LSR Working Group Louis Chan INTERNET-DRAFT Krzysztof Szarkowicz Intended status: Standard Track Juniper Networks Expires: Sep 6, 2022 Mar 6, 2022 IGP extensions for Advertising Offset for Flex-Algorithm draft-chan-lsr-igp-adv-offset-00.txt Abstract This document describes the IGP extensions to provide predictable Adjacency-SIDs per Flex-Algorithm [FLEXALGO] in segment routing. We propose some methods to allow the advertisement of additional TLV in IGP so that the Flex-Algorithm specific Adjacency-SIDs could be automatically derived. With the proposed method, the size of advertisement on per node per link basis is greatly reduced. Each participating router would derive the required labels automatically. Extensions for offset to derive Flex-Algorithm Prefix-SID is also included in the document. 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 http://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 Sep 6, 2022. Copyright Notice Copyright (c) 2017 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 (http://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 Chan Expires Sep 6, 2022 [Page 1] Internet-Draft draft-chan-lsr-igp-adv-offset-00 March 2022 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. Conventions used in this document..............................2 3. ISIS extension.................................................2 3.1. Algorithm Offset for Adj-SID..............................3 3.2. Algorithm Offset for LAN based Adj-SID....................4 3.3. Algorithm Offset for Prefix SID...........................5 4. Compatibility..................................................6 5. OSPF extension.................................................6 6. Security Consideration.........................................6 7. References.....................................................7 7.1. Normative References......................................7 7.2. Informative References....................................7 8. Acknowledgments................................................7 1. Introduction The draft proposes methods for routers to announce Flex-Algorithm specific Adjacency-SID with minimal advertisement in IGP. When the other routers need a SR policy (aka SR-TE) or TI-LFA path, the Flex-Algorithm specific Adjacency-SID would be taken into the path label construction. Hence, the top most label, either node or link related, in a SR policy stack would be used to identify a certain Flex-Algo with full identification. 2. Conventions used in this document 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]. In this document, these words will appear with that interpretation only when in ALL CAPS. Lower case uses of these words are not to be interpreted as carrying significance described in RFC 2119. 3. ISIS extension With reference to RFC8667, the information could be advertised in SR-Capabilities sub-TLV in Section 3. Chan Expires Sep 6, 2022 [Page 2] Internet-Draft draft-chan-lsr-igp-adv-offset-00 March 2022 3.1. Algorithm Offset for Adj-SID 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID/Label | Base offset/Index offset (variable) ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Flags/ Algo/ Base offset/ Index offset ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where: Type: TDB Length: variable; multiple advertisements Flags: 1 octet field of the following flags: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | |B|V|L| | +-+-+-+-+-+-+-+-+ where: B-Flag: Backup Flag. If set, the Adj-SID is eligible for protection (e.g., using IP Fast Reroute (IPFRR) or MPLS Fast Reroute (MPLS-FRR)) as described in [RFC8402]. V-Flag: Value Flag. If set, then it carries a label value. If not set, it is an index value. L-Flag: Local Flag. Always set to 1 Algorithm: 1 octet Flex-Algo value is between 128 and 255. Base Offset: 3 octets Local label base for Adjacency-SIDs for given Flex- Algorithm. The derived Adjacency-SID is the sum of the base offset and the Algo 0 label Index Offset: 4 octets If Adjacency-SID is advertised as index, this provides an Chan Expires Sep 6, 2022 [Page 3] Internet-Draft draft-chan-lsr-igp-adv-offset-00 March 2022 offset index value. The new label is sum of (SRGB base + index + index offset) The format of Base Offset and Index Offset is the same as RFC8667. The choice of advertising Base Offset or Index Offset must match the advertisement of original Adjacency-SID method from the same router. 3.2. Algorithm Offset for LAN based Adj-SID 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Neighbor System-ID (ID length octets) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID/Label Base Offset/Index Offset (variable) ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Flags/ Algo/NB Sys-ID/ SID/Label/Index Offset (variable) ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where: Type: TDB Length: variable; multiple advertisements Flags: 1 octet field of the following flags: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | |B|V|L| | +-+-+-+-+-+-+-+-+ where: B-Flag: Backup Flag. If set, the Adj-SID is eligible for protection (e.g., using IP Fast Reroute (IPFRR) or MPLS Fast Reroute (MPLS-FRR)) as described in [RFC8402]. V-Flag: Value Flag. If set, then it carries a label value. If not set, it is an index value. L-Flag: Local Flag. Always set to 1 Algorithm: 1 octet. Same as Section 5.1 Chan Expires Sep 6, 2022 [Page 4] Internet-Draft draft-chan-lsr-igp-adv-offset-00 March 2022 Neighbor System-ID: IS-IS System-ID of length "ID Length" as defined in [ISO10589]. Base Offset: 3 octets. Same as Section 5.1 Index Offset: 4 octets. Same as Section 5.1 3.3. Algorithm Offset for Prefix SID Prefix-SID for Algorithm could also be generated by adding an index offset value or a base offset for label. This advertisement is an sub-TLV in RFC8667 Section 2. 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID/Label Base offset/ Index offset ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Flags/ Algorithm/ Base Offset/ Index offset ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: TDB Length: variable Flags: 1 octet field of the following flags: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |R|N| |V|L| | +-+-+-+-+-+-+-+-+ where: R-Flag: Re-advertisement Flag. If set, then the prefix to which this Prefix-SID is attached has been propagated by the router from either another level (i.e., from Level-1 to Level-2 or the opposite) or redistribution (e.g., from another protocol). N-Flag: Node-SID Flag. If set, then the Prefix-SID refers to the router identified by the prefix. Typically, the N-Flag is set on Prefix-SIDs that are attached to a router loopback address. The Chan Expires Sep 6, 2022 [Page 5] Internet-Draft draft-chan-lsr-igp-adv-offset-00 March 2022 N-Flag is set when the Prefix-SID is a Node-SID as described in [RFC8402]. V-Flag: Value Flag. If set, then it carries a label value. If not set, it is an index value. L-Flag: Local Flag. Always set to 0 Algorithm: 1 octet Flex-Algo value is between 128 and 255 Base offset: 3 octets Label base for Prefix-SIDs for given Algorithm The derived Prefix-SID is the sum of the base Offset and the Algo 0 label Index Offset: 4 octets Index offset counting from Algo 0 The new label for Prefix is sum of (SRGB base + index + index offset) The format of Base offset and Index Offset is the same as RFC8667. The choice of advertising Base Offset or Index Offset MUST match the advertisement of original Prefix-SID method from the same router. 4. Compatibility For nodes that do not support Algorithm Offset for Adj-SID extension, the label stack could use normal Adj-SID, providing that the node still supports Flex-Algo Prefix SID. For TI-LFA, there would be two modes of operation - loose or strict. For strict mode, all Adj-SID involved in TI-LFA candidate path must be derived with offset method. For loose mode, Adj-SID in the TI-LFA candidate path could be a mix of Adj-SID's with and without offset. This allows backward compatibility with routers which only support Flex-Algo. 5. OSPF extension TBD 6. Security Consideration TBD Chan Expires Sep 6, 2022 [Page 6] Internet-Draft draft-chan-lsr-igp-adv-offset-00 March 2022 7. References 7.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 7.2. Informative References [RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., Bashandy, A., Gredler, H., and B. Decraene, "IS-IS Extensions for Segment Routing", RFC 8667, DOI 10.17487/RFC8667, December 2019, . [TI-LFA] Litkowski, S., Bashandy, A., Filsfils, C., Francois, P., Decraene, B., and D. Voyer, "Topology Independent Fast Reroute using Segment Routing", [FLEXAGLO] S. Hegde, P. Psenak and etc, IGP Flexible Algorithm https://datatracker.ietf.org/doc/draft-ietf-lsr-flex-algo [ISO10589] International Organization for Standardization, "Information technology -- Telecommunications and information exchange between systems -- Intermediate system to Intermediate system intra-domain routeing information exchange protocol for use in conjunction with the protocol for providing the connectionless-mode network service (ISO 8473)", ISO/IEC 10589:2002, Second Edition, November 2002. 8. Acknowledgments The following people have contributed to this document: Shraddha Hegde, Juniper Networks Author Address Louis Chan Juniper Networks 2604, Cityplaza One, 1111 King's Road Taikoo Shing Hong Kong Phone: +852-25876659 Chan Expires Sep 6, 2022 [Page 7] Internet-Draft draft-chan-lsr-igp-adv-offset-00 March 2022 Email: louisc@juniper.net Krzysztof Grzegorz Szarkowicz Juniper Networks Parkring 10 A-1010 Wien Austria Phone: +49 89 203012127 Email: kszarkowicz@juniper.net Chan Expires Sep 6, 2022 [Page 8]