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IPv6 Operations Working Group (v6ops)                            F. Gont
Internet-Draft                                              SI6 Networks
Intended status: Informational                                   J. Zorz
Expires: May 4, 2020
                                                            R. Patterson
                                                                  Sky UK
                                                        November 1, 2019


 Improving the Reaction of Customer Edge Routers to Renumbering Events
                  draft-gont-v6ops-cpe-slaac-renum-00

Abstract

   In scenarios where network configuration information related to IPv6
   prefixes becomes invalid without any explicit signaling of that
   condition (such as when a CPE 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 May 4, 2020.

Copyright Notice

   Copyright (c) 2019 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 CPE behavior . . . . . . . . . . . . . . . . . . . .   2
     2.1.  Interaction Between DHCPv6-PD and SLAAC . . . . . . . . .   3
     2.2.  Signaling Stale Configuration Information . . . . . . . .   3
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   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 Routers that
   help mitigate the aforementioned problem for residential or small
   office scenarios.

2.  Improved CPE behavior

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

   The updated behaviour is as follows:

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



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

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

2.1.  Interaction Between DHCPv6-PD and SLAAC

   The "Preferred Lifetime" and "Valid Lifetime" of 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 CPE 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
      network segment.

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



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      *  Any prefixes that were previously advertised via SLAAC, but
         that are not currently intended for address configuration, MUST
         be advertised with a PIO option with the "A" bit set to 1 and
         the "Valid Lifetime" and a "Preferred Lifetime" set to 0.

      *  Any prefixes that were previously advertised via SLAAC as "on-
         link", but that are not currently not considered "on-link",
         MUST be advertised with a PIO option with the "L" bit set to 1
         and the "Valid Lifetime" and a "Preferred Lifetime" set to 0.

      *  If both of the previous conditions are met (a prefix was
         previously advertised with both the "A" and "L" bits set, but
         is currently *not* intended for address configuration and is
         *not* considered on-link), the prefix MUST be advertised with a
         PIO option with both the "A" and "L" bits set to 1 and the
         "Valid Lifetime" and a "Preferred Lifetime" set to 0.  That is.
         the advertisements of the previous two steps can be coalesced
         into a single one with both the "A" and "L" bits set.

      *  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.





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5.  Acknowledgments

   The authors would lie to thank (in alphabetical order) Mikael
   Abrahamsson, Luis Balbinot, 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, Tarko Tikan, and
   Ole Troan, for providing valuable comments 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. and J. Zorz, "Reaction of Stateless Address
              Autoconfiguration (SLAAC) to Renumbering Events", draft-
              gont-6man-slaac-renum-01 (work in progress), February
              2019.







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   [I-D.gont-v6ops-slaac-renum]
              Gont, F., Zorz, J., and R. Patterson, "Reaction of
              Stateless Address Autoconfiguration (SLAAC) to Renumbering
              Events", draft-gont-v6ops-slaac-renum-00 (work in
              progress), July 2019.

   [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>.

Authors' Addresses

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

   Phone: +54 11 4650 8472
   Email: fgont@si6networks.com
   URI:   https://www.si6networks.com


   Jan Zorz
   Frankovo n. 165
   Skofja Loka
   Slovenia

   Email: jan@go6.si


   Richard Patterson
   Sky UK

   Email: richard.patterson@sky.uk















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