China Telecom

Beiqijia Town Changping District Beijing 102209 China wangaj3@chinatelecom.cn

Cisco Systems, Inc.

301 Midenhall Way Cary NC 27513 United States of America acee@cisco.com

Huawei Technologies

Huawei Campus, No. 156 Beiqing Rd. Beijing 100095 China jie.dong@huawei.com

Cisco Systems, Inc.

Pribinova Street 10 Bratislava Eurovea Centre, Central 3 81109 Slovakia ppsenak@cisco.com

Cisco Systems, Inc.

India ketant@cisco.com

RTG LSR OSPF This document defines OSPF extensions to include information associated with the node originating a prefix along with the prefix advertisement. These extensions do not change the core OSPF route computation functionality but provide useful information for network analysis, troubleshooting, and use cases like traffic engineering.

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 .

Copyright Notice Copyright (c) 2021 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 () 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 Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

Table of Contents

• .  Introduction
  • .  Requirements Language
• .  Protocol Extensions
  • .  Prefix Source OSPF Router-ID Sub-TLV
  • .  Prefix Source Router Address Sub-TLV
• .  Elements of Procedure
• .  Security Considerations
• .  Operational Considerations
• .  IANA Considerations
• .  References
  • .  Normative References
  • .  Informative References
• Acknowledgement
• Authors' Addresses

Introduction Prefix attributes are advertised in OSPFv2 using the Extended Prefix Opaque Link State Advertisement (LSA) and in OSPFv3 using the various Extended Prefix LSA types . The procedures for identification of the originating router for a prefix in OSPF vary by the type of the prefix and, currently, it is not always possible to produce an accurate result. For intra-area prefixes, the originating router is identified by the Advertising Router field of the area-scoped LSA used for those prefix advertisements. However, for inter-area prefixes advertised by an Area Border Router (ABR), the Advertising Router field of their area-scoped LSAs is set to the ABR itself and the information about the router originating the prefix advertisement is lost in the process of prefix propagation across areas. For Autonomous System (AS) external prefixes, the originating router may be considered as the Autonomous System Border Router (ASBR) and is identified by the Advertising Router field of the AS-scoped LSA used. However, the actual originating router for the prefix may be a remote router outside the OSPF domain. Similarly, when an ABR performs translation of Not-So-Stubby Area (NSSA) LSAs to AS-external LSAs, the information associated with the NSSA ASBR (or the router outside the OSPF domain) is not propagated across the OSPF domain. While typically the originator of information in OSPF is identified by its OSPF Router ID, it does not necessarily represent a reachable address for the router since the OSPF Router ID is a 32-bit number that is unique in the OSPF domain. For OSPFv2, a common practice is to use one of the IPv4 addresses of the node (e.g., a loopback interface) as the OSPF Router ID. However, this cannot always be assumed and this approach does not apply to IPv6 addresses with OSPFv3. The IPv4/IPv6 Router Address, as respectively defined in and for OSPFv2 and OSPFv3, provides an address to reach the advertising router. The primary use case for the extensions proposed in this document is to be able to identify the originator of a prefix in the network. In cases where multiple prefixes are advertised by a given router, it is also useful to be able to associate all these prefixes with a single router even when prefixes are advertised outside of the area in which they originated. It also helps to determine when the same prefix is being originated by multiple routers across areas. This document proposes extensions to the OSPF protocol for the inclusion of information associated with the router originating the prefix along with the prefix advertisement. These extensions do not change the core OSPF route computation functionality. They provide useful information for topology analysis and traffic engineering, especially on a controller when this information is advertised as an attribute of the prefixes via mechanisms such as Border Gateway Protocol - Link State (BGP-LS) .

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 when, and only when, they appear in all capitals, as shown here.

Protocol Extensions This document defines the Prefix Source OSPF Router-ID and the Prefix Source Router Address Sub-TLVs. They are used, respectively, to include the Router ID of, and a reachable address of, the router that originates the prefix as a prefix attribute.

Prefix Source OSPF Router-ID Sub-TLV For OSPFv2, the Prefix Source OSPF Router-ID Sub-TLV is an optional sub-TLV of the OSPFv2 Extended Prefix TLV . For OSPFv3, the Prefix Source OSPF Router-ID Sub-TLV is an optional sub-TLV of the Intra-Area-Prefix TLV, Inter-Area-Prefix TLV, and External-Prefix TLV when originating either an IPv4 or an IPv6 prefix advertisement. The Prefix Source OSPF Router-ID Sub-TLV has the following format:

Prefix Source OSPF Router-ID Sub-TLV Format 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OSPF Router ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Where:

Type:

4 for OSPFv2 and 27 for OSPFv3

Length:

4

OSPF Router ID:

the OSPF Router ID of the OSPF router that originated the prefix advertisement in the OSPF domain

The parent TLV of a prefix advertisement MAY include more than one Prefix Source OSPF Router-ID Sub-TLV, one corresponding to each of the Equal-Cost Multipath (ECMP) nodes that originated the advertised prefix. For intra-area prefix advertisements, the Prefix Source OSPF Router-ID Sub-TLV MUST be considered invalid and ignored if the OSPF Router ID field is not the same as the Advertising Router field in the containing LSA. Similar validation cannot be reliably performed for inter-area and external prefix advertisements. A received Prefix Source OSPF Router-ID Sub-TLV with the OSPF Router ID field set to 0 MUST be considered invalid and ignored. Additionally, reception of such sub-TLVs SHOULD be logged as an error (subject to rate limiting).

Prefix Source Router Address Sub-TLV For OSPFv2, the Prefix Source Router Address Sub-TLV is an optional sub-TLV of the OSPFv2 Extended Prefix TLV . For OSPFv3, the Prefix Source Router Address Sub-TLV is an optional sub-TLV of the Intra-Area-Prefix TLV, Inter-Area-Prefix TLV, and External-Prefix TLV when originating either an IPv4 or an IPv6 prefix advertisement. The Prefix Source Router Address Sub-TLV has the following format:

Prefix Source Router Address Sub-TLV Format 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Router Address (4 or 16 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Where:

Type:

5 for OSPFv2 and 28 for OSPFv3

Length:

4 or 16

Router Address:

A reachable IPv4 or IPv6 router address for the router that originated the IPv4 or IPv6 prefix advertisement, respectively. Such an address would be semantically equivalent to what may be advertised in the OSPFv2 Router Address TLV or in the OSPFv3 Router IPv6 Address TLV .

The parent TLV of a prefix advertisement MAY include more than one Prefix Source Router Address Sub-TLV, one corresponding to each of the Equal-Cost Multipath (ECMP) nodes that originated the advertised prefix. A received Prefix Source Router Address Sub-TLV that has an invalid length (i.e., not consistent with the prefix's address family) MUST be considered invalid and ignored. Additionally, reception of such sub-TLVs SHOULD be logged as an error (subject to rate limiting).

Elements of Procedure This section describes the procedure for the advertisement of the Prefix Source OSPF Router-ID and Prefix Source Router Address Sub-TLVs along with the prefix advertisement. The OSPF Router ID of the Prefix Source OSPF Router-ID is set to the OSPF Router ID of the node originating the prefix in the OSPF domain. If the originating node is advertising an OSPFv2 Router Address TLV or an OSPFv3 Router IPv6 Address TLV , then the same address MUST be used in the Router Address field of the Prefix Source Router Address Sub-TLV. When the originating node is not advertising such an address, implementations can select a unique and reachable local address (for example, advertised with the N-Flag set or N-bit set ) on the originating node to advertise in the Router Address field. When an ABR generates inter-area prefix advertisements into its non-backbone areas corresponding to an inter-area prefix advertisement from the backbone area, the only way to determine the originating node information is based on the Prefix Source OSPF Router-ID and Prefix Source Router Address Sub-TLVs present in the inter-area prefix advertisement originated into the backbone area by an ABR from another non-backbone area. The ABR performs its prefix calculation to determine the set of nodes that contribute to ECMP paths for the prefix. It MUST only use the prefix originator information from this set of nodes. The ABR MUST NOT include the Prefix Source OSPF Router-ID or the Prefix Source Router Address Sub-TLVs when it is unable to determine the information for the originating nodes contributing ECMP paths. Implementations may support the propagation of the originating node information along with a redistributed prefix into the OSPF domain from another routing domain. The details of such mechanisms are outside the scope of this document. Such implementations may also provide control on whether the Router Address in the Prefix Source Router Address Sub-TLV is set as the ASBR node address or as the address of the actual node outside the OSPF domain that owns the prefix. When translating NSSA prefix advertisements to AS external prefix advertisements, the NSSA ABR follows the same procedures as an ABR generating inter-area prefix advertisements for the propagation of the originating node information.

Security Considerations Since this document extends the OSPFv2 Extended Prefix LSA, the security considerations for are applicable. Similarly, since this document extends the OSPFv3 E-Intra-Area-Prefix-LSA, E-Inter-Area-Prefix-LSA, E-AS-External-LSA, and E-NSSA-LSA, the security considerations for are applicable. The new sub-TLVs introduced in this document are optional and do not affect the OSPF route computation and therefore do not affect the security aspects of OSPF protocol operations. A rogue node that can inject prefix advertisements may use the extensions introduced in this document to advertise bogus prefix source information.

Operational Considerations Consideration should be given to the operational impact of the increase in the size of the OSPF Link-State Database as a result of the protocol extensions in this document. Based on deployment design and requirements, a subset of prefixes may be identified for which originating node information is required to be included in prefix advertisements. The propagation of prefix source node information for prefix advertisements advertised across an OSPF area or domain boundaries will expose information outside of an area or domain where it would normally be hidden or abstracted by the base OSPF protocol. Based on deployment design and requirements, the propagation of node information across area or domain boundaries may be limited to a subset of prefixes in the ABRs or ASBRs, respectively. The identification of the node that is originating a specific prefix in the network may aid in the debugging of issues related to prefix reachability within an OSPF network.

IANA Considerations Per this document, IANA has allocated the following codepoints from the "OSPFv2 Extended Prefix TLV Sub-TLVs" registry under the "Open Shortest Path First v2 (OSPFv2) Parameters" registry. Codepoints in OSPFv2 Extended Prefix TLV Sub-TLVs

Value	Description	Reference
4	Prefix Source OSPF Router-ID	RFC 9084
5	Prefix Source Router Address	RFC 9084

Per this document, IANA has allocated the following codepoints from the "OSPFv3 Extended-LSA Sub-TLVs" registry under the "Open Shortest Path First v3 (OSPFv3) Parameters" registry. Codepoints in OSPFv3 Extended-LSA Sub-TLVs

Value	Description	Reference
27	Prefix Source OSPF Router-ID	RFC 9084
28	Prefix Source Router Address	RFC 9084

References Normative References In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This memo documents version 2 of the OSPF protocol. OSPF is a link- state routing protocol. [STANDARDS-TRACK] This document describes extensions to the OSPF protocol version 2 to support intra-area Traffic Engineering (TE), using Opaque Link State Advertisements. This document describes extensions to OSPFv3 to support intra-area Traffic Engineering (TE). This document extends OSPFv2 TE to handle IPv6 networks. A new TLV and several new sub-TLVs are defined to support IPv6 networks. [STANDARDS-TRACK] This document describes the modifications to OSPF to support version 6 of the Internet Protocol (IPv6). The fundamental mechanisms of OSPF (flooding, Designated Router (DR) election, area support, Short Path First (SPF) calculations, etc.) remain unchanged. However, some changes have been necessary, either due to changes in protocol semantics between IPv4 and IPv6, or simply to handle the increased address size of IPv6. These modifications will necessitate incrementing the protocol version from version 2 to version 3. OSPF for IPv6 is also referred to as OSPF version 3 (OSPFv3). Changes between OSPF for IPv4, OSPF Version 2, and OSPF for IPv6 as described herein include the following. Addressing semantics have been removed from OSPF packets and the basic Link State Advertisements (LSAs). New LSAs have been created to carry IPv6 addresses and prefixes. OSPF now runs on a per-link basis rather than on a per-IP-subnet basis. Flooding scope for LSAs has been generalized. Authentication has been removed from the OSPF protocol and instead relies on IPv6's Authentication Header and Encapsulating Security Payload (ESP). Even with larger IPv6 addresses, most packets in OSPF for IPv6 are almost as compact as those in OSPF for IPv4. Most fields and packet- size limitations present in OSPF for IPv4 have been relaxed. In addition, option handling has been made more flexible. All of OSPF for IPv4's optional capabilities, including demand circuit support and Not-So-Stubby Areas (NSSAs), are also supported in OSPF for IPv6. [STANDARDS-TRACK] OSPFv2 requires functional extension beyond what can readily be done with the fixed-format Link State Advertisements (LSAs) as described in RFC 2328. This document defines OSPFv2 Opaque LSAs based on Type-Length-Value (TLV) tuples that can be used to associate additional attributes with prefixes or links. Depending on the application, these prefixes and links may or may not be advertised in the fixed-format LSAs. The OSPFv2 Opaque LSAs are optional and fully backward compatible. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. OSPFv3 requires functional extension beyond what can readily be done with the fixed-format Link State Advertisement (LSA) as described in RFC 5340. Without LSA extension, attributes associated with OSPFv3 links and advertised IPv6 prefixes must be advertised in separate LSAs and correlated to the fixed-format LSAs. This document extends the LSA format by encoding the existing OSPFv3 LSA information in Type-Length-Value (TLV) tuples and allowing advertisement of additional information with additional TLVs. Backward-compatibility mechanisms are also described. This document updates RFC 5340, "OSPF for IPv6", and RFC 5838, "Support of Address Families in OSPFv3", by providing TLV-based encodings for the base OSPFv3 unicast support and OSPFv3 address family support. Informative References This memo documents an optional type of Open Shortest Path First (OSPF) area that is somewhat humorously referred to as a "not-so-stubby" area (or NSSA). NSSAs are similar to the existing OSPF stub area configuration option but have the additional capability of importing AS external routes in a limited fashion. The OSPF NSSA Option was originally defined in RFC 1587. The functional differences between this memo and RFC 1587 are explained in Appendix F. All differences, while expanding capability, are backward-compatible in nature. Implementations of this memo and of RFC 1587 will interoperate. [STANDARDS-TRACK] This document describes a mechanism for supporting multiple address families (AFs) in OSPFv3 using multiple instances. It maps an AF to an OSPFv3 instance using the Instance ID field in the OSPFv3 packet header. This approach is fairly simple and minimizes extensions to OSPFv3 for supporting multiple AFs. [STANDARDS-TRACK] In a number of environments, a component external to a network is called upon to perform computations based on the network topology and current state of the connections within the network, including Traffic Engineering (TE) information. This is information typically distributed by IGP routing protocols within the network. This document describes a mechanism by which link-state and TE information can be collected from networks and shared with external components using the BGP routing protocol. This is achieved using a new BGP Network Layer Reachability Information (NLRI) encoding format. The mechanism is applicable to physical and virtual IGP links. The mechanism described is subject to policy control. Applications of this technique include Application-Layer Traffic Optimization (ALTO) servers and Path Computation Elements (PCEs).

Acknowledgement Many thanks to for his suggestions on this document. Also, thanks to , , , , , , , and for their review and valuable comments. The authors would also like to thank for his detailed review and suggestions for the improvement of this document.

Authors' Addresses China Telecom

Beiqijia Town Changping District Beijing 102209 China wangaj3@chinatelecom.cn

Cisco Systems, Inc.

301 Midenhall Way Cary NC 27513 United States of America acee@cisco.com

Huawei Technologies

Huawei Campus, No. 156 Beiqing Rd. Beijing 100095 China jie.dong@huawei.com

Cisco Systems, Inc.

Pribinova Street 10 Bratislava Eurovea Centre, Central 3 81109 Slovakia ppsenak@cisco.com

Cisco Systems, Inc.

India ketant@cisco.com