IDR WG Yao. Liu Internet-Draft Shaofu. Peng Intended status: Standards Track ZTE Corporation Expires: April 17, 2021 October 14, 2020 BGP extensions of SR policy for path protection draft-lp-idr-sr-path-protection-00 Abstract This document proposes extensions of BGP in order to provide path protection within a candidate path when delivering SR policy. And it also extends BGP-LS to provide some extra information of the segment list in a candidate path in the advertisement. 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 April 17, 2021. Copyright Notice Copyright (c) 2020 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 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. Liu & Peng Expires April 17, 2021 [Page 1] Internet-Draft BGP-LS for Shorter SRv6 SID October 2020 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. BGP Extensions for Advertising Segment List . . . . . . . . . 3 2.1. Extensions of Segment List sub-TLV . . . . . . . . . . . 3 2.2. List Identifier Sub-TLV . . . . . . . . . . . . . . . . . 3 2.2.1. List Protection Sub-TLV . . . . . . . . . . . . . . . 4 3. BGP-LS Extensions for Distributing Segment List States . . . 5 4. Security Considerations . . . . . . . . . . . . . . . . . . . 5 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 6. Normative References . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 1. Introduction Segment Routing [RFC8402] allows a headend node to steer a packet flow along any path. [I-D.ietf-spring-segment-routing-policy] details the concepts of SR Policy and steering into an SR Policy. An SR Policy is a set of candidate paths, each consisting of one or more segment lists. The headend of an SR Policy may learn multiple candidate paths for an SR Policy. When SR policies are involved and a strict compliance of the policy is required, an end-to-end protection should be preferred over a local repair mechanism. Candidate path can be used for path protection, that is, the lower preference candidate path may be designated as the backup for a specific or all (active) candidate path(s). Despite using candidate path for protection, protection at segment list level within an candidate path is also useful. [I-D.ietf-idr-segment-routing-te-policy] specifies BGP extensions for the advertisement of SR Policies and each candidate path is carried in an NLRI, if candidate path is used for protection ,the BGP origin must generate multiple NLRIs. If protection at segment list level is possible, only one NLRI is needed which makes the advertisement more simple. On the other hand, protection in and between candidate path can be combined together to provide a more comprehensive protection mechanism. This document proposes extensions of BGP in order to provide path protection in an candidate path when delivering SR policy. Liu & Peng Expires April 17, 2021 [Page 2] Internet-Draft BGP-LS for Shorter SRv6 SID October 2020 [I-D.ietf-idr-te-lsp-distribution] describes a mechanism to collect the SR policy information that is locally available in a node and advertise it into BGP Link State (BGP-LS) updates. This document also extends it to provide some extra information of the segment list in a candidate path in the BGP-LS advertisement. 2. BGP Extensions for Advertising Segment List 2.1. Extensions of Segment List sub-TLV Segment List sub-TLV is introduced in [I-D.ietf-idr-segment-routing-te-policy] and it includes the elements of the paths (i.e., segments). This document introduces a one-bit flag in the RESERVED field. 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 |B| RESERVED | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // sub-TLVs // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Segment List sub-TLV B-Flag(Backup Flag): one bit. When set to 0, it indicates that the segment list acts as the active member in the candidate path. When set to 1, it indicates that the segment list acts as the backup path in the candidate path. Using segment lists for path protection can be compatible with using candidate paths. When a path fails, the backup segment list within the same candidate path is used preferentially for path protection. If the backup list is also invalid, then other candidate path can be enabled for protection. 2.2. List Identifier Sub-TLV This document introduces a new sub-sub-tlv of Segment List sub-TLV, where, Liu & Peng Expires April 17, 2021 [Page 3] Internet-Draft BGP-LS for Shorter SRv6 SID October 2020 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 | RESERVED | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | List Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Optional TLVs ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: List Identifier Sub-TLV Type: 1 octet. TBD. Length: 1 octet, specifies the length of the value field not including Type and Length fields. RESERVED: 2 octet of reserved bits. SHOULD be unset on transmission and MUST be ignored on receipt. List Identifier: 4 octets. It is the identifier of the corresponding segment list, so that the segment list can be operated according to the specified Segment List identifier. This sub-TLV is optional and it MUST NOT appear more than once inside the Segment List sub-TLV. 2.2.1. List Protection Sub-TLV 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 | RESERVED | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Backup List ID 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Backup List ID N | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: List Identifier Sub-TLV Type: 1 octet. TBD. Length: 1 octet, specifies the length of the value field not including Type and Length fields. Liu & Peng Expires April 17, 2021 [Page 4] Internet-Draft BGP-LS for Shorter SRv6 SID October 2020 RESERVED: 2 octet of reserved bits. SHOULD be unset on transmission and MUST be ignored on receipt. Backup List ID: 4 octets. It is the List Identifier of the backup segment list that protects this segment list. If there're multiple backup paths, the list ID of each path should be included in the TLV. 3. BGP-LS Extensions for Distributing Segment List States [I-D.ietf-idr-te-lsp-distribution] describes a mechanism to collect the SR Policy information that is locally available in a node and advertise it into BGP Link State (BGP-LS) updates. The SR Policy information includes status of the candidate path, e.g, whether the candidate path is administrative shut or not. SR Segment List TLV is defined in [I-D.ietf-idr-te-lsp-distribution] to to report the SID-List(s) of a candidate path. Figure 4 shows the flags in SR Segment List TLV. 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |D|E|C|V|R|F|A|T|M|S|B| | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: Flag Field of SR Segment List TLV The meaning of the D,E,C,V,R,F,A,M can be found in [I-D.ietf-idr-te-lsp-distribution] section 6.5. This document introduces two new flags, where, S-Flag : Indicates the segment list is in administrative shut state when set. B-Flag : Indicates the segment list is the backup path within the candidate path when set, otherwise it is the active path. 4. Security Considerations Procedures and protocol extensions defined in this document do not affect the security considerations discussed in [I-D.ietf-idr-segment-routing-te-policy] and [I-D.ietf-idr-te-lsp-distribution]. Liu & Peng Expires April 17, 2021 [Page 5] Internet-Draft BGP-LS for Shorter SRv6 SID October 2020 5. IANA Considerations TBD 6. Normative References [I-D.ietf-idr-segment-routing-te-policy] Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P., Rosen, E., Jain, D., and S. Lin, "Advertising Segment Routing Policies in BGP", draft-ietf-idr-segment-routing- te-policy-09 (work in progress), May 2020. [I-D.ietf-idr-te-lsp-distribution] Previdi, S., Talaulikar, K., Dong, J., Chen, M., Gredler, H., and J. Tantsura, "Distribution of Traffic Engineering (TE) Policies and State using BGP-LS", draft-ietf-idr-te- lsp-distribution-13 (work in progress), April 2020. [I-D.ietf-spring-segment-routing-policy] Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and P. Mattes, "Segment Routing Policy Architecture", draft- ietf-spring-segment-routing-policy-08 (work in progress), July 2020. [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, July 2018, . Authors' Addresses Liu Yao ZTE Corporation Nanjing China Email: liu.yao71@zte.com.cn Peng Shaofu ZTE Corporation Nanjing China Email: peng.shaofu@zte.com.cn Liu & Peng Expires April 17, 2021 [Page 6]