



Internet Engineering Task Force (IETF)                    A. Lindem, Ed.
Request for Comments: 9825                       LabN Consulting, L.L.C.
Category: Standards Track                                      P. Psenak
ISSN: 2070-1721                                            Cisco Systems
                                                                   Y. Qu
                                                  Futurewei Technologies
                                                               July 2025


     Extensions to OSPF for Advertising Prefix Administrative Tags

Abstract

   It is useful for routers in OSPFv2 and OSPFv3 routing domains to be
   able to associate tags with prefixes.  Previously, OSPFv2 and OSPFv3
   were relegated to a single tag and only for Autonomous System (AS)
   External and Not-So-Stubby-Area (NSSA) prefixes.  With the flexible
   encodings provided by OSPFv2 Prefix/Link Attribute Advertisement and
   OSPFv3 Extended Link State Advertisements (LSAs), multiple
   administrative tags may be advertised for all types of prefixes.
   These administrative tags can be used for many applications including
   route redistribution policy, selective prefix prioritization,
   selective IP Fast Reroute (IPFRR) prefix protection, and many others.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9825.

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.  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
     1.1.  Requirements Language
   2.  Administrative Tag Sub-TLV
   3.  Administrative Tag Applicability
   4.  Protocol Operation
     4.1.  Equal-Cost Multipath Applicability
   5.  BGP-LS Advertisement
   6.  Management Considerations
   7.  YANG Data Model
     7.1.  Tree for the YANG Data Model
     7.2.  YANG Data Model for OSPF Prefix Administrative Tags
   8.  Security Considerations
   9.  IANA Considerations
   10. References
     10.1.  Normative References
     10.2.  Informative References
   Acknowledgments
   Authors' Addresses

1.  Introduction

   It is useful for routers in OSPFv2 [RFC2328] and OSPFv3 [RFC5340]
   routing domains to be able to associate tags with prefixes.
   Previously, OSPFv2 and OSPFv3 were relegated to a single tag and only
   for Autonomous System (AS) External and Not-So-Stubby-Area (NSSA)
   prefixes.  With the flexible encodings provided by OSPFv2 Prefix/Link
   Attribute Advertisement [RFC7684] and OSPFv3 Extended Link State
   Advertisement (LSA) [RFC8362], multiple administrative tags may be
   advertised for all types of prefixes.  These administrative tags can
   be used in many applications including (but not limited to):

   1.  Controlling which routes are redistributed into other protocols
       for re-advertisement.

   2.  Prioritizing selected prefixes for faster convergence and
       installation in the forwarding plane.

   3.  Identifying selected prefixes for Loop-Free Alternative (LFA)
       protection.

   Throughout this document, "OSPF" is used when the text applies to
   both OSPFv2 and OSPFv3.  "OSPFv2" or "OSPFv3" is used when the text
   is specific to one version of the OSPF protocol.

   The definition of the 64-bit tag was considered but discarded, given
   that there is no strong requirement or use case.

   The IS-IS protocol supports a similar mechanism that is described in
   [RFC5130].

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.  Administrative Tag Sub-TLV

   This document creates a new Administrative Tag Sub-TLV for OSPFv2 and
   OSPFv3.  This sub-TLV specifies one or more 32-bit unsigned integers
   that may be associated with an OSPF advertised prefix.  The precise
   usage of these tags is beyond the scope of this document.

   The format of the Administrative Tag Sub-TLV is as follows:

       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |             First Administrative Tag                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             o                                 |
                                    o
      |                             o                                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |             Last Administrative Tag                           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 1: Administrative Tag Sub-TLV

   Type:  A 16-bit field set to:

      13:  "OSPFv2 Extended Prefix TLV Sub-TLVs" registry

      39:  "OSPFv3 Extended-LSA Sub-TLVs" registry

      6:  "OSPFv3 SRv6 Locator LSA Sub-TLVs" registry

   Length:  A 16-bit field that indicates the length of the value
      portion in octets and MUST be a multiple of 4 octets dependent on
      the number of administrative tags advertised.  At least one
      administrative tag MUST be advertised.

   Value:  A variable length list of one or more administrative tags.

   This sub-TLV will carry one or more 32-bit unsigned integer values
   that will be used as administrative tags.  If the length is 0 or not
   a multiple of 4 octets, the sub-TLV MUST be ignored, and the
   reception SHOULD be logged for further analysis (subject to rate-
   limiting).

3.  Administrative Tag Applicability

   The Administrative Tag Sub-TLV specified herein will be valid as a
   sub-TLV of the following TLVs specified in [RFC7684]:

   *  Extended Prefix TLV advertised in the OSPFv2 Extended Prefix
      Opaque LSA

   The Administrative Tag Sub-TLV specified herein will be valid as a
   sub-TLV of the following TLVs specified in [RFC8362]:

   *  Inter-Area-Prefix TLV advertised in the E-Inter-Area-Prefix-LSA

   *  Intra-Area-Prefix TLV advertised in the E-Intra-Area-Prefix-LSA

   *  External-Prefix TLV advertised in the E-AS-External-LSA and the E-
      NSSA-LSA

   The Administrative Tag Sub-TLV specified herein will be valid as a
   sub-TLV of the following TLVs specified in [RFC9513]:

   *  SRv6 Locator TLV advertised in the SRv6 Locator LSA

4.  Protocol Operation

   An OSPF router supporting this specification MUST be able to
   advertise and interpret at least one tag for all types of prefixes.
   An OSPF router supporting this specification MAY be able to advertise
   prefixes with multiple tags and propagate prefixes with multiple tags
   between areas.  The maximum tags that an implementation supports is a
   local matter depending upon supported applications using prefix tags.
   Depending on the application, the number of tags supported by the
   OSPF routers in the OSPF routing domain may limit the deployment of
   that application.

   When tags are advertised for AS External or NSSA LSA prefixes, the
   existing tag in the OSPFv2 and OSPFv3 AS-External-LSA and NSSA-LSA
   encodings MUST be utilized for the first tag.  Additional tags MAY be
   advertised using the Administrative Tag Sub-TLV specified in this
   document.  This will facilitate backward compatibility with
   implementations that do not support this specification.

   An OSPF router supporting this specification SHOULD propagate
   administrative tags when acting as an Area Border Router (ABR) and
   when originating summary advertisements into other areas (unless
   inhibited by local policy (Section 6)).  Similarly, an OSPF router
   supporting this specification and acting as an ABR for a NSSA SHOULD
   propagate tags when translating NSSA routes to AS External
   advertisements [RFC3101] (also subject to local policy (Section 6)).

   There is no implied meaning to the ordering of the tags that
   indicates a certain operation or set of operations need to be
   performed based on the order of the tags.  Each tag SHOULD be treated
   as an autonomous identifier that MAY be used in policy to perform a
   policy action.  Whether or not tag A precedes or succeeds, tag B
   SHOULD NOT change the meaning of the tags.  The number of tags
   supported by an ABR MAY limit the number of tags that are propagated.
   When propagating multiple tags between areas as previously described,
   the order of the tags MUST be preserved so that implementations
   supporting fewer tags will have a consistent view across areas.

   For configured area ranges, NSSA ranges, and configured aggregation
   of redistributed routes, tags from component routes SHOULD NOT be
   propagated to the summary.  Implementations SHOULD provide a
   mechanism to configure multiple tags for area ranges, NSSA ranges,
   and redistributed route summaries.

4.1.  Equal-Cost Multipath Applicability

   When multiple LSAs contribute to an OSPF route, it is possible that
   these LSAs will all have different tags.  In this situation, the OSPF
   ABR propagating the route to other areas with inter-area LSAs MUST
   associate the tags from one of the LSAs contributing a path and, if
   the implementation supports multiple tags, MAY associate tags from
   multiple contributing LSAs up to the maximum number of tags
   supported.  It is RECOMMENDED that tags from LSAs are added to the
   path in ascending order of the LSA originator Router-ID.

5.  BGP-LS Advertisement

   Border Gateway Protocol - Link State (BGP-LS) [RFC9552] introduced
   the support for advertising administrative tags associated with
   prefixes using the BGP-LS IGP Route Tag TLV (TLV 1153).  This BGP-LS
   TLV is used to advertise the OSPF Administrative Tags specified in
   this document.

6.  Management Considerations

   Implementations MAY include configuration of policies to modify the
   advertisement of tags for redistributed prefixes.  Implementations
   MAY also include configuration of policies to modify the propagation
   of administrative tags between areas (OSPFv2 Extended Prefix Opaque
   LSAs, OSPFv3 E-Inter-Area-Prefix-LSAs, and translated OSPFv3 E-AS-
   External-LSAs).  However, the default behavior SHOULD be to advertise
   or propagate the lesser number of all the tags associated with the
   prefix or the maximum number of tags supported by the implementation.

   Both the support of this specification and the number of tags
   supported by OSPF routers within an OSPF routing domain will limit
   the usefulness and deployment of applications utilizing tags.

7.  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 Network Configuration Protocol (NETCONF) [RFC6241]
   or RESTCONF [RFC8040].

   This section defines a YANG data model that can be used to configure
   and manage the prefix administrative tags defined in this document,
   which augments the OSPF YANG data model [RFC9129], the OSPFv3
   Extended LSA YANG data model [RFC9587], and the Routing Management
   YANG data model [RFC8349].  Additionally, the YANG data models
   defined in [RFC6991] are imported.

7.1.  Tree for the YANG Data Model

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

   The following shows the tree diagram of the module:

   module: ietf-ospf-admin-tags

     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas/ospf:area
               /ospf:ranges/ospf:range:
       +--rw admin-tags
          +--rw admin-tag*   uint32
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas/ospf:area
               /ospf:interfaces/ospf:interface:
       +--rw local-prefix-admin-tags
          +--rw default-admin-tag*           uint32
          +--rw specific-prefix-admin-tag* [prefix]
             +--rw prefix       inet:ip-prefix
             +--rw admin-tag*   uint32
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:local-rib
               /ospf:route/ospf:next-hops/ospf:next-hop:
       +--ro admin-tag*   uint32
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas/ospf:area
               /ospf:interfaces/ospf:interface/ospf:database
               /ospf:link-scope-lsa-type/ospf:link-scope-lsas
               /ospf:link-scope-lsa/ospf:version/ospf:ospfv2/ospf:ospfv2
               /ospf:body/ospf:opaque/ospf:extended-prefix-opaque
               /ospf:extended-prefix-tlv:
       +--ro prefix-admin-tag-sub-tlv
          +--ro admin-tag*   uint32
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas/ospf:area
               /ospf:database/ospf:area-scope-lsa-type
               /ospf:area-scope-lsas/ospf:area-scope-lsa/ospf:version
               /ospf:ospfv2/ospf:ospfv2/ospf:body/ospf:opaque
               /ospf:extended-prefix-opaque/ospf:extended-prefix-tlv:
       +--ro prefix-admin-tag-sub-tlv
          +--ro admin-tag*   uint32
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:database
               /ospf:as-scope-lsa-type/ospf:as-scope-lsas
               /ospf:as-scope-lsa/ospf:version/ospf:ospfv2/ospf:ospfv2
               /ospf:body/ospf:opaque/ospf:extended-prefix-opaque
               /ospf:extended-prefix-tlv:
       +--ro prefix-admin-tag-sub-tlv
          +--ro admin-tag*   uint32
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas/ospf:area
               /ospf:database/ospf:area-scope-lsa-type
               /ospf:area-scope-lsas/ospf:area-scope-lsa/ospf:version
               /ospf:ospfv3/ospf:ospfv3/ospf:body
               /ospfv3-e-lsa:e-inter-area-prefix
               /ospfv3-e-lsa:e-inter-prefix-tlvs
               /ospfv3-e-lsa:inter-prefix-tlv:
       +--ro prefix-admin-tag-sub-tlv
          +--ro admin-tag*   uint32
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas/ospf:area
               /ospf:database/ospf:area-scope-lsa-type
               /ospf:area-scope-lsas/ospf:area-scope-lsa/ospf:version
               /ospf:ospfv3/ospf:ospfv3/ospf:body
               /ospfv3-e-lsa:e-intra-area-prefix
               /ospfv3-e-lsa:e-intra-prefix-tlvs
               /ospfv3-e-lsa:intra-prefix-tlv:
       +--ro prefix-admin-tag-sub-tlv
          +--ro admin-tag*   uint32
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:database
               /ospf:as-scope-lsa-type/ospf:as-scope-lsas
               /ospf:as-scope-lsa/ospf:version/ospf:ospfv3/ospf:ospfv3
               /ospf:body/ospfv3-e-lsa:e-as-external
               /ospfv3-e-lsa:e-external-tlvs
               /ospfv3-e-lsa:external-prefix-tlv:
       +--ro prefix-admin-tag-sub-tlv
          +--ro admin-tag*   uint32
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas/ospf:area
               /ospf:database/ospf:area-scope-lsa-type
               /ospf:area-scope-lsas/ospf:area-scope-lsa/ospf:version
               /ospf:ospfv3/ospf:ospfv3/ospf:body/ospfv3-e-lsa:e-nssa
               /ospfv3-e-lsa:e-external-tlvs
               /ospfv3-e-lsa:external-prefix-tlv:
       +--ro prefix-admin-tag-sub-tlv
          +--ro admin-tag*   uint32

7.2.  YANG Data Model for OSPF Prefix Administrative Tags

   The following is the YANG module:

   <CODE BEGINS> file "ietf-ospf-admin-tags@2025-07-31.yang"
   module ietf-ospf-admin-tags {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-ospf-admin-tags";
     prefix ospf-admin-tags;

     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";
     }
     import ietf-inet-types {
       prefix inet;
       reference
         "RFC 6991: Common YANG Data Types";
     }
     import ietf-ospfv3-extended-lsa {
       prefix ospfv3-e-lsa;
       reference
         "RFC 9587: YANG Data Model for OSPFv3 Extended Link
                    State Advertisements (LSAs)";
     }

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

        Author:   Yingzhen Qu
                  <mailto:yingzhen.ietf@gmail.com>
        Author:   Acee Lindem
                  <mailto:acee.ietf@gmail.com>
        Author:   Peter Psenak
                  <mailto:ppsenak@cisco.com>";
     description
       "This YANG module defines the configuration
        and operational state for OSPF administrative tags.

        This YANG data model 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 9825;
        see the RFC itself for full legal notices.";
     reference
       "RFC 9825: Extensions to OSPF for Advertising Prefix
                  Administrative Tags.";

     revision 2025-07-31 {
       description
         "Initial revision.";
       reference
         "RFC 9825: Extensions to OSPF for Advertising Prefix
                    Administrative Tags.";
     }

     grouping prefix-admin-tag-sub-tlv {
       description
         "Prefix Administrative Tag Sub-TLVs.";
       container prefix-admin-tag-sub-tlv {
         config false;
         description
           "Prefix Administrative Tag Sub-TLV.";
         leaf-list admin-tag {
           type uint32;
           description
             "Administrative tags.";
         }
       }
     }

     /* Configuration */

     augment "/rt:routing/rt:control-plane-protocols"
           + "/rt:control-plane-protocol/ospf:ospf"
           + "/ospf:areas/ospf:area/ospf:ranges/ospf:range" {
       when "derived-from-or-self(../../../../.."
          + "/rt:type, 'ospf:ospf')" {
         description
           "This augments the OSPF routing protocol area range
            configuration.";
       }
       description
         "This augments the OSPF protocol area range configuration
          with administrative tags.  The configured tags will be
          advertised with summary prefix when it is active.";
       container admin-tags {
         when "../ospf:advertise = 'true'";
         leaf-list admin-tag {
           type uint32;
           description
             "Administrative tags.";
         }
         description
           "OSPF prefix administrative tags.";
       }
     }

     augment "/rt:routing/rt:control-plane-protocols"
           + "/rt:control-plane-protocol/ospf:ospf"
           + "/ospf:areas/ospf:area/ospf:interfaces/ospf:interface" {
       when "derived-from-or-self(../../../../.."
          + "/rt:type, 'ospf:ospf')" {
         description
           "This augments the OSPF routing protocol interface
            configuration.";
       }
       description
         "This augments the OSPF protocol interface configuration
          with Administrative Tags.  The configured tags will be
          advertised with local prefixes configured for the interface.";
       container local-prefix-admin-tags {
         leaf-list default-admin-tag {
           type uint32;
           description
             "Administrative tags that will be associated with
              local prefixes if the prefix is not specified explicitly.
              If omitted, no administrative tags are associated with
              local prefixes by default.";
         }
         list specific-prefix-admin-tag {
           key "prefix";
           leaf prefix {
             type inet:ip-prefix;
             description
               "IPv4 or IPv6 prefix.";
           }
           leaf-list admin-tag {
             type uint32;
             description
               "Administrative tags that will be associated with
                the specified local prefix.  If omitted, no
                administrative tags are associated with the specified
                local prefix.";
           }
           description
             "Administrative tags that are explicitly associated with
              the specified prefix.";
         }
         description
           "List of administrative tags that are to be advertised
            with interface local prefixes.";
       }
     }

     /* Local-RIB */

     augment "/rt:routing"
           + "/rt:control-plane-protocols/rt:control-plane-protocol"
           + "/ospf:ospf/ospf:local-rib/ospf:route/ospf:next-hops"
           + "/ospf:next-hop" {
       description
         "This augments local-rib next-hop with administrative tags.";
       leaf-list admin-tag {
         type uint32;
         description
           "Administrative tags.";
       }
     }

     /* Database */

     augment "/rt:routing"
           + "/rt:control-plane-protocols/rt:control-plane-protocol"
           + "/ospf:ospf/ospf:areas/ospf:area"
           + "/ospf:interfaces/ospf:interface/ospf:database"
           + "/ospf:link-scope-lsa-type/ospf:link-scope-lsas"
           + "/ospf:link-scope-lsa/ospf:version/ospf:ospfv2"
           + "/ospf:ospfv2/ospf:body/ospf:opaque"
           + "/ospf:extended-prefix-opaque/ospf:extended-prefix-tlv" {
       when "derived-from-or-self(../../../../../../../../../.."
          + "/../../../../rt:type, 'ospf:ospfv2')" {
         description
           "This augmentation is only valid for OSPFv2.";
       }
       description
         "Prefix Administrative Tag Sub-TLVs for OSPFv2 extended prefix
          TLV in type 9 opaque LSA.";
       uses prefix-admin-tag-sub-tlv;
     }

     augment "/rt:routing"
           + "/rt:control-plane-protocols/rt:control-plane-protocol"
           + "/ospf:ospf/ospf:areas"
           + "/ospf:area/ospf:database"
           + "/ospf:area-scope-lsa-type/ospf:area-scope-lsas"
           + "/ospf:area-scope-lsa/ospf:version/ospf:ospfv2"
           + "/ospf:ospfv2/ospf:body/ospf:opaque"
           + "/ospf:extended-prefix-opaque/ospf:extended-prefix-tlv" {
       when "derived-from-or-self(../../../../../../../../../.."
          + "/../../rt:type, 'ospf:ospfv2')" {
         description
           "This augmentation is only valid for OSPFv2.";
       }
       description
         "Prefix Administrative Tag Sub-TLVs for OSPFv2 extended prefix
          TLV in type 10 opaque LSA.";
       uses prefix-admin-tag-sub-tlv;
     }

     augment "/rt:routing"
           + "/rt:control-plane-protocols/rt:control-plane-protocol"
           + "/ospf:ospf/ospf:database"
           + "/ospf:as-scope-lsa-type/ospf:as-scope-lsas"
           + "/ospf:as-scope-lsa/ospf:version/ospf:ospfv2"
           + "/ospf:ospfv2/ospf:body/ospf:opaque"
           + "/ospf:extended-prefix-opaque/ospf:extended-prefix-tlv" {
       when "derived-from-or-self(../../../../../../../.."
          + "/../../rt:type, 'ospf:ospfv2')" {
         description
           "This augmentation is only valid for OSPFv2.";
       }
       description
         "Prefix Administrative Tag Sub-TLVs for OSPFv2 extended prefix
          TLV in type 11 opaque LSA.";
       uses prefix-admin-tag-sub-tlv;
     }

     augment "/rt:routing"
           + "/rt:control-plane-protocols/rt:control-plane-protocol"
           + "/ospf:ospf/ospf:areas/ospf:area/ospf:database"
           + "/ospf:area-scope-lsa-type/ospf:area-scope-lsas"
           + "/ospf:area-scope-lsa/ospf:version/ospf:ospfv3"
           + "/ospf:ospfv3/ospf:body/ospfv3-e-lsa:e-inter-area-prefix"
           + "/ospfv3-e-lsa:e-inter-prefix-tlvs"
           + "/ospfv3-e-lsa:inter-prefix-tlv" {
       when "derived-from-or-self(../../../../../../../../../.."
          + "/../../rt:type, 'ospf:ospfv3')" {
         description
           "This augmentation is only valid for OSPFv3.";
       }
       description
         "Augment OSPFv3 Inter-Area-Prefix TLV in the
          E-Inter-Area-Prefix-LSA.";
       uses prefix-admin-tag-sub-tlv;
     }

     augment "/rt:routing"
           + "/rt:control-plane-protocols/rt:control-plane-protocol"
           + "/ospf:ospf/ospf:areas/ospf:area/ospf:database"
           + "/ospf:area-scope-lsa-type/ospf:area-scope-lsas"
           + "/ospf:area-scope-lsa/ospf:version/ospf:ospfv3"
           + "/ospf:ospfv3/ospf:body/ospfv3-e-lsa:e-intra-area-prefix"
           + "/ospfv3-e-lsa:e-intra-prefix-tlvs"
           + "/ospfv3-e-lsa:intra-prefix-tlv" {
       when "/rt:routing/rt:control-plane-protocols"
          + "/rt:control-plane-protocol/rt:type = 'ospf:ospfv3'" {
         description
           "This augmentation is only valid for OSPFv3.";
       }
       description
         "Augment OSPFv3 Intra-Area-Prefix TLV in the
          E-Intra-Area-Prefix-LSA.";
       uses prefix-admin-tag-sub-tlv;
     }

     augment "/rt:routing"
           + "/rt:control-plane-protocols/rt:control-plane-protocol"
           + "/ospf:ospf/ospf:database"
           + "/ospf:as-scope-lsa-type/ospf:as-scope-lsas"
           + "/ospf:as-scope-lsa/ospf:version/ospf:ospfv3"
           + "/ospf:ospfv3/ospf:body/ospfv3-e-lsa:e-as-external"
           + "/ospfv3-e-lsa:e-external-tlvs"
           + "/ospfv3-e-lsa:external-prefix-tlv" {
       when "derived-from-or-self(../../../../../../../.."
          + "/../../rt:type, 'ospf:ospfv3')" {
         description
           "This augmentation is only valid for OSPFv3.";
       }
       description
         "Augment OSPFv3 External-Prefix TLV in the E-AS-External-LSA.";
       uses prefix-admin-tag-sub-tlv;
     }

     augment "/rt:routing"
           + "/rt:control-plane-protocols/rt:control-plane-protocol"
           + "/ospf:ospf/ospf:areas/ospf:area/ospf:database"
           + "/ospf:area-scope-lsa-type/ospf:area-scope-lsas"
           + "/ospf:area-scope-lsa/ospf:version/ospf:ospfv3"
           + "/ospf:ospfv3/ospf:body/ospfv3-e-lsa:e-nssa"
           + "/ospfv3-e-lsa:e-external-tlvs"
           + "/ospfv3-e-lsa:external-prefix-tlv" {
       when "/rt:routing/rt:control-plane-protocols"
          + "/rt:control-plane-protocol/rt:type = 'ospf:ospfv3'" {
         description
           "This augmentation is only valid for OSPFv3.";
       }
       description
         "Augment OSPFv3 External-Prefix TLV in the E-NSSA-LSA.";
       uses prefix-admin-tag-sub-tlv;
     }
   }
   <CODE ENDS>

8.  Security Considerations

   This document describes a generic mechanism for advertising
   administrative tags for OSPF prefixes.  The administrative tags are
   generally less critical than the topology information currently
   advertised by the base OSPF protocol.  The security considerations
   for the generic mechanism are dependent on their application.  One
   such application is to control leaking of OSPF routes to other
   protocols (e.g., BGP [RFC4271]).  If an attacker were able to modify
   the administrative tags associated with OSPF routes, and they were
   being used for this application, such routes could be prevented from
   being advertised in routing domains where they are required (subtle
   denial of service) or they could be advertised into routing domains
   where they shouldn't be advertised (routing vulnerability).  Security
   considerations for the base OSPF protocol are covered in [RFC2328]
   and [RFC5340].

   The "ietf-ospf-admin-tag" 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 YANG-based
   management protocols (1) have to use a secure transport layer (e.g.,
   SSH [RFC4252], TLS [RFC8446], and QUIC [RFC9000]) and (2) have to use
   mutual authentication.

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

   There are a number of data nodes defined in this YANG module that are
   writable/creatable/deletable (i.e., "config true", which is the
   default).  All writable data nodes are likely to be sensitive or
   vulnerable in some network environments.  Write operations (e.g.,
   edit-config) and delete operations to these data nodes without proper
   protection or authentication can have a negative effect on network
   operations.  The following subtrees and data nodes have particular
   sensitivities/vulnerabilities:

   *  /ospf:ospf/ospf:areas/ospf:area/ospf:interfaces/ospf:interface/
      local-prefix-admin-tags

   *  /ospf:ospf/ospf:areas/ospf:area/ospf:ranges/ospf:range/admin-tags

   Some of the readable data nodes in this YANG module may be considered
   sensitive or vulnerable in some network environments.  Thus, it is
   important to control read access (e.g., via get, get-config, or
   notification) to these data nodes.  Exposure of the OSPF link state
   database may be useful in mounting a Denial-of-Service (DoS) attack.
   Specifically, the following subtrees and data nodes have particular
   sensitivities:

   *  /ospf:ospf/ospf:areas/ospf:area/ospf:interfaces/ospf:interface/
      local-prefix-admin-tags

   *  /ospf:ospf/ospf:areas/ospf:area/ospf:ranges/ospf:range/admin-tags

   *  /prefix-admin-tag-sub-tlv

9.  IANA Considerations

   The following value has been allocated in the "OSPFv2 Extended Prefix
   TLV Sub-TLVs" registry [RFC7684] in the "Open Shortest Path First v2
   (OSPFv2) Parameters" registry group:

   13:  Administrative Tag

   The following value has been allocated in the "OSPFv3 Extended-LSA
   Sub-TLVs" registry [RFC8362] in the "Open Shortest Path First v3
   (OSPFv3) Parameters" registry group:

   39:  Administrative Tag

      Since this sub-TLV only applies to prefixes and not links, the
      value of the Layer-2 Bundle Member (L2BM) field will be "X".

   The following value has been allocated in the "OSPFv3 SRv6 Locator
   LSA Sub-TLVs" registry [RFC9513] in the "Open Shortest Path First v3
   (OSPFv3) Parameters" registry group:

   6:  Administrative Tag

   IANA has assigned one new URI in the "IETF XML Registry" [RFC3688]:

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

   This document also registers one new YANG module name in the "YANG
   Module Names" registry [RFC6020] with the following:

   Name:  ietf-ospf-admin-tags
   Namespace:  urn:ietf:params:xml:ns:yang:ietf-ospf-admin-tags
   Prefix:  ospf-admin-tags
   Reference:  RFC 9825

10.  References

10.1.  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>.

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

   [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>.

   [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>.

   [RFC6991]  Schoenwaelder, J., Ed., "Common YANG Data Types",
              RFC 6991, DOI 10.17487/RFC6991, July 2013,
              <https://www.rfc-editor.org/info/rfc6991>.

   [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>.

   [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>.

   [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>.

   [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>.

   [RFC9513]  Li, Z., Hu, Z., Talaulikar, K., Ed., and P. Psenak,
              "OSPFv3 Extensions for Segment Routing over IPv6 (SRv6)",
              RFC 9513, DOI 10.17487/RFC9513, December 2023,
              <https://www.rfc-editor.org/info/rfc9513>.

   [RFC9552]  Talaulikar, K., Ed., "Distribution of Link-State and
              Traffic Engineering Information Using BGP", RFC 9552,
              DOI 10.17487/RFC9552, December 2023,
              <https://www.rfc-editor.org/info/rfc9552>.

   [RFC9587]  Lindem, A., Palani, S., and Y. Qu, "YANG Data Model for
              OSPFv3 Extended Link State Advertisements (LSAs)",
              RFC 9587, DOI 10.17487/RFC9587, June 2024,
              <https://www.rfc-editor.org/info/rfc9587>.

10.2.  Informative References

   [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>.

   [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>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.

   [RFC5130]  Previdi, S., Shand, M., Ed., and C. Martin, "A Policy
              Control Mechanism in IS-IS Using Administrative Tags",
              RFC 5130, DOI 10.17487/RFC5130, February 2008,
              <https://www.rfc-editor.org/info/rfc5130>.

   [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>.

   [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>.

   [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>.

Acknowledgments

   The authors of [RFC5130] are acknowledged, since this document draws
   upon both the IS-IS specification and deployment experience.  The
   text in Section 4 is adopted from [RFC5130].

   Thanks to Donnie Savage for his comments and questions.

   Thanks to Ketan Talaulikar for his comments and providing the BGP-LS
   text.

   Thanks to Tony Przygienda and Les Ginsberg for discussions on tag
   selection.

   Thanks to Russ White for his Routing Directorate review.

   Thanks to Bruno Decraene and Changwang Lin for working group last
   call comments.

   Thanks to Gunter Van de Velde for has AD review and comments.

   Thanks to David Dong for IANA review and comments.

   Thanks to Deb Cooley, Roman Danyliw, and John Scudder for IESG review
   and comments.

   Thanks to Mahesh Jethanandani for an extensive IESG review of the
   YANG data model.

Authors' Addresses

   Acee Lindem (editor)
   LabN Consulting, L.L.C.
   301 Midenhall Way
   Cary, NC 27513
   United States of America
   Email: acee.ietf@gmail.com


   Peter Psenak
   Cisco Systems
   Apollo Business Center
   Mlynske nivy 43
   821 09 Bratislava
   Slovakia
   Email: ppsenak@cisco.com


   Yingzhen Qu
   Futurewei Technologies
   2330 Central Expressway
   Santa Clara, CA 95050
   United States of America
   Email: yingzhen.ietf@gmail.com
