LSR Working Group                                                A. Wang
Internet-Draft                                             China Telecom
Intended status: Standards Track                               A. Lindem
Expires: May 28, 2020 January 1, 2021                                   Cisco Systems
                                                                 J. Dong
                                                     Huawei Technologies
                                                               P. Psenak
                                                           K. Talaulikar
                                                           Cisco Systems
                                                       November 25, 2019
                                                           June 30, 2020

                   OSPF Prefix Originator Extension
                draft-ietf-lsr-ospf-prefix-originator-05 Extensions
                draft-ietf-lsr-ospf-prefix-originator-06

Abstract

   This document defines Open Shortest Path First (OSPF) encodings OSPF extensions to
   advertise include information
   associated with the router-id of node originating a prefix along with the originator of inter-area prefixes for
   OSPFv2 and OSPFv3 Link-State Advertisements (LSAs).  The source
   originator is needed in several multi-area OSPF use cases. prefix
   advertisement.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document
     1.1.  Requirements Language . . . . . . . . . . . . . .   3
   3.  Terminology . . . .   3
   2.  Protocol Extensions . . . . . . . . . . . . . . . . . . . . .   3
   4.  Inter-Area
     2.1.  Prefix Source Advertisement Use Cases Router-ID Sub-TLV . . . . . .   4
   5.  External Prefix Source Advertisement Use Cases . . . . . . .   5
   6.   4
     2.2.  Prefix Source Router-ID sub-TLV Originator Sub-TLV . . . . . . . . . . . . . . .   6
   7. .   4
   3.  Elements of Procedure . . . . . . . . . . . . . . . . . . . .   7
     7.1.  Inter-Area Prefixes . . . . . . . . . . . . . . . . . . .   7
     7.2.  External Prefixes . . . . . . . . . . . . . . . . . . . .   7
   8.   5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   9.   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   10.   7
   6.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .   8
   11.   7
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     11.1.   7
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     11.2.   7
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  10   8
   Appendix A.  Inter-Area Topology Retrieval Process  . . . . . . .  10   9
   Appendix B.  Special Considerations on Inter-Area Topology
                Retrieval  . . . . . . . . . . . . . . . . . . . . .  11  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11  10

1.  Introduction

   [I-D.ietf-ospf-mpls-elc] defines mechanisms to advertise Entropy
   Readable Label Depth (ERLD) for ingress Label Switching Routers (LSR)
   to discover other LSR's capability of performing Entropy Label based
   load-balancing

   Prefix attributes are advertised in MPLS networks.  The ingress LSR can use this
   information to construct OSPFv2 [RFC2328] using the appropriate label stack for specific
   traffic requirements, especially in segment routed networks
   Extended Prefix Opaque Link State Advertisement (LSA) [RFC7684] and other
   deployments requiring stacked LSPs.

   However,
   in inter-area scenarios, OSPFv3 [RFC5340] using the Area Border Router (ABR) does
   not advertise various Extended Prefix LSA types
   [RFC8362].

   The identification of the originating OSPF router-id for inter-area prefixes.
   An OSPF router for a prefix in one area doesn't know OSPF
   varies by the origin area type of inter-area
   prefixes the prefix and can't determine is currently not always
   possible.  For intra-area prefixes, the originating router that originated these
   prefixes or is
   identified by the ERLD capabilities advertising Router ID field of the destination.  Therefore, it
   is necessary to advertise area-scoped LSA
   used for those prefix advertisements.  However, for the originator of these inter-area
   prefixes
   to ensure advertised by the ingress LSR can construct Area Border Router (ABR), the appropriate label stack.

   More generally, [RFC8476] defines a mechanism to advertise multiple
   types advertising
   Router ID field of supported Maximum SID Depths (MSD) at node and/or link
   granularity.  This their area-scoped LSAs is set to the ABR itself
   and the information will be referred when about the head-end router starts to send traffic to destination prefixes.  In inter-area
   scenario, it originating the prefix
   advertisement is also necessary lost in this process of prefix propagation across
   areas.  For Autonomous System (AS) external prefixes, the originating
   router may be considered as the Autonomous System Border Router
   (ASBR) and is identified by the advertising Router ID field of the
   AS-scoped LSA used.  However, the actual originating router for the sender to learn
   prefix may be a remote router outside the
   capabilities OSPF domain.  Similarly,
   when an ABR performs translation of Not-So-Stubby Area (NSSA)
   [RFC3101] LSAs to AS-external LSAs, the receivers information associated with
   the inter-area
   prefixes.

   There NSSA ASBR (or the router outside the OSPF domain) is another scenario where knowing not conveyed
   across the OSPF domain.

   While typically the originator of inter-area
   prefixes is useful.  For example, Border Gateway Protocol Link-State
   (BGP-LS) [RFC7752] describes mechanisms using the BGP protocol to
   advertise Link-State information.  This information can enable a
   Software Definition Network (SDN) controller to automatically
   determine the underlay network topology.

   However, if the underlay network in OSPF is partitioned into multiple areas
   and running the identified
   by its OSPF protocol, Router ID, it is does not easy necessarily represent a reachable
   address for the SDN controller router.  The IPv4/IPv6 Router Address as defined in
   [RFC3630] and [RFC5329] for OSPFv2 and OSPFv3 respectively provide an
   address to rebuild the multi-area topology since ABR reach that connects multiple
   areas will normally hide the detailed topology router.

   The primary use case for these non-backbone
   areas.  If only the internal routers within backbone area run the
   BGP-LS protocol, they just learn and report the summary network
   information from the non-backbone areas.  If the SDN controller can
   learn extensions proposed in this document is
   to be able to identify the originator of the inter-area prefixes, prefix in the network.
   In cases where multiple prefixes are advertised by a given router, it
   is possible to
   rebuild the inter-area topology.

   [RFC7794] introduces the Intermediate System also useful to Intermediate System
   (IS-IS) "IPv4/IPv6 Source Router IDs" Type-Length-Value (TLV) be able to
   advertise the source of associate all these prefixes leaked from with a different IS-IS level.
   This TLV can be used in the above scenarios.  Such solution can also
   be applied
   single router even when prefixes are advertised outside of the area
   in networks that run which they originated.  It also helps to determine when the OSPF protocol, but existing OSPF
   LSAs TLVs must be extended same
   prefix is being originated by multiple routers across areas.

   This document proposes extensions to include the OSPF protocol for inclusion
   of information associated with the router originating the
   prefix.

   This draft provides such solution prefix
   along with the prefix advertisement.  These extensions do not change
   the core OSPF route computation functionality.  They provide useful
   information for topology analysis and traffic engineering, especially
   on a controller when this information is advertised as an attribute
   of the OSPFv2 [RFC2328] prefixes via mechanisms such as Border Gateway Protocol Link-
   State (BGP-LS) [RFC7752].

   Applications related to use of the prefix originating node
   information for topology reconstruction process on a controller and OSPFv3
   [RFC5340] protocols.

2.  Conventions used
   the associated limitations are described in this document Appendix A and
   Appendix B.

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.

3.  Terminology

   The following terms are used in this document:

   o  ABR: Area Border Router
   o  ASBR: Autonomous System Border Router

   o  ERLD: Entropy Readable Label Depth

   o  EL: Entropy Label

   o  IS-IS: Intermediate System to Intermediate System

   o  LSA: Link-State Advertisement

   o  MSD: Maximum SID Depths

   o  NLRI: Network Layer Reachability Information

   o  OSPF: Open Shortest Path First

   o  SID: Segment IDentifier

   o  SDN: Software Definition Network

4.  Inter-Area

2.  Protocol Extensions

   This document defines the Prefix Source Advertisement Use Cases

   Figure 1 illustrates a topology where OSPF is running in multiple
   areas.  R0-R4 are routers in the backbone area, S1-S4 are internal
   routers in area 1, and T1-T4 are internal routers in area 2.  R1 and
   R3 are ABRs between area 0 and area 1.  R2 and R4 are ABRs between
   area 0 Router-ID and area 2.  N1 is the network between router S1 and S2 Prefix
   Originator Sub-TLVs for inclusion of the Router ID and N2
   is a reachable
   address information for the network between router T1 and T2.  Ls1 is originating the loopback address
   of Node S1 and Lt1 is the loopback address of Node T1.

                            +-----------------+
                            |IP SDN Controller|
                            +--------+--------+
                                     |
                                     | BGP-LS
                                     |
        +---------------------+------+--------+-----+--------------+
        | +--+        +--+   ++-+   ++-+    +-++   + -+        +--+|
        | |S1+--------+S2+---+R1+---|R0+----+R2+---+T1+--------+T2||
        | +-++   N1   +-++   ++-+   +--+    +-++   ++++   N2   +-++|
        |   |           |     |               |     ||           | |
        |   |           |     |               |     ||           | |
        | +-++        +-++   ++-+           +-++   ++++        +-++|
        | |S4+--------+S3+---+R3+-----------+R4+---+T3+--------+T4||
        | +--+        +--+   ++-+           +-++   ++-+        +--+|
        |                     |               |                    |
        |                     |               |                    |
        |         Area 1      |     Area 0    |      Area 2        |
        +---------------------+---------------+--------------------+

              Figure 1: OSPF Inter-Area Prefix Originator Scenario

   If S1 wants to send traffic to prefix Lt1 that is connected to T1 in
   another area, it should know the ERLD and MSD values associated with
   the node T1, and then construct the right label stack at the ingress
   node for traffic destined to as a prefix Lt1.

   In another scenario, If R0 has some method to learn
   attribute.

2.1.  Prefix Source Router-ID Sub-TLV

   For OSPFv2, the originator of
   network N1 and reports such information to IP SDN controller, then it Prefix Source Router-ID Sub-TLV is possible for the controller to reconstruct the topology in an optional Sub-
   TLV of the
   non-backbone areas.  The topology reconstruction process and its
   limitations are described in OSPFv2 Extended Prefix TLV [RFC7684].  For OSPFv3, the Appendix A and Appendix B.

5.  External
   Prefix Source Advertisement Use Cases

   Figure 2 illustrates a topology where OSPF is running in different
   domain that Router-ID Sub-TLV is connected by an Autonomous System Border Router
   (ASBR).  A, B, and C are routers in optional Sub-TLV of the Domain 1; C, D, Intra-
   Area-Prefix TLV, Inter-Area-Prefix TLV, and E are
   routers in Domain 2.  Router C is the ASBR between the two domains.

   When router E receives External-Prefix TLV
   [RFC8362] when originating either an external prefix, it will redistribute it as IPv4 [RFC5838] or an AS-External LSA within domain 2.  When C receives such LSA, the
   originator information for such external prefix will be lost when it
   encodes the IPv6 prefix information with the current LSA format field.  In
   some situations, it will be helpful if C can advertise such
   originator information.

   +-------------------------------------------------------------------+
   |                              |                    External
   advertisement.

   The Prefix Source Router-ID Sub-TLV has the following format:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |               Type            | +---+       +---+          +---+         +---+         +-|-+      |
   | | A +-------+ B +----------| C +---------+ D +---------+ E |------|
   | +---+       +---+          +---+         +---+         +---+      |              Length           |        Domain 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                 Domain 2                        OSPF Router ID                         |
   +-------------------------------------------------------------------+
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 2: OSPF External 1: Prefix Originator Scenario

   From Source Router-ID Sub-TLV Format

    Where:

   o  Type: 4 for OSPFv2 and 27 for OSPFv3

   o  Length: 4

   o  OSPF Router ID : the above scenarios, we can conclude OSPF Router ID of the OSPF router that it is useful to define
      originated the prefix advertisement in the OSPF domain.

   A prefix originator sub TLV .

6. advertisement MAY include more than one Prefix Source
   Router-ID sub-TLV

   [RFC7684] and [RFC8362] respectively define TLV-based LSAs for OSPFv2
   and OSPFv3.  These documents facilitate addition sub-TLV, one corresponding to each of new attributes
   for prefixes and provide the basis for a sub-TLV to advertise Equal-Cost Multi-
   Path (ECMP) nodes that originated the
   "Prefix given prefix.

   A received Prefix Source Router-ID Sub-TLV with OSPF Router ID". ID set to
   0 MUST be considered invalid and ignored.  Additionally, reception of
   such Sub-TLV SHOULD be logged as an error (subject to rate-limiting).

2.2.  Prefix Originator Sub-TLV

   For OSPFv2, this sub-TLV the Prefix Originator Sub-TLV is a sub-TLV an optional Sub-TLV of
   the OSPFv2 Extended Prefix TLV which SHOULD be included in the "OSPFv2
   Extended Prefix Opaque LSA" [RFC7684] for inter-area prefixes. [RFC7684].  For OSPFv3, this sub-TLV the Prefix
   Originator Sub-TLV is a sub-TLV an optional Sub-TLV of "Inter-Area-Prefix TLV", which
   SHOULD be included in the "E-Inter-Area-Prefix-LSA" [RFC8362]. Intra-Area-Prefix
   TLV, Inter-Area-Prefix TLV, and External-Prefix TLV [RFC8362] when
   originating either an IPv4 [RFC5838] or an IPv6 prefix advertisement.

   The "Prefix Source Router-ID" sub-TLV Prefix Originator Sub-TLV has the following format:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |               Type            |              Length           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Prefix Source Router-ID              Router Address (4 or 16 octects)                 |
    +---------------------------------------------------------------+
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 3: 2: Prefix Source Router-ID sub-TLV Originator Sub-TLV Format

    Where:

   o  Source Router-ID Sub-TLV  Type: 4 (IANA TEMPORARY allocation)
      [RFC7684] or 27 (IANA TEMPORARY allocation) [RFC8362] TBD1 for OSPFv2 and TBD2 for OSPFv3

   o  Length: 4 or 16

   o  Value: Router-ID  Router Address: A reachable IPv4 or IPv6 router address for the
      router that originated the IPv4 or IPv6 prefix advertisement.
      Such an address would be semantically equivalent to what may be
      advertised in the OSPFv2 Router Address TLV [RFC3630] or in the
      OSPFv3 Router IPv6 Address TLV [RFC5329].

   A prefix advertisement MAY include more than one Prefix Originator
   sub-TLV, one corresponding to each of the Equal-Cost Multi-Path
   (ECMP) nodes that originated the given prefix.

   A received Prefix Originator Sub-TLV that has an invalid length (not
   4 or 16) or a Reachable Address containing an invalid IPv4 or IPv6
   address (dependent on address family of OSPFv2/OSPFv3 router that is the source associated prefix) MUST
   be considered invalid and ignored.  Additionally, reception of the
      prefix.

   This sub-TLV such
   Sub-TLV SHOULD be logged as an error (subject to rate-limiting).

   [RFC7794] provides the same similar functionality as for the IS-IS "IPv4/IPv6
   Source Router" TLV defined in [RFC7794].

7. Intermediate System
   to Intermediate System (IS-IS) protocol.

3.  Elements of Procedure

   The following sections describe

   This section describes the procedure to include the newly
   defined "Source Router-ID Sub-TLV" in the related LSA for inter-area
   prefixes and external prefixes respectively.

7.1.  Inter-Area Prefixes

   When an ABR, for example R2 in Figure 1, receives a Router-LSA advertisement in area 2, it SHOULD originate of the corresponding
   "OSPFv2 Extended Prefix Opaque LSA" for OSPFv2 or "E-Inter-Area-
   Prefix-LSA" for OSPFv3 that includes the
   Source Router-ID sub-TLV for and Prefix Originator Sub-TLVs along with the network prefixes.  For example, prefix
   advertisement.

   The OSPF Router ID of the Prefix Source Router-ID is set to identify the source router OSPF
   Router ID of the node originating the prefix Lt1 and other inter-area prefixes in Figure 1.

   When a router in another area, e.g., S1, receives such LSA, it the OSPF domain.

   If the originating node is advertising an OSPFv2 Router Address TLV
   [RFC3630] or an OSPFv3 Router IPv6 Address TLV [RFC5329], then
   can ascertain that prefix Lt1
   value is associated with node T1 and obtain set in the ERLD or MSD value from T1's Router-Information LSA [RFC7770] and
   construct Router Address field of the right label stack at Prefix Originator
   Sub-TLV.  When the ingress orignating node S1 is not advertising such an
   address, implementations MAY support mechanisms to determine a
   reachable address belonging to the originating node to set in the
   Router Address field.  Such mechanisms are outside the scope of this
   document.

   Implementations MAY support the selection of specific prefixes for traffic
   destined
   which the originating node information needs to be included with
   their prefix Lt1. advertisements.

   When a router in another an ABR generates inter-area prefix advertisements into its non-
   backbone areas corresponding to an inter-area prefix advertisement
   from the backbone area, e.g., R0, receives such LSA, it learns the only way to determine the originating
   node information is based on the Prefix Source Router-id Router-ID and includes it Prefix
   Originator Sub-TLVs present in the prefix information
   advertised to inter-area prefix advertisement
   originated into the backbone area by an SDN controller as described in
   [I-D.ietf-idr-bgp-ls-segment-routing-ext]. ABR for another non-backbone
   area.  The SDN controller can
   then use such information ABR performs its prefix calculation to build determine the inter-area topology according set
   of nodes that contribute to the process described in the Appendix A.  The topology retrieval
   process may not suitable for some environments as stated in
   Appendix B.

7.2.  External Prefixes

   When an ASBR, for example C in Figure 2, receives an AS-External LSA
   for an external best prefix in domain 2, it SHOULD extract reachability.  It MUST
   use the prefix originator information only from this set of nodes.
   The ABR MUST NOT include the "Advertising Router" field from Prefix Source Router-ID or the LSA header.
   When Prefix
   Originator Sub-TLVs when it is unable to determine the information of
   the best originating node.

   Implementations MAY provide control on ABRs to selectively disable
   the propagation of the originating node information across area
   boundaries.

   Implementations MAY support the propagation of the originating node
   information along with a redistributed prefix is advertised into the OSPF domain 1 as an AS-External LSA,
   router C may
   from another routing domain.  The details of such mechanisms are
   outside the scope of this document.  Such implementations MAY also advertise
   provide control on whether the Source Router-ID using a AS-scoped
   OSPFv2 Extended Prefix Opaque LSA or as a Sub-TLV Router Address in the OSPFv3 AS-
   External LSA.

8.  Security Considerations

   Since this document extends the "OSPFv2 Extended Prefix LSA" and
   "OSPFv3 E-Inter-Area-Prefix LSA",
   Originator Sub-TLV is set as the security considerations for
   [RFC7684] and [RFC8362] are applicable.

   Modification of ABSR node address or as the "Prefix Source Sub-TLV" could be used for a
   Denial-of-Service attack and could inhibit address
   of the use cases described in
   Section 4.  If actual node outside the OSPF domain is vulnerable that owns the prefix.

   When translating the NSSA prefix advertisements [RFC3101] to such attacks, OSPF
   authentication should be used as defined for OSPFv2 in [RFC5709] and
   [RFC7474] and for OSPFv3 in [RFC7166].

   Additionally, advertisement of the AS
   external prefix source for advertisements, the NSSA ABR, follows the same
   procedures as an ABR generating inter-area
   prefixes facilitates reconstruction prefix advertisements for
   the propagation of the OSPF topology originating node information.

4.  Security Considerations

   Since this document extends the OSPFv2 Extended Prefix LSA, the
   security considerations for other
   areas.  Network operators may consider their topologies to be
   sensitive confidential data.  For OSPFv3, IPsec can be used to
   provide confidentiality [RFC4552].  Since there is no standard
   defined [RFC7684] are applicable.  Similarly,
   since this document extends the OSPFv3 E-Intra-Area-Prefix-LSA, E-
   Inter-Area-Prefix-LSA, E-AS-External LSA and E-NSSA-LSA, the security
   considerations for native OSPFv2 IPsec, some form of secure tunnel is
   required to provide confidentiality.

9. [RFC8362] are applicable.

5.  IANA Considerations

   This specification defines document requests IANA for the Prefix Source Router-ID sub-TLV as
   described in Section 6.  This value should be added to allocation of the both
   existing "OSPFv2 Extended Prefix TLV Sub-TLVs" and "OSPFv3 Extended-
   LSA Sub-TLVs" registries.

   The following sub-TLV is added to codepoint from
   the "OSPFv2 Extended Prefix TLV Sub-TLVs" registry under the "Open
   Shortest Path First v2 (OSPFv2) Parameters" registry.  The allocation policy is IETF Review as defined
   in [RFC7684]

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Code Point  |               Description           |    IANA Allocation    |
 | Point |                                     |        Status         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   4   |  Prefix Source Router-ID Sub-TLV    |   Allocation from IANA early allocation done |
 |  TBD1 |    Prefix Originator Sub-TLV        |       pending         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Figure 4: 3:  Code Point Points in "OSPFv2 OSPFv2 Extended Prefix TLV Sub-TLVs"

   The following sub-TLV is added to Sub-TLVs

   This document requests IANA for the allocation of the codepoint from
   the "OSPFv3 Extended-LSA Extended Prefix TLV Sub-TLVs" registry under the "Open
   Shortest Path First v3 (OSPFv3) Parameters" registry.  The allocation policy is IETF Review as defined in
   [RFC8362]

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Code Point  |               Description           |    IANA Allocation    |
 | Point |                                     |        Status         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  27   |   Prefix Source Router-ID Sub-TLV   |   Allocation from IANA early allocation done |
 | TBD2  |    Prefix Originator Sub-TLV        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+       pending         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Figure 5: 4:  Code Point Points in "OSPFv3 OSPFv3 Extended-LSA Sub-TLVs"

10. Sub-TLVs

6.  Acknowledgement

   Many thanks to Les Ginsberg for his suggestions on this draft.  Also
   thanks to Jeff Tantsura, Rob Shakir, Gunter Van De Velde, Goethals
   Dirk, Smita Selot, Shaofu Peng, and John E Drake for their valuable
   comments.

11.

7.  References

11.1.

7.1.  Normative References

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

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998,
              <https://www.rfc-editor.org/info/rfc2328>.

   [RFC4552]  Gupta, M. and N. Melam, "Authentication/Confidentiality
              for OSPFv3",

   [RFC3101]  Murphy, P., "The OSPF Not-So-Stubby Area (NSSA) Option",
              RFC 4552, 3101, DOI 10.17487/RFC4552, June 2006,
              <https://www.rfc-editor.org/info/rfc4552>. 10.17487/RFC3101, January 2003,
              <https://www.rfc-editor.org/info/rfc3101>.

   [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>.

   [RFC5709]  Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M.,
              Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic
              Authentication", RFC 5709, DOI 10.17487/RFC5709, October
              2009, <https://www.rfc-editor.org/info/rfc5709>.

   [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>.

   [RFC7474]  Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed.,
              "Security Extension for OSPFv2 When Using Manual Key
              Management", RFC 7474, DOI 10.17487/RFC7474, April 2015,
              <https://www.rfc-editor.org/info/rfc7474>.

   [RFC7684]  Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
              Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
              Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
              2015, <https://www.rfc-editor.org/info/rfc7684>.

   [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>.

   [RFC7794]  Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and
              U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4
              and IPv6 Reachability", RFC 7794, DOI 10.17487/RFC7794,
              March 2016, <https://www.rfc-editor.org/info/rfc7794>.

   [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, 8362, DOI 10.17487/RFC8362, April
              2018, <https://www.rfc-editor.org/info/rfc8362>.

7.2.  Informative References

   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630,
              DOI 10.17487/RFC8362, April
              2018, <https://www.rfc-editor.org/info/rfc8362>.

   [RFC8476]  Tantsura, J., Chunduri, U., Aldrin, S., 10.17487/RFC3630, September 2003,
              <https://www.rfc-editor.org/info/rfc3630>.

   [RFC5329]  Ishiguro, K., Manral, V., Davey, A., and P. Psenak,
              "Signaling Maximum SID Depth (MSD) Using OSPF", A. Lindem, Ed.,
              "Traffic Engineering Extensions to OSPF Version 3",
              RFC 8476, 5329, DOI 10.17487/RFC8476, December 2018,
              <https://www.rfc-editor.org/info/rfc8476>.

11.2.  Informative References

   [I-D.ietf-idr-bgp-ls-segment-routing-ext]
              Previdi, 10.17487/RFC5329, September 2008,
              <https://www.rfc-editor.org/info/rfc5329>.

   [RFC5838]  Lindem, A., Ed., Mirtorabi, S., Talaulikar, K., Filsfils, C., Gredler, H., Roy, A., Barnes, M., and M. Chen, "BGP Link-State extensions for Segment
              Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-16
              (work
              R. Aggarwal, "Support of Address Families in progress), June 2019.

   [I-D.ietf-ospf-mpls-elc]
              Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S.,
              and M. Bocci, "Signaling Entropy Label Capability and
              Entropy Readable Label-stack Depth Using OSPF", draft-
              ietf-ospf-mpls-elc-12 (work in progress), October 2019. OSPFv3",
              RFC 5838, DOI 10.17487/RFC5838, April 2010,
              <https://www.rfc-editor.org/info/rfc5838>.

   [RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
              S. Ray, "North-Bound Distribution of Link-State and
              Traffic Engineering (TE) Information Using BGP", RFC 7752,
              DOI 10.17487/RFC7752, March 2016,
              <https://www.rfc-editor.org/info/rfc7752>.

Appendix A.  Inter-Area Topology Retrieval Process

   When an IP SDN Controller receives BGP-LS [RFC7752] information, it
   should compare the prefix Network Layer Reachability Information
   (NLRI) that is included in the BGP-LS NLRI.  When it encounters the
   same prefix but with different source router ID, it should extract
   the corresponding area-ID, rebuild the link between these two source
   routers in the non-backbone area.  Below is one example that based on
   the Figure 1: 5 which illustrates a topology where OSPF is running in
   multiple areas.

                            +-----------------+
                            |IP SDN Controller|
                            +--------+--------+
                                     |
                                     | BGP-LS
                                     |
        +---------------------+------+--------+-----+--------------+
        | +--+        +--+   ++-+   ++-+    +-++   + -+        +--+|
        | |S1+--------+S2+---+R1+---|R0+----+R2+---+T1+--------+T2||
        | +-++   N1   +-++   ++-+   +--+    +-++   ++++   N2   +-++|
        |   |           |     |               |     ||           | |
        |   |           |     |               |     ||           | |
        | +-++        +-++   ++-+           +-++   ++++        +-++|
        | |S4+--------+S3+---+R3+-----------+R4+---+T3+--------+T4||
        | +--+        +--+   ++-+           +-++   ++-+        +--+|
        |                     |               |                    |
        |                     |               |                    |
        |         Area 1      |     Area 0    |      Area 2        |
        +---------------------+---------------+--------------------+

              Figure 5: OSPF Inter-Area Prefix Originator Scenario

   R0-R4 are routers in the backbone area, S1-S4 are internal routers in
   area 1, and T1-T4 are internal routers in area 2.  R1 and R3 are ABRs
   between area 0 and area 1.  R2 and R4 are ABRs between area 0 and
   area 2.  N1 is the network between router S1 and S2 and N2 is the
   network between router T1 and T2.  Ls1 is the loopback address of
   Node S1 and Lt1 is the loopback address of Node T1.

   Assuming we want to rebuild the connection between router S1 and
   router S2 located in area 1:

   a.  Normally, router S1 will advertise prefix N1 within its router-
       LSA.

   b.  When this router-LSA reaches the ABR router R1, it will convert
       it into summary-LSA, add the Prefix Source Router-ID sub-TLV,
       which is router id of S1 Sub-TLV and the
       Prefix Originator Sub-TLV, as described in this example. Section 3.

   c.  R1 then floods this extension summary-LSA to R0, which is using
       the BGP-LS protocol with IP SDN Controller.  The controller then
       knows the prefix for N1 is from S1.

   d.  Router S2 will perform a similar process, and the controller will
       also learn that prefix N1 is also from S2.

   e.  Then it can reconstruct the link between S1 and S2, using the
       prefix N1.  The topology within Area 1 can then be reconstructed
       accordingly.

   Iterating the above process continuously, the IP SDN controller can
   retrieve a detailed topology that spans multiple areas.

Appendix B.  Special Considerations on Inter-Area Topology Retrieval

   The above topology retrieval process can be applied in the case where
   each point-to-point or multi-access link connecting routers is
   assigned a unique prefix.  However, there are some situations where
   this heuristic cannot be applied.  Specifically, the cases where the
   link is unnumbered or the prefix corresponding to the link is an
   anycast prefix.

   The Appendix A heuristic to rebuild the topology can normally be used
   if all links are numbered.  For anycast prefixes, if it corresponds
   to the loopback interface and has a host prefix length, i.e., 32 for
   IPv4 prefixes and 128 for IPv6 prefixes, Appendix A can also applied
   since these anycast prefixes are not required to reconstruct the
   topology.

Authors' Addresses
   Aijun Wang
   China Telecom
   Beiqijia Town, Changping District
   Beijing  102209
   China

   Email: wangaj3@chinatelecom.cn

   Acee Lindem
   Cisco Systems
   301 Midenhall Way
   Cary, NC  27513
   USA

   Email: acee@cisco.com

   Jie Dong
   Huawei Technologies
   Beijing
   China

   Email: jie.dong@huawei.com

   Peter Psenak
   Cisco Systems
   Pribinova Street 10
   Bratislava, Eurovea Centre, Central 3  81109
   Slovakia

   Email: ppsenak@cisco.com

   Ketan Talaulikar
   Cisco Systems
   S.No. 154/6, Phase I, Hinjawadi
   Pune  411 057
   India

   Email: ketant@cisco.com