LSR Working Group L. Gong Internet-Draft W. Cheng Updates: 6987, 8770 (if approved) China Mobile Intended status: Standards Track C. Lin Expires: 1 April 2026 New H3C Technologies A. Lindem Arrcus, Inc. R. Chen ZTE Corporation 28 September 2025 Advertising Unreachable Links in OSPF draft-ietf-lsr-ospf-ls-link-infinity-11 Abstract In certain scenarios, it is necessary to advertise OSPF links that are not applicable to the default SPF (Shortest Path First) calculation for other purposes. In order to advertise these links and not use them in the base SPF calculation, the metric LSLinkInfinity (0xffff) is used to specify that the link is unreachable. Stub Router Advertisement (RFC 6987) defines MaxLinkMetric (0xffff) to indicate a router-LSA link should not be used for transit traffic. When an OSPFv2 router supports the Unreachable Link support capability defined in this document, OSPFv2 Stub Router links are advertised as MaxReachableLinkMetric (0xfffe) rather than MaxLinkMetric (0xffff). This document updates RFC 6987 and RFC 8770 with respect to the advertisement of MaxReachableLinkMetric rather than MaxLinkMetric. 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." Gong, et al. Expires 1 April 2026 [Page 1] Internet-Draft Advertising Unreachable Links in OSPF September 2025 This Internet-Draft will expire on 1 April 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. 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 . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Case 1: Traffic Engineering . . . . . . . . . . . . . . . 3 2.2. Case 2: Flexible Algorithm . . . . . . . . . . . . . . . 4 3. LSLinkInfinity-Based Solution . . . . . . . . . . . . . . . . 5 3.1. Unreachable Link Advertisement . . . . . . . . . . . . . 5 3.2. Unreachable Link Backward Compatibility . . . . . . . . . 5 3.3. Stub Router Advertisement Backward Compatibility . . . . 6 4. Operational Considerations . . . . . . . . . . . . . . . . . 7 4.1. Configuration Parameters . . . . . . . . . . . . . . . . 7 4.2. YANG Data Model . . . . . . . . . . . . . . . . . . . . . 7 4.2.1. Tree for OSPF Functional Capability . . . . . . . . . 8 4.2.2. Tree for OSPF Advertising Unreachable Links . . . . . 8 4.2.3. IANA Module for OSPF Functional Capability Bits . . . 9 4.2.4. YANG Module for OSPF Functional Capability . . . . . 11 4.2.5. YANG Module for OSPF Advertising Unreachable Links . 14 5. Security Considerations . . . . . . . . . . . . . . . . . . . 17 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 6.1. Registering OSPF Router Functional Capability Bits . . . 17 6.2. Registering YANG Modules . . . . . . . . . . . . . . . . 18 6.3. IANA Module for OSPF Functional Capability Bits . . . . . 19 7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 20 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 9.1. Normative References . . . . . . . . . . . . . . . . . . 20 9.2. Informative References . . . . . . . . . . . . . . . . . 22 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23 Gong, et al. Expires 1 April 2026 [Page 2] Internet-Draft Advertising Unreachable Links in OSPF September 2025 1. Introduction In certain scenarios, it is necessary to advertise OSPF links that are not applicable to the default SPF calculation for other purposes. For example, a link may be available for Traffic Engineering (TE) purposes but not suitable for hop-by-hop routing. Another example is an OSPF link used exclusively by a Flexible Algorithm [RFC9350] but excluded from the default algorithm. In order to advertise these links as unreachable, the metric LSLinkInfinity (0xffff) is used to specify that the link is unreachable and OSPF routers supporting this specification will exclude the link from SPF calculations (subject to backward- compatibility constraints, refer to Section 3.2). 1.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 2. Use Cases 2.1. Case 1: Traffic Engineering A network topology is shown in Figure 1. The OSPF link between Node A and E is only to be used for traffic engineering. Since the OSPF link is advertised by default, it will be included in the base SPF calculation for the default topology and may be used for hop-by-hop routing in the default topology. TE Link --------- / \ / \ A------C------E | | | | | | | | | B------D------F Figure 1: Network Topology Gong, et al. Expires 1 April 2026 [Page 3] Internet-Draft Advertising Unreachable Links in OSPF September 2025 2.2. Case 2: Flexible Algorithm A network topology is shown in Figure 2. The links between nodes A and B and between C and D are to be used exclusively for a flex- algorithm [RFC9350] devoted to specific traffic. These links have an Extended Administrative Group (EAG) [RFC7308] attribute specifying the "Red" color. ****** A------C------E |* |* | |* |* | ******: "Red" link |* |* | B------D------F ****** Figure 2: Network Topology Flex-Algorithm 128 is enabled on Nodes A, B, C, and D, with an EAG rule including "Red" and the Metric-Type is designated to be a type other than the IGP metric. OSPF will compute routes for Flex- Algorithm 128 using these links. The topology associated with Flex- Algorithm 128 is shown in Figure 3. A******C * * * * * * B******D Figure 3: Topology of Flex-Algorithm 128 The "Red" links that are used by Flex-Algorithm 128 calculation. However, these "Red" links are also included in the default algorithm calculation [RFC9350] since they are reachable. Note that links used by the default algorithm are omitted from Figure 3 for clarity. If the IGP metrics for all the "Red" links are advertised as unreachable, they will be excluded from the default SPF calculation as shown in Figure 4, This allows the "Red" links from A to B and C to D to be used exclusively by the Flex-Algorithm 128 calculation. Gong, et al. Expires 1 April 2026 [Page 4] Internet-Draft Advertising Unreachable Links in OSPF September 2025 A------C------E | | | | | | | | | B------D------F Figure 4: Base SPF Topology Excluding Unreachable Links 3. LSLinkInfinity-Based Solution 3.1. Unreachable Link Advertisement This document specifies that if the IGP metric of a link is advertised as LSLinkInfinity (0xffff), it MUST NOT be considered during the associated SPF computation. This applies to both the Flex-Algorithm SPF and the base SPF as long as LSLinkInfinity is specified for the IGP metric. While the interpretation of LSLinkInfinity is only required in the base topology as other topologies are optional [RFC4915], OSPF routers supporting this specification MUST consistently interpret LSLinkInfinity as unreachable during the associated SPF computation. This applies to both the Flex-Algorithm SPF and the base SPF as long as LSLinkInfinity is specified for the IGP metric. An IGP metric with LSLinkInfinity indicating a link is unreachable is applicable to the following TLVs/LSAs: * The Router-LSA [RFC2328] [RFC5340] * The OSPFv2 Extended Link TLV of OSPFv2 Extended Link Opaque LSA [RFC7684] * The Router-Link TLV of OSPFv3 E-Router-LSA [RFC8362] 3.2. Unreachable Link Backward Compatibility Prior to this specification, OSPF treated links advertised as LSLinkInfinity as reachable [RFC2328]. Hence, partial deployment of this specification may result in routing loops due to inconsistent interpretation of LSLinkInfinity. For example, in the network shown in Figure 5, link D-F is advertised with LSLinkInfinity (65535/0xffff). Router B supports LSLinkInfinity as unreachable, but router A doesn't. Router A considers link D-F as reachable, and the shortest path to F is A->B->D->F. Router B considers link D-F as unreachable, and the shortest path to F is B->A->C->E->F. As a result, A forwards the packets to B, but B returns them to A, which results in a routing loop. Gong, et al. Expires 1 April 2026 [Page 5] Internet-Draft Advertising Unreachable Links in OSPF September 2025 40000 40000 Traffic: A->F A------C------E A considers link D-F as reachable | | A's shortest path: A->B->D->F 5| |5 B considers link D-F as unreachable | | B's shortest path: B->A->C->E->F B------D------F 5 65535 Figure 5: Inconsistent LSLinkInfinity Interpretation Causing Loops To provide backward compatibility, this document defines that routers supporting LSLinkInfinity for unreachable links MUST advertise a Router Information (RI) LSA with a Router Functional Capabilities TLV [RFC7770] including the following Router Functional Capability Bit: +=====+==========================+ | Bit | Capabilities | +=====+==========================+ | TBA | Unreachable Link support | +-----+--------------------------+ Table 1 OSPF Routers MUST NOT treat links with an advertised metric of LSLinkInfinity as unreachable unless all routers in the OSPF area have advertised this capability. If all OSPF Routers in the area have advertised this capability, then links with an advertised metric of LSLinkInfinity MUST be treated as unreachable. Upon detection of a change in the number of routers in the area not supporting the Unreachable Link support capability changes to 0 or from 0 to greater than 0, all OSPF routers in the area MUST recalculate their routes. 3.3. Stub Router Advertisement Backward Compatibility Stub Router Advertisement [RFC6987] defines MaxLinkMetric (0xffff) to indicate a router-LSA link should not be used for transit traffic. When an OSPFv2 router supports the Unreachable Link support capability defined in this document, the OSPFv2 stub router MaxLinkMetric (0xffff) MUST be updated to MaxReachableLinkMetric (0xfffe). This document updates [RFC6987] and [RFC8770] with respect to the advertisement of MaxReachableLinkMetric rather than MaxLinkMetric. When an OSPFv2 router supports [RFC6987] and the Unreachable Link support capability defined in this document, it MUST also support advertisement all its non-stub links with a link cost of MaxReachableLinkMetric (0xfffe). Since MaxLinkMetric will not be Gong, et al. Expires 1 April 2026 [Page 6] Internet-Draft Advertising Unreachable Links in OSPF September 2025 used to indicate a link is unreachable unless all OSPFv2 routers in the area support this specification as specified in Section 3.2, all routers in the area will also support the usage of MaxReachableLinkMetric to discourage the usage of stub router links for transit traffic. An OSPFv3 router can simply advertise R-bit in its router-LSA options [RFC5340] to prevent usage stub router links for transit traffic. Similarly, OSPFv2 routers supporting [RFC8770] can advertise the H-bit in the router-LSA options. 4. Operational Considerations 4.1. Configuration Parameters Support of the Unreachable Link support capability SHOULD be configurable. In some networks, the operator may still want links with maximum metric (0xffff) to be treated as reachable. For example, when the cost of links is automatically computed based on the inverse of the link's bandwidth and and there is a mix of low-speed and high-speed links, the computation may result in the maximum metric. In this case, OSPF routers supporting this specification can disable the Unreachable Link support capability and still treat links with maximum metric as reachable. It is also RECOMMENDED that implementations supporting this document and auto-costing limit the maximum computed cost to MaxReachableLinkMetric (0xfffe). 4.2. 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 three YANG modules. Module iana-ospf- functional-cap-bits defines the identities for OSPF Functional Capabilities as per the "OSPF Router Functional Capability Bits" IANA registry [IANA-OSPF-FC-Bits]. Module ietf-ospf-functional-capability and module ietf-ospf-unreachable-links can be used to configure and manage the usage of OSPF LSLinkInfinity for unreachable links as defined in this document, which augments the OSPF YANG data model [RFC9129] and the YANG Data Model for Routing Management [RFC8349]. This document uses the graphical representation of data model per [RFC8340]. Gong, et al. Expires 1 April 2026 [Page 7] Internet-Draft Advertising Unreachable Links in OSPF September 2025 4.2.1. Tree for OSPF Functional Capability The following shows the tree diagram of the module for OSPF Functional Capability: module: ietf-ospf-functional-capability 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:ri-opaque/ospf:router-capabilities-tlv: +--ro router-functional-capabilities +--ro functional-capability* identityref 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:ri-opaque /ospf:router-capabilities-tlv: +--ro router-functional-capabilities +--ro functional-capability* identityref 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/ospf:router-information /ospf:router-capabilities-tlv: +--ro router-functional-capabilities +--ro functional-capability* identityref 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/ospf:router-information /ospf:router-capabilities-tlv: +--ro router-functional-capabilities +--ro functional-capability* identityref 4.2.2. Tree for OSPF Advertising Unreachable Links The following shows the tree diagram of the module for OSPF Advertising Unreachable Links: Gong, et al. Expires 1 April 2026 [Page 8] Internet-Draft Advertising Unreachable Links in OSPF September 2025 module: ietf-ospf-unreachable-links augment /rt:routing/rt:control-plane-protocols /rt:control-plane-protocol/ospf:ospf: +--rw unreachable-link-advertisement +--rw enabled? boolean 4.2.3. IANA Module for OSPF Functional Capability Bits IANA has created a registry titled "OSPF Router Functional Capability Bits" under the "Open Shortest Path First (OSPF) Parameters" registry group to identify OSPF Router Functional Capabilities. Module iana- ospf-functional-cap-bits is an IANA-maintained module, which defines the identities for the OSPF Functional Capabilities as in the IANA "OSPF Router Functional Capability Bits" registry. This module is maintained by IANA and will be updated if and when there is any change to the registry. This document defines the initial version of the IANA-maintained YANG module for OSPF Router Functional Capabilities that mirrors the IANA "OSPF Router Functional Capability Bits" registry [IANA-OSPF-FC-Bits]. file "iana-ospf-functional-cap-bits@2025-09-28.yang" module iana-ospf-functional-cap-bits { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:" + "iana-ospf-functional-cap-bits"; prefix iana-ospf-fc-bits; organization "Internet Assigned Numbers Authority (IANA)"; contact "Internet Assigned Numbers Authority ICANN 12025 Waterfront Drive, Suite 300 Los Angeles, CA 90094-2536 United States of America Tel: +1 310 301 5800 "; description "This YANG module defines the identities for OSPF Router Functional Capabilities. This YANG module is maintained by IANA and reflects the 'OSPF Gong, et al. Expires 1 April 2026 [Page 9] Internet-Draft Advertising Unreachable Links in OSPF September 2025 Router Functional Capability Bits' registry. 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). All revisions of IETF and IANA published modules can be found at the YANG Parameters registry group (https://www.iana.org/assignments/yang-parameters). This initial version of this YANG module is part of RFC XXXX (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself for full legal notices. The latest version of this YANG module is available at https://www.iana.org/assignments/yang-parameters."; revision 2025-09-28 { description "Initial version"; reference "RFC XXXX: Advertising Unreachable Links in OSPF"; } identity functional-capability { description "Base identity for OSPF Router Functional Capabilities. The functional capabilities are defined in IANA OSPF Router Functional Capability Bits registry."; } identity unreachable-link { base functional-capability; description "Indicates that the OSPF router is capable of advertising unreachable links."; reference "RFC XXXX: Advertising Unreachable Links in OSPF"; } } Gong, et al. Expires 1 April 2026 [Page 10] Internet-Draft Advertising Unreachable Links in OSPF September 2025 4.2.4. YANG Module for OSPF Functional Capability The following is the YANG module for OSPF Functional Capability: file "ietf-ospf-functional-capability@2025-09-28.yang" module ietf-ospf-functional-capability { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:" + "ietf-ospf-functional-capability"; prefix ospf-fc; 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 iana-ospf-functional-cap-bits { prefix iana-ospf-fc-bits; reference "RFC XXXX: Advertising Unreachable Links in OSPF"; } organization "IETF Link State Routing (LSR) Working Group"; contact "WG Web: WG List: Author: Yingzhen Qu Author: Acee Lindem Author: Liyan Gong Author: Weiqiang Cheng Author: Changwang Lin Author: Ran Chen "; description "This YANG module defines the operational state for Gong, et al. Expires 1 April 2026 [Page 11] Internet-Draft Advertising Unreachable Links in OSPF September 2025 Functional Capability in OSPF as defined in RFC 7770. 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). All revisions of IETF and IANA published modules can be found at the YANG Parameters registry group (https://www.iana.org/assignments/yang-parameters). This version of this YANG module is part of RFC XXXX; see the RFC itself for full legal notices."; revision 2025-09-28 { description "Initial version"; reference "RFC XXXX: Advertising Unreachable Links in OSPF"; } grouping router-functional-capabilities { description "Grouping for OSPF router capabilities TLV types."; reference "RFC 7770: Extensions to OSPF for Advertising Optional Router Capabilities"; container router-functional-capabilities { leaf-list functional-capability { type identityref { base iana-ospf-fc-bits:functional-capability; } description "List of functional capabilities. This list contains the identities for the functional capabilities supported by the router."; } description "OSPF Router Functional identity definitions."; } } augment "/rt:routing/" Gong, et al. Expires 1 April 2026 [Page 12] Internet-Draft Advertising Unreachable Links in OSPF September 2025 + "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:ri-opaque/ospf:router-capabilities-tlv" { when "derived-from-or-self(/rt:routing/" + "rt:control-plane-protocols/" + "rt:control-plane-protocol/rt:type, 'ospf:ospfv2')" { description "This augmentation is only valid for OSPFv2."; } description "OSPFv2 Opaque Area-Scoped Router-Information LSA Router Functional capabilities."; uses router-functional-capabilities; reference "RFC 7770: Extensions to OSPF for Advertising Optional Router Capabilities"; } 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:ri-opaque/ospf:router-capabilities-tlv" { when "derived-from-or-self(/rt:routing/" + "rt:control-plane-protocols/" + "rt:control-plane-protocol/rt:type, 'ospf:ospfv2')" { description "This augmentation is only valid for OSPFv2."; } description "OSPFv2 Opaque AS-Scoped Router-Information LSA Router Functional capabilities."; uses router-functional-capabilities; reference "RFC 7770: Extensions to OSPF for Advertising Optional Router Capabilities"; } augment "/rt:routing/" + "rt:control-plane-protocols/rt:control-plane-protocol/" + "ospf:ospf/ospf:database/" + "ospf:as-scope-lsa-type/ospf:as-scope-lsas/" Gong, et al. Expires 1 April 2026 [Page 13] Internet-Draft Advertising Unreachable Links in OSPF September 2025 + "ospf:as-scope-lsa/ospf:version/ospf:ospfv3/" + "ospf:ospfv3/ospf:body/ospf:router-information/" + "ospf:router-capabilities-tlv" { when "derived-from-or-self(/rt:routing/" + "rt:control-plane-protocols/" + "rt:control-plane-protocol/rt:type, 'ospf:ospfv3')" { description "This augmentation is only valid for OSPFv3."; } description "OSPFv3 Area-Scoped Router-Information LSA Router Functional capabilities."; uses router-functional-capabilities; reference "RFC 7770: Extensions to OSPF for Advertising Optional Router Capabilities"; } 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/ospf:router-information/" + "ospf:router-capabilities-tlv" { when "derived-from-or-self(/rt:routing/" + "rt:control-plane-protocols/" + "rt:control-plane-protocol/rt:type, 'ospf:ospfv3')" { description "This augmentation is only valid for OSPFv3."; } description "OSPFv3 AS-Scoped Router-Information LSA Router Functional capabilities."; uses router-functional-capabilities; reference "RFC 7770: Extensions to OSPF for Advertising Optional Router Capabilities"; } } 4.2.5. YANG Module for OSPF Advertising Unreachable Links The following is the YANG module for OSPF Advertising Unreachable Links: Gong, et al. Expires 1 April 2026 [Page 14] Internet-Draft Advertising Unreachable Links in OSPF September 2025 file "ietf-ospf-unreachable-links@2025-09-28.yang" module ietf-ospf-unreachable-links { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:" + "ietf-ospf-unreachable-links"; prefix ospf-unreach-link; import ietf-routing { prefix rt; reference "RFC 8349: A YANG Data Model for Routing Management (NMDA Version)"; } import ietf-ospf { prefix ospf; reference "RFC 9129: YANG Data Model for the OSPF Protocol"; } organization "IETF Link State Routing (LSR) Working Group"; contact "WG Web: WG List: Author: Yingzhen Qu Author: Acee Lindem Author: Liyan Gong Author: Weiqiang Cheng Author: Changwang Lin Author: Ran Chen "; description "This YANG module defines the configuration and operational state for Advertising Unreachable Links in OSPF as defined in RFC XXXX. 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 Gong, et al. Expires 1 April 2026 [Page 15] Internet-Draft Advertising Unreachable Links in OSPF September 2025 set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info). All revisions of IETF and IANA published modules can be found at the YANG Parameters registry group (https://www.iana.org/assignments/yang-parameters). This version of this YANG module is part of RFC XXXX; see the RFC itself for full legal notices."; revision 2025-09-28 { description "Initial version"; reference "RFC XXXX: Advertising Unreachable Links in OSPF"; } augment "/rt:routing/rt:control-plane-protocols" + "/rt:control-plane-protocol/ospf:ospf" { when "derived-from-or-self(../rt:type, 'ospf:ospfv2') or " + "derived-from-or-self(../rt:type, 'ospf:ospfv3')" { description "This augments the OSPF routing protocol when used."; } description "This augments OSPF protocol with unreachable link advertisement."; container unreachable-link-advertisement { leaf enabled { type boolean; default "false"; description "Controls advertisement of unreachable links. It is enabled when set to true and desabled when set to false."; } description "OSPF unreachable link advertisement parameters."; } } } Gong, et al. Expires 1 April 2026 [Page 16] Internet-Draft Advertising Unreachable Links in OSPF September 2025 5. Security Considerations The document does not introduce any new security issues for the OSPF protocol. The security considerations for [RFC2328],[RFC5340], [RFC6987], and [RFC7770] are applicable to protocol extension. The ietf-ospf-unreachable-links YANG module and the ietf-ospf- functional-capability YANG module each define 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 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 ietf-ospf-unreachable-links YANG module that are writable/creatable/deletable (i.e., config true, which is the default). The modifications to these data nodes without proper protection can have prevent interpreting the OSPF LSLinkInfinity metric as unreachable. /ospf:ospf/ospf-unreach-link:unreachable-link-advertisement/ospf- unreach-link:enabled Some of the readable data nodes in the ietf-ospf-unreachable-links 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-unreach-link:unreachable-link-advertisement/ospf- unreach-link:enabled 6. IANA Considerations 6.1. Registering OSPF Router Functional Capability Bits This document defines a new bit in the registry "OSPF Router Functional Capability Bits": Gong, et al. Expires 1 April 2026 [Page 17] Internet-Draft Advertising Unreachable Links in OSPF September 2025 +============+==========================+===============+ | Bit Number | Capability Name | Reference | +============+==========================+===============+ | 0(TBD) | Unreachable Link support | This document | +------------+--------------------------+---------------+ Table 2 6.2. Registering YANG Modules The IANA is requested to assign three new URIs from the IETF XML registry ([RFC3688]). Authors are suggesting the following URIs: URI: urn:ietf:params:xml:ns:yang:iana-ospf-functional-cap-bits Registrant Contact: The IESG. XML: N/A, the requested URI is an XML namespace URI: urn:ietf:params:xml:ns:yang:ietf-ospf-functional-capability Registrant Contact: The IESG. XML: N/A, the requested URI is an XML namespace URI: urn:ietf:params:xml:ns:yang:ietf-ospf-unreachable-links Registrant Contact: The IESG. XML: N/A, the requested URI is an XML namespace This document also requests three new YANG module names in the YANG Module Names registry ([RFC6020]) with the following suggestion : Name: iana-ospf-functional-cap-bits Maintained by IANA? Y Namespace: urn:ietf:params:xml:ns:yang:iana-ospf-functional-cap-bits Prefix: iana-ospf-fc-bits Reference: RFC XXXX Name: ietf-ospf-functional-capability Maintained by IANA? N Namespace: urn:ietf:params:xml:ns:yang: ietf-ospf-functional-capability Prefix: ospf-fc Reference: RFC XXXX Name: ietf-ospf-unreachable-links Maintained by IANA? N Namespace: urn:ietf:params:xml:ns:yang:ietf-ospf-unreachable-links Prefix: ospf-unreach-link Reference: RFC XXXX Gong, et al. Expires 1 April 2026 [Page 18] Internet-Draft Advertising Unreachable Links in OSPF September 2025 6.3. IANA Module for OSPF Functional Capability Bits This document defines the initial version of the IANA-maintained "iana-ospf-functional-cap-bits" YANG module (Section 4.2). The most recent version of the YANG module is available from the "YANG Parameters" registry [IANA-YANG-Parameters]. IANA is requested to add this note to the registry: | New values must not be directly added to the "iana-ospf- | functional-cap-bits" YANG module. They must instead be added to | the "OSPF Router Functional Capability Bits" registry in the "Open | Shortest Path First (OSPF) Parameters" registry group | [IANA-OSPF-FC-Bits]. When a value is added to the "OSPF Router Functional Capability Bits" registry, a new "identity" statement needs to be added to the "iana- ospf-functional-cap-bits" YANG module. The name of the "identity" MUST be the name as provided in the registry. The "identity" statement should have the following sub-statements defined: "base": Contains 'functional-capability'. "description": Replicates the description from the registry. "reference": Replicates the reference(s) from the registry with the title of the document(s) added. When the "iana-ospf-functional-cap-bits" YANG module is updated, a new "revision" statement with a unique revision date must be added in front of the existing revision statements. The "revision" statement MUST contain both "description" and "reference" substatements as follows. The "description" substatement captures what changed in the revised version. Typically, the description enumerates the changes such as udpates to existing entries (e.g., update a description or a reference) or notes which identities were added or had their status changed (e.g., deprecated, discouraged, or obsoleted). The "reference" substatement points specifically to the published module (i.e., IANA_FOO_URL_With_REV). It may also point to an authoritative event triggering the update to the YANG module. In all cases, this event is cited from the underlying IANA registry. If the update is triggered by an RFC, that RFC must also be included in the "reference" substatement. IANA is requested to add this note to [IANA-OSPF-FC-Bits]: Gong, et al. Expires 1 April 2026 [Page 19] Internet-Draft Advertising Unreachable Links in OSPF September 2025 | When this registry is modified, the YANG module "iana-ospf- | functional-cap-bits" must be updated as defined in RFC XXXX. 7. Contributors The following individuals have contributed to this document: Mengxiao Chen New H3C Technologies China Email: chen.mengxiao@h3c.com Yanrong Liang Ruijie Networks Co., Ltd. China Email: liangyanrong@ruijie.com.cn 8. Acknowledgments Thanks to Yingzhen Qu for providing the YANG model. Thanks to Dhruv Dhody for OPS Directorate review and comments. 9. References 9.1. Normative References [IANA-OSPF-FC-Bits] IANA, "OSPF Router Functional Capability Bits", . [IANA-YANG-Parameters] IANA, "YANG Module Names", . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, DOI 10.17487/RFC2328, April 1998, . [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004, . Gong, et al. Expires 1 April 2026 [Page 20] Internet-Draft Advertising Unreachable Links in OSPF September 2025 [RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", RFC 4915, DOI 10.17487/RFC4915, June 2007, . [RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010, . [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, . [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, . [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and S. Shaffer, "Extensions to OSPF for Advertising Optional Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, February 2016, . [RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016, . [RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration Access Control Model", STD 91, RFC 8341, DOI 10.17487/RFC8341, March 2018, . [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, . Gong, et al. Expires 1 April 2026 [Page 21] Internet-Draft Advertising Unreachable Links in OSPF September 2025 [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, . [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, . 9.2. Informative References [RFC4252] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252, January 2006, . [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, . [RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D. McPherson, "OSPF Stub Router Advertisement", RFC 6987, DOI 10.17487/RFC6987, September 2013, . [RFC7308] Osborne, E., "Extended Administrative Groups in MPLS Traffic Engineering (MPLS-TE)", RFC 7308, DOI 10.17487/RFC7308, July 2014, . [RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018, . [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, . [RFC8770] Patel, K., Pillay-Esnault, P., Bhardwaj, M., and S. Bayraktar, "Host Router Support for OSPFv2", RFC 8770, DOI 10.17487/RFC8770, April 2020, . [RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based Multiplexed and Secure Transport", RFC 9000, DOI 10.17487/RFC9000, May 2021, . Gong, et al. Expires 1 April 2026 [Page 22] Internet-Draft Advertising Unreachable Links in OSPF September 2025 [RFC9350] Psenak, P., Ed., Hegde, S., Filsfils, C., Talaulikar, K., and A. Gulko, "IGP Flexible Algorithm", RFC 9350, DOI 10.17487/RFC9350, February 2023, . Authors' Addresses Liyan Gong China Mobile China Email: gongliyan@chinamobile.com Weiqiang Cheng China Mobile China Email: chengweiqiang@chinamobile.com Changwang Lin New H3C Technologies China Email: linchangwang.04414@h3c.com Acee Lindem Arrcus, Inc. United States of America Email: acee.ietf@gmail.com Ran Chen ZTE Corporation China Email: chen.ran@zte.com.cn Gong, et al. Expires 1 April 2026 [Page 23]