RFC 9825

Extensions to OSPF for Advertising Prefix Administrative Tags

📅 published July 2025, from ietf

RFC 9825: Extensions to OSPF for Advertising Prefix Administrative Tags 🎀

Okay bestie, this is an Internet Standards Track document 💅 from the IETF, dated July 2025, with ISSN 2070-1721. The authors are A. Lindem (Ed.) at LabN Consulting, L.L.C., P. Psenak at Cisco Systems, and Y. Qu at Futurewei Technologies. The title block doesn't list anything it obsoletes or updates, so this is a brand new spec 🌸.

Abstract ✨

Okay so routers in OSPFv2 and OSPFv3 routing domains need to be able to stick tags on prefixes 🏷️. Before this, OSPFv2 and OSPFv3 were stuck with a single tag, and only for Autonomous System (AS) External and Not-So-Stubby-Area (NSSA) prefixes 😭. Now the flexible encodings from OSPFv2 Prefix/Link Attribute Advertisement and OSPFv3 Extended Link State Advertisements (LSAs) let you advertise multiple administrative tags for every type of prefix 🙌. These tags can power route redistribution policy, selective prefix prioritization, selective IP Fast Reroute (IPFRR) prefix protection, and a bunch of other stuff too 🔥.

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 ⚖️

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 🌟

Okay so it's useful for routers in OSPFv2 [RFC2328] and OSPFv3 [RFC5340] routing domains to tag 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 😤. Thanks to the flexible encodings in OSPFv2 Prefix/Link Attribute Advertisement [RFC7684] and OSPFv3 Extended Link State Advertisement (LSA) [RFC8362], you can now advertise multiple administrative tags for all types of prefixes ✨. These tags can be used in lots of ways, including (but not limited to):

Controlling which routes get redistributed into other protocols for re-advertisement. 📤
Prioritizing selected prefixes for faster convergence and installation in the forwarding plane. 🚀
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 🎀

Okay so this document creates a brand new Administrative Tag Sub-TLV for OSPFv2 and OSPFv3 🆕. This sub-TLV carries one or more 32-bit unsigned integers that can 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 looks like this:

    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

Here's what each field does 👇

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. It MUST be a multiple of 4 octets, depending 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 carries one or more 32-bit unsigned integer values that are 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 here is 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 here is 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 here is valid as a sub-TLV of the following TLVs specified in [RFC9513]:

SRv6 Locator TLV advertised in the SRv6 Locator LSA

4. Protocol Operation ⚙️

Okay so 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 number of tags an implementation supports is a local matter, depending on the applications using prefix tags 🤓. Depending on the application, the number of tags supported by the OSPF routers in the routing domain may limit how well that application can be deployed 😬.

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 used for the first tag. Additional tags MAY be advertised using the Administrative Tag Sub-TLV specified in this document. This keeps things backward compatible with implementations that don't 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 an 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 says a certain operation or set of operations needs to happen based on tag order. Each tag SHOULD be treated as an autonomous identifier that MAY be used in policy to perform a policy action. Whether tag A comes before or after 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 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, those LSAs may 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. If the implementation supports multiple tags, it 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 💜.

7. YANG Data Model 💅

okay so YANG [RFC7950] is a data definition language 🎀 that lets you describe a conceptual data store, so networked devices can be managed with NETCONF [RFC6241] or RESTCONF [RFC8040]. it's giving config management energy ✨

this section defines a YANG data model for configuring and managing the prefix administrative tags from this document 🏷️ it augments the OSPF YANG data model [RFC9129], the OSPFv3 Extended LSA YANG data model [RFC9587], and the Routing Management YANG data model [RFC8349]. it also imports the YANG data models defined in [RFC6991]. the whole thing fits together so cleanly, I'm obsessed 😭🫶

7.1. Tree for the YANG Data Model 🌸

this document uses the graphical representation of data models per [RFC8340], so the tree diagram is the way to read it 🧚

here's 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 ✨

okay so this is the actual YANG module 💖 it's the machine-readable blueprint for the OSPF prefix admin tag stuff, and it covers both the config and the operational state. the module is fully written out below, so you can see every bit of it 🎀

<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 ✨

Okay bestie, security time 🔒 This doc is a generic mechanism for advertising administrative tags on OSPF prefixes. The tags are lowkey less critical than the topology info the base OSPF protocol already advertises 💅 But how risky they are depends on what they're used for. One big use case is controlling leaking of OSPF routes into other protocols (e.g., BGP [RFC4271]).

Here's the drama 😭 If an attacker could modify the tags on OSPF routes, and those tags were driving that leaking, routes could get blocked from showing up where they're needed (subtle denial of service 💀) or get advertised into routing domains where they absolutely should not be (routing vulnerability 🚨). The base OSPF security stuff is covered in [RFC2328] and [RFC5340], so go read those too 🫶

The "ietf-ospf-admin-tag" YANG module is a data model meant to be accessed through YANG-based management protocols like NETCONF [RFC6241] and RESTCONF [RFC8040]. These 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. No shortcuts, periodt 🔐

The Network Configuration Access Control Model (NACM) [RFC8341] is the bouncer 💅 It lets you restrict particular NETCONF or RESTCONF users to a preconfigured subset of protocol operations and content.

Now the writable nodes 👀 A bunch of data nodes in this module are writable, creatable, and deletable (that's config true, which is the default). All of them are likely to be sensitive or vulnerable in some network environments. Writes and deletes to these nodes without proper protection or authentication can seriously mess with network operations. The most sensitive ones are:

/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 readable nodes can be sensitive too 🙈 So it's important to control read access (e.g., via get, get-config, or notification). Exposing the OSPF link state database could be useful for mounting a Denial-of-Service (DoS) attack, so lock that down. The particularly sensitive ones are:

/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 📋

Here's what got allocated, no cap 🧁 In the "OSPFv2 Extended Prefix TLV Sub-TLVs" registry [RFC7684], inside the "Open Shortest Path First v2 (OSPFv2) Parameters" registry group, this value got the green light:

13:  Administrative Tag

Next, the "OSPFv3 Extended-LSA Sub-TLVs" registry [RFC8362], inside the "Open Shortest Path First v3 (OSPFv3) Parameters" registry group, gave us:

39:  Administrative Tag

Since this sub-TLV only applies to prefixes and not links, the Layer-2 Bundle Member (L2BM) field will be "X". Makes total sense, iykyk ✨

Then the "OSPFv3 SRv6 Locator LSA Sub-TLVs" registry [RFC9513], also in the "Open Shortest Path First v3 (OSPFv3) Parameters" registry group, got this one:

6:  Administrative Tag

IANA also 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.

And this document registers one new YANG module name in the "YANG Module Names" registry [RFC6020] 🦋

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

These are the must-read ones, the foundation of the whole vibe 💜

[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

These are the extra context bits, bonus content for the curious 🧚

[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 🫶

Huge shoutout to the authors of [RFC5130] 👑 This document draws on both the IS-IS specification and deployment experience from that work, and 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 for 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 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

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