IPv6 Maintenance                                              J. Linkova
Internet-Draft                                                    Google
Updates: 4861, 8028 (if approved)                           3 March 2025
Intended status: Standards Track                                        
Expires: 4 September 2025


 Using Prefix-Specific Link-Local Addresses to Improve SLAAC Robustness
                        draft-link-6man-gulla-01

Abstract

   When an IPv6 prefix assigned to a link changes, hosts may not be
   explicitly notified about the change.  Similarly, in some scenario a
   link attachement for the host may change without the host detecting
   it.  In both cases the host does not receive any signals to trigger
   the network stack configuration refresh, so it may continue to use
   "old" addresses which are not valid for the link.  This leads to
   packet loss and service disruption.  This document proposes a
   mechanism to mitigate this issue.  Routers are advised to send Router
   Advertisements containing distinct Prefix Information Options (PIOs)
   from different link-local addresses.  This, in conjunction with
   RFC6724 (Default Source Address Selection) Rule 5.5 and RFC8028
   (first-hop selection requirements), enables hosts to detect prefix
   changes more rapidly and select the correct source address, thereby
   improving the robustness of SLAAC.

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 4 September 2025.

Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.



Linkova                 Expires 4 September 2025                [Page 1]

Internet-Draft                    gulla                       March 2025


   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
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Benefits of Subnet-Specific Link-Local Addresses in Renumbering
           Scenarios . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Subnet Change Scenarios . . . . . . . . . . . . . . . . .   4
     4.2.  Renumbering with Subnet-Specific Link-Local Addresses . .   6
       4.2.1.  RFC8028 and Default Router Selection  . . . . . . . .   7
     4.3.  Outage Duration During Renumbering Event  . . . . . . . .   8
   5.  Generating Subnet-Specific Link-Local Addresses for Router
           Interfaces  . . . . . . . . . . . . . . . . . . . . . . .   9
     5.1.  Subnet-Specific and Stable Link-Local Addresses . . . . .  10
   6.  Solution Applicability  . . . . . . . . . . . . . . . . . . .  10
   7.  Updates to RFC4861  . . . . . . . . . . . . . . . . . . . . .  11
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   9.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  12
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  12
     11.2.  Informative References . . . . . . . . . . . . . . . . .  13
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  14
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   IPv6 Stateless Address AutoConfugration (SLAAC, [RFC4862] provides
   IPv6 hosts with a mechanism to configure their IPv6 stack based on
   the information (such as an IPv6 prefix and the default router
   address) received from the on-link routers.  If that information
   changes (e.g. a prefix assigned to the link is changed), the routers
   need to explicitly invalidate the outdated information (e.g. by
   sending a Router Advertisement packet which deprecates the old
   prefix).  In the absence of an explicit signal the host would be
   using the outdated information until its lifetime expires.  If the
   host selects a source IPv6 address from a prefix which is not
   assigned to the link anymore, packets might be dropped either due to
   anti-spoofing policies on the routers, or just because the return



Linkova                 Expires 4 September 2025                [Page 2]

Internet-Draft                    gulla                       March 2025


   traffic can not reach the host.  This leads to degraded user
   experience.

   Multiple documents discuss the SLAAC so-called flash renumbering
   problem and proposed various improvements to the host and router
   behaviour (see [RFC9096] and [I-D.ietf-6man-slaac-renum]).

   The problem of selecting "a correct" source address is not unique for
   flash renumbering scenarions.  In multihomed (more specifically,
   multi-prefix multi-router) network, where different prefixes are
   signalled to hosts by different routers, a host need to choose both a
   first-hop router and a source address for a given packet.  Rule 5.5
   of the default source address selection algorithm [RFC6724] instructs
   hosts to prefer a source address from a prefix, advertized by the
   chosen first-hop router.  Additionally, [RFC8028] requires hosts to
   select default routers for each prefix it is assigned an address in.

   As a result, when there are two routers on a link, and each router
   advertizes its own PIO, hosts supporting Rule 5.5 and [RFC8028] would
   be capable of selecting the correct {source address, next-hop} pair,
   and send packets from a source belonging to a given prefix to the
   router which adverized that prefix in RAs.

   If, when the link is renumebered, the old and new prefixes are seen
   as advertized by two different routers, the renumbering scenario
   becomes a specific corner case of a multihoming: the host has
   addresses in multiple prefixes, advertized by different routers, and
   needs to select a correct address (one from a prefix which is
   currently assigned to the link).  Therefore, the mechanisms (Rule 5.5
   of the source address selection and ones proposed by [RFC8028]) can
   be used for both multihoming and flash renumering scenarios.

   To ensure that during the renumbering each prefix is seen as
   advertized by a different first-hop router, this document suggests
   that routers sent Router Advertisements with different Prefix
   Information Options (PIOs) from different link-local addresses.  That
   allows the hosts to select the source address from the prefix
   advertized by the reachable next-hop and recover from a renumbering
   or network segment change events much faster.

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.




Linkova                 Expires 4 September 2025                [Page 3]

Internet-Draft                    gulla                       March 2025


3.  Terminology

   DHCPv6-PD: DHCPv6 Prefix Delegation [RFC8415]; a mechanism to
   delegate IPv6 prefixes to clients.

   Flash renumbering: a network renumbering event, when an old prefix,
   used to address hosts, becomes invalid and is replaced by a new
   prefix (or just removed, without any replacement).  Before the flash
   renumbering only the old prefix provides connectivity, and after the
   flash renumbering only the new one can be used.  In other words,
   there is no period of time when addresses from both prefixes provide
   connectivity.  Examples of flash renumbering include, but are not
   limited to a change of prefix delegated via DHCPv6-PD, or removal of
   one prefix from the router configuration and replacing it with
   another.  See [RFC8978] for more detailed discussion of various
   flash-renumbering scenarios.

   LLA: Link-Local Address, Section 2.5.6 of [RFC4291].

   PIO: Prefix Information Option, [RFC4861].

   RA: Router Advertisement, [RFC4861].

   SLAAC: IPv6 Stateless Address AutoConfugration, [RFC4862].

   SLAAC host: a host which uses SLAAC to configure addresses.

   SLAAC Router: a router which advertizes at least one prefix in a PIO
   with the A flag set to 1, so that prefix can be used for SLAAC.

   VRRPv3: Virtual Router Redundancy Protocol verion 3, [RFC9568].

4.  Benefits of Subnet-Specific Link-Local Addresses in Renumbering
    Scenarios

4.1.  Subnet Change Scenarios

   In various scenarios, an IPv6 subnet assigned to a host's connected
   link can change without explicit notification to the host.  This can
   result in outdated IPv6 address configurations, leading to
   connectivity disruptions and a degraded user experience.










Linkova                 Expires 4 September 2025                [Page 4]

Internet-Draft                    gulla                       March 2025


   One common scenario is flash renumbering, where a host's connected
   link undergoes a change in its assigned prefix.  For example, a
   Customer Premises Equipment (CPE) router might receive a new prefix
   via DHCPv6-PD without deprecating the old prefix.  Consequently,
   hosts may use addresses from both the old and new prefixes until the
   old prefix's lifetime expires.  Flash renumbering scenarios are
   discussed in detail in [RFC8978].

   Another situation arises when a host changes its link attachment.
   Even without changes in prefixes assigned to links, a host may move
   from one link to another without detecting the disconnection.  For
   instance, a host connected to a wired port may experience a VLAN (and
   its corresponding IPv6 subnet) change without detecting it.  This
   often occurs when a switch port is reconfigured to modify the
   assigned VLAN (e.g., manually by an administrator or by an automated
   provisioning system), and the host does not reset its interface
   configuration.  Similarly, if the VLAN is configured via 802.1X or
   MAC-based authentication (e.g., provided by RADIUS), an 802.1X
   reauthentication event can lead to VLAN assignment changes.  Some
   802.1X supplicants do not consistently reset the IPv6 stack when the
   wired interface's 802.1X state changes (e.g., between
   'unauthenticated' and 'authenticated'), potentially causing the host
   to retain IPv6 configurations from the previous VLAN.

   A further example involves a host roaming between wireless access
   points advertising the same SSID but different IPv6 subnets.

   The Detecting Network Attachment (DNA) algorithm [RFC6059] allows
   hosts to determine the validity of their network stack configuration
   after a link attachment change.  However, DNA relies on the
   assumption that the combination of the link-layer address and the
   link-local IPv6 address of a router is unique across links.  This
   assumption often fails to hold.  For example, network administrators
   may configure the same, easily remembered link-local address (e.g.,
   'fe80::1') on router interfaces on different links.  Furthermore,
   some router implementations use the virtual router MAC address to
   generate Modified Extended Unique Identifier (EUI)-64 identifiers for
   VRRPv3 virtual link-local addresses, which violates Section 7.4 of
   [RFC9568].  As a result, all links with the same VRRP ID (and thus
   the same virtual router MAC address) would also share the same
   virtual link-local address.

   In all those scenarios a host might move between IPv6 subnets without
   complete disconnection and without detecting the network change.  As
   a result the following sequence of events may occur, leading to
   broken connectivity:





Linkova                 Expires 4 September 2025                [Page 5]

Internet-Draft                    gulla                       March 2025


   *  The host is connected to a network A, receives an RA from the
      router with a PIO containing pref_a, forms IPv6 addresses from
      that prefix using SLAAC.

   *  The host attachment changes from network A to network B or an IPv6
      prefix configured on the network changes from pref_a to pref_b.
      The host doesn’t detect the network change and doesn’t clear the
      IPv6 stack.

   *  The host receives an RA from the router with a new PIO for pref_b
      and forms new addresses from that prefix.

   *  Now the host has two sets of IPv6 addresses - one from pref_a and
      one from pref_b.  Addresses from pref_a are unusable: even if the
      outgoing packets are not dropped by anti-spoofing filters,the
      return traffic wouldn’t be able to reach the host.  So if the host
      selects an address from pref_a as a source address for outgoing
      communication (as per RFC6724 or by using any other custom
      algorithms), the traffic would be dropped, causing user-visible
      outages.

4.2.  Renumbering with Subnet-Specific Link-Local Addresses

   Rule 5.5 of the Default Source Address Selection ([RFC6724]) requires
   the host to prefer addresses in a prefix advertised by the next-hop.
   It allows the multihomed host to select the source address correctly:
   when two routers advertize different prefixes, the host will be
   sending packets with source address from a given prefix to the router
   the prefix was received from.

   In case of renumbering if both old and new prefixes are advertized by
   the same router (received from a router with the same link-local
   address), then Rule 5.5 doesn't help selecting the correct (working)
   source address.  However, if the prefix change also leads to the
   default router address change, then a host implementing Rule 5.5
   could recover from the renumbering quickly, i.e.:

   *  The host receives a Router Advertisement (RA, [RFC4861]) from the
      router (link-local address LLA_A) with a PIO containing pref_a,
      forms IPv6 addresses from that prefix using SLAAC.

   *  An IPv6 prefix configured on the link changes from pref_a to
      pref_b.  The host does not receive any explicit signal about the
      prefix change and does not clear stale IPv6 configuration from its
      interface.






Linkova                 Expires 4 September 2025                [Page 6]

Internet-Draft                    gulla                       March 2025


   *  The host receives an RA from the router (link-local address LLA_B)
      with a new PIO for pref_b and forms new addresses from that
      prefix.  The host adds the LLA_B to the Default Router List.

   *  The host changes the network attachement or the router interface
      on the link doesn't have the original pref_a confgured (so LLA_A
      is not used by the router anymore).  Neighbor Unreachability
      Detection ([RFC4861]) detects that the next-hop is no longer
      reachable.  As per Section 6.3.6 of [RFC4861], the default router
      LLA_B is now preferred over the unreachable default router LLA_A.

   *  The host is using LLA_B as a next-hop for outgoing traffic, so, as
      per Rule 5.5 of [RFC6724] addresses from the pref_b are selected,
      while addresses from pref_a are not used anymore.

   It should be noted that [RFC6724] does not require all
   implementations to support Rule 5.5, limiting the support to systems
   which track which router advertized which prefix.  However
   [I-D.ietf-6man-rfc6724-update] elevates Rule 5.5 support to MUST for
   all systems.

   The proposed solution can still benefit hosts without Rule 5.5
   support, as they can use DNA to validate their IPv6 address
   configuration after a change in link attachment.

4.2.1.  RFC8028 and Default Router Selection

   [RFC8028] requires that "a host SHOULD select default routers for
   each prefix it is assigned an address in" and that "Routers that have
   advertised the prefix in their Router Advertisement message SHOULD be
   preferred over routers that do not advertise the prefix, regardless
   of Default Router Preference. ".  However it should be noted that as
   per Section 6.3.6 of [RFC4861], the host can still select default
   routers even if the router is not reachable (its Neighbor Cache entry
   is INCOMPLETE).  Selecting such router would be undersirable, as it
   would prevent eliminating unreachable nexthop and defeating the whole
   purpose of per-prefix link-local addresses.  Therefore this document
   updates [RFC8028]

   OLD TEXT:

   =====

   Routers that have advertised the prefix in their Router Advertisement
   message SHOULD be preferred over routers that do not advertise the
   prefix, regardless of Default Router Preference.

   =====



Linkova                 Expires 4 September 2025                [Page 7]

Internet-Draft                    gulla                       March 2025


   NEW TEXT

   =====

   Routers that that are reachable or probably reachable (i.e., in any
   state other than INCOMPLETE) and have advertised the prefix in their
   Router Advertisement message SHOULD be preferred over routers that do
   not advertise the prefix, regardless of Default Router Preference.

   =====

   If the host complies with [RFC8028], including the proposed
   modifications described above, then the proposed mechanism would work
   even better, and would provide fast recovery from a renumbering
   event:

   *  The host selects a default router with link-local address LLA_A
      for pref_a.

   *  The prefix on the link changes from pref_a to pref_b.

   *  When the host receives an RA from LLA_B, containing a PIO for
      pref_b, the host selects another default gateway, LLA_B.

   *  Neighbor Unreachability Detection detects that LLA_A is not
      reachable, and removes it from the neighbor cache table, so the
      host can not use it as a default gateway anymore.  The host
      switches to using LLA_B as a default gateway and, in accordance
      with Rule 5.5, starts using addresses from pref_b.

4.3.  Outage Duration During Renumbering Event

   When the IPv6 subnet changes (either because the given link has been
   renumbered, or because the client has moved to another link), there
   are two factors contributing to the duration of the outage:

   *  Time required for the host to receive new configuration
      information (RAs containing new PIOs).

   *  Time required for the host to deprecate the old configuration
      information.

   Without changes proposed in this document, a host might be using the
   outdated prefix for the duration of the PIO preferred lifetime.  As
   per [RFC4861], the default value for preferred lifetime is 604800
   secs (7 days).  While [I-D.ietf-6man-slaac-renum] proposes to reduce
   that value to 14400 seconds (4 hours), it still much longer than can
   be considered acceptable.



Linkova                 Expires 4 September 2025                [Page 8]

Internet-Draft                    gulla                       March 2025


   The solution proposed in this document allows hosts which implement
   Rule 5.5 of the source address selection ([RFC6724]) to stop using
   the outdated prefix much faster.  The time required for the host to
   detect that the old prefix shouldn't be used for initiating new
   session is the time required for Neighbor Unreachability Detection
   (NUD, [RFC4861]) to remove an unreachable entry for the old link-
   local address of the default router.  The default value would be
   (without taking randomisation factors into account): ReachableTime
   milliseconds (to move from REACHABLE to STALE) +
   DELAY_FIRST_PROBE_TIME + MAX_UNICAST_SOLICIT*RetransTimer = 30
   seconds + 5 second + 3*1 = 38 seconds.

5.  Generating Subnet-Specific Link-Local Addresses for Router
    Interfaces

   Prefix-specific link-local addresses, as described above, allow hosts
   to quickly identify renumbering or changes to the prefixes advertised
   in PIOs, improving SLAAC robustness to renumbering.  Routers
   supporting prefix-specific link-local addresses functionality SHOULD:

   *  Support multiple link-local addresses per interface.

   *  Generate (using [RFC7217] algorithm but with Prefix set to the
      prefix in question) or allowing the administrator to configure a
      dedicated link-local address for each prefix in AdvPrefixList
      ([RFC4861]);

   *  Send a PIO for each prefix in a separate RA, using that dedicated
      link-local address as a source.  When populating fields in each RA
      as per Section 6.2.3 of [RFC4861], AdvPrefixList is treated as
      containing one specific prefix only.  When the AdvPrefixList
      contains multiple prefixes, so multiple RAs need to be sent, the
      router SHOULD minimize the time interval between them.  Doing so
      reduces the energy consumption of battery-powered devices that
      must awaken to receive those RAs.  Ideally, all RAs shall be sent
      together, as a bundle, so MaxRtrAdvInterval and MinRtrAdvInterval
      are applied to the whole bundle.

   *  Remove the prefix-specific link-local address from the interface
      when the corresponding prefix is no longer advertized in a PIO
      sent from that interface.  The router SHOULD also follow
      recommendations from Section 6.2.8 of [RFC4861] to inform hosts of
      this change.

   When interface subnets are configured statically, network
   administrators can also configure link-local addresses statically.
   In some cases, it may be feasible to derive the interface ID directly
   from the global subnet prefix.  For example, if a router has two



Linkova                 Expires 4 September 2025                [Page 9]

Internet-Draft                    gulla                       March 2025


   interfaces configured with the subnets 2001:db8:1:1::/64 and
   2001:db8:2:2::/64, respectively, the link-local addresses
   fe80::2001:db8:1:1 and fe80::2001:db8:2:2 could be configured for
   those interfaces.  It is important to note that this approach assumes
   a single router per link; otherwise, duplicate link-local addresses
   will result.  In deployments employing first-hop redundancy with
   VRRPv3, static link-local interface addresses are not required.
   Instead, the virtual link-local address SHOULD be configured.

   As discussed in Section 6.2.8 of [RFC4861], using multiple link-local
   address for the same router on the same link may prevent hosts from
   processing ICMPv6 redirects sent by the router.  Therefore, if a
   router has prefix-specific link-local addresses enabled on its
   interface, the router needs to select the correct source link-local
   address when sending ICMPv6 redirects on that interface.  In
   particular, if the source address of the invoking packet belongs to a
   prefix advertized in a PIO on that interface, the router MUST use the
   link-local address specific to this prefix as a source address for
   the ICMPv6 redirects.

5.1.  Subnet-Specific and Stable Link-Local Addresses

   In many cases it might be beneficial for a router to have a stable
   link-local address (e.g. if that address is advertized as a DNS
   server, or for management purposes.  Router MAY generate prefix-
   specific link-local addresses in addition to a stable link-local
   address.

   It should be noted that the proposed mechanism assumes that the
   router does not use the modified EUI-64 format for generating
   interface ID.  As per Section 3 of [RFC8064], nodes SHOULD NOT use
   the modified EUI-64 format, and SHOULD use the algorithm defined in
   [RFC7217] instead.

6.  Solution Applicability

   While the proposed solution enables hosts to detect IPv6 subnet
   changes more rapidly, it also has some drawbacks, particularly if the
   router interface has multiple prefixes configured and advertised in
   PIOs:

   *  The router sends an RA for each prefix, increasing the total
      number of RAs sent within MaxRtrAdvInterval by a factor of the
      number of prefixes.  In some topologies, this can significantly
      impact host battery life.






Linkova                 Expires 4 September 2025               [Page 10]

Internet-Draft                    gulla                       March 2025


   *  The solution requires the router to support multiple link-local
      addresses per interface.  While [RFC4861] does not explicitly
      prohibit this (and any router with VRRPv3 enabled needs to support
      multiple link-local addresses), some implementations are known to
      assume that only one link-local address is permitted per
      interface.

   Some deployments (e.g. residential networks where CPEs obtain
   prefixes via DHCPv6-PD, or enterprise networks where hosts can move
   between VLANs) benefit from the proposed solution more than others.
   Therefore the mechanism described in this document is considered
   optional and is not required to be supported by all routers.  If the
   router supports prefix-specific link-local addresses, that
   functionality SHOULD be configurable and MAY be enabled by default
   only on interfaces susceptible to flash renumbering, e.g., if
   AdvPrefixList contains prefixes obtained dynamically from DHCPv6-PD.
   In all other cases, prefix-specific link-local addresses MUST be
   disabled by default and MAY be enabled by the administrator.

7.  Updates to RFC4861

   This document also modifies Section 6.2.8 of [RFC4861]:

   ===

   OLD TEXT:

   ===

   Using the link-local address to uniquely identify routers on the link
   has the benefit that the address a router is known by should not
   change when a site renumbers.

   ===

   NEW TEXT:

   ===

   Using the link-local address to uniquely identify routers on the link
   has the benefit that the address a router is known by should not
   change when a site renumbers and the renumbering event is explicitly
   signalled and properly propagated to all hosts.  However, in case of
   flash renumbering without explicit signalling the router SHOULD be
   able change the link-local address of an interface following
   renumbering events, to help hosts detect prefix changes and update
   their configuration accordingly.




Linkova                 Expires 4 September 2025               [Page 11]

Internet-Draft                    gulla                       March 2025


   ===

8.  Security Considerations

   To be added.

9.  Privacy Considerations

   This document does not introduce any privacy considerations.

10.  IANA Considerations

   This memo does not introduce any requests to IANA.

11.  References

11.1.  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>.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/info/rfc4291>.

   [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>.

   [RFC6724]  Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown,
              "Default Address Selection for Internet Protocol Version 6
              (IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012,
              <https://www.rfc-editor.org/info/rfc6724>.

   [RFC6877]  Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT:
              Combination of Stateful and Stateless Translation",
              RFC 6877, DOI 10.17487/RFC6877, April 2013,
              <https://www.rfc-editor.org/info/rfc6877>.

   [RFC7050]  Savolainen, T., Korhonen, J., and D. Wing, "Discovery of
              the IPv6 Prefix Used for IPv6 Address Synthesis",
              RFC 7050, DOI 10.17487/RFC7050, November 2013,
              <https://www.rfc-editor.org/info/rfc7050>.





Linkova                 Expires 4 September 2025               [Page 12]

Internet-Draft                    gulla                       March 2025


   [RFC7217]  Gont, F., "A Method for Generating Semantically Opaque
              Interface Identifiers with IPv6 Stateless Address
              Autoconfiguration (SLAAC)", RFC 7217,
              DOI 10.17487/RFC7217, April 2014,
              <https://www.rfc-editor.org/info/rfc7217>.

   [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>.

   [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>.

   [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>.

   [RFC8925]  Colitti, L., Linkova, J., Richardson, M., and T.
              Mrugalski, "IPv6-Only Preferred Option for DHCPv4",
              RFC 8925, DOI 10.17487/RFC8925, October 2020,
              <https://www.rfc-editor.org/info/rfc8925>.

   [I-D.ietf-6man-slaac-renum]
              Gont, F., Zorz, J., Patterson, R., and J. Linkova,
              "Improving the Robustness of Stateless Address
              Autoconfiguration (SLAAC) to Flash Renumbering Events",
              Work in Progress, Internet-Draft, draft-ietf-6man-slaac-
              renum-09, 3 March 2025,
              <https://datatracker.ietf.org/api/v1/doc/document/draft-
              ietf-6man-slaac-renum/>.

   [I-D.ietf-6man-rfc6724-update]
              Buraglio, N., Chown, T., and J. Duncan, "Prioritizing
              known-local IPv6 ULAs through address selection policy",
              Work in Progress, Internet-Draft, draft-ietf-6man-rfc6724-
              update-17, 27 January 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-6man-
              rfc6724-update-17>.

11.2.  Informative References



Linkova                 Expires 4 September 2025               [Page 13]

Internet-Draft                    gulla                       March 2025


   [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>.

   [RFC6059]  Krishnan, S. and G. Daley, "Simple Procedures for
              Detecting Network Attachment in IPv6", RFC 6059,
              DOI 10.17487/RFC6059, November 2010,
              <https://www.rfc-editor.org/info/rfc6059>.

   [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>.

   [RFC8064]  Gont, F., Cooper, A., Thaler, D., and W. Liu,
              "Recommendation on Stable IPv6 Interface Identifiers",
              RFC 8064, DOI 10.17487/RFC8064, February 2017,
              <https://www.rfc-editor.org/info/rfc8064>.

   [RFC8978]  Gont, F., Žorž, J., and R. Patterson, "Reaction of IPv6
              Stateless Address Autoconfiguration (SLAAC) to Flash-
              Renumbering Events", RFC 8978, DOI 10.17487/RFC8978, March
              2021, <https://www.rfc-editor.org/info/rfc8978>.

   [RFC9096]  Gont, F., Žorž, J., Patterson, R., and B. Volz, "Improving
              the Reaction of Customer Edge Routers to IPv6 Renumbering
              Events", BCP 234, RFC 9096, DOI 10.17487/RFC9096, August
              2021, <https://www.rfc-editor.org/info/rfc9096>.

   [RFC9568]  Lindem, A. and A. Dogra, "Virtual Router Redundancy
              Protocol (VRRP) Version 3 for IPv4 and IPv6", RFC 9568,
              DOI 10.17487/RFC9568, April 2024,
              <https://www.rfc-editor.org/info/rfc9568>.

Acknowledgements

   Thanks to Dale W.  Carder, Brian Carpenter, Lorenzo Colitti, Fernando
   Gont, Alexandre Petrescu, Mark Smith, Ole Troan, Eduard Vasilenko,
   Eric Vyncke, Tim Winters for the discussions, the input and all
   contribution.

Author's Address








Linkova                 Expires 4 September 2025               [Page 14]

Internet-Draft                    gulla                       March 2025


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













































Linkova                 Expires 4 September 2025               [Page 15]