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RFC 8362

Proposed STD
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OSPFv3 Link State Advertisement (LSA) Extensibility

Part 1 of 2, p. 1 to 16
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Updates:    5340    5838


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Internet Engineering Task Force (IETF)                         A. Lindem
Request for Comments: 8362                                        A. Roy
Updates: 5340, 5838                                        Cisco Systems
Category: Standards Track                                    D. Goethals
ISSN: 2070-1721                                                    Nokia
                                                         V. Reddy Vallem
 
                                                                F. Baker
                                                              April 2018


          OSPFv3 Link State Advertisement (LSA) Extensibility

Abstract

   OSPFv3 requires functional extension beyond what can readily be done
   with the fixed-format Link State Advertisement (LSA) as described in
   RFC 5340.  Without LSA extension, attributes associated with OSPFv3
   links and advertised IPv6 prefixes must be advertised in separate
   LSAs and correlated to the fixed-format LSAs.  This document extends
   the LSA format by encoding the existing OSPFv3 LSA information in
   Type-Length-Value (TLV) tuples and allowing advertisement of
   additional information with additional TLVs.  Backward-compatibility
   mechanisms are also described.

   This document updates RFC 5340, "OSPF for IPv6", and RFC 5838,
   "Support of Address Families in OSPFv3", by providing TLV-based
   encodings for the base OSPFv3 unicast support and OSPFv3 address
   family support.

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/rfc8362.

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Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Notation . . . . . . . . . . . . . . . . . .   4
     1.2.  OSPFv3 LSA Terminology  . . . . . . . . . . . . . . . . .   4
   2.  OSPFv3 Extended LSA Types . . . . . . . . . . . . . . . . . .   4
   3.  OSPFv3 Extended LSA TLVs  . . . . . . . . . . . . . . . . . .   5
     3.1.  Prefix Options Extensions . . . . . . . . . . . . . . . .   6
       3.1.1.  N-bit Prefix Option . . . . . . . . . . . . . . . . .   7
     3.2.  Router-Link TLV . . . . . . . . . . . . . . . . . . . . .   8
     3.3.  Attached-Routers TLV  . . . . . . . . . . . . . . . . . .   9
     3.4.  Inter-Area-Prefix TLV . . . . . . . . . . . . . . . . . .  10
     3.5.  Inter-Area-Router TLV . . . . . . . . . . . . . . . . . .  11
     3.6.  External-Prefix TLV . . . . . . . . . . . . . . . . . . .  12
     3.7.  Intra-Area-Prefix TLV . . . . . . . . . . . . . . . . . .  13
     3.8.  IPv6 Link-Local Address TLV . . . . . . . . . . . . . . .  14
     3.9.  IPv4 Link-Local Address TLV . . . . . . . . . . . . . . .  14
     3.10. IPv6-Forwarding-Address Sub-TLV . . . . . . . . . . . . .  15
     3.11. IPv4-Forwarding-Address Sub-TLV . . . . . . . . . . . . .  15
     3.12. Route-Tag Sub-TLV . . . . . . . . . . . . . . . . . . . .  16
   4.  OSPFv3 Extended LSAs  . . . . . . . . . . . . . . . . . . . .  16
     4.1.  OSPFv3 E-Router-LSA . . . . . . . . . . . . . . . . . . .  16
     4.2.  OSPFv3 E-Network-LSA  . . . . . . . . . . . . . . . . . .  18
     4.3.  OSPFv3 E-Inter-Area-Prefix-LSA  . . . . . . . . . . . . .  19
     4.4.  OSPFv3 E-Inter-Area-Router-LSA  . . . . . . . . . . . . .  20
     4.5.  OSPFv3 E-AS-External-LSA  . . . . . . . . . . . . . . . .  21
     4.6.  OSPFv3 E-NSSA-LSA . . . . . . . . . . . . . . . . . . . .  22
     4.7.  OSPFv3 E-Link-LSA . . . . . . . . . . . . . . . . . . . .  22
     4.8.  OSPFv3 E-Intra-Area-Prefix-LSA  . . . . . . . . . . . . .  24
   5.  Malformed OSPFv3 Extended LSA Handling  . . . . . . . . . . .  25
   6.  LSA Extension Backward Compatibility  . . . . . . . . . . . .  25
     6.1.  Full Extended LSA Migration . . . . . . . . . . . . . . .  25
     6.2.  Extended LSA Sparse-Mode Backward Compatibility . . . . .  26

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     6.3.  LSA TLV Processing Backward Compatibility . . . . . . . .  26
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  27
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  27
     8.1.  OSPFv3 Extended LSA TLV Registry  . . . . . . . . . . . .  27
     8.2.  OSPFv3 Extended LSA Sub-TLV Registry  . . . . . . . . . .  28
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  29
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  29
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  30
   Appendix A.  Global Configuration Parameters  . . . . . . . . . .  31
   Appendix B.  Area Configuration Parameters  . . . . . . . . . . .  31
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  32
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  32
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  33

1.  Introduction

   OSPFv3 requires functional extension beyond what can readily be done
   with the fixed-format Link State Advertisement (LSA) as described in
   RFC 5340 [OSPFV3].  Without LSA extension, attributes associated with
   OSPFv3 links and advertised IPv6 prefixes must be advertised in
   separate LSAs and correlated to the fixed-format LSAs.  This document
   extends the LSA format by encoding the existing OSPFv3 LSA
   information in Type-Length-Value (TLV) tuples and allowing
   advertisement of additional information with additional TLVs.
   Backward-compatibility mechanisms are also described.

   This document updates RFC 5340, "OSPF for IPv6", and RFC 5838,
   "Support of Address Families in OSPFv3", by providing TLV-based
   encodings for the base OSPFv3 support [OSPFV3] and OSPFv3 address
   family support [OSPFV3-AF].

   A similar extension was previously proposed in support of multi-
   topology routing.  Additional requirements for the OSPFv3 LSA
   extension include source/destination routing, route tagging, and
   others.

   A final requirement is to limit the changes to OSPFv3 to those
   necessary for TLV-based LSAs.  For the most part, the semantics of
   existing OSPFv3 LSAs are retained for their TLV-based successor LSAs
   described herein.  Additionally, encoding details, e.g., the
   representation of IPv6 prefixes as described in Appendix A.4.1 in RFC
   5340 [OSPFV3], have been retained.  This requirement was included to
   increase the expedience of IETF adoption and deployment.

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   The following aspects of the OSPFv3 LSA extension are described:

   1.  Extended LSA Types

   2.  Extended LSA TLVs

   3.  Extended LSA Formats

   4.  Backward Compatibility

1.1.  Requirements Notation

   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.

1.2.  OSPFv3 LSA Terminology

   The TLV-based OSPFv3 LSAs described in this document will be referred
   to as Extended LSAs.  The OSPFv3 fixed-format LSAs [OSPFV3] will be
   referred to as Legacy LSAs.

2.  OSPFv3 Extended LSA Types

   In order to provide backward compatibility, new LSA codes must be
   allocated.  There are eight fixed-format LSAs defined in RFC 5340
   [OSPFV3].  For ease of implementation and debugging, the LSA function
   codes are the same as the fixed-format LSAs only with 32, i.e., 0x20,
   added.  The alternative to this mapping was to allocate a bit in the
   LS Type indicating the new LSA format.  However, this would have used
   one half the LSA function code space for the migration of the eight
   original fixed-format LSAs.  For backward compatibility, the U-bit
   MUST be set in the LS Type so that the LSAs will be flooded by OSPFv3
   routers that do not understand them.

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            LSA function code   LS Type   Description
            ----------------------------------------------------
            33                  0xA021    E-Router-LSA
            34                  0xA022    E-Network-LSA
            35                  0xA023    E-Inter-Area-Prefix-LSA
            36                  0xA024    E-Inter-Area-Router-LSA
            37                  0xC025    E-AS-External-LSA
            38                  N/A       Unused (Not to be allocated)
            39                  0xA027    E-Type-7-LSA
            40                  0x8028    E-Link-LSA
            41                  0xA029    E-Intra-Area-Prefix-LSA


                         OSPFv3 Extended LSA Types

3.  OSPFv3 Extended LSA TLVs

   The format of the TLVs within the body of the Extended LSAs is the
   same as the format used by the Traffic Engineering Extensions to OSPF
   [TE].  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...                           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                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.

   This document defines the following top-level TLV types:

   o  0 - Reserved

   o  1 - Router-Link TLV

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   o  2 - Attached-Routers TLV

   o  3 - Inter-Area-Prefix TLV

   o  4 - Inter-Area-Router TLV

   o  5 - External-Prefix TLV

   o  6 - Intra-Area-Prefix TLV

   o  7 - IPv6 Link-Local Address TLV

   o  8 - IPv4 Link-Local Address TLV

   Additionally, this document defines the following sub-TLV types:

   o  0 - Reserved

   o  1 - IPv6-Forwarding-Address sub-TLV

   o  2 - IPv4-Forwarding-Address sub-TLV

   o  3 - Route-Tag sub-TLV

   In general, TLVs and sub-TLVs MAY occur in any order, and the
   specification should define whether the TLV or sub-TLV is required
   and the behavior when there are multiple occurrences of the TLV or
   sub-TLV.  While this document only describes the usage of TLVs and
   sub-TLVs, sub-TLVs may be nested to any level as long as the sub-TLVs
   are fully specified in the specification for the subsuming sub-TLV.

   For backward compatibility, an LSA is not considered malformed from a
   TLV perspective unless either a required TLV is missing or a
   specified TLV is less than the minimum required length.  Refer to
   Section 6.3 for more information on TLV backward compatibility.

3.1.  Prefix Options Extensions

   The prefix options are extended from Appendix A.4.1.1 [OSPFV3].  The
   applicability of the LA-bit is expanded, and it SHOULD be set in
   Inter-Area-Prefix TLVs and MAY be set in External-Prefix TLVs when
   the advertised host IPv6 address, i.e., PrefixLength = 128 for the
   IPv6 Address Family or PrefixLength = 32 for the IPv4 Address Family
   [OSPFV3-AF], is an interface address.  In RFC 5340, the LA-bit is
   only set in Intra-Area-Prefix-LSAs (Section 4.4.3.9 of [OSPFV3]).
   This will allow a stable address to be advertised without having to
   configure a separate loopback address in every OSPFv3 area.

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3.1.1.  N-bit Prefix Option

   Additionally, the N-bit prefix option is defined.  The figure below
   shows the position of the N-bit in the prefix options (value 0x20).

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

                         The Prefix Options Field

   The N-bit is set in PrefixOptions for a host address
   (PrefixLength=128 for the IPv6 Address Family or PrefixLength=32 for
   the IPv4 Address Family [OSPFV3-AF]) that identifies the advertising
   router.  While it is similar to the LA-bit, there are two
   differences.  The advertising router MAY choose NOT to set the N-bit
   even when the above conditions are met.  If the N-bit is set and the
   PrefixLength is NOT 128 for the IPv6 Address Family or 32 for the
   IPv4 Address Family [OSPFV3-AF], the N-bit MUST be ignored.
   Additionally, the N-bit is propagated in the PrefixOptions when an
   OSPFv3 Area Border Router (ABR) originates an Inter-Area-Prefix-LSA
   for an Intra-Area route that has the N-bit set in the PrefixOptions.
   Similarly, the N-bit is propagated in the PrefixOptions when an
   OSPFv3 Not-So-Stubby Area (NSSA) ABR originates an E-AS-External-LSA
   corresponding to an NSSA route as described in Section 3 of RFC 3101
   [NSSA].  The N-bit is added to the Inter-Area-Prefix TLV
   (Section 3.4), External-Prefix TLV (Section 3.6), and
   Intra-Area-Prefix-TLV (Section 3.7).  The N-bit is used as hint to
   identify the preferred address to reach the advertising OSPFv3
   router.  This would be in contrast to an anycast address
   [IPV6-ADDRESS-ARCH], which could also be a local address with the
   LA-bit set.  It is useful for applications such as identifying the
   prefixes corresponding to Node Segment Identifiers (SIDs) in Segment
   Routing [SEGMENT-ROUTING].  There may be future applications
   requiring selection of a prefix associated with an OSPFv3 router.

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3.2.  Router-Link TLV

   The Router-Link TLV defines a single router link, and the field
   definitions correspond directly to links in the OSPFv3 Router-LSA;
   see Appendix A.4.3 of [OSPFV3].  The Router-Link TLV is only
   applicable to the E-Router-LSA (Section 4.1).  Inclusion in other
   Extended LSAs MUST be ignored.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          1 (Router-Link)      |       TLV Length              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Type      |       0       |           Metric              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Interface ID                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   Neighbor Interface ID                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    Neighbor Router ID                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      .                                                               .
      .                            Sub-TLVs                           .
      .                                                               .
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                              Router-Link TLV

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3.3.  Attached-Routers TLV

   The Attached-Routers TLV defines all the routers attached to an
   OSPFv3 multi-access network.  The field definitions correspond
   directly to content of the OSPFv3 Network-LSA; see Appendix A.4.4 of
   [OSPFV3].  The Attached-Routers TLV is only applicable to the
   E-Network-LSA (Section 4.2).  Inclusion in other Extended LSAs MUST
   be ignored.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        2 (Attached-Routers)   |       TLV Length              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |              Adjacent Neighbor Router ID                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      .                                                               .
      .              Additional Adjacent Neighbors                    .
      .                                                               .
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                           Attached-Routers TLV

   There are two reasons for not having a separate TLV or sub-TLV for
   each adjacent neighbor.  The first is to discourage using the
   E-Network-LSA for more than its current role of solely advertising
   the routers attached to a multi-access network.  The router's metric
   as well as the attributes of individual attached routers should be
   advertised in their respective E-Router-LSAs.  The second reason is
   that there is only a single E-Network-LSA per multi-access link with
   the Link State ID set to the Designated Router's Interface ID, and
   consequently, compact encoding has been chosen to decrease the
   likelihood that the size of the E-Network-LSA will require IPv6
   fragmentation when advertised in an OSPFv3 Link State Update packet.

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3.4.  Inter-Area-Prefix TLV

   The Inter-Area-Prefix TLV defines a single OSPFV3 inter-area prefix.
   The field definitions correspond directly to the content of an OSPFv3
   IPv6 Prefix, as defined in Appendix A.4.1 of [OSPFV3], and an OSPFv3
   Inter-Area-Prefix-LSA, as defined in Appendix A.4.5 of [OSPFV3].
   Additionally, the PrefixOptions are extended as described in
   Section 3.1.  The Inter-Area-Prefix TLV is only applicable to the
   E-Inter-Area-Prefix-LSA (Section 4.3).  Inclusion in other Extended
   LSAs MUST be ignored.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       3 (Inter-Area Prefix)   |       TLV Length              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      0        |                  Metric                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | PrefixLength  | PrefixOptions |              0                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Address Prefix                         |
      |                             ...                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      .                                                               .
      .                            Sub-TLVs                           .
      .                                                               .
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                           Inter-Area-Prefix TLV

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3.5.  Inter-Area-Router TLV

   The Inter-Area-Router TLV defines a single OSPFv3 Autonomous System
   Boundary Router (ASBR) that is reachable in another area.  The field
   definitions correspond directly to the content of an OSPFv3
   Inter-Area-Router-LSA, as defined in Appendix A.4.6 of [OSPFV3].  The
   Inter-Area-Router TLV is only applicable to the
   E-Inter-Area-Router-LSA (Section 4.4).  Inclusion in other Extended
   LSAs MUST be ignored.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       4 (Inter-Area Router)   |       TLV Length              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      0        |                Options                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      0        |                Metric                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Destination Router ID                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      .                                                               .
      .                            Sub-TLVs                           .
      .                                                               .
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                           Inter-Area-Router TLV

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3.6.  External-Prefix TLV

   The External-Prefix TLV defines a single OSPFv3 external prefix.
   With the exception of omitted fields noted below, the field
   definitions correspond directly to the content of an OSPFv3 IPv6
   Prefix, as defined in Appendix A.4.1 of [OSPFV3], and an OSPFv3
   AS-External-LSA, as defined in Appendix A.4.7 of [OSPFV3].  The
   External-Prefix TLV is only applicable to the E-AS-External-LSA
   (Section 4.5) and the E-NSSA-LSA (Section 4.6).  Additionally, the
   PrefixOptions are extended as described in Section 3.1.  Inclusion in
   other Extended LSAs MUST be ignored.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       5 (External Prefix)     |       TLV Length              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         |E| | |                Metric                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | PrefixLength  | PrefixOptions |              0                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Address Prefix                         |
      |                             ...                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      .                                                               .
      .                            Sub-TLVs                           .
      .                                                               .
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                            External-Prefix TLV

   In the External-Prefix TLV, the optional IPv6/IPv4 Forwarding Address
   and External Route Tag are now sub-TLVs.  Given the Referenced LS
   Type and Referenced Link State ID from the AS-External-LSA have never
   been used or even specified, they have been omitted from the
   External-Prefix TLV.  If there were ever a requirement for a
   referenced LSA, it could be satisfied with a sub-TLV.

   The following sub-TLVs are defined for optional inclusion in the
   External-Prefix TLV:

   o  1 - IPv6-Forwarding-Address sub-TLV (Section 3.10)

   o  2 - IPv4-Forwarding-Address sub-TLV (Section 3.11)

   o  3 - Route-Tag sub-TLV (Section 3.12)

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3.7.  Intra-Area-Prefix TLV

   The Intra-Area-Prefix TLV defines a single OSPFv3 intra-area prefix.
   The field definitions correspond directly to the content of an OSPFv3
   IPv6 Prefix, as defined in Appendix A.4.1 of [OSPFV3], and an OSPFv3
   Link-LSA, as defined in Appendix A.4.9 of [OSPFV3].  The
   Intra-Area-Prefix TLV is only applicable to the E-Link-LSA
   (Section 4.7) and the E-Intra-Area-Prefix-LSA (Section 4.8).
   Additionally, the PrefixOptions are extended as described in
   Section 3.1.  Inclusion in other Extended LSAs MUST be ignored.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       6 (Intra-Area Prefix)   |       TLV Length              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      0        |                  Metric                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | PrefixLength  | PrefixOptions |              0                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Address Prefix                         |
      |                             ...                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      .                                                               .
      .                            Sub-TLVs                           .
      .                                                               .
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                           Intra-Area-Prefix TLV

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3.8.  IPv6 Link-Local Address TLV

   The IPv6 Link-Local Address TLV is to be used with IPv6 address
   families as defined in [OSPFV3-AF].  The IPv6 Link-Local Address TLV
   is only applicable to the E-Link-LSA (Section 4.7).  Inclusion in
   other Extended LSAs MUST be ignored.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  7 (IPv6 Local-Local Address) |       TLV Length              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +-                                                             -+
      |                                                               |
      +-            IPv6 Link-Local Interface Address                -+
      |                                                               |
      +-                                                             -+
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      .                                                               .
      .                            Sub-TLVs                           .
      .                                                               .
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        IPv6 Link-Local Address TLV

3.9.  IPv4 Link-Local Address TLV

   The IPv4 Link-Local Address TLV is to be used with IPv4 address
   families as defined in [OSPFV3-AF].  The IPv4 Link-Local Address TLV
   is only applicable to the E-Link-LSA (Section 4.7).  Inclusion in
   other Extended LSAs MUST be ignored.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  8 (IPv4 Local-Local Address) |       TLV Length              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |             IPv4 Link-Local Interface Address                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      .                                                               .
      .                            Sub-TLVs                           .
      .                                                               .
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        IPv4 Link-Local Address TLV

Top      ToC       Page 15 
3.10.  IPv6-Forwarding-Address Sub-TLV

   The IPv6-Forwarding-Address TLV has identical semantics to the
   optional forwarding address in Appendix A.4.7 of [OSPFV3].  The IPv6-
   Forwarding-Address TLV is applicable to the External-Prefix TLV
   (Section 3.6).  Specification as a sub-TLV of other TLVs is not
   defined herein.  The sub-TLV is optional and the first specified
   instance is used as the forwarding address as defined in [OSPFV3].
   Instances subsequent to the first MUST be ignored.

   The IPv6-Forwarding-Address TLV is to be used with IPv6 address
   families as defined in [OSPFV3-AF].  It MUST be ignored for other
   address families.  The IPv6-Forwarding-Address TLV length must meet a
   minimum length (16 octets), or it will be considered malformed as
   described in Section 6.3.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       1 - Forwarding Address  |          sub-TLV Length       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +-                                                             -+
      |                                                               |
      +-                    Forwarding Address                       -+
      |                                                               |
      +-                                                             -+
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        IPv6-Forwarding-Address TLV

3.11.  IPv4-Forwarding-Address Sub-TLV

   The IPv4-Forwarding-Address TLV has identical semantics to the
   optional forwarding address in Appendix A.4.7 of [OSPFV3].  The
   IPv4-Forwarding-Address TLV is applicable to the External-Prefix TLV
   (Section 3.6).  Specification as a sub-TLV of other TLVs is not
   defined herein.  The sub-TLV is optional, and the first specified
   instance is used as the forwarding address as defined in [OSPFV3].
   Instances subsequent to the first MUST be ignored.

   The IPv4-Forwarding-Address TLV is to be used with IPv4 address
   families as defined in [OSPFV3-AF].  It MUST be ignored for other
   address families.  The IPv4-Forwarding-Address TLV length must meet a
   minimum length (4 octets), or it will be considered malformed as
   described in Section 6.3.

Top      ToC       Page 16 
       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       2 - Forwarding Address  |          sub-TLV Length       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Forwarding Address                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        IPv4-Forwarding-Address TLV

3.12.  Route-Tag Sub-TLV

   The optional Route-Tag sub-TLV has identical semantics to the
   optional External Route Tag in Appendix A.4.7 of [OSPFV3].  The
   Route-Tag sub-TLV is applicable to the External-Prefix TLV
   (Section 3.6).  Specification as a sub-TLV of other TLVs is not
   defined herein.  The sub-TLV is optional, and the first specified
   instance is used as the Route Tag as defined in [OSPFV3].  Instances
   subsequent to the first MUST be ignored.

   The Route-Tag TLV length must meet a minimum length (4 octets), or it
   will be considered malformed as described in Section 6.3.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       3 - Route Tag           |          sub-TLV Length       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Route Tag                            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                             Route-Tag Sub-TLV



(page 16 continued on part 2)

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