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Versions: 00                                                            
IPv6 Maintenance (6man) Working Group                       Loba Olopade
Internet-Draft                                              Virgin Media
Updates: 4862 (if approved)                             October 19, 2020
Intended status: Standards Track
Expires: April 22, 2021


  Explicit signaling of Stateless Address Autoconfiguration (SLAAC)
                      to Renumbering Events
                 draft-olopade-6man-slaac-signaling-00

Abstract

   After a renumbering event in an IPv6 network utilizing SLAAC, hosts
   might continue to use stale addresses, as they are unaware of the
   changes. Likewise, routers, who may deprecate the use of these
   prefixes, are unaware of their use on the hosts. This scenario could
   have an adverse effect on communication with the host. This document
   proposes changes to the SLAAC algorithm that will explicitly allow
   routers to learn of these stale prefixes that are still assigned on
   the network.

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
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   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 November 19, 2020.

Copyright Notice

   Copyright (c) 2020 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



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

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  SLAAC reaction to new PIOs . . . . . . . . . . . . . . . . . .  3
     3.1.  Proposed Change  . . . . . . . . . . . . . . . . . . . . .  4
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  4
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  4
   6.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  4
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     7.1.  Normative References . . . . . . . . . . . . . . . . . . .  4
     7.2.  Informative References . . . . . . . . . . . . . . . . . .  6
   Appendix A.  Suggested Garbage collection of stale prefix
            information . . . . . . . . . . . . . . . . . . . . . . .  6
     A.1  Prefix Validation . . . . . . . . . . . . . . . . . . . . .  7
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .  7





























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1.  Introduction

   After a renumbering event in an IPv6 network utilizing SLAAC, hosts
   might continue to use stale addresses, as they are unaware of the
   changes. Likewise, routers, who may deprecate the use of these
   prefixes, are unaware of their use on the hosts. This scenario, with
   its causes and impacts are well documented in [I-D.ietf-v6ops-slaac-
   renum] and [I-D.linkova-6man-default-addr-selection-update]. A key
   factor with this issue is the lack of explicit signaling. For various
   reasons, routers might not explicitly signal the network that there
   is a renumbering event. Once the renumbering event has occurred,
   there are no means to learn of the stale prefixes that might still be
   present on the network. Without a means to do a garbage collection,
   the network is limited to the aging out process of stale
   information.

   Rather than aging out, it would be better for routers to learn of
   this information, in a proactive manner. Using Neighbor Discovery
   messages, the router could learn of the stale prefixes.

   While it is not the objective of this document to propose how the
   stale prefix information is validated and deprecated, an example of
   how this might be done is given in Appendix A.


2.  Terminology

   The term "globally reachable" is used in this document as defined in
   [RFC8190].

   The term "Global Unicast Address" (or its acronym "GUA") is used
   throughout this document to refer to "globally reachable" [RFC8190]
   addresses.  That is, when used throughout this document, GUAs do NOT
   include Unique Local Addresses (ULAs) [RFC4193].  Similarly, the term
   "Global Unicast prefix" (or "GUA prefix") is employed throughout this
   document to refer to network prefixes that specify GUAs, and does NOT
   include the ULA prefix (FC00::/7) [RFC4193].


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

3.  SLAAC reaction to new PIOs

   In the absence of RA messages to deprecate stale prefixes, when RAs



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   are received with new PIO information, SLAAC hosts will form
   additional IPv6 address on the interface. This could lead to a
   situation where there are multiple addresses assigned to an
   interface, while only a subset of them are valid. As previously
   stated, with the current algorithm, there is no explicit way to
   inform routers of the stale prefixes that are currently assigned to
   the interfaces.

3.1.  Proposed Change

   When an address transitions from being tentative to preferred, for
   each SLAAC assigned GUA address on the interface, the host should
   send router solicitation messages, using the GUA as the source
   address. Routers receiving the solicitation messages can deduce the
   prefixes that are currently assigned to interfaces on the network.
   They can then determine if these prefixes are still valid, and
   proceed to deprecate them if they are not.

   An alternate solution would use unsolicited Neighbor Advertisement,
   similar to what is proposed in [I-D.ietf-6man-grand-03]. This would
   still require NA messages for each SLAAC assigned GUA address on the
   interface.


4.  IANA Considerations

   This document has no actions for IANA.


5.  Security Considerations

   It is not believed that this introduces any additional security risk.

6.  Acknowledgments

   The author would like to acknowledge Jen Linkova, Fernando Gont, Jan
   Zorz and Richard Patterson for the work they have previously done on
   this issue.

7.  References

7.1.  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>.




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   [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>.

   [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>.

   [RFC8028]  Baker, F. and B. Carpenter, "First-Hop Router Selection by
              Hosts in a Multi-Prefix Network", RFC 8028,
              DOI 10.17487/RFC8028, November 2016,
              <https://www.rfc-editor.org/info/rfc8028>.

   [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>.

   [RFC8190]  Bonica, R., Cotton, M., Haberman, B., and L. Vegoda,
              "Updates to the Special-Purpose IP Address Registries",
              BCP 153, RFC 8190, DOI 10.17487/RFC8190, June 2017,
              <https://www.rfc-editor.org/info/rfc8190>.

   [RFC8504]  Chown, T., Loughney, J., and T. Winters, "IPv6 Node
              Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504,
              January 2019, <https://www.rfc-editor.org/info/rfc8504>.




















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7.2.  Informative References


   [I-D.ietf-v6ops-cpe-slaac-renum]
              Gont, F., Zorz, J., Patterson, R., and B. Volz, "Improving
              the Reaction of Customer Edge Routers to Renumbering
              Events", draft-ietf-v6ops-cpe-slaac-renum-02 (work in
              progress), May 2020.

   [I-D.ietf-v6ops-slaac-renum]
              Gont, F., Zorz, J., and R. Patterson, "Reaction
              of Stateless Address Autoconfiguration (SLAAC) to Flash-
              Renumbering Events", draft-ietf-v6ops-slaac-renum-04
              (work in progress), September 2020.

   [I-D.ietf-6man-slaac-renum]
              Gont, F., Zorz, J., and R. Patterson, "Improving the
              Robustness of Stateless Address Autoconfiguration (SLAAC)
              to Flash Renumbering Events",
              draft-ietf-6man-slaac-renum-01 (work in progress),
              September 2020.

   [I-D.linkova-6man-default-addr-selection-update]
              Linkova, J., "Default Address Selection and Subnet
              Renumbering",
              draft-linkova-6man-default-addr-selection-00
              (work in progress), March 2017.

   [I-D.ietf-6man-grand-03]
              Linkova, J., "Gratuitous Neighbor Discovery: Creating
              Neighbor Cache Entries on First-Hop Routers",
              draft-ietf-6man-grand-03 (work in progress), March 2017.


Appendix A.  Suggested Garbage collection of stale prefix information

   Consider a scenario where a service provider is using non-persistent
   prefixes. If the router were to reboot, for whatever reason, then the
   a new PD is assigned to the router. The router will then start to
   include the new PIOs in its RA messages. At this point, hosts on the
   LAN will assign additional IPv6 addresses from the new prefix, on
   their interface. Using the proposed algorithm, the router will
   receive RS messages from hosts with source address from the stale
   prefixes.

   Upon receipt of the RS messages, the router can proceed to create a
   neighbor cache for the address. Before creating the neighbor cache,
   it should validate that the prefix is valid for the LAN interface.



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   Once validated, the neighbor cache entry can be created. A list of
   unmanaged on-link prefixes should also be maintained. These prefixes
   should not be included in its RA messages.

   If the prefix validation is not successful, the router should
   deprecate the prefix in its RA messages.

A.1  Prefix Validation
   Routers should maintain a list for "unmanaged on-link prefixes".
   These are prefixes that the router has determined are on-link, but
   are not included in its RA messages. The list may be maintained by
   static configuration, dynamic methods or both.

   To validate a prefix, the router may do the following

   o  Check if the prefix is included in the list of unmanaged on-link
      prefixes for the received interface. If not included, continue
      with other validation steps. Otherwise, conclude the validation
      with a success.
   o  Use a protocol (e.g. DHCPv6 leasequery) to check who the prefix is
      assigned to. If assigned to itself, it should begin to include the
      prefix in its RA messages and conclude the validation process with
      a success.
   o  Send a RS message on the interface, and listen to see if the
      prefix is included in received RA messages. RS messages must be
      sent with unspecified source address, so that hosts will not
      change the IsRouter flag for the router. If the prefix is
      included, the unmanaged on-link list should be updated, and the
      validation concluded as successful.


Authors' Addresses

      Loba Olopade
      Virgin Media

      Email: loba.olopade@virginmedia.co.uk














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