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Versions: (draft-gont-v6ops-cpe-slaac-renum) 00 01 02 03 04 05 Draft is active
In: IESG_Evaluation
IPv6 Operations Working Group (v6ops)                            F. Gont
Internet-Draft                                              SI6 Networks
Intended status: Informational                                   J. Zorz
Expires: September 10, 2020                                Go6 Institute
                                                            R. Patterson
                                                                  Sky UK
                                                           March 9, 2020


 Improving the Reaction of Customer Edge Routers to Renumbering Events
                  draft-ietf-v6ops-cpe-slaac-renum-01

Abstract

   In scenarios where network configuration information related to IPv6
   prefixes becomes invalid without any explicit signaling of that
   condition (such as when a Customer Edge Router crashes and reboots
   without knowledge of the previously-employed prefixes), hosts on the
   local network will continue using stale prefixes for an unacceptably
   long period of time, thus resulting in connectivity problems.  This
   document specifies improvements to Customer Edge Routers that help
   mitigate the aforementioned problem for typical residential and small
   office scenarios.

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 September 10, 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



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   (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
   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.  Improved Customer Edge Router Behavior  . . . . . . . . . . .   2
     2.1.  Interface Between DHCPv6-PD and SLAAC . . . . . . . . . .   3
     2.2.  Signaling Stale Configuration Information . . . . . . . .   3
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   In scenarios where network configuration information related to IPv6
   prefixes becomes invalid without any explicit signaling of that
   condition, nodes on the local network will continue using stale
   prefixes for an unacceptably long period of time, thus resulting in
   connectivity problems.  This problem is documented in detail in
   [I-D.gont-v6ops-slaac-renum].

   This document specifies improvements to Customer Edge (CE) Routers
   that help mitigate the aforementioned problem for residential or
   small office scenarios.

2.  Improved Customer Edge Router Behavior

   This section specifies and clarifies requirements for Customer Edge
   Routers -- particularly when they advertise with Stateless Address
   Autoconfiguration (SLAAC) [RFC4862] prefixes learned via
   DHCPv6-Prefix Delegation (DHCPv6-PD) [RFC8415] or prefixes derived
   from them -- that can help mitigate the problem discussed in
   Section 1.  This would obviously make robustness dependent on the
   Customer Edge Router (on which the user or ISP may have no control),
   as opposed to the host itself.

   The updated behaviour is as follows:




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   o  CE routers MUST signal stale configuration information as
      specified in Section 2.2

   o  CE routers MUST implement the DHCPv6-PD/SLAAC interface specified
      in Section 2.1

   o  CE routers SHOULD NOT automatically send DHCPv6-PD RELEASE
      messages upon reboot events

2.1.  Interface Between DHCPv6-PD and SLAAC

   The "Preferred Lifetime" and "Valid Lifetime" of Prefix Information
   Options (PIOs) [RFC4861] corresponding to prefixes learned via
   DHCPv6-PD MUST NOT span past the lease time of the DHCPv6-PD
   prefixes.  This means that the advertised "Preferred Lifetime" and
   "Valid Lifetime" MUST be dynamically adjusted such that the
   advertised lifetimes never span past the lease time of the prefixes
   delegated via DHCPv6-PD.

   This is in line with these existing requirements from other
   specifications, which we reference here for clarity:

   o  [RFC8415] specifies, in Section 6.3, that "if the delegated prefix
      or a prefix derived from it is advertised for stateless address
      autoconfiguration [RFC4862], the advertised preferred and valid
      lifetimes MUST NOT exceed the corresponding remaining lifetimes of
      the delegated prefix."

   RATIONALE:

      *  The lifetime values employed for the "Preferred Lifetime"
         (AdvPreferredLifetime) and "Valid Lifetime" (AdvValidLifetime)
         should never be larger than the remaining lease time for the
         corresponding prefix (as learned via DHCPv6-PD).

      *  The lifetime values advertised for prefixes corresponding to a
         prefix leased via DHCPv6-PD should be dynamically updated
         (rather than static values), since otherwise the advertised
         lifetimes would eventually span past the DHCPv6-PD lease time.

2.2.  Signaling Stale Configuration Information

   In order to phase-out stale configuration information:

   o  A CE router sending RAs that advertise dynamically-learned
      prefixes (e.g. via DHCPv6-PD) on an interface MUST record, on
      stable storage, the list of prefixes being advertised on each




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      network segment, and the "A" and "L" flags of the corresponding
      PIOs.

   o  Upon changes to the advertised prefixes, and after bootstrapping,
      the CE router advertising prefix information via SLAAC should
      proceed as follows:

      *  Any prefixes that were previously advertised via Router
         Advertisement (RA) messages, but that have now become stale,
         MUST be advertised with a "Valid Lifetime" and a "Preferred
         Lifetime" set to 0, and the "A" and "L" bits unchanged.

      *  The aforementioned advertisement SHOULD be performed for at
         least the "Valid Lifetime" previously employed for such prefix.

   The aforementioned improved behaviour assumes compliance with the
   following existing requirements from other specifications, which we
   reference here for clarity:

   o  [RFC7084] specifies (requirement LE-13, in Section 4.3) that when
      the delegated prefix changes (i.e., the current prefix is replaced
      with a new prefix without any overlapping time period), "the IPv6
      CE router MUST immediately advertise the old prefix with a
      Preferred Lifetime of zero and a Valid Lifetime of either a) zero
      or b) the lower of the current Valid Lifetime and two hours (which
      must be decremented in real time) in a Router Advertisement
      message as described in Section 5.5.3, (e) of [RFC4862]"

3.  IANA Considerations

   This document has no actions for IANA.

4.  Security Considerations

   This document discusses a problem that may arise in scenarios where
   dynamic IPv6 prefixes are employed, and proposes improvements to
   Customer Edge Routers [RFC7084] to mitigate the problem for
   residential or small office scenarios.  It does not introduce new
   security issues.

5.  Acknowledgments

   The authors would lie to thank (in alphabetical order) Mikael
   Abrahamsson, Luis Balbinot, Tim Chown, Brian Carpenter, Owen DeLong,
   Gert Doering, Steinar Haug, Nick Hilliard, Philip Homburg, Lee
   Howard, Christian Huitema, Ted Lemon, Albert Manfredi, Jordi Palet
   Martinez, Richard Patterson, Michael Richardson, Mark Smith, Job
   Snijders, Tarko Tikan, and Ole Troan, for providing valuable comments



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   on [I-D.gont-6man-slaac-renum], on which this document is
   based.earlier versions of this document.

   Fernando would like to thank Alejandro D'Egidio and Sander Steffann
   for a discussion of these issues.  Fernando would also like to thank
   Brian Carpenter who, over the years, has answered many questions and
   provided valuable comments that has benefited his protocol-related
   work.

6.  References

6.1.  Normative References

   [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>.

   [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>.

6.2.  Informative References

   [I-D.gont-6man-slaac-renum]
              Gont, F., Zorz, J., and R. Patterson, "Improving the
              Robustness of Stateless Address Autoconfiguration (SLAAC)
              to Flash Renumbering Events", draft-gont-6man-slaac-
              renum-02 (work in progress), February 2020.

   [I-D.gont-v6ops-slaac-renum]
              Gont, F., Zorz, J., and R. Patterson, "Reaction of
              Stateless Address Autoconfiguration (SLAAC) to Flash-
              Renumbering Events", draft-gont-v6ops-slaac-renum-02 (work
              in progress), February 2020.

   [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>.




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Authors' Addresses

   Fernando Gont
   SI6 Networks
   Segurola y Habana 4310, 7mo Piso
   Villa Devoto, Ciudad Autonoma de Buenos Aires
   Argentina

   Email: fgont@si6networks.com
   URI:   https://www.si6networks.com


   Jan Zorz
   Go6 Institute
   Frankovo naselje 165
   Skofja Loka  4220
   Slovenia

   Email: jan@go6.si
   URI:   https://www.go6.si


   Richard Patterson
   Sky UK

   Email: richard.patterson@sky.uk

























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