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

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


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

Abstract

   This document defines OSPF extensions to include information
   associated with the node originating a prefix along with the prefix
   advertisement.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on January 1, 2021.

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   carefully, as they describe your rights and restrictions with respect



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Protocol Extensions . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Prefix Source Router-ID Sub-TLV . . . . . . . . . . . . .   4
     2.2.  Prefix Originator Sub-TLV . . . . . . . . . . . . . . . .   4
   3.  Elements of Procedure . . . . . . . . . . . . . . . . . . . .   5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .   7
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Appendix A.  Inter-Area Topology Retrieval Process  . . . . . . .   9
   Appendix B.  Special Considerations on Inter-Area Topology
                Retrieval  . . . . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   Prefix attributes are advertised in OSPFv2 [RFC2328] using the
   Extended Prefix Opaque Link State Advertisement (LSA) [RFC7684] and
   in OSPFv3 [RFC5340] using the various Extended Prefix LSA types
   [RFC8362].

   The identification of the originating router for a prefix in OSPF
   varies by the type of the prefix and is currently not always
   possible.  For intra-area prefixes, the originating router is
   identified by the advertising Router ID field of the area-scoped LSA
   used for those prefix advertisements.  However, for the inter-area
   prefixes advertised by the Area Border Router (ABR), the advertising
   Router ID field of their area-scoped LSAs is set to the ABR itself
   and the information about the router originating the prefix
   advertisement is 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
   prefix may be a remote router outside the OSPF domain.  Similarly,
   when an ABR performs translation of Not-So-Stubby Area (NSSA)
   [RFC3101] LSAs to AS-external LSAs, the information associated with




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   the NSSA ASBR (or the router outside the OSPF domain) is not conveyed
   across the OSPF domain.

   While typically the originator of information in OSPF is identified
   by its OSPF Router ID, it does not necessarily represent a reachable
   address for the router.  The IPv4/IPv6 Router Address as defined in
   [RFC3630] and [RFC5329] for OSPFv2 and OSPFv3 respectively provide an
   address to reach that router.

   The primary use case for the extensions proposed in this document is
   to be able to identify the originator of the prefix in the network.
   In cases where multiple prefixes are advertised by a given router, it
   is also useful to be able to associate all these prefixes with a
   single router even when prefixes are advertised outside of the area
   in which they originated.  It also helps to determine when the same
   prefix is being originated by multiple routers across areas.

   This document proposes extensions to the OSPF protocol for inclusion
   of information associated with the router originating the 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 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
   the associated limitations are described in 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.

2.  Protocol Extensions

   This document defines the Prefix Source Router-ID and the Prefix
   Originator Sub-TLVs for inclusion of the Router ID and a reachable
   address information for the router originating the prefix as a prefix
   attribute.






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2.1.  Prefix Source Router-ID Sub-TLV

   For OSPFv2, the Prefix Source Router-ID Sub-TLV is an optional Sub-
   TLV of the OSPFv2 Extended Prefix TLV [RFC7684].  For OSPFv3, the
   Prefix Source Router-ID Sub-TLV is an optional Sub-TLV of the 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 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           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        OSPF Router ID                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 1: Prefix Source Router-ID Sub-TLV Format

    Where:

   o  Type: 4 for OSPFv2 and 27 for OSPFv3

   o  Length: 4

   o  OSPF Router ID : the OSPF Router ID of the OSPF router that
      originated the prefix advertisement in the OSPF domain.

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

   A received Prefix Source Router-ID Sub-TLV with OSPF Router 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, the Prefix Originator Sub-TLV is an optional Sub-TLV of
   the OSPFv2 Extended Prefix TLV [RFC7684].  For OSPFv3, the Prefix
   Originator Sub-TLV is an optional Sub-TLV of the 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 Originator 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           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |              Router Address (4 or 16 octects)                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 2: Prefix Originator Sub-TLV Format

    Where:

   o  Type: TBD1 for OSPFv2 and TBD2 for OSPFv3

   o  Length: 4 or 16

   o  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 the associated prefix) MUST
   be considered invalid and ignored.  Additionally, reception of such
   Sub-TLV SHOULD be logged as an error (subject to rate-limiting).

   [RFC7794] provides similar functionality for the Intermediate System
   to Intermediate System (IS-IS) protocol.

3.  Elements of Procedure

   This section describes the procedure for advertisement of the Prefix
   Source Router-ID and Prefix Originator Sub-TLVs along with the prefix
   advertisement.

   The OSPF Router ID of the Prefix Source Router-ID is set to the OSPF
   Router ID of the node originating the prefix in the OSPF domain.

   If the originating node is advertising an OSPFv2 Router Address TLV
   [RFC3630] or an OSPFv3 Router IPv6 Address TLV [RFC5329], then that
   value is set in the Router Address field of the Prefix Originator
   Sub-TLV.  When the orignating node is not advertising such an



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   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
   which the originating node information needs to be included with
   their prefix advertisements.

   When an ABR generates inter-area prefix advertisements into its non-
   backbone areas corresponding to an inter-area prefix advertisement
   from the backbone area, the only way to determine the originating
   node information is based on the Prefix Source Router-ID and Prefix
   Originator Sub-TLVs present in the inter-area prefix advertisement
   originated into the backbone area by an ABR for another non-backbone
   area.  The ABR performs its prefix calculation to determine the set
   of nodes that contribute to the best prefix reachability.  It MUST
   use the prefix originator information only from this set of nodes.
   The ABR MUST NOT include the Prefix Source Router-ID or the 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 into the OSPF domain
   from another routing domain.  The details of such mechanisms are
   outside the scope of this document.  Such implementations MAY also
   provide control on whether the Router Address in the Prefix
   Originator Sub-TLV is set as the ABSR node address or as the address
   of the actual node outside the OSPF domain that owns the prefix.

   When translating the NSSA prefix advertisements [RFC3101] to the AS
   external prefix advertisements, the NSSA ABR, follows the same
   procedures as an ABR generating inter-area prefix advertisements for
   the propagation of the originating node information.

4.  Security Considerations

   Since this document extends the OSPFv2 Extended Prefix LSA, the
   security considerations for [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 [RFC8362] are applicable.





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5.  IANA Considerations

   This document requests IANA for the allocation of the codepoint from
   the "OSPFv2 Extended Prefix TLV Sub-TLVs" registry under the "Open
   Shortest Path First v2 (OSPFv2) Parameters" registry.

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

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


   This document requests IANA for the allocation of the codepoint from
   the "OSPFv3 Extended Prefix TLV Sub-TLVs" registry under the "Open
   Shortest Path First v3 (OSPFv3) Parameters" registry.

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

     Figure 4:  Code Points in OSPFv3 Extended-LSA 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.

7.  References

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>.




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

   [RFC3101]  Murphy, P., "The OSPF Not-So-Stubby Area (NSSA) Option",
              RFC 3101, DOI 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>.

   [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>.

   [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, 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/RFC3630, September 2003,
              <https://www.rfc-editor.org/info/rfc3630>.

   [RFC5329]  Ishiguro, K., Manral, V., Davey, A., and A. Lindem, Ed.,
              "Traffic Engineering Extensions to OSPF Version 3",
              RFC 5329, DOI 10.17487/RFC5329, September 2008,
              <https://www.rfc-editor.org/info/rfc5329>.

   [RFC5838]  Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and
              R. Aggarwal, "Support of Address Families in OSPFv3",
              RFC 5838, DOI 10.17487/RFC5838, April 2010,
              <https://www.rfc-editor.org/info/rfc5838>.




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   [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 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.





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   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 Source Router-ID Sub-TLV and the
       Prefix Originator Sub-TLV, as described in 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










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   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
   India

   Email: ketant@cisco.com











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