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Versions: (draft-bashandy-isis-srv6-extensions) 00 01 02 03 04 05 06 07 08 09 10 11 12 Draft is active
In: AD_Evaluation
Networking Working Group                                  P. Psenak, Ed.
Internet-Draft                                               C. Filsfils
Updates: 7370 (if approved)                                Cisco Systems
Intended status: Standards Track                             A. Bashandy
Expires: October 10, 2021                                     Individual
                                                             B. Decraene
                                                                  Orange
                                                                   Z. Hu
                                                     Huawei Technologies
                                                           April 8, 2021


     IS-IS Extension to Support Segment Routing over IPv6 Dataplane
                 draft-ietf-lsr-isis-srv6-extensions-12

Abstract

   The Segment Routing (SR) allows for a flexible definition of end-to-
   end paths by encoding paths as sequences of topological sub-paths,
   called "segments".  Segment routing architecture can be implemented
   over an MPLS data plane as well as an IPv6 data plane.  This document
   describes the IS-IS extensions required to support Segment Routing
   over an IPv6 data plane.

   This documents updates [RFC7370] by modifying an existing registry.

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/.

   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."



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   This Internet-Draft will expire on October 10, 2021.

Copyright Notice

   Copyright (c) 2021 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 and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  SRv6 Capabilities sub-TLV . . . . . . . . . . . . . . . . . .   3
   3.  Advertising Supported Algorithms  . . . . . . . . . . . . . .   4
   4.  Advertising Maximum SRv6 SID Depths . . . . . . . . . . . . .   4
     4.1.  Maximum Segments Left MSD Type  . . . . . . . . . . . . .   5
     4.2.  Maximum End Pop MSD Type  . . . . . . . . . . . . . . . .   5
     4.3.  Maximum H.Encaps MSD Type . . . . . . . . . . . . . . . .   5
     4.4.  Maximum End D MSD Type  . . . . . . . . . . . . . . . . .   5
   5.  SRv6 SIDs and Reachability  . . . . . . . . . . . . . . . . .   6
   6.  Advertising Anycast Property  . . . . . . . . . . . . . . . .   7
   7.  Advertising Locators and End SIDs . . . . . . . . . . . . . .   8
     7.1.  SRv6 Locator TLV Format . . . . . . . . . . . . . . . . .   8
     7.2.  SRv6 End SID sub-TLV  . . . . . . . . . . . . . . . . . .  10
   8.  Advertising SRv6 Adjacency SIDs . . . . . . . . . . . . . . .  11
     8.1.  SRv6 End.X SID sub-TLV  . . . . . . . . . . . . . . . . .  12
     8.2.  SRv6 LAN End.X SID sub-TLV  . . . . . . . . . . . . . . .  13
   9.  SRv6 SID Structure Sub-Sub-TLV  . . . . . . . . . . . . . . .  15
   10. Advertising Endpoint Behaviors  . . . . . . . . . . . . . . .  16
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
     11.1.  SRv6 Locator TLV . . . . . . . . . . . . . . . . . . . .  16
       11.1.1.  SRv6 End SID sub-TLV . . . . . . . . . . . . . . . .  17
       11.1.2.  Revised sub-TLV table  . . . . . . . . . . . . . . .  17
     11.2.  SRv6 Capabilities sub-TLV  . . . . . . . . . . . . . . .  18
     11.3.  SRv6 End.X SID and SRv6 LAN End.X SID sub-TLVs . . . . .  18
     11.4.  MSD Types  . . . . . . . . . . . . . . . . . . . . . . .  19
     11.5.  Sub-Sub-TLVs for SID Sub-TLVs  . . . . . . . . . . . . .  19
     11.6.  Prefix Attribute Flags Sub-TLV . . . . . . . . . . . . .  20
   12. Security Considerations . . . . . . . . . . . . . . . . . . .  20
   13. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  20



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   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  21
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  21
     14.2.  Informative References . . . . . . . . . . . . . . . . .  24
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  24

1.  Introduction

   With Segment Routing (SR) [RFC8402], a node steers a packet through
   an ordered list of instructions, called segments.

   Segments are identified through Segment Identifiers (SIDs).

   Segment Routing can be directly instantiated on the IPv6 data plane
   through the use of the Segment Routing Header defined in [RFC8754].
   SRv6 refers to this SR instantiation on the IPv6 dataplane.

   The network programming paradigm [RFC8986] is central to SRv6.  It
   describes how any behavior can be bound to a SID and how any network
   program can be expressed as a combination of SIDs.

   This document specifies IS-IS extensions that allow the IS-IS
   protocol to encode some of these SIDs and their behaviors.

   Familiarity with the network programming paradigm [RFC8986] is
   necessary to understand the extensions specified in this document.

   The new SRv6 Locator top level TLV announces SRv6 locators - a form
   of summary address for the set of topology/algorithm specific SIDs
   instantiated at the node.

   The SRv6 Capabilities sub-TLV announces the ability to support SRv6.

   Several new sub-TLVs are defined to advertise various SRv6 Maximum
   SID Depths.

   The SRv6 End SID sub-TLV, the SRv6 End.X SID sub-TLV, and the SRv6
   LAN End.X SID sub-TLV are used to advertise which SIDs are
   instantiated at a node and what Endpoint behavior is bound to each
   instantiated SID.

   This documents updates [RFC7370] by modifying an existing registry
   Section 11.1.2.

2.  SRv6 Capabilities sub-TLV

   A node indicates that it supports the SR Segment Endpoint Node
   functionality as specified in [RFC8754] by advertising a new SRv6
   Capabilities sub-TLV of the router capabilities TLV [RFC7981].



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   The SRv6 Capabilities sub-TLV may contain optional sub-sub-TLVs.  No
   sub-sub-TLVs are currently defined.

   The SRv6 Capabilities sub-TLV has the following format:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Type        |     Length    |            Flags              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   optional sub-sub-TLVs...

        Type: 25

        Length: 2 + length of sub-sub-TLVs

        Flags: 2 octets  The following flags are defined:

         0                   1
          0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         | |O|                           |
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         where:

           O-flag: If set, the router supports use of the O-bit
           in the Segment Routing Header (SRH) as defined in
           [I-D.ietf-6man-spring-srv6-oam].


3.  Advertising Supported Algorithms

   An SRv6 capable router indicates supported algorithm(s) by
   advertising the SR Algorithm sub-TLV as defined in [RFC8667].

4.  Advertising Maximum SRv6 SID Depths

   [RFC8491] defines the means to advertise node/link specific values
   for Maximum SID Depths (MSD) of various types.  Node MSDs are
   advertised in a sub-TLV of the Router Capabilities TLV [RFC7981].
   Link MSDs are advertised in a sub-TLV of TLVs 22, 23, 141, 222, and
   223.

   This document defines the relevant SRv6 MSDs and requests MSD type
   assignments in the MSD Types registry created by [RFC8491].





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4.1.  Maximum Segments Left MSD Type

   The Maximum Segments Left MSD Type specifies the maximum value of the
   "Segments Left" field [RFC8754] in the SRH of a received packet
   before applying the Endpoint behavior associated with a SID.

      SRH Max Segments Left Type: 41

      If no value is advertised the supported value is 0.

4.2.  Maximum End Pop MSD Type

   The Maximum End Pop MSD Type signals the maximum number of SIDs in
   the SRH to which the router can apply "Penultimate Segment Pop of the
   SRH" or "Ultimate Segment Pop of the SRH" behavior, as defined in
   [RFC8986] flavors.

      SRH Max End Pop Type: 42

      If the advertised value is zero or no value is advertised
      then the router cannot apply PSP or USP flavors.

4.3.  Maximum H.Encaps MSD Type

   The Maximum H.Encaps MSD Type signals the maximum number of SIDs that
   can be added as part of the "H.Encaps" behavior as defined in
   [RFC8986].

   SRH Max H.encaps Type: 44

   If the advertised value is zero or no value is advertised then the
   headend can apply an SR Policy that only contains one segment, without
   inserting any SRH header.

   A non-zero SRH Max H.encaps MSD indicates that the headend can insert
   an SRH up to the advertised value.


4.4.  Maximum End D MSD Type

   The Maximum End D MSD Type specifies the maximum number of SIDs
   present in an SRH when performing decapsulation.  These includes, but
   not limited to, End.DX6, End.DT4, End.DT46, End with USD, End.X with
   USD as defined in [RFC8986]).







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      SRH Max End D Type: 45

      If the advertised value is zero or no value is advertised
      then the router cannot apply any behavior that results in
      decapsulation and forwarding of the inner packet if the
      other IPv6 header contains an SRH.

5.  SRv6 SIDs and Reachability

   As discussed in [RFC8986], an SRv6 Segment Identifier (SID) is 128
   bits and consists of Locator, Function and Argument parts.

   A node is provisioned with topology/algorithm specific locators for
   each of the topology/algorithm pairs supported by that node.  Each
   locator is a covering prefix for all SIDs provisioned on that node
   which have the matching topology/algorithm.

   Locators MUST be advertised in the SRv6 Locator TLV (see
   Section 7.1).  Forwarding entries for the locators advertised in the
   SRv6 Locator TLV MUST be installed in the forwarding plane of
   receiving SRv6 capable routers when the associated topology/algorithm
   is supported by the receiving node.  The processing of the prefix
   advertised in the SRv6 Locator TLV, the calculation of its
   reachability and the installation in the forwarding plane follows the
   process defined for the Prefix Reachability TLV 236 [RFC5308], or TLV
   237 [RFC5120].

   Locators associated with algorithm 0 and 1 (for all supported
   topologies) SHOULD be advertised in a Prefix Reachability TLV (236 or
   237) so that legacy routers (i.e., routers which do NOT support SRv6)
   will install a forwarding entry for algorithm 0 and 1 SRv6 traffic.

   In cases where a locator advertisement is received in both a Prefix
   Reachability TLV and an SRv6 Locator TLV - (e.g. prefix, prefix-
   length, MTID all being equal and Algorithm being 0 in Locator TLV),
   the Prefix Reachability advertisement MUST be preferred when
   installing entries in the forwarding plane.  This is to prevent
   inconsistent forwarding entries between SRv6 capable and SRv6
   incapable routers.  Such preference of Prefix Reachability
   advertisement does not have any impact on the rest of the data
   advertised in the SRv6 Locator TLV.

   Locators associated with Flexible Algorithms (see Section 4 of
   [I-D.ietf-lsr-flex-algo]) SHOULD NOT be advertised in Prefix
   Reachability TLVs (236 or 237).  Advertising the Flexible Algorithm
   locator in regular Prefix Reachability TLV (236 or 237) would make
   the forwarding for it to follow algo 0 path.




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   SRv6 SIDs are advertised as sub-TLVs in the SRv6 Locator TLV except
   for SRv6 SIDs which are associated with a specific Neighbor/Link and
   are therefore advertised as sub-TLVs in TLVs 22, 23, 222, 223, and
   141.

   SRv6 SIDs received from other nodes are not directly routable and
   MUST NOT be installed in the forwarding plane.  Reachability to SRv6
   SIDs depends upon the existence of a covering locator.

   Adherence to the rules defined in this section will assure that SRv6
   SIDs associated with a supported topology/algorithm pair will be
   forwarded correctly, while SRv6 SIDs associated with an unsupported
   topology/algorithm pair will be dropped.  NOTE: The drop behavior
   depends on the absence of a default/summary route covering a given
   locator.

   In order for forwarding to work correctly, the locator associated
   with SRv6 SID advertisements must be the longest match prefix
   installed in the forwarding plane for those SIDs.  In order to ensure
   correct forwarding, network operators should take steps to make sure
   that this requirement is not compromised.  For example, the following
   situations should be avoided:

   o  Another locator associated with a different topology/algorithm is
      the longest match

   o  Another prefix advertisement (i.e., from TLV 236 or 237) is the
      longest match

6.  Advertising Anycast Property

   Both prefixes and SRv6 Locators may be configured as anycast and as
   such the same value can be advertised by multiple routers.  It is
   useful for other routers to know that the advertisement is for an
   anycast identifier.

   A new flag in Prefix Attribute Flags Sub-TLV [RFC7794] is defined to
   advertise the anycast property:

       Bit #: 4
       Name: Anycast Flag (A-flag)

       When the prefix/SRv6 locator is configured as anycast, the A-flag
       SHOULD be set. Otherwise, this flag MUST be clear.


   The A-flag MUST be preserved when the advertisement is leaked between
   levels.



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   The A-flag and the N-flag MUST NOT both be set.  If both N-flag and
   A-flag are set in the prefix/SRv6 Locator advertisement, the
   receiving routers MUST ignore the N-flag.

   The same prefix/SRv6 Locator can be advertised by multiple routers.
   If at least one of them sets the A-Flag in its advertisement, the
   prefix/SRv6 Locator SHOULD be considered as anycast.

   A prefix/SRv6 Locator that is advertised by a single node and without
   an A-Flag is considered node specific.

   All the nodes advertising the same anycast locator MUST instantiate
   the exact same set of SIDs under such anycast locator.  Failure to do
   so may result in traffic being black-holed or mis-routed.

   The Prefix Attribute Flags Sub-TLV can be carried in the SRv6 Locator
   TLV as well as the Prefix Reachability TLVs.  When a router
   originates both the Prefix Reachability TLV and the SRv6 Locator TLV
   for a given prefix, and the router is originating the Prefix
   Attribute Flags Sub-TLV in one of the TLVs, the router SHOULD
   advertise the same flags in the Prefix Attribute Flags Sub-TLV in
   both TLVs.  However, unlike TLVs 236 [RFC5308] and 237 [RFC5120] the
   X-flag in the Prefix Attributes Flags sub-TLV is valid when sent in
   the SRv6 Locator TLV.  The state of the X-flag in the Prefix
   Attributes Flags sub-TLV when included in the Locator TLV MUST match
   the setting of the embedded "X-bit" in any advertisement of the same
   prefix in TLVs 236 [RFC5308] and 237 [RFC5120].  In case of any
   inconsistency between the Prefix Attribute Flags advertised in the
   Locator TLV and in the Prefix Reachability TLV, the ones advertised
   in Prefix Reachability TLV MUST be preferred.

7.  Advertising Locators and End SIDs

   The SRv6 Locator TLV is introduced to advertise SRv6 Locators and End
   SIDs associated with each locator.

   This new TLV shares the sub-TLV space defined for TLVs 135, 235, 236
   and 237.

7.1.  SRv6 Locator TLV Format

   The SRv6 Locator TLV has the following format:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Type        |     Length    |R|R|R|R|    MT ID              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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      Type: 27

        Length: variable.

        R bits: reserved for future use. They MUST be
        set to zero on transmission and MUST be ignored on receipt.

        MT ID: Multitopology Identifier as defined in [RFC5120].
        Note that the value 0 is legal.

   Followed by one or more locator entries of the form:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Metric                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Flags       |  Algorithm    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Loc Size     | Locator (variable)...
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Sub-TLV-len  |         Sub-TLVs (variable) . . .             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


        Metric: 4 octets. As described in [RFC5305].

        Flags: 1 octet. The following flags are defined

          0
          0 1 2 3 4 5 6 7
         +-+-+-+-+-+-+-+-+
         |D|    Reserved |
         +-+-+-+-+-+-+-+-+

         where:
           D bit: Same as described in section 4.1. of [RFC5305].

           The remaining bits are reserved for future use. They MUST be
           set to zero on transmission and MUST be ignored on receipt.

        Algorithm: 1 octet. As defined in [RFC8665].

        Loc-Size: 1 octet. Number of bits in the SRv6 Locator field.
        MUST be from the range (1 - 128). The TLV MUST be ignored if
        the Loc-Size is outside of this range.

        Locator: 1-16 octets. This field encodes the advertised SRv6



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        Locator. The Locator is encoded in the minimal number of
        octets for the given number of bits. Trailing bits MUST be set
        to zero and ignored when received.

        Sub-TLV-length: 1 octet. Number of octets used by sub-TLVs

        Optional sub-TLVs: Sub-TLVs 1, 2, 4, 5, 11, 12 are allowed.
        Any other Sub-TLVs MUST be ignored.


7.2.  SRv6 End SID sub-TLV

   The SRv6 End SID sub-TLV is introduced to advertise SRv6 Segment
   Identifiers (SID) with Endpoint behaviors which do not require a
   particular neighbor in order to be correctly applied.  SRv6 SIDs
   associated with a neighbor are advertised using the sub-TLVs defined
   in Section 8.

   Supported behavior values together with parent TLVs in which they
   area advertised are specified in Section 10 of this document.  Please
   note that not all behaviors defined in [RFC8986] are defined in this
   document, e.g.  END.T is not.

   This new sub-TLV is advertised in the SRv6 Locator TLV defined in the
   previous section.  SRv6 End SIDs inherit the topology/algorithm from
   the parent locator.

   The SRv6 End SID sub-TLV has the following format:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Type       |     Length    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Flags      |       Endpoint Behavior       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | SID (128 bits) . . .                                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | SID (cont . . .)                                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | SID (cont . . .)                                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | SID (cont . . .)                                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |Sub-sub-TLV-len|         Sub-sub-TLVs (variable) . . .         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type: 5.



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      Length: variable.

      Flags: 1 octet.  No flags are currently defined.

      Endpoint Behavior: 2 octets, as defined in [RFC8986].  Supported
      behavior values for this sub-TLV are defined in Section 10 of this
      document.  Unsupported or unrecognized behavior values are ignored
      by the receiver.

      SID: 16 octets.  This field encodes the advertised SRv6 SID.

      Sub-sub-TLV-length: 1 octet.  Number of octets used by sub-sub-
      TLVs.

      Optional Sub-sub-TLVs.

   The SRv6 End SID MUST be a subnet of the associated Locator.  SRv6
   End SIDs which are not a subnet of the associated locator MUST be
   ignored.

   Multiple SRv6 End SIDs MAY be associated with the same locator.  In
   cases where the number of SRv6 End SID sub-TLVs exceeds the capacity
   of a single TLV, multiple Locator TLVs for the same locator MAY be
   advertised.  For a given MTID/Locator the algorithm MUST be the same
   in all TLVs.  If this restriction is not met all TLVs for that MTID/
   Locator MUST be ignored.

8.  Advertising SRv6 Adjacency SIDs

   Certain SRv6 Endpoint behaviors [RFC8986] are associated with a
   particular adjacency.

   This document defines two new sub-TLVs of TLV 22, 23, 222, 223, and
   141 - namely "SRv6 End.X SID sub-TLVs" and "SRv6 LAN End.X SID sub-
   TLVs".

   IS-IS Neighbor advertisements are topology specific - but not
   algorithm specific.  SIDs advertised in SRv6 End.X SID and SRv6 LAN
   End.X SID sub-TLVs therefore inherit the topology from the associated
   neighbor advertisement, but the algorithm is specified in the
   individual SID.

   All SIDs advertised in SRv6 End.X SID and SRv6 LAN End.X SID sub-TLVs
   MUST be a subnet of a Locator with matching topology and algorithm
   which is advertised by the same node in an SRv6 Locator TLV.  SIDs
   that do not meet this requirement MUST be ignored.  This ensures that
   the node advertising these SIDs is also advertising its corresponding




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   Locator with the algorithm that will be used for computing paths
   destined to the SID.

8.1.  SRv6 End.X SID sub-TLV

   This sub-TLV is used to advertise an SRv6 SID associated with a point
   to point adjacency.  Multiple SRv6 End.X SID sub-TLVs MAY be
   associated with the same adjacency.

   The SRv6 End.X SID sub-TLV has the following format:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Type        |     Length    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Flags       |   Algorithm   |   Weight      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |        Endpoint Behavior      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | SID (128 bits) . . .                                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | SID (cont . . .)                                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | SID (cont . . .)                                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | SID (cont . . .)                                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |Sub-sub-tlv-len|         Sub-sub-TLVs (variable) . . .         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      Type: 43

      Length: variable.

      Flags: 1 octet.


           0 1 2 3 4 5 6 7
          +-+-+-+-+-+-+-+-+
          |B|S|P|Reserved |
          +-+-+-+-+-+-+-+-+

         where:

         B-Flag: Backup flag.  If set, the SID is eligible for
         protection (e.g., using IPFRR) as described in [RFC8355].



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         S-Flag.  Set flag.  When set, the S-Flag indicates that the SID
         refers to a set of adjacencies (and therefore MAY be assigned
         to other adjacencies as well).

         P-Flag.  Persistent flag.  When set, the P-Flag indicates that
         the SID is persistently allocated, i.e., the SID value remains
         consistent across router restart and/or interface flap.

         Reserved bits: MUST be zero when originated and ignored when
         received.

      Algorithm: 1 octet.  As defined in [RFC8665].

      Weight: 1 octet.  The value represents the weight of the SID for
      the purpose of load balancing.  The use of the weight is defined
      in [RFC8402].

      Endpoint Behavior: 2 octets.  As defined in [RFC8986].  Supported
      behavior values for this sub-TLV are defined in Section 10 of this
      document.  Unsupported or unrecognized behavior values are ignored
      by the receiver.

      SID: 16 octets.  This field encodes the advertised SRv6 SID.

      Sub-sub-TLV-length: 1 octet.  Number of octets used by sub-sub-
      TLVs.

   Note that multiple TLVs for the same neighbor may be required in
   order to advertise all of the SRv6 SIDs associated with that
   neighbor.

8.2.  SRv6 LAN End.X SID sub-TLV

   This sub-TLV is used to advertise an SRv6 SID associated with a LAN
   adjacency.  Since the parent TLV is advertising an adjacency to the
   Designated Intermediate System (DIS) for the LAN, it is necessary to
   include the System ID of the physical neighbor on the LAN with which
   the SRv6 SID is associated.  Given that a large number of neighbors
   may exist on a given LAN a large number of SRv6 LAN END.X SID sub-
   TLVs may be associated with the same LAN.  Note that multiple TLVs
   for the same DIS neighbor may be required in order to advertise all
   of the SRv6 SIDs associated with that neighbor.

   The SRv6 LAN End.X SID sub-TLV has the following format:







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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Type        |     Length    |                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
      |             Neighbor System-ID (ID length octets)             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Flags       |   Algorithm   |   Weight      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       Endpoint Behavior       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | SID (128 bits) . . .                                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | SID (cont . . .)                                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | SID (cont . . .)                                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | SID (cont . . .)                                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |Sub-sub-TLV-len|      sub-sub-TLVs (variable) . . .            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      Type: 44

      Length: variable.

      Neighbor System-ID: IS-IS System-ID of length "ID Length" as
      defined in [ISO10589].

      Flags: 1 octet.


           0 1 2 3 4 5 6 7
          +-+-+-+-+-+-+-+-+
          |B|S|P|Reserved |
          +-+-+-+-+-+-+-+-+


         where B,S, and P flags are as described in Section 8.1.
         Reserved bits MUST be zero when originated and MUST be ignored
         when received.

      Algorithm: 1 octet.  As defined in [RFC8665].

      Weight: 1 octet.  The value represents the weight of the SID for
      the purpose of load balancing.  The use of the weight is defined
      in [RFC8402].



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      Endpoint Behavior: 2 octets.  As defined in [RFC8986].  Supported
      behavior values for this sub-TLV are defined in Section 10 of this
      document.  Unsupported or unrecognized behavior values are ignored
      by the receiver.

      SID: 16 octets.  This field encodes the advertised SRv6 SID.

      Sub-sub-TLV-length: 1 octet.  Number of octets used by sub-sub-
      TLVs.

9.  SRv6 SID Structure Sub-Sub-TLV

   SRv6 SID Structure Sub-Sub-TLV is an optional Sub-Sub-TLV of:

      SRv6 End SID Sub-TLV (Section 7.2)

      SRv6 End.X SID Sub-TLV (Section 8.1)

      SRv6 LAN End.X SID Sub-TLV (Section 8.2)

   SRv6 SID Structure Sub-Sub-TLV is used to advertise the as defined in
   [RFC8986].  It has the following format:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Type     |    Length     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    LB Length  |  LN Length    | Fun. Length   |  Arg. Length  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

      Type: 1

      Length: 4 octets.

      LB Length: 1 octet.  SRv6 SID Locator Block length in bits.

      LN Length: 1 octet.  SRv6 SID Locator Node length in bits.

      Fun. Length: 1 octet.  SRv6 SID Function length in bits.

      Arg. Length: 1 octet.  SRv6 SID Arguments length in bits.

   ISIS SRv6 SID Structure Sub-Sub-TLV MUST NOT appear more than once in
   its parent Sub-TLV.  If it appears more than once in its parent Sub-
   TLV, the parent Sub-TLV MUST be ignored by the receiver.



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   The sum of all four sizes advertised in ISIS SRv6 SID Structure Sub-
   Sub-TLV MUST be lower or equal to 128 bits.  If the sum of all four
   sizes advertised in the ISIS SRv6 SID Structure Sub-Sub-TLV is larger
   than 128 bits, the parent Sub-TLV MUST be ignored by the receiver.

   The SRv6 SID Structure Sub-Sub-TLV indicates the structure of the SID
   associated with it.  It's usage is outside of the scope of this
   document.

10.  Advertising Endpoint Behaviors

   Endpoint behaviors are defined in [RFC8986].  The codepoints for the
   Endpoint behaviors are defined in the "SRv6 Endpoint Behaviors"
   registry defined in [RFC8986].  If this behavior is advertised it
   MUST only be advertised in the TLV[s] as indicated by "Y" in the
   table below, and MUST NOT be advertised in the TLV[s] as indicated by
   "N" in the table below.

     Endpoint             |Endpoint          | End | End.X | Lan End.X |
     Behavior             |Behavior Codepoint| SID | SID   |   SID     |
    ----------------------|------------------|-----|-------|-----------|
     End   (PSP, USP, USD)| 1-4, 28-31       |  Y  |   N   |    N      |
    ----------------------|------------------|-----|-------|-----------|
     End.X (PSP, USP, USD)| 5-8, 32-35       |  N  |   Y   |    Y      |
    ----------------------|------------------|-----|-------|-----------|
     End.DX6              | 16               |  N  |   Y   |    Y      |
    ----------------------|------------------|-----|-------|-----------|
     End.DX4              | 17               |  N  |   Y   |    Y      |
    ----------------------|------------------|-----|-------|-----------|
     End.DT6              | 18               |  Y  |   N   |    N      |
    ----------------------|------------------|-----|-------|-----------|
     End.DT4              | 19               |  Y  |   N   |    N      |
    ----------------------|------------------|-----|-------|-----------|
     End.DT46             | 20               |  Y  |   N   |    N      |



11.  IANA Considerations

   This document requests allocation for the following TLVs, sub-TLVs,
   and sub-sub-TLVs as well updating the ISIS TLV registry and defining
   a new registry.

11.1.  SRv6 Locator TLV

   This document makes the following registrations in the the IS-IS TLV
   Codepoints registry.




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    Type  Description             IIH LSP SNP Purge
    ----  ---------------------   --- --- --- -----
     27   SRv6 Locator TLV         n   y   n    n

11.1.1.  SRv6 End SID sub-TLV

   The SRv6 Locator TLV shares sub-TLV space with TLVs 135, 235, 236 and
   237.  This document updates the "Sub-TLVs for TLVs 135, 235, 236, and
   237 (Extended IP reachability, MT IP.  Reach, IPv6 IP.  Reach, and MT
   IPv6 IP.  Reach TLVs)" registry defined in [RFC7370].  IANA is
   requested to update the name of the "Sub-TLVs for TLVs 135, 235, 236,
   and 237 (Extended IP reachability, MT IP.  Reach, IPv6 IP.  Reach,
   and MT IPv6 IP.  Reach TLVs)" registry to "Sub-TLVs for TLVs 27, 135,
   235, 236, and 237 (SRv6 Locator, Extended IP reachability, MT IP.
   Reach, IPv6 IP.  Reach, and MT IPv6 IP.  Reach TLVs)".

   IANA is asked to add this document as a reference to (renamed) "Sub-
   TLVs for TLVs 27, 135, 235, 236, and 237 (SRv6 Locator, Extended IP
   reachability, MT IP.  Reach, IPv6 IP.  Reach, and MT IPv6 IP.  Reach
   TLVs)" registry.

   This document makes the following registrations in the (renamed)
   "Sub-TLVs for TLVs 27, 135, 235, 236, and 237 (SRv6 Locator, Extended
   IP reachability, MT IP.  Reach, IPv6 IP.  Reach, and MT IPv6 IP.
   Reach TLVs)" registry:

      Type: 5

      Description: SRv6 End SID sub-TLV.

      Reference: This document (Section 7.2).

11.1.2.  Revised sub-TLV table

   The revised table of sub-TLVs for the (renamed) "Sub-TLVs for TLVs
   27, 135, 235, 236, and 237 (SRv6 Locator, Extended IP reachability,
   MT IP.  Reach, IPv6 IP.  Reach, and MT IPv6 IP.  Reach TLVs)"
   registry is shown below:













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      Type  27 135 235 236 237

      1     y   y   y   y   y
      2     y   y   y   y   y
      3     n   y   y   y   y
      4     y   y   y   y   y
      5     y   n   n   n   n
      6     n   y   y   y   y
      11    y   y   y   y   y
      12    y   y   y   y   y
      32    n   y   y   y   y

11.2.  SRv6 Capabilities sub-TLV

   This document makes the following registrations in the "Sub-TLVs for
   TLV 242 (IS-IS Router CAPABILITY TLV)":

      Type: 25

      Description: SRv6 Capabilities sub-TLV.

      Reference: This document (Section 2).

   This document requests the creation of a new IANA managed registry,
   under "IS-IS TLV Codepoints" registry - sub-sub-TLVs of the SRv6
   Capability sub-TLV.  The registration procedure is "Expert Review" as
   defined in [RFC8126].  Guidance for the Designated Experts is
   provided in [RFC7370].  Suggested registry name is "sub-sub-TLVs for
   SRv6 Capability sub-TLV".  No sub-sub-TLVs are defined by this
   document except for the reserved value.

   0: Reserved

   1-255: Unassigned

11.3.  SRv6 End.X SID and SRv6 LAN End.X SID sub-TLVs

   This document makes the following registrations in the "Sub-TLVs for
   TLVs 22, 23, 25, 141, 222, and 223 (Extended IS reachability, IS
   Neighbor Attribute, L2 Bundle Member Attributes, inter-AS
   reachability information, MT-ISN, and MT IS Neighbor Attribute TLVs)"
   registry:

      Type: 43

      Description: SRv6 End.X SID sub-TLV.

      Reference: This document (Section 8.1).



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      Type: 44

      Description: SRv6 LAN End.X SID sub-TLV.

      Reference: This document (Section 8.2).

      Type  22 23 25 141 222 223

      43     y  y  y  y   y   y
      44     y  y  y  y   y   y


11.4.  MSD Types

   This document makes the following registrations in the IGP MSD-Types
   registry:

   Value    Name                  Reference
   ------------------
    41      SRH Max SL            Section 4.1
    42      SRH Max End Pop       Section 4.2
    44      SRH Max H.encaps      Section 4.3
    45      SRH Max End D         Section 4.4

11.5.  Sub-Sub-TLVs for SID Sub-TLVs

   This document requests a new IANA registry be created under the IS-IS
   TLV Codepoints Registry to control the assignment of sub-TLV types
   for the SID Sub-TLVs specified in this document - Section 7.2,
   Section 8.1, Section 8.2.  The suggested name of the new registry is
   "sub-sub-TLVs for SRv6 End SID (5) (sub-TLV of TLVs 27, 135, 235, 236
   and 237) and SRv6 End.X SID (43)/SRv6 LAN End.X SID (44) (sub-TLVs of
   TLVs 27, 135, 235, 236 and 237)".  The registration procedure is
   "Expert Review" as defined in [RFC8126].  Guidance for the Designated
   Experts is provided in [RFC7370]The following assignments are made by
   this document:















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    Type   Description                          Encoding
                                                Reference
   ---------------------------------------------------------
    0      Reserved
    1      SRv6 SID Structure Sub-Sub-TLV       Section 9
    2-255  Unassigned


   Type    5  43 44

    1      y  y  y


11.6.  Prefix Attribute Flags Sub-TLV

   This document adds a new bit in the "Bit Values for Prefix Attribute
   Flags Sub-TLV" registry:

      Bit #: 4

      Description: Anycast Flag (A-flag)

      Reference: This document (Section 6).

12.  Security Considerations

   Security concerns for IS-IS are addressed in [ISO10589], [RFC5304],
   and [RFC5310].  While IS-IS is deployed under a single administrative
   domain, there can be deployments where potential attackers have
   access to one or more networks in the IS-IS routing domain.  In these
   deployments, the stronger authentication mechanisms defined in the
   aforementioned documents SHOULD be used.

   This document describes the IS-IS extensions required to support
   Segment Routing over an IPv6 data plane.  The security considerations
   for Segment Routing are discussed in [RFC8402].  [RFC8986] defines
   the SRv6 Network Programming concept and specifies the main Segment
   Routing behaviors to enable the creation of interoperable overlays;
   the security considerations from that document apply too.

   The advertisement of an incorrect MSD value may have negative
   consequences, see [RFC8491] for additional considerations.

13.  Contributors

   The following people gave a substantial contribution to the content
   of this document and should be considered as co-authors:




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     Stefano Previdi
     Huawei Technologies
     Email: stefano@previdi.net

     Paul Wells
     Cisco Systems
     Saint Paul,
     Minnesota
     United States
     Email: pauwells@cisco.com

     Daniel Voyer
     Email:  daniel.voyer@bell.ca

     Satoru Matsushima
     Email: satoru.matsushima@g.softbank.co.jp

     Bart Peirens
     Email: bart.peirens@proximus.com

     Hani Elmalky
     Email: hani.elmalky@ericsson.com

     Prem Jonnalagadda
     Email: prem@barefootnetworks.com

     Milad Sharif
     Email: msharif@barefootnetworks.com>

     Robert Hanzl
     Cisco Systems
     Millenium Plaza Building, V Celnici 10, Prague 1,
     Prague, Czech Republic
     Email rhanzl@cisco.com

     Ketan Talaulikar
     Cisco Systems, Inc.
     Email: ketant@cisco.com


14.  References

14.1.  Normative References








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   [I-D.ietf-6man-spring-srv6-oam]
              Ali, Z., Filsfils, C., Matsushima, S., Voyer, D., and M.
              Chen, "Operations, Administration, and Maintenance (OAM)
              in Segment Routing Networks with IPv6 Data plane (SRv6)",
              draft-ietf-6man-spring-srv6-oam-08 (work in progress),
              October 2020.

   [I-D.ietf-lsr-flex-algo]
              Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
              A. Gulko, "IGP Flexible Algorithm", draft-ietf-lsr-flex-
              algo-13 (work in progress), October 2020.

   [ISO10589]
              International Organization for Standardization,
              "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)", Nov 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>.

   [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>.

   [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>.

   [RFC7370]  Ginsberg, L., "Updates to the IS-IS TLV Codepoints
              Registry", RFC 7370, DOI 10.17487/RFC7370, September 2014,
              <https://www.rfc-editor.org/info/rfc7370>.

   [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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   [RFC7981]  Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions
              for Advertising Router Information", RFC 7981,
              DOI 10.17487/RFC7981, October 2016,
              <https://www.rfc-editor.org/info/rfc7981>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [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>.

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.

   [RFC8491]  Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
              "Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491,
              DOI 10.17487/RFC8491, November 2018,
              <https://www.rfc-editor.org/info/rfc8491>.

   [RFC8665]  Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler,
              H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
              Extensions for Segment Routing", RFC 8665,
              DOI 10.17487/RFC8665, December 2019,
              <https://www.rfc-editor.org/info/rfc8665>.

   [RFC8667]  Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C.,
              Bashandy, A., Gredler, H., and B. Decraene, "IS-IS
              Extensions for Segment Routing", RFC 8667,
              DOI 10.17487/RFC8667, December 2019,
              <https://www.rfc-editor.org/info/rfc8667>.

   [RFC8754]  Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
              <https://www.rfc-editor.org/info/rfc8754>.

   [RFC8986]  Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
              D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
              (SRv6) Network Programming", RFC 8986,
              DOI 10.17487/RFC8986, February 2021,
              <https://www.rfc-editor.org/info/rfc8986>.





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14.2.  Informative References

   [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>.

   [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>.

   [RFC8355]  Filsfils, C., Ed., Previdi, S., Ed., Decraene, B., and R.
              Shakir, "Resiliency Use Cases in Source Packet Routing in
              Networking (SPRING) Networks", RFC 8355,
              DOI 10.17487/RFC8355, March 2018,
              <https://www.rfc-editor.org/info/rfc8355>.

Authors' Addresses

   Peter Psenak (editor)
   Cisco Systems
   Pribinova Street 10
   Bratislava 81109
   Slovakia

   Email: ppsenak@cisco.com


   Clarence Filsfils
   Cisco Systems
   Brussels
   Belgium

   Email: cfilsfil@cisco.com


   Ahmed Bashandy
   Individual

   Email: abashandy.ietf@gmail.com


   Bruno Decraene
   Orange
   Issy-les-Moulineaux
   France

   Email: bruno.decraene@orange.com



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   Zhibo Hu
   Huawei Technologies

   Email: huzhibo@huawei.com















































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