IPv6 CE Routers LAN Prefix Delegation
draft-winters-v6ops-cpe-lan-pd-04

Internet Engineering Task Force                               T. Winters
Internet-Draft                                                   QA Cafe
Updates: 7084 (if approved)                              23 October 2023
Intended status: Informational                                          
Expires: 25 April 2024

                 IPv6 CE Routers LAN Prefix Delegation
                   draft-winters-v6ops-cpe-lan-pd-04

Abstract

   This document defines requirements for IPv6 CE Routers to support
   DHCPv6 Prefix Delegation for redistributing any unused prefix(es)
   that were delegated to the IPv6 CE Router.  This document updates RFC
   7084.

Status of This Memo

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   This Internet-Draft will expire on 25 April 2024.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Architecture  . . . . . . . . . . . . . . . . . . . . . . . .   3
   5.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   This document defines DHCPv6 Prefix Delegation in IPv6 CE Routers
   ([RFC7084]) in order to properly utilize the IPv6 prefixes assigned
   by service providers.  Many ISP will assign a prefix larger then /64
   to the CE Router, as recommended in [RFC6177].  If an IPv6 CE Router
   doesn't support IA_PD on the LAN it will not be able to assign any
   prefixes beyond itself, limiting the usefulness of assigning prefixes
   larger than /64.  Supporting IA_PD on the LAN interfaces will allow
   for those unused prefixes to be distributed into a network.

   Two models, hierachical prefix and flat, have been proposed in the
   past for prefix sub-delegation.  Hierachical prefix delegation
   requires a IPv6 CE Router to sub delegate IPv6 prefixes based on set
   of rules.  If more then one router uses hierachical prefix
   delegation, a IPv6 prefix tree is created.  When no routing protocol
   is present to discover the network topology it's possible to have
   unbalanced prefix delegation tree which leads to running out of
   prefixes.  For more information on heirachical prefix delegation is
   contained in Section 8.5 of CableLabs IPv6 eRouter Specifiction.  A
   flat prefix delegation requires the router provisioned with a the
   initial prefix then assign /64 prefixes to all other prefix request
   from routers downstream.

   This document does not cover dealing with multi-provisioned networks
   with more than one provider.  Due to complexity of a solution that
   will requires routing, provisioning, and policy this is out of scope
   of this document.

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2.  Requirements Language

   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 also makes use of internal conceptual variables to
   describe protocol behavior and external variables that an
   implementation must allow system administrators to change.  The
   specific variable names, how their values change, and how their
   settings influence protocol behavior are provided to demonstrate
   protocol behavior.  An implementation is not required to have them in
   the exact form described here, as long as its external behavior is
   consistent with that described in this document.

3.  Terminology

   The following terminology is defined for this document.

   *  IPv6 CE Router: A router intended for home or small-office use
      that forwards packets not explicitly addressed to itself as
      defined in [RFC7084].

   *  Internet Service Provider (ISP): An entity that provides access to
      the Internet.  In this document, a service provider specifically
      offers Internet access using IPv6, and may also offer IPv4
      Internet access.  The service provider can provide such access
      over a variety of different transport methods such as DSL, cable,
      wireless, and others.

4.  Architecture

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                        +-----------+
                        |  Service  |
                        |  Provider |
                        |   Router  |
                        +-----+-----+
                              |
                              |
                              |  Customer
                              |  Internet Connection
                              |
                        +-----v-----+
                        |   IPv6    |
                        |    CE     |
                        |  Router   |
                        +-----+-----+
                              |
                       +----+-+-------+
                       |              |
                       |              |
                   +---+----+   +-----+------+
                   |  IPv6  |   |            |
                   |  Host  |   |  Router    |
                   |        |   |            |
                   +--------+   +------------+

5.  Requirements

   The IPv6 CE Router distributes configuration information obtained
   during WAN interface provisioning to IPv6 hosts and routers.
   Previously, a router based on [RFC7084] would only provide IPv6 hosts
   with individual addresses; this update allows for addressing and
   routing of IPv6 prefixes to both hosts and routers.

   LAN Prefix Delegation (LPD) Requirements

   LPD-1: The IPv6 CE Router MUST support a DHCPv6 server capable of
   IPv6 prefix assignment according to [RFC8415] (Identity Association
   for Prefix Delegation (IA_PD) option).

   LPD-2: The IPv6 CE Router MUST assign a prefix from the delegated
   prefix to each of its LAN links.  If not enough addresses are
   available the IPv6 CE Router SHOULD log a system management error.

   LPD-3: The prefix assigned to a link MUST NOT change in the absence
   of topology or configuration changes.

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   LPD-4: After LAN link prefix assignment the IPv6 CE Router MUST make
   the remaining IPv6 prefixes available to other routers via Prefix
   Delegation.

   LPD-5: The IPv6 CE Router MUST support either heirachical prefix
   delegation or flat prefix delegation.

   LAN Hierachical Prefix Deletation (HPD) Requirements

   HPD-1: If the provisioned IA_PD is smaller than a /56 (e.g., a /60)
   the IPv6 CE Router MUST divide the delegated prefix on three 3-bit
   boundaries into eight sub-prefixes by default.

   HPD-2: If the provisioned IA_PD is a /56 or larger the IPv6 CE Router
   MUST divide the delegated prefix on four (4)-bit boundaries into 16
   sub-prefixes by default.

   HPD-3: If the provisioned IA_PD is too small to divide in the manner
   described, the IPv6 CE Router MUST divide the delegated prefix into
   as many /64 sub-prefixes as possible and log an error message
   indicating the fault.

   LAN Flat Prefix Delegation (FPD) Requirements

   FPD-2: Available prefixes MUST be provisioned as IA_PD IA prefixes
   MUST with a prefix-length of 64.

   FPD-3: The IPv6 CE Router MUST install a route to the assigned IA_PD
   with a next-hop of the IPv6 node that was assigned the prefix.  The
   IPv6 CE Router MUST remove the route when IA_PD lease expires.

   FPD-4: By default, the IPv6 CE Router firewall MUST allow forwarding
   of packets with an outer IPv6 header containing a source address
   belonging to Delegated Prefixes, along with reciprocal packets from
   the same flow, following the recommendations of [RFC6092]

   FPD-5: If an IPv6 CE Router receives a single IA_PD IA Prefix with a
   prefix-length of 64, it MUST act as delegating relay according to
   [RFC8987], specifically requirements G-2 to G-7, G-9, and S-2.
   DHCPv6 messages without IA-PD option MUST NOT be relayed.

   FPD-6: A CE Router MUST only be a delegating relay with DHCPv6
   messages with IA_PD options present.

   FPD-7: A CE Router assigning prefixes MUST NOT assign IA_NA in the
   same DHCPv6 exchange.

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6.  Security Considerations

   This document does not add any new security considerations beyond
   those mentioned in Section 4 of [RFC8213] and Section 22 of
   [RFC8415].

7.  IANA Considerations

   This document makes no request of IANA.

8.  Acknowledgements

   Thanks to the following people for their guidance and feedback:
   Marion Dillon, Erik Auerswald, Esko Dijk, Tim Carlin, Richard
   Patterson, Ted Lemon, Michael Richardson, Martin Hunek.

9.  References

9.1.  Normative References

   [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>.

   [RFC6092]  Woodyatt, J., Ed., "Recommended Simple Security
              Capabilities in Customer Premises Equipment (CPE) for
              Providing Residential IPv6 Internet Service", RFC 6092,
              DOI 10.17487/RFC6092, January 2011,
              <https://www.rfc-editor.org/info/rfc6092>.

   [RFC6177]  Narten, T., Huston, G., and L. Roberts, "IPv6 Address
              Assignment to End Sites", BCP 157, RFC 6177,
              DOI 10.17487/RFC6177, March 2011,
              <https://www.rfc-editor.org/info/rfc6177>.

   [RFC7084]  Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic
              Requirements for IPv6 Customer Edge Routers", RFC 7084,
              DOI 10.17487/RFC7084, November 2013,
              <https://www.rfc-editor.org/info/rfc7084>.

   [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>.

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   [RFC8213]  Volz, B. and Y. Pal, "Security of Messages Exchanged
              between Servers and Relay Agents", RFC 8213,
              DOI 10.17487/RFC8213, August 2017,
              <https://www.rfc-editor.org/info/rfc8213>.

   [RFC8415]  Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
              Richardson, M., Jiang, S., Lemon, T., and T. Winters,
              "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
              RFC 8415, DOI 10.17487/RFC8415, November 2018,
              <https://www.rfc-editor.org/info/rfc8415>.

   [RFC8987]  Farrer, I., Kottapalli, N., Hunek, M., and R. Patterson,
              "DHCPv6 Prefix Delegating Relay Requirements", RFC 8987,
              DOI 10.17487/RFC8987, February 2021,
              <https://www.rfc-editor.org/info/rfc8987>.

9.2.  Informative References

   [RFC7695]  Pfister, P., Paterson, B., and J. Arkko, "Distributed
              Prefix Assignment Algorithm", RFC 7695,
              DOI 10.17487/RFC7695, November 2015,
              <https://www.rfc-editor.org/info/rfc7695>.

Author's Address

   Timothy Winters
   QA Cafe
   100 Main Street, Suite #212
   Dover, NH 03820
   United States of America
   Email: tim@qacafe.com

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