LSR R. Chen Internet-Draft D. Zhao Intended status: Standards Track ZTE Corporation Expires: 18 August 2025 P. Psenak K. Talaulikar Cisco Systems L. Gong China mobile 14 February 2025 Prefix Flag Extension for OSPFv2 and OSPFv3 draft-ietf-lsr-ospf-prefix-extended-flags-06 Abstract Each OSPF prefix can be advertised with an 8-bit field to indicate specific properties of that prefix. However, all the OSPFv3 Prefix Options bits have already been assigned and only a few bits remain unassigned in the flags field of the OSPFv2 Extended Prefix TLV. This document solves the problem of insufficient prefix options bits by defining variable-length Prefix Attribute Flags Sub-TLV for OSPF. 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 18 August 2025. Copyright Notice Copyright (c) 2025 IETF Trust and the persons identified as the document authors. All rights reserved. Chen, et al. Expires 18 August 2025 [Page 1] Internet-Draft Prefix Flag Extension for OSPF February 2025 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 . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2. Variable-Length Prefix Attribute Flags Sub-TLVs . . . . . . . 3 3. Backward Compatibility . . . . . . . . . . . . . . . . . . . 4 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 5.1. OSPFv2 Prefix Attribute Flags Sub-TLV Registry . . . . . 5 5.1.1. OSPFv2 Prefix Extended Flags Field Registry . . . . . 5 5.2. OSPFv3 Prefix Attribute Flags Sub-TLV Registry . . . . . 5 5.2.1. OSPFv3 Prefix Extended Flags Field Registry . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 7.1. Normative References . . . . . . . . . . . . . . . . . . 6 7.2. Informative References . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction Each OSPF prefix can be advertised with an 8-bit field to indicate specific properties of that prefix. This is done using the OSPFv3 Prefix Options [RFC5340] and the flags field in the OSPFv2 Extended Prefix TLV [RFC7684]. The rest of this document refers to these 8-bit fields in both OSPFv2 and OSPFv3 as the "existing fixed-size prefix attribute flags". However, all the OSPFv3 Prefix Options bits have already been assigned (see OSPFv3 Prefix Options IANA registries [IANA-OSPFv3-PO] and only 5 bits remain unassigned (at the time of publication of this document) in the flags field of the OSPFv2 Extended Prefix TLV (see OSPFv2 Extended Prefix TLV Flags IANA registries [IANA-OSPFv2-EPF]). This document solves the problem of insufficient flag bits for the signaling of prefix properties in OSPF by defining variable-length Prefix Attribute Flags Sub-TLVs for OSPFv2 and OSPFv3. Chen, et al. Expires 18 August 2025 [Page 2] Internet-Draft Prefix Flag Extension for OSPF February 2025 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. Variable-Length Prefix Attribute Flags Sub-TLVs This document defines variable-Length Prefix Attribute Flags Sub-TLVs for OSPFv2 and OSPFv3. These Sub-TLVs specify the variable-flag fields to advertise additional attributes associated with OSPF prefixs i.e., the advertisement and processing of the existing fixed- size prefix attribute flags remains unchanged. The format of OSPFv2/OSPFv3 Prefix Attribute Flags Sub-TLVs is: 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // Prefix Attribute Flags (Variable) // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where: Type: 11 for OSPFv2 and 37 for OSPFv3. Length: Variable, dependent on the included Prefix Attribute Flags. This indicates the length of the value portion in bytes. The length MUST be a multiple of 4 octets. If the length is not a multiple of 4 octets, the LSA MUST be considered malformed. Prefix Attribute Flags: Variable. The extended flag field. This contains a variable number of 32-bit flags. Currently, no bits are defined in this document. Unassigned bits MUST be set to zero on transmission and MUST be ignored on receipt. Chen, et al. Expires 18 August 2025 [Page 3] Internet-Draft Prefix Flag Extension for OSPF February 2025 An implementation MUST limit the length of the sub-TLV so as to signal the bits that are set to 1. Defined prefix flags that are not transmitted due to being beyond the transmitted length MUST be treated as being set to 0. If any trailing 32-bit block(s) are received without any bit being set in it, then the LSA MUST be considered malformed. OSPFv2 Prefix Attribute Flags Sub-TLV is advertised as a Sub-TLV of the OSPFv2 Extended Prefix TLV as defined in [RFC7684]. OSPFv3 Prefix Attribute Flags Sub-TLV is advertised as a Sub-TLV of the following OSPFv3 TLVs: * Inter-Area-Prefix TLV [RFC8362]. * Intra-Area-Prefix TLV [RFC8362]. * External-Prefix TLV [RFC8362]. * SRv6 Locator TLV [RFC9513]. When multiple instances of an OSPFv2/OSPFv3 Prefix Attribute Flags Sub-TLVs are received within the same TLV, an implementation MUST use only the first occurrence of the Sub-TLV and MUST ignore all subsequent instances of the Sub-TLV. 3. Backward Compatibility The Prefix Attribute Flags Sub-TLVs defined in this document does not introduce any backward compatibility issues. An implementation that does not recognize the OSPFv2/OSPFv3 Prefix Attribute Flags Sub-TLV MUST ignore the Sub-TLV. 4. Acknowledgements The authors thank Shraddha Hegde, Changwang Lin, Tom Petch and many others for their suggestions and comments. The authors would like to thank Acee Lindem for aligning the terminology with existing OSPF documents and for editorial improvements. 5. IANA Considerations This document requests allocation for the following registry. Chen, et al. Expires 18 August 2025 [Page 4] Internet-Draft Prefix Flag Extension for OSPF February 2025 5.1. OSPFv2 Prefix Attribute Flags Sub-TLV Registry This document requests IANA to make permanent the early allocation of the following codepoint for the "OSPFv2 Prefix Attribute Flags" in the "OSPFv2 Extended Prefix TLV Sub-TLVs" registry to be made permanent: Value Description Reference --------- ----------------------------------- --------------- 11 OSPFv2 Prefix Attribute Flags This document 5.1.1. OSPFv2 Prefix Extended Flags Field Registry This document requests the creation of "OSPFv2 Prefix Extended Flag Field" Registry under "Open Shortest Path First v2 (OSPFv2) Parameters". The registry defines the bits in the Prefix Attribute Flags field in the OSPFv2 Prefix Attribute Flags Sub-TLV as specified in section 2. The bits are to be allocated via IETF Review [RFC8126]. Each bit definition will include: * Bit number (counting from bit 0 as the most significant bit) * Description * Reference No bits are currently defined. Bits 0-31 are to be initially marked as "Unassigned". IANA is requested to add subsequent blocks of 32 bits upon exhaustion of the preceding 32-bit block. 5.2. OSPFv3 Prefix Attribute Flags Sub-TLV Registry This document requests IANA to make permanent the early allocation of the following codepoint for the "OSPFv3 Prefix Attribute Flags" in the "OSPFv3 Extended-LSA Sub-TLVs" registry: Value Description Reference -------- ---------------------------------- -------------- 37 OSPFv3 Prefix Attribute Flags This document 5.2.1. OSPFv3 Prefix Extended Flags Field Registry This document requests the creation of "OSPFv3 Prefix Extended Flag Field" registry under "Open Shortest Path First v3 (OSPFv3)" Parameters. The registry defines the bits in the Prefix Attribute Flags field in the OSPFv2 Prefix Attribute Flags Sub-TLV as specified in section 2. The bits are to be allocated via IETF Review [RFC8126]. Each bit definition will include: Chen, et al. Expires 18 August 2025 [Page 5] Internet-Draft Prefix Flag Extension for OSPF February 2025 * Bit number (counting from bit 0 as the most significant bit) * Description * Reference No bits are currently defined. Bits 0-31 are to be initially marked as "Unassigned". IANA is requested to add subsequent blocks of 32 bits upon exhaustion of the preceding 32-bit block. 6. Security Considerations Procedures and protocol extensions defined in this document do not affect the OSPFv2 or OSPFv3 security models. See the "Security Considerations" section of [RFC7684] for a discussion of OSPFv2 TLV- encoding considerations, and the "Security Considerations" section of [RFC8362] for a discussion of OSPFv3 security. 7. References 7.1. 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, . [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, . [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, . [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [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, . Chen, et al. Expires 18 August 2025 [Page 6] Internet-Draft Prefix Flag Extension for OSPF February 2025 [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, . 7.2. Informative References [IANA-OSPFv2-EPF] "", . [IANA-OSPFv3-PO] "", . 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 Slovakia Email: ppsenak@cisco.com Ketan Talaulikar Cisco Systems India Email: ketant.ietf@gmail.com Liyan Gong China mobile China Email: gongliyan@chinamobile.com Chen, et al. Expires 18 August 2025 [Page 7]