LSR R. Chen Internet-Draft D. Zhao Intended status: Standards Track ZTE Corporation Expires: 14 March 2022 P. Psenak Cisco Systems 10 September 2021 Updates to Anycast Property advertisement for OSPF draft-chen-lsr-anycast-flag-00 Abstract Both SR-MPLS prefixes-SID and IPv4/IPv6 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 updates [RFC7684] and [RFC8362], by defining a new flag in OSPFv2 Extended Prefix Opaque LSA [RFC7684] and Prefix Options [RFC8362] to advertise the anycast property, and also updates the corresponding interpretation of the Flags field of the Prefix Attribute Flags TLV in [RFC9085]. 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 14 March 2022. Copyright Notice Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved. Chen, et al. Expires 14 March 2022 [Page 1] Internet-Draft Anycast Property advertisement September 2021 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 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 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2. Updates to Anycast Property advertisement for OSPFv3 . . . . 3 3. Updates to Anycast Property advertisement for OSPFv2 . . . . 4 4. Updates to Anycast Property advertisement for BGP-LS . . . . 4 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 6.1. OSPFv3 Prefix Options . . . . . . . . . . . . . . . . . . 5 6.2. OSPFv2 Extended Prefix TLV . . . . . . . . . . . . . . . 5 7. Security Considerations . . . . . . . . . . . . . . . . . . . 5 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 8.1. Normative References . . . . . . . . . . . . . . . . . . 5 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 1. Introduction Both SR-MPLS prefixes-SID and IPv4/IPv6 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 the prefix, but the definition of anycast flag to identify the prefix as anycast has not yet been defined. [RFC8362] 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. Each prefix is advertised along with an 8-bit field of capabilities,by using the Prefix Options, but the definition of anycast capability bit to identify the prefix as anycast has not yet been defined. Chen, et al. Expires 14 March 2022 [Page 2] Internet-Draft Anycast Property advertisement September 2021 [RFC9085] defines the Prefix Attribute Flags TLV carries IPv4/IPv6 prefix attribute flags information, and the Flags field of this TLV is interpreted according to OSPFv2 [RFC7684] and OSPFv3 [RFC8362], but the anycast flag isnot included. This document updates [RFC7684] and [RFC8362], by defining a new flag in OSPFv2 Extended Prefix Opaque LSA [RFC7684] and Prefix Options [RFC8362] to advertise the anycast property, and also updates the corresponding interpretation of the Flags field of the Prefix Attribute Flags TLV in [RFC9085]. 1.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. 2. Updates to Anycast Property advertisement for OSPFv3 The prefix may be configured as anycast and it is useful for other routers to know that the advertisement is for an anycast identifier. A new flag in Prefix Options [RFC8362] is defined to advertise the anycast property, The figure below shows the position of the A-bit in the prefix options. 0 1 2 3 4 5 6 7 +--+--+--+--+--+--+--+--+ | | A| N|DN| P| x|LA|NU| +--+--+--+--+--+--+--+--+ Figure 1 When the prefix is configured as anycast, the A-flag SHOULD be set. Otherwise, this flag MUST be clear.If both N-flag and A-flag are set, the receiving routers MUST ignore the N-flag. A-flag MUST be preserved when the prefix is propagated between areas. The same prefix can be advertised by multiple routers, and that if at least one of them sets the A-Flag in its advertisement, the prefix SHOULD be considered as anycast. Chen, et al. Expires 14 March 2022 [Page 3] Internet-Draft Anycast Property advertisement September 2021 3. Updates to Anycast Property advertisement for OSPFv2 [RFC7684] defines one-octet field contains flags applicable to the prefix, and it only defines two flag (A-Flag (Attach Flag) and N-Flag (Node Flag). This section extends a new flag: An(Anycast Flag). An-flag: A new flag in OSPFv2 Extended Prefix Opaque LSA [RFC7684] is defined to advertise the anycast property. When the prefix is configured as anycast, the An-flag SHOULD be set. Otherwise, this flag MUST be clear.If both N-flag and An-flag are set, the receiving routers MUST ignore the N-flag. An-flag MUST be preserved when the prefix is propagated between areas. The same prefix can be advertised by multiple routers, and that if at least one of them sets the An-Flag in its advertisement, the prefix SHOULD be considered as anycast. 4. Updates to Anycast Property advertisement for BGP-LS [RFC9085] defines the Prefix Attribute Flags TLV carries IPv4/IPv6 prefix attribute flags information, and the Flags field of this TLV is interpreted according to OSPFv2 [RFC7684]and OSPFv3 [RFC8362].This section extends the interpretation of the Flags field of the Prefix Attribute Flags TLV. Flags: * IS-IS flags refer to Section 2.3.2 of [RFC9085] . * OSPFv2 flags correspond to the Flags field of the OSPFv2 Extended Prefix TLV defined in Section 2.1 of [RFC7684] and extended in Section 3 of this draft. * OSPFv3 flags map to the Prefix Options field defined in Appendix A.4.1.1 of [RFC5340] and extended in Section 3.1 of [RFC8362] and Section 4 of this draft. 5. Acknowledgements TBD. 6. IANA Considerations This document requests allocation for the following bits registry. Chen, et al. Expires 14 March 2022 [Page 4] Internet-Draft Anycast Property advertisement September 2021 6.1. OSPFv3 Prefix Options This document adds a new bit in the "OSPFv3 Prefix Options" registry: A-flag (Anycast Flag). 6.2. OSPFv2 Extended Prefix TLV This document adds a new bit in the "OSPFv2 Extended Prefix TLV" registry: An-flag (Anycast Flag). 7. Security Considerations Procedures and protocol extensions defined in this document do not affect the OSPFv2 , OSPFv3 and BGP-LS security model. See the "Security Considerations"section of [RFC7684] for a discussion of OSPFv2 security, the "Security Considerations"section of [RFC8362] for a discussion of OSPFv3 security and the "Security Considerations"section of [RFC9085] for a discussion of SR BGP-LS 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., "OSPF for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, . [RFC7684] Psenak, P., "Key words for use in RFCs to Indicate Requirement Levels", RFC 7684, DOI 10.17487/RFC7684, November 2015, . [RFC8362] Lindem, A., "OSPFv3 Link State Advertisement (LSA) Extensibility", RFC 8362, DOI 10.17487/RFC8362, April 2018, . [RFC9085] Previdi, S., "Border Gateway Protocol - Link State (BGP- LS) Extensions for Segment Routing", RFC 9085, DOI 10.17487/RFC9085, August 2021, . Chen, et al. Expires 14 March 2022 [Page 5] Internet-Draft Anycast Property advertisement September 2021 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 Chen, et al. Expires 14 March 2022 [Page 6]