OSPF prefix tags: Extensions to OSPF for Advertising Prefix Administrative Tags
Let routers label networks with multiple administrative tags for policy and optimization.
Lindem, A., Ed., Psenak, P., and Y. Qu, "Extensions to OSPF for Advertising Prefix Administrative Tags", RFC 9825, DOI 10.17487/RFC9825, July 2025, <https://www.rfc-editor.org/info/rfc9825>.
@misc{rfc9825,
series = {Request for Comments},
number = 9825,
howpublished = {RFC 9825},
publisher = {RFC Editor},
doi = {10.17487/RFC9825},
url = {https://www.rfc-editor.org/info/rfc9825},
author = {A. Lindem and P. Psenak and Y. Qu},
title = {{Extensions to OSPF for Advertising Prefix Administrative Tags}},
pagetotal = 18,
year = 2025,
month = jul,
} RFC text
Contents
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
AI ELI5
On this page
§1The Problem with One Tag
In the original OSPF specification, routers could attach a single tag to routes that came from outside the autonomous system (AS) or from not-so-stubby areas (NSSAs). These tags were useful for policy decisions: a router could say, for example, "if this route has tag 100, send it to BGP; if it has tag 200, drop it." But this mechanism had limitations.
First, only AS-external and NSSA routes could carry tags; routes learned from other routers in the same OSPF domain had no way to be labeled. Second, each route could carry only one tag, even though operators often wanted to apply multiple independent policies. Network operators needed a way to label any prefix with multiple tags, similar to the mechanism already deployed in IS-IS.
The old OSPF could only put one sticker on certain types of packages, and not on others. Network managers wanted to put many stickers on any package, so they could route it based on multiple rules at once.
§2The Administrative Tag Sub-TLV
RFC 9825 defines a new sub-TLV (a sub-component of OSPF's link state advertisements) called the Administrative Tag Sub-TLV. It carries a list of one or more 32-bit unsigned integers that represent tags.
The sub-TLV has a simple structure: a type field (which varies depending on the OSPF version and prefix type), a length field that indicates how many bytes follow (always a multiple of 4, since each tag is 4 bytes), and then the tag values themselves. The RFC specifies three type values: 13 for OSPFv2 Extended Prefix TLVs, 39 for OSPFv3 Extended LSAs, and 6 for OSPFv3 SRv6 locators.
Routers MUST support at least one tag per prefix. Most routers will support multiple tags, though the exact number depends on the implementation and the local policy. Tags have no inherent meaning or ordering; each tag is simply an autonomous identifier that policies can act upon.
The tag sub-TLV is like a sticky note. It says "I am a tag" (the type), how many bytes come next (the length), and then lists the numbers. Each number is a sticker you can stick on a network.
§3Where Tags Appear
Before RFC 9825, the single tag field was hardcoded into the AS-External and NSSA LSA formats themselves. The new Administrative Tag Sub-TLV takes a different approach: it is a sub-component that plugs into the more flexible advertisement mechanisms defined in RFC 7684 (OSPFv2 Prefix/Link Attribute Advertisement) and RFC 8362 (OSPFv3 Extended Link State Advertisements).
In OSPFv2, tags attach to the Extended Prefix TLV advertised in opaque LSAs (types 9, 10, and 11). In OSPFv3, tags can appear in four places: the Inter-Area-Prefix TLV, the Intra-Area-Prefix TLV, the External-Prefix TLV in AS-External LSAs, and the External-Prefix TLV in NSSA LSAs. There is also support for tags on SRv6 locators (RFC 9513). For backward compatibility, when a router advertises the first tag on an AS-External or NSSA prefix, it SHOULD use the existing tag field in the LSA itself; additional tags use the new sub-TLV.
This flexibility means any prefix type—internal, summarized, external, or SRv6 locator—can now carry multiple tags, whereas before only external and NSSA prefixes had any tag at all.
Tags used to go in special places for special routes. Now they fit into the newer, more flexible advertisement format, so any route type can have them.
| Feature | Before RFC 9825 | After RFC 9825 |
|---|---|---|
| Prefix types with tags | Only AS-External and NSSA | All prefix types |
| Number of tags per prefix | One | Multiple (implementation-dependent) |
| Tag encoding | Hardcoded LSA field | Flexible sub-TLV in extended advertisements |
| Backward compatibility THIS RFC | N/A | First tag uses legacy field |
§4How Routers Use and Propagate Tags
An OSPF router that supports this RFC will advertise tags when it originates prefixes (for example, routes it learns from local interfaces, or routes it redistributes from another protocol). When a router receives prefixes with tags from its neighbors, it can use those tags in its local policies.
Area Border Routers (ABRs) act as translators between areas. When an ABR advertises a summary route into another area, the RFC recommends that it carry the tags from the contributing intra-area routes along with it, so downstream routers can apply the same policies. Similarly, when an ABR translates NSSA routes to AS-External routes, it should preserve the tags if possible. However, local policy can suppress tag propagation if needed—for example, a network operator might not want external routes leaking specific tags into an internal area.
When multiple router paths contribute to a route (equal-cost multipath), and those paths have different tags, an ABR MUST choose which tags to advertise. The RFC recommends adding tags in ascending order of the originating router's Router-ID. The number of tags an ABR propagates is limited by its implementation and its configured policies.
For aggregated or summarized routes created locally (area ranges, NSSA ranges, redistributed summaries), the RFC says tags SHOULD NOT be automatically inherited from the component routes; instead, operators SHOULD configure tags explicitly on the summary itself if needed.
Routers put tags on the routes they advertise. When one router hears about a route from another, it remembers the tags. When the first router tells a neighboring area about that route, it passes the tags along—unless someone says not to. When different paths have different tags, the router picks one set to use.
§5Practical Applications
Tags enable several important routing policies. The RFC itself mentions three main use cases, though others are possible.
First, redistribution control: a router can be configured to leak OSPF routes into BGP only if they carry a specific tag. This lets operators segment their network so that internal routes stay internal while tagged routes are advertised externally, all based on policy.
Second, convergence optimization: some prefixes are more critical than others. Operators can tag high-priority prefixes and instruct routers to install and converge on them faster, ahead of lower-priority routes.
Third, fast reroute protection: IP Fast Reroute (IPFRR) and Loop-Free Alternatives (LFA) compute backup paths in case a primary link fails. Operators can tag prefixes to indicate which ones deserve protection, allowing routers to prioritize LFA computation for critical services.
Tags can also be used for traffic engineering, for VPN route isolation, and for many application-specific purposes. The RFC explicitly states that the meaning of tags is a local matter; there is no global registry of tag numbers. Two network operators might use tag 100 to mean entirely different things.
Tags help routers make better decisions. One example: "Routes with tag 100 go to BGP." Another: "Tag 200 means route this fast." A third: "Tag 300 means protect this with a backup path." Each network decides what its tags mean.
§6BGP-LS and the Broader Ecosystem
OSPF is one of several link-state routing protocols. Another important tool in the routing ecosystem is BGP-LS (Border Gateway Protocol - Link State), which lets routers advertise OSPF or IS-IS topology information via BGP. RFC 9552 defined the BGP-LS IGP Route Tag TLV (code 1153) specifically to carry administrative tags learned from IS-IS or OSPF.
RFC 9825 confirms that the OSPF tags defined here will be advertised via BGP-LS using that TLV. This means a network can use BGP-LS to export its OSPF tagging policies to external systems—for example, to a central traffic engineering controller, a path computation server, or a network-wide analytics system. These external systems can then make informed decisions about which routes to use and how to engineer traffic based on the tags visible in OSPF.
BGP-LS is a system that talks about OSPF routes in a different language, so other parts of the network (like traffic controllers) can understand them. It now includes OSPF tags so the external systems see the full picture.
§7Security and Management
The RFC is explicit about the security model. The tags themselves are less sensitive than the underlying OSPF topology; if an attacker modifies a tag, the network does not immediately break. However, if tags are used for important policies—like controlling which routes are redistributed or which prefixes get fast reroute protection—then tag integrity matters.
The RFC includes a complete YANG data model (a machine-readable schema) for configuring and monitoring OSPF administrative tags. This data model is accessed via NETCONF or RESTCONF, both of which MUST use secure transport (SSH, TLS, or QUIC) and mutual authentication. The Network Configuration Access Control Model (NACM) provides fine-grained access control, so that only authorized network operators can change tag configurations.
The RFC identifies several sensitive data nodes: the local-prefix-admin-tags and area range admin-tags configurations are sensitive because they control which tags are advertised; the link-state database contents are sensitive because they could be used to mount denial-of-service attacks if exposed to unauthorized parties. Implementations SHOULD rate-limit logging of malformed tags (for example, tags with invalid lengths) to avoid flooding the system log.
Tags are not as critical as the network topology itself, but they still matter for policy. Access to the configuration tools MUST be secured with passwords and encryption. Only trusted operators should be able to change tags.
§8Status and Deployment
RFC 9825 is a Proposed Standard, approved by the Internet Engineering Steering Group (IESG) in July 2025. It has been registered with IANA: type 13 for OSPFv2 Extended Prefix TLVs, type 39 for OSPFv3 Extended LSAs, and type 6 for OSPFv3 SRv6 Locator LSA sub-TLVs. The YANG module name ietf-ospf-admin-tags has also been registered.
Deployment will depend on router vendor support. Early implementations will likely focus on the core use cases: redistribution control and fast reroute prioritization. Over time, operators will find additional applications—traffic engineering, service routing, network slicing, and others. Unlike the fixed single-tag model, this extensible mechanism allows operators to adapt tagging policies to their evolving needs without waiting for IETF standards updates.
The standard is official as of July 2025. Router vendors are starting to add support. Once routers understand tags, network operators can use them for many different policies.