SPRING WG Y. Liu Internet-Draft S. Peng Intended status: Standards Track ZTE Corporation Expires: July 31, 2021 January 27, 2021 SR Policy for Reverse Path draft-lp-spring-sr-policy-reverse-path-00 Abstract This document introduces a method of dynamically configuring the return path for an SR path. 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 July 31, 2021. 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 (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 July 31, 2021 [Page 1] Internet-Draft SR Policy for Reverse Segment List January 2021 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. SR Policy for Bidirectional Path . . . . . . . . . . . . . . 2 2.1. BGP Extensions for Advertising Segment List . . . . . . . 3 2.2. Illustration . . . . . . . . . . . . . . . . . . . . . . 4 2.3. Difference from Path Segment . . . . . . . . . . . . . . 5 3. Security Considerations . . . . . . . . . . . . . . . . . . . 5 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 5. Normative References . . . . . . . . . . . . . . . . . . . . 5 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 1. Introduction Echo-BFD [RFC5880] can be used to monitor an SR Policy between the local and the remote BFD peers. As defined in [RFC5880], the remote BFD system does not process the payload of an Echo BFD. A BSID can be used to specify the return path of an Echo BFD packet. As introduced in [I-D.ietf-spring-bfd], the sender MAY use a Binding SID (BSID) [RFC8402] that has been bound with the SR Policy that ensures the return of a packet to that particular node and a BSID MAY be associated with the SR Policy that is the reverse to the SR Policy programmed onto the BFD Echo packet by the sender. One way to implement this is through static configuration, e.g, configure the BSID corresponding to the return path for each segment list when enable BFD for an SR policy or an segment list. This document introduces a method of dynamically configuring the return path for an SR path, which can be used to specify the return path in Echo BFD for SR, ICMPv6 for SRv6, etc. 2. SR Policy for Bidirectional Path In order to specify the return path for an segment list when delivering the SR Policy, and the tail node can return the packet according to the specified return path, this document proposes extensions of SR Policy. It allows the segment list to have its own BSID. When delivering SR policy, the BSID of the segment list and the corresponding BSID of the return segment list can be carried together. Liu & Peng Expires July 31, 2021 [Page 2] Internet-Draft SR Policy for Reverse Segment List January 2021 2.1. BGP Extensions for Advertising Segment List 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 two optional sub-sub-tlvs of Segment List sub-TLV, Binding SID Sub-TLV and Reverse Binding SID Sub-TLV. The Binding SID sub-TLV has the following 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 | Flags | RESERVED | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Binding SID (variable, optional) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Binding SID Sub-TLV where: Type: TBD. Length: specifies the length of the value field not including Type and Length fields. Binding SID: the BSID of the segment list. The Reverse Binding SID sub-TLV has the following 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 | Flags | RESERVED | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reverse Binding SID (variable, optional) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: Reverse Binding SID Sub-TLV where: Type: TBD Length: specifies the length of the value field not including Type and Length fields. Liu & Peng Expires July 31, 2021 [Page 3] Internet-Draft SR Policy for Reverse Segment List January 2021 Reverse Binding SID: the BSID of the reverse SR path. If it is encapsulated in the packet, the Reverse Binding SID must the last segment to be processed. The extended SR Policy Encoding structure is as follows: SR Policy SAFI NLRI: Attributes: Tunnel Encaps Attribute (23) Tunnel Type: SR Policy Binding SID SRv6 Binding SID Preference Priority Policy Name Policy Candidate Path Name Explicit NULL Label Policy (ENLP) Segment List Binding SID Reverse Binding SID Weight Segment Segment ... Whether to carry RBSID in the packet can be configured according to service requirements. For example, when echo BFD packets are encapsulated, RBSID is carried in segment list, while packets of other services do not carry RBSID by default. Thus BFD packets and common service packets can share the same SR Policy. 2.2. Illustration +-+ +-+ +-+ +-+ |A|------|B|------|C|------|D| +-+ +-+ +-+ +-+ Figure 3: Reference Topology The content of Segment List1 in SR Policy1 received by A is: Segment List1 Reverse Binding SID D1 Segment B Segment C Segment D The content of Segment List2 in SR Policy2 received by D is: Liu & Peng Expires July 31, 2021 [Page 4] Internet-Draft SR Policy for Reverse Segment List January 2021 Segment List2 Binding SID D1 Segment C Segment B Segment A The SID-List of the BFD ECHO sent by A is < B, C, D, D1 >. After the packet arrives at node D, D1 is Segment List2 BSID. BFD packets are returned from node D according to segment list < C, B, A >. 2.3. Difference from Path Segment TBD 3. 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-spring-segment-routing-policy]. 4. IANA Considerations TBD 5. 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-11 (work in progress), November 2020. [I-D.ietf-spring-bfd] Mirsky, G., Tantsura, J., Varlashkin, I., Chen, M., and J. Wenying, "Bidirectional Forwarding Detection (BFD) in Segment Routing Networks Using MPLS Dataplane", draft- ietf-spring-bfd-00 (work in progress), September 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-09 (work in progress), November 2020. Liu & Peng Expires July 31, 2021 [Page 5] Internet-Draft SR Policy for Reverse Segment List January 2021 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, . [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 July 31, 2021 [Page 6]