



LSR                                                              R. Chen
Internet-Draft                                                   D. Zhao
Intended status: Standards Track                         ZTE Corporation
Expires: 7 March 2026                                          P. Psenak
                                                           K. Talaulikar
                                                           Cisco Systems
                                                                  C. Lin
                                                                     H3C
                                                        3 September 2025


                 OSPFv2 Anycast Property Advertisement
                     draft-ietf-lsr-anycast-flag-05

Abstract

   An IPv4 prefix may be configured as anycast and as such the same
   value can be advertised by multiple routers.  It is useful for other
   routers to know that the advertisement is for an anycast identifier.

   This document defines a new flag in the OSPFv2 Extended Prefix TLV
   Flags to advertise the anycast property.

Status of This Memo

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

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

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 7 March 2026.

Copyright Notice

   Copyright (c) 2025 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.



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   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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Use-case  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  OSPFv2 Anycast Property Advertisement . . . . . . . . . . . .   3
   4.  BGP-LS Anycast Property advertisement . . . . . . . . . . . .   4
   5.  YANG Data Model . . . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  Tree for the YANG Data Model  . . . . . . . . . . . . . .   4
     5.2.  YANG Data Model for OSPFv2 Anycast Property
           Advertisement . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     7.1.  OSPFv2 Extended Prefix TLV Flags Registry . . . . . . . .   7
     7.2.  OSPFv2 Anycast Flag YANG Module Registry  . . . . . . . .   7
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   An IPv4 prefix may be configured as anycast and as such the same
   value can be advertised by multiple routers.  It is useful for other
   routers to know that the advertisement is for an anycast identifier.

   [RFC7684] defines OSPFv2 Opaque LSAs based on Type-Length-Value (TLV)
   tuples that can be used to associate additional attributes with
   prefixes or links.  The OSPFv2 Extended Prefix TLV that is contained
   in the OSPFv2 Extended Prefix Opaque LSA is used to advertise
   additional attributes associated with an IPv4 prefix, but the
   definition of anycast flag to identify the IPv4 prefix as anycast has
   not yet been defined.

   The flags field of the OSPFv2 Extended Prefix TLV (Section 2.1 of
   [RFC7684]) can be found in "OSPFv2 Extended Prefix TLV Flags" IANA
   registry [IANA-OSPFv2-EPF].

   This document defines a new flag in the OSPFv2 Extended Prefix TLV
   Flags [RFC7684] to advertise the anycast property for an IPv4 prefix.




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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.  Use-case

   In the absence of the N-flag, the node specific prefixes need to be
   identified from the anycast prefixs.  A prefix that is advertised by
   a single node and without an Anycast Flag (AC-flag) MUST be
   considered node specific.

3.  OSPFv2 Anycast Property Advertisement

   An IPv4 prefix may be configured as anycast and it is useful for
   other routers to know that the advertisement is for an anycast
   identifier.

   [RFC7684] defines one-octet field contains flags applicable to the
   prefix, and it has been defined the below flags(see "OSPFv2 Extended
   Prefix TLV Flags" IANA registry [IANA-OSPFv2-EPF]):

                    +=======+=============+===========+
                    | Value | Description | Reference |
                    +=======+=============+===========+
                    |  0x80 |      A      | [RFC7684] |
                    +-------+-------------+-----------+
                    |  0x40 |      N      | [RFC7684] |
                    +-------+-------------+-----------+
                    |  0x02 |    E-Flag   | [RFC9089] |
                    +-------+-------------+-----------+

                      Table 1: OSPFv2 Extended Prefix
                                 TLV Flags

   A new bit in OSPFv2 Extended Prefix TLV Flags[RFC7684] is defined to
   advertise the anycast property:

   Value: TBD

   Description:Anycast Flag (AC-flag)

   When a prefix is configured as anycast, the AC-flag SHOULD be set.
   Otherwise, this flag MUST be clear.




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   The AC-flag and the N-bit MUST NOT both be set.  If both N-flag and
   AC-flag are set, the receiving routers MUST ignore the N-flag.

   The AC-flag MUST be preserved when re-advertising the prefix across
   areas.

   The same prefix can be advertised by multiple routers, and that if at
   least one of them sets the AC-flag in its advertisement, the prefix
   SHOULD be considered as anycast.

   A prefix that is advertised by a single node and without an AC-flag
   MUST be considered node specific prefix.

4.  BGP-LS Anycast Property advertisement

   [RFC9085] defines the Prefix Attribute Flags TLV carries IPv4 prefix
   attribute flags information, and the Flags field of this TLV is
   interpreted according to OSPFv2 [RFC7684].  This section extends the
   interpretation of the Flags field of the Prefix Attribute Flags TLV.

   Flags:

   *  OSPFv2 flags correspond to the Flags field of the OSPFv2 Extended
      Prefix TLV defined in [RFC7684] and extended in this draft.

5.  YANG Data Model

   YANG [RFC7950] is a data definition language used to define the
   contents of a conceptual data store that allows networked devices to
   be managed using NETCONF [RFC6241] or RESTCONF [RFC8040].

   This section defines a YANG data model that can be used to configure
   and manage the usage of OSPFv2 Anycast Property as defined in this
   document, which augments the OSPF YANG data model [RFC9129] and the
   YANG Data Model for Routing Management [RFC8349].

5.1.  Tree for the YANG Data Model

   This document uses the graphical representation of data models per
   [RFC8340].

   The following show the tree diagram of the module:









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   module: ietf-ospf-anycast-flag

     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas/ospf:area
               /ospf:interfaces/ospf:interface:
       +--rw anycast-flag?   boolean


5.2.  YANG Data Model for OSPFv2 Anycast Property Advertisement

   The following is the YANG module:

   <CODE BEGINS> file "ietf-ospf-anycast-flag@2025-08-28.yang"
   module ietf-ospf-anycast-flag {
     yang-version 1.1;
     namespace
       "urn:ietf:params:xml:ns:yang:ietf-ospf-anycast-flag";
     prefix ospf-anycast-flag;

     import ietf-routing {
       prefix rt;
       reference
         "RFC 8349: A YANG Data Model for Routing
          Management (NMDA Version)";
     }
     import ietf-ospf {
       prefix ospf;
       reference
         "RFC 9129: YANG Data Model for the OSPF Protocol";
     }

     organization
       "IETF LSR - Link State Routing Working Group";
     contact
       "WG Web:   <https://datatracker.ietf.org/wg/lsr/>
        WG List:  <mailto:lsr@ietf.org>

        Author:   Ran Chen
                  <mailto:chen.ran@zte.com.cn>
        Author:   Detao Zhao
                  <mailto:zhao.detao@zte.com.cn>
        Author:   Peter Psenak
                  <mailto:ppsenak@cisco.com>
        Author:   Ketan Talaulikar
                  <mailto:ketan.ietf@gmail.com>
        Author:   Changwang Lin
                  <mailto:linchangwang.04414@h3c.com>";




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     description
       "This YANG module adds the support of configuring an OSPFv2
        prefix as anycast.

        This YANG module conforms to the Network Management
        Datastore Architecture (NMDA) as described in RFC 8342.

        Copyright (c) 2025 IETF Trust and the persons identified as
        authors of the code.  All rights reserved.

        Redistribution and use in source and binary forms, with or
        without modification, is permitted pursuant to, and subject to
        the license terms contained in, the Revised BSD License set
        forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents
        (https://trustee.ietf.org/license-info).

        This version of this YANG module is part of RFC XXXX;
        see the RFC itself for full legal notices.";
     reference
       "RFC XXXX";

     revision 2025-08-28 {
       description
         "Initial version";
       reference
         "RFC XXXX: OSPFv2 Anycast Property Advertisement";
     }

     identity ac-flag {
       base ospf:ospfv2-extended-prefix-flag;
       description
         "Anycast flag.  When set, it indicates that the prefix
          is configured as anycast.";
     }

     /* Configuration */
     augment "/rt:routing/rt:control-plane-protocols/"
           + "rt:control-plane-protocol/ospf:ospf/"
           + "ospf:areas/ospf:area/ospf:interfaces/ospf:interface" {
       when "derived-from(/rt:routing/rt:control-plane-protocols/"
          + "rt:control-plane-protocol/rt:type, 'ospf:ospfv2')" {
         description
           "This augments the OSPFv2 interface configuration.";
       }
       description
         "This augments OSPFv2 interface configuration with anycast
          property advertisement.";



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       leaf anycast-flag {
         type boolean;
         default "false";
         description
           "Sets the prefix as an anycast address.";
       }
     }
   }
   <CODE ENDS>

6.  Acknowledgements

   The authors would like to thank Acee Lindem for aligning the
   terminology with existing OSPF documents and for editorial
   improvements.  The author would also like to thank Yingzhen Qu for
   providing the YANG model and tree, as well as for valuable editorial
   comments.

7.  IANA Considerations

   This document requests allocation for the following registry.

7.1.  OSPFv2 Extended Prefix TLV Flags Registry

   This document adds a new bit in the "OSPFv2 Extended Prefix TLV
   Flags"registry:

   AC-flag (Anycast Flag).

7.2.  OSPFv2 Anycast Flag YANG Module Registry

   IANA is requested to register the following URI in the "ns" registry
   within the "IETF XML Registry" group ([RFC3688]):

   URI: urn:ietf:params:xml:ns:yang:ietf-ospf-anycast-flag
   Registrant Contact: The IESG.
   XML: N/A, the requested URI is an XML namespace

   IANA is requested to register the following YANG module in the "YANG
   Module Names" registry ([RFC6020]) within the "YANG Parameters"
   registry group.

   name: ietf-ospf-anycast-flag
   Maintained by IANA?  N
   namespace: urn:ietf:params:xml:ns:yang:ietf-ospf-anycast-flag
   prefix: ospf-anycast-flag
   reference: RFC XXXX




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8.  Security Considerations

   Procedures and protocol extensions defined in this document do not
   affect the OSPFv2 security model.  See the "Security
   Considerations"section of [RFC7684] for a discussion of OSPFv2
   security.

   The ietf-ospf-anycast-flag YANG module defines a data model that is
   designed to be accessed via YANG-based management protocols, such as
   NETCONF [RFC6241] and RESTCONF [RFC8040].  These protocols have to
   use a secure transport layer (e.g., SSH [RFC4252], TLS [RFC8446], and
   QUIC [RFC9000]) and have to use mutual authentication.

   The NETCONF Access Control Model (NACM) [RFC8341] provides the means
   to restrict access for particular NETCONF or RESTCONF users to a pre-
   configured subset of all available NETCONF or RESTCONF protocol
   operations and content.

   The following data nodes defined in the YANG module that are
   writable/creatable/deletable (i.e., config true).  The modifications
   to these data nodes without proper protection could have prevent
   interpreting the IPv4 prefix as anycast.

      /ospf:ospf/ospf:areas/ospf:area/ospf:interfaces/ospf:interface/
      ospf-anycast-flag:anycast-flag

   Some of the readable data nodes in this YANG module may be considered
   sensitive or vulnerable in some network environments.  Exposure of
   the OSPF link state database may be useful in mounting a Denial-of-
   Service (DoS) attacks.  These are the readable data nodes:

      /ospf:ospf/ospf:areas/ospf:area/ospf:interfaces/ospf:interface/
      ospf-anycast-flag:anycast-flag

9.  References

9.1.  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>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.





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   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

   [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>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

   [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>.

   [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
              Access Control Model", STD 91, RFC 8341,
              DOI 10.17487/RFC8341, March 2018,
              <https://www.rfc-editor.org/info/rfc8341>.

   [RFC8349]  Lhotka, L., Lindem, A., and Y. Qu, "A YANG Data Model for
              Routing Management (NMDA Version)", RFC 8349,
              DOI 10.17487/RFC8349, March 2018,
              <https://www.rfc-editor.org/info/rfc8349>.

   [RFC9085]  Previdi, S., Talaulikar, K., Ed., Filsfils, C., Gredler,
              H., and M. Chen, "Border Gateway Protocol - Link State
              (BGP-LS) Extensions for Segment Routing", RFC 9085,
              DOI 10.17487/RFC9085, August 2021,
              <https://www.rfc-editor.org/info/rfc9085>.

   [RFC9089]  Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S.,
              and M. Bocci, "Signaling Entropy Label Capability and
              Entropy Readable Label Depth Using OSPF", RFC 9089,
              DOI 10.17487/RFC9089, August 2021,
              <https://www.rfc-editor.org/info/rfc9089>.



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   [RFC9129]  Yeung, D., Qu, Y., Zhang, Z., Chen, I., and A. Lindem,
              "YANG Data Model for the OSPF Protocol", RFC 9129,
              DOI 10.17487/RFC9129, October 2022,
              <https://www.rfc-editor.org/info/rfc9129>.

9.2.  Informative References

   [IANA-OSPFv2-EPF]
              "OSPFv2 Extended Prefix TLV Flags",
              <https://www.iana.org/assignments/ospfv2-parameters/
              ospfv2-parameters.xhtml#extended-prefix-tlv-flags>.

   [RFC4252]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252,
              January 2006, <https://www.rfc-editor.org/info/rfc4252>.

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
              <https://www.rfc-editor.org/info/rfc8340>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC9000]  Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", RFC 9000,
              DOI 10.17487/RFC9000, May 2021,
              <https://www.rfc-editor.org/info/rfc9000>.

Authors' Addresses

   Ran Chen
   ZTE Corporation
   Nanjing
   China
   Email: chen.ran@zte.com.cn


   Detao Zhao
   ZTE Corporation
   Nanjing
   China
   Email: zhao.detao@zte.com.cn


   Peter Psenak
   Cisco Systems
   Email: ppsenak@cisco.com



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   Ketan Talaulikar
   Cisco Systems
   Email: ketan.ietf@gmail.com


   Changwang Lin
   H3C
   Email: linchangwang.04414@h3c.com











































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