Interdomain Routing Working Group C. Li Internet-Draft M. Chen Intended status: Standards Track J. Dong Expires: October 5, 2018 Z. Li Huawei Technologies April 3, 2018 Segment Routing Policies for Path Segment and Bi-directional Path draft-li-idr-sr-policy-path-segment-distribution-00 Abstract An SR policy is a set of candidate SR paths consisting of one or more segment lists with necessary path attributes. For each SR path, it may also have its own path attributes, and Path Segment is one of them. A Path Segment is defined to identify an SR path, which can be used for performance measurement, path correlation, and end-2-end path protection. Path Segment can be also used to correlate two unidirctional SR paths into a bi-directional SR path which is required in some scenarios, for example, mobile backhaul transport network. This document defines extensions to BGP to distribute SR policies carriying Path segment and bi-directional path information. 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]. 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 October 5, 2018. Li, et al. Expires October 5, 2018 [Page 1] Internet-Draft Abbreviated-Title April 2018 Copyright Notice Copyright (c) 2018 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. SR Policy for Path Identifier . . . . . . . . . . . . . . . . 3 3.1. SR Path ID Sub-TLV . . . . . . . . . . . . . . . . . . . 4 4. SR Policy for Bi-directional Path . . . . . . . . . . . . . . 5 4.1. SR Bi-directional Path Sub-TLV . . . . . . . . . . . . . 6 4.2. SR Reverse Path Segment List Sub-TLV . . . . . . . . . . 7 5. Operations . . . . . . . . . . . . . . . . . . . . . . . . . 8 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 7. Security Considerations . . . . . . . . . . . . . . . . . . . 8 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 9.1. Normative References . . . . . . . . . . . . . . . . . . 8 9.2. Informative References . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction Segment routing (SR) [I-D.ietf-spring-segment-routing] is a source routing paradigm that explicitly indicates the forwarding path for packets at the ingress node. The ingress node steers packets into a specific path according to the Segment Routing Policy ( SR Policy) as defined in [I-D.filsfils-spring-segment-routing-policy]. For distributing SR policies to the headend, [I-D.ietf-idr-segment-routing-te-policy] specifies a mechanism by using BGP, and new sub-TLVs are defined for SR Policies in BGP UPDATE message. In many use cases such as performance measurement, the path to which the packets belong is required to be identified. Futhermore, in some scenarios, for example, mobile backhaul transport network, there are Li, et al. Expires October 5, 2018 [Page 2] Internet-Draft Abbreviated-Title April 2018 requirements to support bi-directional path. However, there is no path ID for each Segment List in the SR Policies defined in [I-D.filsfils-spring-segment-routing-policy]. Also, the SR Policies defined in [I-D.filsfils-spring-segment-routing-policy] only supports uni-directional SR paths. Therefore, this document defines the extension to SR policies that carry path ID information in the Segment List and support bi- directional path. The path ID can be a path segment in SR-MPLS [I-D.cheng-spring-mpls-path-segment] , or a path ID in SRv6 [I-D.li-spring-passive-pm-for-srv6-np], or other IDs that can identify a path. Also, this document defines extensions to BGP to distribute SR policies carriying Path segment and bi-directional path information. 2. Terminology This memo makes use of the terms defined in [I-D.ietf-spring-segment-routing] and [I-D.ietf-idr-segment-routing-te-policy]. It also introduces the following terminologies. 3. SR Policy for Path Identifier As defined in [I-D.ietf-idr-segment-routing-te-policy] , the SR Policy Encoding structure is as follows: SR Policy SAFI NLRI: Attributes: Tunnel Encaps Attribute (23) Tunnel Type: SR Policy Binding SID Preference Segment List Weight Segment Segment ... An SR path can be specified by an Segment List sub-TLV that contains a set of segment sub-TLVs and other sub-TLVs as shown above. As introduced in Section 1, each SR path may have a dedicated path identifier, an SR policy carrying a SR path identifier is expressed as below: Li, et al. Expires October 5, 2018 [Page 3] Internet-Draft Abbreviated-Title April 2018 SR Policy SAFI NLRI: Attributes: Tunnel Encaps Attribute (23) Tunnel Type: SR Policy Binding SID Preference Segment List Weight Path ID Segment Segment ... 3.1. SR Path ID Sub-TLV This section defines an SR Path ID sub-TLV to specify an SR path, and it is included in the segment list sub-TLV. An SR Path ID sub-TLV is associated with an SR path specified by a segment list sub-TLV, and it MUST appear only once within a Segment List sub-TLV. It 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 | Flag | PIT | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Path ID (Variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1. Path ID sub-TLV Where: Type: to be assigned by IANA (suggested value 10). Length: the total length of the value field not including Type and Length fields. Flag: 8 bits of flags. Following flags are defined: 0 1 2 3 4 5 6 7 +--+--+--+--+--+--+--+--+ | Reserved |G |E | +--+--+--+--+--+--+--+--+ G-Flag: Global flag. Set when the Path segment/ID is global within an SR domain. Li, et al. Expires October 5, 2018 [Page 4] Internet-Draft Abbreviated-Title April 2018 E-Flag: Egress flag for local sgement/ID. The E-flag should be set when a path segment/ID is a local segment/ID allocated by the egress node. Else, the path segment/ID is a local segment/ID allocated by the ingress node. When the Path segment/ID is global within an SR domain(G-flag is set), this flag should be ignored. Reserved: 5 bits reserved and MUST be set to 0 on transmission and MUST be ignored on receipt. PIT: Path ID type, specifies the type of the Path ID, and it has following types: o 0: SR-MPLS Path Label o 1: 4-octets integer Path ID o 2: SRv6 SID o 3-255:Reserved Path ID: The Path ID of an SR path. The Path ID type is indicated by the Path ID Type(PIT) field. It can be a path segment [I-D.cheng-spring-mpls-path-segment], or it can be a 4 octets integer ID as defined in [I-D.li-spring-passive-pm-for-srv6-np], or other IDs that can identify a path. When the type of Path ID is 0, and the E-flag and the G-flag are unset, meaning the Path ID is a local path label allocated by the ingress node in SR-MPLS, a path can be identified by a combination of this path ID and a non-routable Source label, as defined at section 2.2 in [I-D.cheng-spring-mpls-path-segment]. The non-routable Source Label, as known as a non-routable source node ID, can be configured by many ways like CLI, and it is out of scope of this document and will be discussed in other documents. 4. SR Policy for Bi-directional Path In some scenarios, for example, mobile backhaul transport network, there are requirements to support bi-directional path. In SR, a bi- directional path can be represented as a binding of two uni- directional SR paths. This document also defines new sub-TLVs to describe an SR bi-directional path. An SR policy carrying SR bi- directional path information is expressed as below: Li, et al. Expires October 5, 2018 [Page 5] Internet-Draft Abbreviated-Title April 2018 SR Policy SAFI NLRI: Attributes: Tunnel Encaps Attribute (23) Tunnel Type: SR Policy Binding SID Preference Bi-directioanl Path Segment List Weight Path ID Segment Segment ... Reverse Segment List Weight Path ID Segment Segment ... 4.1. SR Bi-directional Path Sub-TLV This section defines an SR bi-directional path sub-TLV to specify a bi-directional path, which contains a Segment List sub-TLV [I-D.ietf-idr-segment-routing-te-policy] and an associated Reverse Path Segment List as defined at section 4.2. The SR bi-directional path 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 | RESERVED | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sub-TLVs (Variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2. SR Bi-directional path sub-TLV Where: Type: TBA, and the suggest value is 14. Length: the total length of the sub-TLVs encoded within the SR Bi- directional Path Sub-TLV not including Type and Length fields. RESERVED: 1 octet of reserved bits. SHOULD be unset on transmission and MUST be ignored on receipt. Sub-TLVs: Li, et al. Expires October 5, 2018 [Page 6] Internet-Draft Abbreviated-Title April 2018 o An Segment List sub-TLV o An associated Reverse Path Segment List sub-TLV 4.2. SR Reverse Path Segment List Sub-TLV An SR Reverse Path Segment List sub-TLV is defined to specify an SR reverse path associated with the path specified by the Segment List in the same SR Bi-directional Path Sub-TLV, and it 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 | RESERVED | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sub-TLVs (Variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2. SR Reverse Path Segment List Sub-TLV where: Type: TBA, and suggest value is 127. Length: the total length of the sub-TLVs encoded within the SR Reverse Path Segment List Sub-TLV not including the Type and Length fields. RESERVED: 1 octet of reserved bits. SHOULD be unset on transmission and MUST be ignored on receipt. sub-TLVs: o An optional single Weight sub-TLV. o An mandatory SR Path ID sub-TLV that contains the path ID of the reverse SR path. o Zero or more Segment sub-TLVs to specify the reverse SR path. The Segment sub-TLVs in the Reverse Path Segment List sub-TLV provides the information of the reverse SR path, which can be used for directing egress BFD peer to use specific path for the reverse direction of the BFD session [I-D.ietf-mpls-bfd-directed] or other applications. Li, et al. Expires October 5, 2018 [Page 7] Internet-Draft Abbreviated-Title April 2018 5. Operations The document does not bring new operation beyong the description of operations defined in [I-D.ietf-idr-segment-routing-te-policy]. The existing operations defined in [I-D.ietf-idr-segment-routing-te-policy] can apply to this document directly. Typically but not limit to, the uni-directional or bi-directional SR policies carrying path identification infomation are configured by a controller. After configuration, the uni-directional or bi-directional SR policies carrying path identification infomation will be advertised by BGP update messages. The operation of advertisement is the same as defined in [I-D.ietf-idr-segment-routing-te-policy], as well as the receiption. The consumer of the uni-directional or bi-directional SR policies is not the BGP process, it can be any applications, such as performance measurement. The operation of sending information to consumers is out of scope of this document. 6. IANA Considerations TBA 7. Security Considerations TBA 8. Acknowledgements TBA 9. References 9.1. Normative References [I-D.cheng-spring-mpls-path-segment] Cheng, W., Wang, L., Li, H., Chen, M., Zigler, R., and S. Zhan, "Path Segment in MPLS Based Sement Routing Network", draft-cheng-spring-mpls-path-segment-01 (work in progress), March 2018. Li, et al. Expires October 5, 2018 [Page 8] Internet-Draft Abbreviated-Title April 2018 [I-D.filsfils-spring-segment-routing-policy] Filsfils, C., Sivabalan, S., Raza, K., Liste, J., Clad, F., Talaulikar, K., Ali, Z., Hegde, S., daniel.voyer@bell.ca, d., Lin, S., bogdanov@google.com, b., Krol, P., Horneffer, M., Steinberg, D., Decraene, B., Litkowski, S., and P. Mattes, "Segment Routing Policy for Traffic Engineering", draft-filsfils-spring-segment- routing-policy-05 (work in progress), February 2018. [I-D.ietf-idr-segment-routing-te-policy] Previdi, S., Filsfils, C., Jain, D., Mattes, P., Rosen, E., and S. Lin, "Advertising Segment Routing Policies in BGP", draft-ietf-idr-segment-routing-te-policy-02 (work in progress), March 2018. [I-D.ietf-spring-segment-routing] Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing Architecture", draft-ietf-spring-segment-routing-15 (work in progress), January 2018. [I-D.li-spring-passive-pm-for-srv6-np] Li, C. and M. Chen, "Passive Performance Measurement for SRv6 Network Programming", draft-li-spring-passive-pm-for- srv6-np-00 (work in progress), March 2018. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . 9.2. Informative References [I-D.ietf-mpls-bfd-directed] Mirsky, G., Tantsura, J., Varlashkin, I., and M. Chen, "Bidirectional Forwarding Detection (BFD) Directed Return Path", draft-ietf-mpls-bfd-directed-08 (work in progress), December 2017. Authors' Addresses Cheng Li Huawei Technologies Huawei Campus, No. 156 Beiqing Rd. Beijing 100095 China Email: chengli13@huawei.com Li, et al. Expires October 5, 2018 [Page 9] Internet-Draft Abbreviated-Title April 2018 Mach(Guoyi) Chen Huawei Technologies Huawei Campus, No. 156 Beiqing Rd. Beijing 100095 China Email: Mach.chen@huawei.com Jie Dong Huawei Technologies Huawei Campus, No. 156 Beiqing Rd. Beijing 100095 China Email: jie.dong@huawei.com Zhenbin Li Huawei Technologies Huawei Campus, No. 156 Beiqing Rd. Beijing 100095 China Email: lizhenbin@huawei.com Li, et al. Expires October 5, 2018 [Page 10]