



ANIMA WG                                                   S. Jiang, Ed.
Internet-Draft                                                     Z. Du
Intended status: Informational              Huawei Technologies Co., Ltd
Expires: June 18, 2018                                      B. Carpenter
                                                       Univ. of Auckland
                                                                  Q. Sun
                                                           China Telecom
                                                       December 15, 2017


     Autonomic IPv6 Edge Prefix Management in Large-scale Networks
                 draft-ietf-anima-prefix-management-07

Abstract

   This document defines two autonomic technical objectives for IPv6
   prefix management at the edge of large-scale ISP networks, with an
   extension to support IPv4 prefixes.  An important purpose of the
   document is to use it for validation of the design of various
   components of the autonomic networking infrastructure.

Status of This Memo

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

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

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

   This Internet-Draft will expire on June 18, 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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Intended User and Administrator Experience  . . . . . . .   4
     3.2.  Analysis of Parameters and Information Involved . . . . .   5
       3.2.1.  Parameters each device can define for itself  . . . .   5
       3.2.2.  Information needed from network operations  . . . . .   6
       3.2.3.  Comparison with current solutions . . . . . . . . . .   6
     3.3.  Interaction with other devices  . . . . . . . . . . . . .   7
       3.3.1.  Information needed from other devices . . . . . . . .   7
       3.3.2.  Monitoring, diagnostics and reporting . . . . . . . .   7
   4.  Autonomic Edge Prefix Management Solution . . . . . . . . . .   8
     4.1.  Behaviors on prefix requesting device . . . . . . . . . .   8
     4.2.  Behaviors on prefix providing device  . . . . . . . . . .   9
     4.3.  Behavior after Successful Negotiation . . . . . . . . . .  10
     4.4.  Prefix logging  . . . . . . . . . . . . . . . . . . . . .  10
   5.  Autonomic Prefix Management Objectives  . . . . . . . . . . .  10
     5.1.  Edge Prefix Objective Option  . . . . . . . . . . . . . .  10
     5.2.  IPv4 extension  . . . . . . . . . . . . . . . . . . . . .  11
   6.  Prefix Management Parameters  . . . . . . . . . . . . . . . .  11
     6.1.  Example of Prefix Management Parameters . . . . . . . . .  12
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   10. Change log [RFC Editor: Please remove]  . . . . . . . . . . .  14
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  15
     11.2.  Informative References . . . . . . . . . . . . . . . . .  16
   Appendix A.  Deployment Overview  . . . . . . . . . . . . . . . .  17
     A.1.  Address & Prefix management with DHCP . . . . . . . . . .  17
     A.2.  Prefix management with ANI/GRASP  . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22

1.  Introduction

   The original purpose of this document was to validate the design of
   the Autonomic Networking Infrastructure (ANI) for a realistic use
   case.  It shows how the ANI can be applied to IP prefix delegation
   and it outlines approaches to build a system to do this.  A fully
   standardized solution would require more details, so this document is
   informational in nature.



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   This document defines two autonomic technical objectives for IPv6
   prefix management in large-scale networks, with an extension to
   support IPv4 prefixes.  The background to Autonomic Networking (AN)
   is described in [RFC7575] and [RFC7576].  The GeneRic Autonomic
   Signaling Protocol (GRASP) is specified by [I-D.ietf-anima-grasp] and
   can make use of the proposed technical objectives to provide a
   solution for autonomic prefix management.  An important purpose of
   the present document is to use it for validation of the design of
   GRASP and other components of the autonomic networking infrastructure
   described in [I-D.ietf-anima-reference-model].

   This document is not a complete functional specification of an
   autonomic prefix management system and it does not describe all
   detailed aspects of the GRASP objective parameters and Autonomic
   Service Agent (ASA) procedures necessary to build a complete system.
   Instead, it describes the architectural framework utilizing the
   components of the ANI, outlines the different deployment options and
   aspects, and defines GRASP objectives for use in building the system.
   It also provides some basic parameter examples.

   This document is not intended to solve all cases of IPv6 prefix
   management.  In fact, it assumes that the network's main
   infrastructure elements already have addresses and prefixes.  The
   document is dedicated to how to make IPv6 prefix management at the
   edges of large-scale networks as autonomic as possible.  It is
   specifically written for service provider (ISP) networks.  Although
   there are similarities between ISPs and large enterprise networks,
   the requirements for the two use cases differ.  In any case, the
   scope of the solution is expected to be limited, like any autonomic
   network, to a single management domain.

   However, the solution is designed in a general way.  Its use for a
   broader scope than edge prefixes, including some or all
   infrastructure prefixes, is left for future discussion.

   A complete solution has many aspects that are not discussed here.
   Once prefixes have been assigned to routers, they need to be
   communicated to the routing system as they are brought into use.
   Similarly, when prefixes are released, they need to be removed from
   the routing system.  Different operators may have different policies
   about prefix lifetimes, and they may prefer to have centralized or
   distributed pools of spare prefixes.  In an autonomic network, these
   are properties decided by the design of the relevant ASAs.  The GRASP
   objectives are simply building blocks.

   A particular risk of distributed prefix allocation in large networks
   is that over time, it might lead to fragmentation of the address
   space and an undesirable increase in the interior routing protocol



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   tables.  The extent of this risk depends on the algorithms and
   policies used by the ASAs.  Mitigating this risk might even become an
   autonomic function in itself.

2.  Terminology

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

   This document uses terminology defined in [RFC7575].

3.  Problem Statement

   The autonomic networking use case considered here is autonomic IPv6
   prefix management at the edge of large-scale ISP networks.

   Although DHCPv6 Prefix Delegation [RFC3633] supports automated
   delegation of IPv6 prefixes from one router to another, prefix
   management still largely depends on human planning.  In other words,
   there is no basic information or policy to support autonomic
   decisions on the prefix length that each router should request or be
   delegated, according to its role in the network.  Roles could be
   defined separately for individual devices or could be generic (edge
   router, interior router, etc.).  Furthermore, IPv6 prefix management
   by humans tends to be rigid and static after initial planning.

   The problem to be solved by autonomic networking is how to
   dynamically manage IPv6 address space in large-scale networks, so
   that IPv6 addresses can be used efficiently.  Here, we limit the
   problem to assignment of prefixes at the edge of the network, close
   to access routers that support individual fixed-line subscribers,
   mobile customers, and corporate customers.  We assume that the core
   infrastructure of the network has already been established with
   appropriately assigned prefixes.  The AN approach discussed in this
   document is based on the assumption that there is a generic discovery
   and negotiation protocol that enables direct negotiation between
   intelligent IP routers.  GRASP [I-D.ietf-anima-grasp] is intended to
   be such a protocol.

3.1.  Intended User and Administrator Experience

   The intended experience is, for the administrators of a large-scale
   network, that the management of IPv6 address space at the edge of the
   network can be run with minimum effort, as devices at the edge are
   added and removed and as customers of all kinds join and leave the



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   network.  In the ideal scenario, the administrators only have to
   specify a single IPv6 prefix for the whole network and the initial
   prefix length for each device role.  As far as users are concerned,
   IPv6 prefix assignment would occur exactly as it does in any other
   network.

   The actual prefix usage needs to be logged for potential offline
   management operations including audit and security incident tracing.

3.2.  Analysis of Parameters and Information Involved

   For specific purposes of address management, a few parameters are
   involved on each edge device (some of them can be pre-configured
   before they are connected).  They include:

   o  Identity, authentication and authorization of this device.  This
      is expected to use the autonomic networking secure bootstrap
      process [I-D.ietf-anima-bootstrapping-keyinfra], following which
      the device could safely take part in autonomic operations.

   o  Role of this device.  Some example roles are discussed in
      Section 6.1.

   o  An IPv6 prefix length for this device.

   o  An IPv6 prefix that is assigned to this device and its downstream
      devices.

   A few parameters are involved in the network as a whole.  They are:

   o  Identity of a trust anchor, which is a certification authority
      (CA) maintained by the network administrators, used during the
      secure bootstrap process.

   o  Total IPv6 address space available for edge devices.  It is a pool
      of one or several IPv6 prefixes.

   o  The initial prefix length for each device role.

3.2.1.  Parameters each device can define for itself

   This section identifies those of the above parameters that do not
   need external information in order for the devices concerned to set
   them to a reasonable default value after bootstrap or after a network
   disruption.  There are few of these:

   o  Default role of this device.




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   o  Default IPv6 prefix length for this device.

   o  Cryptographic identity of this device, as needed for secure
      bootstrapping [I-D.ietf-anima-bootstrapping-keyinfra].

   The device may be shipped from the manufacturer with pre-configured
   role and default prefix length, which could be modified by an
   autonomic mechanism.  Its cryptographic identity will be installed by
   its manufacturer.

3.2.2.  Information needed from network operations

   This section identifies those parameters that might need operational
   input in order for the devices concerned to set them to a non-default
   value.

   o  Non-default value for the IPv6 prefix length for this device.
      This needs to be decided based on the role of this device.

   o  The initial prefix length for each device role.

   o  Whether to allow the device to request more address space.

   o  The policy when to request more address space, for example, if the
      address usage reaches a certain limit or percentage.

3.2.3.  Comparison with current solutions

   This section briefly compares the above use case with current
   solutions.  Currently, the address management is still largely
   dependent on human planning.  It is rigid and static after initial
   planning.  Address requests will fail if the configured address space
   is used up.

   Some autonomic and dynamic address management functions may be
   achievable by extending the existing protocols, for example,
   extending DHCPv6-PD (DHCPv6 Prefix Delegation, [RFC3633]) to request
   IPv6 prefixes according to the device role.  However, defining
   uniform device roles may not be a practical task.  Some functions are
   not suitable to be achieved by any existing protocols.

   Using a generic autonomic discovery and negotiation protocol instead
   of specific solutions has the advantage that additional parameters
   can be included in the autonomic solution without creating new
   mechanisms.  This is the principal argument for a generic approach.






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3.3.  Interaction with other devices

3.3.1.  Information needed from other devices

   This section identifies those of the above parameters that need
   external information from neighbor devices (including the upstream
   devices).  In many cases, two-way dialogue with neighbor devices is
   needed to set or optimize them.

   o  Identity of a trust anchor.

   o  The device will need to discover a device, from which it can
      acquire IPv6 address space.

   o  The initial prefix length for each device role, particularly for
      its own downstream devices.

   o  The default value of the IPv6 prefix length may be overridden by a
      non-default value.

   o  The device will need to request and acquire one or more IPv6
      prefixes that can be assigned to this device and its downstream
      devices.

   o  The device may respond to prefix delegation requests from its
      downstream devices.

   o  The device may require to be assigned more IPv6 address space, if
      it used up its assigned IPv6 address space.

3.3.2.  Monitoring, diagnostics and reporting

   This section discusses what role devices should play in monitoring,
   fault diagnosis, and reporting.

   o  The actual address assignments need to be logged for potential
      offline management operations.

   o  In general, the usage situation of address space should be
      reported to the network administrators, in an abstract way, for
      example, statistics or visualized report.

   o  A forecast of address exhaustion should be reported.








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4.  Autonomic Edge Prefix Management Solution

   This section introduces the building blocks for an autonomic edge
   prefix management solution.  As noted in Section 1, this is not a
   complete description of a solution, which will depend on the detailed
   design of the relevant Autonomic Service Agents.  It uses the generic
   discovery and negotiation protocol defined by [I-D.ietf-anima-grasp].
   The relevant GRASP objectives are defined in Section 5.

   The procedures described below are carried out by an Autonomic
   Service Agent (ASA) in each device that participates in the solution.
   We will refer to this as the PrefixManager ASA.

4.1.  Behaviors on prefix requesting device

   If the device containing a PrefixManager ASA has used up its address
   pool, it can request more space according to its requirements.  It
   should decide the length of the requested prefix and request it by
   the mechanism described in Section 6.  Note that although the
   device's role may define certain default allocation lengths, those
   defaults might be changed dynamically, and the device might request
   more, or less, address space due to some local operational heuristic.

   A PrefixManager ASA that needs additional address space should
   firstly discover peers that may be able to provide extra address
   space.  The ASA should send out a GRASP Discovery message that
   contains a PrefixManager Objective option (see Section 5.1) in order
   to discover peers also supporting that option.  Then it should choose
   one such peer, most likely the first to respond.

   If the GRASP discovery Response message carries a divert option
   pointing to an off-link PrefixManager ASA, the requesting ASA may
   initiate negotiation with that ASA diverted device to find out
   whether it can provide the requested length prefix.

   In any case, the requesting ASA will act as a GRASP negotiation
   initiator by sending a GRASP Request message with a PrefixManager
   Objective option.  The ASA indicates in this option the length of the
   requested prefix.  This starts a GRASP negotiation process.

   During the subsequent negotiation, the ASA will decide at each step
   whether to accept the offered prefix.  That decision, and the
   decision to end negotiation, is an implementation choice.

   The ASA could alternatively initiate rapid mode GRASP discovery with
   an embedded negotiation request, if it is implemented.





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4.2.  Behaviors on prefix providing device

   At least one device on the network must be configured with the
   initial pool of available prefixes mentioned in Section 3.2.  Apart
   from that requirement, any device may act as a prefix providing
   device.

   A device that receives a Discovery message with a PrefixManager
   Objective option should respond with a GRASP Response message if it
   contains a PrefixManager ASA.  Further details of the discovery
   process are described in [I-D.ietf-anima-grasp].  When this ASA
   receives a subsequent Request message, it should conduct a GRASP
   negotiation sequence, using Negotiate, Confirm-waiting, and
   Negotiation-ending messages as appropriate.  The Negotiate messages
   carry a PrefixManager Objective option, which will indicate the
   prefix and its length offered to the requesting ASA.  As described in
   [I-D.ietf-anima-grasp], negotiation will continue until either end
   stops it with a Negotiation-ending message.  If the negotiation
   succeeds, the prefix providing ASA will remove the negotiated prefix
   from its pool, and the requesting ASA will add it.  If the
   negotiation fails, the party sending the Negotiation-ending message
   may include an error code string.

   During the negotiation, the ASA will decide at each step how large a
   prefix to offer.  That decision, and the decision to end negotiation,
   is an implementation choice.

   The ASA could alternatively negotiate in response to rapid mode GRASP
   discovery, if it is implemented.

   This specification is independent of whether the PrefixManager ASAs
   are all embedded in routers, but that would be a rather natural
   scenario.  In a hierarchical network topology, a given router
   typically provide prefixes for routers below it in the hierarchy, and
   it is also likely to contain the first PrefixManager ASA discovered
   by those downstream routers.  However, the GRASP discovery model,
   including its Redirect feature, means that this is not an exclusive
   scenario, and a downstream PrefixManager ASA could negotiate a new
   prefix with a device other than its upstream router.

   A resource shortage may cause the gateway router to request more
   resource in turn from its own upstream device.  This would be another
   independent GRASP discovery and negotiation process.  During the
   processing time, the gateway router should send a Confirm-waiting
   Message to the initial requesting router, to extend its timeout.
   When the new resource becomes available, the gateway router responds
   with a GRASP Negotiate message with a prefix length matching the
   request.



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   The algorithm to choose which prefixes to assign on the prefix
   providing devices is an implementation choice.

4.3.  Behavior after Successful Negotiation

   Upon receiving a GRASP Negotiation-ending message that indicates that
   an acceptable prefix length is available, the requesting device may
   use the negotiated prefix without further messages.

   There are use cases where the ANI/GRASP based prefix management
   approach can work together with DHCPv6-PD [RFC3633] as a complement.
   For example, the ANI/GRASP based method can be used intra-domain,
   while the DHCPv6-PD method works inter-domain (i.e., across an
   administrative boundary).  Also, ANI/GRASP can be used inside the
   domain, and DHCP/DHCPv6-PD be used on the edge of the domain to
   client (non-ANI devices).  Another similar use case would be ANI/
   GRASP inside the domain, with RADIUS [RFC2865] providing prefixes to
   client devices.

4.4.  Prefix logging

   Within the autonomic prefix management, all the prefix assignment is
   done by devices without human intervention.  It may be required to
   record all the prefix assignment history, for example to detect or
   trace lost prefixes after outages, or to meet legal requirements.
   However, the logging and reporting process is out of scope for this
   document.

5.  Autonomic Prefix Management Objectives

   This section defines the GRASP technical objective options that are
   used to support autonomic prefix management.

5.1.  Edge Prefix Objective Option

   The PrefixManager Objective option is a GRASP objective option
   conforming to [I-D.ietf-anima-grasp].  Its name is "PrefixManager"
   (see Section 8) and it carries the following data items as its value:
   the prefix length, and the actual prefix bits.  Since GRASP is based
   on CBOR (Concise Binary Object Representation [RFC7049]), the format
   of the PrefixManager Objective option is described as follows in CBOR
   data definition language (CDDL) [I-D.ietf-cbor-cddl]:









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     objective = ["PrefixManager", objective-flags, loop-count,
                  [length, ?prefix]]

     loop-count = 0..255         ; as in the GRASP specification
     objective-flags /=          ; as in the GRASP specification
     length = 0..128             ; requested or offered prefix length
     prefix = bytes .size 16     ; offered prefix in binary format

   The use of the 'dry run' mode of GRASP is NOT RECOMMENDED for this
   objective, because it would require both ASAs to store state about
   the corresponding negotiation, to no real benefit - the requesting
   ASA cannot base any decisions on the result of a successful dry run
   negotiation.

5.2.  IPv4 extension

   This section presents an extended version of the PrefixManager
   Objective that supports IPv4 by adding an extra flag:

     objective = ["PrefixManager", objective-flags, loop-count, prefval]

     loop-count = 0..255         ; as in the GRASP specification
     objective-flags /=          ; as in the GRASP specification

     prefval /= pref6val
     pref6val = [version6, length, ?prefix]
     version6 = 6
     length = 0..128             ; requested or offered prefix length
     prefix = bytes .size 16     ; offered prefix in binary format

     prefval /= pref4val
     pref4val = [version4, length4, ?prefix4]
     version4 = 4
     length4 = 0..32             ; requested or offered prefix length
     prefix4 = bytes .size 4     ; offered prefix in binary format

   Prefix and address management for IPv4 is considerably more difficult
   than for IPv6, due to the prevalence of NAT, ambiguous addresses
   [RFC1918], and address sharing [RFC6346].  These complexities might
   require further extending the objective with additional fields which
   are not defined by this document.

6.  Prefix Management Parameters

   An implementation of a prefix manager MUST include default settings
   of all necessary parameters.  However, within a single administrative
   domain, the network operator MAY change default parameters for all
   devices with a certain role.  Thus it would be possible to apply an



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   intended policy for every device in a simple way, without traditional
   configuration files.  As noted in Section 4.1, individual autonomic
   devices may also change their own behavior dynamically.

   For example, the network operator could change the default prefix
   length for each type of role.  A prefix management parameters
   objective, which contains mapping information of device roles and
   their default prefix lengths, MAY be flooded in the network, through
   the Autonomic Control Plane (ACP)
   [I-D.ietf-anima-autonomic-control-plane].  The objective is defined
   in CDDL as follows:

     objective = ["PrefixManager.Params", objective-flags, any]

     loop-count = 0..255         ; as in the GRASP specification
     objective-flags /=          ; as in the GRASP specification


   The 'any' object would be the relevant parameter definitions (such as
   the example below) transmitted as a CBOR object in an appropriate
   format.

   This could be flooded to all nodes, and any PrefixManager ASA that
   did not receive it for some reason could obtain a copy using GRASP
   unicast synchronization.  Upon receiving the prefix management
   parameters, every device can decide its default prefix length by
   matching its own role.

6.1.  Example of Prefix Management Parameters

   The parameters comprise mapping information of device roles and their
   default prefix lengths in an autonomic domain.  For example, suppose
   an IPRAN (IP Radio Access Network) operator wants to configure the
   prefix length of Radio Network Controller Site Gateway (RSG) as 34,
   the prefix length of Aggregation Site Gateway (ASG) as 44, and the
   prefix length of Cell Site Gateway (CSG) as 56.  This could be
   described in the value of the PrefixManager.Params objective as:

   [
      [["role", "RSG"],["prefix_length", 34]],
      [["role", "ASG"],["prefix_length", 44]],
      [["role", "CSG"],["prefix_length", 56]]
   ]

   This example is expressed in JSON notation [RFC7159], which is easy
   to represent in CBOR.





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   An alternative would be to express the parameters in YANG [RFC7950]
   using the YANG-to-CBOR mapping [I-D.ietf-core-yang-cbor].

   For clarity, the background of the example is introduced below, which
   can also be regarded as a use case of the mechanism proposed in this
   document.

   An IPRAN network is used for mobile backhaul, including radio
   stations, RNC (in 3G) or the packet core (in LTE), and the IP network
   between them as shown in Figure 1.  The eNB (Evolved Node B), RNC
   (Radio Network Controller), SGW (Service Gateway), and MME (Mobility
   Management Entity) are mobile network entities defined in 3GPP.  The
   CSG, ASG, and RSG are entities defined in the IPRAN solution.

   The IPRAN topology shown in Figure 1 includes Ring1 which is the
   circle following ASG1->RSG1->RSG2->ASG2->ASG1, Ring2 following
   CSG1->ASG1->ASG2->CSG2->CSG1, and Ring3 following
   CSG3->ASG1->ASG2->CSG3.  In a real deployment of IPRAN, there may be
   more stations, rings, and routers in the topology, and normally the
   network is highly dependent on human design and configuration, which
   is neither flexible nor cost-effective.

   +------+   +------+
   | eNB1 |---| CSG1 |\
   +------+   +------+  \   +-------+       +------+           +-------+
                  |       \ |  ASG1 |-------| RSG1 |-----------|SGW/MME|
                  |  Ring2  +-------+       +------+ \        /+-------+
   +------+   +------+     /     |              |      \    /
   | eNB2 |---| CSG2 | \  /      |      Ring1   |        \/
   +------+   +------+   \  Ring3|              |        /\
                        / \      |              |      /   \
   +------+   +------+ /    \ +-------+      +------+/       \+-------+
   | eNB3 |---| CSG3 |--------|  ASG2 |------| RSG2 |---------|  RNC  |
   +------+   +------+        +-------+      +------+         +-------+

                   Figure 1: IPRAN Topology Example

   If ANI/GRASP is supported in the IPRAN network, the network nodes
   should be able to negotiate with each other, and make some autonomic
   decisions according to their own status and the information collected
   from the network.  The Prefix Management Parameters should be part of
   the information they communicate.

   The routers should know the role of their neighbors, the default
   prefix length for each type of role, etc.  An ASG should be able to
   request prefixes from an RSG, and an CSG should be able to request
   prefixes from an ASG.  In each request, the ASG/CSG should indicate




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   the required prefix length, or its role, which implies what length it
   needs by default.

7.  Security Considerations

   Relevant security issues are discussed in [I-D.ietf-anima-grasp].
   The preferred security model is that devices are trusted following
   the secure bootstrap procedure
   [I-D.ietf-anima-bootstrapping-keyinfra] and that a secure Autonomic
   Control Plane (ACP) [I-D.ietf-anima-autonomic-control-plane] is in
   place.

   It is RECOMMENDED that DHCPv6-PD, if used, should be operated using
   DHCPv6 authentication or Secure DHCPv6.

8.  IANA Considerations

   This document defines two new GRASP Objective Option names,
   "PrefixManager" and "PrefixManager.Params".  The IANA is requested to
   add these to the GRASP Objective Names Table registry defined by
   [I-D.ietf-anima-grasp] (if approved).

9.  Acknowledgements

   Valuable comments were received from William Atwood, Fred Baker,
   Michael Behringer, Ben Campbell, Laurent Ciavaglia, Toerless Eckert,
   Joel Halpern, Russ Housley, Geoff Huston, Warren Kumari, Dan
   Romascanu, and Chongfeng Xie.

10.  Change log [RFC Editor: Please remove]

   draft-jiang-anima-prefix-management-00: original version, 2014-10-25.

   draft-jiang-anima-prefix-management-01: add intent example and
   coauthor Zongpeng Du, 2015-05-04.

   draft-jiang-anima-prefix-management-02: update references and the
   format of the prefix management intent, 2015-10-14.

   draft-ietf-anima-prefix-management-00: WG adoption, clarify scope and
   purpose, update text to match latest GRASP spec, 2016-01-11.

   draft-ietf-anima-prefix-management-01: minor update, 2016-07-08.

   draft-ietf-anima-prefix-management-02: replaced intent discussion by
   parameter setting, 2017-01-10.





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   draft-ietf-anima-prefix-management-03: corrected object format,
   improved parameter setting example, 2017-03-10.

   draft-ietf-anima-prefix-management-04: add more explanations about
   the solution, add IPv4 options, removed PD flag, 2017-06-23.

   draft-ietf-anima-prefix-management-05: selected one IPv4 option,
   updated references, 2017-08-14.

   draft-ietf-anima-prefix-management-06: handled IETF Last Call
   comments, 2017-10-18.

   draft-ietf-anima-prefix-management-07: handled IESG comments,
   2017-12-18.

11.  References

11.1.  Normative References

   [I-D.ietf-anima-autonomic-control-plane]
              Behringer, M., Eckert, T., and S. Bjarnason, "An Autonomic
              Control Plane (ACP)", draft-ietf-anima-autonomic-control-
              plane-12 (work in progress), October 2017.

   [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-09 (work in progress), October 2017.

   [I-D.ietf-anima-grasp]
              Bormann, C., Carpenter, B., and B. Liu, "A Generic
              Autonomic Signaling Protocol (GRASP)", draft-ietf-anima-
              grasp-15 (work in progress), July 2017.

   [I-D.ietf-cbor-cddl]
              Birkholz, H., Vigano, C., and C. Bormann, "Concise data
              definition language (CDDL): a notational convention to
              express CBOR data structures", draft-ietf-cbor-cddl-00
              (work in progress), July 2017.

   [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>.






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   [RFC3633]  Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
              Host Configuration Protocol (DHCP) version 6", RFC 3633,
              DOI 10.17487/RFC3633, December 2003,
              <https://www.rfc-editor.org/info/rfc3633>.

   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
              2014, <https://www.rfc-editor.org/info/rfc7159>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

11.2.  Informative References

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

   [I-D.ietf-core-yang-cbor]
              Veillette, M., Pelov, A., Somaraju, A., Turner, R., and A.
              Minaburo, "CBOR Encoding of Data Modeled with YANG",
              draft-ietf-core-yang-cbor-05 (work in progress), August
              2017.

   [I-D.liu-dhc-dhcp-yang-model]
              Liu, B., Lou, K., and C. Chen, "Yang Data Model for DHCP
              Protocol", draft-liu-dhc-dhcp-yang-model-06 (work in
              progress), March 2017.

   [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>.

   [RFC2865]  Rigney, C., Willens, S., Rubens, A., and W. Simpson,
              "Remote Authentication Dial In User Service (RADIUS)",
              RFC 2865, DOI 10.17487/RFC2865, June 2000,
              <https://www.rfc-editor.org/info/rfc2865>.






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   [RFC3046]  Patrick, M., "DHCP Relay Agent Information Option",
              RFC 3046, DOI 10.17487/RFC3046, January 2001,
              <https://www.rfc-editor.org/info/rfc3046>.

   [RFC6221]  Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A.
              Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221,
              DOI 10.17487/RFC6221, May 2011,
              <https://www.rfc-editor.org/info/rfc6221>.

   [RFC6346]  Bush, R., Ed., "The Address plus Port (A+P) Approach to
              the IPv4 Address Shortage", RFC 6346,
              DOI 10.17487/RFC6346, August 2011,
              <https://www.rfc-editor.org/info/rfc6346>.

   [RFC7049]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
              October 2013, <https://www.rfc-editor.org/info/rfc7049>.

   [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>.

Appendix A.  Deployment Overview

   This Appendix includes logical deployment models, and explanations of
   the target deployment models.  The purpose is to help in
   understanding the mechanism of the document.

   This Appendix includes two sub-sections: A.1 for the two most common
   DHCP deployment models, and A.2 for the proposed PD deployment model.
   It should be noted that these are just examples, and there are many
   more deployment models.

A.1.  Address & Prefix management with DHCP

   Edge DHCP server deployment requires every edge router connecting to
   CPE to be a DHCP server assigning IPv4/IPv6 addresses to CPE - and
   optionally IPv6 prefixes via DHCPv6-PD for IPv6 capable CPE that are
   router and have LANs behind them.





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                                                edge
           dynamic, "netconf/YANG"            interfaces
            <---------------> +-------------+
   +------+    <- telemetry   | edge router/|-+  -----  +-----+
   |config|  .... Domain ...  | DHCP server | |  ...    | CPE |+  LANs
   |server|                   +-------------+ |  -----  +-----+| (---| )
   +------+                    +--------------+  DHCP/   +-----+
                                              DHCPv6 / PD

      Figure 2: DHCP Deployment Model without a Central DHCP Server

   This requires various coordination functions via some backend system
   depicted as "config server": The address prefixes on the edge
   interfaces should be slightly larger than required for the number of
   CPEs connected so that the overall address space is best used.

   The config server needs to provision edge interface address prefixes
   and DHCP parameters for every edge router.  If too fine grained
   prefixes are used, this will result in large routing tables across
   the "Domain".  If too coarse grained prefixes are used, address space
   is wasted.  (This is less of a concern for IPv6, but if the model
   includes IPv4, it is a very serious concern.)

   There is no standard describing algorithms for how configuration
   servers would best perform this ongoing dynamic provisioning to
   optimize routing table size and address space utilization.

   There are currently no complete YANG models that a config server
   could use to perform these actions (including telemetry of assigned
   addresses from such distributed DHCP servers).

   For example, a YANG model for controlling DHCP server operations is
   still in draft [I-D.liu-dhc-dhcp-yang-model].

   Due to these and other problems of the above model, the more common
   DHCP deployment model is as follows:

   +------+                                      edge
   |config|    initial, "CLI"                   interfaces
   |server| ----------------> +-------------+
   +------+                   | edge router/|-+  -----  +-----+
      |     .... Domain ...   | DHCP relay  | |  ...    | CPE |+  LANs
   +------+                   +-------------+ |  -----  +-----+| (---| )
   |DHCP  |                    +--------------+   DHCP/  +-----+
   |server|                                   DHCPv6 / PD
   +------+

       Figure 3: DHCP Deployment Model with a Central DHCP Server



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   Dynamic provisioning changes to edge routers are avoided by using a
   central DHCP server and reducing the edge router from DHCP server to
   DHCP relay.  The "configuration" on the edge routers is static, the
   DHCP relay function inserts "edge interface" and/or subscriber
   identifying options into DHCP requests from CPE (e.g., [RFC3046],
   [RFC6221]), the DHCP server has complete policies for address
   assignments and prefixes useable on every edge-router/interface/
   subscriber-group.  When the DHCP relay sees the DHCP reply, it
   inserts static routes for the assigned address/address-prefix into
   the routing table of the edge router which are then to be distributed
   by the IGP (or BGP) inside the domain to make the CPE and LANs
   reachable across the Domain.

   There is no comprehensive standardization of these solutions.
   [RFC3633] section 14, for example, simply refers to "a [non-defined]
   protocol or other out-of-band communication to add routing
   information for delegated prefixes into the provider edge router".

A.2.  Prefix management with ANI/GRASP

   With the proposed use of ANI and Prefix-management ASAs using GRASP,
   the deployment model is intended to look as follows:

   |<............ ANI Domain / ACP............>| (...) ........->

                                      Roles
                                        |
                                        v   "Edge routers"
   GRASP parameter               +----------+
    Network wide                 |  PM-ASA  | downstream
   parameters/policies           |  (DHCP-  | interfaces
        |                        |functions)| ------
        v  "central device"      +----------+
   +------+                            ^             +--------+
   |PM-ASA|      <............GRASP ....      ....   |  CPE   |-+ (LANs)
   +------+             .              v             |(PM-ASA)| |  ---|
        .           +........+   +----------+        +--------+ |
   +...........+    . PM-ASA .   |  PM-ASA  | ------  +---------+
   .DHCP server.    +........+   |  (DHCP-  | SLAAC/
   +...........+  "intermediate  |functions)| DHCP/DHCP-PD
                     router"     +----------+

          Figure 4: Proposed Deployment Model using ANI/GRASP

   The network runs an ANI domain with ACP
   [I-D.ietf-anima-autonomic-control-plane] between some central device
   (e.g., router or ANI enabled management device) and the edge routers.
   ANI/ACP provides a secure, zero-touch communication channel between



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   the devices and enables the use of GRASP[I-D.ietf-anima-grasp] not
   only for p2p communication, but also for distribution/flooding.

   The central devices and edge routers run software in the form of
   "Autonomic Service Agents" (ASA) to support this document's autonomic
   IPv6 edge prefix management (PM).  The ASAs for prefix management are
   called PM-ASAs below, and together comprise the Autonomic Prefix
   Management Function.

   Edge routers can have different roles based on the type and number of
   CPE attaching to them.  Each edge router could be an RSG, ASG, or CSG
   in mobile aggregation networks (see Section 6.1).  Mechanisms outside
   the scope of this document make routers aware of their roles.

   Some considerations about the proposed deployment model are listed as
   follows.

   1.  In a minimum Prefix Management solution, the central device uses
   the "PrefixManager.Params" GRASP Objective introduced in this
   document to disseminate network wide, per-role parameters to edge
   routers.  The PM-ASA uses the parameters applying to its role to
   locally configure pre-existing addressing functions.  Because PM-ASA
   does not manage the dynamic assignment of actual IPv6 address
   prefixes in this case, the following options can be considered:

   1.a The edge router connects via downstream interfaces to (host) CPE
   that each requires an address.  The PM-ASA sets up for each such
   interface a DHCP requesting router (according to [RFC3633]) to
   request an IPv6 prefix for the interface.  The router's address on
   the downstream interface can be another parameter from the GRASP
   Objective.  The CPEs assign addresses in the prefix via RAs from the
   router or the PM-ASA manages a local DHCPv6 server to assign
   addresses to the CPEs.  A central DHCP server acting as the DHCP
   delegating router (according to [RFC3633]) is required.  Its address
   can be another parameter from the GRASP Objective.

   1.b The edge router also connects via downstream interfaces to
   (customer managed) CPEs that are routers and act as DHCPv6 requesting
   routers.  The need to support this could be derived from role and/or
   GRASP parameters and the PM-ASA sets up a DHCP relay function to pass
   on requests to the central DHCP server as in 1.a.

   2.  In a solution without a central DHCP server, the PM-ASA on the
   edge routers not only learn parameters from "PrefixManager.Params"
   but also utilize GRASP to request/negotiate actual IPv6 prefix
   delegation via the GRASP "PrefixManager" objective described in more
   detail below.  In the most simple case, these prefixes are delegated
   via this GRASP objective from the PM-ASA in the central device.  This



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   device must be provisioned initially with a large pool of prefixes.
   The delegated prefixes are then used by the PM-ASA on the edge
   routers to edge routers to configure prefixes on their downstream
   interfaces to assign addresses via RA/SLAAC to host CPEs.  The PM-ASA
   may also start local DHCP servers (as in 1.a) to assign addresses via
   DHCP to CPE from the prefixes it received.  This includes both host
   CPEs requesting IPv6 addresses as well as router CPEs that request
   IPv6 prefixes.  The PM-ASA needs to manage the address pool(s) it has
   requested via GRASP and allocate sub-address pools to interfaces and
   the local DHCP servers it starts.  It needs to monitor the address
   utilization and accordingly request more address prefixes if its
   existing prefixes are exhausted, or return address prefixes when they
   are unneeded.

   This solution is quite similar to the initial described IPv6 DHCP
   deployment model without central DHCP server, and ANI/ACP/GRASP and
   the PM-ASA do provide the automation to make this approach work more
   easily than it is possible today.

   3.  The address pool(s) from which prefixes are allocated does not
   need to be taken all from one central location.  Edge router PM-ASA
   that received a big (short) prefix from a central PM-ASA could offer
   smaller sub-prefixes to neighboring edge-router PM-ASA.  GRASP could
   be used in such a way that the PM-ASA would find and select the
   objective from the closest neighboring PM-ASA, therefore allowing to
   maximize aggregation: A PM-ASA would only request further (smaller/
   shorter) prefixes when it exhausts its own poll (from the central
   location) and can not get further large prefixes from that central
   location anymore.  Because the overflow prefixes taken from a
   topological nearby PM-ASA, the number of longer prefixes that have to
   be injected into the routing tables is limited and the topological
   proximity increases the chances that aggregation of prefixes in the
   IGP can most likely limit the geography in which the longer prefixes
   need to be routed.

   4.  Instead of peer-to-peer optimization of prefix delegation, a
   hierarchy of PM-ASA can be built (indicated in the picture via a
   dotted intermediate router).  This would require additional
   parameters to the "PrefixManager" objective to allow creating a
   hierarchy of PM-ASA across which the prefixes can be delegated.  This
   is not detailed further below.

   5.  In cases where CPEs are also part of the ANI Domain (e.g.,
   "Managed CPE"), then GRASP will extend into the actual customer sites
   and can equally run a PM-ASA.  All the options described in points 1
   to 4 above would then apply to the CPE as the edge router with the
   mayor changes being that a) a CPE router will most likley not need to
   run DHCPv6-PD itself, but only DHCP address assignment, b) The edge



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   routers to which the CPE connect would most likely become ideal
   places to run a hierarchical instance of PD-ASAs on as outlined in
   point 1.

Authors' Addresses

   Sheng Jiang (editor)
   Huawei Technologies Co., Ltd
   Q14, Huawei Campus, No.156 Beiqing Road
   Hai-Dian District, Beijing, 100095
   P.R. China

   Email: jiangsheng@huawei.com


   Zongpeng Du
   Huawei Technologies Co., Ltd
   Q14, Huawei Campus, No.156 Beiqing Road
   Hai-Dian District, Beijing, 100095
   P.R. China

   Email: duzongpeng@huawei.com


   Brian Carpenter
   Department of Computer Science
   University of Auckland
   PB 92019
   Auckland  1142
   New Zealand

   Email: brian.e.carpenter@gmail.com


   Qiong Sun
   China Telecom
   No.118, Xizhimennei Street
   Beijing  100035
   P. R. China

   Email: sunqiong@ctbri.com.cn










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