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 Gont, et al. Expires September 10, 2020 [Page 1] Internet-Draft Reaction to Renumbering Events March 2020 (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: Gont, et al. Expires September 10, 2020 [Page 2] Internet-Draft Reaction to Renumbering Events March 2020 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 Gont, et al. Expires September 10, 2020 [Page 3] Internet-Draft Reaction to Renumbering Events March 2020 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 Gont, et al. Expires September 10, 2020 [Page 4] Internet-Draft Reaction to Renumbering Events March 2020 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, . [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", RFC 4862, DOI 10.17487/RFC4862, September 2007, . [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, . 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, . Gont, et al. Expires September 10, 2020 [Page 5] Internet-Draft Reaction to Renumbering Events March 2020 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 Gont, et al. Expires September 10, 2020 [Page 6]