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Versions: (draft-behringer-anima-autonomic-control-plane) 00 01 02 03 04 05 06 07 08 09 10 11 12

ANIMA WG                                               M. Behringer, Ed.
Internet-Draft
Intended status: Standards Track                          T. Eckert, Ed.
Expires: April 15, 2018                                           Huawei
                                                            S. Bjarnason
                                                          Arbor Networks
                                                        October 12, 2017


                    An Autonomic Control Plane (ACP)
              draft-ietf-anima-autonomic-control-plane-12

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 OAM (Operations Administration and
   Management) communications over a network that is secure and reliable
   even when the network is not configured, or not misconfigured.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on April 15, 2018.

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents



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   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Acronyms and Terminology  . . . . . . . . . . . . . . . . . .   6
   3.  Use Cases for an Autonomic Control Plane  . . . . . . . . . .  10
     3.1.  An Infrastructure for Autonomic Functions . . . . . . . .  10
     3.2.  Secure Bootstrap over a not configured Network  . . . . .  10
     3.3.  Data-Plane Independent Permanent Reachability . . . . . .  11
   4.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .  12
   5.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .  12
   6.  Self-Creation of an Autonomic Control Plane (ACP) (Normative)  14
     6.1.  ACP Domain, Certificate and Network . . . . . . . . . . .  14
       6.1.1.  Certificate Domain Information Field  . . . . . . . .  15
       6.1.2.  ACP domain membership check . . . . . . . . . . . . .  18
       6.1.3.  Certificate Maintenance . . . . . . . . . . . . . . .  18
     6.2.  ACP Adjacency Table . . . . . . . . . . . . . . . . . . .  20
     6.3.  Neighbor Discovery with DULL GRASP  . . . . . . . . . . .  21
     6.4.  Candidate ACP Neighbor Selection  . . . . . . . . . . . .  23
     6.5.  Channel Selection . . . . . . . . . . . . . . . . . . . .  24
     6.6.  Candidate ACP Neighbor verification . . . . . . . . . . .  26
     6.7.  Security Association protocols  . . . . . . . . . . . . .  26
       6.7.1.  ACP via IKEv2 . . . . . . . . . . . . . . . . . . . .  26
       6.7.2.  ACP via dTLS  . . . . . . . . . . . . . . . . . . . .  27
       6.7.3.  ACP Secure Channel Requirements . . . . . . . . . . .  28
     6.8.  GRASP in the ACP  . . . . . . . . . . . . . . . . . . . .  28
       6.8.1.  GRASP as a core service of the ACP  . . . . . . . . .  28
       6.8.2.  ACP as the Security and Transport substrate for GRASP  29
     6.9.  Context Separation  . . . . . . . . . . . . . . . . . . .  33
     6.10. Addressing inside the ACP . . . . . . . . . . . . . . . .  33
       6.10.1.  Fundamental Concepts of Autonomic Addressing . . . .  33
       6.10.2.  The ACP Addressing Base Scheme . . . . . . . . . . .  35
       6.10.3.  ACP Zone Addressing Sub-Scheme . . . . . . . . . . .  35
       6.10.4.  ACP Manual Addressing Sub-Scheme . . . . . . . . . .  38
       6.10.5.  ACP Vlong Addressing Sub-Scheme  . . . . . . . . . .  39
       6.10.6.  Other ACP Addressing Sub-Schemes . . . . . . . . . .  40
     6.11. Routing in the ACP  . . . . . . . . . . . . . . . . . . .  40
       6.11.1.  RPL Profile  . . . . . . . . . . . . . . . . . . . .  41
     6.12. General ACP Considerations  . . . . . . . . . . . . . . .  44
       6.12.1.  Performance  . . . . . . . . . . . . . . . . . . . .  44
       6.12.2.  Addressing of Secure Channels in the data-plane  . .  45



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       6.12.3.  MTU  . . . . . . . . . . . . . . . . . . . . . . . .  45
       6.12.4.  Multiple links between nodes . . . . . . . . . . . .  46
       6.12.5.  ACP interfaces . . . . . . . . . . . . . . . . . . .  46
   7.  ACP support on L2 switches/ports (Normative)  . . . . . . . .  49
     7.1.  Why . . . . . . . . . . . . . . . . . . . . . . . . . . .  49
     7.2.  How (per L2 port DULL GRASP)  . . . . . . . . . . . . . .  50
   8.  Support for Non-ACP Components (Normative)  . . . . . . . . .  52
     8.1.  ACP Connect . . . . . . . . . . . . . . . . . . . . . . .  52
       8.1.1.  Non-ACP Controller / NMS system . . . . . . . . . . .  52
       8.1.2.  Software Components . . . . . . . . . . . . . . . . .  54
       8.1.3.  Auto Configuration  . . . . . . . . . . . . . . . . .  55
       8.1.4.  Combined ACP/Data-Plane Interface (VRF Select)  . . .  56
       8.1.5.  Use of GRASP  . . . . . . . . . . . . . . . . . . . .  57
     8.2.  ACP through Non-ACP L3 Clouds (Remote ACP neighbors)  . .  58
       8.2.1.  Configured Remote ACP neighbor  . . . . . . . . . . .  58
       8.2.2.  Tunneled Remote ACP Neighbor  . . . . . . . . . . . .  59
       8.2.3.  Summary . . . . . . . . . . . . . . . . . . . . . . .  60
   9.  Benefits (Informative)  . . . . . . . . . . . . . . . . . . .  60
     9.1.  Self-Healing Properties . . . . . . . . . . . . . . . . .  60
     9.2.  Self-Protection Properties  . . . . . . . . . . . . . . .  61
       9.2.1.  From the outside  . . . . . . . . . . . . . . . . . .  61
       9.2.2.  From the inside . . . . . . . . . . . . . . . . . . .  62
     9.3.  The Administrator View  . . . . . . . . . . . . . . . . .  63
   10. Further Considerations (Informative)  . . . . . . . . . . . .  63
     10.1.  BRSKI Bootstrap (ANI)  . . . . . . . . . . . . . . . . .  63
     10.2.  ACP (and BRSKI) Diagnostics  . . . . . . . . . . . . . .  65
     10.3.  Enabling and disabling ACP/ANI . . . . . . . . . . . . .  69
       10.3.1.  Filtering for non-ACP/ANI packets  . . . . . . . . .  70
       10.3.2.  Admin Down State . . . . . . . . . . . . . . . . . .  70
       10.3.3.  Interface level ACP/ANI enable . . . . . . . . . . .  73
       10.3.4.  Which interfaces to auto-enable ?  . . . . . . . . .  73
       10.3.5.  Node Level ACP/ANI enable  . . . . . . . . . . . . .  75
       10.3.6.  Undoing ANI/ACP enable . . . . . . . . . . . . . . .  76
       10.3.7.  Summary  . . . . . . . . . . . . . . . . . . . . . .  77
     10.4.  ACP Neighbor discovery protocol selection  . . . . . . .  77
       10.4.1.  LLDP . . . . . . . . . . . . . . . . . . . . . . . .  77
       10.4.2.  mDNS and L2 support  . . . . . . . . . . . . . . . .  78
       10.4.3.  Why DULL GRASP . . . . . . . . . . . . . . . . . . .  78
     10.5.  Choice of routing protocol (RPL) . . . . . . . . . . . .  78
     10.6.  Extending ACP channel negotiation (via GRASP)  . . . . .  80
     10.7.  CAs, domains and routing subdomains  . . . . . . . . . .  81
     10.8.  Adopting ACP concepts for other environments . . . . . .  83
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  85
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  86
   13. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  87
   14. Change log [RFC Editor: Please remove]  . . . . . . . . . . .  87
     14.1.  Initial version  . . . . . . . . . . . . . . . . . . . .  87
     14.2.  draft-behringer-anima-autonomic-control-plane-00 . . . .  87



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     14.3.  draft-behringer-anima-autonomic-control-plane-01 . . . .  87
     14.4.  draft-behringer-anima-autonomic-control-plane-02 . . . .  88
     14.5.  draft-behringer-anima-autonomic-control-plane-03 . . . .  88
     14.6.  draft-ietf-anima-autonomic-control-plane-00  . . . . . .  88
     14.7.  draft-ietf-anima-autonomic-control-plane-01  . . . . . .  88
     14.8.  draft-ietf-anima-autonomic-control-plane-02  . . . . . .  89
     14.9.  draft-ietf-anima-autonomic-control-plane-03  . . . . . .  89
     14.10. draft-ietf-anima-autonomic-control-plane-04  . . . . . .  90
     14.11. draft-ietf-anima-autonomic-control-plane-05  . . . . . .  90
     14.12. draft-ietf-anima-autonomic-control-plane-06  . . . . . .  91
     14.13. draft-ietf-anima-autonomic-control-plane-07  . . . . . .  91
     14.14. draft-ietf-anima-autonomic-control-plane-08  . . . . . .  93
     14.15. draft-ietf-anima-autonomic-control-plane-09  . . . . . .  94
     14.16. draft-ietf-anima-autonomic-control-plane-10  . . . . . .  96
     14.17. draft-ietf-anima-autonomic-control-plane-11  . . . . . .  98
     14.18. draft-ietf-anima-autonomic-control-plane-12  . . . . . .  98
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . . 100
     15.1.  Normative References . . . . . . . . . . . . . . . . . . 100
     15.2.  Informative References . . . . . . . . . . . . . . . . . 102
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . 105

1.  Introduction

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

   Autonomic functions need an autonomously built communications
   infrastructure or network plane (there is no well-established name
   for this).  This infrastructure needs to be secure, resilient and re-
   usable by all autonomic functions.  Section 5 of [RFC7575] introduces
   that infrastructure and calls it the "Autonomic Control Plane" (ACP).
   More descriptively it would be the "Autonomic communications
   infrastructure for Management and Control".  For naming consistency
   with that prior document, this document continues to use the name ACP
   though.

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



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   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 achieved are defined in Section 6.  The ACP is designed to
   remains 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-plen 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:

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

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

   o  A controller or network management system can use it to securely
      bootstrap network devices in remote locations, even if the network
      in between is not yet configured; no data-plane dependent
      bootstrap configuration is required.  An example of such a secure
      bootstrap process is described in
      [I-D.ietf-anima-bootstrapping-keyinfra]

   This document describes these 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, and in Section 6 the process is defined
   in detail.  Section 7 defines how to support ACP on L2 switches.
   Section 8 explains how non-ACP nodes and networks can be integrated.
   The following sections are non-normative: Section 7 reviews benefits
   of the ACP (after all the details have been defined), Section 10
   provides additional explanations and describes additional details or



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   future work possibilities that where considered not to be appropriate
   for standardization in this document but nevertheless assumed to be
   helpful for candidate adopters of the ACP.

   The ACP as defined in this document can be implemented and operated
   without dependency against other components of autonomous networks
   except for the GRASP protocol on which it depends.  The document
   "Autonomic Network Stable Connectivity"
   [I-D.ietf-anima-stable-connectivity] describes how the ACP alone can
   be used to provide stable connectivity for autonomic and non-
   autonomic OAM applications ("Operations Administration and
   Management").  It also explains on how existing management solutions
   can leverage the ACP in parallel with traditional management models,
   when to use the ACP and, how to integrate IPv4 based management, etc.

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

2.  Acronyms and Terminology

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

   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 defined in
      this document.  It provides secure zero-touch transitive (network
      wide) IPv6 connectivity for all nodes in the same ACP domain.  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.





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   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:  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 domain
      certificates that allow them to authenticate each other as members
      of the ACP domain.  See Section 6.1.2.

   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 interface in the ACP 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
      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 prefixes routed across the ACP.  In the
      normal/simple case, the ACP has one ULA prefix, see Section 6.10.
      The ACP routing table may include multiple ULA prefixes if the
      "rsub" option is used to create addresses from more than one ULA
      prefix.  See Section 6.1.1.  The ACP may also include non-ULA
      prefixes if those are configured on ACP connect interfaces.  See
      Section 8.1.1.

   ACP secure channel:  A security association established hop-by-hop
      between adjacent ACP nodes to carry traffic of the ACP VRF
      separated from data-plane traffic in-band over the same links as
      the data-plane.

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

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





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   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 bootstrap and
      stable connectivity for SDN networks - see
      [I-D.ietf-anima-stable-connectivity].

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

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

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

   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 VRFs
      other than the ACP VRF.  In a simple ACP or ANI node, the data-
      plane is typically provisioned non-autonomic, for example manually
      (including across the ACP) or via SDN controllers.  In a full
      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!

   ACP (ANI/AN) Domain Certificate:  A provisioned 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.

   device:  A physical system, or physical node.



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   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" which is run inside the ACP to support
      BRSKI and other future 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].

   Intent:  Northbound operator and automation facing interface of an
      Autonomic Network according to [I-D.ietf-anima-reference-model].

   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.

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

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





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   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:  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]).

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

   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
   [RFC2119] when they appear in ALL CAPS.  When these words are not in
   ALL CAPS (such as "should" or "Should"), they have their usual
   English meanings, and are not to be interpreted as [RFC2119] key
   words.

3.  Use Cases for an Autonomic Control Plane

3.1.  An Infrastructure for Autonomic Functions

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

3.2.  Secure Bootstrap over 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 can happen without
   requiring any configuration such as the transit connectivity to



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   bootstrap further devices.  A new device can automatically be
   bootstrapped in a secure fashion and be deployed with a domain
   certificate.  This does not require any configuration on intermediate
   nodes, because they can communicate zero-touch and securely through
   the ACP.

3.3.  Data-Plane Independent Permanent Reachability

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

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

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

   The ACP provides reachability that is independent of the data-plane
   (except for the dependency discussed in Section 6.12.2 which can be
   removed through future work), which allows control plane and
   management plane to operate more robustly:

   o  For management plane protocols, the ACP provides the functionality
      of a "Virtual-out-of-band (VooB) channel", by providing
      connectivity to all nodes regardless of their configuration or
      global routing table.

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




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

4.  Requirements

   The Autonomic Control Plane has the following requirements:

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

   ACP2:  The ACP MUST have a separate address space from the data-
          plane.  Reason: traceability, debug-ability, separation from
          data-plane, security (can block easily at edge).

   ACP3:  The ACP MUST use autonomically managed address space.  Reason:
          easy bootstrap and setup ("autonomic"); robustness (admin
          can't mess things up so easily).  This document suggests to
          use ULA addressing for this purpose ("Unique Local Address",
          see [RFC4193]).

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

   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

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

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




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

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

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

   Note:

   o  Non-autonomic NMS ("Network Management Systems") or SDN
      controllers have to be manually connected into the ACP.

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

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

   The following figure illustrates the ACP.

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

                                 Figure 1



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   The resulting overlay network is normally based exclusively on hop-
   by-hop tunnels.  This is because addressing used on links is IPv6
   link local addressing, which does not require any prior set-up.  This
   way the ACP can be built even if there is no configuration on the
   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 a certificate, as
   well as an (empty) ACP Adjacency Table (described in Section 6.2).
   It then can start to discover ACP neighbors and build the ACP.  This
   is described step by step in the following sections:

6.1.  ACP Domain, Certificate and Network

   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, the ACP requires certificates: An ACP node MUST have keying
   material consisting of a certificate (LDevID), with which it can
   cryptographically assert its membership in the ACP domain and trust
   anchor(s) associated with that certificate with which it can verify
   the membership of other nodes (see Section 6.1.2).  The certificate
   is called the ACP domain certificate, the trust anchor(s) are the CA
   ("Certificate Authority") 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
   following ACP specific information field in its domain certificate as
   well as those of candidate ACP peers.  See Section 10.1 for more
   information about enrollment or provisioning options.

   Note: LDevID ("Local Device IDentification") is the term used to
   indicate a certificate that was provisioned by the owner of a node as
   opposed to IDevID ("Initial Device IDentifier") that may has been
   loaded on the node during manufacturing time.  Those IDevID do not
   include owner and deployment specific information to allows autonomic
   establishment of trust for the operations of an ACP domain (e.g.:
   between two ACP nodes without relying on any third party).

   This document uses the term ACP in many places where its reference
   document use the word autonomic.  This is done because those



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   reference document consider fully autonomic network and nodes, but
   support of ACP does not require support for other components of
   autonomic networks.  Therefore the word autonomic would be irritating
   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 can and should be used for any
   authentication between ACP nodes where the required security is
   domain membership.  Section 6.1.2 defines this "ACP domain membership
   check".  The uses of this check that are standardized in this
   document are for the establishment of ACP secure channels
   (Section 6.6) and for ACP GRASP (Section 6.8.2).  Other uses are
   subject to future work, but it is recommended that it is the default
   security check for any end-to-end connections between ASA.  It is
   equally useable by other functions such as legacy OAM functions.

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 with
   the RFC number assigned to this document and remove this comment
   line]

   domain-information = local-part "@" domain

   local-part = key "." local-info

   key = "rfcSELF"

   local-info = [ acp-address ] [ "+" rsub extensions ]

   acp-address = 32hex-dig

   hex-dig = DIGIT / "a" / "b" / "c" / "d" / "e" / "f"




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   rsub = [ domain-name ] ; empty if not used

   domain = domain-name

   routing-subdomain = [ rsub " ." ] domain

   domain-name = ; <domain> according to section 3.5 of [RFC1034]

   extensions = *( "+" extension )

   extension = ; future definition.  Must fit into [RFC5322] simple dot-
   atom format.

   Example:

   domain-information =   rfcSELF+fda379a6f6ee00000200000064000000+area5
   1.research@acp.example.com

   routing-subdomain = area51.research.acp.example.com

   "acp-address" MUST be the ACP address of the node.  It is optional to
   support variations of the ACP mechanisms, for example other means for
   nodes to assign ACP addresses to themselves.  Such methods are
   subject to future work though.

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

   "domain" is used to indicate the ACP Domain across which all ACP
   nodes trust each other and are willing to build ACP channel to each
   other.  See Section 6.1.2.  Domain SHOULD be the FQDN of a domain
   owned by the operator assigning the certificate.  This is a simple
   method to ensure that the domain is globally unique and collision of
   ACP addresses would therefore only happen due to ULA hash collisions.
   If the operator does not own any FQDN, it should choose a string in
   FQDN format that intends to be equally unique.

   "routing-subdomain" is the autonomic subdomain that is used to
   calculate the hash for the ULA prefix of the ACP address of the node.
   "rsub" is optional and should only be used when its impacts are
   understood.  When "rsub" is not used, "routing-subdomain" is the same
   as "domain".

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





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

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

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

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

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

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

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




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   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:

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

   o  The peers certificate is signed by one of the trust anchors
      associated with the ACP domain certificate.

   o  If the node certificates indicate a CDP (or OCSP) then the peer's
      certificate must be valid according to those criteria. e.g.: OCSP
      check across the ACP or not listed in the CRL retrieved from the
      CDP.

   o  The peers certificate has a syntactically valid domain information
      field (subjectAltName / rfc822Name) and the domain name in that
      peers domain information field is the same as in this ACP node
      certificate.  Note that future Intent rules may modify this.  See
      Section 10.7.

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.  The
   mechanism by which the domain certificate was initially provisioned
   SHOULD provide a mechanism to store the URL of one EST server with
   its ACP address into the node for later renewal.  This server does
   not have to be the same as the one performing the initial certificate
   enrolment.




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

        Example:

        [M_FLOOD, 12340815, h'fda379a6f6ee0000200000064000001', 210000,
            ["SRV.est", 4, 255, "EST-TLS"],
            [O_IPv6_LOCATOR,
                 h'fda379a6f6ee0000200000064000001', TCP, 80]
        ]

   The formal CDDL definition is:

    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 = text       ; name of the (list of) of supported
                                 ; protocols: "EST-TLS" for RFC7030.

   The objective value "SRV.est" indicates that the objective is an
   [RFC7030] compliant EST server.

   The M_FLOOD message MUST be sent periodically.  The default SHOULD be
   60 seconds, the value SHOULD be operator configurable.  It must be so
   high that the aggregate amount of periodic M_FLOODs from all flooded
   objectives causes only negligible traffic across the ACP.  The 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.

   Domain certificates SHOULD by default be renewed 50% into their
   lifetime.  When performing renewal, the node SHOULD attempt to
   connect to the remembered EST server.  If that fails, it SHOULD
   attempt to connect to EST server(s) 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.



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

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

   Certificate lifetime should be set to be as short as feasible.  Given
   how certificate renewal is fully automated via ACP and EST, the
   primarily limiting factor for shorter certificate lifetimes (than the
   typical one year) is load on the EST server(s) and CA.  It is
   therefore recommended that ACP domain certificates are managed via a
   CA chain where the assigning CA has enough performance to manage
   short lived certificates.

   See Section 10.1 for further optimizations of certificate maintenance
   when BRSKI can be used ("Bootstrapping Remote Secure Key
   Infrastructures", see [I-D.ietf-anima-bootstrapping-keyinfra]).

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, Link-
   local IPv6 address (discovered by GRASP as explained below), domain,
   certificate.  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.

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



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   Interaction between ACP and other autonomic elements like GRASP (see
   below) or ASAs should be via an API that allows (appropriately access
   controlled) read/write access to the ACP Adjacency Table.
   Specification of such an API is subject to future work.

6.3.  Neighbor Discovery with DULL GRASP

   The ACP uses one instance of DULL GRASP ( See section 3.5.2.2 of
   [I-D.ietf-anima-grasp] for its formal definition) for every physical
   L2 subnet of the ACP node to discover physically adjacent candidate
   ACP neighbors.  Native interfaces (e.g.: physical interfaces on
   physical nodes) SHOULD be brought up automatically enough so that 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
   link-local address assignment (SLAAC) and DULL GRASP works and then
   only the following ACP secure channel setup packets - but not any
   other unnecessary traffic (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 MLD ([RFC3810]) to
   announce the desire to receive packets for that address.  Otherwise
   DULL GRASP could fail to operate correctly in the presence of MLD
   snooping, non-ACP enabled L2 switches - because those would stop
   forwarding DULL GRASP packets.  Switches not supporting MLD snooping
   simply need to operate as pure L2 bridges for IPv6 multicast packets
   for DULL GRASP to work.

   ACP discovery SHOULD NOT be enabled by default on non-native
   interfaces.  In particular, ACP discovery MUST NOT run inside the ACP
   across ACP virtual interfaces.  See Section 10.3 for further, non-
   normative suggestions 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 (see Section 10.1) then
   the above considerations also apply to discovery for BRSKI.  Each
   DULL instance of GRASP set up for ACP is then also used for the
   discovery of a bootstrap proxy via BRSKI when the 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



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   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:

         Example:

         [M_FLOOD, 12340815, h'fe80000000000000c0011001FEEF0000, 180000,
             ["AN_ACP", 4, 1, "IKEv2"],
             [O_IPv6_LOCATOR,
                  h'fe80000000000000c0011001FEEF0000, UDP, 15000]
         ]

   The formal CDDL definition is:

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

           objective = ["AN_ACP", objective-flags, loop-count,
                                                  objective-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 = text ; name of the (list of) secure
                                  ; channel negotiation protocol(s)

   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 (recommended) example the period of sending of the
   objective could be 60 seconds the indicated ttl of 180000 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 (normally) a string indicating the
   secure channel protocol available at the specified or implied
   locator.



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   The locator is optional and only required when the secure channel
   protocol is not offered at a well-defined port number, or if there is
   no well-defined port number.  "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", see [RFC4301]).  We therefore use the term "IKEv2" and not
   "IPsec" in the GRASP definitions below 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).

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

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

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

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

   Note that a node serving both as an ACP node and BRSKI Join Proxy may
   choose to distribute the "AN_ACP" objective and 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.





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   The ACP is by default established exclusively between nodes in the
   same domain.  This includes all routing subdomains.  Section 10.7
   explains how ACP connections across multiple routing subdomains are
   special.

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

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

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

   Since Intent is transported over the ACP, the first ACP connection a
   node establishes is always following the default behavior.  See
   Section 10.7 for more details.

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

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 ("datagram Transport Layer Security
   version 1.2", see [RFC6347]) because that code exists already on them
   for end-to-end security, but low-end in-ceiling L2 switches may only
   want to support MacSec because that is also supported in their chips.



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   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:

   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.

   Once the first secure channel protocol succeeds, the two peers know
   each other's certificates because it 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.

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

   For example, originally Bob could have been the initiator of one ACP
   secure channel protocol that Bob 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 could have been
   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 connecting determined a
   working profile with Bob, Alice might prefer some other secure
   protocol (e.g.: dTLS) and try to set that up with Bob.  If that
   succeeds, she would close the IPsec connection.  If no better
   protocol attempt succeeds, she would keep the IPsec 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



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   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 (with
   throttling).

6.7.  Security Association protocols

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

6.7.1.  ACP via IKEv2

   An ACP node announces its ability to support IKEv2 as the ACP secure
   channel protocol in GRASP as "IKEv2".

6.7.1.1.  Native IPsec

   To run ACP via IPsec natively, no further IANA assignments/
   definitions are required.  An ACP node supporting native IPsec MUST
   use IPsec security setup via IKEv2, tunnel mode, local and peer link-
   local IPv6 addresses used for encapsulation, ESP with AES256 for
   encryption and SHA256 hash.

   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.







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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.  The ACP node MUST support IPsec security setup via IKEv2,
   IPsec transport mode, local and peer link-local IPv6 addresses used
   for encapsuation, 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)
   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 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




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   association mechanisms such as re-keying are used as they would be
   for any transport application relying solely on dTLS.

6.7.3.  ACP Secure Channel Requirements

   A baseline ACP node MUST support IPsec natively and MAY support IPsec
   via GRE.  A constrained ACP node MUST support dTLS.  ACP nodes
   connecting constrained areas with baseline areas MUST therefore
   support IPsec and dTLS.

   ACP nodes need to specify in documentation the set of secure ACP
   mechanisms they support.

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

6.8.  GRASP in the ACP

6.8.1.  GRASP as a core service of the ACP

   The ACP MUST run an instance of GRASP inside of it.  It is a key part
   of the ACP services.  They function in GRASP that makes it
   fundamental as a service is the ability for ACP wide service
   discovery (called objectives in GRASP).  In most other solution
   designs such distributed discovery does not exist at all or was added
   as an afterthought and relied upon inconsistently.

   ACP provides IP unicast routing via the RPL routing protocol
   (described below).

   The ACP does not use IP multicast routing nor does it provide generic
   IP multicast services.  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).

   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 autoconfiguring
   solution for ASM (Any Source Multicast - original form of IP
   multicast defined in [RFC1112]), which would be quite complex and



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   difficult to justify.  One aspect of complexity that has never been
   attempted to be solved in IETF documents is the automatic-selection
   of routers that should be 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.

   Future ASA may need high performance in-network data replication.
   That is the case when the use of IP multicast is justified.  These
   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 constrained flooded 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.

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 to ensure that this instance
   of GRASP is only sending messages across the ACP GRASP virtual



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   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.  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:

   [RFC Editor: please try to put the following picture on a single page
   and remove this note.  We cannot figure out how to do this with XML.
   The picture does fit on a single page.]

            ACP:
       ...............................................................
       .                                                             .
       .         /-GRASP-flooding-\         ACP GRASP instance       .
       .        /                  \                                 .
       .    GRASP      GRASP      GRASP                              .
       .  link-local   unicast  link-local                           .
       .   multicast  messages   multicast                           .
       .   messages      |       messages                            .
       .      |          |          |                                .
       ...............................................................
       .      v          v          v    ACP security and transport  .
       .      |          |          |    substrate for GRASP         .
       .      |          |          |                                .
       .      |       ACP GRASP     |       - ACP GRASP              .
       .      |       loopback      |         loopback interface     .
       .      |       interface     |       - AN-cert auth           .
       .      |         TLS         |                                .
       .   ACP GRASP     |       ACP GRASP  - ACP GRASP virtual      .
       .   subnet1       |       subnet2      virtual interfaces     .
       .     TCP         |         TCP                               .
       .      |          |          |                                .
       ...............................................................
       .      |          |          |   ^^^ Users of ACP (GRASP/ASA) .
       .      |          |          |   ACP interfaces/addressing    .
       .      |          |          |                                .
       .      |          |          |                                .
       .      | ACP-loopback Interf.|      <- ACP loopback interface .
       .      |      ACP-address    |       - address (global ULA)   .
       .    subnet1      |        subnet2  <- ACP virtual interfaces .



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       .  link-local     |      link-local  - link-local addresses   .
       ...............................................................
       .      |          |          |   ACP routing and forwarding   .
       .      |     RPL-routing     |                                .
       .      |   /IP-Forwarding\   |                                .
       .      |  /               \  |                                .
       .  ACP IPv6 packets   ACP IPv6 packets                        .
       .      |/                   \|                                .
       .    IPsec/dTLS        IPsec/dTLS  - AN-cert auth             .
       ...............................................................
                |                   |   data-plane
                |                   |
                |                   |     - ACP secure channel
            link-local        link-local  - encap addresses
              subnet1            subnet2  - data-plane interfaces
                |                   |
             ACP-Nbr1            ACP-Nbr2

                                 Figure 2

   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 equally built ACP GRASP virtual interface 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



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   the probability for loss free transmission so much that applications
   would want to increase the frequency with which they send these
   messages.  This would result in more traffic flooding than hop-by-hop
   reliable retransmission as provided for by TCP.

   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:

   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 semantic of the GRASP negotiation
   to an extend that allows it to proxy it without being detected, but
   in an AN environment this is quite likely public knowledge or evens
   standardized.

   The GRASP TLS connections are run like any other ACP traffic through
   the ACP secure channels.  This leads to double authentication/
   encryption.  Future work optimizations could avoid this but it is
   unclear how beneficial/feasible this is:

   o  The security considerations for GRASP change against attacks from
      non-ACP (e.g.: "outside") nodes: TLS is subject to reset attacks
      while secure channel protocols may be not (e.g.: IPsec is not).

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

   o  The GRASP TLS connections need to implement any additional
      security options that are required for secure channels.  For
      example the closing of connections when the peers certificate has
      expired.




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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 systems, 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 global routing table.  Also, configuration errors
   from the data-plane setup do not affect the ACP.

6.10.  Addressing inside the ACP

   The channels explained above typically only establish communication
   between two adjacent nodes.  In order for communication to happen
   across multiple hops, the autonomic control plane requires 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 global ID prefix.  Conversely, ULA
   global IDs from different domains are unlikely to clash, such that
   two networks can be merged, as long as the policy allows that merge.
   See also Section 9.1 for a discussion on merging domains.

   Links inside the ACP only use link-local IPv6 addressing, such that
   each node 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).





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   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 specified in [RFC4193].  An alternative scheme
      was discussed, using assigned ULA addressing.  The consensus was
      to use ULA-random [[RFC4193] with L=1], because it was deemed to
      be sufficient.

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

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





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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 3: ACP Addressing Base Scheme

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

   o  "fd" identifies a locally defined ULA address.

   o  The 40 bits ULA "global ID" (term from [RFC4193]) for ACP
      addresses carried in the domain information field of domain
      certificates are the first 40 bits of the SHA256 hash of the
      routing subdomain from the same domain information field.  In the
      example of Section 6.1.1, the routing subdomain is
      "area51.research.acp.example.com" and the 40 bits ULA "global ID"
      a379a6f6ee.

   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
      registrar will create the domain information field in response to
      the CSR Attribute Request 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.

6.10.3.  ACP Zone Addressing Sub-Scheme

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







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


                 Figure 4: 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.

   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 registrar which assigned the Node-ID to the node.
      A MAC address of the registrar can be used for this purpose.

   o  Node-Number: A number which is unique for a given 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 Zone addressing sub-scheme, the ACP address in the certificate
   has Zone and V fields as all zero bits.  The ACP address set includes
   addresses with any Zone 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).  A address with zone-ID = 0 is an
   identifier, with another zone-ID as a locator.  See Section 6.10.3.1
   for a description of the zone bits.

   The Virtual bit in this sub-scheme allows to easily add the ACP as a
   component to existing systems without causing problems in the port
   number space between the services in the ACP and the existing system.



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   V:0 is the ACP router (autonomous node base system), V:1 is the host
   with pre-existing transport endpoints on it that could collide with
   the transport endpoints used by the ACP router.  The ACP host could
   for example have a p2p virtual interface with the V:0 address as its
   router into the ACP.  Depending on the SW design of ASA (outside the
   scope of this specification), they may use the V:0 or V:1 address.

   The location of the V bit(s) at the end of the address allows to
   announce a single prefix for each ACP node.  For example, in a
   network with 20,000 ACP nodes, this avoid 20,000 additional routes in
   the routing table.

6.10.3.1.  Usage of the Zone Field

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

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

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

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

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

   Note: The Zone-ID is one method to introduce structure or hierarchy
   into the ACP.  Another way is the use of the routing subdomain field
   in the ACP that leads to different /40 ULA prefixes within an ACP
   domain.  This gives future work two options to consider.






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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.



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


                Figure 5: 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).  Future work may define
   mechanisms for auto-coordination between ACP nodes and auto-
   allocation of Subnet-IDs between them.

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

   Manual addressing sub-scheme addresses SHOULD only be used in domain
   certificates assigned to nodes that cannot fully participate in the
   automatic establishment of ACP secure channels or ACP routing.  The
   intended use are nodes connecting to the ACP via an ACP edge node and



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   ACP connect (see Section 8.1) - such as legacy NOC equipment.  They
   would not use their domain certificate for ACP secure channel
   creation and therefore do not need to participate in ACP routing
   either.  They would use the certificate for authentication of any
   transport services.  The value of the Interface Identifier is left
   for future definitions.

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 |
   +---------------------++--------------+--------------+----------+
                               46             33/17          8/16

                 Figure 6: ACP Vlong Addressing Sub-Scheme

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

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

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

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

   o  If the first bit of the "Node-Number" is "1", then the Node-Number
      is 17 bit long and the V field is 16 bit long.  Otherwise the
      Node-Number is 33 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) nof the ACP
      that require separate V(irtual) addresses.  "1" bit Node-Numbers
      are intended for ACP nodes that are ACP edge nodes (see



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      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-schemes is intended to enable optimized routing in
   large networks by reserving bits for zones.  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 should consider to be
   extensible in itself (e.g.: by reserving bits from it for further
   extensions.

6.11.  Routing in the ACP

   Once ULA address are set up all autonomic entities should run a
   routing protocol within the autonomic control plane context.  This
   routing protocol distributes the ULA created in the previous section
   for reachability.  The use of the autonomic control plane specific
   context eliminates the probable clash with the global routing table
   and also secures the ACP from interference from the configuration
   mismatch or incorrect routing updates.

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

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

   The routing protocol inside the ACP is RPL ([RFC6550]).  See
   Section 10.5 for more details on the choice of RPL.



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   RPL adjacencies are set up across all ACP channels in the same domain
   including all its routing subdomains.  See Section 10.7 for more
   details.

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 reasonable fast links so that RPL convergence will
   be triggered immediately upon recognition of link failure/recovery.

   The key limitation of the chosen profile is that it is designed to
   not require any 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 VRF control plane.  Many devices will have their
   VRF forwarding code designed into 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 (containing one
   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 can reconfigure itself when it detects data plane forwarding
   failures.

   The lack of a RPI (the header 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 TTL of the packet reaches
   zero.  This the same behavior as that of other IGPs that do not have
   the data-plane options as RPPL.  There are a variety of heuristics




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   that can be used to signal from the data-plane to the RPL control
   plane that a new route is needed.

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

   Future Extensions to this RPL profile can provide optimality for
   multiple NOCs.  This requires utilizing data-plane artifact including
   IPinIP encap/decap on ACP routers and processing of IPv6 RPI headers.
   Alternatively, (Src,Dst) routing table entries could be used.  A
   decision for the preferred technology would have to be done when such
   extension is defined.

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): mode 3 "Storing Mode of Operations with
   multicast support".  Implementations should support also other modes.
   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.

   rank_factor: Derived from link speed: <= 100Mbps:
   LOW_SPEED_FACTOR(5), else HIGH_SPEED_FACTOR(1)





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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 ([RFC6552], 3.2.6 - to become root):
   Indicated in DODAGPreference field of DIO message.

   o  Explicit configured "root": 0b100

   o  Registrar (Default): 0b011

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

   o  Default: 0b001.

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, but that
   determination is for future work.  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




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   operations, e.g.: when the data-plane is not available.  See
   [I-D.ietf-anima-stable-connectivity] for more details.

6.12.2.  Addressing of Secure Channels in the data-plane

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

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

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

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 a standard issue
   with tunneling, not specific to running the ACP across it.  Transport
   stacks running across ACP can perform normal PMTUD (Path MTU
   Discovery).  Because the ACP is meant to be prioritize reliability
   over performance, they MAY opt to only expect IPv6 minimum MTU (1280)
   to avoid running into PMTUD implementation bugs or underlying link
   MTU mismatch problems.








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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 where 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).

   ACP secure channels, e.g.: IPsec, dTLS or other future security
   associations with neighboring ACP nodes can be mapped to ACP virtual
   interfaces in different ways:

   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.

   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.

   ACP nodes MUST NOT derive their ACP virtual interface IPv6 link local
   address from their IPv6 link-local address used on the underlying
   interface (e.g.: the address that is used as the encapsulation
   address in the ACP secure channel protocols defined in this
   document).  This ensures that the ACP virtual interface operations
   will not depend on the specifics of the encapsulation used by the ACP
   secure channel and that attacks against SLAAC on the physical
   interface will not introduce new attack vectors against the
   operations of the ACP virtual interface.

   The link-layer address of an ACP virtual interface is the address
   used for the underlying interface across which the secure tunnels are



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   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 Charlies 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.

   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



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   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.  These requirements can be avoided by coupling the ACP
   flooding mechanism for GRASP messages directly to RPL (flood GRASP
   across DODAG), but such an enhancement is subject for future work.

   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 7

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



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   Predictable scaling requirements for ACP neighbors can most easily be
   achieved if in topologies like 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
   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



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

   A generic issue with ACP in L2 switched networks is the interaction
   with the Spanning Tree Protocol.  Ideally, the ACP should be built
   also across ports that are blocked in STP so that the ACP does not



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   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, just like 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 connect
   "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" ||
  |        |   .   |  [   VRF    ]  | .          ^    |             ||
  +--------+   .   +----------------+  .         .    +-------------+|
               .                        .        .     +-------------+
               .                        .        .
            data-plane "native"         .     ACP "native" (unencrypted)
          + ACP auto-negotiated         .    "ACP connect subnet"
            and encrypted               .
                                        ACP connect interface
                                        e.g.: "vrf ACP native" (config)


                           Figure 8: 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
   "Autonomic Network Stable Connectivity"
   [I-D.ietf-anima-stable-connectivity] explains in more detail how the
   ACP can be integrated in a mixed NOC environment.

   The ACP connect interface must be (auto-)configured with an IPv6
   address prefix.  Is prefix SHOULD be covered by one of the (ULA)
   prefix(es) used in the ACP.  If using non-autonomic configuration, it
   SHOULD use the ACP Manual Addressing Sub-Scheme (Section 6.10.4).  It
   SHOULD NOT use a prefix that is also routed outside the ACP so that
   the addresses clearly indicate whether it is used inside the ACP or
   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 (such as those physically secure locations like a
   NOC).  For example, the certificate of such node could include an
   extension required to permit configuration of ACP connect interfaces.
   This prohibits that a random ACP node with easy physical access that
   is not meant to run ACP connect could start leaking the ACP when it
   becomes compromised and the intruder configures ACP connect on it.
   The full workflow including the mechanism by which a registrar would
   select which node to give such a certificate to is subject to future
   work.

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



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   data-plane.  Like in the physical setup for NMS hosts this can be
   realized via two internal virtual subnets.  One that is connecting to
   the ACP (which could be a container or virtual machine by itself),
   and one (or more) connecting into the data-plane.

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

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

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 autoconfiguration
   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 (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



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   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.

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]           |        |              ||
     |        |   .   |  [VRF  ]           |        +--------------+|
     +--------+   .   +--------------------+         +--------------+
                  .
           data-plane "native" and + ACP auto-negotiated/encrypted


                           Figure 9: 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 VRF.  This is sometimes called "VRF select".  If the ACP
   VRF has no overlapping IPv6 addresses with the data-plane (as it
   should), then this function can use the IPv6 Destination address.
   The problem is Source Address Selection on the NMS Host(s) according
   to RFC6724.

   Consider the simple case: The ACP uses only one ULA prefix, the ACP
   IPv6 prefix for the Combined ACP and data-plane interface is covered
   by that ULA prefix.  The ACP edge node announces both the ACP IPv6



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   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.

   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.

   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



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   allowed to participate in the ACP GRASP domain is one of the main
   reasons why the ACP section describes no solution with non-ACP
   routers participating in the ACP routing table.

   ACP connect interfaces can be dealt with in the GRASP ACP domain like
   any other ACP interface assuming that any physical ACP connect
   interface is physically protected from attacks and that the connected
   Software or NMS Hosts are equally trusted as that on other ACP nodes.
   ACP edge nodes SHOULD have options to filter GRASP 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 as follows:

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



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

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

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

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

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

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

8.2.2.  Tunneled Remote ACP Neighbor

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



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   Neighbor.  Benefits of tunnels are that it may be easier to implement
   because there is no change to the ACP functionality - just running it
   over a virtual (tunnel) interface instead of only native interfaces.
   The tunnel itself may also provide PMTUD while the secure channel
   method may not.  Or the tunnel mechanism is permitted/possible
   through some firewall while the secure channel method may not.

8.2.3.  Summary

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

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

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

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.




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

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

   After a network partition, a re-merge will just establish the
   previous status, certificates can be renewed, the CRL is available,
   and new 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 like DTLS or IPsec which provide
   additional authentication during channel establishment, data
   integrity and data confidentiality protection of data inside the ACP
   and in addition, provide replay protection.



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   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 AN
   protocols themselves, either via directed attacks or by denial-of-
   service attacks.  However, as the ACP is built using link-local IPv6
   address, remote attacks are impossible.  The ULA addresses are only
   reachable inside the ACP context, therefore, unreachable from the
   data-plane.  Also, the ACP protocols should be implemented to be
   attack resistant and not consume unnecessary resources even while
   under 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 overall the secured so that there are no easy way
   to compromise them, such as data-plane accessible privilege level
   with simple passwords.  This is a lot easier to do in devices whose
   software is designed from the ground up with security in mind than
   with legacy software based system where ACP is added on as another
   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).





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

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.  Further Considerations (Informative)

   The following sections cover topics that are beyond the primary cope
   of this document (e.g.: bootstrap), that explain decisions made in
   this document (e.g.: choice of GRASP) or that explain desirable
   extensions or implementation details for the ACP that are not
   considered to be appropriate to standardize in this document.

10.1.  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/DS forwarding/server setup).  This includes otherwise



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   not configured networks as described in Section 3.2.  Therefore BRSKI
   in conjunction with ACP provides for a secure and zero-touch
   management solution for complete networks.  Nodes supporting such an
   infrastructure (BRSKI and ACP) are called ANI nodes (Autonomic
   Networking Infrastructure), see [I-D.ietf-anima-reference-model].
   Nodes that do not support an IDevID but only an (insecure) vendor
   specific Unique Device Identifier (UDI) or nodes whose manufacturer
   does not support a MASA could use some future security reduced
   version of BRSKI.

   When BRSKI is used to provision a domain certificate (which is called
   enrollment), the registrar (acting as an 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 "no-not-renew" list would be
   necessary on 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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10.2.  ACP (and BRSKI) Diagnostics

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

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

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

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

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

   o  Developing the logic to identify common issues requires
      operational experience with the components of the ANI.  Letting
      each management system define its own analysis is inefficient.  As
      much as possible, future work should attempt to standardize data
      models that support common error diagnostic.

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

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




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   The most simple form of diagnostics answering questions like 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 ?

      *  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 neighborships.

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





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

      *  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.



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            -  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)

   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:



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

   2.  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".

   Desirable options for additional diagnostics subject to future work
   include:

   1.  Determine if LLDP should be a recommended functionality for ANI
       devices to improve diagnostics, and if so, which information
       elements it should signal (insecure).

   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.

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.




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   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
   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).

   To provide ACP/ANI resilience against operators configuring
   interfaces to "down" state, this document recommends to separate the



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   "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
   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.







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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 (autonomous) 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 autoconfigure a BFD 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 10.2 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
   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
   autoconfiguring links.

   In addition to "Physical down", low level diagnostics of Ethernet or
   other interfaces also involve the creation of other states on



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   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

   Power consumption of "physical down" interfaces may be significantly
   lower than those in "admin down" state, for example on long range
   fiber interfaces.  Assuming reasonable clocks on devices, mechanisms
   for infrequent periodic probing could allow to automatically
   establish ACP connectivity across such links.  Bring up interfaces
   for 5 seconds to probe if there is an ACP neighbor on the remote end
   every 500 seconds = 1% power consumption.

10.3.3.  Interface level ACP/ANI enable

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

10.3.4.  Which interfaces to auto-enable ?

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

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

   Consider an ACP domain of ACP nodes transitively connected via native
   interfaces.  A data-plane tunnel between two of these nodes that are



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   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".

   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



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   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".

   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



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   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 could lead to
   immediate termination of BRSKI, while other parallel
   autoconfiguration 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
   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.



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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.

10.4.  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.

10.4.1.  LLDP

   LLDP (and Cisco's similar CDP) are example of L2 discovery protocols
   that terminate their messages on L2 ports.  If those protocols would
   be chosen for ACP neighbor discovery, ACP neighbor discovery would
   therefore also terminate on L2 ports.  This would prevent ACP
   construction over non-ACP capable but LLDP or CDP enabled L2
   switches.  LLDP has extensions using different MAC addresses and this
   could have been an option for ACP discovery as well, but the
   additional required IEEE standardization and definition of a profile
   for such a modified instance of LLDP seemed to be more work than the
   benefit of "reusing the existing protocol" LLDP for this very simple
   purpose.








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10.4.2.  mDNS and L2 support

   mDNS [RFC6762] with DNS-SD RRs (Resource Records) as defined in
   [RFC6763] is a key contender as an ACP discovery protocol. because it
   relies on link-local IP multicast, it does operates at the subnet
   level, and is also found in L2 switches.  The authors of this
   document are not aware of mDNS implementation that terminate their
   mDNS messages on L2 ports instead of the subnet level.  If mDNS was
   used as the ACP discovery mechanism on an ACP capable (L3)/L2 switch
   as outlined in Section 7, then this would be necessary to implement.
   It is likely that termination of mDNS messages could only be applied
   to all mDNS messages from such a port, which would then make it
   necessary to software forward any non-ACP related mDNS messages to
   maintain prior non-ACP mDNS functionality.  Adding support for ACP
   into such L2 switches with mDNS could therefore create regression
   problems for prior mDNS functionality on those nodes.  With low
   performance of software forwarding in many L2 switches, this could
   also make the ACP risky to support on such L2 switches.

10.4.3.  Why DULL GRASP

   LLDP was not considered because of the above mentioned issues. mDNS
   was not selected because of the above L2 mDNS considerations and
   because of the following additional points:

   If mDNS was not already existing in a node, it would be more work to
   implement than DULL GRASP, and if an existing implementation of mDNS
   was used, it would likely be more code space than a separate
   implementation of DULL GRASP or a shared implementation of DULL GRASP
   and GRASP in the ACP.

10.5.  Choice of routing protocol (RPL)

   This Appendix explains why RPL - "IPv6 Routing Protocol for Low-Power
   and Lossy Networks ([RFC6550] was chosen as the default (and in this
   specification only) routing protocol for the ACP.  The choice and
   above explained profile was derived from a pre-standard
   implementation of ACP that was successfully deployed in operational
   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]).



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   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
      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.




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   o  No need for path optimisation: RPL does not necessarily compute
      the optimal path between any two nodes.  However, the ACP does not
      require this today, since it carries mainly non-delay-sensitive
      feedback loops.  It is possible that different optimisation
      schemes become necessary in the future, but RPL can be expanded
      (see point "Extensibility" above).

10.6.  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.

   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 802.1AE ([MACSEC]) are to be added as
   negotiation options - and the performance objective should work
   across all IPsec, dDTLS and 802.1AE options.  In the case of MacSEC,
   the negotiation would also need to determine a key for the peering.
   It is unclear if it would be even appropriate to consider extending
   the scope of negotiation in IKEv2 to those cases.  Even if feasible
   to define, it is unclear if implementations of IKEv2 would be eager
   to adopt those type of extension given the long cycles of security



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   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,
   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.

10.7.  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



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

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

   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".





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

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

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

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

10.8.  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 /50 IPv6
   prefix.  This prefix could simply be a configuration of the
   registrars when using BRSKI to enroll the domain certificates -
   instead of the registrar deriving the /50 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



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   decide who is Alice and who is Bob during secure channel building.
   Note though that future work may leverage the acp address to
   authenticate "ownership" of the address by the device.  If the
   address used by a device is derived from some pre-existing permanent
   local ID (such as MAC address), then it would be useful to store that
   address in the certificate using the format of the access address
   information field or in a similar way.

   The ACP is defined as a separate VRF because it intends to support
   well managed networks with a wide variety of configurations.
   Therefore, reliable, configuration-indestructible connectivity cannot
   be achieved from the data-plane itself.  In solutions where all
   transit connectivity impacting functions are fully automated
   (including security), indestructible and resilient, it would be
   possible to eliminate the need for the ACP to be a separate VRF.
   Consider the most simple example system in which there is no separate
   data-plane, but the ACP is the data-plane.  Add BRSKI, and it becomes
   a fully autonomic network - except that it does not support automatic
   addressing for user equipment.  This gap can then be closed for
   example by adding a solution derived from
   [I-D.ietf-anima-prefix-management].

   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.

   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 enrolment, still
   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.  Secure channels may
   even be replaced by simple neighbor authentication to create
   simplified ACP variations for environments where no real security is
   required but just protection against non-malicious misconfiguration.
   Or for environments where all traffic is known or forced to be end-
   to-end protected and other means for infrastructure protection are
   used.  Any future network OAM should always use end-to-end security




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   anyhow and can leverage the domain certificates and is therefore not
   dependent on security to be provided for by ACP secure channels.

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.

   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
      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
   nodes 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.



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   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 Section 10.6.

   The ACP is designed to minimize attacks from the outside by
   minimizing its dependency against any non-ACP operations on a node.
   The only dependency in the specification in this document is the need
   to share link-local addresses for the ACP secure channel
   encapsulation with the data-plane.  See 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 Section 10.1.

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.

   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 4) / ACP Manual
   Addressing Sub-Scheme (ACP RFC Section 6.10.4)
   1: ACP Vlong Addressing Sub-Scheme (ACP RFC Section 6.10.5)



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

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.








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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.

   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.




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   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.

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.



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   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).

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.




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   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.

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.





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   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
      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.



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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.

   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



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   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.

   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 autoconfiguration of routing by NMS hosts.
   This came after review of stable connectivity draft where ACP connect
   is being referred to.

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

   Added text in response to Brian Carpenters review of draft-ietf-
   anima-stable-connectivity-04.

   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



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      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.

   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:



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   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):

   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.



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   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.

   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.





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   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.

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.



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   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.

   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.






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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.

   [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>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [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>.



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   [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>.

   [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>.

   [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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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-07 (work in progress), July 2017.

   [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-05 (work in progress),
              August 2017.

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

   [I-D.ietf-anima-stable-connectivity]
              Eckert, T. and M. Behringer, "Using Autonomic Control
              Plane for Stable Connectivity of Network OAM", draft-ietf-
              anima-stable-connectivity-06 (work in progress), September
              2017.

   [I-D.ietf-netconf-zerotouch]
              Watsen, K., Abrahamsson, M., and I. Farrer, "Zero Touch
              Provisioning for NETCONF or RESTCONF based Management",
              draft-ietf-netconf-zerotouch-17 (work in progress),
              September 2017.

   [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-16 (work in progress), July 2017.

   [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>.




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   [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>.

   [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>.

   [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>.




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   [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>.

   [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>.

   [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>.

   [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>.

   [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>.

   [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>.






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   [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>.

   [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>.

   [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>.

Authors' Addresses

   Michael H. Behringer (editor)

   Email: michael.h.behringer@gmail.com


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

   Email: tte+ietf@cs.fau.de




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

   Email: sbjarnason@arbor.net












































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