LSR R. Chen Internet-Draft D. Zhao Intended status: Standards Track ZTE Corporation Expires: 18 July 2025 P. Psenak K. Talaulikar Cisco Systems L. Gong China mobile 14 January 2025 Prefix Flag Extension for OSPFv2 and OSPFv3 draft-ietf-lsr-ospf-prefix-extended-flags-04 Abstract Each OSPF prefix is advertised with an 8-bit options field, using the Prefix Options (OSPFv3) and the flag field in the OSPFv2 Extended Prefix TLV (OSPFv2). However for OSPFv3, all the Prefix Options bits have already been assigned, and for OSPFv2, there are not many bits left unassigned in the OSPFv2 Extended Prefix TLV. This document solves the problem of insufficient options bit by defining variable-length Prefix Attribute Flags Sub-TLVs for OSPFv2 and OSPFv3. 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 July 2025. Copyright Notice Copyright (c) 2025 IETF Trust and the persons identified as the document authors. All rights reserved. Chen, et al. Expires 18 July 2025 [Page 1] Internet-Draft Prefix Flag Extension for OSPF January 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 . . . . . . . . . . . . . . . . . . 4 2. Variable-Length Prefix Attribute Flags Sub-TLVs . . . . . . . 4 2.1. OSPFv2 Prefix Attribute Flags Sub-TLV . . . . . . . . . . 4 2.2. OSPFv3 Prefix Attribute Flags Sub-TLV . . . . . . . . . . 5 3. Processing . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. Backward Compatibility . . . . . . . . . . . . . . . . . . . 6 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 6.1. OSPFv2 Prefix Attribute Flags Sub-TLV Registry . . . . . 7 6.1.1. OSPFv2 Prefix Extended Flags Field Registry . . . . . 7 6.2. OSPFv3 Prefix Attribute Flags Sub-TLV Registry . . . . . 7 6.2.1. OSPFv3 Prefix Extended Flags Field Registry . . . . . 8 7. Security Considerations . . . . . . . . . . . . . . . . . . . 8 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 8.1. Normative References . . . . . . . . . . . . . . . . . . 8 8.2. Informative References . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction Each OSPF prefix is advertised with an 8-bit options field, using the Prefix Options [RFC5340] and the flag field in the OSPFv2 Extended Prefix TLV [RFC7684]. However for OSPFv3, all the Prefix Options bits have already been assigned, and for OSPFv2, at the time of writing, only 4 bits remain undefined in the OSPFv2 Extended Prefix TLV. For OSPFv2, as defined in [RFC7684], the length of the Flag field is 8 bits, and the flags defined in the OSPFv2 Extended Prefix TLV are listed in Table 1. Chen, et al. Expires 18 July 2025 [Page 2] Internet-Draft Prefix Flag Extension for OSPF January 2025 +=======+==================+=============================+ | Value | Description | Reference | +=======+==================+=============================+ | 0x80 | A | [RFC7684] | +-------+------------------+-----------------------------+ | 0x40 | N | [RFC7684] | +-------+------------------+-----------------------------+ | 0x20 | E-Flag(ELC Flag) | [RFC9089] | +-------+------------------+-----------------------------+ | TBD | AC | [I-D.ietf-lsr-anycast-flag] | +-------+------------------+-----------------------------+ Table 1: OSPFv2 Extended Prefix TLV Flags (8 bits) For OSPFv3 [RFC5340], the length of the Flag field is 8 bits, and all of the bits have already been defined as shown in Table 2. +=======+===================+===========+ | Value | Description | Reference | +=======+===================+===========+ | 0x01 | NU-bit | [RFC5340] | +-------+-------------------+-----------+ | 0x02 | LA-bit | [RFC5340] | +-------+-------------------+-----------+ | 0x04 | Deprecated | [RFC5340] | +-------+-------------------+-----------+ | 0x08 | P-bit | [RFC5340] | +-------+-------------------+-----------+ | 0x10 | DN-bit | [RFC5340] | +-------+-------------------+-----------+ | 0x20 | N-bit | [RFC8362] | +-------+-------------------+-----------+ | 0x40 | E-Flag (ELC Flag) | [RFC9089] | +-------+-------------------+-----------+ | 0x80 | AC-bit | [RFC9513] | +-------+-------------------+-----------+ Table 2: OSPFv3 Prefix Options (8 bits) This document solves the problem of insufficient flag bit by defining variable-length Prefix Attribute Flags Sub-TLVs for OSPFv2 and OSPFv3. Chen, et al. Expires 18 July 2025 [Page 3] Internet-Draft Prefix Flag Extension for OSPF January 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 the 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. 2.1. OSPFv2 Prefix Attribute Flags Sub-TLV The format of OSPFv2 Prefix Attribute Flags Sub-TLV 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: TBD1. 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. 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. Bits that are NOT transmitted MUST be treated as if they are set to 0 on receipt. Chen, et al. Expires 18 July 2025 [Page 4] Internet-Draft Prefix Flag Extension for OSPF January 2025 OSPFv2 Prefix Attribute Flags Sub-TLV is a Sub-TLV of the OSPFv2 Extended Prefix TLV as defined in [RFC7684]. 2.2. OSPFv3 Prefix Attribute Flags Sub-TLV The format of OSPFv3 Prefix Attribute Flags Sub-TLV 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: TBD2. 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. Prefix Attribute Flags: Variable. The extended flag fields. This contains a variable number of 32-bit flags. Currently, no bits are defined. Unassigned bits MUST be set to zero on transmission and MUST be ignored on receipt. Bits that are NOT transmitted MUST be treated as if they are set to 0 on receipt. OSPFv3 Prefix Attribute Flags Sub-TLV is a Sub-TLV of the following OSPFv3 TLVs as defined in [RFC8362]: * Intra-Area-Prefix TLV * Inter-Area-Prefix TLV * External-Prefix TLV Chen, et al. Expires 18 July 2025 [Page 5] Internet-Draft Prefix Flag Extension for OSPF January 2025 3. Processing The Extended Flags field is a variable-length multiple of 32-bits with flags allocated from starting with the most significant bit. The bits in the Extended Flags field will be assigned in future documents. This document does not define any flags. Unrecognized flags in the Prefix Attribute Flags Sub-TLVs for OSPFv2 and OSPFv3 must be forwarded without modification. Specifically, the entire flag field must be copied unchanged into outgoing messages, regardless of whether the implementation recognizes all the flags. Implementations MUST handle variable-length Prefix Attribute Flags Sub-TLVs and beyond the flags field length supported MUST be ignored. An OSPFv2 router receiving multiple OSPFv2 Prefix Attribute Flags Sub-TLVs in the same OSPFv2 Extended Prefix TLV MUST use the first advertisement of this Sub-TLV and MUST ignore all remaining instances of the Sub-TLV. An OSPFv3 router receiving multiple OSPFv3 Prefix Attribute Flags Sub-TLVs in a subsuming TLV MUST use the first advertisement of the Sub-TLV and MUST ignore all remaining instances of the Sub-TLV in the subsuming TLV. 4. 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 Prefix Attribute Flags Sub-TLV MUST ignore the Sub-TLV. Further, any additional bits in the OSPFv2/OSPFv3 Prefix Attribute Flags Sub-TLV that are not recognized by an implementation MUST be ignored. 5. 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. 6. IANA Considerations This document requests allocation for the following registry. Chen, et al. Expires 18 July 2025 [Page 6] Internet-Draft Prefix Flag Extension for OSPF January 2025 6.1. OSPFv2 Prefix Attribute Flags Sub-TLV Registry This document requests the allocation of "OSPFv2 Prefix Attribute Flags" in the "OSPFv2 Extended Prefix TLV Sub-TLVs" registry: The following flag (TEMPORARY - registered 2024-04-05, expires 2025-04-05) has been allocated by IANA: Value Description Reference ------ ---------------------------------- -------------- 11 OSPFv2 Prefix Attribute Flags This document 6.1.1. OSPFv2 Prefix Extended Flags Field Registry This document requests an allocation of "OSPFv2 Prefix Extended Flag Field" Registry under "Open Shortest Path First v2 (OSPFv2) Parameters". The registry defines the bits in the 32-bit Flags field in the OSPFv2 Prefix Attribute Flags Sub-TLV. Additionaly bits can be allocated via IETF Review or IESG Approval [RFC8126]. Each bit definition will include: * Bit number (counting from bit 0 as the most significant bit) * Description * Reference No values are currently defined. Bits 0-31 are initially marked as "Unassigned". Bits with an ordinal higher than 31 will be added to the registry as required by future documents. 6.2. OSPFv3 Prefix Attribute Flags Sub-TLV Registry This document requests the allocation of "OSPFv3 Prefix Attribute Flags" in the "OSPFv3 Extended-LSA Sub-TLVs" registry: The following flag (TEMPORARY - registered 2024-04-05, expires 2025-04-05) has been allocated by IANA: Value Description Reference ------ ---------------------------------- -------------- 37 OSPFv3 Prefix Attribute Flags This document Chen, et al. Expires 18 July 2025 [Page 7] Internet-Draft Prefix Flag Extension for OSPF January 2025 6.2.1. OSPFv3 Prefix Extended Flags Field Registry This document requests an allocation of "OSPFv3 Prefix Extended Flag Field" registry under "Open Shortest Path First v3 (OSPFv3) Parameters". Additional bits can be allocated via IETF Review or IESG Approval [RFC8126]. Each bit definition will include: * Bit number (counting from bit 0 as the most significant bit) * Description * Reference Bits 0-31 are initially marked as "Unassigned". Bits with an ordinal higher than 31 will be added to the registry as required by future documents. 7. 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. 8. References 8.1. 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, . Chen, et al. Expires 18 July 2025 [Page 8] Internet-Draft Prefix Flag Extension for OSPF January 2025 [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, . 8.2. Informative References [I-D.ietf-lsr-anycast-flag] Chen, R., Zhao, D., Psenak, P., Talaulikar, K., and C. Lin, "Updates to Anycast Property advertisement for OSPFv2", Work in Progress, Internet-Draft, draft-ietf-lsr- anycast-flag-01, 20 October 2024, . [RFC9089] Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S., and M. Bocci, "Signaling Entropy Label Capability and Entropy Readable Label Depth Using OSPF", RFC 9089, DOI 10.17487/RFC9089, August 2021, . [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, . 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 Chen, et al. Expires 18 July 2025 [Page 9] Internet-Draft Prefix Flag Extension for OSPF January 2025 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 July 2025 [Page 10]