Link State Routing                                                 Z. Li
Internet-Draft                                                     Z. Hu
Intended status: Standards Track                     Huawei Technologies
Expires: 19 March 2023                                K. Talaulikar, Ed.
                                                              Arrcus Inc
                                                               P. Psenak
                                                           Cisco Systems
                                                       15 September 2022


                       OSPFv3 Extensions for SRv6
                draft-ietf-lsr-ospfv3-srv6-extensions-08

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 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 19 March 2023.

Copyright Notice

   Copyright (c) 2022 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



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  SRv6 Capabilities TLV . . . . . . . . . . . . . . . . . . . .   4
   3.  Advertisement of Supported Algorithms . . . . . . . . . . . .   5
   4.  Advertisement of Maximum SRv6 SID Depths  . . . . . . . . . .   5
     4.1.  Maximum Segments Left MSD Type  . . . . . . . . . . . . .   6
     4.2.  Maximum End Pop MSD Type  . . . . . . . . . . . . . . . .   6
     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 . . . . . . . . . . . . . . . . .   8
   6.  Advertisement of Anycast Property . . . . . . . . . . . . . .   9
   7.  SRv6 Locator LSA  . . . . . . . . . . . . . . . . . . . . . .  10
     7.1.  SRv6 Locator TLV  . . . . . . . . . . . . . . . . . . . .  11
     7.2.  SRv6 Locator Sub-TLVs . . . . . . . . . . . . . . . . . .  13
   8.  Advertisement of SRv6 End SIDs  . . . . . . . . . . . . . . .  13
   9.  Advertisement of SRv6 SIDs Associated with Adjacencies  . . .  15
     9.1.  SRv6 End.X SID Sub-TLV  . . . . . . . . . . . . . . . . .  16
     9.2.  SRv6 LAN End.X SID Sub-TLV  . . . . . . . . . . . . . . .  17
   10. SRv6 SID Structure Sub-TLV  . . . . . . . . . . . . . . . . .  19
   11. Advertising Endpoint Behaviors  . . . . . . . . . . . . . . .  21
   12. Security Considerations . . . . . . . . . . . . . . . . . . .  21
   13. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  22
     13.1.  OSPF Router Information TLVs . . . . . . . . . . . . . .  22
     13.2.  OSPFv3 LSA Function Codes  . . . . . . . . . . . . . . .  22
     13.3.  OSPFv3 Prefix Options  . . . . . . . . . . . . . . . . .  22
     13.4.  OSPFv3 Extended-LSA Sub-TLVs . . . . . . . . . . . . . .  23
     13.5.  OSPFv3 Locator LSA TLVs  . . . . . . . . . . . . . . . .  23
     13.6.  OSPFv3 Locator LSA Sub-TLVs  . . . . . . . . . . . . . .  23
   14. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  24
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . .  24
     15.1.  Normative References . . . . . . . . . . . . . . . . . .  25
     15.2.  Informative References . . . . . . . . . . . . . . . . .  26
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  27

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 OSPFv3 extensions to support SRv6 as defined
   in [RFC8986].  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 are defined 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 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.










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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.

   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 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 LSA 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.

   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...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      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.



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   *  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-bit 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] 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 and this needs 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
   [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:








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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.

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
   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 when the
   outer IPv6 header contains an SRH.

5.  SRv6 SIDs and Reachability

   An SRv6 Segment Identifier (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



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   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 similar to existing OSPFv3 route types - Intra-Area, Inter-
   Area, External, and NSSA.  The advertisement and propagation of the
   SRv6 Locator LSAs also follow the OSPFv3 [RFC5340] specifications for
   the respective route 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 route types.

   Locators associated with algorithms 0 and 1 SHOULD be advertised
   using the respective OSPFv3 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 be also advertised using the respective legacy OSPFv3 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 OSPFv3 LSAs and/or
   Extended Prefix TLVs using OSPFv3 Extended LSAs) and an SRv6 Locator
   TLV, the prefix reachability advertisement in the OSPFv3 legacy LSA
   or Extended LSA 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 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/LAN End.X SIDs which are associated with a
   specific Neighbor/Link and are therefore advertised as Sub-TLVs of E-
   Router-Link TLV.





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   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 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 matching the locator prefix.

   For forwarding to work correctly, the locator associated with SRv6
   SID advertisements must be the longest prefix match installed in the
   forwarding plane for those SIDs.  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:

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

   *  Another prefix advertised via OSPFv3 legacy or Extended LSA
      advertisement is the longest prefix 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 Flexible Algorithm and the same applies to supporting
   SRv6 Flexible Algorithm 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 [I-D.ietf-lsr-flex-algo] 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 them available for non-Flexible Algorithm
   forwarding (i.e., algorithm 0).

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






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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.

   A new bit in OSPFv3 PrefixOptions [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

   Value: 0x80

   Description: Anycast (AC-bit)

   When the prefix/SRv6 Locator is configured as anycast, the AC-bit
   SHOULD 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 both N-bit and AC-
   bit are 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 SHOULD be 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] and 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



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   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 prefix reachability advertisement MUST be preferred.

7.  SRv6 Locator LSA

   The SRv6 Locator LSA has a function code of 42 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 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:






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

                   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 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.

   The format of SRv6 Locator TLV is 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            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Route Type   |  Algorithm    | Locator Length| PrefixOptions |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                             Metric                            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Locator (128 bits) ...                                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Locator continued ...                                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Locator continued ...                                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Locator continued ...                                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                      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 Type
      registry.

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



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      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.

      Locator: 16-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 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 13.6:

   *  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].

   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 continued ...                                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID continued ...                                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID continued ...                                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   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 further nested Sub-TLVs.

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

      Flags: 1-octet field.  It 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.

      Endpoint Behavior: 2 octets 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.



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      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 that 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.

   The advertisement of SRv6 SIDs that are specific to a particular
   neighbor is accomplished 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.  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 which is advertised by the same
   OSPFv3 router in an SRv6 Locator TLV.  End.X SIDs which 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.




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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 continued ...                                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    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 further 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.



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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.

      -  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 Type registry.

      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:

















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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 continued ...                                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID continued ...                                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID continued ...                                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | 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 further 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).




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      -  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 Type registry.

   *  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 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

   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:








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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 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 bit 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/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:

   *  validation of SRv6 SIDs being instantiated in the network and
      advertised via OSPFv3.  These can be learned 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].

   *  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.

11.  Advertising Endpoint Behaviors

   Endpoint behaviors are defined in [RFC8986].  The codepoints for the
   Endpoint behaviors are defined in the "SRv6 Endpoint Behaviors"
   registry 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 10: SRv6 Endpoint Behaviors in OSPFv3

12.  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
   rate-limited to prevent a Denial of Service (DoS) attack (distributed
   or otherwise) from overloading the OSPFv3 control plane.



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   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 [RFC9259].

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

13.  IANA Considerations

   This document requests IANA to perform allocations from OSPF and
   OSPFv3 related registries as well as creating of new registries as
   follows.

13.1.  OSPF Router Information TLVs

   IANA has allocated a code point via the early allocation process in
   the "OSPF Router Information (RI) TLVs" registry under the "OSPF
   Parameters" registry for the new TLV below that needs to be made
   permanent:

      Type 20: SRv6-Capabilities TLV: Refer to Section 2 of this
      document.

13.2.  OSPFv3 LSA Function Codes

   IANA has allocated a code point via the early allocation process in
   the "OSPFv3 LSA Function Codes" registry under the "OSPFv3
   Parameters" registry for the new LSA below that needs to be made
   permanent:

   *  Type 42: SRv6 Locator LSA: Refer to Section 7 of this document.

13.3.  OSPFv3 Prefix Options

   IANA has allocated a code point via the early allocation process in
   the "OSPFv3 Prefix Options" registry under the "OSPFv3 Parameters"
   registry as below that needs to be made permanent:

   *  Value 0x80: AC-bit: Refer to Section 6 of this document.



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13.4.  OSPFv3 Extended-LSA Sub-TLVs

   IANA has allocated the following code points via the early allocation
   process in the "OSPFv3 Extended-LSA Sub-TLVs" registry under the
   "OSPFv3 Parameters" registry for the new Sub-TLVs below that need to
   be made permanent:

   *  Type 30: SRv6 SID Structure Sub-TLV: Refer to Section 10 of this
      document.

   *  Type 31: SRv6 End.X SID Sub-TLV: Refer to Section 9.1 of this
      document.

   *  Type 32: SRv6 LAN End.X SID Sub-TLV: Refer to Section 9.2 of this
      document.

13.5.  OSPFv3 Locator LSA TLVs

   This document requests the creation of an "OSPFv3 Locator LSA TLVs"
   registry, that defines top-level TLVs for the OSPFv3 SRv6 Locator
   LSA, under the "OSPFv3 Parameters" registry.  The initial code-points
   assignment is as below:

   *  Type 0: Reserved.

   *  Type 1: SRv6 Locator TLV: Refer to Section 7.1 of this document.

   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.

13.6.  OSPFv3 Locator LSA Sub-TLVs

   This document requests the creation of an "OSPFv3 Locator LSA Sub-
   TLVs" registry, that defines Sub-TLVs at any level of nesting for the
   SRv6 Locator LSA, to be added under the "OSPFv3 Parameters" registry.
   The initial code-points assignment is as below:



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   *  Type 0: Reserved.

   *  Type 1: SRv6 End SID Sub-TLV: Refer to Section 8 of this document.

   *  Type 2: IPv6-Forwarding-Address sub-TLV: Refer to [RFC8362] and
      Section 7.2 of this document.

   *  Type 3: Route-Tag sub-TLV: Refer to [RFC8362] and Section 7.2 of
      this document.

   *  Type 4: Prefix Source OSPF Router-ID sub-TLV: Refer to [RFC9084]
      and Section 7.2 of this document.

   *  Type 5: Prefix Source Router Address sub-TLV: Refer to [RFC9084]
      and Section 7.2 of this document.

   *  Type 10: SRv6 SID Structure Sub-TLV: Refer to Section 10 of this
      document.

   Types in the range 6-9 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.

14.  Acknowledgements

   The authors would like to acknowledge the contributions of Dean Cheng
   in the early 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, and Dhruv Dhody 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.

15.  References



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15.1.  Normative References

   [I-D.ietf-lsr-flex-algo]
              Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
              A. Gulko, "IGP Flexible Algorithm", Work in Progress,
              Internet-Draft, draft-ietf-lsr-flex-algo-22, 12 September
              2022, <https://www.ietf.org/archive/id/draft-ietf-lsr-
              flex-algo-22.txt>.

   [I-D.ietf-lsr-isis-srv6-extensions]
              Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
              Z. Hu, "IS-IS Extensions to Support Segment Routing over
              IPv6 Dataplane", Work in Progress, Internet-Draft, draft-
              ietf-lsr-isis-srv6-extensions-18, 20 October 2021,
              <https://www.ietf.org/archive/id/draft-ietf-lsr-isis-srv6-
              extensions-18.txt>.

   [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>.

   [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>.







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   [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>.

15.2.  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>.



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

   [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


   Ketan Talaulikar (editor)
   Arrcus Inc
   India
   Email: ketant.ietf@gmail.com


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




















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