IGP Unreachable Prefix Announcement
draft-ietf-lsr-igp-ureach-prefix-announce-02

Networking Working Group                                  P. Psenak, Ed.
Internet-Draft                                               C. Filsfils
Intended status: Standards Track                            S. Litkowski
Expires: 24 October 2024                                   Cisco Systems
                                                                D. Voyer
                                                             Bell Canada
                                                              A. Dhamija
                                                                  Arrcus
                                                                S. Hegde
                                                  Juniper Networks, Inc.
                                                         G. Van de Velde
                                                                   Nokia
                                                               G. Mishra
                                                            Verizon Inc.
                                                           22 April 2024

                  IGP Unreachable Prefix Announcement
              draft-ietf-lsr-igp-ureach-prefix-announce-02

Abstract

   In the presence of summarization, there is a need to signal loss of
   reachability to an individual prefix covered by the summary in order
   to enable fast convergence away from paths to the node which owns the
   prefix which is no longer reachable.

   This document describes how to use the existing protocol mechanisms
   in IS-IS and OSPF, together with the two new flags, to advertise such
   prefix reachability loss.

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.

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/.

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   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 24 October 2024.

Copyright Notice

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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Supporting UPA in IS-IS . . . . . . . . . . . . . . . . . . .   3
     2.1.  Advertisement of UPA in IS-IS . . . . . . . . . . . . . .   4
     2.2.  Propagation of UPA in IS-IS . . . . . . . . . . . . . . .   5
   3.  Supporting UPA in OSPF  . . . . . . . . . . . . . . . . . . .   5
     3.1.  Advertisement of UPA in OSPF  . . . . . . . . . . . . . .   6
     3.2.  Propagation of UPA in OSPF  . . . . . . . . . . . . . . .   6
   4.  Generation of the UPA . . . . . . . . . . . . . . . . . . . .   6
   5.  Signaling UPA . . . . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  Signaling UPA in IS-IS  . . . . . . . . . . . . . . . . .   7
     5.2.  Signaling UPA in OSPF . . . . . . . . . . . . . . . . . .   7
       5.2.1.  Signaling UPA in OSPFv2 . . . . . . . . . . . . . . .   8
       5.2.2.  Signaling UPA in OSPFv3 . . . . . . . . . . . . . . .   8
     5.3.  Treatement of the U-Flag and UP-Flag  . . . . . . . . . .   8
   6.  Deployment Considerations for UPA . . . . . . . . . . . . . .   9
   7.  Processing of the UPA . . . . . . . . . . . . . . . . . . . .  10
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
     8.1.  IS-IS Prefix Attribute Flags Sub-TLV  . . . . . . . . . .  10
     8.2.  OSPFv2 and OSPFv3 Prefix Extended TLV Flag Field  . . . .  10
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     11.2.  Informative References . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

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1.  Introduction

   Link-state IGP protocols like IS-IS and OSPF are primarily used to
   distribute routing information between routers belonging to a single
   Autonomous System (AS) and to calculate the reachability for IPv4 or
   IPv6 prefixes advertised by the individual nodes inside the AS.  Each
   node advertises the state of its local adjacencies, connected
   prefixes, capabilities, etc.  The collection of these states from all
   the routers inside the area form a link-state database (LSDB) that
   describes the topology of the area and holds additional state
   information about the prefixes, router capabilities, etc.

   The growth of networks running a link-state routing protocol results
   in the addition of more state which leads to scalability and
   convergence challenges.  The organization of networks into levels/
   areas and IGP domains helps limit the scope of link-state information
   within certain boundaries.  However, the state related to prefix
   reachability often requires propagation across a multi-area/level
   and/or multi-domain IGP network.  Techniques such as summarization
   have been used traditionally to address the scale challenges
   associated with advertising prefix state outside of the local area/
   domain.  However, this results in suppression of the individual
   prefix state that is useful for triggering fast-convergence
   mechanisms outside of the IGPs - e.g., BGP PIC Edge [I-D.ietf-rtgwg-
   bgp-pic].

   This document defines two new flags in IS-IS and OSPF.  These flags,
   together with the existing protocol mechanisms, provide the support
   for the necessary functionality.  The functionality being described
   is called Unreachable Prefix Announcement (UPA).

   Similarly, when an egress router needs to be taken out for
   maintenance, the traffic is drained from the node before taking it
   down.  This is typically achieved by setting OL-bit together with
   using max-metric for all prefixes advertised by the node in IS-IS, or
   by setting max-metric on all-links and prefixes advertised by the
   node in OSPF.  When prefixes from such node are summarized by the
   ABR/ASBR, nodes outside of the area or domain are unaware of such
   prefixes becoming unreachable.  This document proposes protocol
   extensions to carry information about such prefixes in a backward
   compatible manner.

2.  Supporting UPA in IS-IS

   [RFC5305] defines the encoding for advertising IPv4 prefixes using 4
   octets of metric information.  Section 4 specifies:

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   "If a prefix is advertised with a metric larger then MAX_PATH_METRIC
   (0xFE000000, see paragraph 3.0), this prefix MUST NOT be considered
   during the normal SPF computation.  This allows advertisement of a
   prefix for purposes other than building the normal IP routing table.
   "

   Similarly, [RFC5308] defines the encoding for advertising IPv6
   prefixes using 4 octets of metric information.  Section 2 states:

   "...if a prefix is advertised with a metric larger than
   MAX_V6_PATH_METRIC (0xFE000000), this prefix MUST NOT be considered
   during the normal Shortest Path First (SPF) computation.  This will
   allow advertisement of a prefix for purposes other than building the
   normal IPv6 routing table."

   This functionality can be used to advertise a prefix (IPv4 or IPv6)
   in a manner which indicates that reachability has been lost - and to
   do so without requiring all nodes in the network to be upgraded to
   support the functionality.

2.1.  Advertisement of UPA in IS-IS

   Existing nodes in a network that do not suport UPA will not use UPAs
   during the route calculation, but will continue to flood them.  This
   allows flooding of such advertisements to occur without the need to
   upgrade all nodes in a network.

   Recognition of the advertisement as UPA is only required on routers
   which have a use case for this information.  Area Border Routers
   (ABRs), which would be responsible for propagating UPA advertisements
   into other areas would need to recognize such advertisements.

   As per the definitions referenced in the preceding section, any
   prefix advertisement with a metric value greater than 0xFE000000 can
   be used for purposes other than normal routing calculations.  Such an
   advertisement can be interpreted by the receiver as a UPA.

   Optionally, an implementation may use local configuration to limit
   the set of metric values which will be interpreted as UPA.  The only
   restriction is that such values MUST be greater than 0xFE000000.

   UPA in IS-IS is supported for all IS-IS Sub-TLVs Advertising Prefix
   Reachability, e.g., SRv6 Locator [I-D.ietf-lsr-isis-srv6-extensions],
   Extended IP reachability [RFC5305], MT IP Reach [RFC5120], IPv6 IP
   Reach [RFC5308], MT IPv6 IP Reach [RFC5120], IPv4 Algorithm Prefix
   Reachability TLV [I-D.ietf-lsr-ip-flexalgo], and IPv6 Algorithm
   Prefix Reachability TLV [I-D.ietf-lsr-ip-flexalgo]

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2.2.  Propagation of UPA in IS-IS

   IS-IS allows propagation of IP prefixes in both directions between
   level 1 and level 2.  For reachable prefixes this is only done if the
   prefix is reachable in source level - e.g., the prefix needs to be
   reachable in level 1 to be propagated to level 2 and vice verse.
   Such requirement of reachability MUST NOT be applied for UPAs, as
   they are propagating unreachability.

   IS-IS L1/L2 routers may wish to advertise received UPAs into other
   areas (upwards and/or downwards).  When propagating UPAs the original
   metric value MUST be preserved.  The cost to reach the originator of
   the received UPA MUST NOT be considered when readvertising the UPA.

3.  Supporting UPA in OSPF

   [RFC2328] Appendix B defines the following architectural constant for
   OSPF:

   "LSInfinity The metric value indicating that the destination
   described by an LSA is unreachable.  Used in summary-LSAs and AS-
   external-LSAs as an alternative to premature aging (see
   Section 14.1).  It is defined to be the 24-bit binary value of all
   ones: 0xffffff."

   [RFC5340] Appendix B states:

   "Architectural constants for the OSPF protocol are defined in
   Appendix B of OSPFV2."

   indicating that these same constants are applicable to OSPFv3.

   [RFC2328] section 14.1. also describes the usage of LSInfinity as a
   way to indicate loss of prefix reachability:

   "Premature aging can also be used when, for example, one of the
   router's previously advertised external routes is no longer
   reachable.  In this circumstance, the router can flush its AS-
   external-LSA from the routing domain via premature aging.  This
   procedure is preferable to the alternative, which is to originate a
   new LSA for the destination specifying a metric of LSInfinity."

   In addition, NU-bit is defined for OSPFv3 [RFC5340].  Prefixes having
   the NU-bit set in their PrefixOptions field SHOULD NOT be included in
   the routing calculation.

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   UPA in OSPFv2 is supported for OSPFv2 Summary-LSA [RFC2328], AS-
   external-LSAs [RFC2328], NSSA AS-external LSA.[RFC3101], and OSPFv2
   Extended Prefix TLV [I-D.ietf-lsr-ip-flexalgo].

   UPA in OSPFv3 is supported for Inter-Area-Prefix-LSA [RFC5340], AS-
   External-LSA [RFC5340], NSSA-LSA [RFC5340], E-Inter-Area-Prefix-LSA
   [RFC8362], E-AS-External-LSA [RFC8362], E-Type-7-LSA [RFC8362], and
   SRv6 Locator LSA [I-D.ietf-lsr-ospfv3-srv6-extensions].

3.1.  Advertisement of UPA in OSPF

   Using the existing mechanism already defined in the standards, as
   described in previous section, an advertisement of the inter-area or
   external prefix inside OSPF or OSPFv3 LSA that has the age set to
   value lower than MaxAge and metic set to LSInfinity can be
   interpreted by the receiver as a UPA.

   Existing nodes in a network which receive UPA advertisements will
   propagate it following existing standard procedures defined by OSPF.

   OSPF Area Border Routers (ABRs), which would be responsible for
   propagating UPA advertisements into other areas would need to
   recognize such advertisements.

3.2.  Propagation of UPA in OSPF

   Advertising prefix reachability between OSPF areas assumes prefix
   reachability in a source area.  Such requirement of reachability MUST
   not be applied for UPAs, as they are propagating unreachability.

   OSPF ABRs may wish to advertise received UPAs into other connected
   areas.  When doing so, the original LSInfinity metric value in UPA
   MUST be preserved.  The cost to reach the originator of the received
   UPA MUST NOT be considered when readvertising the UPA to connected
   areas.

4.  Generation of the UPA

   UPA MAY be generated by the ABR or ASBR that is performing the
   summarization, when all of the following conditions are met:

      - reachability of a prefix that was reachable earlier was lost

      - a summary address which covers the prefix is being advertised by
      the ABR/ASBR

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   Implementations are free to limit the UPA generation to specific
   prefixes, e.g.  host prefixes, SRv6 locators, or similar.  Such
   filtering is optional and MAY be controlled via configuration.

5.  Signaling UPA

   In IS-IS a prefix can be advertised with metric higher than
   0xFE000000, in OSPF with metric LSInfinity, or in OSPFv3 with NU-bit
   set in PrefixOptions, for various reasons.  Even though in all cases
   the treatment of such metric, or NU-bit, is specified for IS-IS, OSPF
   and OSPFv3, having an explicit way to signal that the prefix was
   advertised in order to signal unreachability is required to
   distinguish it from other cases where the prefix with such metric is
   advertised.

5.1.  Signaling UPA in IS-IS

   Two new bits in the IPv4/IPv6 Extended Reachability Attribute Flags
   [RFC7794] are defined:

      U-Flag: - Unreachable Prefix Flag (Bit TBD).  When set, it
      indicates that the prefix is unreachable due to the unplanned
      reason.

      UP-Flag: - Unreachable Planned Prefix Flag (Bit TBD).  When set,
      it indicates that the prefix is unreachable due to the planned
      reason, e.g., planned maintenance.

   The prefix that is advertised with U-Flag or UP-Flag MUST have the
   metric set to a value larger than 0xFE000000.  If the prefix metric
   is less than or equal 0xFE000000, both of these flags MUST be
   ignored.

5.2.  Signaling UPA in OSPF

   A new Prefix Attributes Sub-TLV has been defined in
   [I-D.chen-lsr-prefix-extended-flags] for advertising additional
   prefix attribute flags in OSPFv2 and OSPFv3.

   Two new bits in Prefix Attributes Sub-TLV are defined:

      U-Flag: - Unreachable Prefix Flag (Bit TBD).  When set, it
      indicates that the prefix is unreachable due to the unplanned
      reason.

      UP-Flag: - Unreachable Planned Prefix Flag (Bit TBD).  When set,
      it indicates that the prefix is unreachable due to the planned
      reason, e.g., planned maintenance.

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5.2.1.  Signaling UPA in OSPFv2

   In OSPFv2 the Prefix Attributes Sub-TLV is a Sub-TLV of the OSPFv2
   Extended Prefix TLV [RFC7684].

   The prefix that is advertised with U-Flag or UP-Flag MUST have the
   metric set to a value LSInfinity.  If the prefix metric is not equal
   to LSInfinity, both of these flags MUST be ignored.  For default
   algorithm 0 prefixes with U-Flag or UP-Flag, it is therefore REQUIRED
   to advertise the unreachable prefix in the base OSPFv2 LSA - e.g.,
   OSPFv2 Summary-LSA [RFC2328], or AS-external-LSAs [RFC2328], or NSSA
   AS-external LSA [RFC3101].

5.2.2.  Signaling UPA in OSPFv3

   In OSPFv3 the Prefix Attribute Flags Sub-TLV is defined as a Sub-TLV
   of the following OSPFv3 TLVs as defined in [RFC8362]:

      Intra-Area Prefix TLV

      Inter-Area Prefix TLV

      External Prefix TLV

   The prefix that is advertised with U-Flag or UP-flag MUST have the
   metric set to a value LSInfinity.  For default algorithm 0 prefixes,
   the LSInfinity MUST be set in the parent TLV.  For IP Algorithm
   Prefixes [I-D.ietf-lsr-ip-flexalgo], the LSInfinity MUST be set in
   OSPFv3 IP Algorithm Prefix Reachability sub-TLV.  If the prefix
   metric is not equal to LSInfinity, both of these flags MUST be
   ignored.

   The prefix that is advertised with U-Flag or UP-Flag MUST have the
   NU-bit set in the PrefixOptions of the parent TLV.  If the NU-bit in
   PrefixOptions of the parent TLV is not set, both of these flags MUST
   be ignored.

5.3.  Treatement of the U-Flag and UP-Flag

   The setting of the U-Flag or the UP-Flag signals that the prefix is
   unreachable.  They constitute the UPA signals.  Treatment of these
   flags on the receiver is optional and the usage of them is outside of
   scope of this document.

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6.  Deployment Considerations for UPA

   The intent of UPA is to provide an event driven signal of the
   transition of a destination from reachable to unreachable.  It is not
   intended to advertise a persistent state.  UPA advertisements SHOULD
   therefore be withdrawn after a modest amount of time, that would
   provides sufficient time for UPA to be flooded network-wide and acted
   upon by receiving nodes, but limits the presence of UPA in the
   network to a short time period.  The time the UPA is kept in the
   network SHOULD also reflect the intended use-case for which the UPA
   was advertised.

   As UPA advertisements in IS-IS are advertised in existing Link State
   PDUs (LSPs) and the unit of flooding in IS-IS is an LSP, it is
   recommended that, when possible, UPAs are advertised in LSPs
   dedicated to this type of advertisement.  This will minimize the
   number of LSPs which need to be updated when UPAs are advertised and
   withdrawn.

   In OSPF and OSPFv3, each inter-area and external prefix is advertised
   in it's own LSA, so the above optimisation does not apply to OSPF.

   It is also recommended that implementations limit the number of UPA
   advertisements which can be originated at a given time.

   UPA is not meant to address an area/domain partition.  When an area
   partitions, while multiple ABRs advertise the same summary, each of
   the ABRs can only reach portion of the summarized prefix.  As a
   result, depending on which ABR the traffic is using to enter a
   partitioned area, the traffic could be dropped or be delivered to its
   final destination.  UPA does not make the problem of an area
   partition any worse.  In case of an area partition each of the ABRs
   will generate UPAs for the destinations for which the reachability
   was lost locally.  As the UPA propagates to the nodes outside of a
   partitioned area, it may result in such nodes picking an alternative
   egress node for the traffic, if such alternate egress node exists.
   If such alternate egress node resides outside of a partitioned area,
   traffic will be restored.  If such alternate egress node resides in a
   partitioned area and is covered by the summary, the trafic will be
   dropped if it enters a partitioned area via the ABR that can not
   reach the alternate egress node - resulting in similar behavior as
   without the UPA.  Above is similarly applicable to a domain
   partition.

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7.  Processing of the UPA

   Processing of the received UPAs is optional and SHOULD be controlled
   by the configuration at the receiver.  The receiver itself, based on
   its configuration, decides what the UPA will be used for and what
   applications, if any, will be notified when UPA is received.

8.  IANA Considerations

8.1.  IS-IS Prefix Attribute Flags Sub-TLV

   This document adds two new bits in the "IS-IS Bit Values for Prefix
   Attribute Flags Sub-TLV" registry:

      Bit #: TBD

      Description: U-Flag

      Reference: This document (Section 5.1).

      Bit #: TDB

      Description: UP-Flag

      Reference: This document (Section 5.1).

8.2.  OSPFv2 and OSPFv3 Prefix Extended TLV Flag Field

   This document adds two new bits in the "OSPFv2 Prefix Extended TLV
   Flag Field" and "OSPFv3 Prefix Extended TLV Flag Field" registres:

      Bit #: TBD

      Description: U-Flag

      Reference: This document (Section 5.2).

      Bit #: TDB

      Description: UP-Flag

      Reference: This document (Section 5.2).

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9.  Security Considerations

   The use of UPAs introduces the possibility that an attacker could
   inject a false, but apparently valid, UPA.  However, the risk of this
   occurring is no greater than the risk today of an attacker injecting
   any other type of false advertisement .

   The risks can be reduced by the use of existing security extensions
   as described in [RFC5304] and [RFC5310] for IS-IS, in [RFC2328][ and
   [RFC7474] for OSPFv2, and in [RFC5340] and [RFC4552] for OSPFv3.

10.  Acknowledgements

   The authors would like to thank Kamran Raza, Michael MacKenzie and
   Luay Jalil for their contribution and support of the overall solution
   proposed in this document.

11.  References

11.1.  Normative References

   [I-D.chen-lsr-prefix-extended-flags]
              Chen, R., Zhao, D., Psenak, P., and K. Talaulikar, "Prefix
              Flag Extension for OSPFv2 and OSPFv3", Work in Progress,
              Internet-Draft, draft-chen-lsr-prefix-extended-flags-03, 5
              November 2023, <https://datatracker.ietf.org/doc/html/
              draft-chen-lsr-prefix-extended-flags-03>.

   [ISO10589] ISO, "Intermediate system to Intermediate system intra-
              domain routeing information exchange protocol for use in
              conjunction with the protocol for providing the
              connectionless-mode Network Service (ISO 8473)", November
              2002.

   [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>.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998,
              <https://www.rfc-editor.org/info/rfc2328>.

   [RFC3101]  Murphy, P., "The OSPF Not-So-Stubby Area (NSSA) Option",
              RFC 3101, DOI 10.17487/RFC3101, January 2003,
              <https://www.rfc-editor.org/info/rfc3101>.

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   [RFC4552]  Gupta, M. and N. Melam, "Authentication/Confidentiality
              for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006,
              <https://www.rfc-editor.org/info/rfc4552>.

   [RFC5120]  Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
              Topology (MT) Routing in Intermediate System to
              Intermediate Systems (IS-ISs)", RFC 5120,
              DOI 10.17487/RFC5120, February 2008,
              <https://www.rfc-editor.org/info/rfc5120>.

   [RFC5304]  Li, T. and R. Atkinson, "IS-IS Cryptographic
              Authentication", RFC 5304, DOI 10.17487/RFC5304, October
              2008, <https://www.rfc-editor.org/info/rfc5304>.

   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, DOI 10.17487/RFC5305, October
              2008, <https://www.rfc-editor.org/info/rfc5305>.

   [RFC5308]  Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
              DOI 10.17487/RFC5308, October 2008,
              <https://www.rfc-editor.org/info/rfc5308>.

   [RFC5310]  Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
              and M. Fanto, "IS-IS Generic Cryptographic
              Authentication", RFC 5310, DOI 10.17487/RFC5310, February
              2009, <https://www.rfc-editor.org/info/rfc5310>.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
              <https://www.rfc-editor.org/info/rfc5340>.

   [RFC7474]  Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed.,
              "Security Extension for OSPFv2 When Using Manual Key
              Management", RFC 7474, DOI 10.17487/RFC7474, April 2015,
              <https://www.rfc-editor.org/info/rfc7474>.

   [RFC7684]  Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
              Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
              Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
              2015, <https://www.rfc-editor.org/info/rfc7684>.

   [RFC7794]  Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and
              U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4
              and IPv6 Reachability", RFC 7794, DOI 10.17487/RFC7794,
              March 2016, <https://www.rfc-editor.org/info/rfc7794>.

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   [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>.

   [RFC8362]  Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
              F. Baker, "OSPFv3 Link State Advertisement (LSA)
              Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
              2018, <https://www.rfc-editor.org/info/rfc8362>.

11.2.  Informative References

   [I-D.ietf-lsr-ip-flexalgo]
              Britto, W., Hegde, S., Kaneriya, P., Shetty, R., Bonica,
              R., and P. Psenak, "IGP Flexible Algorithms (Flex-
              Algorithm) In IP Networks", Work in Progress, Internet-
              Draft, draft-ietf-lsr-ip-flexalgo-17, 24 July 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-lsr-ip-
              flexalgo-17>.

   [I-D.ietf-lsr-isis-srv6-extensions]
              Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
              Z. Hu, "IS-IS Extensions to Support Segment Routing over
              IPv6 Dataplane", Work in Progress, Internet-Draft, draft-
              ietf-lsr-isis-srv6-extensions-19, 14 November 2022,
              <https://datatracker.ietf.org/doc/html/draft-ietf-lsr-
              isis-srv6-extensions-19>.

   [I-D.ietf-lsr-ospfv3-srv6-extensions]
              Li, Z., Hu, Z., Talaulikar, K., and P. Psenak, "OSPFv3
              Extensions for SRv6", Work in Progress, Internet-Draft,
              draft-ietf-lsr-ospfv3-srv6-extensions-15, 21 June 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-lsr-
              ospfv3-srv6-extensions-15>.

Authors' Addresses

   Peter Psenak (editor)
   Cisco Systems
   Pribinova Street 10
   Bratislava 81109
   Slovakia
   Email: ppsenak@cisco.com

   Clarence Filsfils
   Cisco Systems
   Brussels
   Belgium

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   Email: cfilsfil@cisco.com

   Stephane Litkowski
   Cisco Systems
   La Rigourdiere
   Cesson Sevigne
   France
   Email: slitkows@cisco.com

   Daniel Voyer
   Bell Canada
   Email: daniel.voyer@bell.ca

   Amit Dhamija
   Arrcus
   Email: amitd@arrcus.com

   Shraddha Hegde
   Juniper Networks, Inc.
   Embassy Business Park
   Bangalore, KA
   560093
   India
   Email: shraddha@juniper.net

   Gunter Van de Velde
   Nokia
   Antwerp
   Belgium
   Email: gunter.van_de_velde@nokia.com

   Gyan Mishra
   Verizon Inc.
   Email: gyan.s.mishra@verizon.com

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