neighbor can only be to try
first to establish a security association with that neighbor using a
well-known security association method.
At this time in the lifecycle of ACP nodes, it is unclear whether it
is feasible to even decide on a single MTI (mandatory to implement)
security association protocol across all ACP nodes.
From the use-cases it seems clear that not all type of ACP nodes can
or need to connect directly to each other or are able to support or
prefer all possible mechanisms. For example, code space limited IoT
devices may only support DTLS because that code exists already on
them for end-to-end security, but low-end in-ceiling L2 switches may
only want to support Media Access Control Security (MacSec, see
802.1AE ([MACSEC]) because that is also supported in their chips.
Only a flexible gateway device may need to support both of these
mechanisms and potentially more.
To support extensible secure channel protocol selection without a
single common MTI protocol, ACP nodes must try all the ACP secure
channel protocols it supports and that are feasible because the
candidate ACP neighbor also announced them via its AN_ACP GRASP
parameters (these are called the "feasible" ACP secure channel
protocols).
To ensure that the selection of the secure channel protocols always
succeeds in a predictable fashion without blocking, the following
rules apply:
o An ACP node may choose to attempt initiate the different feasible
ACP secure channel protocols it supports according to its local
policies sequentially or in parallel, but it MUST support acting
as a responder to all of them in parallel.
o Once the first secure channel protocol succeeds, the two peers
know each other's certificates because they must be used by all
secure channel protocols for mutual authentication. The node with
the lower Node-ID in the ACP address becomes Bob, the one with the
higher Node-ID in the certificate Alice.
o Bob becomes passive, he does not attempt to further initiate ACP
secure channel protocols with Alice and does not consider it to be
an error when Alice closes secure channels. Alice becomes the
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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 prefers and the security association
succeeded. The roles of Bob and Alice are then assigned. At this
stage, the protocol may not even have completed negotiating a common
security profile. The protocol could for example be IPsec via IKEv2
("IP security", see [RFC4301] and "Internet Key Exchange protocol
version 2", see [RFC7296]. It is now up to Alice to decide how to
proceed. Even if the IPsec connection from Bob succeeded, Alice
might prefer another secure protocol over IPsec (e.g., FOOBAR), and
try to set that up with Bob. If that preference of Alice succeeds,
she would close the IPsec connection. If no better protocol attempt
succeeds, she would keep the IPsec connection.
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 node must not
assume that neighbors with the same L2 or link-local IPv6 addresses
on different L2 interfaces are the same node. This can only be
determined after examining the certificate after a successful
security association attempt.
6.6. Candidate ACP Neighbor verification
Independent of the security association protocol chosen, candidate
ACP neighbors need to be authenticated based on their domain
certificate. This implies that any secure channel protocol MUST
support certificate based authentication that can support the ACP
domain membership check as defined in Section 6.1.2. If it fails,
the connection attempt is aborted and an error logged. Attempts to
reconnect MUST be throttled. The RECOMMENDED default is exponential
backoff with a a minimum delay of 10 seconds and a maximum delay of
640 seconds.
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 ACP node announces its ability to support IKEv2 as the ACP secure
channel protocol in GRASP as "IKEv2".
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6.7.1.1. Native IPsec
To run ACP via IPsec natively, no further IANA assignments/
definitions are required. An ACP node that is supporting native
IPsec MUST use IPsec security setup via IKEv2, tunnel mode, local and
peer link-local IPv6 addresses used for encapsulation. It MUST then
support ESP with AES256 for encryption and SHA256 hash and MUST NOT
permit weaker crypto options.
In terms of IKEv2, this means the initiator will offer to support
IPsec tunnel mode with next protocol equal 41 (IPv6).
IPsec tunnel mode is required because the ACP will route/forward
packets received from any other ACP node across the ACP secure
channels, and not only its own generated ACP packets. With IPsec
transport mode, it would only be possible to send packets originated
by the ACP node itself.
ESP is used because ACP mandates the use of encryption for ACP secure
channels.
6.7.1.2. IPsec with GRE encapsulation
In network devices it is often more common to implement high
performance virtual interfaces on top of GRE encapsulation than on
top of a "native" IPsec association (without any other encapsulation
than those defined by IPsec). On those devices it may be beneficial
to run the ACP secure channel on top of GRE protected by the IPsec
association.
To run ACP via GRE/IPsec, no further IANA assignments/definitions are
required. An ACP node that is supporting ACP via GRE/IPsec MUST then
support IPsec security setup via IKEv2, IPsec transport mode, local
and peer link-local IPv6 addresses used for encapsulation, ESP with
AES256 encryption and SHA256 hash.
When GRE is used, transport mode is sufficient because the routed ACP
packets are not "tunneled" by IPsec but rather by GRE: IPsec only has
to deal with the GRE/IP packet which always uses the local and peer
link-local IPv6 addresses and is therefore applicable to transport
mode.
ESP is used because ACP mandates the use of encryption for ACP secure
channels.
In terms of IKEv2 negotiation, this means the initiator must offer to
support IPsec transport mode with next protocol equal to GRE (47)
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followed by the offer for native IPsec as described above (because
that option is mandatory to support).
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 ACP nodes supporting DTLS as a
secure channel protocol MUST support AES256 encryption and MUST 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
As explained in the beginning of Section 6.5, there is no single
secure channel mechanism mandated for all ACP nodes. Instead, this
section defines two ACP profiles (baseline and constrained) for ACP
nodes that do introduce such requirements.
A baseline ACP node MUST support IPsec natively and MAY support IPsec
via GRE. A constrained ACP node that can not support IPsec MUST
support DTLS. An ACP node connecting an area of constrained ACP
nodes with an area of baseline ACP nodes MUST therefore support IPsec
and DTLS and supports threefore the baseline and constrained profile.
ACP nodes need to specify in documentation the set of secure ACP
mechanisms they support and should declare which profile they support
according to above requirements.
An ACP secure channel MUST immediately be terminated when the
lifetime of any certificate in the chain used to authenticate the
neighbor expires or becomes revoked. Note that this is not standard
behavior in secure channel protocols such as IPsec because the
certificate authentication only influences the setup of the secure
channel in these protocols.
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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. The function in GRASP that makes it fundamental
as a service of the ACP is the ability to provide ACP wide service
discovery (using objectives in GRASP).
ACP provides IP unicast routing via the RPL routing protocol (see
Section 6.11).
The ACP does not use IP multicast routing nor does it provide generic
IP multicast services (the handling of GRASP link-local multicast
messages is explained in Section 6.8.2). Instead, the ACP provides
service discovery via the objective discovery/announcement and
negotiation mechanisms of the ACP GRASP instance (services are a form
of objectives). These mechanisms use hop-by-hop reliable flooding of
GRASP messages for both service discovery (GRASP M_DISCOVERY
messages) and service announcement (GRASP M_FLOOD messages).
See Appendix A.5 for discussion about this design choice of the ACP.
6.8.2. ACP as the Security and Transport substrate for GRASP
In the terminology of GRASP ([I-D.ietf-anima-grasp]), the ACP is the
security and transport substrate for the GRASP instance run inside
the ACP ("ACP GRASP").
This means that the ACP is responsible for ensuring that this
instance of GRASP is only sending messages across the ACP GRASP
virtual interfaces. Whenever the ACP adds or deletes such an
interface because of new ACP secure channels or loss thereof, the ACP
needs to indicate this to the ACP instance of GRASP. The ACP exists
also in the absence of any active ACP neighbors. It is created when
the node has a domain certificate, and continues to exist even if all
of its neighbors cease operation.
In this case ASAs using GRASP running on the same node would still
need to be able to discover each other's objectives. When the ACP
does not exist, ASAs leveraging the ACP instance of GRASP via APIs
MUST still be able to operate, and MUST be able to understand that
there is no ACP and that therefore the ACP instance of GRASP can not
operate.
The way ACP acts as the security and transport substrate for GRASP is
visualized in the following picture:
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..............................ACP..............................
. .
. /-GRASP-flooding-\ ACP GRASP instance .
. / \ A
. GRASP GRASP GRASP C
. link-local unicast link-local P
. multicast messages multicast .
. messages | messages .
. | | | .
...............................................................
. v v v ACP security and transport .
. | | | substrate for GRASP .
. | | | .
. | ACP GRASP | - ACP GRASP A
. | Loopback | Loopback interface C
. | interface | - ACP-cert auth P
. | TLS | .
. ACP GRASP | ACP GRASP - ACP GRASP virtual .
. subnet1 | subnet2 virtual interfaces .
. TCP | TCP .
. | | | .
...............................................................
. | | | ^^^ Users of ACP (GRASP/ASA) .
. | | | ACP interfaces/addressing .
. | | | .
. | | | A
. | ACP-Loopback Interf.| <- ACP Loopback interface C
. | ACP-address | - address (global ULA) P
. subnet1 | subnet2 <- ACP virtual interfaces .
. link-local | link-local - link-local addresses .
...............................................................
. | | | ACP routing and forwarding .
. | RPL-routing | .
. | /IP-Forwarding\ | A
. | / \ | C
. ACP IPv6 packets ACP IPv6 packets P
. |/ \| .
. IPsec/DTLS IPsec/DTLS - ACP-cert auth .
...............................................................
| | Data-Plane
| |
| | - ACP secure channel
link-local link-local - encapsulation addresses
subnet1 subnet2 - Data-Plane interfaces
| |
ACP-Nbr1 ACP-Nbr2
Figure 7: ACP as security and transport substrate for GRASP
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GRASP unicast messages inside the ACP always use the ACP address.
Link-local ACP addresses must not be used inside objectives. GRASP
unicast messages inside the ACP are transported via TLS 1.2
([RFC5246]) connections with AES256 encryption and SHA256. Mutual
authentication uses the ACP domain membership check defined in
(Section 6.1.2).
GRASP link-local multicast messages are targeted for a specific ACP
virtual interface (as defined Section 6.12.5) but are sent by the ACP
into an ACP GRASP virtual interface that is constructed from the TCP
connection(s) to the IPv6 link-local neighbor address(es) on the
underlying ACP virtual interface. If the ACP GRASP virtual interface
has two or more neighbors, the GRASP link-local multicast messages
are replicated to all neighbor TCP connections.
TLS and TLS connections for GRASP in the ACP use the IANA assigned
TCP port for GRASP (7107). Effectively the transport stack is
expected to be TLS for connections from/to the ACP address (e.g.,
global scope address(es)) and TCP for connections from/to link-local
addresses on the ACP virtual interfaces. The latter ones are only
used for flooding of GRASP messages.
6.8.2.1. Discussion
TCP encapsulation for GRASP M_DISCOVERY and M_FLOOD link local
messages is used because these messages are flooded across
potentially many hops to all ACP nodes and a single link with even
temporary packet loss issues (e.g., WiFi/Powerline link) can reduce
the probability for loss free transmission so much that applications
would want to increase the frequency with which they send these
messages. Such shorter periodic retransmission of datagrams would
result in more traffic and processing overhead in the ACP than the
hop-by-hop reliable retransmission mechanism by TCP and duplicate
elimination by GRASP.
TLS is mandated for GRASP non-link-local unicast because the ACP
secure channel mandatory authentication and encryption protects only
against attacks from the outside but not against attacks from the
inside: Compromised ACP members that have (not yet) been detected and
removed (e.g., via domain certificate revocation / expiry).
If GRASP peer connections would just use TCP, compromised ACP members
could simply eavesdrop passively on GRASP peer connections for whom
they are on-path ("Man In The Middle" - MITM). Or intercept and
modify them. With TLS, it is not possible to completely eliminate
problems with compromised ACP members, but attacks are a lot more
complex:
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Eavesdropping/spoofing by a compromised ACP node is still possible
because in the model of the ACP and GRASP, the provider and consumer
of an objective have initially no unique information (such as an
identity) about the other side which would allow them to distinguish
a benevolent from a compromised peer. The compromised ACP node would
simply announce the objective as well, potentially filter the
original objective in GRASP when it is a MITM and act as an
application level proxy. This of course requires that the
compromised ACP node understand the semantics of the GRASP
negotiation to an extent that allows it to proxy it without being
detected, but in an ACP environment this is quite likely public
knowledge or even standardized.
The GRASP TLS connections are run the same as any other ACP traffic
through the ACP secure channels. This leads to double
authentication/encryption, which has the following benefits:
o Secure channel methods such as IPsec may provide protecation
against additional attacks from such as reset-attacks.
o The secure channel method may leverage hardware acceleration and
there may be little or no gain in eliminating it.
o There is no different security model for ACP GRASP from other ACP
traffic. Instead, there is just another layer of protection
against certain attacks from the inside which is important due to
the role of GRASP in the ACP.
6.9. Context Separation
The ACP is in a separate context from the normal Data-Plane of the
node. This context includes the ACP channels' IPv6 forwarding and
routing as well as any required higher layer ACP functions.
In classical network system, a dedicated so called Virtual routing
and forwarding instance (VRF) is one logical implementation option
for the ACP. If possible by the systems software architecture,
separation options that minimize shared components are preferred,
such as a logical container or virtual machine instance. The context
for the ACP needs to be established automatically during bootstrap of
a node. As much as possible it should be protected from being
modified unintentionally by ("Data-Plane") configuration.
Context separation improves security, because the ACP is not
reachable from the Data-Plane routing or forwarding table(s). Also,
configuration errors from the Data-Plane setup do not affect the ACP.
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6.10. Addressing inside the ACP
The channels explained above typically only establish communication
between two adjacent nodes. In order for communication to happen
across multiple hops, the autonomic control plane requires ACP
network wide valid addresses and routing. Each ACP node must create
a Loopback interface with an ACP network wide unique address inside
the ACP context (as explained in in Section 6.9). This address may
be used also in other virtual contexts.
With the algorithm introduced here, all ACP nodes in the same routing
subdomain have the same /48 ULA prefix. Conversely, ULA global IDs
from different domains are unlikely to clash, such that two ACP
networks can be merged, as long as the policy allows that merge. See
also Section 9.1 for a discussion on merging domains.
Links inside the ACP only use link-local IPv6 addressing, such that
each nodes ACP only requires one routable virtual address.
6.10.1. Fundamental Concepts of Autonomic Addressing
o Usage: Autonomic addresses are exclusively used for self-
management functions inside a trusted domain. They are not used
for user traffic. Communications with entities outside the
trusted domain use another address space, for example normally
managed routable address space (called "Data-Plane" in this
document).
o Separation: Autonomic address space is used separately from user
address space and other address realms. This supports the
robustness requirement.
o Loopback-only: Only ACP Loopback interfaces (and potentially those
configured for "ACP connect", see Section 8.1) carry routable
address(es); all other interfaces (called ACP virtual interfaces)
only use IPv6 link local addresses. The usage of IPv6 link local
addressing is discussed in [RFC7404].
o Use-ULA: For Loopback interfaces of ACP nodes, we use Unique Local
Addresses (ULA), as defined in [RFC4193] with L=1 (as defined in
section 3.1 of [RFC4193]). Note that the random hash for ACP
Loopback addresses uses the definition in Section 6.10.2 and not
the one of [RFC4193] section 3.2.2.
o No external connectivity: They do not provide access to the
Internet. If a node requires further reaching connectivity, it
should use another, traditionally managed address scheme in
parallel.
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o Addresses in the ACP are permanent, and do not support temporary
addresses as defined in [RFC4941].
o Addresses in the ACP are not considered sensitive on privacy
grounds because ACP nodes are not expected to be end-user devices.
Therefore, ACP addresses do not need to be pseudo-random as
discussed in [RFC7721]. Because they are not propagated to
untrusted (non ACP) nodes and stay within a domain (of trust), we
also consider them not to be subject to scanning attacks.
The ACP is based exclusively on IPv6 addressing, for a variety of
reasons:
o Simplicity, reliability and scale: If other network layer
protocols were supported, each would have to have its own set of
security associations, routing table and process, etc.
o Autonomic functions do not require IPv4: Autonomic functions and
autonomic service agents are new concepts. They can be
exclusively built on IPv6 from day one. There is no need for
backward compatibility.
o OAM protocols do not require IPv4: The ACP may carry OAM
protocols. All relevant protocols (SNMP, TFTP, SSH, SCP, Radius,
Diameter, ...) are available in IPv6. See also [RFC8368] for how
ACP could be made to interoperate with IPv4 only OAM.
6.10.2. The ACP Addressing Base Scheme
The Base ULA addressing scheme for ACP nodes has the following
format:
8 40 2 78
+--+-------------------------+------+------------------------------+
|fd| hash(routing-subdomain) | Type | (sub-scheme) |
+--+-------------------------+------+------------------------------+
Figure 8: ACP Addressing Base Scheme
The first 48 bits follow the ULA scheme, as defined in [RFC4193], to
which a type field is added:
o "fd" identifies a locally defined ULA address.
o The 40 bits ULA "global ID" (term from [RFC4193]) for ACP
addresses carried in the domain information field of domain
certificates are the first 40 bits of the SHA256 hash of the
routing subdomain from the same domain information field. In the
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example of Section 6.1.1, the routing subdomain is
"area51.research.acp.example.com" and the 40 bits ULA "global ID"
89b714f3db.
o To allow for extensibility, the fact that the ULA "global ID" is a
hash of the routing subdomain SHOULD NOT be assumed by any ACP
node during normal operations. The hash function is only executed
during the creation of the certificate. If BRSKI is used then the
BRSKI registrar will create the domain information field in
response to the EST Certificate Signing Request (CSR) Attribute
Request message by the pledge.
o Type: This field allows different address sub-schemes. This
addresses the "upgradability" requirement. Assignment of types
for this field will be maintained by IANA.
The sub-scheme may imply a range or set of addresses assigned to the
node, this is called the ACP address range/set and explained in each
sub-scheme.
Please refer to Section 6.10.7 and Appendix A.1 for further
explanations why the following Sub-Addressing schemes are used and
why multiple are necessary.
6.10.3. ACP Zone Addressing Sub-Scheme
The sub-scheme defined here is defined by the Type value 00b (zero)
in the base scheme and 0 in the Z bit.
64 64
+-----------------+---+---------++-----------------------------+---+
| (base scheme) | Z | Zone-ID || Node-ID |
| | | || Registrar-ID | Node-Number| V |
+-----------------+---+---------++--------------+--------------+---+
50 1 13 48 15 1
Figure 9: ACP Zone Addressing Sub-Scheme
The fields are defined as follows:
o Zone-ID: If set to all zero bits: The Node-ID bits are used as an
identifier (as opposed to a locator). This results in a non-
hierarchical, flat addressing scheme. Any other value indicates a
zone. See Section 6.10.3.1 on how this field is used in detail.
o Z: MUST be 0.
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o Node-ID: A unique value for each node.
The 64 bit Node-ID is derived and composed as follows:
o Registrar-ID (48 bit): A number unique inside the domain that
identifies the ACP registrar which assigned the Node-ID to the
node. A MAC address of the ACP registrar can be used for this
purpose.
o Node-Number: A number which is unique for a given ACP registrar,
to identify the node. This can be a sequentially assigned number.
o V (1 bit): Virtualization bit: 0: Indicates the ACP itself ("ACP
node base system); 1: Indicates the optional "host" context on the
ACP node (see below).
In the ACP Zone Addressing Sub-Scheme, the ACP address in the
certificate has Zone-ID and V fields as all zero bits. The ACP
address set includes addresses with any Zone-ID value and any V
value.
The "Node-ID" itself is unique in a domain (i.e., the Zone-ID is not
required for uniqueness). Therefore, a node can be addressed either
as part of a flat hierarchy (Zone-ID = 0), or with an aggregation
scheme (any other Zone-ID). An address with Zone-ID = 0 is an
identifier, with a Zone-ID !=0 it is a locator. See Section 6.10.3.1
for more details.
The Virtual bit in this sub-scheme allows the easy addition of the
ACP as a component to existing systems without causing problems in
the port number space between the services in the ACP and the
existing system. V:0 is the ACP router (autonomic node base system),
V:1 is the host with pre-existing transport endpoints on it that
could collide with the transport endpoints used by the ACP router.
The ACP host could for example have a p2p virtual interface with the
V:0 address as its router into the ACP. Depending on the software
design of ASAs, which is outside the scope of this specification,
they may use the V:0 or V:1 address.
The location of the V bit(s) at the end of the address allows the
announcement of a single prefix for each ACP node. For example, in a
network with 20,000 ACP nodes, this avoid 20,000 additional routes in
the routing table.
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6.10.3.1. Usage of the Zone-ID Field
The Zone-ID allows for the introduction of route prefixes in the
addressing scheme.
Zone-ID = 0 is the default addressing scheme in an ACP domain. Every
ACP node with a Zone Addressing Sub-Scheme address MUST respond to
its ACP address with Zone-ID = 0. Used on its own this leads to a
non-hierarchical address scheme, which is suitable for networks up to
a certain size. Zone-ID = 0 addresses act as identifiers for the
nodes, and aggregation of these address in the ACP routing table is
not possible.
If aggregation is required, the 13 bit Zone-ID value allows for up to
8191 zones. The allocation of Zone-ID's may either happen
automatically through a to-be-defined algorithm; or it could be
configured and maintained explicitly.
If a node learns (see Appendix A.10.1) that it is part of a zone, it
MUST also respond to its ACP address with that Zone-ID. In this case
the ACP Loopback is configured with two ACP addresses: One for Zone-
ID = 0 and one for the assigned Zone-ID. This method allows for a
smooth transition between a flat addressing scheme and a hierarchical
one.
A node knowing it is in a zone MUST also use that Zone-ID != 0
address in GRASP locator fields. This eliminates the use of the
identifier address (Zone-ID = 0) in forwarding and the need for
network wide reachability of those non-aggregatable identifier
addresses. Zone-ID != 0 addresses are assumed to be aggregatable in
routing/forwarding based on how they are allocated in the ACP
topology.
Note: The Zone-ID is one method to introduce structure or hierarchy
into the ACP. Another way is the use of the routing subdomain field
in the ACP that leads to multiple /48 Global IDs within an ACP
domain.
Note: Zones and Zone-ID as defined here are not related to [RFC4007]
zones or zone_id. ACP zone addresses are not scoped (reachable only
from within an RFC4007 zone) but reachable across the whole ACP. An
RFC4007 zone_id is a zone index that has only local significance on a
node, whereas an ACP Zone-ID is an identifier for an ACP zone that is
unique across that ACP.
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6.10.4. ACP Manual Addressing Sub-Scheme
The sub-scheme defined here is defined by the Type value 00b (zero)
in the base scheme and 1 in the Z bit.
64 64
+---------------------+---+----------++-----------------------------+
| (base scheme) | Z | Subnet-ID|| Interface Identifier |
+---------------------+---+----------++-----------------------------+
50 1 13
Figure 10: ACP Manual Addressing Sub-Scheme
The fields are defined as follows:
o Subnet-ID: Configured subnet identifier.
o Z: MUST be 1.
o Interface Identifier.
This sub-scheme is meant for "manual" allocation to subnets where the
other addressing schemes cannot be used. The primary use case is for
assignment to ACP connect subnets (see Section 8.1.1).
"Manual" means that allocations of the Subnet-ID need to be done
today with pre-existing, non-autonomic mechanisms. Every subnet that
uses this addressing sub-scheme needs to use a unique Subnet-ID
(unless some anycast setup is done).
The Z bit field was added to distinguish Zone addressing and manual
addressing sub-schemes without requiring one more bit in the base
scheme and therefore allowing for the Vlong scheme (described below)
to have one more bit available.
Manual addressing sub-scheme addresses SHOULD NOT be used in ACP
domain certificates. Any node capable to build ACP secure channels
and permitted by Registrar policy to participate in building ACP
secure channels SHOULD receive an ACP address (prefix) from one of
the other ACP addressing sub-schemes. Nodes not capable (or
permitted) to participate in ACP secure channels can connect to the
ACP via ACP connect interfaces of ACP edge nodes (see xref
target="ACPconnect"/>), without setting up an ACP secure channel.
Their ACP domain certificate MUST include an empty acp-address to
indicate that their ACP domain certificate is only usable for non-
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ACP secure channel authentication, such as end-to-end transport
connections across the ACP or Data-Plane.
Address management of ACP connect subnets is done using traditional
assignment methods and existing IPv6 protocols. See Section 8.1.3
for details.
6.10.5. ACP Vlong Addressing Sub-Scheme
The sub-scheme defined here is defined by the Type value 01b (one) in
the base scheme.
50 78
+---------------------++-----------------------------+----------+
| (base scheme) || Node-ID |
| || Registrar-ID | Node-Number| V |
+---------------------++--------------+--------------+----------+
50 46 24/16 8/16
Figure 11: ACP Vlong Addressing Sub-Scheme
This addressing scheme foregoes the Zone-ID field to allow for
larger, flatter routed networks (e.g., as in IoT) with 8421376 Node-
Numbers (2^23+2^15). It also allows for up to 2^16 (i.e. 65536)
different virtualized addresses within a node, which could be used to
address individual software components in an ACP node.
The fields are the same as in the Zone-ID sub-scheme with the
following refinements:
o V: Virtualization bit: Values 0 and 1 are assigned in the same way
as in the Zone-ID sub-scheme.
o Registrar-ID: To maximize Node-Number and V, the Registrar-ID is
reduced to 46 bits. This still permits the use of the MAC address
of an ACP registrar by removing the V and U bits from the 48 bits
of a MAC address (those two bits are never unique, so they cannot
be used to distinguish MAC addresses).
o If the first bit of the "Node-Number" is "1", then the Node-Number
is 16 bit long and the V field is 16 bit long. Otherwise the
Node-Number is 24 bit long and the V field is 8 bit long.
"0" bit Node-Numbers are intended to be used for "general purpose"
ACP nodes that would potentially have a limited number (< 256) of
clients (ASA/Autonomic Functions or legacy services) of the ACP that
require separate V(irtual) addresses. "1" bit Node-Numbers are
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intended for ACP nodes that are ACP edge nodes (see Section 8.1.1) or
that have a large number of clients requiring separate V(irtual)
addresses. For example large SDN controllers with container modular
software architecture (see Section 8.1.2).
In the Vlong addressing sub-scheme, the ACP address in the
certificate has all V field bits as zero. The ACP address set for
the node includes any V value.
6.10.6. Other ACP Addressing Sub-Schemes
Before further addressing sub-schemes are defined, experience with
the schemes defined here should be collected. The schemes defined in
this document have been devised to allow hopefully sufficiently
flexible setup of ACPs for a variety of situation. These reasons
also lead to the fairly liberal use of address space: The Zone
Addressing Sub-Scheme is intended to enable optimized routing in
large networks by reserving bits for Zone-ID's. The Vlong addressing
sub-scheme enables the allocation of 8/16 bit of addresses inside
individual ACP nodes. Both address spaces allow distributed,
uncoordinated allocation of node addresses by reserving bits for the
registrar-ID field in the address.
IANA is asked need to assign a new "type" for each new addressing
sub-scheme. With the current allocations, only 2 more schemes are
possible, so the last addressing scheme MUST provide further
extensions (e.g., by reserving bits from it for further extensions).
6.10.7. ACP Registrars
The ACP address prefix is assigned to the ACP node during enrollment/
provisioning of the ACP domain certificate to the ACP node. It is
intended to persist unchanged through the lifetime of the ACP node.
Because of the ACP addressing sub-schemes explained above, ACP nodes
for a single ACP domain can be enrolled by multiple distributed and
uncoordinated entities called ACP registrars. These ACP registrars
are responsible to enroll ACP domain certificates and associated
trust anchor(s) to candidate ACP nodes and are also responsible that
an ACP domain information field is included in the ACP domain
certificate.
6.10.7.1. Use of BRSKI or other Mechanism/Protocols
Any protocols or mechanisms may be used as ACP registrars, as long as
the resulting ACP certificate and trust anchors allow to perform the
ACP domain membership described in Section 6.1.2 with other ACP
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domain members, and meet the ACP addressing requirements for its ACP
domain information field as described further below in this section.
An ACP registrar could be a person deciding whether to enroll a
candidate ACP node and then orchestrating the enrollment of the ACP
certificate and associated trust anchor, using command line or web
based commands on the candidate ACP node and trust anchor to generate
and sign the ACP domain certificate and configure certificate and
trust anchors onto the node.
The only currently defined protocol for ACP registrars is BRSKI
([I-D.ietf-anima-bootstrapping-keyinfra]). When BRSKI is used, the
ACP nodes are called ANI nodes, and the ACP registrars are called
BRSKI or ANI registrars. The BRSKI specification does not define the
handling of the ACP domain information field because the rules do not
depend on BRSKI but apply equally to any protocols/mechanisms an ACP
registrar may use.
6.10.7.2. Unique Address/Prefix allocation
ACP registrars MUST NOT allocate ACP address prefixes to ACP nodes
via the ACP domain information field that would collide with the ACP
address prefixes of other ACP nodes in the same ACP domain. This
includes both prefixes allocated by the same ACP registrar to
different ACP nodes as well as prefixes allocated by other ACP
registrars for the same ACP domain.
For this purpose, an ACP registrar MUST have one or more unique 46
bit identifiers called Registrar-IDs used to allocate ACP address
prefixes. The lower 46 bits of a EUI-48 MAC addresses are globally
unique 46 bit identifiers, so ACP registrars with known unique EUI-48
MAC addresses can use these as Registrar-IDs. Registrar-IDs do not
need to be globally unique but only unique across the set of ACP
registrars for an ACP domain, so other means to assign unique
Registrar-IDs to ACP registrars can be used, such as configuration on
the ACP registrars.
When the candidate ACP device (called Pledge in BRSKI) is to be
enrolled into an ACP domain, the ACP registrar needs to allocate a
unique ACP address to the node and ensure that the ACP certificate
gets a domain information field (Section 6.1.1) with the appropriate
information - ACP domain-name, ACP-address, and so on. If the ACP
registrar uses BRSKI, it signals the ACP information field to the
Pledge via the EST /csraddrs command (see
[I-D.ietf-anima-bootstrapping-keyinfra], section 5.8.2 - "EST CSR
Attributes").
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[RFC Editor: please update reference to section 5.8.2 accordingly
with latest BRSKI draft at time of publishing, or RFC]
6.10.7.3. Addressing Sub-Scheme Policies
The ACP registrar selects for the candidate ACP node a unique address
prefix from an appropriate ACP addressing sub-scheme, either a zone
addressing sub-scheme prefix (see Section 6.10.3), or a Vlong
addressing sub-scheme prefix (see Section 6.10.5). The assigned ACP
address prefix encoded in the domain information field of the ACP
domain certificate indicates to the ACP node its ACP address
information. The sub-addressing scheme indicates the prefix length:
/127 for zone address sub-scheme, /120 or /112 for Vlong address sub-
scheme. The first address of the prefix is the ACP address, all
other addresses in the prefix are for other uses by the ACP node as
described in the zone and Vlong addressing sub scheme sections. The
ACP address prefix itself is then signaled by the ACP node into the
ACP routing protocol (see Section 6.11) to establish IPv6
reachability across the ACP.
The choice of addressing sub-scheme and prefix-length in the Vlong
address sub-scheme is subject to ACP registrar policy. It could be
an ACP domain wide policy, or a per ACP node or per ACP node type
policy. For example, in BRSKI, the ACP registrar is aware of the
IDevID of the candidate ACP node, which contains a serialNnumber that
is typically indicating the nodes vendor and device type and can be
used to drive a policy selecting an appropriate addressing sub-scheme
for the (class of) node(s).
ACP registrars SHOULD default to allocate ACP zone sub-address scheme
addresses with Subnet-ID 0. Allocation and use of zone sub-addresses
with Subnet-ID != 0 is outside the scope of this specification
because it would need to go along with rules for extending ACP
routing to multiple zones, which is outside the scope of this
specification.
ACP registrars that can use the IDevID of a candidate ACP device
SHOULD be able to choose the zone vs. Vlong sub-address scheme for
ACP nodes based on the serialNumber of the IDevID, for example by the
PID (Product Identifier) part which identifies the product type, or
the complete serialNumber.
In a simple allocation scheme, an ACP registrar remembers
persistently across reboots for its currently used Registrar-ID and
for each addressing scheme (zone with Subnet-ID 0, Vlong with /112,
Vlong with /120), the next Node-Number available for allocation and
increases it after successful enrollment to an ACP node. In this
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simple allocation scheme, the ACP registrar would not recycle ACP
address prefixes from no longer used ACP nodes.
6.10.7.4. Address/Prefix Persistence
When an ACP domain certificate is renewed or rekeyed via EST or other
mechanisms, the ACP address/prefix in the ACP domain information
field MUST be maintained unless security issues or violations of the
unique address assignment requirements exist or are suspected by the
ACP registrar. Even when the renewing/rekeying ACP registrar is not
the same as the one that enrolled the prior ACP certificate. See
Section 10.2.4 for an example. ACP address information SHOULD also
be maintained even after an ACP certificate did expire or failed.
See Section 6.1.3.5 and Section 6.1.3.6.
6.10.7.5. Further Details
Section 10.2 discusses further informative details of ACP registrars:
What interactions registrars need, what parameters they require,
certificate renewal and limitations, use of sub-CAs on registrars and
centralized policy control.
6.11. Routing in the ACP
Once ULA address are set up all autonomic entities should run a
routing protocol within the autonomic control plane context. This
routing protocol distributes the ULA created in the previous section
for reachability. The use of the autonomic control plane specific
context eliminates the probable clash with Data-Plane routing tables
and also secures the ACP from interference from the configuration
mismatch or incorrect routing updates.
The establishment of the routing plane and its parameters are
automatic and strictly within the confines of the autonomic control
plane. Therefore, no explicit configuration is required.
All routing updates are automatically secured in transit as the
channels of the 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
Appendix A.4 for more details on the choice of RPL.
RPL adjacencies are set up across all ACP channels in the same domain
including all its routing subdomains. See Appendix A.7 for more
details.
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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.
6.11.1.1. Summary
In summary, the profile chosen for RPL is one that expects a fairly
reliable network with reasonably fast links so that RPL convergence
will be triggered immediately upon recognition of link failure/
recovery.
The key limitation of the chosen profile is that it is designed to
not require any Data-Plane 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 can
be handled as non-RPL-aware leafs (or "Internet") according to the
Data-Plane 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 forwarding
plane, especially to support devices with silicon forwarding planes
that can not support insertion/removal of these headers in silicon.
In this profile choice, RPL has no Data-Plane artifacts. A simple
destination prefix based upon the routing table is used. A
consequence of supporting only a single instanceID that is containing
one Destination Oriented Directed Acyclic Graph (DODAG), the ACP will
only accommodate only a single class of routing table and cannot
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 will reconfigure itself when it detects data plane forwarding
failures. See Appendix A.10.4 for more details.
The lack of RPL Packet Information (RPI, the IPv6 header for RPL
defined by [RFC6553]), means that the Data-Plane will have no rank
value that can be used to detect loops. As a result, traffic may
loop until the time-to-live (TTL) of the packet reaches zero. This
the same behavior as that of other IGPs that do not have the Data-
Plane options as RPL.
Since links in the ACP are assumed to be mostly reliable (or have
link layer protection against loss) and because there is no stretch
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according to Section 6.11.1.7, loops should be exceedingly rare
though.
There are a variety of mechanisms possible in RPL to further avoid
temporary loops: DODAG Information Objects (DIOs) SHOULD be sent
2...3 times to inform children when losing the last parent. The
technique in [RFC6550] section 8.2.2.6. (Detaching) SHOULD be
favored over that in section 8.2.2.5., (Poisoning) because it allows
local connectivity. Nodes SHOULD select more than one parent, at
least 3 if possible, and send Destination Advertisement Objects
(DAO)s to all of then in parallel.
Additionally, failed ACP tunnels will be detected by IKEv2 Dead Peer
Detection (which can function as a replacement for a Low-power and
Lossy Networks' (LLN's) Expected Transmission Count (ETX). A failure
of an ACP tunnel should signal the RPL control plane to pick a
different parent.
6.11.1.2. RPL Instances
Single RPL instance. Default RPLInstanceID = 0.
6.11.1.3. Storing vs. Non-Storing Mode
RPL Mode of Operations (MOP): MUST support mode 2 - "Storing Mode of
Operations with no multicast support". Implementations MAY support
mode 3 ("... with multicast support" as that is a superset of mode
2). Note: Root indicates mode in DIO flow.
6.11.1.4. 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.
6.11.1.5. Path Metric
Hopcount.
6.11.1.6. Objective Function
Objective Function (OF): Use OF0 [RFC6552]. No use of metric
containers.
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rank_factor: Derived from link speed: <= 100Mbps:
LOW_SPEED_FACTOR(5), else HIGH_SPEED_FACTOR(1)
6.11.1.7. DODAG Repair
Global Repair: we assume stable links and ranks (metrics), so no need
to periodically rebuild DODAG. DODAG version only incremented under
catastrophic events (e.g., administrative action).
Local Repair: As soon as link breakage is detected, send No-Path DAO
for all the targets that 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.
6.11.1.8. Multicast
Not used yet but possible because of the selected mode of operations.
6.11.1.9. Security
[RFC6550] security not used, substituted by ACP security.
6.11.1.10. P2P communications
Not used.
6.11.1.11. IPv6 address configuration
Every ACP node (RPL node) announces an IPv6 prefix covering the
address(es) used in the ACP node. The prefix length depends on the
chosen addressing sub-scheme of the ACP address provisioned into the
certificate of the ACP node, e.g., /127 for Zone Addressing Sub-
Scheme or /112 or /120 for Vlong addressing sub-scheme. See
Section 6.10 for more details.
Every ACP node MUST install a black hole (aka null) route for
whatever ACP address space that it advertises (i.e.: the /96 or
/127). This is avoid routing loops for addresses that an ACP node
has not (yet) used.
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6.11.1.12. Administrative parameters
Administrative Preference ([RFC6550], 3.2.6 - to become root):
Indicated in DODAGPreference field of DIO message.
o Explicit configured "root": 0b100
o ACP registrar (Default): 0b011
o ACP-connect (non-registrar): 0b010
o Default: 0b001.
6.11.1.13. RPL Data-Plane artifacts
RPI (RPL Packet Information [RFC6553]): Not used as there is only a
single instance, and data path validation is not being used.
SRH (RPL Source Routing - RFC6552): Not used. Storing mode is being
used.
6.11.1.14. Unknown Destinations
Because RPL minimizes the size of the routing and forwarding table,
prefixes reachable through the same interface as the RPL root are not
known on every ACP node. Therefore traffic to unknown destination
addresses can only be discovered at the RPL root. The RPL root
SHOULD have attach safe mechanisms to operationally discover and log
such packets.
6.12. General ACP Considerations
Since channels are by default established between adjacent neighbors,
the resulting overlay network does hop-by-hop encryption. Each node
decrypts incoming traffic from the ACP, and encrypts outgoing traffic
to its neighbors in the ACP. Routing is discussed in Section 6.11.
6.12.1. Performance
There are no performance requirements against ACP implementations
defined in this document because the performance requirements depend
on the intended use case. It is expected that full autonomic node
with a wide range of ASA can require high forwarding plane
performance in the ACP, for example for telemetry. Implementations
of ACP to solely support traditional/SDN style use cases can benefit
from ACP at lower performance, especially if the ACP is used only for
critical operations, e.g., when the Data-Plane is not available. The
design of the ACP as specified in this document is intended to
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support a wide range of performance options: It is intended to allow
software-only implementations at potentially low performance, but can
also support high performance options. See [RFC8368] for more
details.
6.12.2. Addressing of Secure Channels
In order to be independent of the Data-Plane (routing and addressing)
the GRASP discovered (autonomic) ACP secure channels use IPv6 link
local addresses between adjacent neighbors. Note: Section 8.2
specifies extensions in which secure channels are configured tunnels
operating over the Data-Plane, so those secure channels can not be
independent of the Data-Plane.
To avoid that Data-Plane configuration can impact the operations of
the IPv6 (link-local) interface/address used for ACP channels,
appropriate implementation considerations are required. If the IPv6
interface/link-local address is shared with the Data-Plane it needs
to be impossible to unconfigure/disable it through configuration.
Instead of sharing the IPv6 interface/link-local address, a separate
(virtual) interface with a separate IPv6 link-local addresss can be
used. For example, the ACP interface could be run over a separate
MAC addres of an underlying L2 (Ethernet) interface. For more
details and options, see Appendix A.10.2.
Note that other (non-ideal) implementation choices may introduce
additional undesired dependencies against the Data-Plane. For
example shared code and configuration of the secure channel protocols
(IPsec / DTLS).
6.12.3. MTU
The MTU for ACP secure channels must be derived locally from the
underlying link MTU minus the secure channel encapsulation overhead.
ACP secure Channel protocols do not need to perform MTU discovery
because they are built across L2 adjacencies - the MTU on both sides
connecting to the L2 connection are assumed to be consistent.
Extensions to ACP where the ACP is for example tunneled need to
consider how to guarantee MTU consistency. This is an issue of
tunnels, not an issue of running the ACP across a tunnel. Transport
stacks running across ACP can perform normal PMTUD (Path MTU
Discovery). Because the ACP is meant to be prioritize reliability
over performance, they MAY opt to only expect IPv6 minimum MTU (1280)
to avoid running into PMTUD implementation bugs or underlying link
MTU mismatch problems.
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6.12.4. Multiple links between nodes
If two nodes are connected via several links, the ACP SHOULD be
established across every link, but it is possible to establish the
ACP only on a sub-set of links. Having an ACP channel on every link
has a number of advantages, for example it allows for a faster
failover in case of link failure, and it reflects the physical
topology more closely. Using a subset of links (for example, a
single link), reduces resource consumption on the node, because state
needs to be kept per ACP channel. The negotiation scheme explained
in Section 6.5 allows Alice (the node with the higher ACP address) to
drop all but the desired ACP channels to Bob - and Bob will not re-
try to build these secure channels from his side unless Alice shows
up with a previously unknown GRASP announcement (e.g., on a different
link or with a different address announced in GRASP).
6.12.5. ACP interfaces
The ACP VRF has conceptually two type of interfaces: The "ACP
Loopback interface(s)" to which the ACP ULA address(es) are assigned
and the "ACP virtual interfaces" that are mapped to the ACP secure
channels.
The term "Loopback interface" was introduced initially to refer to an
internal interface on a node that would allow IP traffic between
transport endpoints on the node in the absence or failure of any or
all external interfaces, see [RFC4291] section 2.5.3.
Even though Loopback interfaces were originally designed to hold only
Loopback addresses not reachable from outside the node, these
interfaces are also commonly used today to hold addresses reachable
from the outside. They are meant to be reachable independent of any
external interface being operational, and therefore to be more
resilient. These addresses on Loopback interfaces can be thought of
as "node addresses" instead of "interface addresses", and that is
what ACP address(es) are. This construct makes it therefore possible
to address ACP nodes with a well-defined set of addresses independent
of the number of external interfaces.
For these reason, the ACP (ULA) address(es) are assigned to Loopback
interface(s).
Any type of ACP secure channels to another ACP node can be mapped to
ACP virtual interfaces in tollowing ways. This is independent of the
choosen secure channel protocol (IPsec, DTLS or other future protocol
- standards or non-standards):
ACP point-to-point virtual interface:
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Each ACP secure channel is mapped into a separate point-to-point ACP
virtual interface. If a physical subnet has more than two ACP
capable nodes (in the same domain), this implementation approach will
lead to a full mesh of ACP virtual interfaces between them.
ACP multi-access virtual interface:
In a more advanced implementation approach, the ACP will construct a
single multi-access ACP virtual interface for all ACP secure channels
to ACP capable nodes reachable across the same underlying (physical)
subnet. IPv6 link-local multicast packets sent into an ACP multi-
access virtual interface are replicated to every ACP secure channel
mapped into the ACP multicast-access virtual interface. IPv6 unicast
packets sent into an ACP multi-access virtual interface are sent to
the ACP secure channel that belongs to the ACP neighbor that is the
next-hop in the ACP forwarding table entry used to reach the packets
destination address.
There is no requirement for all ACP nodes on the same multi-access
subnet to use the same type of ACP virtual interface. This is purely
a node local decision.
ACP nodes MUST perform standard IPv6 operations across ACP virtual
interfaces including SLAAC (Stateless Address Auto-Configuration) -
[RFC4862]) to assign their IPv6 link local address on the ACP virtual
interface and ND (Neighbor Discovery - [RFC4861]) to discover which
IPv6 link-local neighbor address belongs to which ACP secure channel
mapped to the ACP virtual interface. This is independent of whether
the ACP virtual interface is point-to-point or multi-access.
"Optimistic Duplicate Address Detection (DAD)" according to [RFC4429]
is RECOMMENDED because the likelihood for duplicates between ACP
nodes is highly improbable as long as the address can be formed from
a globally unique local assigned identifier (e.g., EUI-48/EUI-64, see
below).
ACP nodes MAY reduce the amount of link-local IPv6 multicast packets
from ND by learning the IPv6 link-local neighbor address to ACP
secure channel mapping from other messages such as the source address
of IPv6 link-local multicast RPL messages - and therefore forego the
need to send Neighbor Solicitation messages.
The ACP virtual interface IPv6 link local address can be derived from
any appropriate local mechanism such as node local EUI-48 or EUI-64
("EUI" stands for "Extended Unique Identifier"). It MUST NOT depend
on something that is attackable from the Data-Plane such as the IPv6
link-local address of the underlying physical interface, which can be
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attacked by SLAAC, or parameters of the secure channel encapsulation
header that may not be protected by the secure channel mechanism.
The link-layer address of an ACP virtual interface is the address
used for the underlying interface across which the secure tunnels are
built, typically Ethernet addresses. Because unicast IPv6 packets
sent to an ACP virtual interface are not sent to a link-layer
destination address but rather an ACP secure channel, the link-layer
address fields SHOULD be ignored on reception and instead the ACP
secure channel from which the message was received should be
remembered.
Multi-access ACP virtual interfaces are preferable implementations
when the underlying interface is a (broadcast) multi-access subnet
because they do reflect the presence of the underlying multi-access
subnet into the virtual interfaces of the ACP. This makes it for
example simpler to build services with topology awareness inside the
ACP VRF in the same way as they could have been built running
natively on the multi-access interfaces.
Consider also the impact of point-to-point vs. multi-access virtual
interface on the efficiency of flooding via link local multicasted
messages:
Assume a LAN with three ACP neighbors, Alice, Bob and Carol. Alice's
ACP GRASP wants to send a link-local GRASP multicast message to Bob
and Carol. If Alice's ACP emulates the LAN as one point-to-point
virtual interface to Bob and one to Carol, The sending applications
itself will send two copies, if Alice's ACP emulates a LAN, GRASP
will send one packet and the ACP will replicate it. The result is
the same. The difference happens when Bob and Carol receive their
packet. If they use ACP point-to-point virtual interfaces, their
GRASP instance would forward the packet from Alice to each other as
part of the GRASP flooding procedure. These packets are unnecessary
and would be discarded by GRASP on receipt as duplicates (by use of
the GRASP Session ID). If Bob and Charly's ACP would emulate a
multi-access virtual interface, then this would not happen, because
GRASPs flooding procedure does not replicate back packets to the
interface that they were received from.
Note that link-local GRASP multicast messages are not sent directly
as IPv6 link-local multicast UDP messages into ACP virtual
interfaces, but instead into ACP GRASP virtual interfaces, that are
layered on top of ACP virtual interfaces to add TCP reliability to
link-local multicast GRASP messages. Nevertheless, these ACP GRASP
virtual interfaces perform the same replication of message and,
therefore, result in the same impact on flooding. See Section 6.8.2
for more details.
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RPL does support operations and correct routing table construction
across non-broadcast multi-access (NBMA) subnets. This is common
when using many radio technologies. When such NBMA subnets are used,
they MUST NOT be represented as ACP multi-access virtual interfaces
because the replication of IPv6 link-local multicast messages will
not reach all NBMA subnet neighbors. In result, GRASP message
flooding would fail. Instead, each ACP secure channel across such an
interface MUST be represented as a ACP point-to-point virtual
interface. See also Appendix A.10.4.
Care must also be taken when creating multi-access ACP virtual
interfaces across ACP secure channels between ACP nodes in different
domains or routing subdomains. The policies to be negotiated may be
described as peer-to-peer policies in which case it is easier to
create ACP point-to-point virtual interfaces for these secure
channels.
7. ACP support on L2 switches/ports (Normative)
7.1. Why
ANrtr1 ------ ANswitch1 --- ANswitch2 ------- ANrtr2
.../ \ \ ...
ANrtrM ------ \ ------- ANrtrN
ANswitchM ...
Figure 12: Topology with L2 ACP switches
Consider a large L2 LAN with ANrtr1...ANrtrN connected via some
topology of L2 switches. Examples include large enterprise campus
networks with an L2 core, IoT networks or broadband aggregation
networks which often have even a multi-level L2 switched topology.
If the discovery protocol used for the ACP is operating at the subnet
level, every ACP router will see all other ACP routers on the LAN as
neighbors and a full mesh of ACP channels will be built. If some or
all of the AN switches are autonomic with the same discovery
protocol, then the full mesh would include those switches as well.
A full mesh of ACP connections can create fundamental scale
challenges. The number of security associations of the secure
channel protocols will likely not scale arbitrarily, especially when
they leverage platform accelerated encryption/decryption. Likewise,
any other ACP operations (such as routing) needs to scale to the
number of direct ACP neighbors. An ACP router with just 4 physical
interfaces might be deployed into a LAN with hundreds of neighbors
connected via switches. Introducing such a new unpredictable scaling
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factor requirement makes it harder to support the ACP on arbitrary
platforms and in arbitrary deployments.
Predictable scaling requirements for ACP neighbors can most easily be
achieved if in topologies such as these, ACP capable L2 switches can
ensure that discovery messages terminate on them so that neighboring
ACP routers and switches will only find the physically connected ACP
L2 switches as their candidate ACP neighbors. With such a discovery
mechanism in place, the ACP and its security associations will only
need to scale to the number of physical interfaces instead of a
potentially much larger number of "LAN-connected" neighbors. And the
ACP topology will follow directly the physical topology, something
which can then also be leveraged in management operations or by ASAs.
In the example above, consider ANswitch1 and ANswitchM are ACP
capable, and ANswitch2 is not ACP capable. The desired ACP topology
is that ANrtr1 and ANrtrM only have an ACP connection to ANswitch1,
and that ANswitch1, ANrtr2, ANrtrN have a full mesh of ACP connection
amongst each other. ANswitch1 also has an ACP connection with
ANswitchM and ANswitchM has ACP connections to anything else behind
it.
7.2. How (per L2 port DULL GRASP)
To support ACP on L2 switches or L2 switched ports of an L3 device,
it is necessary to make those L2 ports look like L3 interfaces for
the ACP implementation. This primarily involves the creation of a
separate DULL GRASP instance/domain on every such L2 port. Because
GRASP has a dedicated link-local IPv6 multicast address
(ALL_GRASP_NEIGHBORS), it is sufficient that all packets for this
address are being extracted at the port level and passed to that DULL
GRASP instance. Likewise the IPv6 link-local multicast packets sent
by that DULL GRASP instance need to be sent only towards the L2 port
for this DULL GRASP instance.
If the device with L2 ports is supporting per L2 port ACP DULL GRASP
as well as MLD snooping ([RFC4541]), then MLD snooping must be
changed to never forward packets for ALL_GRASP_NEIGHBORS because that
would cause the problem that per L2 port ACP DULL GRASP is meant to
overcome (forwarding DULL GRASP packets across L2 ports).
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
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bound to the L3 (VLAN) interface. It will simply use link-local IPv6
multicast packets to the candidate ACP neighbor. Once a secure
channel is established to such a neighbor, the virtual interface to
which this secure channel is mapped should then actually be the L2
port and not the L3 interface to best map the actual physical
topology into the ACP virtual interfaces. See Section 6.12.5 for
more details about how to map secure channels into ACP virtual
interfaces. Note that a single L2 port can still have multiple ACP
neighbors if it connect for example to multiple ACP neighbors via a
non-ACP enabled switch. The per L2 port ACP virtual interface can
therefore still be a multi-access virtual LAN.
For example, in the above picture, ANswitch1 would run separate DULL
GRASP instances on its ports to ANrtr1, ANswitch2 and ANswitchI, even
though all those three ports may be in the data plane in the same
(V)LAN and perform L2 switching between these ports, ANswitch1 would
perform ACP L3 routing between them.
The description in the previous paragraph was specifically meant to
illustrate that on hybrid L3/L2 devices that are common in
enterprise, IoT and broadband aggregation, there is only the GRASP
packet extraction (by Ethernet address) and GRASP link-local
multicast per L2-port packet injection that has to consider L2 ports
at the hardware forwarding level. The remaining operations are
purely ACP control plane and setup of secure channels across the L3
interface. This hopefully makes support for per-L2 port ACP on those
hybrid devices easy.
This L2/L3 optimized approach is subject to "address stealing", e.g.,
where a device on one port uses addresses of a device on another
port. This is a generic issue in L2 LANs and switches often already
have some form of "port security" to prohibit this. They rely on NDP
or DHCP learning of which port/MAC-address and IPv6 address belong
together and block duplicates. This type of function needs to be
enabled to prohibit DoS attacks. Likewise the GRASP DULL instance
needs to ensure that the IPv6 address in the locator-option matches
the source IPv6 address of the DULL GRASP packet.
In devices without such a mix of L2 port/interfaces and L3 interfaces
(to terminate any transport layer connections), implementation
details will differ. Logically most simply every L2 port is
considered and used as a separate L3 subnet for all ACP operations.
The fact that the ACP only requires IPv6 link-local unicast and
multicast should make support for it on any type of L2 devices as
simple as possible.
A generic issue with ACP in L2 switched networks is the interaction
with the Spanning Tree Protocol. Ideally, the ACP should be built
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also across ports that are blocked in STP so that the ACP does not
depend on STP and can continue to run unaffected across STP topology
changes (where re-convergence can be quite slow). The above
described simple implementation options are not sufficient for this.
Instead they would simply have the ACP run across the active STP
topology and the ACP would equally be interrupted and re-converge
with STP changes.
8. Support for Non-ACP Components (Normative)
8.1. ACP Connect
8.1.1. Non-ACP Controller / NMS system
The Autonomic Control Plane can be used by management systems, such
as controllers or network management system (NMS) hosts (henceforth
called simply "NMS hosts"), to connect to devices (or other type of
nodes) through it. For this, an NMS host must have access to the
ACP. The ACP is a self-protecting overlay network, which allows by
default access only to trusted, autonomic systems. Therefore, a
traditional, non-ACP NMS system does not have access to the ACP by
default, such as any other external node.
If the NMS host is not autonomic, i.e., it does not support autonomic
negotiation of the ACP, then it can be brought into the ACP by
explicit configuration. To support connections to adjacent non-ACP
nodes, an ACP node must support "ACP connect" (sometimes also called
"autonomic connect"):
"ACP connect" is a function on an autonomic node that is called an
"ACP edge node". With "ACP connect", interfaces on the node 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
encryption/novel-signaling).
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Data-Plane "native" (no ACP)
.
+--------+ +----------------+ . +-------------+
| ACP | |ACP Edge Node | . | |
| Node | | | v | |
| |-------|...[ACP VRF]....+-----------------| |+
| | ^ |. | | NOC Device ||
| | . | .[Data-Plane]..+-----------------| "NMS hosts" ||
| | . | [ ] | . ^ | ||
+--------+ . +----------------+ . . +-------------+|
. . . +-------------+
. . .
Data-Plane "native" . ACP "native" (unencrypted)
+ ACP auto-negotiated . "ACP connect subnet"
and encrypted .
ACP connect interface
e.g., "VRF ACP native" (config)
Figure 13: ACP connect
ACP connect has security consequences: All systems and processes
connected via ACP connect have access to all ACP nodes on the entire
ACP, without further authentication. Thus, the ACP connect interface
and (NOC) systems connected to it must be physically controlled/
secured. For this reason the mechanisms described here do explicitly
not include options to allow for a non-ACP router to be connected
across an ACP connect interface and addresses behind such a router
routed inside the ACP.
An ACP connect interface provides exclusively access to only the ACP.
This is likely insufficient for many NMS hosts. Instead, they would
require a second "Data-Plane" interface outside the ACP for
connections between the NMS host and administrators, or Internet
based services, or for direct access to the Data-Plane. The document
"Using Autonomic Control Plane for Stable Connectivity of Network
OAM" [RFC8368] explains in more detail how the ACP can be integrated
in a mixed NOC environment.
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
not.
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The prefix of ACP connect subnets MUST be distributed by the ACP edge
node into the ACP routing protocol (RPL). The NMS hosts MUST connect
to prefixes in the ACP routing table via its ACP connect interface.
In the simple case where the ACP uses only one ULA prefix and all ACP
connect subnets have prefixes covered by that ULA prefix, NMS hosts
can rely on [RFC6724] - 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
interface.
ACP Edge Nodes 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, nodes supporting it
SHOULD implement a security mechanism to allow configuration/use of
ACP connect interfaces only on nodes explicitly targeted to be
deployed with it (those in physically secure locations such as a
NOC). For example, the registrar could disable the ability to enable
ACP connect on devices during enrollment and that property could only
be changed through re-enrollment. See also Appendix A.10.5.
8.1.2. Software Components
The ACP connect mechanism be only be used to connect physically
external systems (NMS hosts) to the ACP but also other applications,
containers or virtual machines. In fact, one possible way to
eliminate the security issue of the external ACP connect interface is
to collocate an ACP edge node and an NMS host by making one a virtual
machine or container inside the other; and therefore converting the
unprotected external ACP subnet into an internal virtual subnet in a
single device. This would ultimately result in a fully ACP enabled
NMS host with minimum impact to the NMS hosts software architecture.
This approach is not limited to NMS hosts but could equally be
applied to devices consisting of one or more VNF (virtual network
functions): An internal virtual subnet connecting out-of-band
management interfaces of the VNFs to an ACP edge router VNF.
The core requirement is that the software components need to have a
network stack that permits access to the ACP and optionally also the
Data-Plane. Like in the physical setup for NMS hosts this can be
realized via two internal virtual subnets. One that is connecting to
the ACP (which could be a container or virtual machine by itself),
and one (or more) connecting into the Data-Plane.
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This "internal" use of ACP connect approach should not considered to
be a "workaround" because in this case it is possible to build a
correct security model: It is not necessary to rely on unprovable
external physical security mechanisms as in the case of external NMS
hosts. Instead, the orchestration of the ACP, the virtual subnets
and the software components can be done by trusted software that
could be considered to be part of the ANI (or even an extended ACP).
This software component is responsible for ensuring that only trusted
software components will get access to that virtual subnet and that
only even more trusted software components will get access to both
the ACP virtual subnet and the Data-Plane (because those ACP users
could leak traffic between ACP and Data-Plane). This trust could be
established for example through cryptographic means such as signed
software packages.
8.1.3. Auto Configuration
ACP edge nodes, NMS hosts and software components that as described
in the previous section are meant to be composed via virtual
interfaces SHOULD support on the ACP connect subnet StateLess Address
Autoconfiguration (SLAAC - [RFC4862]) and route auto configuration
according to [RFC4191].
The ACP edge node acts as the router on the ACP connect subnet,
providing the (auto-)configured prefix for the ACP connect subnet to
NMS hosts and/or software components. The ACP edge node uses route
prefix option of RFC4191 to announce the default route (::/) with a
lifetime of 0 and aggregated prefixes for routes in the ACP routing
table with normal lifetimes. This will ensure that the ACP edge node
does not become a default router, but that the NMS hosts and software
components will route the prefixes used in the ACP to the ACP edge
node.
Aggregated prefix means that the ACP edge node needs to only announce
the /48 ULA prefixes used in the ACP but none of the actual /64
(Manual Addressing Sub-Scheme), /127 (ACP Zone Addressing Sub-
Scheme), /112 or /120 (Vlong Addressing Sub-Scheme) routes of actual
ACP nodes. If ACP interfaces are configured with non ULA prefixes,
then those prefixes cannot be aggregated without further configured
policy on the ACP edge node. This explains the above recommendation
to use ACP ULA prefix covered prefixes for ACP connect interfaces:
They allow for a shorter list of prefixes to be signaled via RFC4191
to NMS hosts and software components.
The ACP edge nodes that have a Vlong ACP address MAY allocate a
subset of their /112 or /120 address prefix to ACP connect
interface(s) to eliminate the need to non-autonomically configure/
provision the address prefixes for such ACP connect interfaces.
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8.1.4. Combined ACP/Data-Plane Interface (VRF Select)
Combined ACP and Data-Plane interface
.
+--------+ +--------------------+ . +--------------+
| ACP | |ACP Edge No | . | NMS Host(s) |
| Node | | | . | / Software |
| | | [ACP ]. | . | |+
| | | .[VRF ] .[VRF ] | v | "ACP address"||
| +-------+. .[Select].+--------+ "Date Plane ||
| | ^ | .[Data ]. | | Address(es)"||
| | . | [Plane] | | ||
| | . | [ ] | +--------------+|
+--------+ . +--------------------+ +--------------+
.
Data-Plane "native" and + ACP auto-negotiated/encrypted
Figure 14: VRF select
Using two physical and/or virtual subnets (and therefore interfaces)
into NMS Hosts (as per Section 8.1.1) or Software (as per
Section 8.1.2) may be seen as additional complexity, for example with
legacy NMS Hosts that support only one IP interface.
To provide a single subnet into both ACP and Data-Plane, the ACP Edge
node needs to de-multiplex packets from NMS hosts into ACP VRF and
Data-Plane. This is sometimes called "VRF select". If the ACP VRF
has no overlapping IPv6 addresses with the Data-Plane (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 node announces both the ACP IPv6
prefix and one (or more) prefixes for the Data-Plane. Without
further policy configurations on the NMS Host(s), it may select its
ACP address as a source address for Data-Plane ULA destinations
because of Rule 8 of RFC6724. The ACP edge node can pass on the
packet to the Data-Plane, but the ACP source address should not be
used for Data-Plane traffic, and return traffic may fail.
If the ACP carries multiple ULA prefixes or non-ULA ACP connect
prefixes, then the correct source address selection becomes even more
problematic.
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With separate ACP connect and Data-Plane subnets and RFC4191 prefix
announcements that are to be routed across the ACP connect interface,
RFC6724 source address selection Rule 5 (use address of outgoing
interface) will be used, so that above problems do not occur, even in
more complex cases of multiple ULA and non-ULA prefixes in the ACP
routing table.
To achieve the same behavior with a Combined ACP and Data-Plane
interface, the ACP Edge Node needs to behave as two separate routers
on the interface: One link-local IPv6 address/router for its ACP
reachability, and one link-local IPv6 address/router for its Data-
Plane reachability. The Router Advertisements for both are as
described above (Section 8.1.3): For the ACP, the ACP prefix is
announced together with RFC4191 option for the prefixes routed across
the ACP and lifetime=0 to disqualify this next-hop as a default
router. For the Data-Plane, the Data-Plane prefix(es) are announced
together with whatever dafault router parameters are used for the
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 preferable method of
attachment. Hosts implementing [RFC8028] should (instead of may)
implement [RFC6724] Rule 5.5, so it is preferred for hosts to support
[RFC8028].
ACP edge nodes MAY support the Combined ACP and Data-Plane interface.
8.1.5. Use of GRASP
GRASP can and should be possible to use across ACP connect
interfaces, especially in the architectural correct solution when it
is used as a mechanism to connect Software (e.g., ASA or legacy NMS
applications) to the ACP. Given how the ACP is the security and
transport substrate for GRASP, the trustworthiness of nodes/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 the
same as 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 nodes. ACP edge nodes SHOULD have options to filter GRASP
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messages in and out of ACP connect interfaces (permit/deny) and MAY
have more fine-grained filtering (e.g., based on IPv6 address of
originator or objective).
When using "Combined ACP and Data-Plane Interfaces", care must be
taken that only GRASP messages intended for the ACP GRASP domain
received from Software or NMS Hosts are forwarded by ACP edge nodes.
Currently there is no definition for a GRASP security and transport
substrate beside the ACP, so there is no definition how such
Software/NMS Host could participate in two separate GRASP Domains
across the same subnet (ACP and Data-Plane domains). At current it
is assumed that all GRASP packets on a Combined ACP and Data-Plane
interface belong to the GRASP ACP Domain. They must all use the ACP
IPv6 addresses of the Software/NMS Hosts. The link-local IPv6
addresses of Software/NMS Hosts (used for GRASP M_DISCOVERY and
M_FLOOD messages) are also assumed to belong to the ACP address
space.
8.2. ACP through Non-ACP L3 Clouds (Remote ACP neighbors)
Not all nodes in a network may support the ACP. If non-ACP Layer-2
devices are between ACP nodes, the ACP will work across it since it
is IP based. However, the autonomic discovery of ACP neighbors via
DULL GRASP is only intended to work across L2 connections, so it is
not sufficient to autonomically create ACP connections across non-ACP
Layer-3 devices.
8.2.1. Configured Remote ACP neighbor
On the ACP node, remote ACP neighbors are configured explicitly. The
parameters of such a "connection" are described in the following
ABNF.
connection = [ method , local-addr, remote-addr, ?pmtu ]
method = [ "IKEv2" , ?port ]
method //= [ "DTLS", port ]
local-addr = [ address , ?vrf ]
remote-addr = [ address ]
address = ("any" | ipv4-address | ipv6-address )
vrf = tstr ; Name of a VRF on this node with local-address
Figure 15: Parameters for remote ACP neighbors
Explicit configuration of a remote-peer according to this ABNF
provides all the information to build a secure channel without
requiring a tunnel to that peer and running DULL GRASP inside of it.
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The configuration includes the parameters otherwise signaled via DULL
GRASP: local address, remote (peer) locator and method. The
differences over DULL GRASP local neighbor discovery and secure
channel creation are as follows:
o The local and remote address can be IPv4 or IPv6 and are typically
global scope addresses.
o The VRF across which the connection is built (and in which local-
addr exists) can to be specified. If vrf is not specified, it is
the default VRF on the node. In DULL GRASP the VRF is implied by
the interface across which DULL GRASP operates.
o If local address is "any", the local address used when initiating
a secure channel connection is decided by source address selection
([RFC6724] for IPv6). As a responder, the connection listens on
all addresses of the node in the selected VRF.
o Configuration of port is only required for methods where no
defaults exist (e.g., "DTLS").
o If remote address is "any", the connection is only a responder.
It is a "hub" that can be used by multiple remote peers to connect
simultaneously - without having to know or configure their
addresses. Example: Hub site for remote "spoke" sites reachable
over the Internet.
o Pmtu should be configurable to overcome issues/limitations of Path
MTU Discovery (PMTUD).
o IKEv2/IPsec to remote peers should support the optional NAT
Traversal (NAT-T) procedures.
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
document.
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
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over a virtual (tunnel) interface instead of only native interfaces.
The tunnel itself may also provide PMTUD while the secure channel
method may not. Or the tunnel mechanism is permitted/possible
through some firewall while the secure channel method may not.
8.2.3. Summary
Configured/Tunneled Remote ACP neighbors are less "indestructible"
than L2 adjacent ACP neighbors based on link local addressing, since
they depend on more correct Data-Plane operations, such as routing
and global addressing.
Nevertheless, these options may be crucial to incrementally deploy
the ACP, especially if it is meant to connect islands across the
Internet. Implementations SHOULD support at least Tunneled Remote
ACP Neighbors via GRE tunnels - which is likely the most common
router-to-router tunneling protocol in use today.
9. Benefits (Informative)
9.1. Self-Healing Properties
The ACP is self-healing:
o New neighbors will automatically join the ACP after successful
validation and will become reachable using their unique ULA
address across the ACP.
o When any changes happen in the topology, the routing protocol used
in the ACP will automatically adapt to the changes and will
continue to provide reachability to all nodes.
o If the domain certificate of an existing ACP node 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 node 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. Nodes authenticate each other using the domain certificates
to establish the ACP locally. Addressing inside the ACP remains
unchanged, and the routing protocol inside both parts of the ACP will
lead to two working (although partitioned) ACPs.
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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, an ACP registrar or
Certificate Authority might not be available during a partition.
This may delay renewal of certificates that are to expire in the
future, and it may prevent the enrollment of new nodes during the
partition.
Highly resilient ACP designs can be built by using ACP registrars
with embedded sub-CA, as outlined in Section 10.2.4. As long a a
partition is left with one or more of such ACP registrars, it can
continue to enroll new candidate ACP nodes as long as the ACP
registrars sub-CA certificate does not expire. Because the ACP
addressing relies on unique Registrar-IDs, a later re-merge of
partitions will also not cause problems with ACP addresses assigned
during partitioning.
After a network partition, a re-merge will just establish the
previous status, certificates can be renewed, the CRL is available,
and new nodes can be enrolled everywhere. Since all nodes use the
same trust anchor, 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 which the ACP is
running. Especially if bringing down the ACP is known to disconnect
the operator from the node. For example any such down administrative
action could perform a dependency check to see if the transport
connection across which this action is performed is affected by the
down action (with default RPL routing used, packet forwarding will be
symmetric, so this is actually possible to check).
9.2. Self-Protection Properties
9.2.1. From the outside
As explained in Section 6, the ACP is based on secure channels built
between nodes that have mutually authenticated each other with their
domain certificates. The channels themselves are protected using
standard encryption technologies such as DTLS or IPsec which provide
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additional authentication during channel establishment, data
integrity and data confidentiality protection of data inside the ACP
and in addition, provide replay protection.
An attacker will not be able to join the ACP unless having a valid
domain certificate, also packet injection and sniffing traffic will
not be possible due to the security provided by the encryption
protocol.
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 ACP
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 attack.
9.2.2. From the inside
The security model of the ACP is based on trusting all members of the
group of nodes that 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 be protected against attackers so that there is no
easy way to compromise them, or use them as a proxy for attacking
other devices across the ACP. For example, management plane
functions (transport ports) should only be reachable from the ACP but
not the Data-Plane. Especially for those management plane functions
that have no good protection by themselves because they do not have
secure end-to-end transport and to whom ACP does not only provides
automatic reliable connectivity but also protection against attacks.
Protection across all potential attack vectors is typically easier to
do in devices whose software is designed from the ground up with
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security in mind than with legacy software based systems where the
ACP is added on as another feature.
As explained above, traffic across the ACP SHOULD still be end-to-end
encrypted whenever possible. This includes traffic such as GRASP,
EST and BRSKI inside the ACP. This minimizes man in the middle
attacks by compromised ACP group members. Such attackers cannot
eavesdrop or modify communications, they can just filter them (which
is unavoidable by any means).
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 nodes, 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 node not supporting the ACP, or
without a valid domain certificate cannot connect to it. This means
that by default a traditional controller or network management system
cannot connect to an ACP. See Section 8.1.1 for more details on how
to connect an NMS host into the ACP.
10. ACP Operations (Informative)
The following sections document important operational aspects of the
ACP. They are not normative because they do not impact the
interoperability between components of the ACP, but they include
recommendations/requirements for the internal operational model
beneficial or necessary to achieve the desired use-case benefits of
the ACP (see Section 3).
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o Section 10.1 describes recommended operator diagnostics
capabilities of ACP nodes. The have been derived from diagnostic
of a commercially available ACP implementation.
o Section 10.2 describes high level how an ACP registrar needs to
work, what its configuration parameters are and specific issues
impacting the choices of deployment design due to renewal and
revocation issues. It describes a model where ACP Registrars have
their own sub-CA to provide the most disributed deployment option
for ACP Registrars, and it describes considerations for
centralized policy control of ACP Registrar operations.
o Section 10.3 describes suggested ACP node behavior and operational
interfaces (configuration options) to manage the ACP in so-called
greenfield devices (previously unconfigured) and brownfield
devices (preconfigured).
The recommendations and suggestions of this chapter were derived from
operational experience gained with a commercially available pre-
standard ACP implementation.
10.1. ACP (and BRSKI) Diagnostics
Even though ACP and ANI in general are taking out many manual
configuration mistakes through their automation, it is important to
provide good diagnostics for them.
The basic diagnostics is support of (yang) data models representing
the complete (auto-)configuration and operational state of all
components: BRSKI, GRASP, ACP and the infrastructure used by them:
TLS/DTLS, IPsec, certificates, trust anchors, time, VRF and so on.
While necessary, this is not sufficient:
Simply representing the state of components does not allow operators
to quickly take action - unless they do understand how to interpret
the data, and that can mean a requirement for deep understanding of
all components and how they interact in the ACP/ANI.
Diagnostic supports should help to quickly answer the questions
operators are expected to ask, such as "is the ACP working
correctly?", or "why is there no ACP connection to a known
neighboring node?"
In current network management approaches, the logic to answer these
questions is most often built as centralized diagnostics software
that leverages the above mentioned data models. While this approach
is feasible for components utilizing the ANI, it is not sufficient to
diagnose the ANI itself:
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o Developing the logic to identify common issues requires
operational experience with the components of the ANI. Letting
each management system define its own analysis is inefficient.
o When the ANI is not operating correctly, it may not be possible to
run diagnostics from remote because of missing connectivity. The
ANI should therefore have diagnostic capabilities available
locally on the nodes themselves.
o Certain operations are difficult or impossible to monitor in real-
time, such as initial bootstrap issues in a network location where
no capabilities exist to attach local diagnostics. Therefore it
is important to also define means of capturing (logging)
diagnostics locally for later retrieval. Ideally, these captures
are also non-volatile so that they can survive extended power-off
conditions - for example when a device that fails to be brought up
zero-touch is being sent back for diagnostics at a more
appropriate location.
The most simple form of diagnostics answering questions such as the
above is to represent the relevant information sequentially in
dependency order, so that the first non-expected/non-operational item
is the most likely root cause. Or just log/highlight that item. For
example:
Q: Is ACP operational to accept neighbor connections:
o Check if any potentially necessary configuration to make ACP/ANI
operational are correct (see Section 10.3 for a discussion of such
commands).
o Does the system time look reasonable, or could it be the default
system time after clock chip battery failure (certificate checks
depend on reasonable notion of time).
o Does the node have keying material - domain certificate, trust
anchors.
o If no keying material and ANI is supported/enabled, check the
state of BRSKI (not detailed in this example).
o Check the validity of the domain certificate:
* Does the certificate authenticate against the trust anchor?
* Has it been revoked?
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* Was the last scheduled attempt to retrieve a CRL successful
(e.g., do we know that our CRL information is up to date).
* Is the certificate valid: validity start time in the past,
expiration time in the future?
* Does the certificate have a correctly formatted ACP information
field?
o Was the ACP VRF successfully created?
o Is ACP enabled on one or more interfaces that are up and running?
If all this looks good, the ACP should be running locally "fine" -
but we did not check any ACP neighbor relationships.
Question: why does the node not create a working ACP connection to a
neighbor on an interface?
o Is the interface physically up? Does it have an IPv6 link-local
address?
o Is it enabled for ACP?
o Do we successfully send DULL GRASP messages to the interface (link
layer errors)?
o Do we receive DULL GRASP messages on the interface? If not, some
intervening L2 equipment performing bad MLD snooping could have
caused problems. Provide e.g., diagnostics of the MLD querier
IPv6 and MAC address.
o Do we see the ACP objective in any DULL GRASP message from that
interface? Diagnose the supported secure channel methods.
o Do we know the MAC address of the neighbor with the ACP objective?
If not, diagnose SLAAC/ND state.
o When did we last attempt to build an ACP secure channel to the
neighbor?
o If it failed, why:
* Did the neighbor close the connection on us or did we close the
connection on it because the domain certificate membership
failed?
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* If the neighbor closed the connection on us, provide any error
diagnostics from the secure channel protocol.
* If we failed the attempt, display our local reason:
+ There was no common secure channel protocol supported by the
two neighbors (this could not happen on nodes supporting
this specification because it mandates common support for
IPsec).
+ The ACP domain certificate membership check (Section 6.1.2)
fails:
- The neighbors certificate does not have the required
trust anchor. Provide diagnostics which trust anchor it
has (can identify whom the device belongs to).
- The neighbors certificate does not have the same domain
(or no domain at all). Diagnose domain-name and
potentially other other cert info.
- The neighbors certificate has been revoked or could not
be authenticated by OCSP.
- The neighbors certificate has expired - or is not yet
valid.
* Any other connection issues in e.g., IKEv2 / IPsec, DTLS?.
Question: Is the ACP operating correctly across its secure channels?
o Are there one or more active ACP neighbors with secure channels?
o Is the RPL routing protocol for the ACP running?
o Is there a default route to the root in the ACP routing table?
o Is there for each direct ACP neighbor not reachable over the ACP
virtual interface to the root a route in the ACP routing table?
o Is ACP GRASP running?
o Is at least one SRV.est objective cached (to support certificate
renewal)?
o Is there at least one BRSKI registrar objective cached (in case
BRSKI is supported)
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o Is BRSKI proxy operating normally on all interfaces where ACP is
operating?
o ...
These lists are not necessarily complete, but illustrate the
principle and show that there are variety of issues ranging from
normal operational causes (a neighbor in another ACP domain) over
problems in the credentials management (certificate lifetimes),
explicit security actions (revocation) or unexpected connectivity
issues (intervening L2 equipment).
The items so far are illustrating how the ANI operations can be
diagnosed with passive observation of the operational state of its
components including historic/cached/counted events. This is not
necessary sufficient to provide good enough diagnostics overall:
The components of ACP and BRSKI are designed with security in mind
but they do not attempt to provide diagnostics for building the
network itself. Consider two examples:
1. BRSKI does not allow for a neighboring device to identify the
pledges certificate (IDevID). Only the selected BRSKI registrar
can do this, but it may be difficult to disseminate information
about undesired pledges from those BRSKI registrars to locations/
nodes where information about those pledges is desired.
2. The Link Layer Discovery Protocol (LLDP, [LLDP]) disseminates
information about nodes to their immediate neighbors, such as
node model/type/software and interface name/number of the
connection. This information is often helpful or even necessary
in network diagnostics. It can equally considered to be too
insecure to make this information available unprotected to all
possible neighbors.
An "interested adjacent party" can always determine the IDevID of a
BRSKI pledge by behaving like a BRSKI proxy/registrar. Therefore the
IDevID of a BRSKI pledge is not meant to be protected - it just has
to be queried and is not signaled unsolicited (as it would be in
LLDP) so that other observers on the same subnet can determine who is
an "interested adjacent party".
10.2. ACP Registrars
As described in Section 6.10.7, the ACP addressing mechanism is
designed to enable lightweight, distributed and uncoordinated ACP
registrars that are providing ACP address prefixes to candidate ACP
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nodes by enrolling them with an ACP domain certificate into an ACP
domain via any appropriate mechanism/protocol, automated or not.
This section discusses informatively more details and options for ACP
registrars.
10.2.1. Registrar interactions
This section summarizes and discusses the interactions with other
entities required by an ACP registrar.
In a simple instance of an ACP network, no central NOC component
beside a trust anchor (root CA) is required. One or more
uncoordinated acting ACP registrar can be set up, performing the
following interactions:
To orchestrate enrolling a candidate ACP node autonomically, the ACP
registrar can rely on the ACP and use Proxies to reach the candidate
ACP node, therefore allowing minimum pre-existing (auto-)configured
network services on the candidate ACP node. BRSKI defines the BRSKI
proxy, a design that can be adopted for various protocols that
Pledges/candidate ACP nodes could want to use, for example BRSKI over
CoAP (Constrained Application Protocol), or proxying of Netconf.
To reach a trust anchor unaware of the ACP, the ACP registrar would
use the Data-Plane. ACP and Data-Plane in an ACP registrar could
(and by default should be) completely isolated from each other at the
network level. Only applications such as the ACP registrar would
need the ability for their transport stacks to access both.
In non autonomic enrollment options, the Data-Plane between a ACP
registrar and the candidate ACP node needs to be configured first.
This includes the ACP registrar and the candidate ACP node. Then any
appropriate set of protocols can be used between ACP registrar and
candidate ACP node to discover the other side, and then connect and
enroll (configure) the candidate ACP node with an ACP domain
certificate. Netconf ZeroTouch ([I-D.ietf-netconf-zerotouch]) is an
example protocol that could be used for this. BRSKI using optional
discovery mechanisms is equally a possibility for candidate ACP nodes
attempting to be enrolled across non-ACP networks, such as the
Internet.
When candidate ACP nodes have secure bootstrap, such as BRSKI
Pledges, they will not trust to be configured/enrolled across the
network, unless being presented with a voucher (see [RFC8366])
authorizing the network to take possession of the node. An ACP
registrar will then need a method to retrieve such a voucher, either
offline, or online from a MASA (Manufacturer Authorized Signing
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Authority). BRSKI and Netconf ZeroTouch are two protocols that
include capabilities to present the voucher to the candidate ACP
node.
An ACP registrar could operate EST for ACP certificate renewal and/or
act as a CRL Distribution point. A node performing these services
does not need to support performing (initial) enrollment, but it does
require the same above described connectivity as an ACP registrar:
via the ACP to ACP nodes and via the Data-Plane to the trust anchor
and other sources of CRL information.
10.2.2. Registrar Parameter
The interactions of an ACP registrar outlined Section 6.10.7 and
Section 10.2.1 above depend on the following parameters:
A URL to the trust anchor (root CA) and credentials so that the
ACP registrar can let the trust anchor sign candidate ACP member
certificates.
The ACP domain-name.
The Registrar-ID to use. This could default to a MAC address of
the ACP registrar.
For recovery, the next-useable Node-IDs for zone (Zone-ID=0) sub-
addressing scheme, for Vlong /112 and for Vlong /1120 sub-
addressing scheme. These IDs would only need to be provisioned
after recovering from a crash. Some other mechanism would be
required to remember these IDs in a backup location or to recover
them from the set of currently known ACP nodes.
Policies if candidate ACP nodes should receive a domain
certificate or not, for example based on the devices LDevID as in
BRSKI. The ACP registrar may have a whitelist or blacklist of
devices serialNumbers from teir LDevID.
Policies what type of address prefix to assign to a candidate ACP
devices, based on likely the same information.
For BRSKI or other mechanisms using vouchers: Parameters to
determine how to retrieve vouchers for specific type of secure
bootstrap candidate ACP nodes (such as MASA URLs), unless this
information is automatically learned such as from the LDevID of
candidate ACP nodes (as defined in BRSKI).
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10.2.3. Certificate renewal and limitations
When an ACP node renews/rekeys its certificate, it may end up doing
so via a different registrar (e.g., EST server) than the one it
originally received its ACP domain certificate from, for example
because that original ACP registrar is gone. The ACP registrar
through which the renewal/rekeying is performed would by default
trust the ACP domain information from the ACP nodes current ACP
domain certificate and maintain this information so that the ACP node
maintains its ACP address prefix. In EST renewal/rekeying, the ACP
nodes current ACP domain certificate is signaled during the TLS
handshake.
This simple scenario has two limitations:
1. The ACP registrars can not directly assign certificates to nodes
and therefore needs an "online" connection to the trust anchor
(root CA).
2. Recovery from a compromised ACP registrar is difficult. When an
ACP registrar is compromised, it can insert for example
conflicting ACP domain information and create thereby an attack
against other ACP nodes through the ACP routing protocol.
Even when such a malicious ACP registrar is detected, resolving the
problem may be difficult because it would require identifying all the
wrong ACP domain certificates assigned via the ACP registrar after it
was was compromised. And without additional centralized tracking of
assigned certificates there is no way to do this - assuming one can
not retrieve this information from the .
10.2.4. ACP Registrars with sub-CA
In situations, where either of the above two limitations are an
issue, ACP registrars could also be sub-CAs. This removes the need
for connectivity to a root-CA whenever an ACP node is enrolled, and
reduces the need for connectivity of such an ACP registrar to a root-
CA to only those times when it needs to renew its own certificate.
The ACP registrar would also now use its own (sub-CA) certificate to
enroll and sign the ACP nodes certificates, and therefore it is only
necessary to revoke a compromised ACP registrars sub-CA certificate.
Or let it expire and not renew it, when the certificate of the sub-CA
is appropriately short-lived.
As the ACP domain membership check verifies a peer ACP node's ACP
domain certicate trust chain, it will also verify the signing
certificate which is the compromised/revoked sub-CA certificate.
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Therefore ACP domain membership for an ACP node enrolled from a
compromised ACP registrar will fail.
ACP nodes enrolled by a compromised ACP registrar would automatically
fail to establish ACP channels and ACP domain certificate renewal via
EST and therefore revert to their role as a candidate ACP members and
attempt to get a new ACP domain certificate from an ACP registrar -
for example via BRSKI. In result, ACP registrars that have an
associated sub-CA makes isolating and resolving issues with
compromised registrars easier.
Note that ACP registrars with sub-CA functionality also can control
the lifetime of ACP domain certificates easier and therefore also be
used as a tool to introduce short lived certificates and not rely on
CRL, whereas the certificates for the sub-CAs themselves could be
longer lived and subject to CRL.
10.2.5. Centralized Policy Control
When using multiple, uncoordinated ACP registrars, several advanced
operations are potentially more complex than with a single, resilient
policy control backend, for example including but not limited to:
Which candidate ACP node is permitted or not permitted into an ACP
domain. This may not be a decision to be taken upfront, so that a
per-serialNumber policy can be loaded into ever ACP registrar.
Instead, it may better be decided in real-time including
potentially a human decision in a NOC.
Tracking of all enrolled ACP nodes and their certificate
information. For example in support of revoking individual ACP
nodes certificates.
More flexible policies what type of address prefix or even what
specific address prefix to assign to a candidate ACP node.
These and other operations could be introduced more easily by
introducing a centralized Policy Management System (PMS) and
modifying ACP registrar behavior so that it queries the PMS for any
policy decision occuring during the candidate ACP node enrollment
process and/or the ACP node certificate renewal process. For
example, which ACP address prefix to assign. Likewise the ACP
registrar would report any relevant state change information to the
PMS as well, for example when a certificate was successfully enrolled
onto a candidate ACP node.
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10.3. Enabling and disabling ACP/ANI
Both ACP and BRSKI require interfaces to be operational enough to
support sending/receiving their packets. In node types where
interfaces are by default (e.g., without operator configuration)
enabled, such as most L2 switches, this would be less of a change in
behavior than in most L3 devices (e.g.: routers), where interfaces
are by default disabled. In almost all network devices it is common
though for configuration to change interfaces to a physically
disabled state and that would break the ACP.
In this section, we discuss a suggested operational model to enable/
disable interfaces and nodes for ACP/ANI in a way that minimizes the
risk of operator action to break the ACP in this way, and that also
minimizes operator surprise when ACP/ANI becomes supported in node
software.
10.3.1. Filtering for non-ACP/ANI packets
Whenever this document refers to enabling an interface for ACP (or
BRSKI), it only requires to permit the interface to send/receive
packets necessary to operate ACP (or BRSKI) - but not any other Data-
Plane packets. Unless the Data-Plane is explicitly configured/
enabled, all packets not required for ACP/BRSKI should be filtered on
input and output:
Both BRSKI and ACP require link-local only IPv6 operations on
interfaces and DULL GRASP. IPv6 link-local operations means the
minimum signaling to auto-assign an IPv6 link-local address and talk
to neighbors via their link-local address: SLAAC (Stateless Address
Auto-Configuration - [RFC4862]) and ND (Neighbor Discovery -
[RFC4861]). When the device is a BRSKI pledge, it may also require
TCP/TLS connections to BRSKI proxies on the interface. When the
device has keying material, and the ACP is running, it requires DULL
GRASP packets and packets necessary for the secure-channel mechanism
it supports, e.g., IKEv2 and IPsec ESP packets or DTLS packets to the
IPv6 link-local address of an ACP neighbor on the interface. It also
requires TCP/TLS packets for its BRSKI proxy functionality, if it
does support BRSKI.
10.3.2. Admin Down State
Interfaces on most network equipment have at least two states: "up"
and "down". These may have product specific names. "down" for
example could be called "shutdown" and "up" could be called "no
shutdown". The "down" state disables all interface operations down
to the physical level. The "up" state enables the interface enough
for all possible L2/L3 services to operate on top of it and it may
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also auto-enable some subset of them. More commonly, the operations
of various L2/L3 services is controlled via additional node-wide or
interface level options, but they all become only active when the
interface is not "down". Therefore an easy way to ensure that all
L2/L3 operations on an interface are inactive is to put the interface
into "down" state. The fact that this also physically shuts down the
interface is in many cases just a side effect, but it may be
important in other cases (see below, Section 10.3.2.2).
To provide ACP/ANI resilience against operators configuring
interfaces to "down" state, this document recommends to separate the
"down" state of interfaces into an "admin down" state where the
physical layer is kept running and ACP/ANI can use the interface and
a "physical down" state. Any existing "down" configurations would
map to "admin down". In "admin down", any existing L2/L3 services of
the Data-Plane should see no difference to "physical down" state. To
ensure that no Data-Plane packets could be sent/received, packet
filtering could be established automatically as described above in
Section 10.3.1.
As necessary (see discussion below) new configuration options could
be introduced to issue "physical down". The options should be
provided with additional checks to minimize the risk of issuing them
in a way that breaks the ACP without automatic restoration. For
example they could be denied to be issued from a control connection
(netconf/ssh) that goes across the interface itself ("do not
disconnect yourself"). Or they could be performed only temporary and
only be made permanent with additional later reconfirmation.
In the following sub-sections important aspects to the introduction
of "admin down" state are discussed.
10.3.2.1. Security
Interfaces are physically brought down (or left in default down
state) as a form of security. "Admin down" state as described above
provides also a high level of security because it only permits ACP/
ANI operations which are both well secured. Ultimately, it is
subject to security review for the deployment whether "admin down" is
a feasible replacement for "physical down".
The need to trust into the security of ACP/ANI operations need to be
weighed against the operational benefits of permitting this: Consider
the typical example of a CPE (customer premises equipment) with no
on-site network expert. User ports are in physical down state unless
explicitly configured not to be. In a misconfiguration situation,
the uplink connection is incorrectly plugged into such a user port.
The device is disconnected from the network and therefore no
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diagnostics from the network side is possible anymore.
Alternatively, all ports default to "admin down". The ACP (but not
the Data-Plane) would still automatically form. Diagnostics from the
network side is possible and operator reaction could include to
either make this port the operational uplink port or to instruct re-
cabling. Security wise, only ACP/ANI could be attacked, all other
functions are filtered on interfaces in "admin down" state.
10.3.2.2. Fast state propagation and Diagnostics
"Physical down" state propagates on many interface types (e.g.,
Ethernet) to the other side. This can trigger fast L2/L3 protocol
reaction on the other side and "admin down" would not have the same
(fast) result.
Bringing interfaces to "physical down" state is to the best of our
knowledge always a result of operator action, but today, never the
result of (autonomic) L2/L3 services running on the nodes. Therefore
one option is to change the operator action to not rely on link-state
propagation anymore. This may not be possible when both sides are
under different operator control, but in that case it is unlikely
that the ACP is running across the link and actually putting the
interface into "physical down" state may still be a good option.
Ideally, fast physical state propagation is replaced by fast software
driven state propagation. For example a DULL GRASP "admin-state"
objective could be used to auto configure a Bidirectional Forwarding
Protocol (BFD, [RFC5880]) session between the two sides of the link
that would be used to propagate the "up" vs. admin down state.
Triggering physical down state may also be used as a mean of
diagnosing cabling in the absence of easier methods. It is more
complex than automated neighbor diagnostics because it requires
coordinated remote access to both (likely) sides of a link to
determine whether up/down toggling will cause the same reaction on
the remote side.
See Section 10.1 for a discussion about how LLDP and/or diagnostics
via GRASP could be used to provide neighbor diagnostics, and
therefore hopefully eliminating the need for "physical down" for
neighbor diagnostics - as long as both neighbors support ACP/ANI.
10.3.2.3. Low Level Link Diagnostics
"Physical down" is performed to diagnose low-level interface behavior
when higher layer services (e.g., IPv6) are not working. Especially
Ethernet links are subject to a wide variety of possible wrong
configuration/cablings if they do not support automatic selection of
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variable parameters such as speed (10/100/1000 Mbps), crossover
(Auto-MDIX) and connector (fiber, copper - when interfaces have
multiple but can only enable one at a time). The need for low level
link diagnostic can therefore be minimized by using fully auto
configuring links.
In addition to "Physical down", low level diagnostics of Ethernet or
other interfaces also involve the creation of other states on
interfaces, such as physical Loopback (internal and/or external) or
bringing down all packet transmissions for reflection/cable-length
measurements. Any of these options would disrupt ACP as well.
In cases where such low-level diagnostics of an operational link is
desired but where the link could be a single point of failure for the
ACP, ASA on both nodes of the link could perform a negotiated
diagnostics that automatically terminates in a predetermined manner
without dependence on external input ensuring the link will become
operational again.
10.3.2.4. Power Consumption Issues
Power consumption of "physical down" interfaces, may be significantly
lower than those in "admin down" state, for example on long-range
fiber interfaces. Bringing up interfaces, for example to probe
reachabiliy, may also consume additional power. This can make these
type of interfaces inappropriate to operate purely for the ACP when
they are not currently needed for the Data-Plane.
10.3.3. Interface level ACP/ANI enable
The interface level configuration option "ACP enable" enables ACP
operations on an interface, starting with ACP neighbor discovery via
DULL GRAP. The interface level configuration option "ANI enable" on
nodes supporting BRSKI and ACP starts with BRSKI pledge operations
when there is no domain certificate on the node. On ACP/BRSKI nodes,
"ACP enable" may not need to be supported, but only "ANI enable".
Unless overridden by global configuration options (see later), "ACP/
ANI enable" will result in "down" state on an interface to behave as
"admin down".
10.3.4. Which interfaces to auto-enable?
(Section 6.3) requires that "ACP enable" is automatically set on
native interfaces, but not on non-native interfaces (reminder: a
native interface is one that exists without operator configuration
action such as physical interfaces in physical devices).
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Ideally, ACP enable is set automatically on all interfaces that
provide access to additional connectivity that allows to reach more
nodes of the ACP domain. The best set of interfaces necessary to
achieve this is not possible to determine automatically. Native
interfaces are the best automatic approximation.
Consider an ACP domain of ACP nodes transitively connected via native
interfaces. A Data-Plane tunnel between two of these nodes that are
non-adjacent is created and "ACP enable" is set for that tunnel. ACP
RPL sees this tunnel as just as a single hop. Routes in the ACP
would use this hop as an attractive path element to connect regions
adjacent to the tunnel nodes. In result, the actual hop-by-hop paths
used by traffic in the ACP can become worse. In addition, correct
forwarding in the ACP now depends on correct Data-Plane forwarding
config including QoS, filtering and other security on the Data-Plane
path across which this tunnel runs. This is the main issue why "ACP/
ANI enable" should not be set automatically on non-native interfaces.
If the tunnel would connect two previously disjoint ACP regions, then
it likely would be useful for the ACP. A Data-Plane tunnel could
also run across nodes without ACP and provide additional connectivity
for an already connected ACP network. The benefit of this additional
ACP redundancy has to be weighed against the problems of relying on
the Data-Plane. If a tunnel connects two separate ACP regions: how
many tunnels should be created to connect these ACP regions reliably
enough? Between which nodes? These are all standard tunneled
network design questions not specific to the ACP, and there are no
generic fully automated answers.
Instead of automatically setting "ACP enable" on these type of
interfaces, the decision needs to be based on the use purpose of the
non-native interface and "ACP enable" needs to be set in conjunction
with the mechanism through which the non-native interface is created/
configured.
In addition to explicit setting of "ACP/ANI enable", non-native
interfaces also need to support configuration of the ACP RPL cost of
the link - to avoid the problems of attracting too much traffic to
the link as described above.
Even native interfaces may not be able to automatically perform BRSKI
or ACP because they may require additional operator input to become
operational. Example include DSL interfaces requiring PPPoE
credentials or mobile interfaces requiring credentials from a SIM
card. Whatever mechanism is used to provide the necessary config to
the device to enable the interface can also be expanded to decide on
whether or not to set "ACP/ANI enable".
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The goal of automatically setting "ACP/ANI enable" on interfaces
(native or not) is to eliminate unnecessary "touches" to the node to
make its operation as much as possible "zero-touch" with respect to
ACP/ANI. If there are "unavoidable touches" such a creating/
configuring a non-native interface or provisioning credentials for a
native interface, then "ACP/ANI enable" should be added as an option
to that "touch". If a wrong "touch" is easily fixed (not creating
another high-cost touch), then the default should be not to enable
ANI/ACP, and if it is potentially expensive or slow to fix (e.g.,
parameters on SIM card shipped to remote location), then the default
should be to enable ACP/ANI.
10.3.5. Node Level ACP/ANI enable
A node level command "ACP/ANI enable [up-if-only]" enables ACP or ANI
on the node (ANI = ACP + BRSKI). Without this command set, any
interface level "ACP/ANI enable" is ignored. Once set, ACP/ANI will
operate interface where "ACP/ANI enable" is set. Setting of
interface level "ACP/ANI enable" is either automatic (default) or
explicit through operator action as described in the previous
section.
If the option "up-if-only" is selected, the behavior of "down"
interfaces is unchanged, and ACP/ANI will only operate on interfaces
where "ACP/ANI enable" is set and that are "up". When it is not set,
then "down" state of interfaces with "ACP/ANI enable" is modified to
behave as "admin down".
10.3.5.1. Brownfield nodes
A "brownfield" node is one that already has a configured Data-Plane.
Executing global "ACP/ANI enable [up-if-only]" on each node is the
only command necessary to create an ACP across a network of
brownfield nodes once all the nodes have a domain certificate. When
BRSKI is used ("ANI enable"), provisioning of the certificates only
requires set-up of a single BRSKI registrar node which could also
implement a CA for the network. This is the most simple way to
introduce ACP/ANI into existing (== brownfield) networks.
The need to explicitly enable ACP/ANI is especially important in
brownfield nodes because otherwise software updates may introduce
support for ACP/ANI: Automatic enablement of ACP/ANI in networks
where the operator does not only not want ACP/ANI but where he likely
never even heard of it could be quite irritating to him. Especially
when "down" behavior is changed to "admin down".
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Automatically setting "ANI enable" on brownfield nodes where the
operator is unaware of it could also be a critical security issue
depending on the vouchers used by BRKSI on these nodes. An attacker
could claim to be the owner of these devices and create an ACP that
the attacker has access/control over. In network where the operator
explicitly wants to enable the ANI this could not happen, because he
would create a BRSKI registrar that would discover attack attempts.
Nodes requiring "ownership vouchers" would not be subject to that
attack. See [I-D.ietf-anima-bootstrapping-keyinfra] for more
details. Note that a global "ACP enable" alone is not subject to
these type of attacks, because it always depends on some other
mechanism first to provision domain certificates into the device.
10.3.5.2. Greenfield nodes
A "greenfield" node is one that did not have any prior configuration.
For greenfield nodes, only "ANI enable" is relevant. If another
mechanism than BRSKI is used to (zero-touch) bootstrap a node, then
it is up to that mechanism to provision domain certificates and to
set global "ACP enable" as desired.
Nodes supporting full ANI functionality set "ANI enable"
automatically when they decide that they are greenfield, e.g., that
they are powering on from factory condition. They will then put all
native interfaces into "admin down" state and start to perform BRSKI
pledge functionality - and once a domain certificate is enrolled they
automatically enable ACP.
Attempts for BRSKI pledge operations in greenfield state should
terminate automatically when another method of configuring the node
is used. Methods that indicate some form of physical possession of
the device such as configuration via the serial console port could
lead to immediate termination of BRSKI, while other parallel auto
configuration methods subject to remote attacks might lead to BRSKI
termination only after they were successful. Details of this may
vary widely over different type of nodes. When BRSKI pledge
operation terminates, this will automatically unset "ANI enable" and
should terminate any temporarily needed state on the device to
perform BRSKI - DULL GRASP, BRSKI pledge and any IPv6 configuration
on interfaces.
10.3.6. Undoing ANI/ACP enable
Disabling ANI/ACP by undoing "ACP/ANI enable" is a risk for the
reliable operations of the ACP if it can be executed by mistake or
unauthorized. This behavior could be influenced through some
additional property in the certificate (e.g., in the domain
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information extension field) subject to future work: In an ANI
deployment intended for convenience, disabling it could be allowed
without further constraints. In an ANI deployment considered to be
critical more checks would be required. One very controlled option
would be to not permit these commands unless the domain certificate
has been revoked or is denied renewal. Configuring this option would
be a parameter on the BRSKI registrar(s). As long as the node did
not receive a domain certificate, undoing "ANI/ACP enable" should not
have any additional constraints.
10.3.7. Summary
Node-wide "ACP/ANI enable [up-if-only]" commands enable the operation
of ACP/ANI. This is only auto-enabled on ANI greenfield devices,
otherwise it must be configured explicitly.
If the option "up-if-only" is not selected, interfaces enabled for
ACP/ANI interpret "down" state as "admin down" and not "physical
down". In "admin-down" all non-ACP/ANI packets are filtered, but the
physical layer is kept running to permit ACP/ANI to operate.
(New) commands that result in physical interruption ("physical down",
"loopback") of ACP/ANI enabled interfaces should be built to protect
continuance or reestablishment of ACP as much as possible.
Interface level "ACP/ANI enable" control per-interface operations.
It is enabled by default on native interfaces and has to be
configured explicitly on other interfaces.
Disabling "ACP/ANI enable" global and per-interface should have
additional checks to minimize undesired breakage of ACP. The degree
of control could be a domain wide parameter in the domain
certificates.
11. 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
configuration. See Section 9.2 for details of how the ACP protects
itself against attacks from the outside and to a more limited degree
from the inside as well.
However, the security of the ACP depends on a number of other
factors:
o The usage of domain certificates depends on a valid supporting PKI
infrastructure. If the chain of trust of this PKI infrastructure
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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
node.
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
technologies.
Many details of ACP are designed with security in mind and discussed
elsewhere in the document:
IPv6 addresses used by nodes in the ACP are covered as part of the
node's domain certificate as described in Section 6.1.1. This allows
even verification of ownership of a peers IPv6 address when using a
connection authenticated with the domain certificate.
The ACP acts as a security (and transport) substrate for GRASP inside
the ACP such that GRASP is not only protected by attacks from the
outside, but also by attacks from compromised inside attackers - by
relying not only on hop-by-hop security of ACP secure channels, but
adding end-to-end security for those GRASP messages. See
Section 6.8.2.
ACP provides for secure, resilient zero-touch discovery of EST
servers for certificate renewal. See Section 6.1.3.
ACP provides extensible, auto-configuring hop-by-hop protection of
the ACP infrastructure via the negotiation of hop-by-hop secure
channel protocols. See Section 6.5 and Appendix A.6.
The ACP is designed to minimize attacks from the outside by
minimizing its dependency against any non-ACP (Data-Plane)
operations/configuration on a node. See also Section 6.12.2.
In combination with BRSKI, ACP enables a resilient, fully zero-touch
network solution for short-lived certificates that can be renewed or
re-enrolled even after unintentional expiry (e.g., because of
interrupted connectivity). See Appendix A.2.
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12. IANA Considerations
This document defines the "Autonomic Control Plane".
The IANA is requested to register the value "AN_ACP" (without quotes)
to the GRASP Objectives Names Table in the GRASP Parameter Registry.
The specification for this value is this document, Section 6.3.
The IANA is requested to register the value "SRV.est" (without
quotes) to the GRASP Objectives Names Table in the GRASP Parameter
Registry. The specification for this value is this document,
Section 6.1.3.
Note that the objective format "SRV.<service-name>" is intended to be
used for any <service-name> that is an [RFC6335] registered service
name. This is a proposed update to the GRASP registry subject to
future work and only mentioned here for informational purposed to
explain the unique format of the objective name.
The IANA is requested to create an ACP Parameter Registry with
currently one registry table - the "ACP Address Type" table.
"ACP Address Type" Table. The value in this table are numeric values
0...3 paired with a name (string). Future values MUST be assigned
using the Standards Action policy defined by [RFC8126]. The
following initial values are assigned by this document:
0: ACP Zone Addressing Sub-Scheme (ACP RFC Figure 9) / ACP Manual
Addressing Sub-Scheme (ACP RFC Section 6.10.4)
1: ACP Vlong Addressing Sub-Scheme (ACP RFC Section 6.10.5)
13. Acknowledgements
This work originated from an Autonomic Networking project at Cisco
Systems, which started in early 2010. Many people contributed to
this project and the idea of the Autonomic Control Plane, amongst
which (in alphabetical order): Ignas Bagdonas, Parag Bhide, Balaji
BL, Alex Clemm, Yves Hertoghs, Bruno Klauser, Max Pritikin, Michael
Richardson, Ravi Kumar Vadapalli.
Special thanks to Brian Carpenter, Elwyn Davies, Joel Halpern and
Sheng Jiang for their thorough reviews and to Pascal Thubert and
Michael Richardson to provide the details for the recommendations of
the use of RPL in the ACP.
Further input, review or suggestions were received from: Rene Struik,
Brian Carpenter, Benoit Claise, William Atwood and Yongkang Zhang.
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14. Change log [RFC Editor: Please remove]
14.1. Initial version
First version of this document: draft-behringer-autonomic-control-
plane
14.2. draft-behringer-anima-autonomic-control-plane-00
Initial version of the anima document; only minor edits.
14.3. 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
term.
14.4. 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
overlapping.
o Clarified the relationship with draft-ietf-anima-stable-
connectivity
14.5. draft-behringer-anima-autonomic-control-plane-03
o Took out requirement for IPv6 --> that's in the reference doc.
o Added requirement section.
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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.
14.6. draft-ietf-anima-autonomic-control-plane-00
No changes; re-submitted as WG document.
14.7. 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
protocol.
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.
o Updated links, lots of small edits.
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14.8. 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.
14.9. 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
subjectAltName.
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
now.
o Included information on how ANIMA information must be encoded in
the domain certificate in section "preconditions".
o Editorial changes, updated draft references, etc.
14.10. 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
original explanations why GRASP would be useful (current text is
meant to be better).
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14.11. 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
RFC4941.
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).
14.12. 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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14.13. 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 signaled via GRASP.
14.14. 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 Zero-Touch. 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, e.g., 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
name.
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Added V8 (now called Vlong) addressing sub-scheme according to
suggestion from mcr in his mail from 30 Nov 2016
(https://mailarchive.ietf.org/arch/msg/anima/
nZpEphrTqDCBdzsKMpaIn2gsIzI). Also modified the explanation of the
single V bit in the first sub-scheme now renamed to Zone sub-scheme
to distinguish it.
14.15. draft-ietf-anima-autonomic-control-plane-09
Added reference to RFC4191 and explained how it should be used on ACP
edge routers to allow auto configuration 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.
o 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 e.g., 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 (e.g.,
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 (e.g., 6man WG.).
Added changes from Michael Richardsons review https://github.com/
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 black hole route to avoid loops in RPL.
Added requirement to terminate ACP channels upon cert expiry/
revocation.
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.
14.16. draft-ietf-anima-autonomic-control-plane-10
Used the term routing subdomain more consistently where previously
only subdomain was used. Clarified use of routing subdomain in
creation of ULA "global ID" addressing prefix.
6.7.1.* Changed native IPsec encapsulation to tunnel mode
(necessary), explaned why. Added notion that ESP is used, added
explanations why tunnel/transport mode in native vs. GRE cases.
6.10.3/6.10.5 Added term "ACP address range/set" to be able to better
explain how the address in the ACP certificate is actually the base
address (lowest address) of a range/set that is available to the
device.
6.10.4 Added note that manual address sub-scheme addresses must not
be used within domain certificates (only for explicit configuration).
6.12.5 Refined explanation of how ACP virtual interfaces work (p2p
and multipoint). Did seek for pre-existing RFCs that explain how to
built a multi-access interface on top of a full mesh of p2p
connections (6man WG, anima WG mailing lists), but could not find any
prior work that had a succinct explanation. So wrote up an
explanation here. Added hopefully all necessary and sufficient
details how to map ACP unicast packets to ACP secure channel, how to
deal with ND packet details. Added verbage for ACP not to assign the
virtual interface link-local address from the underlying interface.
Addd note that GRAP link-local messages are treated specially but
logically the same. Added paragraph about NBMA interfaces.
remaining changes from Brian Carpenters review. See Github file
draft-ietf-anima-autonomic-control-plane/08-carpenter-review-reply.tx
for more detailst:
Added multiple new RFC references for terms/technologies used.
Fixed verbage in several places.
2. (terminology) Added 802.1AR as reference.
2. Fixed up definition of ULA.
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6.1.1 Changed definition of ACP information in cert into ABNF format.
Added warning about maximum size of ACP address field due to domain-
name limitations.
6.2 Mentioned API requirement between ACP and clients leveraging
adjacency table.
6.3 Fixed TTL in GRASP example: msec, not hop-count!.
6.8.2 MAYOR: expanded security/transport substrate text:
Introduced term ACP GRASP virtual interface to explain how GRASP
link-local multicast messages are encapsulated and replicated to
neighbors. Explain how ACP knows when to use TLS vs. TCP (TCP only
for link-local address (sockets). Introduced "ladder" picture to
visualize stack.
6.8.2.1 Expanded discussion/explanation of security model. TLS for
GRASP unicsast connections across ACP is double encryption (plus
underlying ACP secure channel), but highly necessary to avoid very
simple man-in-the-middle attacks by compromised ACP members on-path.
Ultimately, this is done to ensure that any apps using GRASP can get
full end-to-end secrecy for information sent across GRASP. But for
publically known ASA services, even this will not provide 100%
security (this is discussed). Also why double encryption is the
better/easier solution than trying to optimize this.
6.10.1 Added discussion about pseudo-random addressing, scanning-
attaacks (not an issue for ACP).
6.12.2 New performance requirements section added.
6.10.1 Added notion to first experiment with existing addressing
schemes before defining new ones - we should be flexible enough.
6.3/7.2 clarified the interactions between MLD and DULL GRASP and
specified what needs to be done (e.g., in 2 switches doing ACP per L2
port).
12. Added explanations and cross-references to various security
aspects of ACP discussed elsewhere in the document.
13. Added IANA requirements.
Added RFC2119 boilerplate.
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14.17. draft-ietf-anima-autonomic-control-plane-11
Same text as -10 Unfortunately when uploading -10 .xml/.txt to
datatracker, a wrong version of .txt got uploaded, only the .xml was
correct. This impacts the -10 html version on datatra cker and the
PDF versions as well. Because rfcdiff also compares the .txt
version, this -11 version was crea ted so that one can compare
changes from -09 and changes to the next version (-12).
14.18. draft-ietf-anima-autonomic-control-plane-12
Sheng Jiangs extensive review. Thanks! See Github file draft-ietf-
anima-autonomic-control-plane/09-sheng-review-reply.txt for more
details. Many of the larger changes listed below where inspired by
the review.
Removed the claim that the document is updating RFC4291,RFC4193 and
the section detailling it. Done on suggestion of Michael Richardson
- just try to describe use of addressing in a way that would not
suggest a need claim update to architecture.
Terminology cleanup:
o Replaced "device" with "node" in text. Kept "device" only when
referring to "physical node". Added definitions for those words.
Includes changes of derived terms, especially in addressing:
"Node-ID" and "Node-Number" in the addressing details.
o Replaced term "autonomic FOOBAR" with "acp FOOBAR" as whereever
appropriate: "autonomic" would imply that the node would need to
support more than the ACP, but that is not correct in most of the
cases. Wanted to make sure that implementers know they only need
to support/implement ACP - unless stated otherwise. Includes
"AN->ACP node", "AN->ACP adjacency table" and so on.
1 Added explanation in the introduction about relationship between
ACP, BRSKI, ANI and Autonomic Networks.
6.1.1 Improved terminology and features of the certificate
information field. Now called domain information field instead of
ACP information field. The acp-address field in the domain
information field is now optional, enabling easier introduction of
various future options.
6.1.2 Moved ACP domainer membership check from section 6.6 to (ACP
secure channels setup) here because it is not only used for ACP
secure channel setup.
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6.1.3 Fix text about certificate renewal after discussion with Max
Pritikin/Michael Richardson/Brian Carpenter:
o Version 10 erroneously assumed that the certificate itself could
store a URL for renewal, but that is only possible for CRL URLs.
Text now only refers to "remembered EST server" without implying
that this is stored in the certificate.
o Objective for RFC7030/EST domain certificate renewal was changed
to "SRV.est" See also IANA section for explanation.
o Removed detail of distance based service selection. This can be
better done in future work because it would require a lot more
detail for a good DNS-SD compatible approach.
o Removed detail about trying to create more security by using ACP
address from certificate of peer. After rethinking, this does not
seem to buy additional security.
6.10 Added reference to 6.12.5 in initial use of "loopback interface"
in section 6.10 in result of email discussion michaelR/michaelB.
10.2 Introduced informational section (diagnostics) because of
operational experience - ACP/ANI undeployable without at least
diagnostics like this.
10.3 Introduced informational section (enabling/disabling) ACP.
Important to discuss this for security reasons (e.g., why to never
never auto-enable ANI on brownfield devices), for implementers and to
answer ongoing questions during WG meetings about how to deal with
shutdown interface.
10.8 Added informational section discussing possible future
variations of the ACP for potential adopters that cannot directly use
the complete solution described in this document unmodified.
14.19. draft-ietf-anima-autonomic-control-plane-13
Swap author list (with permission).
6.1.1. Eliminate blank lines in definition by making it a picture
(reformatting only).
6.10.3.1 New paragraph: Explained how nodes using Zone-ID != 0 need
to use Zone-ID != 0 in GRASP so that we can avoid routing/forwarding
of Zone-ID = 0 prefixes.
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Rest of feedback from review of -12, see
https://raw.githubusercontent.com/anima-wg/autonomic-control-
plane/master/draft-ietf-anima-autonomic-control-plane/12-feedback-
reply.txt
Review from Brian Carpenter:
various: Autonomous -> autonomic(ally) in all remaining occurences.
various: changed "manual (configured)" to "explicitly (configured)"
to not exclude the option of (SDN controller) automatic configuration
(no humans involved).
1. Fixed reference to section 9.
2. Added definition of loopback interface == internal interface.
After discus on WG mailing lists, including 6man.
6.1.2 Defined CDP/OCSP and pointed to RFC5280 for them.
6.1.3 Removed "EST-TLS", no objective value needed or beneficial,
added explanation paragraph why.
6.2 Added to adjacency table the interface that a neighbor is
discovered on.
6.3 Simplified CDDL syntax: Only one method per AN_ACP objective
(because of locators). Example with two objectives in GRASP message.
6.8.1 Added note about link-local GRASP multicast message to avoid
confusion.
8.1.4 Added RFC8028 as recommended on hosts to better support VRF-
select with ACP.
8.2.1 Rewrote and Simplified CDDL for configured remote peer and
explanations. Removed pattern option for remote peer. Not important
enough to be mandated.
Review thread started by William Atwood:
2. Refined definition of VRF (vs. MPLS/VPN, LISP, VRF-LITE).
2. Refined definition of ACP (ACP includes ACP GRASP instance).
2. Added explanation for "zones" to terminology section and into
Zone Addressing Sub Scheme section, relating it to RFC4007 zones
(from Brian Carpenter).
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4. Fixed text for ACP4 requirement (Clients of the ACP must not be
tied to specific protocol.).
5. Fixed step 4. with proposed text.
6.1.1 Included suggested explanation for rsub semantics.
6.1.3 must->MUST for at least one EST server in ACP network to
autonomically renew certs.
6.7.2 normative: AND MUST NOT (permit weaker crypto options.
6.7.1.1 also included text denying weaker IPsec profile options.
6.8.2 Fixed description how to build ACP GRASP virtual interfaces.
Added text that ACP continues to exist in absence of ACP neighbors.
various: Make sure all "zone" words are used consistently.
6.10.2/various: fixed 40 bit RFC4193 ULA prefix in all examples to
89b714f3db (thanks MichaelR).
6.10.1 Removed comment about assigned ULA addressing. Decision not
to use it now ancient history of WG decision making process, not
worth nothing anymore in the RFC.
Review from Yongkang Zhang:
6.10.5 Fixed length of Node-Numbers in ACP Vlong Addressing Sub-
Scheme.
14.20. draft-ietf-anima-autonomic-control-plane-14
Disclaimer: All new text introduced by this revision provides only
additional explanations/ details based on received reviews and
analysis by the authors. No changes to beavior already specified in
prior revisions.
Joel Halpern, review part 3:
Define/explain "ACP registrar" in reply to Joel Halpern review part
3, resolving primarily 2 documentation issues::
1. Unclear how much ACP depends on BRSKI. ACP document was
referring unqualified to registrars and Registrar-ID in the
addressing section without explaining what a registrar is,
leading to the assumption it must be a BRSKI Registrar.
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2. Unclear how the ACP addresses in ACP domain certificates are
assigned because the BRSKI document does not defines this, but
refers to this ACP document.
Wrt. 1: ACP does NOT depend on BRSKI registrars, instead ANY
appropriate automated or manual mechanism can be used to enroll ACP
nodes with ACP domain certificates. This revision calls defines such
mechanisms the "ACP registrar" and defines requirements. this is
non-normative, because it does not define specific mechanisms that
need to be support. In ANI devices, ACP Registrars are BRSKI
Registrars. In non-ANI ACP networks, the registrar may simply be a
person using CLI/web-interfaces to provision domain certificates and
set the ACP address correctly in the ACP domain certificate.
Wrt. 2.: The BRSKI document does rightfully not define how the ACP
address assignment and creation of the ACP domain information field
has to work because this is independent of BRSKI and needs to follow
the same rules whatever protocol/mechanisms are used to implement an
ACP Registrar. Another set of protocols that could be used instead
of BRSKI is Netconf/Netconf-Call-Home, but such an alternative ACP
Registrar solution would need to be speficied in it's own document.
Additional text/sections had to be added to detail important
conditions so that automatic certificate maintenance for ACP nodes
(with BRSKI or other mechanisms) can be done in a way that as good as
possible maintains ACP address information of ACP nodes across the
nodes lifetime because that ACP address is intended as an identifier
of the ACP node.
Summary of sections added:
o 6.1.3.5/6.1.3.6 (normative): re-enrollment of ACP nodes after
certificate exiry/failure in a way that allows to maintain as much
as possible ACP address information.
o 6.10.7 (normative): defines "ACP Registrar" including requirements
and how it can perform ACP address assignment.
o 10.3 (informative): details / examples about registrars to help
implementers and operators understand easier how they operate, and
provide suggestion of models that a likely very ueful (sub-CA and/
or centralized policy manaement).
o 10.4 (informative): Explains the need for the multiple address
sub-spaces defined in response to discuss with Joel.
Other changes:
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Updated references (RFC8366, RFC8368).
Introduced sub-section headings for 6.1.3 (certificate maintenance)
because section became too long with newly added sub-sections. Also
some small text fixups/remove of duplicate text.
Gen-ART review, Elwyn Davies:
[RFC Editor: how can i raise the issue of problematic cross
references of terms in the terminology section - rendering is
problematic. ].
4. added explanation for ACP4 (finally).
6.1.1 Simplified text in bullet list explaining rfc822 encoding.
6.1.3 refined second paragraph defining remembering of previous EST
server and explaiing how to do this with BRSKI.
9.1 Added paragraph outlining the benefit of the sub-CA Registrar
option for supporting partitioned networks.
Roughly 100 more nits/minor fixes throughout the document. See:
https://raw.githubusercontent.com/anima-wg/autonomic-control-
plane/master/draft-ietf-anima-autonomic-control-plane/13-elwynd-
reply.txt
Joel Halpern, review part 2:
6.1.1: added note about "+ +" format in address field when acp-
address and rsub are empty.
6.5.10 - clarified text about V bit in Vlong addressing scheme.
6.10.3/6.10.4 - moved the Z bit field up front (directly after base
scheme) and indicated more explicitly Z is part of selecting of the
sub-addressing scheme.
Refined text about reaching CRL Distribution Point, explain why
address as indicator to use ACP.
Note from Brian Carpenter: RFC Editor note for section reference into
GRASP.
IOT directorate review from Pascal Thubert:
Various Nits/typos.
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TBD: Punted wish for mentioning RFC reference titles to RFC editor
for now.
1. Added section 1.1 - applicability, discussing protocol choices
re. applicability to constrained devices (or not). Added notion of
TCP/TLS va CoAP/DTLS to section 10.4 in support of this.
2. Added in-band / out-of-band into terminology.
5. Referenced section 8.2 for remote ACP channel configuration.
6.3 made M_FLOOD periods RECOMMENDED (less guesswork)
6.7.x Clarified conditional nature of MUST for the profile details of
IPsec parameters (aka: onlt 6.7.3 defines actual MUST for nodes,
prior notions only define the requirements for IPsec profiles IF
IPsec is supported.
6.8.1 Moved discussion about IP multicast, IGP, RPL for GRASP into a
new subsection in the informative part (section 10) to tighten up
text in normative part.
6.10.1 added another reference to stable-connectivity for interop
with IPv4 management.
6.10.1 removed mentioning of ULA-Random, term was used in email
discus of ULA with L=1, but term actually not defined in rfc4193, so
mentioning it is just confusing/redundant. Also added note about the
random hash being defined in this document, not using SHA1 from
rfc4193.
6.11.1.1 added suggested text about mechanisms to further reduce
opportunities for loop during reconvergence (active signaling options
from RFC6550).
6.11.1.3 made mode 2 MUST and mode 2 MAY (RPL MOP - mode of
operations). Removes ambiguity ambiguity.
6.12.5 Added recommendation for RFC4429 (optimistic DAD).
Nits from Benjamin Kaduk: dTLS -> DTLS:
Review from Joel Halpern:
1. swapped order of "purposes" for ACP to match order in section 3.
1. Added notion about manageability of ACP gong beyond RFC7575
(before discussion of stable connectivity).
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2. Changed definition of Intent to be same as reference model
(policy lanuage instead of API).
6.1.1 changed BNF specification so that a local-part without acp-
address (for future extensions) would not be rfcSELF.+rsub but
simpler rfcSELF+rsub. Added explanation why rsub is in local-part.
Tried to eliminate unnecessary references to VRF to minimize
assumption how system is designed.
6.1.3 Explained how to make CDP reachable via ACP.
6.7.2 Made it clearer that constrained devices MUST support DTLS if
they can not support IPsec.
6.8.2.1 clarified first paragraph (TCP restransmissions lightweight).
6.11.1 fixed up RPL profile text - to remove "VRF". Text was also
buggy. mentioned control plane, but its a forwarding/silicon issue to
have these header.
6.12.5 Clarified how link-local ACP channel address can be derived,
and how not.
8.2.1 Fixed up text to distinguish between configuration and model
describing parameters of the configuration (spec only provides
parameter model).
Various Nits.
14.21. draft-ietf-anima-autonomic-control-plane-15
Only reshuffling and formatting changes, but wanted to allow
reviewers later to easily compare -13 with -14, and these changes in
-15 mess that up too much.
increased TOC depth to 4.
Separated and reordered section 10 into an operational and a
background and futures section. The background and futures could
also become appendices if the layout of appendices in RFC format
wasn't so horrible that you really only want to avoid using them (all
the way after a lot of text like references that stop most readers
from proceeding any further).
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14.22. draft-ietf-anima-autonomic-control-plane-16
Mirja Kuehlewind:
Tightened requirements for ACP related GRASP objective timers.
Better text to introduce/explaine baseline and constrained ACP
profiles.
IANA guideline: MUST only accept extensible last allocation for
address sub-scheme.
Moved section 11 into appendix.
Warren Kumari:
Removed "global routing table", replacced with "Data-Plane routing
(and forwarding) tables.
added text to indicate how routing protocols do like to have data-
plane dependencies.
Changed power consumption section re. admin-down state. Power needed
to bring up such interfaces make t inappropriate to probe. Need to
think more about best sugests -> beyond scope.
Replaced "console" with out-of-band... (console/management ethernet).
Various nits.
Joel Halpern:
Fixed up domain information field ABNF to eliminate confusion that
rsub is not an FQDN but only a prefix to routing-subdomain.
Corrected certcheck to separate out cert verification into lifetime
validity and proof of ownership of private key.
Fixed pagination for "ACP as security and transport substrate for
GRASP" picture.
14.23. draft-ietf-anima-autonomic-control-plane-17
Review Alissa Cooper:
Main discuss point fixed by untangling two specific node type cases:
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NOC nodes have ACP domain cert without acp-address field. Are ACP
domain members, but can not build ACP secure channels (just end-to-
end or nay other authentications.
ACP nodes may have other methods to assign ACP address than getting
it through the cert. This is indicated through new vlue 0 for acp-
address in certificate.
Accordingly modified texts in ABNF/explanation and Cert-Check
section.
Other:
Better separation of normative text and considerations for "future"
work:
- Marked missing chapters as Informative. Reworded requirements
section to indicate its informative nature, changed reqirements to
_MUST_/_SHOULD_ to indicate these are not RFC2119 requirements but
that this requirements section is really just in place of a separate
solutions requirements document (that ANIMA was not allowed to
produce).
- removed ca. 20 instances of "futures" in normative part of
document.
- moved important instances of "futures" into new section A.10 (last
section of appendix). These serve as reminder os work discussed
dduring WG but not able to finish specifying it.
Eliminated perception that "rsub" (routing subdomain) is only
beneficial with future work. Example in A.7.
Added RFC-editor note re formatting of references to terms defined in
terminology section.
Using now correct RFC 8174 boilerplate.
Clarified semantic and use of manual ACP sub-scheme. Not used in
certificates, only assigned via traditional methods. Use for ACP-
connect subnets or the like.
Corrected text about Data-Plane dependencies of ACP. Appropriate
implementations can be fully data-plane independent (without more
spec work) if not sharing link-local address with Data-Plane. 6.12.2
text updated to discuss those (MAC address), A.10.2 discusses options
that would require new standards work.
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Moved all text about Intent into A.8 to clearl mark it as futures.
Changed suggestion of future insecure ACP option to future "end-to-
end-security-only" option.
Various textual fixes.
Gen-ART review by Elwyn Davies:
Some fixes also mentioned by Alissa.
Added reference for OT.
Fixed notion that secure channel is not only a security association.
>20 good textual fixes. Thanks!
Other:
Added picture requested by Pascal Thubert about Dual-NOC (A.10.4).
Moved RFC-editor request for better first RFC reference closer to the
top of the document.
Fixed typo /126 -> 127 for prefix length with zone address scheme.
Overlooked early SecDir review from frank.xialiang@huawei.com:
most issues fixed through other review in -16. Added reference to
self-protection section 9.2 into security considerations section.
15. References
15.1. Normative References
[I-D.ietf-anima-grasp]
Bormann, C., Carpenter, B., and B. Liu, "A Generic
Autonomic Signaling Protocol (GRASP)", draft-ietf-anima-
grasp-15 (work in progress), July 2017.
[I-D.ietf-cbor-cddl]
Birkholz, H., Vigano, C., and C. Bormann, "Concise data
definition language (CDDL): a notational convention to
express CBOR data structures", draft-ietf-cbor-cddl-03
(work in progress), July 2018.
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[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.
[RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
DOI 10.17487/RFC3810, June 2004,
<https://www.rfc-editor.org/info/rfc3810>.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191,
November 2005, <https://www.rfc-editor.org/info/rfc4191>.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
<https://www.rfc-editor.org/info/rfc4193>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <https://www.rfc-editor.org/info/rfc4301>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<https://www.rfc-editor.org/info/rfc4862>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
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[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,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
DOI 10.17487/RFC5322, October 2008,
<https://www.rfc-editor.org/info/rfc5322>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[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,
<https://www.rfc-editor.org/info/rfc6550>.
[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,
<https://www.rfc-editor.org/info/rfc6552>.
[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,
<https://www.rfc-editor.org/info/rfc6553>.
[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
"Enrollment over Secure Transport", RFC 7030,
DOI 10.17487/RFC7030, October 2013,
<https://www.rfc-editor.org/info/rfc7030>.
[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <https://www.rfc-editor.org/info/rfc7296>.
[RFC7676] Pignataro, C., Bonica, R., and S. Krishnan, "IPv6 Support
for Generic Routing Encapsulation (GRE)", RFC 7676,
DOI 10.17487/RFC7676, October 2015,
<https://www.rfc-editor.org/info/rfc7676>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
15.2. Informative References
[AR8021] IEEE SA-Standards Board, "IEEE Standard for Local and
metropolitan area networks - Secure Device Identity",
December 2009, <http://standards.ieee.org/findstds/
standard/802.1AR-2009.html>.
[I-D.ietf-anima-bootstrapping-keyinfra]
Pritikin, M., Richardson, M., Behringer, M., Bjarnason,
S., and K. Watsen, "Bootstrapping Remote Secure Key
Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping-
keyinfra-16 (work in progress), June 2018.
[I-D.ietf-anima-prefix-management]
Jiang, S., Du, Z., Carpenter, B., and Q. Sun, "Autonomic
IPv6 Edge Prefix Management in Large-scale Networks",
draft-ietf-anima-prefix-management-07 (work in progress),
December 2017.
[I-D.ietf-anima-reference-model]
Behringer, M., Carpenter, B., Eckert, T., Ciavaglia, L.,
and J. Nobre, "A Reference Model for Autonomic
Networking", draft-ietf-anima-reference-model-06 (work in
progress), February 2018.
[I-D.ietf-netconf-zerotouch]
Watsen, K., Abrahamsson, M., and I. Farrer, "Zero Touch
Provisioning for Networking Devices", draft-ietf-netconf-
zerotouch-22 (work in progress), June 2018.
[I-D.ietf-roll-applicability-template]
Richardson, M., "ROLL Applicability Statement Template",
draft-ietf-roll-applicability-template-09 (work in
progress), May 2016.
[I-D.ietf-roll-useofrplinfo]
Robles, I., Richardson, M., and P. Thubert, "When to use
RFC 6553, 6554 and IPv6-in-IPv6", draft-ietf-roll-
useofrplinfo-23 (work in progress), May 2018.
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[IEEE-802.1X]
IEEE SA-Standards Board, "IEEE Standard for Local and
Metropolitan Area Networks: Port-Based Network Access
Control", February 2010,
<http://standards.ieee.org/findstds/
standard/802.1X-2010.html>.
[LLDP] IEEE SA-Standards Board, "IEEE Standard for Local and
Metropolitan Area Networks: Station and Media Access
Control Connectivity Discovery", June 2016,
<https://standards.ieee.org/findstds/
standard/802.1AB-2016.html>.
[MACSEC] IEEE SA-Standards Board, "IEEE Standard for Local and
Metropolitan Area Networks: Media Access Control (MAC)
Security", June 2006,
<https://standards.ieee.org/findstds/
standard/802.1AE-2006.html>.
[RFC1112] Deering, S., "Host extensions for IP multicasting", STD 5,
RFC 1112, DOI 10.17487/RFC1112, August 1989,
<https://www.rfc-editor.org/info/rfc1112>.
[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
and E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996,
<https://www.rfc-editor.org/info/rfc1918>.
[RFC2315] Kaliski, B., "PKCS #7: Cryptographic Message Syntax
Version 1.5", RFC 2315, DOI 10.17487/RFC2315, March 1998,
<https://www.rfc-editor.org/info/rfc2315>.
[RFC2821] Klensin, J., Ed., "Simple Mail Transfer Protocol",
RFC 2821, DOI 10.17487/RFC2821, April 2001,
<https://www.rfc-editor.org/info/rfc2821>.
[RFC4007] Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and
B. Zill, "IPv6 Scoped Address Architecture", RFC 4007,
DOI 10.17487/RFC4007, March 2005,
<https://www.rfc-editor.org/info/rfc4007>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <https://www.rfc-editor.org/info/rfc4364>.
[RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD)
for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006,
<https://www.rfc-editor.org/info/rfc4429>.
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[RFC4541] Christensen, M., Kimball, K., and F. Solensky,
"Considerations for Internet Group Management Protocol
(IGMP) and Multicast Listener Discovery (MLD) Snooping
Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006,
<https://www.rfc-editor.org/info/rfc4541>.
[RFC4604] Holbrook, H., Cain, B., and B. Haberman, "Using Internet
Group Management Protocol Version 3 (IGMPv3) and Multicast
Listener Discovery Protocol Version 2 (MLDv2) for Source-
Specific Multicast", RFC 4604, DOI 10.17487/RFC4604,
August 2006, <https://www.rfc-editor.org/info/rfc4604>.
[RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for
IP", RFC 4607, DOI 10.17487/RFC4607, August 2006,
<https://www.rfc-editor.org/info/rfc4607>.
[RFC4610] Farinacci, D. and Y. Cai, "Anycast-RP Using Protocol
Independent Multicast (PIM)", RFC 4610,
DOI 10.17487/RFC4610, August 2006,
<https://www.rfc-editor.org/info/rfc4610>.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,
<https://www.rfc-editor.org/info/rfc4941>.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
DOI 10.17487/RFC5321, October 2008,
<https://www.rfc-editor.org/info/rfc5321>.
[RFC5790] Liu, H., Cao, W., and H. Asaeda, "Lightweight Internet
Group Management Protocol Version 3 (IGMPv3) and Multicast
Listener Discovery Version 2 (MLDv2) Protocols", RFC 5790,
DOI 10.17487/RFC5790, February 2010,
<https://www.rfc-editor.org/info/rfc5790>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>.
[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,
<https://www.rfc-editor.org/info/rfc6241>.
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[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
Cheshire, "Internet Assigned Numbers Authority (IANA)
Procedures for the Management of the Service Name and
Transport Protocol Port Number Registry", BCP 165,
RFC 6335, DOI 10.17487/RFC6335, August 2011,
<https://www.rfc-editor.org/info/rfc6335>.
[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,
<https://www.rfc-editor.org/info/rfc6724>.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013,
<https://www.rfc-editor.org/info/rfc6762>.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<https://www.rfc-editor.org/info/rfc6763>.
[RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
Locator/ID Separation Protocol (LISP)", RFC 6830,
DOI 10.17487/RFC6830, January 2013,
<https://www.rfc-editor.org/info/rfc6830>.
[RFC7404] Behringer, M. and E. Vyncke, "Using Only Link-Local
Addressing inside an IPv6 Network", RFC 7404,
DOI 10.17487/RFC7404, November 2014,
<https://www.rfc-editor.org/info/rfc7404>.
[RFC7426] Haleplidis, E., Ed., Pentikousis, K., Ed., Denazis, S.,
Hadi Salim, J., Meyer, D., and O. Koufopavlou, "Software-
Defined Networking (SDN): Layers and Architecture
Terminology", RFC 7426, DOI 10.17487/RFC7426, January
2015, <https://www.rfc-editor.org/info/rfc7426>.
[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,
<https://www.rfc-editor.org/info/rfc7575>.
[RFC7576] Jiang, S., Carpenter, B., and M. Behringer, "General Gap
Analysis for Autonomic Networking", RFC 7576,
DOI 10.17487/RFC7576, June 2015,
<https://www.rfc-editor.org/info/rfc7576>.
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[RFC7721] Cooper, A., Gont, F., and D. Thaler, "Security and Privacy
Considerations for IPv6 Address Generation Mechanisms",
RFC 7721, DOI 10.17487/RFC7721, March 2016,
<https://www.rfc-editor.org/info/rfc7721>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
[RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by
Hosts in a Multi-Prefix Network", RFC 8028,
DOI 10.17487/RFC8028, November 2016,
<https://www.rfc-editor.org/info/rfc8028>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8366] Watsen, K., Richardson, M., Pritikin, M., and T. Eckert,
"A Voucher Artifact for Bootstrapping Protocols",
RFC 8366, DOI 10.17487/RFC8366, May 2018,
<https://www.rfc-editor.org/info/rfc8366>.
[RFC8368] Eckert, T., Ed. and M. Behringer, "Using an Autonomic
Control Plane for Stable Connectivity of Network
Operations, Administration, and Maintenance (OAM)",
RFC 8368, DOI 10.17487/RFC8368, May 2018,
<https://www.rfc-editor.org/info/rfc8368>.
15.3. URIs
[1] https://en.wikipedia.org/wiki/Operational_Technology
[2] https://en.wikipedia.org/wiki/Single-root_input/
output_virtualization
Appendix A. Background and Futures (Informative)
The following sections discuss additional background information
about aspects of the normative parts of this document or associated
mechanisms such as BRSKI (such as why specific choices where made by
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the ACP) and they provide discussion about possble future variations
of the ACP.
A.1. ACP Address Space Schemes
This document defines the Zone, Vlong and Manual sub address schemes
primarily to support address prefix assignment via distributed,
potentially uncoordinated ACP registrars as defined in
Section 6.10.7. This costs 48/46 bit identifier so that these ACP
registrar can assign non-conflicting address prefixes. This design
does not leave enough bits to simultaneously support a large number
of nodes (Node-ID) plus a large prefix of local addresses for every
node plus a large enough set of bits to identify a routing Zone. In
result, Zone, Vlong 8/16 attempt to support all features, but in via
separate prefixes.
In networks that always expect to rely on a centralized PMS as
described above (Section 10.2.5), the 48/46 bits for the Registrar-ID
could be saved. Such variations of the ACP addressing mecchanisms
could be introduct through future work in different ways. If the
prefix rfcSELF in the ACP information field was changed, incompatible
ACP variations could be created where every design aspect of the ACP
could be changed. Including all addressing choices. If instead a
new addressing sub-type would be defined, it could be a backward
compatible extension of this ACP specification. Information such as
the size of a zone-prefix and the length of the prefix assigned to
the ACP node itself could be encoded via the extension field of the
ACP domain information.
Note that an explicitly defined "Manual" addressing sub-scheme is
always beneficial to provide an easy way for ACP nodes to prohibit
incorrect manual configuration of any non-"Manual" ACP address spaces
and therefore ensure hat "Manual" operations will never impact
correct routing for any non-"Manual" ACP addresses assigned via ACP
domain certificates.
A.2. BRSKI Bootstrap (ANI)
[I-D.ietf-anima-bootstrapping-keyinfra] (BRSKI) describes how nodes
with an IDevID certificate can securely and zero-touch enroll with a
domain certificate (LDevID) to support the ACP. BRSKI also leverages
the ACP to enable zero-touch bootstrap of new nodes across networks
without any configuration requirements across the transit nodes
(e.g., no DHCP/DNS forwarding/server setup). This includes otherwise
not configured networks as described in Section 3.2. Therefore BRSKI
in conjunction with ACP provides for a secure and zero-touch
management solution for complete networks. Nodes supporting such an
infrastructure (BRSKI and ACP) are called ANI nodes (Autonomic
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Networking Infrastructure), see [I-D.ietf-anima-reference-model].
Nodes that do not support an IDevID but only an (insecure) vendor
specific Unique Device Identifier (UDI) or nodes whose manufacturer
does not support a MASA could use some future security reduced
version of BRSKI.
When BRSKI is used to provision a domain certificate (which is called
enrollment), the BRSKI registrar (acting as an enhanced EST server)
must include the subjectAltName / rfc822Name encoded ACP address and
domain name to the enrolling node (called pledge) via its response to
the pledges EST CSR Attribute request that is mandatory in BRSKI.
The Certificate Authority in an ACP network must not change the
subjectAltName / rfc822Name in the certificate. The ACP nodes can
therefore find their ACP address and domain using this field in the
domain certificate, both for themselves, as well as for other nodes.
The use of BRSKI in conjunction with the ACP can also help to further
simplify maintenance and renewal of domain certificates. Instead of
relying on CRL, the lifetime of certificates can be made extremely
small, for example in the order of hours. When a node fails to
connect to the ACP within its certificate lifetime, it cannot connect
to the ACP to renew its certificate across it (using just EST), but
it can still renew its certificate as an "enrolled/expired pledge"
via the BRSKI bootstrap proxy. This requires only that the BRSKI
registrar honors expired domain certificates and that the pledge
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 could also render CRLs unnecessary
because the BRSKI registrar in conjunction with the CA would not
renew revoked certificates - only a "Do-not-renew" list would be
necessary on BRSKI registrars/CA.
In the absence of BRSKI or less secure variants thereof, provisioning
of certificates may involve one or more touches or non-standardized
automation. Node vendors usually support provisioning of
certificates into nodes via PKCS#7 (see [RFC2315]) and may support
this provisioning through vendor specific models via Netconf
([RFC6241]). If such nodes also support Netconf Zero-Touch
([I-D.ietf-netconf-zerotouch]) then this can be combined to zero-
touch provisioning of domain certificates into nodes. Unless there
are equivalent integration of Netconf connections across the ACP as
there is in BRSKI, this combination would not support zero-touch
bootstrap across a not configured network though.
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A.3. ACP Neighbor discovery protocol selection
This section discusses why GRASP DULL was chosen as the discovery
protocol for L2 adjacent candidate ACP neighbors. The contenders
considered where GRASP, mDNS or LLDP.
A.3.1. LLDP
LLDP and Cisco's earlier Cisco Discovery Protocol (CDP) are example
of L2 discovery protocols that terminate their messages on L2 ports.
If those protocols would be chosen for ACP neighbor discovery, ACP
neighbor discovery would therefore also terminate on L2 ports. This
would prevent ACP construction over non-ACP capable but LLDP or CDP
enabled L2 switches. LLDP has extensions using different MAC
addresses and this could have been an option for ACP discovery as
well, but the additional required IEEE standardization and definition
of a profile for such a modified instance of LLDP seemed to be more
work than the benefit of "reusing the existing protocol" LLDP for
this very simple purpose.
A.3.2. mDNS and L2 support
Multicast DNNS (mDNS) [RFC6762] with DNS Service Discovery (DNS-SD)
Resource Records (RRs) as defined in [RFC6763] is a key contender as
an ACP discovery protocol. because it relies on link-local IP
multicast, it does operates at the subnet level, and is also found in
L2 switches. The authors of this document are not aware of mDNS
implementation that terminate their mDNS messages on L2 ports instead
of the subnet level. If mDNS was used as the ACP discovery mechanism
on an ACP capable (L3)/L2 switch as outlined in Section 7, then this
would be necessary to implement. It is likely that termination of
mDNS messages could only be applied to all mDNS messages from such a
port, which would then make it necessary to software forward any non-
ACP related mDNS messages to maintain prior non-ACP mDNS
functionality. Adding support for ACP into such L2 switches with
mDNS could therefore create regression problems for prior mDNS
functionality on those nodes. With low performance of software
forwarding in many L2 switches, this could also make the ACP risky to
support on such L2 switches.
A.3.3. Why DULL GRASP
LLDP was not considered because of the above mentioned issues. mDNS
was not selected because of the above L2 mDNS considerations and
because of the following additional points:
If mDNS was not already existing in a node, it would be more work to
implement than DULL GRASP, and if an existing implementation of mDNS
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was used, it would likely be more code space than a separate
implementation of DULL GRASP or a shared implementation of DULL GRASP
and GRASP in the ACP.
A.4. Choice of routing protocol (RPL)
This section motivates why RPL - "IPv6 Routing Protocol for Low-Power
and Lossy Networks ([RFC6550] was chosen as the default (and in this
specification only) routing protocol for the ACP. The choice and
above explained profile was derived from a pre-standard
implementation of ACP that was successfully deployed in operational
networks.
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 synchronization.
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 behavior.
o Extensibility: Since the Autonomic Networking Infrastructure is a
new concept, it is likely that changes in the way of operation
will happen over time. RPL allows for new objective functions to
be introduced later, which allow changes to the way the routing
protocol creates the DAGs.
o Multi-topology support: It may become necessary in the future to
support more than one DODAG for different purposes, using
different objective functions. RPL allow for the creation of
several parallel DODAGs, should this be required. This could be
used to create different topologies to reach different roots.
o No need for path optimization: RPL does not necessarily compute
the optimal path between any two nodes. However, the ACP does not
require this today, since it carries mainly non-delay-sensitive
feedback loops. It is possible that different optimization
schemes become necessary in the future, but RPL can be expanded
(see point "Extensibility" above).
A.5. ACP Information Distribution and multicast
IP multicast is not used by the ACP because the ANI (Autonomic
Networking Infrastructure) itself does not require IP multicast but
only service announcement/discovery. Using IP multicast for that
would have made it necessary to develop a zero-touch auto configuring
solution for ASM (Any Source Multicast - the original form of IP
multicast defined in [RFC1112]), which would be quite complex and
difficult to justify. One aspect of complexity where no attempt at a
solution has been described in IETF documents is the automatic-
selection of routers that should be PIM Sparse Mode (PIM-SM)
Rendezvous Points (RPs) (see [RFC7761]). The other aspects of
complexity are the implementation of MLD ([RFC4604]), PIM-SM and
Anycast-RP (see [RFC4610]). If those implementations already exist
in a product, then they would be very likely tied to accelerated
forwarding which consumes hardware resources, and that in return is
difficult to justify as a cost of performing only service discovery.
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Some future ASA may need high performance in-network data
replication. That is the case when the use of IP multicast is
justified. Such an ASA can then use service discovery from ACP
GRASP, and then they do not need ASM but only SSM (Source Specific
Multicast, see [RFC4607]) for the IP multicast replication. SSM
itself can simply be enabled in the Data-Plane (or even in an update
to the ACP) without any other configuration than just enabling it on
all nodes and only requires a simpler version of MLD (see [RFC5790]).
LSP (Link State Protocol) based IGP routing protocols typically have
a mechanism to flood information, and such a mechanism could be used
to flood GRASP objectives by defining them to be information of that
IGP. This would be a possible optimization in future variations of
the ACP that do use an LSP routing protocol. Note though that such a
mechanism would not work easily for GRASP M_DISCOVERY messages which
are intelligently (constrained) flooded not across the whole ACP, but
only up to a node where a responder is found. We do expect that many
future services in ASA will have only few consuming ASA, and for
those cases, M_DISCOVERY is the more efficient method than flooding
across the whole domain.
Because the ACP uses RPL, one desirable future extension is to use
RPLs existing notion of loop-free distribution trees (DODAG) to make
GRASPs flooding more efficient both for M_FLOOD and M_DISCOVERY) See
Section 6.12.5 how this will be specifically beneficial when using
NBMA interfaces. This is not currently specified in this document
because it is not quite clear yet what exactly the implications are
to make GRASP flooding depend on RPL DODAG convergence and how
difficult it would be to let GRASP flooding access the DODAG
information.
A.6. 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.
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The two limitations can easier be solved if the solution was more
modular and as few as possible initial secure channel negotiation
protocols would be used, and these protocols would then take on the
responsibility to support more flexible objectives to negotiate the
mutually preferred ACP security channel protocol.
IKEv2 is the IETF standard protocol to negotiate network security
associations. It is meant to be extensible, but it is unclear
whether it would be feasible to extend IKEv2 to support possible
future requirements for ACP secure channel negotiation:
Consider the simple case where the use of native IPsec vs. IPsec via
GRE is to be negotiated and the objective is the maximum throughput.
Both sides would indicate some agreed upon performance metric and the
preferred encapsulation is the one with the higher performance of the
slower side. IKEv2 does not support negotiation with this objective.
Consider DTLS and some form of MacSec are to be added as negotiation
options - and the performance objective should work across all IPsec,
dDTLS and MacSec options. In the case of MacSEC, the negotiation
would also need to determine a key for the peering. It is unclear if
it would be even appropriate to consider extending the scope of
negotiation in IKEv2 to those cases. Even if feasible to define, it
is unclear if implementations of IKEv2 would be eager to adopt those
type of extension given the long cycles of security testing that
necessarily goes along with core security protocols such as IKEv2
implementations.
A more modular alternative to extending IKEv2 could be to layer a
modular negotiation mechanism on top of the multitude of existing or
possible future secure channel protocols. For this, GRASP over TLS
could be considered as a first ACP secure channel negotiation
protocol. The following are initial considerations for such an
approach. A full specification is subject to a separate document:
To explicitly allow negotiation of the ACP channel protocol, GRASP
over a TLS connection using the GRASP_LISTEN_PORT and the nodes 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,
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the GRASP/TLS connection can be kept alive or timed out as long as
the selected channel protocol has a secure association between Alice
and Bob. When it terminates, it needs to be re-negotiated via GRASP/
TLS.
Notes:
o Negotiation of a channel type may require IANA assignments of code
points.
o TLS is subject to reset attacks, which IKEv2 is not. Normally,
ACP connections (as specified in this document) will be over link-
local addresses so the attack surface for this one issue in TCP
should be reduced (note that this may not be true when ACP is
tunneled as described in Section 8.2.2.
o GRASP packets received inside a TLS connection established for
GRASP/TLS ACP negotiation are assigned to a separate GRASP domain
unique to that TLS connection.
A.7. CAs, domains and routing subdomains
There is a wide range of setting up different ACP solution by
appropriately using CAs and the domain and rsub elements in the
domain information field of the domain certificate. We summarize
these options here as they have been explained in different parts of
the document in before and discuss possible and desirable extensions:
An ACP domain is the set of all ACP nodes using certificates from the
same CA using the same domain field. GRASP inside the ACP is run
across all transitively connected ACP nodes in a domain.
The rsub element in the domain information field permits the use of
addresses from different ULA prefixes. One use case is to create
multiple physical networks that initially may be separated with one
ACP domain but different routing subdomains, so that all nodes can
mutual trust their ACP domain certificates (not depending on rsub)
and so that they could connect later together into a contiguous ACP
network.
One instance of such a use case is an ACP for regions interconnected
via a non-ACP enabled core, for example due to the absence of product
support for ACP on the core nodes. ACP connect configurations as
defined in this document can be used to extend and interconnect those
ACP islands to the NOC and merge them into a single ACP when later
that product support gap is closed.
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Note that RPL scales very well. It is not necessary to use multiple
routing subdomains to scale ACP domains in a way it would be possible
if other routing protocols where used. They exist only as options
for the above mentioned reasons.
If different ACP domains are to be created that should not allow to
connect to each other by default, these ACP domains simply need to
have different domain elements in the domain information field.
These domain elements can be arbitrary, including subdomains of one
another: Domains "example.com" and "research.example.com" are
separate domains if both are domain elements in the domain
information element of certificates.
It is not necessary to have a separate CA for different ACP domains:
an operator can use a single CA to sign certificates for multiple ACP
domains that are not allowed to connect to each other because the
checks for ACP adjacencies includes comparison of the domain part.
If multiple independent networks choose the same domain name but had
their own CA, these would not form a single ACP domain because of CA
mismatch. Therefore there is no problem in choosing domain names
that are potentially also used by others. Nevertheless it is highly
recommended to use domain names that one can have high probability to
be unique. It is recommended to use domain names that start with a
DNS domain names owned by the assigning organization and unique
within it. For example "acp.example.com" if you own "example.com".
A.8. Intent for the ACP
Intent is the architecture component of autonomic networks according
to [I-D.ietf-anima-reference-model] that allows operators to issue
policies to the network. In a simple instance, Intent could simply
be policies flooded across ACP GRASP and interpreted on every ACP
node.
One concern for future definitions of Intent solutions is the problem
of circular dependencies when expressing Intent policies about the
ACP itself.
For example, Intent could indicate the desire to build an ACP across
all domains that have a common parent domain (without relying on the
rsub/routing-subdomain solution defined in this document). For
example ACP nodes with domain "example.com", nodes of "example.com",
"access.example.com", "core.example.com" and "city.core.example.com"
should all establish one single ACP.
If each domain has its own source of Intent, then the Intent would
simply have to allow adding the peer domains trust anchors (CA) and
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domain names to the ACP domain membership check (Section 6.1.2) so
that nodes from those other nodes are accepted as ACP peers.
If this Intent was to be originated only from one domain, it could
likely not be made to work because the other domains will not build
any ACP connection amongst each other, whether they use the same or
different CA due to the ACP domain membership check.
If the domains use the same CA one could change the ACP setup to
permit for the ACP to be established between the two ACP nodes even
when the acp-domain-names of the peers are different, but only for
the purpose of disseminating limited information, such as Intent, but
not to set up full ACP connectivity, specifically not RPL routing and
passing of arbitrary GRASP information. Unless the Intent policies
permit this to happen across domain boundaries.
This type of approach where the ACP first allows Intent to operate
and only then sets up the rest of ACP connectivity based on Intent
policy could also be used to enable Intent policies that would limit
functionality across the ACP inside a domain, as long as no policy
would disturb the operations of Intent. For example to limit
reachability across the ACP to certain type of nodes or locations of
nodes.
A.9. Adopting ACP concepts for other environments
The ACP as specified in this document is very explicit about the
choice of options to allow interoperable implementations. The
choices made may not be the best for all environments, but the
concepts used by the ACP can be used to build derived solutions:
The ACP specifies the use of ULA and deriving its prefix from the
domain name so that no address allocation is required to deploy the
ACP. The ACP will equally work not using ULA but any other /48 IPv6
prefix. This prefix could simply be a configuration of the ACP
registrars (for example when using BRSKI) to enroll the domain
certificates - instead of the ACP registrar deriving the /48 ULA
prefix from the AN domain name.
Some solutions may already have an auto-addressing scheme, for
example derived from existing unique device identifiers (e.g., MAC
addresses). In those cases it may not be desirable to assign
addresses to devices via the ACP address information field in the way
described in this document. The certificate may simply serve to
identify the ACP domain, and the address field could be empty/unused.
The only fix required in the remaining way the ACP operate is to
define another element in the domain certificate for the two peers to
decide who is Alice and who is Bob during secure channel building.
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Note though that future work may leverage the acp address to
authenticate "ownership" of the address by the device. If the
address used by a device is derived from some pre-existing permanent
local ID (such as MAC address), then it would be useful to store that
address in the certificate using the format of the access address
information field or in a similar way.
The ACP is defined as a separate VRF because it intends to support
well managed networks with a wide variety of configurations.
Therefore, reliable, configuration-indestructible connectivity cannot
be achieved from the Data-Plane itself. In solutions where all
transit connectivity impacting functions are fully automated
(including security), indestructible and resilient, it would be
possible to eliminate the need for the ACP to be a separate VRF.
Consider the most simple example system in which there is no separate
Data-Plane, but the ACP is the Data-Plane. Add BRSKI, and it becomes
a fully autonomic network - except that it does not support automatic
addressing for user equipment. This gap can then be closed for
example by adding a solution derived from
[I-D.ietf-anima-prefix-management].
TCP/TLS as the protocols to provide reliability and security to GRASP
in the ACP may not be the preferred choice in constrained networks.
For example, CoAP/DTLS (Constrained Application Protocol) may be
preferred where they are already used, allowing to reduce the
additional code space footprint for the ACP on those devices.
Because the transport for GRASP is not only hop-by-hop, but end-to-
end across the ACP, this would require the definition of an
incompatible variant of the ACP. Non-constrained devices could
support both variants (the ACP as defined here, and one using CoAP/
DTLS for GRASP), and the variant used in a deployment could be chosen
for example through a parameter of the domain certificate.
The routing protocol chosen by the ACP design (RPL) does explicitly
not optimize for shortest paths and fastest convergence. Variations
of the ACP may want to use a different routing protocol or introduce
more advanced RPL profiles.
Variations such as what routing protocol to use, or whether to
instantiate an ACP in a VRF or (as suggested above) as the actual
Data-Plane, can be automatically chosen in implementations built to
support multiple options by deriving them from future parameters in
the certificate. Parameters in certificates should be limited to
those that would not need to be changed more often than certificates
would need to be updated anyhow; Or by ensuring that these parameters
can be provisioned before the variation of an ACP is activated in a
node. Using BRSKI, this could be done for example as additional
follow-up signaling directly after the certificate enrollment, still
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leveraging the BRSKI TLS connection and therefore not introducing any
additional connectivity requirements.
Last but not least, secure channel protocols including their
encapsulation are easily added to ACP solutions. ACP hop-by-hop
network layer secure channels could also be replaced by end-to-end
security plus other means for infrastructure protection. Any future
network OAM should always use end-to-end security anyhow and can
leverage the domain certificates and is therefore not dependent on
security to be provided for by ACP secure channels.
A.10. Further options / futures
A.10.1. Auto-aggregation of routes
Routing in the ACP according to this specification only leverages the
standard RPL mechanism of route optimization, e.g. keeping only
routes that are not towards the RPL root. This is known to scale to
networks with 20,000 or more nodes. There is no auto-aggregation of
routes for /48 ULA prefixes (when using rsub in the domain
information field) and/or Zone-ID based prefixes.
Automatic assignment of Zone-ID and auto-aggregation of routes could
be achieved for example by configuring zone-boundaries, announcing
via GRASP into the zones the zone parameters (zone-ID and /48 ULA
prefix) and auto-aggrating routes on the zone-boundaries. Nodes
would assign their Zone-ID and potentially even /48 prefix based on
the GRASP announcements.
A.10.2. More options for avoiding IPv6 Data-Plane dependency
As described in Section 6.12.2, the ACP depends on the Data-Plane to
establish IPv6 link-local addressing on interfaces. Using a separate
MAC address for the ACP allows to fully isolate the ACP from the data
plane in a way that is compatible with this specification. It is
also an ideal option when using Single-root input/output
virtualization (SR-IOV) in an implementation to isolate the ACP
(https://en.wikipedia.org/wiki/Single-root_input/
output_virtualization [2]) because different SR-IOV interfaces use
different MAC addresses.
When additional MAC address(es) are not available to the ACP,
separation of the ACP could be done at different demux points. The
same subnet interface could have a separate IPv6 IPv6 interface for
the ACP and Data-Plane and therefore separate link-local addresses
for both, where the ACP interface is non-configurable on the data-
plane. This too would be compatible with this specification and not
impact interoperability.
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An option that would require additional specification is to use a
different Ethertype from 0x86DD (IPv6) to encapsulate IPv6 packets
for the ACP. This would be a similar approach as used for IP
authentication packets in [IEEE-802.1X] that they use the Extensible
Authentication Protocol over Local Area Network (EAPoL) ethertype
(0x88A2).
Note that in the case of ANI nodes, all the above considerations
equally apply to the encapsulation of BRSKI packets including GRASP
used for BRSKI.
A.10.3. ACP APIs and operational models (YANG)
Future work should define YANG ([RFC7950]) data model and/or node
internal APIs to monitor and manage the ACP.
The elements to include into this model/API include the ACP Adjacency
Table (Section 6.2) and ACP GRASP.
A.10.4. RPL enhancements
..... USA ...... ..... Europe ......
NOC1 NOC2
| |
| metric 100 |
ACP1 --------------------------- ACP2 .
| | . WAN
| metric 10 metric 20 | . Core
| | .
ACP3 --------------------------- ACP4 .
| metric 100 |
| | .
| | . Sites
ACP10 ACP11 .
Figure 16: Dual NOC
The profile for RPL specified in this document builds only one
spanning-tree pathset to a root (NOC). In the presence of multiple
NOCs, routing toward the non-root NOCs may be suboptimal. Figure 16
shows an extreme example. Assuming that node ACP1 becomes the RPL
root, traffic between ACP11 and NOC2 will pass through
ACP4-ACP3-ACP1-ACP2 instead of ACP4-ACP2 because the RPL calculated
DODAG/routes are shortest paths towards the RPL root.
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To overcome these limitations, extensions/modifications to the RPL
profile can provide optimality for multiple NOCs. This requires
utilizing Data-Plane artifact including IPinIP encap/decap on ACP
routers and processing of IPv6 RPI headers. Alternatively, (Src,Dst)
routing table entries could be used.
Flooding of ACP GRASP messages can be further constrained and
therefore optimized by flooding only via links that are part of the
RPL DODAG.
A.10.5. Role assignments
ACP connect is an explicit mechanism to "leak" ACP traffic explicitly
(for example in a NOC). It is therefore also a possible security gap
when it is easy to enable ACP connect on arbitrary compromised ACP
nodes.
One simple solution is to define an extension in the ACP certificates
ACP information field indicating the permission for ACP connect to be
configured on that ACP node. This could similarily be done to decide
whether a node is permitted to be a registrar or not.
Tying the permitted "roles" of an ACP node to the ACP domain
certificate provides fairly strong protection against
misconfiguration, but is still subject to code modifications.
Another interesting role to assign to certificates is that of a NOC
node. This would allow to limit certain type of connections such as
OAM TLS connections to only NOC initiator or responders.
A.10.6. Autonomic L3 transit
In this specification, the ACP can only establish autonomic
connectivity across L2 hops and only explicitly confiured options to
tunnel across L3. Future work should specify mechanisms to
automatically tunnel ACP across L3 networks. A hub&spoke option
would allow to tunnel across the Internet to a cloud or central
instance of the ACP, a peer-to-peer tunneling mechanism could tunnel
ACP islands across an L3VPN infrastructure.
A.10.7. Diagnostics
Section 10.1 describes diagnostics options that can be done without
changing the external, interoperability affecting characteristics of
ACP implementation.
Even better diagnostics of ACP operations is possible with additional
signaling extensions, such as:
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1. Consider if LLDP should be a recommended functionality for ANI
devices to improve diagnostics, and if so, which information
elements it should signal (insecure). Includes potentially new
information elements.
2. In alternative to LLDP, A DULL GRASP diagnostics objective could
be defined to carry these information elements.
3. The IDevID of BRSKI pledges should be included in the selected
insecure diagnostics option.
4. A richer set of diagnostics information should be made available
via the secured ACP channels, using either single-hop GRASP or
network wide "topology discovery" mechanisms.
Authors' Addresses
Toerless Eckert (editor)
Huawei USA - Futurewei Technologies Inc.
2330 Central Expy
Santa Clara 95050
USA
Email: tte+ietf@cs.fau.de
Michael H. Behringer (editor)
Email: michael.h.behringer@gmail.com
Steinthor Bjarnason
Arbor Networks
2727 South State Street, Suite 200
Ann Arbor MI 48104
United States
Email: sbjarnason@arbor.net
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