Triggering Unsolicited Router Advertisements Upon Configuration Changes
draft-link-6man-truce-00

IPv6 Maintenance                                              J. Linkova
Internet-Draft                                                    Google
Updates: 4861 (if approved)                             29 February 2024
Intended status: Standards Track                                        
Expires: 1 September 2024

Triggering Unsolicited Router Advertisements Upon Configuration Changes
                        draft-link-6man-truce-00

Abstract

   IPv6 routers employ Router Advertisements (RAs) to disseminate
   essential network configuration data to hosts.  RAs play a vital role
   in Stateless address autoconfiguration (SLAAC) and providing IPv6
   connectivity.  Timely updates via RAs become paramount as network
   configurations change to prevent service outages.  This document
   modifies RFC4861, recommending immediate propagation of configuration
   information changes by routers.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 1 September 2024.

Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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 carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
   3.  Changes to RFC4861  . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   4
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Router Advertisements (RAs) contain information that IPv6 hosts use
   to configure their networks and establish connectivity.  Examples of
   such information include but are not limited to:

   *  Prefix Information Options ([RFC4861]): Advertise network
      prefixes, allowing hosts to automatically configure IPv6 addresses
      (SLAAC).

   *  Link MTU ([RFC4861]): Informs hosts about the maximum packet size
      supported on the link, preventing fragmentation.

   *  DNS Recursive Server Addresses ([RFC8106]): Provides DNS servers
      for domain name resolution.

   *  NAT64 Prefix ([RFC8781]): Indicates the presence of a NAT64
      translator, enabling communication between IPv6 and IPv4 networks.

   Network configurations can change over time, and these changes must
   be communicated to hosts.  Routers propagate updates either by
   sending unsolicited RAs or by responding with an RA to a host's
   Router Solicitation (RS) message.  While some changes (like adding a
   new prefix or DNS server) can be safely included in the next
   scheduled RA, others require immediate action to prevent service

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   disruptions.  In particular, the removal of a prefix, DNS server, or
   NAT64 service necessitates a timely update to ensure hosts
   discontinue using outdated and non-functional resources.

   A frequent issue arises during network renumbering, when the prefix
   used for SLAAC and/or on-link communication is modified.  If the
   router fails to send an immediate unsolicited RA upon a prefix
   change, hosts might continue selecting source addresses from the
   outdated prefix for up to MaxRtrAdvInterval (65535 seconds,
   [RFC8319]).  Communications using those addresses will fail since the
   old prefix is no longer valid.  Residential networks, where prefixes
   are often delegated to Customer Edge (CE) routers via DHCPv6-PD, are
   particularly susceptible to this issue.

   To ensure timely prefix change notifications, Requirement L-13 of
   [RFC7084] states:

   If the delegated prefix changes, i.e., the current prefix is replaced
   with a new prefix without any overlapping time period, then 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].

   It's important to note that this requirement applies specifically to
   CE routers and addresses prefix changes only.  Section 6.2.4 of
   [RFC4861] says:

   The information contained in Router Advertisements may change through
   actions of system management.  For instance, the lifetime of
   advertised prefixes may change, new prefixes could be added, a router
   could cease to be a router (i.e., switch from being a router to being
   a host), etc.  In such cases, the router MAY transmit up to
   MAX_INITIAL_RTR_ADVERTISEMENTS unsolicited advertisements, using the
   same rules as when an interface becomes an advertising interface.

   Consequently, routers not classified as CE equipment and therefore
   exempt from [RFC7084] are not required to immediately notify hosts
   about network configuration changes.  This can lead to degraded user
   experience and contribute to a negative perception of IPv6
   reliability.

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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.

3.  Changes to RFC4861

   This document makes the following changes to Section 6.2.4 of
   [RFC4861],

   OLD TEXT:

   ===

   The information contained in Router Advertisements may change through
   actions of system management.  For instance, the lifetime of
   advertised prefixes may change, new prefixes could be added, a router
   could cease to be a router (i.e., switch from being a router to being
   a host), etc.  In such cases, the router MAY transmit up to
   MAX_INITIAL_RTR_ADVERTISEMENTS unsolicited advertisements, using the
   same rules as when an interface becomes an advertising interface.

   ===

   NEW TEXT

   ===

   The information contained in Router Advertisements may change through
   actions of system management.  For instance, the lifetime of
   advertised prefixes may change, new prefixes could be added, a router
   could cease to be a router (i.e., switch from being a router to being
   a host), etc.  In such cases, the router SHOULD transmit up to
   MAX_INITIAL_RTR_ADVERTISEMENTS unsolicited advertisements, using the
   same rules as when an interface becomes an advertising interface.

   ===

4.  Security Considerations

   This document does not introduce any security considerations.

5.  Privacy Considerations

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6.  IANA Considerations

   This memo does not introduce any IANA considerations.

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>.

   [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>.

   [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>.

7.2.  Informative References

   [RFC8106]  Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
              "IPv6 Router Advertisement Options for DNS Configuration",
              RFC 8106, DOI 10.17487/RFC8106, March 2017,
              <https://www.rfc-editor.org/info/rfc8106>.

   [RFC8319]  Krishnan, S., Korhonen, J., Chakrabarti, S., Nordmark, E.,
              and A. Yourtchenko, "Support for Adjustable Maximum Router
              Lifetimes per Link", RFC 8319, DOI 10.17487/RFC8319,
              February 2018, <https://www.rfc-editor.org/info/rfc8319>.

   [RFC8781]  Colitti, L. and J. Linkova, "Discovering PREF64 in Router
              Advertisements", RFC 8781, DOI 10.17487/RFC8781, April
              2020, <https://www.rfc-editor.org/info/rfc8781>.

Acknowledgements

   Thanks to Erik Kline for the discussions, the input and all
   contribution.

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Author's Address

   Jen Linkova
   Google
   1 Darling Island Rd
   Pyrmont NSW 2009
   Australia
   Email: furry13@gmail.com, furry@google.com

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