OSPFv2 Anycast Property Advertisement
draft-ietf-lsr-anycast-flag-07
| Document | Type | Active Internet-Draft (lsr WG) | |
|---|---|---|---|
| Authors | Ran Chen , Detao Zhao , Peter Psenak , Ketan Talaulikar , Changwang Lin | ||
| Last updated | 2025-10-22 (Latest revision 2025-09-22) | ||
| Replaces | draft-chen-lsr-anycast-flag | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
| Formats | |||
| Yang Validation | 0 errors, 0 warnings | ||
| Reviews | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Acee Lindem | ||
| Shepherd write-up | Show Last changed 2025-09-02 | ||
| IESG | IESG state | Publication Requested | |
| Action Holder | |||
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | Gunter Van de Velde | ||
| Send notices to | acee.ietf@gmail.com |
draft-ietf-lsr-anycast-flag-07
LSR R. Chen
Internet-Draft D. Zhao
Intended status: Standards Track ZTE Corporation
Expires: 26 March 2026 P. Psenak
K. Talaulikar
Cisco Systems
C. Lin
H3C
22 September 2025
OSPFv2 Anycast Property Advertisement
draft-ietf-lsr-anycast-flag-07
Abstract
An IP prefix may be configured as anycast and as such the same value
can be advertised by multiple routers. It is useful for other
routers to know that the advertisement is for an anycast identifier.
This document defines a new flag in the OSPFv2 Extended Prefix TLV
Flags to advertise the anycast property.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 26 March 2026.
Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
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Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. OSPFv2 Anycast Property Advertisement . . . . . . . . . . . . 3
3. BGP-LS Advertisement . . . . . . . . . . . . . . . . . . . . 3
4. YANG Data Model . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Tree for the YANG Data Model . . . . . . . . . . . . . . 4
4.2. YANG Data Model for OSPFv2 Anycast Property
Advertisement . . . . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5.1. OSPFv2 Extended Prefix TLV Flags Registry . . . . . . . . 6
5.2. OSPFv2 Anycast Flag YANG Module Registry . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Normative References . . . . . . . . . . . . . . . . . . 7
7.2. Informative References . . . . . . . . . . . . . . . . . 9
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 10
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
An IP prefix may be configured as anycast and as such the same value
can be advertised by multiple routers. It is useful for other
routers to know that the advertisement is for an anycast identifier.
[RFC7684] defines OSPFv2 Opaque LSAs based on Type-Length-Value (TLV)
tuples that can be used to associate additional attributes with
prefixes or links. The OSPFv2 Extended Prefix TLV that is contained
in the OSPFv2 Extended Prefix Opaque LSA is used to advertise
additional attributes associated with a prefix.
Extensions related to the anycast property of prefixes have been
specified for IS-IS [RFC9352] and OSPFv3 [RFC9513], even though those
documents are related to Segment Routing over IPv6, the anycast
property applies to any IP prefix advertisement. This document
defines a flag to advertise the anycast property for a prefix
advertisement in OSPFv2 in the Flags field of the OSPFv2 Extended
Prefix TLV Flags (section 2.1 of [RFC7684]).
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1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. OSPFv2 Anycast Property Advertisement
An IP prefix may be configured as anycast and it is useful for other
routers to know that the advertisement is for an anycast identifier.
A bit is introduced in OSPFv2 Extended Prefix TLV Flags [RFC7684] to
advertise the anycast property:
Value: TBD
Description: Anycast Flag (AC-flag)
The only meaning of the AC-flag is that the prefix is intended to be
advertised by multiple nodes.
When a prefix is configured as anycast, the AC-flag MUST be set.
Otherwise, this flag MUST be clear.
The AC-flag and the N-bit MUST NOT both be set. If both N-flag and
AC-flag are set, the receiving routers MUST ignore the N-flag.
The AC-flag MUST be preserved when re-advertising the prefix across
areas.
The same prefix can be advertised by multiple routers, and that if at
least one of them sets the AC-flag in its advertisement, the prefix
is considered as anycast.
A prefix that is advertised by a single node and without an AC-flag
is considered node-specific prefix.
3. BGP-LS Advertisement
[RFC9085] defines the Prefix Attribute Flags TLV for BGP-LS that
carries prefix attribute flags information, and the Flags field of
this TLV is interpreted according to OSPFv2 [RFC7684]. Thus the
Flags field of the BGP-LS Prefix Attribute Flags TLV also conveys the
anycast property introduced by this document.
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4. YANG Data Model
YANG [RFC7950] is a data definition language used to define the
contents of a conceptual data store that allows networked devices to
be managed using NETCONF [RFC6241] or RESTCONF [RFC8040].
This section defines a YANG data model that can be used to configure
and manage the usage of OSPFv2 Anycast Property as defined in this
document, which augments the OSPF YANG data model [RFC9129] and the
YANG Data Model for Routing Management [RFC8349].
4.1. Tree for the YANG Data Model
This document uses the graphical representation of data models per
[RFC8340].
The following show the tree diagram of the module:
module: ietf-ospf-anycast-flag
augment /rt:routing/rt:control-plane-protocols
/rt:control-plane-protocol/ospf:ospf/ospf:areas/ospf:area
/ospf:interfaces/ospf:interface:
+--rw anycast-flag? boolean
4.2. YANG Data Model for OSPFv2 Anycast Property Advertisement
The following is the YANG module:
<CODE BEGINS> file "ietf-ospf-anycast-flag@2025-08-28.yang"
module ietf-ospf-anycast-flag {
yang-version 1.1;
namespace
"urn:ietf:params:xml:ns:yang:ietf-ospf-anycast-flag";
prefix ospf-anycast-flag;
import ietf-routing {
prefix rt;
reference
"RFC 8349: A YANG Data Model for Routing
Management (NMDA Version)";
}
import ietf-ospf {
prefix ospf;
reference
"RFC 9129: YANG Data Model for the OSPF Protocol";
}
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organization
"IETF LSR - Link State Routing Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/lsr/>
WG List: <mailto:lsr@ietf.org>
Author: Ran Chen
<mailto:chen.ran@zte.com.cn>
Author: Detao Zhao
<mailto:zhao.detao@zte.com.cn>
Author: Peter Psenak
<mailto:ppsenak@cisco.com>
Author: Ketan Talaulikar
<mailto:ketant.ietf@gmail.com>
Author: Changwang Lin
<mailto:linchangwang.04414@h3c.com>";
description
"This YANG module adds the support of configuring an OSPFv2
prefix as anycast.
This YANG module conforms to the Network Management
Datastore Architecture (NMDA) as described in RFC 8342.
Copyright (c) 2025 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject to
the license terms contained in, the Revised BSD License set
forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(https://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX;
see the RFC itself for full legal notices.";
reference
"RFC XXXX";
revision 2025-08-28 {
description
"Initial version";
reference
"RFC XXXX: OSPFv2 Anycast Property Advertisement";
}
identity ac-flag {
base ospf:ospfv2-extended-prefix-flag;
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description
"Anycast flag. When set, it indicates that the prefix
is configured as anycast.";
}
/* Configuration */
augment "/rt:routing/rt:control-plane-protocols/"
+ "rt:control-plane-protocol/ospf:ospf/"
+ "ospf:areas/ospf:area/ospf:interfaces/ospf:interface" {
when "derived-from(/rt:routing/rt:control-plane-protocols/"
+ "rt:control-plane-protocol/rt:type, 'ospf:ospfv2')" {
description
"This augments the OSPFv2 interface configuration.";
}
description
"This augments OSPFv2 interface configuration with anycast
property advertisement.";
leaf anycast-flag {
type boolean;
default "false";
description
"Sets the prefix as an anycast address.";
}
}
}
<CODE ENDS>
5. IANA Considerations
This document requests allocation for the following registry.
5.1. OSPFv2 Extended Prefix TLV Flags Registry
This document adds a new bit in the "OSPFv2 Extended Prefix TLV
Flags"registry:
AC-flag (Anycast Flag).
5.2. OSPFv2 Anycast Flag YANG Module Registry
IANA is requested to register the following URI in the "ns" registry
within the "IETF XML Registry" group ([RFC3688]):
URI: urn:ietf:params:xml:ns:yang:ietf-ospf-anycast-flag
Registrant Contact: The IESG.
XML: N/A, the requested URI is an XML namespace
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IANA is requested to register the following YANG module in the "YANG
Module Names" registry ([RFC6020]) within the "YANG Parameters"
registry group.
name: ietf-ospf-anycast-flag
Maintained by IANA? N
namespace: urn:ietf:params:xml:ns:yang:ietf-ospf-anycast-flag
prefix: ospf-anycast-flag
reference: RFC XXXX
6. Security Considerations
Procedures and protocol extensions defined in this document do not
affect the OSPFv2 security model. See the "Security
Considerations"section of [RFC7684] for a discussion of OSPFv2
security.
The ietf-ospf-anycast-flag YANG module defines a data model that is
designed to be accessed via YANG-based management protocols, such as
NETCONF [RFC6241] and RESTCONF [RFC8040]. These protocols have to
use a secure transport layer (e.g., SSH [RFC4252], TLS [RFC8446], and
QUIC [RFC9000]) and have to use mutual authentication.
The NETCONF Access Control Model (NACM) [RFC8341] provides the means
to restrict access for particular NETCONF or RESTCONF users to a pre-
configured subset of all available NETCONF or RESTCONF protocol
operations and content.
The following data nodes defined in the YANG module that are
writable/creatable/deletable (i.e., config true). The modifications
to these data nodes without proper protection could have prevent
interpreting the IPv4 prefix as anycast.
/ospf:ospf/ospf:areas/ospf:area/ospf:interfaces/ospf:interface/
ospf-anycast-flag:anycast-flag
Some of the readable data nodes in this YANG module may be considered
sensitive or vulnerable in some network environments. Exposure of
the OSPF link state database may be useful in mounting a Denial-of-
Service (DoS) attacks. These are the readable data nodes:
/ospf:ospf/ospf:areas/ospf:area/ospf:interfaces/ospf:interface/
ospf-anycast-flag:anycast-flag
7. References
7.1. Normative References
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<https://www.rfc-editor.org/info/rfc3688>.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<https://www.rfc-editor.org/info/rfc6020>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/info/rfc6241>.
[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
2015, <https://www.rfc-editor.org/info/rfc7684>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/info/rfc8040>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration
Access Control Model", STD 91, RFC 8341,
DOI 10.17487/RFC8341, March 2018,
<https://www.rfc-editor.org/info/rfc8341>.
[RFC8349] Lhotka, L., Lindem, A., and Y. Qu, "A YANG Data Model for
Routing Management (NMDA Version)", RFC 8349,
DOI 10.17487/RFC8349, March 2018,
<https://www.rfc-editor.org/info/rfc8349>.
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[RFC9085] Previdi, S., Talaulikar, K., Ed., Filsfils, C., Gredler,
H., and M. Chen, "Border Gateway Protocol - Link State
(BGP-LS) Extensions for Segment Routing", RFC 9085,
DOI 10.17487/RFC9085, August 2021,
<https://www.rfc-editor.org/info/rfc9085>.
[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>.
7.2. Informative References
[I-D.ietf-rtgwg-segment-routing-ti-lfa]
Bashandy, A., Litkowski, S., Filsfils, C., Francois, P.,
Decraene, B., and D. Voyer, "Topology Independent Fast
Reroute using Segment Routing", Work in Progress,
Internet-Draft, draft-ietf-rtgwg-segment-routing-ti-lfa-
21, 12 February 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-rtgwg-
segment-routing-ti-lfa-21>.
[RFC4252] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252,
January 2006, <https://www.rfc-editor.org/info/rfc4252>.
[RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
<https://www.rfc-editor.org/info/rfc8340>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[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>.
[RFC9352] Psenak, P., Ed., Filsfils, C., Bashandy, A., Decraene, B.,
and Z. Hu, "IS-IS Extensions to Support Segment Routing
over the IPv6 Data Plane", RFC 9352, DOI 10.17487/RFC9352,
February 2023, <https://www.rfc-editor.org/info/rfc9352>.
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[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>.
Acknowledgements
The authors would like to thank Acee Lindem for aligning the
terminology with existing OSPF documents and for editorial
improvements.
Contributors
This document has the following contributor:
Yingzhen Qu
Futurewei Technologies
Email: yingzhen.ietf@gmail.com
Authors' Addresses
Ran Chen
ZTE Corporation
Nanjing
China
Email: chen.ran@zte.com.cn
Detao Zhao
ZTE Corporation
Nanjing
China
Email: zhao.detao@zte.com.cn
Peter Psenak
Cisco Systems
Email: ppsenak@cisco.com
Ketan Talaulikar
Cisco Systems
Email: ketant.ietf@gmail.com
Changwang Lin
H3C
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Email: linchangwang.04414@h3c.com
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