Improving the Robustness of Stateless Address Autoconfiguration (SLAAC) to Flash Renumbering Events
draft-ietf-6man-slaac-renum-07

IPv6 Maintenance (6man) Working Group                            F. Gont
Internet-Draft                                              SI6 Networks
Updates: 4191, 4861, 4862, 8106 (if approved)                    J. Zorz
Intended status: Standards Track                                6connect
Expires: 3 November 2023                                    R. Patterson
                                                                  Sky UK
                                                              2 May 2023

Improving the Robustness of Stateless Address Autoconfiguration (SLAAC)
                      to Flash Renumbering Events
                     draft-ietf-6man-slaac-renum-07

Abstract

   In renumbering scenarios where an IPv6 prefix suddenly becomes
   invalid, hosts on the local network will continue using stale
   prefixes for an unacceptably long period of time, thus resulting in
   connectivity problems.  This document improves the reaction of IPv6
   Stateless Address Autoconfiguration to such renumbering scenarios.
   It formally updates RFC 4191, RFC 4861, RFC 4862, and RFC 8106.

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
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   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 3 November 2023.

Copyright Notice

   Copyright (c) 2023 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 (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

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   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.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  SLAAC reaction to Flash-renumbering Events  . . . . . . . . .   3
     3.1.  Renumbering without Explicit Signaling  . . . . . . . . .   3
     3.2.  Renumbering with Explicit Signaling . . . . . . . . . . .   4
   4.  Improvements to Stateless Address Autoconfiguration
           (SLAAC) . . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  More Appropriate Neighbor Discovery Option Lifetimes  . .   6
     4.2.  Honor Small PIO Valid Lifetimes . . . . . . . . . . . . .   7
     4.3.  Interface Initialization  . . . . . . . . . . . . . . . .   8
     4.4.  Conveying Information in Router Advertisement (RA)
           Messages  . . . . . . . . . . . . . . . . . . . . . . . .   9
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   6.  Implementation Status . . . . . . . . . . . . . . . . . . . .  10
     6.1.  More Appropriate Lifetime Values  . . . . . . . . . . . .  10
       6.1.1.  Router Configuration Variables  . . . . . . . . . . .  10
     6.2.  Honor Small PIO Valid Lifetimes . . . . . . . . . . . . .  11
       6.2.1.  Linux Kernel  . . . . . . . . . . . . . . . . . . . .  11
       6.2.2.  NetworkManager  . . . . . . . . . . . . . . . . . . .  11
     6.3.  Conveying Information in Router Advertisement (RA)
           Messages  . . . . . . . . . . . . . . . . . . . . . . . .  11
     6.4.  Recovery from Stale Configuration Information without
           Explicit Signaling  . . . . . . . . . . . . . . . . . . .  11
       6.4.1.  dhcpcd(8) . . . . . . . . . . . . . . . . . . . . . .  11
     6.5.  Other mitigations implemented in products . . . . . . . .  11
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  12
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   In scenarios where network configuration information becomes invalid
   without any explicit signaling of that condition, hosts on the local
   network will continue using stale information for an unacceptably
   long period of time, thus resulting in connectivity problems.  This
   problem has been discussed in detail in [RFC8978].

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   This document updates the Neighbor Discovery specification [RFC4861],
   the Stateless Address Autoconfiguration (SLAAC) specification
   [RFC4862], and other associated specifications ([RFC4191] and
   [RFC8106]), such that hosts can more gracefully deal with the so-
   called flash renumbering events, thus improving the robustness of
   SLAAC.

2.  Terminology

   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.  SLAAC reaction to Flash-renumbering Events

   In some scenarios, the local router triggering the network
   renumbering event may try to deprecate the stale information (by
   explicitly signaling the network about the renumbering event),
   whereas in other scenarios the renumbering event may happen
   inadvertently, without the router explicitly signaling the scenario
   to local hosts.  The following subsections analyze specific
   considerations for each of these scenarios.

3.1.  Renumbering without Explicit Signaling

   In the absence of explicit signalling from SLAAC routers (such as
   sending Prefix Information Options (PIOs) with small lifetimes to
   deprecate stale prefixes), stale prefixes will remain preferred and
   valid according to the Preferred Lifetime and Valid Lifetime
   parameters (respectively) of the last received PIO.  [RFC4861]
   specifies the following default values for PIOs:

   *  Preferred Lifetime (AdvPreferredLifetime): 604800 seconds (7 days)

   *  Valid Lifetime (AdvValidLifetime): 2592000 seconds (30 days)

   This means that, in the absence of explicit signaling by a SLAAC
   router to deprecate a prefix, it will take a host 7 days (one week)
   to deprecate the corresponding addresses, and 30 days (one month) to
   eventually remove any addresses configured for the stale prefix.
   Clearly, employing such long default values is unacceptable for most
   deployment scenarios that may experience flash-renumbering events.

   NOTE:
      [RFC8978] provides an operational recommendation for Customer Edge
      (CE) routers to override the standard default Preferred Lifetime

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      (AdvPreferredLifetime) and Valid Lifetime (AdvValidLifetime) to
      2700 seconds (45 minutes) and 5400 seconds (90 minutes),
      respectively, thus improving the state of affairs for CE router
      scenarios.

   Similarly, other Neighbor Discovery options employ unnecessarily long
   default lifetimes that are unacceptable for most deployment scenarios
   that may experience flash-renumbering events.

   Use of more appropriate timers in Router Advertisement messages can
   help limit the amount of time that hosts will maintain stale
   configuration information.  Thus, Section 4.1 formally specifies the
   use of more appropriate (i.e., shorter) default lifetimes for
   Neighbor Discovery options.

3.2.  Renumbering with Explicit Signaling

   In scenarios where a local router is aware about the renumbering
   event, it may try to phase out the stale network configuration
   information.  In these scenarios, there are two aspects to be
   considered:

   *  The amount of time during which the router should continue trying
      to deprecate the stale network configuration information.

   *  The ability of SLAAC hosts to phase out stale configuration.

   Since the network could be become partitioned at any arbitrary time
   and for an arbitrarily long period of time, routers need to
   contemplate the possible scenario where hosts receive an RA message,
   and the network subsequently becomes partitioned.  This means that in
   order to reliably deprecate stale information, a router would should
   try to deprecate such information for a period of time equal to the
   associated Neighbor Discovery option lifetime used when the
   information was advertised.

   NOTE:
      For example, it should try to deprecate a prefix (via a PIO) for a
      period of time equal to the "Preferred Lifetime" used when
      advertising the prefix, and try to invalidate the prefix for a
      period of time equal to the "Valid Lifetime" (see Section 12 of
      [RFC4861]) used when advertising the prefix.

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      Once the number of seconds in the original "Preferred Lifetime"
      have elapsed, all hosts will have deprecated the corresponding
      addresses, while once the number of seconds in the "Valid
      Lifetime" have elapsed, the corresponding addresses will be
      invalidated and removed.

   Thus, use of more appropriate default lifetimes for Neighor Discovery
   options, as specified in Section 4.1, would reduce the amount of time
   stale options would need to be advertised by a router to ensure that
   the associated information is phased out.

   In the case of Prefix Information Options (PIOs), in scenarios where
   a router has positive knowledge that a prefix has become invalid (and
   thus could signal this condition to local hosts), the current
   specifications will prevent SLAAC hosts from fully recovering from
   such stale information: Item "e)" of Section 5.5.3 of [RFC4862]
   specifies that an RA may never reduce the "RemainingLifetime" to less
   than two hours.  Additionally, if the RemainingLifetime of an address
   is smaller than 2 hours, then a Valid Lifetime smaller than 2 hours
   will be ignored.  The inability to invalidate a stale prefix may
   prevent communications with the new "owners" of a prefix, and thus is
   highly undesirable.  However, the Preferred Lifetime of an address
   *may* be reduced to any value to avoid the use of a stale prefix for
   new communications.

   Section 4.2 formally updates [RFC4862] to remove this restriction,
   such that hosts may react to the advertised "Valid Lifetime" even if
   it is smaller than 2 hours.  Section 4.3 recommends that routers
   disseminate network configuration information when a network
   interface is initialized, such that new configuration information
   propagates in a timelier manner.

4.  Improvements to Stateless Address Autoconfiguration (SLAAC)

   The following subsections update [RFC4861] and [RFC4862], such that
   the problem discussed in this document is mitigated.  The updates in
   the following subsections are mostly orthogonal, and mitigate
   different aspects of SLAAC that prevent a timely reaction to flash
   renumbering events:

   *  Reduce the default Valid Lifetime and Preferred Lifetime of PIOs
      (Section 4.1):

      This helps limit the amount of time a host may employ stale
      information, and also limits the amount of time a router needs to
      try to deprecate stale information.

   *  Honor PIOs with small Valid Lifetimes (Section 4.2):

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      This allows routers to invalidate stale prefixes, since otherwise
      [RFC4861] would prevent hosts from honoring PIOs with a Valid
      Lifetime smaller than two hours.

   *  Recommend routers to retransmit configuration information upon
      interface initialization/reinitialization (Section 4.3):

      This helps spread the new information in a timelier manner.

   *  Recommend routers to always send all options (i.e. the complete
      configuration information) in RA messages, and in the smallest
      possible number of packets (Section 4.4):

      This helps propagate the same information to all hosts.

4.1.  More Appropriate Neighbor Discovery Option Lifetimes

   This document defines the following variables to be employed for the
   default lifetimes of Neighbor Discovery options:

   *  ND_DEFAULT_PREFERRED_LIFETIME: max(AdvDefaultLifetime, 3 *
      MaxRtrAdvInterval)

   *  ND_DEFAULT_VALID_LIFETIME: 2 * ND_DEFAULT_PREFERRED_LIFETIME

   where:

   AdvDefaultLifetime:
      Router configuration variable specified in [RFC4861], which
      specifies the value to be placed in the Router Lifetime field of
      Router Advertisements sent from the interface, in seconds.

   MaxRtrAdvInterval:
      Router configuration variable specified in [RFC4861], which
      specifies the maximum time allowed between sending unsolicited
      multicast Router Advertisements from the interface, in seconds.

   max():
      A function that computes the maximum of its arguments.

   NOTE:
      The expression above computes of maximum among AdvDefaultLifetime
      and "3 * MaxRtrAdvInterval" (the default value of
      AdvDefaultLifetime, as per [RFC4861]) to accommodate the case
      where an operator might simply want to disable one local router
      for maintenance, while still having the router advertise SLAAC
      configuration information.

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      [RFC4861] specifies the default value of MaxRtrAdvInterval as 600
      seconds, and the default value of AdvDefaultLifetime as 3 *
      MaxRtrAdvInterval.  Therefore, when employing default values for
      MaxRtrAdvInterval and AdvDefaultLifetime, the default values of
      ND_DEFAULT_PREFERRED_LIFETIME and ND_DEFAULT_VALID_LIFETIME become
      1800 seconds (30 minutes) and 3600 seconds (1 one hour),
      respectively.  We note that when implementing BCP202 [RFC7772],
      AdvDefaultLifetime will typically be in the range of 45-90
      minutes, and therefore the value of ND_DEFAULT_PREFERRED_LIFETIME
      will be in the range 45-90 minutes, while the value of
      ND_DEFAULT_VALID_LIFETIME will be in the range of 90-180 minutes.

   This document formally updates [RFC4861] to modify the default values
   of the Preferred Lifetime and the Valid Lifetime of PIOs as follows:

   *  AdvPreferredLifetime: ND_DEFAULT_PREFERRED_LIFETIME

   *  AdvValidLifetime: ND_DEFAULT_VALID_LIFETIME

   This document formally updates [RFC4191] to specify the default Route
   Lifetime of Route Information Options (RIOs) as follows:

   *  Route Lifetime: Default: ND_DEFAULT_PREFERRED_LIFETIME

   This document formally updates [RFC8106] to modify the default
   Lifetime of Recursive DNS Server Options as:

   *  Lifetime: Default: ND_DEFAULT_PREFERRED_LIFETIME

   Additionally, this document formally updates [RFC8106] to modify the
   default Lifetime of DNS Search List Options as:

   *  Lifetime: Default: ND_DEFAULT_PREFERRED_LIFETIME

4.2.  Honor Small PIO Valid Lifetimes

   The entire item "e)" (pp. 19-20) from Section 5.5.3 of [RFC4862] is
   replaced with the following text:

      e) If the advertised prefix is equal to the prefix of an address
      configured by stateless autoconfiguration in the list, the valid
      lifetime and the preferred lifetime of the address should be
      updated by processing the Valid Lifetime and the Preferred
      Lifetime (respectively) in the received advertisement.

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   RATIONALE:
      *  This change allows hosts to react to the signal provided by a
         router that has positive knowledge that a prefix has become
         invalid.

      *  The behavior described in [RFC4862] had been incorporated
         during the revision of the original IPv6 Stateless Address
         Autoconfiguration specification ([RFC1971]).  At the time, the
         IPNG working group decided to mitigate the attack vector
         represented by Prefix Information Options with very short
         lifetimes, on the premise that these packets represented a
         bigger risk than other ND-based attack vectors [IPNG-minutes].

         While reconsidering the trade-offs represented by such
         decision, we conclude that the drawbacks of the aforementioned
         mitigation outweigh the possible benefits.

         In scenarios where RA-based attacks are of concern, proper
         mitigations such as RA-Guard [RFC6105] [RFC7113] or SEND
         [RFC3971] should be implemented.

4.3.  Interface Initialization

   When an interface is initialized, it is paramount that network
   configuration information is propagated on the corresponding network
   (particularly in scenarios where an interface has been re-
   initialized, and the conveyed information has changed).  Thus, this
   document replaces the following text from Section 6.2.4 of [RFC4861]:

      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.

   with:

      In such cases, the router SHOULD transmit
      MAX_INITIAL_RTR_ADVERTISEMENTS unsolicited advertisements, using
      the same rules as when an interface becomes an advertising
      interface.

   RATIONALE:
      *  Use of stale information can lead to interoperability problems.
         Therefore, it is important that new configuration information
         propagates in a timelier manner to all hosts.

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   NOTE:
      [RFC9096] specifies recommendations for CPE routers to signal any
      stale network configuration information.

4.4.  Conveying Information in Router Advertisement (RA) Messages

   Intentionally omitting information in Router Advertisements may
   prevent the propagation of such information, and may represent a
   challenge for hosts that need to infer whether they have received a
   complete set of SLAAC configuration information.  As a result, this
   section recommends that, to the extent that is possible, RA messages
   contain a complete set of SLAAC information.

   This document replaces the following text from Section 6.2.3 of
   [RFC4861]:

      A router MAY choose not to include some or all options when
      sending unsolicited Router Advertisements.  For example, if prefix
      lifetimes are much longer than AdvDefaultLifetime, including them
      every few advertisements may be sufficient.  However, when
      responding to a Router Solicitation or while sending the first few
      initial unsolicited advertisements, a router SHOULD include all
      options so that all information (e.g., prefixes) is propagated
      quickly during system initialization.

      If including all options causes the size of an advertisement to
      exceed the link MTU, multiple advertisements can be sent, each
      containing a subset of the options.

   with:

      When sending Router Advertisements, a router SHOULD include all
      options.

      If including all options would cause the size of an advertisement
      to exceed the link MTU, multiple advertisements can be sent, each
      containing a subset of the options.  In all cases, routers SHOULD
      convey all information using the smallest possible number of
      packets, and SHOULD convey options of the same type in the same
      packet to the extent possible.

   RATIONALE:
      *  Sending information in the smallest possible number of packets
         was somewhat already implied by the original text in [RFC4861].
         Including all options when sending RAs leads to simpler code
         (as opposed to dealing with special cases where specific
         information is intentionally omitted), and also helps hosts
         infer when they have received a complete set of SLAAC

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         configuration information.  Note that while [RFC4861] allowed
         some RAs to omit some options, to the best of the authors'
         knowledge, all SLAAC router implementations always send all
         options in the smallest possible number of packets.  Therefore,
         this section simply aligns the protocol specifications with
         existing implementation practice.

5.  IANA Considerations

   This document has no actions for IANA.

6.  Implementation Status

   [NOTE: This section is to be removed by the RFC-Editor before this
   document is published as an RFC.]

   This section summarizes the implementation status of the updates
   proposed in this document.  In some cases, they correspond to
   variants of the mitigations proposed in this document (e.g., use of
   reduced default lifetimes for PIOs, albeit using different values
   than those recommended in this document).  In such cases, we believe
   these implementations signal the intent to deal with the problems
   described in [RFC8978] while lacking any guidance on the best
   possible approach to do it.

6.1.  More Appropriate Lifetime Values

6.1.1.  Router Configuration Variables

6.1.1.1.  rad(8)

   We have produced a patch for OpenBSD's rad(8) [rad] that employs the
   default lifetimes recommended in this document, albeit it has not yet
   been committed to the tree.  The patch is available at:
   <https://www.gont.com.ar/code/fgont-patch-rad-pio-lifetimes.txt>.

6.1.1.2.  radvd(8)

   The radvd(8) daemon [radvd], normally employed by Linux-based router
   implementations, currently employs different default lifetimes than
   those recommended in [RFC4861]. radvd(8) employs the following
   default values [radvd.conf]:

   *  Preferred Lifetime: 14400 seconds (4 hours)

   *  Valid Lifetime: 86400 seconds (1 day)

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   This is not following the specific recommendation in this document,
   but is already a deviation from the current standards.

6.2.  Honor Small PIO Valid Lifetimes

6.2.1.  Linux Kernel

   A Linux kernel implementation of this document has been committed to
   the net-next tree.  The implementation was produced in April 2020 by
   Fernando Gont <fgont@si6networks.com>.  The corresponding patch can
   be found at: <https://patchwork.ozlabs.org/project/netdev/
   patch/20200419122457.GA971@archlinux-current.localdomain/>

6.2.2.  NetworkManager

   NetworkManager [NetworkManager] processes RA messages with a Valid
   Lifetime smaller than two hours as recommended in this document.

6.3.  Conveying Information in Router Advertisement (RA) Messages

   We know of no implementation that splits network configuration
   information into multiple RA messages.

6.4.  Recovery from Stale Configuration Information without Explicit
      Signaling

6.4.1.  dhcpcd(8)

   The dhcpcd(8) daemon [dhcpcd], a user-space SLAAC implementation
   employed by some Linux-based and BSD-derived operating systems, will
   set the Preferred Lifetime of addresses corresponding to a given
   prefix to 0 when a single RA from the router that previously
   advertised the prefix fails to advertise the corresponding prefix.
   However, it does not affect the corresponding Valid Lifetime.
   Therefore, it can be considered a partial implementation of this
   feature.

6.5.  Other mitigations implemented in products

   [FRITZ] is a Customer Edge Router that tries to deprecate stale
   prefixes by advertising stale prefixes with a Preferred Lifetime of
   0, and a Valid Lifetime of 2 hours (or less).  There are two things
   to note with respect to this implementation:

   *  Rather than recording prefixes on stable storage (as recommended
      in [RFC9096]), this implementation checks the source address of
      IPv6 packets, and assumes that usage of any address that does not
      correspond to a prefix currently-advertised by the Customer Edge

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      Router is the result of stale network configuration information.
      Hence, upon receipt of a packet that employs a source address that
      does not correspond to a currently-advertised prefix, this
      implementation will start advertising the corresponding prefix
      with small lifetimes, with the intent of deprecating it.

   *  Possibly as a result of item "e)" (pp. 19-20) from Section 5.5.3
      of [RFC4862] (discussed in Section 4.2 of this document), upon
      first occurrence of a stale prefix, this implementation will
      employ a decreasing Valid Lifetime, starting from 2 hours (7200
      seconds), as opposed to a Valid Lifetime of 0.

7.  Security Considerations

   The protocol update in Section 4.2 could allow an on-link attacker to
   perform a Denial of Service attack against local hosts, by sending a
   forged RA with a PIO with a Valid Lifetime of 0.  Upon receipt of
   that packet, local hosts would invalidate the corresponding prefix,
   and therefore remove any addresses configured for that prefix,
   possibly terminating e.g. associated TCP connections.  However, an
   attacker may achieve similar effects via a number other Neighbor
   Discovery (ND) attack vectors, such as directing traffic to a non-
   existing node until ongoing TCP connections time out, or performing a
   ND-based man-in-the-middle (MITM) attack and subsequently forging TCP
   RST segments to cause on-going TCP connections to be reset.  Thus,
   for all practical purposes, this attack vector does not really
   represent any greater risk than other ND attack vectors.  As noted in
   Section 4.2 , in scenarios where RA-based attacks are of concern,
   proper mitigations such as RA-Guard [RFC6105] [RFC7113] or SEND
   [RFC3971] should be implemented.

8.  Acknowledgments

   The authors would like to thank (in alphabetical order) Mikael
   Abrahamsson, Tore Anderson, Luis Balbinot, Brian Carpenter, Lorenzo
   Colitti, Owen DeLong, Gert Doering, Thomas Haller, Nick Hilliard, Bob
   Hinden, Philip Homburg, Lee Howard, Christian Huitema, Tatuya Jinmei,
   Erik Kline, Ted Lemon, Jen Linkova, Albert Manfredi, Roy Marples,
   Florian Obser, Jordi Palet Martinez, Michael Richardson, Hiroki Sato,
   Mark Smith, Hannes Frederic Sowa, Dave Thaler, Tarko Tikan, Ole
   Troan, Eduard Vasilenko, and Loganaden Velvindron, for providing
   valuable comments on earlier versions of this document.

   Fernando would like to thank Alejandro D'Egidio and Sander Steffann
   for a discussion of these issues, which led to the publication of
   [RFC8978], and eventually to this document.

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   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.

9.  References

9.1.  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>.

   [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>.

   [RFC7772]  Yourtchenko, A. and L. Colitti, "Reducing Energy
              Consumption of Router Advertisements", BCP 202, RFC 7772,
              DOI 10.17487/RFC7772, February 2016,
              <https://www.rfc-editor.org/info/rfc7772>.

   [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>.

9.2.  Informative References

   [dhcpcd]   Marples, R., "dhcpcd - a DHCP client",
              <https://roy.marples.name/projects/dhcpcd/>.

   [FRITZ]    Gont, F., "Quiz: Weird IPv6 Traffic on the Local Network
              (updated with solution)", SI6 Networks Blog, February
              2016, <https://www.si6networks.com/2016/02/16/quiz-weird-
              ipv6-traffic-on-the-local-network-updated-with-solution/>.

   [IPNG-minutes]
              IETF, "IPNG working group (ipngwg) Meeting Minutes",
              Proceedings of the thirty-eightt Internet Engineering Task
              Force , April 1997, <https://www.ietf.org/
              proceedings/38/97apr-final/xrtftr47.htm>.

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   [NetworkManager]
              NetworkManager, "NetworkManager web site",
              <https://wiki.gnome.org/Projects/NetworkManager>.

   [rad]      Obser, F., "OpenBSD Router Advertisement Daemon - rad(8)",
              <https://cvsweb.openbsd.org/src/usr.sbin/rad/>.

   [radvd]    Hawkins, R. and R. Johnson, "Linux IPv6 Router
              Advertisement Daemon (radvd)",
              <http://www.litech.org/radvd/>.

   [radvd.conf]
              Hawkins, R. and R. Johnson, "radvd.conf - configuration
              file of the router advertisement daemon",
              <https://github.com/reubenhwk/radvd/blob/master/
              radvd.conf.5.man>.

   [RFC1971]  Thomson, S. and T. Narten, "IPv6 Stateless Address
              Autoconfiguration", RFC 1971, DOI 10.17487/RFC1971, August
              1996, <https://www.rfc-editor.org/info/rfc1971>.

   [RFC3971]  Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
              "SEcure Neighbor Discovery (SEND)", RFC 3971,
              DOI 10.17487/RFC3971, March 2005,
              <https://www.rfc-editor.org/info/rfc3971>.

   [RFC4191]  Draves, R. and D. Thaler, "Default Router Preferences and
              More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191,
              November 2005, <https://www.rfc-editor.org/info/rfc4191>.

   [RFC6105]  Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J.
              Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105,
              DOI 10.17487/RFC6105, February 2011,
              <https://www.rfc-editor.org/info/rfc6105>.

   [RFC7113]  Gont, F., "Implementation Advice for IPv6 Router
              Advertisement Guard (RA-Guard)", RFC 7113,
              DOI 10.17487/RFC7113, February 2014,
              <https://www.rfc-editor.org/info/rfc7113>.

   [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>.

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   [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>.

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
   6connect
   Email: jan@connect.com

   Richard Patterson
   Sky UK
   Email: richard.patterson@sky.uk

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