LSR Working Group                                                A. Wang
Internet-Draft                                             China Telecom
Intended status: Standards Track                               A. Lindem
Expires: October 9, 2021                                   Cisco Systems
                                                                 J. Dong
                                                     Huawei Technologies
                                                               P. Psenak
                                                      K. Talaulikar, Ed.
                                                           Cisco Systems
                                                           April 7, 2021


                   OSPF Prefix Originator Extensions
                draft-ietf-lsr-ospf-prefix-originator-11

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.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on October 9, 2021.

Copyright Notice

   Copyright (c) 2021 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



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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
   the Trust Legal Provisions and are provided without warranty as
   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 OSPF Router-ID Sub-TLV  . . . . . . . . . .   3
     2.2.  Prefix Source Router Address Sub-TLV  . . . . . . . . . .   4
   3.  Elements of Procedure . . . . . . . . . . . . . . . . . . . .   5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   5.  Operational Considerations  . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .   8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

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




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   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 since the OSPF Router ID is a 32-bit number.
   There exists a prevalent practice to use one of the IPv4 address of
   the node (e.g. a loopback interface) as a OSPF Router ID in the case
   of OSPFv2.  However, this cannot be always assumed and this approach
   does not obviously extend to IPv6 addresses with OSPFv3.  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 a 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] [I-D.ietf-idr-bgp-ls-segment-routing-ext].

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 OSPF Router-ID and the Prefix
   Source Router Address Sub-TLVs.  They are used, respectively, to
   include the Router ID of, and a reachable address of, the router that
   originates the prefix as a prefix attribute.

2.1.  Prefix Source OSPF Router-ID Sub-TLV

   For OSPFv2, the Prefix Source OSPF Router-ID Sub-TLV is an optional
   Sub-TLV of the OSPFv2 Extended Prefix TLV [RFC7684].  For OSPFv3, the
   Prefix Source OSPF Router-ID Sub-TLV is an optional Sub-TLV of the
   Intra-Area-Prefix TLV, Inter-Area-Prefix TLV, and External-Prefix TLV



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   [RFC8362] when originating either an IPv4 [RFC5838] or an IPv6 prefix
   advertisement.

   The Prefix Source OSPF 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 OSPF 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.

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

   For intra-area prefix advertisements, the Prefix Source OSPF Router-
   ID Sub-TLV MUST be considered invalid and ignored if the OSPF Router
   ID field is not the same as Advertising Router field in the
   containing LSA.  Similar validation cannot be reliably performed for
   inter-area and external prefix advertisements.

   A received Prefix Source OSPF 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 Source Router Address Sub-TLV

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



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   The Prefix Source Router Address 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           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |              Router Address (4 or 16 octets)                  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

          Figure 2: Prefix Source Router Address Sub-TLV Format

    Where:

   o  Type: 5 (suggested) for OSPFv2 and 28 (suggested) 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
      respectively.  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].

   The parent TLV of a prefix advertisement MAY include more than one
   Prefix Source Router Address Sub-TLV, one corresponding to each of
   the Equal-Cost Multi-Path (ECMP) nodes that originated the given
   prefix.

   A received Prefix Source Router Address Sub-TLV that has an invalid
   length (i.e. not consistent with the prefix's address family) MUST be
   considered invalid and ignored.  Additionally, reception of such Sub-
   TLV SHOULD be logged as an error (subject to rate-limiting).

3.  Elements of Procedure

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

   The OSPF Router ID of the Prefix Source OSPF 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 the
   same address MUST be used in the Router Address field of the Prefix
   Source Router Address Sub-TLV.  When the originating node is not
   advertising such an address, implementations can determine a unique



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   and reachable address (for example, advertised with the N-flag set
   [RFC7684] or N-bit set [RFC8362]) belonging to the originating node
   to set in the Router Address field.

   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 OSPF Router-ID and
   Prefix Source Router Address Sub-TLVs present in the inter-area
   prefix advertisement originated into the backbone area by an ABR from
   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
   OSPF Router-ID or the Prefix Source Router Address Sub-TLVs when it
   is unable to determine the information of the best originating nodes.

   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 Source
   Router Address 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.  The new sub-TLVs
   introduced in this document are optional and do not affect the OSPF
   route computation and therefore do not affect the security aspects of
   OSPF protocol operations.

   A rogue node that can inject prefix advertisements may use the new
   extensions introduced in this document to indicate incorrect prefix
   source information.






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5.  Operational Considerations

   Consideration should be given to the operational impact of the
   increase in the size of the OSPF Link-State Database as a result of
   the protocol extensions in this document.  Based on deployment design
   and requirements, a subset of prefixes may be identified for which
   the originating node information needs to be included with their
   prefix advertisements.

   The propagation of the prefix source node information when doing
   prefix advertisements across OSPF area or domain boundaries results
   in the exposure of node information outside of an area or domain
   within which it is normally hidden or abstracted by the base OSPF
   protocol.  Based on deployment design and requirements, a subset of
   prefixes may be identified for which the propagation of the
   originating node information across area or domain boundaries is
   disabled at the ABRs or ASBRs respectively.

   The identification of the node that is originating a specific prefix
   in the network may aid in debugging of issues related to prefix
   reachability within an OSPF network.

6.  IANA Considerations

   This document requests IANA for the allocation of the codepoints 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 OSPF Router-ID  | early allocation done |
   |   5   | Prefix Source Router Address  |     suggested         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Figure 3:  Codepoints in OSPFv2 Extended Prefix TLV Sub-TLVs


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









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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Code  |         Description           |    IANA Allocation    |
   | Point |                               |        Status         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  27   | Prefix Source OSPF Router-ID  | early allocation done |
   |  28   | Prefix Source Router Address  |      suggested        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Figure 4:  Codepoints in OSPFv3 Extended-LSA Sub-TLVs


7.  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, John E Drake and Baalajee S for their
   review and valuable comments.  The authors would also like to thank
   Alvaro Retana for his detailed review and suggestions for the
   improvement of this document.

8.  References

8.1.  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>.

   [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>.

   [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>.





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   [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>.

   [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>.

8.2.  Informative References

   [I-D.ietf-idr-bgp-ls-segment-routing-ext]
              Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H.,
              and M. Chen, "BGP Link-State extensions for Segment
              Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-16
              (work in progress), June 2019.

   [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>.

   [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>.

   [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>.

Authors' Addresses

   Aijun Wang
   China Telecom
   Beiqijia Town, Changping District
   Beijing  102209
   China

   Email: wangaj3@chinatelecom.cn





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   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 (editor)
   Cisco Systems
   India

   Email: ketant@cisco.com




















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