SPRING W. Cheng Internet-Draft China Mobile Intended status: Informational S. Steffann Expires: May 3, 2021 SJM Steffann Consultancy October 30, 2020 Compressed SRv6 SID List Requirements draft-srcompdt-spring-compression-requirement-00 Abstract This document specifies requirements for solutions to compress SRv6 SID lists. 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 May 3, 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. Cheng & Steffann Expires May 3, 2021 [Page 1] Internet-Draft SRCOMP Requirements October 2020 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions used in this document . . . . . . . . . . . . . . 3 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 3. SRv6 SID List Compression Requirements . . . . . . . . . . . 4 3.1. Dataplane Efficiency and Performance Requirements . . . . 4 3.1.1. Encapsulation Header Size . . . . . . . . . . . . . . 4 3.1.2. Forwarding Efficiency . . . . . . . . . . . . . . . . 4 3.1.3. State Efficiency . . . . . . . . . . . . . . . . . . 5 4. SRv6 Specific Requirements . . . . . . . . . . . . . . . . . 5 4.1. Functional Requirements . . . . . . . . . . . . . . . . . 5 4.1.1. SRv6 Based . . . . . . . . . . . . . . . . . . . . . 5 4.1.2. SRv6 Functionality . . . . . . . . . . . . . . . . . 5 4.1.3. SID list length . . . . . . . . . . . . . . . . . . . 5 4.1.4. SID summarization . . . . . . . . . . . . . . . . . . 6 4.1.5. Heterogeneous SID lists . . . . . . . . . . . . . . . 6 4.2. Operational Requirements . . . . . . . . . . . . . . . . 6 4.2.1. Lossless Compression . . . . . . . . . . . . . . . . 6 4.3. Scalability Requirements . . . . . . . . . . . . . . . . 6 5. Protocol Design Requirements . . . . . . . . . . . . . . . . 6 5.1. Ships in the Night Deployment . . . . . . . . . . . . . . 7 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 10. Normative References . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction The SPRING working group defined SRv6, with [RFC8402] describing how the Segment Routing (SR) architecture is instantiated on two data- planes: SR over MPLS (SR-MPLS) and SR over IPv6 (SRv6). SRv6 uses a routing header called the SR Header (SRH) [RFC8754], and defines SRv6 SID behaviors and a registry for identifying them in [I-D.ietf-spring-srv6-network-programming]. SRv6 is a proposed standard and is deployed today. The SPRING working group has observed that some use cases, such as strict path TE, may require long SRv6 SID lists. There are several proposed methods to reduce the resulting SRv6 encapsulation size by compressing the SID list. The SPRING working group formed a design team to define requirements for, and analyze, proposals to compress SRv6 SID lists. Cheng & Steffann Expires May 3, 2021 [Page 2] Internet-Draft SRCOMP Requirements October 2020 It is a goal of the design team to identify the solutions to SR over IPv6 list compression. In each category, the requirements are described under several sub- categories including o Efficiency and performance o Functional requirements o Operational requirements o Scalability requirements o Convergence requirements o Security requirements For each requirement, a description, rationale and metrics are described. The design team will produce a separate document to analyze the proposals. 2. Conventions used in this document 2.1. 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. 2.2. Terminology SR: Segment Routing SRH: Segment Routing Header MPLS: Multiprotocol Label Switching SR-MPLS: Segment Routing over MPLS data plane SID: Segment Identifier SRv6: Segment Routing over IPv6 Cheng & Steffann Expires May 3, 2021 [Page 3] Internet-Draft SRCOMP Requirements October 2020 SRv6 SID List: A list of SRv6 SIDs Compression proposal: A proposal to compress SRv6 SID lists SRv6 base: SRv6 as defined in [RFC8402], [RFC8754], [I-D.ietf-spring-srv6-network-programming] 3. SRv6 SID List Compression Requirements 3.1. Dataplane Efficiency and Performance Requirements 3.1.1. Encapsulation Header Size Description: The compression solution MUST reduce the size of the SRv6 encapsulation header. Rationale: A smaller SRv6 encapsulation results in better MTU efficiency. Metric: Compression is the ratio of the IPv6 encapsulation size of SRv6 as defined in [RFC8402], [RFC8754], [I-D.ietf-spring-srv6-network-programming] vs the IPv6 encapsulation size of a given proposal. The encapsulation savings of a compression proposal vs the SRv6 base is a useful measurement to compare proposals. The encapsulation metric (E) records the number of bytes required for a proposal to encapsulate a packet given a specific segment list. o E(proposal, segment list). The encapsulation savings(ES)records the encapsulation savings for a proposal to encapsulate a packet given a specific segment list. o ES(proposal, segment list) = 1 - E(proposal, segment list)/E(SRv6 base, segment list). 3.1.2. Forwarding Efficiency Description:The compression solution SHOULD minimize the number of required hardware resources accessed to process a segment. Rational:Efficiency in bits on the wire and processing efficiency are both important. Optimizing one at the expense of the other may lead to significant performance impact. Cheng & Steffann Expires May 3, 2021 [Page 4] Internet-Draft SRCOMP Requirements October 2020 Metric:The data plane efficiency metric (D) records the data plane forwarding efficiency of the proposed solution. Two metrics are used and recorded at the each segment endpoint: o D.PRS(segment list): number of headers parsed during processing of the segment list. o D.LKU(segment list): number of FIB lookups during processing of the segment list. The type of lookup is also recorded as longest prefix match (LPM) or exact match (EM) 3.1.3. State Efficiency Description:The compression solution SHOULD minimize the amount of additional forwarding statestored at a node Rational: Additional state increases the complexity of the control plane and data plane. It can also result in an increase in memory usage. Metric:The state efficiency metric (S) records the amount of additional forwarding state required by the proposed solution. o S(node parameters): the number of additional forwarding states that need to be stored at a node, given a set of node parameters consisting of number of nodes in the network, number of local interface, number of adjacencies. The forwarding state is counted as entries required in a Forwarding Information Base (FIB) at a node. 4. SRv6 Specific Requirements 4.1. Functional Requirements 4.1.1. SRv6 Based TBD 4.1.2. SRv6 Functionality TBD 4.1.3. SID list length Description: The compression mechanism must be able to represent SR paths that contain up to 16 segments. Cheng & Steffann Expires May 3, 2021 [Page 5] Internet-Draft SRCOMP Requirements October 2020 Rationale: Strict TE paths require SID list lengths proportional to the diameter of the SR domain. Metric: The compression mechanism must be able steer a packet through an SR path that contains up to sixteen segments. 4.1.4. SID summarization Description: The solution MUST be compatible with segment summarization. Rationale: Summarization of segments is a key benefit of SRv6 vs SR MPLS. In interdomain deployments any node can reach any other node via a single prefix segment. Without summarization, border router SIDs must be leaked and an additional global prefix segment is required for each domain border to be traversed. Metric: A solution supports summarization when segments can be summarized for advertisement into other IGP domains or levels. 4.1.5. Heterogeneous SID lists TBD 4.2. Operational Requirements 4.2.1. Lossless Compression Description: The segments of the compressed SID list MUST be equivalent to the original SID List. For example, a strict path TE SID List is not compressed to a loose path TE SID list. Rational: In SRv6 we can represent a path to meet certain objectives. A compressed solution needs to support the objectives in the same way. Metric: Information present in the pre-compression segment list MUST also be present in the post-compression SID list. 4.3. Scalability Requirements TBD 5. Protocol Design Requirements Cheng & Steffann Expires May 3, 2021 [Page 6] Internet-Draft SRCOMP Requirements October 2020 5.1. Ships in the Night Deployment Description: The compression solution MUST support deployment in existing SRv6 networks. Rationale: SRv6 is deployed today. A compression solution that interoperates well with SRv6, as deployed, will reduce the overhead and simplify operations. For Network operators who would migrate to compressed SRv6 SID lists, the move is expected to gradually occur over a period time, as they upgrade networks, domains, device families and software instances. Metric: A compliant compression solution provides the following o Supports simultaneous deployment at a node with current SRv6 SIDs. o Supports simultaneous deployment at a node with current SRv6 control plane. o Supports simultaneous operation of current SRv6 paths with compressed paths. o Supports the behaviors in [I-D.ietf-spring-srv6-network-programming]. o Does not require removal of existing IPv6 planning. 6. IANA Considerations This document has no requests to IANA. 7. Security Considerations TBD 8. Contributors The following individuals contributed to this draft Chongfeng Xie, China Telecom, xiechf@chinatelecom.cn Ron Bonica, Juniper Networks, rbonica@juniper.net Darren Dukes, Cisco Systems, ddukes@cisco.com Cheng Li, Huawei, c.l@huawei.com Peng Shaofu, ZTE, peng.shaofu@zte.com.cn Cheng & Steffann Expires May 3, 2021 [Page 7] Internet-Draft SRCOMP Requirements October 2020 Wim Henderickx, Nokia, wim.henderickx@nokia.com 9. Acknowledgements TBD 10. Normative References [I-D.ietf-6man-spring-srv6-oam] Ali, Z., Filsfils, C., Matsushima, S., Voyer, D., and M. Chen, "Operations, Administration, and Maintenance (OAM) in Segment Routing Networks with IPv6 Data plane (SRv6)", draft-ietf-6man-spring-srv6-oam-07 (work in progress), July 2020. [I-D.ietf-bess-srv6-services] Dawra, G., Filsfils, C., Raszuk, R., Decraene, B., Zhuang, S., and J. Rabadan, "SRv6 BGP based Overlay services", draft-ietf-bess-srv6-services-04 (work in progress), July 2020. [I-D.ietf-idr-bgpls-srv6-ext] Dawra, G., Filsfils, C., Talaulikar, K., Chen, M., daniel.bernier@bell.ca, d., and B. Decraene, "BGP Link State Extensions for SRv6", draft-ietf-idr-bgpls- srv6-ext-03 (work in progress), July 2020. [I-D.ietf-lsr-flex-algo] Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and A. Gulko, "IGP Flexible Algorithm", draft-ietf-lsr-flex- algo-13 (work in progress), October 2020. [I-D.ietf-lsr-isis-srv6-extensions] Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and Z. Hu, "IS-IS Extension to Support Segment Routing over IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-11 (work in progress), October 2020. [I-D.ietf-rtgwg-segment-routing-ti-lfa] Litkowski, S., Bashandy, A., Filsfils, C., Decraene, B., Francois, P., Voyer, D., Clad, F., and P. Camarillo, "Topology Independent Fast Reroute using Segment Routing", draft-ietf-rtgwg-segment-routing-ti-lfa-04 (work in progress), August 2020. Cheng & Steffann Expires May 3, 2021 [Page 8] Internet-Draft SRCOMP Requirements October 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. [I-D.ietf-spring-sr-service-programming] Clad, F., Xu, X., Filsfils, C., daniel.bernier@bell.ca, d., Li, C., Decraene, B., Ma, S., Yadlapalli, C., Henderickx, W., and S. Salsano, "Service Programming with Segment Routing", draft-ietf-spring-sr-service- programming-03 (work in progress), September 2020. [I-D.ietf-spring-srv6-network-programming] Filsfils, C., Camarillo, P., Leddy, J., Voyer, D., Matsushima, S., and Z. Li, "SRv6 Network Programming", draft-ietf-spring-srv6-network-programming-24 (work in progress), October 2020. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [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, . [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, . Authors' Addresses Weiqiang Cheng China Mobile Email: chengweiqiang@chinamobile.com Cheng & Steffann Expires May 3, 2021 [Page 9] Internet-Draft SRCOMP Requirements October 2020 Sanders Steffann SJM Steffann Consultancy Email: sander@steffann.nl Cheng & Steffann Expires May 3, 2021 [Page 10]