Link State Routing                                                 Z. Li
Internet-Draft                                                     Z. Hu
Intended status: Standards Track                                D. Cheng
Expires: May 23, 2022                                Huawei Technologies
                                                      K. Talaulikar, Ed.
                                                               P. Psenak
                                                           Cisco Systems
                                                       November 19, 2021


                       OSPFv3 Extensions for SRv6
                draft-ietf-lsr-ospfv3-srv6-extensions-03

Abstract

   The Segment Routing (SR) architecture allows flexible definition of
   the end-to-end path by encoding it as a sequence of topological
   elements called "segments".  It can be implemented over the MPLS or
   the IPv6 data plane.  This document describes the OSPFv3 extensions
   required to support Segment Routing over the IPv6 data plane (SRv6).

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 May 23, 2022.

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



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  SRv6 Capabilities TLV . . . . . . . . . . . . . . . . . . . .   3
   3.  Advertisement of Supported Algorithms . . . . . . . . . . . .   5
   4.  Advertisement of SRH Operation Limits . . . . . . . . . . . .   5
     4.1.  Maximum Segments Left MSD Type  . . . . . . . . . . . . .   5
     4.2.  Maximum End Pop MSD Type  . . . . . . . . . . . . . . . .   5
     4.3.  Maximum H.Encaps MSD Type . . . . . . . . . . . . . . . .   6
     4.4.  Maximum End D MSD Type  . . . . . . . . . . . . . . . . .   6
   5.  SRv6 SIDs and Reachability  . . . . . . . . . . . . . . . . .   6
     5.1.  SRv6 Flexible Algorithm . . . . . . . . . . . . . . . . .   7
   6.  SRv6 Locator LSA  . . . . . . . . . . . . . . . . . . . . . .   8
     6.1.  SRv6 Locator TLV  . . . . . . . . . . . . . . . . . . . .   9
   7.  Advertisment of SRv6 End SIDs . . . . . . . . . . . . . . . .  11
   8.  Advertisment of SRv6 SIDs Associated with Adjacencies . . . .  13
     8.1.  SRv6 End.X SID Sub-TLV  . . . . . . . . . . . . . . . . .  14
     8.2.  SRv6 LAN End.X SID Sub-TLV  . . . . . . . . . . . . . . .  15
   9.  SRv6 SID Structure Sub-TLV  . . . . . . . . . . . . . . . . .  17
   10. Advertising Endpoint Behaviors  . . . . . . . . . . . . . . .  19
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  19
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  20
     12.1.  OSPF Router Information TLVs . . . . . . . . . . . . . .  20
     12.2.  OSPFv3 LSA Function Codes  . . . . . . . . . . . . . . .  20
     12.3.  OSPFv3 Extended-LSA Sub-TLVs . . . . . . . . . . . . . .  20
     12.4.  OSPFv3 Locator LSA TLVs  . . . . . . . . . . . . . . . .  21
     12.5.  OSPFv3 Locator LSA Sub-TLVs  . . . . . . . . . . . . . .  21
   13. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  22
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  22
     14.2.  Informative References . . . . . . . . . . . . . . . . .  24
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  24

1.  Introduction

   Segment Routing (SR) architecture [RFC8402] specifies how a node can
   steer a packet through an ordered list of instructions, called
   segments.  These segments are identified through Segment Identifiers
   (SIDs).






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

   The network programming paradigm for SRv6 is specified in [RFC8986].
   It describes how any behavior can be bound to a SID and how any
   network program can be expressed as a combination of SIDs.  It also
   describes several well-known behaviors that can be bound to SRv6
   SIDs.

   This document specifies extensions to OSPFv3 in order to support SRv6
   as defined in [RFC8986] by signaling the SRv6 capabilities of the
   node and some of the SRv6 SIDs with their endpoint behaviors that are
   instantiated on an SRv6 capable router.  Familiarity with [RFC8986]
   is necessary to understand the extensions specified in this document.

   At a high level, the extensions to OSPFv3 are comprised of the
   following:

   1.  SRv6 Capabilities TLV to advertise the SRv6 features and SRH
       operations supported by the router

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

   3.  SRv6 Locator TLV to advertise the SRv6 Locator - a form of
       summary address for the algorithm specific SIDs instantiated on
       the router

   4.  TLVs and Sub-TLVs to advertise the SRv6 SIDs instantiated on the
       router along with their endpoint behaviors

1.1.  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.

2.  SRv6 Capabilities TLV

   The SRv6 Capabilities TLV is used by an OSPFv3 router to advertise
   its support for the SR Segment Endpoint Node [RFC8754] functionality
   along with its SRv6 related capabilities.  This is an optional top
   level TLV of the OSPFv3 Router Information LSA [RFC7770] which MUST
   be advertised by an SRv6 enabled router.




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   This TLV SHOULD be advertised only once in the OSPFv3 Router
   Information LSA.  When multiple SRv6 Capabilities TLVs are received
   from a given router, the receiver MUST use the first occurrence of
   the TLV in the OSPFv3 Router Information Opaque LSA.  If the SRv6
   Capabilities TLV appears in multiple OSPFv3 Router Information Opaque
   LSAs that have different flooding scopes, the TLV in the OSPFv3
   Router Information Opaque LSA with the area-scoped flooding scope
   MUST be used.  If the SRv6 Capabilities TLV appears in multiple
   OSPFv3 Router Information Opaque LSAs that have the same flooding
   scope, the TLV in the OSPFv3 Router Information Opaque LSA with the
   numerically smallest Instance ID MUST be used and subsequent
   instances of the TLV MUST be ignored.

   The OSPFv3 Router Information Opaque LSA can be advertised at any of
   the defined opaque flooding scopes (link, area, or Autonomous System
   (AS)).  For the purpose of SRv6 Capabilities TLV advertisement, area-
   scoped flooding is REQUIRED.

   The format of OSPFv3 SRv6 Capabilities TLV is shown below

     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             |            Reserved           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Sub-TLVs...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Where:

   o  Type: TBD.

   o  Length: 4 + sume of the lengths of Sub-TLVs in terms of octets

   o  Reserved : 16 bit field.  SHOULD be set to 0 and MUST be ignored
      on receipt.

   o  Flags: 16 bit field.  The following flags are defined and others
      SHOULD be set to 0 and MUST be ignored on receipt:

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



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      where:

      *  O-flag: If set, then the router is capable of supporting the
         O-bit in the SRH flags, as specified in
         [I-D.ietf-6man-spring-srv6-oam].

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

3.  Advertisement of Supported Algorithms

   SRv6 enabled OSPFv3 router advertises its algorithm support using the
   SR Algorithm TLV defined in [RFC8665] as described in [RFC8666].

4.  Advertisement of SRH Operation Limits

   An SRv6 enabled router may have different capabilities and limits
   when it comes to SRH processing and this needs to be advertised to
   other routers in the SRv6 domain.

   [RFC8476] defines the means to advertise node and link specific
   values for Maximum SID Depth (MSD) types.  Node MSDs are advertised
   using the Node MSD TLV in the OSPFv3 Router Information LSA [RFC7770]
   while Link MSDs are advertised using the Link MSD Sub-TLV of the
   Router-Link TLV [RFC8362].  The format of the MSD types for OSPFv3 is
   defined in [RFC8476].

   The MSD types for SRv6 that are defined in section 4 of
   [I-D.ietf-lsr-isis-srv6-extensions] for IS-IS are also used by
   OSPFv3.  These MSD Types are allocated under the IGP MSD Types
   registry maintained by IANA that are shared by IS-IS and OSPF.  They
   are described below:

4.1.  Maximum Segments Left MSD Type

   The Maximum Segments Left MSD Type signals the maximum value of the
   "Segments Left" field of the SRH of a received packet before applying
   the Endpoint behavior associated with a SID.  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 signals the maximum number of SIDs in
   the SRH to which the router can apply "Penultimate Segment Pop (PSP)
   of the SRH" or "Ultimate Segment Pop (USP) of the SRH", as defined in
   [RFC8986] flavors.  If the advertised value is zero or no value is
   advertised, then the router cannot apply PSP or USP flavors.




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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].  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.  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].  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

   An SRv6 Segment Identifier (SID) is 128 bits and comprises of
   Locator, Function and Argument parts as described in [RFC8986].

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

   Locators MUST be advertised in the SRv6 Locator TLV (see
   Section 6.1).  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 algorithm is
   supported by the receiving node.  Locators can be of different route
   types similar to existing OSPFv3 route types - Intra-Area, Inter-
   Area, External, and NSSA.  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 respective route types in base OSPFv3 [RFC5340].

   Locators associated with algorithm 0 and 1 SHOULD be advertised using
   the respective OSPFv3 Extended LSA types with extended TLVs [RFC8362]
   based on the OSPFv3 route of the locators so that legacy routers
   (i.e., routers which do not support SRv6) will install a forwarding
   entry for algorithm 0 and 1 SRv6 traffic.  When operating in "sparse-
   mode" of compatibility [RFC8362] these locators SHOULD be also
   advertised using the respective base OSPFv3 LSAs [RFC5340].



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   In cases where a locator advertisement is received via in both in a
   prefix reachability advertisement (i.e. via base OSPFv3 LSAs and/or
   Extended Prefix TLVs using OSPFv3 Extended LSAs) and an SRv6 Locator
   TLV, the prefix reachability advertisement in OSPFv3 MUST be
   preferred over the advertisement in the SRv6 Locator TLV 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.

   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 of E-
   Router-Link TLV.

   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 algorithm will be forwarded
   correctly, while SRv6 SIDs associated with an unsupported algorithm
   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 base OSPFv3 prefix advertisement is the longest match

5.1.  SRv6 Flexible Algorithm

   [I-D.ietf-lsr-flex-algo] specifies IGP Flexible Algorithm mechanisms
   for OSPFv3.  Section 14.2 of [I-D.ietf-lsr-flex-algo] explains SRv6
   forwarding for Flex-Algorithm and the same apply for supporting SRv6
   Flexi-Algorithm using OSPFv3.  When the algorithm value that is
   carried in the SRv6 Locator TLV (refer Section 6.1) represents a
   Flex-Algorithm, the procedures described in section 14.2 of
   [I-D.ietf-lsr-flex-algo] are followed for the programming of those
   specific SRv6 Locators.  Locators associated with Flexible Algorithms



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   SHOULD NOT be advertised in the base OSPFv3 prefix reachability
   advertisements.  Advertising the Flexible Algorithm locator as
   regular prefix reachability advertisements would make the forwarding
   for it to follow algo 0 path.

   The procedures like ASBR reachability advertisements and the
   procedures for inter-area, external and NSSA route advertisement and
   computation as specified in [I-D.ietf-lsr-flex-algo] for OSPFv3 Flex-
   Algorithm for SR-MPLS also apply for SRv6.

6.  SRv6 Locator LSA

   The SRv6 Locator LSA has a function code of TBD while the S1/S2 bits
   are dependent on the desired flooding scope for the LSA.  The
   flooding scope of the SRv6 Locator LSA depends on the scope of the
   advertised SRv6 Locator and is under the control of the advertising
   router.  The U bit will be set indicating that the LSA should be
   flooded even if it is not understood.

   Multiple SRv6 Locator LSAs can be advertised by an OSPFv3 router and
   they are distinguished by their Link State IDs (which are chosen
   arbitrarily by the originating router).

   The format of SRv6 Locator LSA is shown below:

     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |            LS age             |1|S12|   Function Code         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       Link State ID                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       Advertising Router                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       LS sequence number                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        LS checksum            |            Length             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    +-                            TLVs                             -+
    |                             ...                               |


                        Figure 1: SRv6 Locator LSA

   The format of the TLVs within the body of the SRv6 Locator LSA is the
   same as the format used by [RFC3630].  The variable TLV section




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   consists of one or more nested TLV tuples.  Nested TLVs are also
   referred to as Sub-TLVs.  The format of each TLV is:

     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            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                            Value                              |
                                   o
                                   o
                                   o
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                   Figure 2: SRv6 Locator LSA TLV Format

   The Length field defines the length of the value portion in octets
   (thus, a TLV with no value portion would have a length of 0).  The
   TLV is padded to 4-octet alignment; padding is not included in the
   Length field (so a 3-octet value would have a length of 3, but the
   total size of the TLV would be 8 octets).  Nested TLVs are also
   32-bit aligned.  For example, a 1-byte value would have the Length
   field set to 1, and 3 octets of padding would be added to the end of
   the value portion of the TLV.  The padding is composed of zeros.

6.1.  SRv6 Locator TLV

   The SRv6 Locator TLV is a top-level TLV of the SRv6 Locator LSA that
   is used to advertise an SRv6 Locator, its attributes, and SIDs
   associated with it.  Multiple SRv6 Locator TLVs MAY be advertised in
   each SRv6 Locator LSA.  However, since the S12 bits define the
   flooding scope, the LSA flooding scope MUST satisfy the application-
   specific requirements for all the locators included in a single SRv6
   Locator LSA.

   When multiple SRv6 Locator TLVs are received from a given router in
   an SRv6 Locator LSA for the same Locator, the receiver MUST use the
   first occurrence of the TLV in the LSA.  If the SRv6 Locator TLV for
   the same Locator appears in multiple SRv6 Locator LSAs that have
   different flooding scopes, the TLV in the SRv6 Locator LSA with the
   area-scoped flooding scope MUST be used.  If the SRv6 Locator TLV for
   the same Locator appears in multiple SRv6 Locator LSAs that have the
   same flooding scope, the TLV in the SRv6 Locator LSA with the
   numerically smallest Link-State ID MUST be used and subsequent
   instances of the TLV MUST be ignored.




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   The format of SRv6 Locator TLV is shown below:

     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            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Route Type   |  Algorithm    | Locator Length|    Flags      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                             Metric                            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Locator (128 bits) ...                                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Locator cont ...                                            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Locator cont ...                                            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Locator cont ...                                            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                      Sub-TLVs (variable)                      |
    +-                                                             -+
    |                             ...                               |


                        Figure 3: SRv6 Locator TLV

   Where:

      Type: 16 bit field.  The value is 1 for this type.

      Length: 16 bit field.  The total length of the value portion of
      the TLV including Sub-TLVs in terms of octets.

      Route Type : 8 bit field.  The type of the locator route.
      Supported types are the ones listed below and any other types MUST
      be ignored on receipt.

     1 - Intra-Area
     2 - Inter-Area
     3 - AS External
     4 - NSSA External

                                 Figure 4

      Algorithm: 8 bit field.  Associated algorithm.  Algorithm values
      are defined in the IGP Algorithm Type registry.





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      Locator Length: 8 bit field.  Carries the length of the Locator
      prefix as the number of locator bits (1-128).

      Flags: 8 bit field.  The following flags are defined

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

                                 Figure 5

      *  N bit : When the locator uniquely identifies a node in the
         network (i.e., it is provisioned on one and only one node), the
         N bit MUST be set.  Otherwise, this bit MUST be clear.

      *  A bit : When the Locator is configured as anycast, the A bit
         SHOULD be set.  Otherwise, this bit MUST be clear.  If both the
         N and A bits are set, then the receiving routers MUST ignore
         the N bit (i.e., consider it as not set).

      *  Other flags are not defined and SHOULD be set to 0 and MUST be
         ignored on receipt.

      Metric : One octet field.  The metric value associated with the
      locator.

      Locator : 6 octet field.  This field encodes the advertised SRv6
      Locator.

      Sub-TLVs : Used to advertise Sub-TLVs that provide additional
      attributes for the given SRv6 Locator and SRv6 SIDs associated
      with it.

7.  Advertisment of SRv6 End SIDs

   The SRv6 End SID Sub-TLV is a Sub-TLV of the SRv6 Locator TLV in the
   SRv6 Locator LSA (defined in Section 6).  It is used to advertise the
   SRv6 SIDs belonging to the node along with their associated endpoint
   behaviors.  SIDs associated with adjacencies are advertised as
   described in Section 8.  Every SRv6 enabled OSPFv3 router SHOULD
   advertise at least one SRv6 SID associated with an END behavior for
   its node as specified in [RFC8986].

   SRv6 End SIDs inherit the algorithm from the parent locator.  The
   SRv6 End SID MUST be allocated from its associated locator.  SRv6 End
   SIDs that are NOT allocated from the associated locator MUST be
   ignored.



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   The router MAY advertise multiple instances of the SRv6 End SID Sub-
   TLV within the SRv6 Locator TLV - one for each of the SRv6 SIDs to be
   advertised.  When multiple SRv6 End SID Sub-TLVs are received in the
   SRv6 Locator TLV from a given router for the same SRv6 SID value, the
   receiver MUST use the first occurrence of the Sub-TLV in the SRv6
   Locator TLV.

   The format of SRv6 End SID Sub-TLV is shown below

     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     |   Reserved    |        Endpoint Behavior      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID (128 bits) ...                                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID cont ...                                                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID cont ...                                                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID cont ...                                                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Sub-TLVs (variable) . . .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                      Figure 6: SRv6 End SID Sub-TLV

   Where:

      Type: 16 bit field.  Value is 1 for this type.

      Length: 16 bit field.  The total length of the value portion of
      the Sub-TLVs.

      Reserved : 8 bit field.  Should be set to 0 and MUST be ignored on
      receipt.

      Flags: 8 bit field which define the flags associated with the SID.
      No flags are currently defined and SHOULD be set to 0 and MUST be
      ignored on receipt.

      Endpoint Behavior: 16 bit field.  The endpoint behavior code point
      for this SRv6 SID as defined in section 9.2 of [RFC8986].

      SID : 6 octet field.  This field encodes the advertised SRv6 SID.



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      Sub-TLVs : Used to advertise Sub-TLVs that provide additional
      attributes for the given SRv6 SID.

8.  Advertisment of SRv6 SIDs Associated with Adjacencies

   The SRv6 endpoint behaviors are defined in [RFC8986] include certain
   behaviors which are specific to links or adjacencies.  The most basic
   of these which is critical for link state routing protocols like
   OSPFv3 is the End.X behavior that is an instruction to forward to a
   specific neighbor on a specific link.  These SRv6 SIDs along with
   others that are defined in [RFC8986] which are specific to links or
   adjacencies need to be advertised by OSPFv3 so that this information
   is available to all routers in the area to influence the packet path
   via these SRv6 SIDs over the specific adjacencies.

   The advertisement of SRv6 SIDs and their behaviors that are specific
   to a particular neighbor is done via two different optional Sub-TLVs
   of the E-Router-Link TLV defined in [RFC8362] as follows:

   o  SRv6 End.X SID Sub-TLV: For OSPFv3 adjacencies over point-to-point
      or point-to-multipoint links and the adjacency to the Designated
      Router (DR) over broadcast and non-broadcast-multi-access (NBMA)
      links.

   o  SRv6 LAN End.X SID Sub-TLV: For OSPFv3 adjacencies on broadcast
      and NBMA links to the Backup DR and DR-Other neighbors.  This Sub-
      TLV includes the OSPFv3 router-id of the neighbor and thus allows
      for an instance of this Sub-TLV for each neighbor to be explicitly
      advertised under the E-Router-Link TLV for the same link.

   Every SRv6 enabled OSPFv3 router SHOULD instantiate at least one
   unique SRv6 End.X SID corresponding to each of its neighbor.  A
   router MAY instantiate more than one SRv6 End.X SID for for a single
   neighbor.  The same SRv6 End.X SID MAY be advertised for more than
   one neighbor.  Thus multiple instances of the SRv6 End.X SID and SRv6
   LAN End.X SID Sub-TLVs MAY be advertised within the E-Router-Link TLV
   for a single link.

   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.






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8.1.  SRv6 End.X SID Sub-TLV

   The format of the SRv6 End.X SID Sub-TLV is shown below

     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               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        Endpoint Behavior      |     Flags     |   Reserved1   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Algorithm   |    Weight     |           Reserved2           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID (128 bits) ...                                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID cont ...                                                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID cont ...                                                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID cont ...                                                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    Sub-TLVs (variable) . . .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Where:

      Type: 16 bit field.  Value is TBD.

      Length: 16 bit field.  The total length of the value portion of
      the TLV.

      Endpoint Behavior: 16 bit field.  The code point for the endpoint
      behavior for this SRv6 SID as defined in section 9.2 of [RFC8986].

      Flags: 8 bit field with the following definition:

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


      *  B-Flag: Backup Flag.  If set, the SID refers to a path that is
         eligible for protection.






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      *  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: If set, the SID is persistently
         allocated, i.e., the SID value remains consistent across router
         restart and session/interface flap.

      *  Reserved bits: Reserved for future use and MUST be zero when
         originated and ignored on receipt.

      Reserved1 : 8 bit field.  Should be set to 0 and MUST be ignored
      on receipt.

      Algorithm : 8 bit field.  Associated algorithm.  Algorithm values
      are defined in the IGP Algorithm Type registry.

      Weight: 8 bit field whose value represents the weight of the End.X
      SID for the purpose of load-balancing.  The use of the weight is
      defined in [RFC8402].

      Reserved2 : 16 bit field.  Should be set to 0 and MUST be ignored
      on receipt.

      SID: 128 bit field.  This field encodes the advertised SRv6 SID.

      Sub-TLVs : Used to advertise Sub-TLVs that provide additional
      attributes for the given SRv6 End.X SID.

8.2.  SRv6 LAN End.X SID Sub-TLV

   The format of the SRv6 LAN End.X SID Sub-TLV is as shown below



















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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               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      Endpoint Behavior        |     Flags     |   Reserved1   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Algorithm   |    Weight     |           Reserved2           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    OSPFv3 Router-ID of neighbor                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID (128 bits) ...                                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID cont ...                                                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID cont ...                                                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID cont ...                                                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Sub-TLVs (variable) . . .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Where

   o  Type: 16 bit field.  Value is TBD.

   o  Length: 16 bit field.  Variable

   o  Endpoint Behavior: 16 bit field.  The code point for the endpoint
      behavior for this SRv6 SID as defined in section 9.2 of [RFC8986].

   o  SID Flags: 8 bit field which define the flags associated with the
      SID.  No flags are currently defined and SHOULD be set to 0 and
      MUST be ignored on receipt.

   o  Flags: 8 bit field with the following definition:

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


      *  B-Flag: Backup Flag.  If set, the SID refers to a path that is
         eligible for protection.





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      *  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: If set, the SID is persistently
         allocated, i.e., the SID value remains consistent across router
         restart and session/interface flap.

      *  Reserved bits: Reserved for future use and MUST be zero when
         originated and ignored on receipt.

   o  Reserved1 : 8 bit field.  Should be set to 0 and MUST be ignored
      on receipt.

   o  Algorithm : 8 bit field.  Associated algorithm.  Algorithm values
      are defined in the IGP Algorithm Type registry.

   o  Weight: 8 bit field whose value represents the weight of the End.X
      SID for the purpose of load balancing.  The use of the weight is
      defined in [RFC8402].

   o  Reserved2 : 16 bit field.  Should be set to 0 and MUST be ignored
      on receipt.

   o  Neighbor ID : 32 bits of OSPFv3 Router-id of the neighbor

   o  SID: 128 bit field.  This field encodes the advertised SRv6 SID.

   o  Sub-TLVs : Used to advertise Sub-TLVs that provide additional
      attributes for the given SRv6 SID.

9.  SRv6 SID Structure Sub-TLV

   SRv6 SID Structure Sub-TLV is used to advertise the structure of the
   SRv6 SID as defined in [RFC8986].  It is used as an optional Sub-TLV
   of the following:

   o  SRv6 End SID Sub-TLV (refer Section 7)

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

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

   The 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               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    LB Length  |  LN Length    | Fun. Length   |  Arg. Length  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                   Figure 7: SRv6 SID Structure Sub-TLV

   Where:

      Type: 16 bit field with value TBD, see Section 12.

      Length: 16 bit field with the value 4.

      LB Length: 8 bit field.  SRv6 SID Locator Block length in bits.

      LN Length: 8 bit field.  SRv6 SID Locator Node length in bits.

      Function Length: 8 bit field.  SRv6 SID Function length in bits.

      Argument Length: 8 bit field.  SRv6 SID Argument length in bits.

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

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

   The SRv6 SID Structure Sub-TLV is intended for informational use by
   the control and management planes.  It MUST NOT be used at a transit
   node (as defined in [RFC8754]) for forwarding packets.  As an
   example, this information could be used for:

   o  validation of SRv6 SIDs being instantiated in the network and
      advertised via OSPFv3.  These can be learnt by controllers via
      BGP-LS and then be monitored for conformance to the SRv6 SID
      allocation scheme chosen by the operator as described in
      Section 3.2 of [RFC8986].

   o  verification and the automation for securing the SRv6 domain by
      provisioning filtering rules at SR domain boundaries as described
      in Section 5 of [RFC8754].



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   The details of these potential applications are outside the scope of
   this document.

10.  Advertising Endpoint Behaviors

   Endpoint behaviors are defined in [RFC8986] and
   [I-D.ietf-6man-spring-srv6-oam].  The codepoints for the Endpoint
   behaviors are defined in the section 9.2 of [RFC8986].  This section
   lists the Endpoint behaviors and their codepoints, which MAY be
   advertised by OSPFv3 and the Sub-TLVs in which each type MAY appear.

|-----------------------|--------------------|-----|-------|-----------|
| 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.DT64              | 20                 |  Y  |   N   |    N      |
|-----------------------|--------------------|-----|-------|-----------|


                Figure 8: SRv6 Endpoint Behaviors in OSPFv3

11.  Security Considerations

   Existing security extensions as described in [RFC5340] and [RFC8362]
   apply to these SRv6 extensions.  While OSPFv3 is under a single
   administrative domain, there can be deployments where potential
   attackers have access to one or more networks in the OSPFv3 routing
   domain.  In these deployments, stronger authentication mechanisms
   such as those specified in [RFC4552] or [RFC7166] SHOULD be used.

   Implementations MUST assure that malformed TLV and Sub-TLV defined in
   this document are detected and do not provide a vulnerability for
   attackers to crash the OSPFv3 router or routing process.  Reception
   of malformed TLV or Sub-TLV SHOULD be counted and/or logged for
   further analysis.  Logging of malformed TLVs and Sub-TLVs SHOULD be




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   rate-limited to prevent a Denial of Service (DoS) attack (distributed
   or otherwise) from overloading the OSPFv3 control plane.

   This document describes the OSPFv3 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 for an incorrect MSD value may have negative
   consequences, see [RFC8476] for additional considerations.

   Security concerns associated with the setting of the O-flag are
   described in [I-D.ietf-6man-spring-srv6-oam].

   Security concerns associated with the usage of Flex-Algorithms are
   described in [I-D.ietf-lsr-flex-algo].

12.  IANA Considerations

   This document specifies updates to multiple OSPF and OSPFv3 related
   IANA registries as follows.

12.1.  OSPF Router Information TLVs

   This document proposes the following new code point in the "OSPF
   Router Information (RI) TLVs" registry under the "OSPF Parameters"
   registry for the new TLVs:

      Type TBD (suggested 20): SRv6-Capabilities TLV: Refer to
      Section 2.

12.2.  OSPFv3 LSA Function Codes

   This document proposes the following new code point in the "OSPFv3
   LSA Function Codes" registry under the "OSPFv3 Parameters" registry
   for the new SRv6 Locator LSA:

   o  Type TBD (suggested 42): SRv6 Locator LSA: Refer to Section 6.

12.3.  OSPFv3 Extended-LSA Sub-TLVs

   This document proposes the following new code points in the "OSPFv3
   Extended-LSA Sub-TLVs" registry under the "OSPFv3 Parameters"
   registry for the new Sub-TLVs:





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   o  Type TBD (suggested 10): SRv6 SID Structure Sub-TLV : Refer to
      Section 9.

   o  Type TBD (suggested 11): SRv6 End.X SID Sub-TLV : Refer to
      Section 8.1.

   o  Type TBD (suggested 12): SRv6 LAN End.X SID Sub-TLV : Refer to
      Section 8.2.

12.4.  OSPFv3 Locator LSA TLVs

   This document proposes setting up of a new "OSPFv3 Locator LSA TLVs"
   registry that defines top-level TLVs for the OSPFv3 SRv6 Locator LSA
   to be added under the "OSPFv3 Parameters" registry.  The initial
   code-points assignment is as below:

   o  Type 0: Reserved.

   o  Type 1: SRv6 Locator TLV : Refer to Section 6.1.

   Types in the range 2-32767 are allocated via IETF Review or IESG
   Approval [RFC8126].

   Types in the range 32768-33023 are Reserved for Experimental Use;
   these will not be registered with IANA and MUST NOT be mentioned by
   RFCs.

   Types in the range 33024-45055 are to be assigned on a First Come
   First Served (FCFS) basis.

   Types in the range 45056-65535 are not to be assigned at this time.
   Before any assignments can be made in the 33024-65535 range, there
   MUST be an IETF specification that specifies IANA Considerations that
   cover the range being assigned.

12.5.  OSPFv3 Locator LSA Sub-TLVs

   This document proposes setting up of a new "OSPFv3 Locator LSA Sub-
   TLVs" registry that defines Sub-TLVs at any level of nesting for the
   SRv6 Locator TLVs to be added under the "OSPFv3 Parameters" registry.
   The initial code-points assignment is as below:

   o  Type 0: Reserved.

   o  Type 1: SRv6 End SID Sub-TLV : Refer to Section 7.

   o  Type 10: SRv6 SID Structure Sub-TLV : Refer to Section 9.




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   Types in the range 2-9 and 11-32767 are allocated via IETF Review or
   IESG Approval [RFC8126].

   Types in the range 32768-33023 are Reserved for Experimental Use;
   these will not be registered with IANA and MUST NOT be mentioned by
   RFCs.

   Types in the range 33024-45055 are to be assigned on a First Come
   First Served (FCFS) basis.

   Types in the range 45056-65535 are not to be assigned at this time.
   Before any assignments can be made in the 33024-65535 range, there
   MUST be an IETF specification that specifies IANA Considerations that
   cover the range being assigned.

13.  Acknowledgements

   The authors would like to thank Acee Lindem and Chenzichao for their
   review and comments on this document.

14.  References

14.1.  Normative References

   [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-11 (work in progress),
              June 2021.

   [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-18 (work in progress), October 2021.

   [I-D.ietf-lsr-isis-srv6-extensions]
              Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
              Z. Hu, "IS-IS Extensions to Support Segment Routing over
              IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-18
              (work in progress), October 2021.

   [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>.





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

   [RFC7770]  Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
              S. Shaffer, "Extensions to OSPF for Advertising Optional
              Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
              February 2016, <https://www.rfc-editor.org/info/rfc7770>.

   [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>.

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

   [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>.

   [RFC8476]  Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak,
              "Signaling Maximum SID Depth (MSD) Using OSPF", RFC 8476,
              DOI 10.17487/RFC8476, December 2018,
              <https://www.rfc-editor.org/info/rfc8476>.

   [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>.

   [RFC8666]  Psenak, P., Ed. and S. Previdi, Ed., "OSPFv3 Extensions
              for Segment Routing", RFC 8666, DOI 10.17487/RFC8666,
              December 2019, <https://www.rfc-editor.org/info/rfc8666>.

   [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>.




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   [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>.

14.2.  Informative References

   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630,
              DOI 10.17487/RFC3630, September 2003,
              <https://www.rfc-editor.org/info/rfc3630>.

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

   [RFC7166]  Bhatia, M., Manral, V., and A. Lindem, "Supporting
              Authentication Trailer for OSPFv3", RFC 7166,
              DOI 10.17487/RFC7166, March 2014,
              <https://www.rfc-editor.org/info/rfc7166>.

Authors' Addresses

   Zhenbin Li
   Huawei Technologies

   Email: lizhenbin@huawei.com


   Zhibo Hu
   Huawei Technologies

   Email: huzhibo@huawei.com


   Dean Cheng
   Huawei Technologies

   Email: dean.cheng@huawei.com


   Ketan Talaulikar (editor)
   Cisco Systems
   India

   Email: ketant.ietf@gmail.com




Li, et al.                Expires May 23, 2022                 [Page 24]


Internet-Draft         OSPFv3 Extensions for SRV6          November 2021


   Peter Psenak
   Cisco Systems
   Slovakia

   Email: ppsenak@cisco.com














































Li, et al.                Expires May 23, 2022                 [Page 25]