LSR Working Group U. Chunduri Internet-Draft Y. Qu Intended status: Standards Track Huawei USA Expires: April 25, 2019 October 22, 2018 Multiple Algorithm support for IS-IS Prefixes draft-chunduri-lsr-isis-prefix-multi-algo-01 Abstract This document specifies an extension to Intermediate System to Intermediate System (IS-IS) protocol by adding an Algorithm support for prefixes advertised. This allows multiple independent algorithm usage for computing the reachability of nodes and prefixes as opposed to only one algorithm. 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 RFC2119 [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 April 25, 2019. 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 Chunduri & Qu Expires April 25, 2019 [Page 1] Internet-DraftMultiple Algorithm support for IS-IS Prefixes October 2018 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. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 3 2. IS-IS Route Computation Algorithm sub-TLV in prefixes . . . . 3 3. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 4 3.1. Single Topology or Multi-Topology Mode . . . . . . . . . 4 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . 5 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 7.1. Normative References . . . . . . . . . . . . . . . . . . 5 7.2. Informative References . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 1. Introduction Reachability of various nodes or prefixes attached to these nodes is done through Shortest Path First (SPF) algorithm as defined in [ISO10589]. This is done today with in a single topology [RFC5305] [RFC5308] or in multi-topology (MT) routing [RFC5120] and with out any explicit advertisement of computation algorithm that is being used. IS-IS Segment Routing (SR) extensions [I-D.ietf-isis-segment-routing-extensions], extended the support for reachability computation for other algorithms other than SPF. This is done by advertising the computation algorithms supported at node level and also by advertising the algorithm being supported by Prefix Segment Identifier (SID) sub-TLV advertised in reachability prefixes. While the above would give the flexibility to use different reachability computation algorithm than the SPF, it is restricted to one particular data plane as opposed to the prefix itself. This document removes that restriction and advertises the algorithm to be used for reachability computation in the prefix itself, thus applying the same to any underlying data plane (E.g. SR-MPLS, SRH, IPv6, IPv4). Section 2 details the details of the sub-TLV and Section 3 talks about how to use te same and restrictions around it. Chunduri & Qu Expires April 25, 2019 [Page 2] Internet-DraftMultiple Algorithm support for IS-IS Prefixes October 2018 1.1. Acronyms IGP - Interior Gateway Protocols IS-IS - Intermediate System to Intermediate System LSR - Link State Routing MT - Multi Topology OSPF - Open Shortest Path First SID - Segment Identifier SR - Segment Routing 2. IS-IS Route Computation Algorithm sub-TLV in prefixes This section defines the encoding of Route Computation Algorithm (RCA) value that MUST be used while calculating the reachability to other nodes or to the prefixes attached to the other nodes. The RCA 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 | Algorithm | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // sub-sub-TLVs // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Route Computation Algorithm - sub-TLV Format Type - TBD (IANA) from Sub-TLVs for TLVs 135, 235, 236, and 237 (Extended IP reachability, MT IP. Reach, IPv6 IP. Reach, and MT IPv6 IP. Reach TLVs) registry. Length - Total length of the value field in bytes (variable). Flags - TBD Algorithm - Route Computation Algorithm value as defined in "IGP Algorithm Types" registry defined under "Interior Gateway Protocol (IGP) Parameters" IANA registries. sub-sub-TLVs - Optional and can be used to specify any information w.r.t to the algorithm being advertised with this prefix (TBD). Chunduri & Qu Expires April 25, 2019 [Page 3] Internet-DraftMultiple Algorithm support for IS-IS Prefixes October 2018 If multiple algorithms have to be adevrtised for the prefix, multiple instances of this sub-TLV with different algorithms can be used. If Algorithm value is '0' is the only algorithm on the prefix, it is optional to advertise it in this sub-TLV. Thus, not including such a sub-TLV in the prefix implies Algorithm value '0' capability only. 3. Elements of Procedure When provisioned an IS-IS node MUST compute reachability for more than one algorithm as indicated in the reachability prefix through this sub-TLV. Default metrics used for computation of any algorithm MUST be as defined in [RFC5120]. However, a particular algorithm can define other than default metrics and can be used while doing the computation. If non-default metrics are being used, those MUST be configured on the links and MUST be advertised through IS-IS Area/ domain. If a prefix is provisioned with multiple algorithms and after the reachability computation, nexthop is different for each algorithm it MUST use the lowest algorithm number to resolve the conflict. Once computation is done with the specified algorithm, this is applicable to all the data planes that are being supported for the prefix. If a particular data plane specific 'algorithms' as defined is in [I-D.ietf-isis-segment-routing-extensions] conflict (for e.g. preference) with data plane independent prefix algorithm (as defined in this draft); preference defined in a particular data plane MUST be used. 3.1. Single Topology or Multi-Topology Mode An SPF trigger can be common to multiple IS-IS Levels or for multiple address families with multi-topologies. Currently there is no specified order for reachability computation today and it is implementation dependent. This document specifies the order of reachability computation MUST be IS-IS area/level, topology [RFC5120] and algorithm specified in the reachability prefix. Doing computation in a particular order is also important for avoiding micro-loops as described in [I-D.ietf-rtgwg-spf-uloop-pb-statement]. If network uses single topology mode with only IPv4 adress family [RFC 5305] or in Single topology mode with IPv6 address family [RFC 5308] - a node configured with multiple algorithms MUST do route computation with all the algorithms as advertised in the prefixes. If network uses MT [RFC 5120], for each MT ID, per algorithm route computation MUST be done. Chunduri & Qu Expires April 25, 2019 [Page 4] Internet-DraftMultiple Algorithm support for IS-IS Prefixes October 2018 4. Acknowledgements TBD. 5. IANA Considerations This document requests IANA to assign a sub-TLV code point from the "Sub-TLVs for TLVs 135, 235, 236, and 237 (Extended IP reachability, MT IP. Reach, IPv6 IP. Reach, and MT IPv6 IP. Reach TLVs)" registry as follows: Route Computation Algorithm - Route Computation Algorithm sub-TLV as described in Section 2. TLV # Name ----- -------------------------------------------------------- TBD Route Computation Algorithm sub-TLV in IS-IS Prefix TLVs 6. Security Considerations Security concerns for IS-IS are addressed in [RFC5304] and [RFC5310]. Further security analysis for IS-IS protocol is done in [RFC7645] including analysis of both the above documents. Advertisement of the additional information defined in this document introduces no new security concerns in IS-IS protocol. 7. References 7.1. Normative References [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and dual environments", RFC 1195, DOI 10.17487/RFC1195, December 1990, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi Topology (MT) Routing in Intermediate System to Intermediate Systems (IS-ISs)", RFC 5120, DOI 10.17487/RFC5120, February 2008, . Chunduri & Qu Expires April 25, 2019 [Page 5] Internet-DraftMultiple Algorithm support for IS-IS Prefixes October 2018 7.2. Informative References [I-D.ietf-isis-segment-routing-extensions] Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A., Gredler, H., Litkowski, S., Decraene, B., and J. Tantsura, "IS-IS Extensions for Segment Routing", draft-ietf-isis- segment-routing-extensions-19 (work in progress), July 2018. [I-D.ietf-rtgwg-spf-uloop-pb-statement] Litkowski, S., Decraene, B., and M. Horneffer, "Link State protocols SPF trigger and delay algorithm impact on IGP micro-loops", draft-ietf-rtgwg-spf-uloop-pb-statement-07 (work in progress), May 2018. [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic Authentication", RFC 5304, DOI 10.17487/RFC5304, October 2008, . [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic Engineering", RFC 5305, DOI 10.17487/RFC5305, October 2008, . [RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308, DOI 10.17487/RFC5308, October 2008, . [RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., and M. Fanto, "IS-IS Generic Cryptographic Authentication", RFC 5310, DOI 10.17487/RFC5310, February 2009, . [RFC7645] Chunduri, U., Tian, A., and W. Lu, "The Keying and Authentication for Routing Protocol (KARP) IS-IS Security Analysis", RFC 7645, DOI 10.17487/RFC7645, September 2015, . Authors' Addresses Uma Chunduri Huawei USA 2330 Central Expressway Santa Clara, CA 95050 USA Email: uma.chunduri@huawei.com Chunduri & Qu Expires April 25, 2019 [Page 6] Internet-DraftMultiple Algorithm support for IS-IS Prefixes October 2018 Yingzhen Qu Huawei USA 2330 Central Expressway Santa Clara, CA 95050 USA Email: yingzhen.qu@huawei.com Chunduri & Qu Expires April 25, 2019 [Page 7]