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Versions: (draft-bashandy-isis-srv6-extensions) 00 01 02 03 04 05 06 07 08 09 10 11

Networking Working Group                                  P. Psenak, Ed.
Internet-Draft                                               C. Filsfils
Intended status: Standards Track                           Cisco Systems
Expires: September 24, 2020                                  A. Bashandy
                                                              Individual
                                                             B. Decraene
                                                                  Orange
                                                                   Z. Hu
                                                     Huawei Technologies
                                                          March 23, 2020


     IS-IS Extension to Support Segment Routing over IPv6 Dataplane
               draft-ietf-lsr-isis-srv6-extensions-07.txt

Abstract

   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 draft describes
   the IS-IS extensions required to support Segment Routing over an IPv6
   data plane.

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."

   This Internet-Draft will expire on September 24, 2020.



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Copyright Notice

   Copyright (c) 2020 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 . . . . . . . . . . . . . . . . . .   4
   3.  Advertising Supported Algorithms  . . . . . . . . . . . . . .   4
   4.  Advertising Maximum SRv6 SID Depths . . . . . . . . . . . . .   5
     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  . . . . . . . . . . . . . . . . .   6
   5.  SRv6 SIDs and Reachability  . . . . . . . . . . . . . . . . .   6
   6.  Advertising Anycast Property  . . . . . . . . . . . . . . . .   7
   7.  Advertising Locators and End SIDs . . . . . . . . . . . . . .   8
     7.1.  SRv6 Locator TLV Format . . . . . . . . . . . . . . . . .   9
     7.2.  SRv6 End SID sub-TLV  . . . . . . . . . . . . . . . . . .  10
   8.  Advertising SRv6 Adjacency SIDs . . . . . . . . . . . . . . .  12
     8.1.  SRv6 End.X SID sub-TLV  . . . . . . . . . . . . . . . . .  12
     8.2.  SRv6 LAN End.X SID sub-TLV  . . . . . . . . . . . . . . .  14
   9.  SRv6 SID Structure Sub-Sub-TLV  . . . . . . . . . . . . . . .  16
   10. Advertising Endpoint Behaviors  . . . . . . . . . . . . . . .  17
   11. Implementation Status . . . . . . . . . . . . . . . . . . . .  18
     11.1.  Cisco  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     11.2.  Huawei . . . . . . . . . . . . . . . . . . . . . . . . .  18
     11.3.  Juniper  . . . . . . . . . . . . . . . . . . . . . . . .  18
     11.4.  Interoperability Testing.  . . . . . . . . . . . . . . .  18
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
     12.1.  SRv6 Locator TLV . . . . . . . . . . . . . . . . . . . .  19
       12.1.1.  SRv6 End SID sub-TLV . . . . . . . . . . . . . . . .  19
       12.1.2.  Revised sub-TLV table  . . . . . . . . . . . . . . .  19
     12.2.  SRv6 Capabilities sub-TLV  . . . . . . . . . . . . . . .  19
     12.3.  SRv6 End.X SID and SRv6 LAN End.X SID sub-TLVs . . . . .  20
     12.4.  MSD Types  . . . . . . . . . . . . . . . . . . . . . . .  20
     12.5.  Sub-Sub-TLVs for SID Sub-TLVs  . . . . . . . . . . . . .  21



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     12.6.  Prefix Attribute Flags Sub-TLV . . . . . . . . . . . . .  21
   13. Security Considerations . . . . . . . . . . . . . . . . . . .  21
   14. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  21
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     15.1.  Normative References . . . . . . . . . . . . . . . . . .  22
     15.2.  Informative References . . . . . . . . . . . . . . . . .  24
     15.3.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . .  25
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  25

1.  Introduction

   With Segment Routing (SR) [I-D.ietf-spring-segment-routing], 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
   [I-D.ietf-6man-segment-routing-header].  SRv6 refers to this SR
   instantiation on the IPv6 dataplane.

   The network programming paradigm
   [I-D.ietf-spring-srv6-network-programming] 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
   [I-D.ietf-spring-srv6-network-programming] is necessary to understand
   the extensions specified in this document.

   This document defines one new top level IS-IS TLV and several new IS-
   IS sub-TLVs.

   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 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 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



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   instantiated at a node and what Endpoint behavior is bound to each
   instantiated SID.

2.  SRv6 Capabilities sub-TLV

   A node indicates that it supports the SR Segment Endpoint Node
   functionality as specified in [I-D.ietf-6man-segment-routing-header]
   by advertising a new SRv6 Capabilities sub-TLV of the router
   capabilities TLV [RFC7981].

   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: Suggested value 25, to be assigned by IANA

        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

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






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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].

4.1.  Maximum Segments Left MSD Type

   The Maximum Segments Left MSD Type specifies the maximum value of the
   "SL" field [I-D.ietf-6man-segment-routing-header] in the SRH of a
   received packet before applying the Endpoint behavior associated with
   a SID.

      SRH Max SL Type: 41 (Suggested value - to be assigned by IANA)

      If no value is advertised the supported value is assumed to be 0.

4.2.  Maximum End Pop MSD Type

   The Maximum End Pop MSD Type specifies the maximum number of SIDs in
   the SRH to which the router can apply "PSP" or USP" behavior, as
   defined in [I-D.ietf-spring-srv6-network-programming] flavors.

     SRH Max End Pop Type: 42 (Suggested value - to be assigned by IANA)

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

4.3.  Maximum H.Encaps MSD Type

   The Maximum H.Encaps MSD Type specifies the maximum number of SIDs
   that can be included as part of the "H.Encaps" behavior as defined in
   [I-D.ietf-spring-srv6-network-programming] .













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    SRH Max H.encaps Type: 44 (Suggested value - to be assigned by IANA)

    If the advertised value is zero then the router can apply H.Encaps
    only by encapsulating the incoming packet in another
    IPv6 header without SRH the same way IPinIP encapsulation is
    performed.

    If the advertised value is non-zero then the router supports both
    IPinIP and SRH encapsulation subject to the SID limitation
    specified by the advertised value.

4.4.  Maximum End D MSD Type

   The Maximum End D MSD Type specifies the maximum number of SIDs in an
   SRH when performing decapsulation associated with "End.Dx" behaviors
   (e.g., "End.DX6" and "End.DT6") as defined in
   [I-D.ietf-spring-srv6-network-programming].

   SRH Max End D Type: 45 (Suggested value - to be assigned by IANA)

   If the advertised value is zero or no value is advertised
   then it is assumed that the router cannot apply
   "End.DX6" or "End.DT6" behaviors if the outer IPv6 header contains an SRH.

5.  SRv6 SIDs and Reachability

   As discussed in [I-D.ietf-spring-srv6-network-programming], 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.

   Locators are routable and MAY also be advertised in Prefix
   Reachability TLVs (236 or 237).

   Locators associated with Flexible Algorithms [I-D.ietf-lsr-flex-algo]
   SHOULD NOT be advertised in Prefix Reachability TLVs (236 or 237).





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   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, 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.

   SRv6 SIDs are advertised as sub-TLVs in the SRv6 Locator TLV except
   for SRv6 End.X SIDs/LAN End.X 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 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.  There are a number
   of ways in which this requirement could be compromised.  In order to
   ensure correct forwarding, network operators should take steps to
   make sure that this requirement is not compromised.

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

   o  A 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.





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

       Bit #: 4 (Suggested - to be assigned by IANA)
       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 leaked between levels.

   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.

   Locator that is advertised by a single node and without an A-Flag
   SHOULD be interpreted as a node specific locator.

   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 identical versions of the Prefix Attribute Flags Sub-TLV in
   both TLVs.

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.








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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|    MTID               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type: 27 (Suggested value to be assigned by IANA)

     Length: variable.

     MTID: 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: When the Locator is leaked from level-2 to level-1, the D
        bit MUST be set.  Otherwise, this bit MUST be clear.  Locators
        with the D bit set MUST NOT be leaked from level-1 to level-2.
        This is to prevent looping.




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

     Algorithm: 1 octet. Associated algorithm. Algorithm values
      are defined in the IGP Algorithm Type registry.

     Loc-Size: 1 octet. Number of bits in the SRv6 Locator field.
     (1 - 128)

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


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
   [I-D.ietf-spring-srv6-network-programming].  SRv6 SIDs associated
   with a neighbor are advertised using the sub-TLVs defined in
   Section 8.

   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:


















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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    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Flags      |       Endpoint Behavior       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | SID (128 bits) . . .                                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | SID (cont . . .)                                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | SID (cont . . .)                                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | SID (cont . . .)                                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |Sub-sub-tlv-len|         sub-sub-TLVs (variable) . . .         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type: 5 (Suggested value to be assigned by IANA).

      Length: variable.

      Flags: 1 octet.  No flags are currently defined.

      Endpoint Behavior: 2 octets, as defined in [I-D.ietf-spring-srv6-
      network-programming].  Legal behavior values for this sub-TLV are
      defined in Section 10 of this document.

      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.






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8.  Advertising SRv6 Adjacency SIDs

   Certain SRv6 Endpoint behaviors
   [I-D.ietf-spring-srv6-network-programming] must be associated with a
   particular neighbor, and in case of multiple links to the same
   neighbor, with a particular link in order to be correctly applied.

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

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

   All End.X SIDs MUST be a subnet of a Locator with matching topology
   and algorithm which is advertised by the same node in an SRv6 Locator
   TLV.  End.X SIDs which do not meet this requirement MUST be ignored.

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

















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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    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Flags       |   Algorithm   |   Weight      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |        Endpoint Behavior      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | SID (128 bits) . . .                                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | SID (cont . . .)                                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | SID (cont . . .)                                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | SID (cont . . .)                                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |Sub-sub-tlv-len|         Sub-sub-TLVs (variable) . . .         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      Type: 43 (Suggested value to be assigned by IANA).

      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 End.X SID is eligible for
         protection (e.g., using IPFRR) as described in [RFC8355].

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





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

      Algorithm: 1 octet.  Associated algorithm.  Algorithm values are
      defined in the IGP Algorithm Type registry.

      Weight: 1 octet.  The value represents the weight of the End.X SID
      for the purpose of load balancing.  The use of the weight is
      defined in [I-D.ietf-spring-segment-routing].

      Endpoint Behavior: 2 octets.  As defined in [I-D.ietf-spring-srv6-
      network-programming] Legal behavior values for this sub-TLV are
      defined in Section 10.

      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 End.X 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 End.X 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    |    System ID (6 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 (Suggested value to be assigned by IANA).

      Length: variable.

      System-ID: 6 octets of 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.  Other
         bits: MUST be zero when originated and ignored when received.

      Algorithm: 1 octet.  Associated algorithm.  Algorithm values are
      defined in the IGP Algorithm Type registry.

      Weight: 1 octet.  The value represents the weight of the End.X SID
      for the purpose of load balancing.  The use of the weight is
      defined in [I-D.ietf-spring-segment-routing].



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      Endpoint Behavior: 2 octets.  As defined in [I-D.ietf-spring-srv6-
      network-programming] Legal behavior values for this sub-TLV are
      defined in Section 10.

      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 length of
   each individual part of the SRv6 SID as defined in
   [I-D.ietf-spring-srv6-network-programming].  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.






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   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.

   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.

10.  Advertising Endpoint Behaviors

   Endpoint behaviors are defined in
   [I-D.ietf-spring-srv6-network-programming] and
   [I-D.ietf-6man-spring-srv6-oam].  The codepoints for the Endpoint
   behaviors are defined in the "SRv6 Endpoint Behaviors" registry
   defined in [I-D.ietf-spring-srv6-network-programming].  This section
   lists the Endpoint behaviors which MAY be advertised by ISIS,
   together with their codepoints.  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.T (PSP, USP, USD) | 9-12, 36-39        |   Y   |   N   |    N      |
  -----------------------|--------------------|-------|-------|-----------|
   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.DT64              | 20                 |   Y   |   N   |    N      |
  -----------------------|--------------------|-------|-------|-----------|
   End.OP                | 40                 |   Y   |   N   |    N      |
  -----------------------|--------------------|-------|-------|-----------|
   End.OTP               | 41                 |   Y   |   N   |    N      |







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11.  Implementation Status

   This section describes the implementation status of the ISIS SRv6
   extensions.

11.1.  Cisco

   Cisco's ISIS SRv6 implementation supports following functionalities:

      Types of SID supported: End, End.X, LAN End.X, END.OP

      Intra/Inter area/level support: Yes

      Anycast SID support: Yes, including A-flag (Section 6)

      SID Structure Sub-Sub-TLV: Yes

11.2.  Huawei

   Huawei's ISIS SRv6 implementation supports following functionalities:

      Types of SID supported: End, End.X, LAN End.X

      Intra/Inter area/level support: Yes

      Anycast SID support: Yes, no A-flag support (Section 6)

      SID Structure Sub-Sub-TLV: No

11.3.  Juniper

   Juniper's ISIS SRv6 implementation supports following
   functionalities:

      Types of SID supported: End, End.X, LAN End.X

      Intra/Inter area/level support: Yes

      Anycast SID support: Yes, no A-flag support (Section 6)

      SID Structure Sub-Sub-TLV: No

11.4.  Interoperability Testing.

   EANTC interoperability testing has been performed in April 2019.
   Results can be found at EANTC site [1].





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12.  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.

12.1.  SRv6 Locator TLV

   This document adds one new TLV to the IS-IS TLV Codepoints registry.

   Value: 27 (suggested - to be assigned by IANA)

   Name: SRv6 Locator

   This TLV shares sub-TLV space with existing "Sub-TLVs for TLVs 135,
   235, 236 and 237 registry".  The name of this registry needs to be
   changed to "Sub-TLVs for TLVs 27, 135, 235, 236 and 237 registry".

12.1.1.  SRv6 End SID sub-TLV

   This document adds the following new sub-TLV to the (renamed) "Sub-
   TLVs for TLVs 27, 135, 235, 236 and 237 registry".

   Value: 5 (suggested - to be assigned by IANA)

   Name: SRv6 End SID

12.1.2.  Revised sub-TLV table

   The revised table of sub-TLVs for the (renamed) "Sub-TLVs for TLVs
   27, 135, 235, 236 and 237 registry" is shown below:

      Type  27 135 235 236 237

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

12.2.  SRv6 Capabilities sub-TLV

   This document adds the definition of a new sub-TLV in the "Sub- TLVs
   for TLV 242 registry".

   Type: 25 (Suggested - to be assigned by IANA)



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   Description: SRv6 Capabilities

   This document requests the creation of a new IANA managed registry
   for sub-sub-TLVs of the SRv6 Capability sub-TLV.  The registration
   procedure is "Expert Review" as defined 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

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

   This document adds the definition of two new sub-TLVs in the "sub-
   TLVs for TLV 22, 23, 25, 141, 222 and 223 registry".

   Type: 43 (suggested - to be assigned by IANA)

   Description: SRv6 End.X SID

   Type: 44 (suggested - to be assigned by IANA)

   Description: SRv6 LAN End.X SID

      Type  22 23 25 141 222 223

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


12.4.  MSD Types

   This document defines the following new MSD types.  These types are
   to be defined in the IGP MSD Types registry defined in [RFC8491] .

   All values are suggested values to be assigned by IANA.

   Type  Description
   ------------------
    41    SRH Max SL
    42    SRH Max End Pop
    44    SRH Max H.encaps
    45    SRH Max End D







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12.5.  Sub-Sub-TLVs for SID Sub-TLVs

   This document creates the following Sub-Sub-TLV Registry within the
   "IS-IS TLV Codepoints" registry:

      Registry: Sub-Sub-TLVs for SID Sub-TLVs

      Registration Procedure: Expert review

      Reference: This document (Section 7.2, Section 8.1, Section 8.2).

   This document defines the following Sub-Sub-TLV in the "Sub-Sub-TLVs
   for SID Sub-TLVs" registry:

      Type: 1

      Description: SRv6 SID Structure Sub-Sub-TLV.

      Reference: This document (Section 9).

12.6.  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: A bit

      Reference: This document (Section 6).

13.  Security Considerations

   Security concerns for IS-IS are addressed in [ISO10589], [RFC5304],
   and [RFC5310].

14.  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


15.  References

15.1.  Normative References








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   [I-D.ietf-6man-segment-routing-header]
              Filsfils, C., Dukes, D., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", draft-ietf-6man-segment-routing-header-26 (work in
              progress), October 2019.

   [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-03 (work in progress),
              December 2019.

   [I-D.ietf-spring-srv6-network-programming]
              Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
              Matsushima, S., and Z. Li, "SRv6 Network Programming",
              draft-ietf-spring-srv6-network-programming-14 (work in
              progress), March 2020.

   [ISO10589]
              Standardization", I. ". O. F., "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), ISO/IEC 10589:2002, Second Edition.", 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>.

   [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>.







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   [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>.

   [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>.

   [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>.

   [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>.

   [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>.

   [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>.

15.2.  Informative References

   [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-06 (work in progress), February 2020.

   [I-D.ietf-spring-segment-routing]
              Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B.,
              Litkowski, S., and R. Shakir, "Segment Routing
              Architecture", draft-ietf-spring-segment-routing-15 (work
              in progress), January 2018.





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   [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>.

15.3.  URIs

   [1] http://www.eantc.de/fileadmin/eantc/downloads/events/2017-
       2020/MPLS2019/Segment_Routing_IPv6__SRv6_.pdf

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


   Zhibo Hu
   Huawei Technologies

   Email: huzhibo@huawei.com



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