path: root/doc/rfc/rfc9513.txt

Internet Engineering Task Force (IETF)                             Z. Li
Request for Comments: 9513                                         Z. Hu
Category: Standards Track                            Huawei Technologies
ISSN: 2070-1721                                       K. Talaulikar, Ed.
                                                               P. Psenak
                                                           Cisco Systems
                                                           December 2023


         OSPFv3 Extensions for Segment Routing over IPv6 (SRv6)

Abstract

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

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9513.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Revised BSD License text as described in Section 4.e of the
   Trust Legal Provisions and are provided without warranty as described
   in the Revised BSD License.

Table of Contents

   1.  Introduction
     1.1.  Requirements Language
   2.  SRv6 Capabilities TLV
   3.  Advertisement of Supported Algorithms
   4.  Advertisement of Maximum SRv6 SID Depths
     4.1.  Maximum Segments Left MSD Type
     4.2.  Maximum End Pop MSD Type
     4.3.  Maximum H.Encaps MSD Type
     4.4.  Maximum End D MSD Type
   5.  SRv6 SIDs and Reachability
     5.1.  SRv6 Flexible Algorithm
   6.  Advertisement of Anycast Property
   7.  SRv6 Locator LSA
     7.1.  SRv6 Locator TLV
     7.2.  SRv6 Locator Sub-TLVs
   8.  Advertisement of SRv6 End SIDs
   9.  Advertisement of SRv6 SIDs Associated with Adjacencies
     9.1.  SRv6 End.X SID Sub-TLV
     9.2.  SRv6 LAN End.X SID Sub-TLV
   10. SRv6 SID Structure Sub-TLV
   11. Advertising Endpoint Behaviors
   12. Security Considerations
   13. IANA Considerations
     13.1.  OSPF Router Information TLVs
     13.2.  OSPFv3 LSA Function Codes
     13.3.  OSPFv3 Prefix Options
     13.4.  OSPFv3 SRv6 Capabilities TLV Flags
     13.5.  OSPFv3 SRv6 End SID Sub-TLV Flags
     13.6.  OSPFv3 SRv6 Adjacency SID Sub-TLV Flags
     13.7.  OSPFv3 Extended-LSA Sub-TLVs
     13.8.  OSPFv3 SRv6 Locator LSA TLVs
     13.9.  OSPFv3 SRv6 Locator LSA Sub-TLVs
     13.10. OSPFv3 Extended-LSA Sub-TLVs
   14. References
     14.1.  Normative References
     14.2.  Informative References
   Acknowledgements
   Authors' Addresses

1.  Introduction

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

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

   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 OSPFv3 extensions to support SRv6
   capabilities as defined in [RFC8986], [RFC8754], and [RFC9259].  The
   extensions include advertisement of an OSPFv3 router's SRv6
   capabilities, SRv6 Locators, and required SRv6 SIDs along with their
   supported Endpoint behaviors.  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.  An SRv6 Capabilities TLV to advertise the SRv6 features and SRH
       operations supported by an OSPFv3 router.

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

   3.  An SRv6 Locator TLV using an SRv6 Locator Link State
       Advertisement (LSA) to advertise the SRv6 Locator -- a form of
       summary address for the IGP algorithm-specific SIDs instantiated
       on an OSPFv3 router.

   4.  TLVs and sub-TLVs to advertise the SRv6 SIDs instantiated on an
       OSPFv3 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] that MUST be
   advertised by an SRv6-enabled router.

   This TLV MUST 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 LSA.  If the SRv6
   Capabilities TLV appears in multiple OSPFv3 Router Information LSAs
   that have different flooding scopes, the TLV in the OSPFv3 Router
   Information LSA with the area-scoped flooding scope MUST be used.  If
   the SRv6 Capabilities TLV appears in multiple OSPFv3 Router
   Information LSAs that have the same flooding scope, the TLV in the
   OSPFv3 Router Information LSA with the numerically smallest Link
   State ID MUST be used, and subsequent instances of the TLV MUST be
   ignored.

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

   The format of the 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...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 1: SRv6 Capabilities TLV

   where:

   Type:  2-octet field.  The value for this type is 20.

   Length:  2-octet field.  The total length (in octets) of the value
      portion of the TLV, including nested sub-TLVs.

   Reserved:  2-octet field.  It MUST be set to 0 on transmission and
      MUST be ignored on receipt.

   Flags:  2-octet field.  The flags are defined as follows:

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

      where:

      O-flag:  If set, then the router is capable of supporting the
         O-flag in the SRH flags, as specified in [RFC9259].

      Other flags are not defined and are reserved for future use.
      They MUST be set to 0 on transmission and MUST be ignored on
      receipt.

   The SRv6 Capabilities TLV may contain optional sub-TLVs.  No sub-TLVs
   are defined in this specification.

3.  Advertisement of Supported Algorithms

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

4.  Advertisement of Maximum SRv6 SID Depths

   An SRv6-enabled router may have different capabilities and limits
   related to SRH processing.  These need to be advertised to other
   OSPFv3 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 [RFC9352] for
   IS-IS are also used by OSPFv3.  These MSD types are allocated in the
   "IGP MSD-Types" registry maintained by IANA and are shared by IS-IS
   and OSPF.  They are described in the subsections 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", which are
   flavors defined in [RFC8986].  If the advertised value is zero or no
   value is advertised, then the router cannot apply the PSP or USP
   flavors.

4.3.  Maximum H.Encaps MSD Type

   The Maximum H.Encaps MSD Type signals the maximum number of SIDs that
   can be added as part of the H.Encaps behavior as defined in
   [RFC8986].  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 with SIDs
   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 include, but
   are not limited to, End.DX6, End.DT4, End.DT46, End with USD, and
   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 when the outer IPv6 header contains an SRH.

5.  SRv6 SIDs and Reachability

   An SRv6 SID is 128 bits and consists of locator, function, and
   argument parts as described in [RFC8986].

   An OSPFv3 router is provisioned with algorithm-specific locators for
   each algorithm supported by that router.  Each locator is a covering
   prefix for all SIDs provisioned on that router that have the matching
   algorithm.

   Locators MUST be advertised within an SRv6 Locator TLV (see
   Section 7.1) using an SRv6 Locator LSA (see Section 7).  The SRv6
   Locator LSA is introduced instead of reusing the respective Extended
   Prefix LSAs [RFC8362] for a clear distinction between the two
   different types of reachability advertisements (viz., the base OSPFv3
   prefix reachability advertisements and the SRv6 Locator reachability
   advertisements).

   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 OSPFv3 router.  Locators can be of different route
   types that map to existing OSPFv3 LSA types: Intra-Area, Inter-Area,
   External, and Not-So-Stubby Area (NSSA).  The advertisement and
   propagation of the SRv6 Locator LSAs also follow the OSPFv3 [RFC5340]
   specifications for the respective LSA types.  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 OSPFv3 [RFC5340] specifications for the respective LSA types.

   Locators associated with algorithms 0 and 1 (refer to Section 3.1.1
   of [RFC8402]) SHOULD also be advertised using Extended LSA types with
   extended TLVs [RFC8362] so that routers that do not support SRv6 will
   install a forwarding entry for SRv6 traffic matching those locators.
   When operating in Extended LSA sparse-mode [RFC8362], these locators
   SHOULD also be advertised using Legacy LSAs [RFC5340].

   When SRv6 Locators are also advertised as Intra-Area-Prefix-LSAs and/
   or E-Intra-Area-Prefix-LSAs, the SRv6 Locator MUST be considered as a
   prefix associated with the router, and the referenced LSA type MUST
   point to the Router LSA of the advertising router as specified in
   Section 4.4.3.9 of [RFC5340].

   In cases where a locator advertisement is received both in a prefix
   reachability advertisement (i.e., via Legacy LSAs and/or Extended
   Prefix TLVs using Extended LSAs) and an SRv6 Locator TLV, the prefix
   reachability advertisement in the Legacy LSA or Extended LSA MUST be
   preferred over the advertisement in the SRv6 Locator TLV when
   installing entries in the forwarding plane.  This prevents
   inconsistent forwarding entries between SRv6-capable and
   SRv6-incapable OSPFv3 routers.  Such preference for 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 and LAN End.X SIDs, which are associated with a
   specific neighbor/link and are therefore advertised as sub-TLVs of
   the E-Router-Link TLV.

   SRv6 SIDs received from other OSFPv3 routers 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 ensure 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 matching the locator prefix.

   If the locator associated with SRv6 SID advertisements is the longest
   prefix match installed in the forwarding plane for those SIDs, this
   will 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:

   *  Another locator associated with a different algorithm is the
      longest prefix match.

   *  Another prefix advertised via Legacy or Extended LSA advertisement
      is the longest prefix match.

5.1.  SRv6 Flexible Algorithm

   [RFC9350] specifies IGP Flexible Algorithm mechanisms for OSPFv3.
   Section 14.2 of [RFC9350] explains SRv6 forwarding for Flexible
   Algorithms, and analogous procedures apply for supporting SRv6
   Flexible Algorithms using OSPFv3.  When the algorithm value that is
   advertised in the SRv6 Locator TLV (refer to Section 7.1) represents
   a Flexible Algorithm, the procedures described in Section 14.2 of
   [RFC9350] are followed for the programming of those specific SRv6
   Locators.

   Locators associated with Flexible Algorithms SHOULD NOT be advertised
   in the base OSPFv3 prefix reachability advertisements.  Advertising
   the Flexible Algorithm locator in a regular prefix reachability
   advertisement would make it available for non-Flexible Algorithm
   forwarding (i.e., algorithm 0).

   The procedures for OSPFv3 Flexible Algorithm for SR-MPLS, as
   specified in [RFC9350], also apply for SRv6; these procedures include
   a) ASBR reachability, b) inter-area, external, and NSSA prefix
   advertisements, and c) the use of those prefix advertisements in
   Flexible Algorithm route computation.

6.  Advertisement of 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.

   The AC-bit (value 0x80) in the OSPFv3 PrefixOptions field [RFC5340]
   is defined to advertise the anycast property:

                          0  1  2  3  4  5  6  7
                         +--+--+--+--+--+--+--+--+
                         |AC|EL| N|DN| P| x|LA|NU|
                         +--+--+--+--+--+--+--+--+

                   Figure 2: OSPFv3 Prefix Options Field

   When the prefix/SRv6 Locator is configured as anycast, the AC-bit
   MUST be set.  Otherwise, this flag MUST be clear.

   The AC-bit MUST be preserved when re-advertising the prefix/SRv6
   Locator across areas.

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

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

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

   All the nodes advertising the same anycast SRv6 Locator MUST
   instantiate the exact same set of SIDs under that anycast SRv6
   Locator.  Failure to do so may result in traffic being dropped or
   misrouted.

   The PrefixOptions field is common to the prefix reachability
   advertisements (i.e., the base OSPFv3 prefix LSA types defined in
   [RFC5340], the OSPFv3 Extended Prefix TLV types defined in
   [RFC8362]), and the SRv6 Locator TLV advertisements specified in
   Section 7.1 of this document.  When a router originates both the
   prefix reachability advertisement and the SRv6 Locator advertisement
   for a given prefix, the router SHOULD advertise the same
   PrefixOptions bits in both advertisements.  In the case of any
   inconsistency between the PrefixOptions advertised in the SRv6
   Locator and in the prefix reachability advertisements, the ones
   advertised in the prefix reachability advertisement MUST be
   preferred.

7.  SRv6 Locator LSA

   The SRv6 Locator LSA has a function code of 42.  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 the 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             |U|S12|   Function Code         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Link State ID                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Advertising Router                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       LS sequence number                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |        LS checksum            |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +-                            TLVs                             -+
     |                             ...                               |

                         Figure 3: 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
   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...                           |
     .                                                               .
     .                                                               .
     .                                                               .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 4: 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.

7.1.  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 has to 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.

   The format of the 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| PrefixOptions |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                             Metric                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Locator (up to 16 octets) ...                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   ... Locator continued ...                                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   ... Locator continued ...                                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   ... Locator concluded                                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Sub-TLVs (variable)                      |
     +-                                                             -+
     |                             ...                               |

                         Figure 5: SRv6 Locator TLV

   where:

   Type:  2-octet field.  The value for this type is 1.

   Length:  2-octet field.  The total length (in octets) of the value
      portion of the TLV, including nested sub-TLVs.

   Route Type:  1-octet field.  The type of the locator route.  The only
      supported types are the ones listed below, and the SRv6 Locator
      TLV MUST be ignored on receipt of any other type.

      1:  Intra-Area
      2:  Inter-Area
      3:  AS External Type 1
      4:  AS External Type 2
      5:  NSSA External Type 1
      6:  NSSA External Type 2

   Algorithm:  1-octet field.  The algorithm associated with the SRv6
      Locator.  Algorithm values are defined in the "IGP Algorithm
      Types" registry [RFC8665].

   Locator Length:  1-octet field.  Specifies the length of the locator
      prefix as the number of locator bits from the range (1-128).

   PrefixOptions:  1-octet field.  Specifies the prefix options bits/
      flags as specified in [RFC5340] and further extended by [RFC8362]
      and Section 6 of this document.

   Metric:  4-octet field.  The metric value associated with the SRv6
      Locator.  The metric value of 0xFFFFFFFF MUST be considered as
      unreachable.

   Locator:  1-16 octets.  This field encodes the advertised SRv6
      Locator as an IPv6 Prefix as specified in Appendix A.4.1 of
      [RFC5340].

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

7.2.  SRv6 Locator Sub-TLVs

   The following OSPFv3 Extended-LSA sub-TLVs corresponding to the
   Extended Prefix LSAs are also applicable for use as sub-TLVs of the
   SRv6 Locator TLV using code points as specified in Section 13.9:

   *  IPv6-Forwarding-Address sub-TLV [RFC8362]

   *  Route-Tag sub-TLV [RFC8362]

   *  Prefix Source OSPF Router-ID sub-TLV [RFC9084]

   *  Prefix Source Router Address sub-TLV [RFC9084]

8.  Advertisement 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 7).  It is used to advertise the
   SRv6 SIDs belonging to the router along with their associated
   Endpoint behaviors.  SIDs associated with adjacencies are advertised
   as described in Section 9.  Every SRv6-enabled OSPFv3 router SHOULD
   advertise at least one SRv6 SID associated with an End behavior for
   itself as specified in [RFC8986], although it MAY omit doing so if
   that node is not going to be used as a Segment Endpoint (e.g., for TE
   or Topology Independent Loop-Free Alternate (TI-LFA)) by any SR
   Source Node.

   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.

   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 the 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 continued ...                                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   ... SID continued ...                                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   ... SID concluded                                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Sub-TLVs (variable) . . .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 6: SRv6 End SID Sub-TLV

   where:

   Type:  2-octet field.  The value for this type is 1.

   Length:  2-octet field.  The total length (in octets) of the value
      portion of the sub-TLV, including its nested sub-TLVs.

   Flags:  1-octet field.  Specifies the flags associated with the SID.
      No flags are currently defined, and this field MUST be set to 0 on
      transmission and MUST be ignored on receipt.

   Reserved:  1-octet field.  It MUST be set to 0 on transmission and
      MUST be ignored on receipt.

   Endpoint Behavior:  2-octet field.  The Endpoint behavior code point
      for this SRv6 SID as defined in [RFC8986].  Supported behavior
      values for this sub-TLV are defined in Section 11 of this
      document.  Unsupported or unrecognized behavior values are ignored
      by the receiver.

   SID:  16-octet field.  This field encodes the advertised SRv6 SID.

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

9.  Advertisement of SRv6 SIDs Associated with Adjacencies

   The SRv6 Endpoint behaviors defined in [RFC8986] include certain
   behaviors that 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, which is an instruction to forward to
   a specific neighbor on a specific link.  These SRv6 SIDs and others
   that are defined in [RFC8986], which are specific to links or
   adjacencies, need to be advertised to OSPFv3 routers within an area
   to steer SRv6 traffic over a specific link or adjacency.

   Therefore, SRv6 SIDs that are specific to a particular neighbor, such
   as End.X, are not advertised as a sub-TLVs of the SRv6 Locator TLV.
   Instead, they are advertised via two different optional sub-TLVs of
   the E-Router-Link TLV defined in [RFC8362]:

   SRv6 End.X SID sub-TLV:  Used for OSPFv3 adjacencies over point-to-
      point or point-to-multipoint links and for the adjacency to the
      Designated Router (DR) over broadcast and Non-Broadcast-Multi-
      Access (NBMA) links.

   SRv6 LAN End.X SID sub-TLV:  Used 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 as a sub-TLV of 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 neighbors,
   although it MAY omit doing so if features like TE or TI-LFA that
   require End.X SID are not in use.  A router MAY instantiate more than
   one SRv6 End.X SID 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 that is advertised by the same
   OSPFv3 router in an SRv6 Locator TLV.  End.X SIDs that do not meet
   this requirement MUST be ignored.  This ensures that the OSPFv3
   router 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.

9.1.  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 continued ...                                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   ... SID continued ...                                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   ... SID concluded                                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Sub-TLVs (variable) . . .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 7: SRv6 End.X SID Sub-TLV

   where:

   Type:  2-octet field.  The value for this type is 31.

   Length:  2-octet field.  The total length (in octets) of the value
      portion of the sub-TLV, including its nested sub-TLVs.

   Endpoint Behavior:  2-octet field.  The Endpoint behavior code point
      for this SRv6 SID as defined in [RFC8986].  Supported behavior
      values for this sub-TLV are defined in Section 11 of this
      document.  Unsupported or unrecognized behavior values are ignored
      by the receiver.

   Flags:  1-octet field.  The flags are defined as follows:

       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.

      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.

      Other flags are not defined and are reserved for future use.
      They MUST be set to 0 on transmission and MUST be ignored on
      receipt.

   Reserved1:  1-octet field.  It MUST be set to 0 on transmission and
      MUST be ignored on receipt.

   Algorithm:  1-octet field.  The algorithm associated with the SRv6
      Locator from which the SID is allocated.  Algorithm values are
      defined in the "IGP Algorithm Types" registry [RFC8665].

   Weight:  1-octet field.  Its value represents the weight of the End.X
      SID for load-balancing.  The use of the weight is defined in
      [RFC8402].

   Reserved2:  2-octet field.  It MUST be set to 0 on transmission and
      MUST be ignored on receipt.

   SID:  16-octet 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.

9.2.  SRv6 LAN End.X SID Sub-TLV

   The format of the SRv6 LAN End.X SID sub-TLV is as 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           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Neighbor Router-ID                                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   SID (128 bits) ...                                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   ... SID continued ...                                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   ... SID continued ...                                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   ... SID concluded                                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Sub-TLVs (variable) . . .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 8: SRv6 LAN End.X SID Sub-TLV

   where:

   Type:  2-octet field.  The value for this type is 32.

   Length:  2-octet field.  The total length (in octets) of the value
      portion of the sub-TLV, including its nested sub-TLVs.

   Endpoint Behavior:  2-octet field.  The code point for the Endpoint
      behavior for this SRv6 SID as defined in Section 9.2 of [RFC8986].

   Flags:  1-octet field.  The flags are defined as follows:

       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.

      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.

      Other flags are not defined and are reserved for future use.
      They MUST be set to 0 on transmission and MUST be ignored on
      receipt.

   Reserved1:  1-octet field.  It MUST be set to 0 on transmission and
      MUST be ignored on receipt.

   Algorithm:  1-octet field.  The algorithm associated with the SRv6
      Locator from which the SID is allocated.  Algorithm values are
      defined in the "IGP Algorithm Types" registry [RFC8665].

   Weight:  1-octet field.  Its value represents the weight of the End.X
      SID for load balancing.  The use of the weight is defined in
      [RFC8402].

   Reserved2:  2-octet field.  It MUST be set to 0 on transmission and
      MUST be ignored on receipt.

   Neighbor Router-ID:  4-octet field.  It specifies the OSPFv3 Router-
      ID of the neighbor.

   SID:  16-octet field.  This field encodes the advertised SRv6 SID.

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

10.  SRv6 SID Structure Sub-TLV

   The 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:

   *  SRv6 End SID sub-TLV (refer to Section 8)

   *  SRv6 End.X SID sub-TLV (refer to Section 9.1)

   *  SRv6 LAN End.X SID sub-TLV (refer to Section 9.2)

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

                    Figure 9: SRv6 SID Structure Sub-TLV

   where:

   Type:  2-octet field.  The value for this type is 30.

   Length:  2-octet field.  The value MUST be 4.

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

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

   Function Length:  1-octet field.  SRv6 SID Function length in bits.

   Argument Length:  1-octet field.  SRv6 SID Argument length in bits.

   The SRv6 SID Structure 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 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-TLV is larger than 128 bits,
   the parent TLV or 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 the following:

   *  Validation of SRv6 SIDs being instantiated in the network and
      advertised via OSPFv3.  These can be learned by controllers via
      BGP-LS [RFC9514] and then monitored for conformance to the SRv6
      SID allocation scheme chosen by the operator as described in
      Section 3.2 of [RFC8986].

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

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

11.  Advertising Endpoint Behaviors

   Endpoint behaviors are defined in [RFC8986].  The code points for the
   Endpoint behaviors are defined in the "SRv6 Endpoint Behaviors"
   registry of [RFC8986].  This section lists the Endpoint behaviors and
   their code points, which MAY be advertised by OSPFv3 and the sub-TLVs
   in which each type MAY appear.

    +===================+===================+=====+=======+===========+
    | Endpoint Behavior | Endpoint Behavior | End | End.X | LAN End.X |
    |                   | Code Point        | SID | SID   | SID       |
    +===================+===================+=====+=======+===========+
    | End (PSP, USP,    | 1-4, 28-31        | Y   | N     | N         |
    | USD)              |                   |     |       |           |
    +-------------------+-------------------+-----+-------+-----------+
    | End.X (PSP, USP,  | 5-8, 32-35        | N   | Y     | Y         |
    | USD)              |                   |     |       |           |
    +-------------------+-------------------+-----+-------+-----------+
    | 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         |
    +-------------------+-------------------+-----+-------+-----------+

                 Table 1: SRv6 Endpoint Behaviors in OSPFv3

12.  Security Considerations

   This document introduces extensions to the OSPFv3 protocol and, as
   such, does not affect existing security considerations for OSPFv3 as
   documented in [RFC5340].  [RFC7166] describes an alternative and
   improved authentication mechanism to IPsec for OSPFv3.  The use of
   authentication is RECOMMENDED for OSPFv3 deployment.

   Reception of a malformed TLV or sub-TLV SHOULD be counted and/or
   logged in a rate-limited manner for further analysis.

   This document describes the OSPFv3 extensions required to support SR
   over an IPv6 data plane.  The security considerations for SR are
   discussed in [RFC8402].  [RFC8986] defines the SRv6 Network
   Programming concept and specifies the main SR behaviors to enable the
   creation of interoperable overlays.  The security considerations from
   that document apply as well.

   The advertisement of 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 [RFC9259].

   Security concerns associated with the usage of Flexible Algorithms
   are described in [RFC9350].

13.  IANA Considerations

   Per this document, IANA has made allocations in OSPF- and
   OSPFv3-related registries and created new registries, as detailed in
   the following subsections.

13.1.  OSPF Router Information TLVs

   IANA has allocated the following code point in the "OSPF Router
   Information (RI) TLVs" registry within the "Open Shortest Path First
   (OSPF) Parameters" registry group:

            +=======+===================+=====================+
            | Value | TLV Name          | Reference           |
            +=======+===================+=====================+
            | 20    | SRv6 Capabilities | RFC 9513, Section 2 |
            +-------+-------------------+---------------------+

                                  Table 2

13.2.  OSPFv3 LSA Function Codes

   IANA has allocated the following code point in the "OSPFv3 LSA
   Function Codes" registry within the "Open Shortest Path First v3
   (OSPFv3) Parameters" registry group:

         +=======+========================+=====================+
         | Value | LSA Function Code Name | Reference           |
         +=======+========================+=====================+
         | 42    | SRv6 Locator LSA       | RFC 9513, Section 7 |
         +-------+------------------------+---------------------+

                                 Table 3

13.3.  OSPFv3 Prefix Options

   IANA has allocated the following code point in the "OSPFv3 Prefix
   Options (8 bits)" registry within the "Open Shortest Path First v3
   (OSPFv3) Parameters" registry group:

               +=======+=============+=====================+
               | Value | Description | Reference           |
               +=======+=============+=====================+
               | 0x80  | AC-bit      | RFC 9513, Section 6 |
               +-------+-------------+---------------------+

                                  Table 4

13.4.  OSPFv3 SRv6 Capabilities TLV Flags

   IANA has created a new subregistry named "OSPFv3 SRv6 Capabilities
   TLV Flags" within the "Open Shortest Path First v3 (OSPFv3)
   Parameters" registry group to control the assignment of bits 0 to 15
   in the Flags field of the OSPFv3 SRv6 Capabilities TLV specified in
   this document.  The registration procedure is "Standards Action" as
   defined in [RFC8126].

   The following assignment has been made per this document:

                +=====+=============+=====================+
                | Bit | Description | Reference           |
                +=====+=============+=====================+
                | 1   | O-flag      | RFC 9513, Section 2 |
                +-----+-------------+---------------------+

                                  Table 5

13.5.  OSPFv3 SRv6 End SID Sub-TLV Flags

   IANA has created a new subregistry named "OSPFv3 SRv6 End SID Sub-TLV
   Flags" within the "Open Shortest Path First v3 (OSPFv3) Parameters"
   registry group to control the assignment of bits 0 to 7 in the Flags
   field of the OSPFv3 SRv6 End SID sub-TLV specified in this document.
   The registration procedure is "Standards Action" as defined in
   [RFC8126].

   No assignments are made by this document.

13.6.  OSPFv3 SRv6 Adjacency SID Sub-TLV Flags

   IANA has created a new subregistry named "OSPFv3 SRv6 Adjacency SID
   Sub-TLV Flags" within the "Open Shortest Path First v3 (OSPFv3)
   Parameters" registry group to control the assignment of bits 0 to 7
   in the Flags field of the OSPFv3 SRv6 End.X SID and OSPFv3 SRv6 LAN
   End.X SID sub-TLVs specified in this document.  The registration
   procedure is "Standards Action" as defined in [RFC8126].

   The following assignments have been made per this document:

          +=====+=============+================================+
          | Bit | Description | Reference                      |
          +=====+=============+================================+
          | 0   | B-flag      | RFC 9513, Sections 9.1 and 9.2 |
          +-----+-------------+--------------------------------+
          | 1   | S-flag      | RFC 9513, Sections 9.1 and 9.2 |
          +-----+-------------+--------------------------------+
          | 2   | P-flag      | RFC 9513, Sections 9.1 and 9.2 |
          +-----+-------------+--------------------------------+

                                 Table 6

13.7.  OSPFv3 Extended-LSA Sub-TLVs

   IANA has allocated the following code points in the "OSPFv3 Extended-
   LSA Sub-TLVs" registry within the "Open Shortest Path First v3
   (OSPFv3) Parameters" registry group:

       +=======+====================+======+=======================+
       | Value | Description        | L2BM | Reference             |
       +=======+====================+======+=======================+
       | 30    | SRv6 SID Structure | Y    | RFC 9513, Section 10  |
       +-------+--------------------+------+-----------------------+
       | 31    | SRv6 End.X SID     | Y    | RFC 9513, Section 9.1 |
       +-------+--------------------+------+-----------------------+
       | 32    | SRv6 LAN End.X SID | Y    | RFC 9513, Section 9.2 |
       +-------+--------------------+------+-----------------------+

                                  Table 7

13.8.  OSPFv3 SRv6 Locator LSA TLVs

   IANA has created a new subregistry named "OSPFv3 SRv6 Locator LSA
   TLVs" within the "Open Shortest Path First v3 (OSPFv3) Parameters"
   registry group to define top-level TLVs for the OSPFv3 SRv6 Locator
   LSA.  The initial assignments are below:

             +=======+==============+=======================+
             | Value | Description  | Reference             |
             +=======+==============+=======================+
             | 0     | Reserved     | RFC 9513              |
             +-------+--------------+-----------------------+
             | 1     | SRv6 Locator | RFC 9513, Section 7.1 |
             +-------+--------------+-----------------------+

                                 Table 8

   Types in the range 0-32767 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 45056-65535 range, there
   MUST be an IETF specification that specifies IANA Considerations that
   cover the range being assigned.

13.9.  OSPFv3 SRv6 Locator LSA Sub-TLVs

   IANA has created a new subregistry named "OSPFv3 SRv6 Locator LSA
   Sub-TLVs" within the "Open Shortest Path First v3 (OSPFv3)
   Parameters" registry group to define sub-TLVs at any level of nesting
   for the SRv6 Locator LSA TLV.  The initial assignment are below:

         +=======+=========================+=====================+
         | Value | Description             | Reference           |
         +=======+=========================+=====================+
         | 0     | Reserved                | RFC 9513            |
         +-------+-------------------------+---------------------+
         | 1     | SRv6 End SID            | RFC 9513, Section 8 |
         +-------+-------------------------+---------------------+
         | 2     | IPv6-Forwarding-Address | [RFC8362]; RFC      |
         |       |                         | 9513, Section 7.2   |
         +-------+-------------------------+---------------------+
         | 3     | Route-Tag               | [RFC8362]; RFC      |
         |       |                         | 9513, Section 7.2   |
         +-------+-------------------------+---------------------+
         | 4     | Prefix Source OSPF      | [RFC9084]; RFC      |
         |       | Router-ID               | 9513, Section 7.2   |
         +-------+-------------------------+---------------------+
         | 5     | Prefix Source Router    | [RFC9084]; RFC      |
         |       | Address                 | 9513, Section 7.2   |
         +-------+-------------------------+---------------------+
         | 10    | SRv6 SID Structure      | RFC 9513,           |
         |       |                         | Section 10          |
         +-------+-------------------------+---------------------+

                                  Table 9

   Types in the range 0-32767 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 FCFS basis.

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

   The following note has been added to this registry to ensure that any
   document requesting allocations in this registry for sub-TLVs of any
   of the OSPFv3 SRv6 Locator TLVs checks if allocations are also
   applicable for the "OSPFv3 Extended-LSA Sub-TLVs" registry.

   |  Note: Allocations made in this registry for sub-TLVs that are
   |  associated with OSPFv3 SRv6 Locator TLVs MUST be evaluated for
   |  their applicability as OSPFv3 Extended-LSA sub-TLVs, which are
   |  required to be allocated in the "OSPFv3 Extended-LSA Sub-TLVs"
   |  registry.

13.10.  OSPFv3 Extended-LSA Sub-TLVs

   IANA has added the following note to the "OSPFv3 Extended-LSA Sub-
   TLVs" registry within the "Open Shortest Path First v3 (OSPFv3)
   Parameters" registry group.  The purpose of this note is to ensure
   that any document requesting allocations in this registry for sub-
   TLVs of any of the OSPFv3 Extended Prefix TLVs checks if allocations
   are also applicable for the "OSPFv3 SRv6 Locator LSA Sub-TLVs"
   registry defined in this document.

   |  Note: Allocations made in this registry for sub-TLVs that are
   |  associated with OSPFv3 Extended TLVs related to prefix
   |  advertisements MUST be evaluated for their applicability as OSPFv3
   |  SRv6 Locator sub-TLVs, which are required to be allocated in the
   |  "OSPFv3 SRv6 Locator LSA Sub-TLVs" registry.

14.  References

14.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [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>.

   [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>.

   [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>.

   [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>.

   [RFC9084]  Wang, A., Lindem, A., Dong, J., Psenak, P., and K.
              Talaulikar, Ed., "OSPF Prefix Originator Extensions",
              RFC 9084, DOI 10.17487/RFC9084, August 2021,
              <https://www.rfc-editor.org/info/rfc9084>.

   [RFC9259]  Ali, Z., Filsfils, C., Matsushima, S., Voyer, D., and M.
              Chen, "Operations, Administration, and Maintenance (OAM)
              in Segment Routing over IPv6 (SRv6)", RFC 9259,
              DOI 10.17487/RFC9259, June 2022,
              <https://www.rfc-editor.org/info/rfc9259>.

   [RFC9350]  Psenak, P., Ed., Hegde, S., Filsfils, C., Talaulikar, K.,
              and A. Gulko, "IGP Flexible Algorithm", RFC 9350,
              DOI 10.17487/RFC9350, February 2023,
              <https://www.rfc-editor.org/info/rfc9350>.

   [RFC9352]  Psenak, P., Ed., Filsfils, C., Bashandy, A., Decraene, B.,
              and Z. Hu, "IS-IS Extensions to Support Segment Routing
              over the IPv6 Data Plane", RFC 9352, DOI 10.17487/RFC9352,
              February 2023, <https://www.rfc-editor.org/info/rfc9352>.

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>.

   [RFC9514]  Dawra, G., Filsfils, C., Talaulikar, K., Ed., Chen, M.,
              Bernier, D., and B. Decraene, "Border Gateway Protocol -
              Link State (BGP-LS) Extensions for Segment Routing over
              IPv6 (SRv6)", RFC 9514, DOI 10.17487/RFC9514, December
              2023, <https://www.rfc-editor.org/info/rfc9514>.

Acknowledgements

   The authors would like to acknowledge the contributions of Dean Cheng
   in the early draft versions of this document.  The authors would like
   to thank Ran Chen and Detao Zhao for their suggestions related to the
   extension of PrefixOptions for the signaling of the anycast property.

   The authors would like to thank Chenzichao, Dirk Goethals, Baalajee
   S, Yingzhen Qu, Shraddha Hegde, Dhruv Dhody, Martin Vigoureux, and
   Reese Enghardt for their review and comments on this document.  The
   authors would like to thank Acee Lindem for his detailed shepherd
   review and feedback for improvement of this document.  The authors
   would like to thank John Scudder for his AD review and suggestions to
   improve this document.

Authors' Addresses

   Zhenbin Li
   Huawei Technologies
   Email: lizhenbin@huawei.com


   Zhibo Hu
   Huawei Technologies
   Email: huzhibo@huawei.com


   Ketan Talaulikar (editor)
   Cisco Systems
   India
   Email: ketant.ietf@gmail.com


   Peter Psenak
   Cisco Systems
   Slovakia
   Email: ppsenak@cisco.com