SPRING WG Ting. Liao Internet-Draft Ting. Ao Intended status: Standards Track Fangwei. Hu Expires: April 21, 2016 ZTE Corporation October 19, 2015 SPRING SID Calculation draft-lt-spring-sid-calculation-00.txt Abstract Segment Routing (SR) allows for a flexible definition of end-to-end paths within IGP topologies by encoding paths as sequences of topological sub-paths, called "segments". These segments are advertised by the link-state routing protocols (IS-IS and OSPF). And a segment is identified by a Segment Routing ID (SID). This document proposes a method to calculate SID forwarding entry within SR topology in a SR domain, and to guarantee the consistency of SR encapsulation forwarding. 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 April 21, 2016. Copyright Notice Copyright (c) 2015 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 Liao, et al. Expires April 21, 2016 [Page 1] Internet-Draft SPRING SID Calculation October 2015 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. Conventions and Abbreviations . . . . . . . . . . . . . . . . 3 3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. SID calculation . . . . . . . . . . . . . . . . . . . . . . . 4 4.1. SR independent topology . . . . . . . . . . . . . . . . . 4 4.2. SID calculation . . . . . . . . . . . . . . . . . . . . . 5 4.3. With SRMN or SRMS . . . . . . . . . . . . . . . . . . . . 5 4.3.1. Default label . . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . 5 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 8. Normative References . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction Segment Routing (SR) allows for a flexible definition of end-to-end paths within IGP topologies by encoding paths as sequences of topological sub-paths, called "segments". The segments for its attached prefixes and adjacencies are advertised by the link-state routing protocols (IS-IS and OSPF). These segments are called IGP segments or IGP SIDs. And an IGP-Prefix Segment is an IGP segment attached to an IGP prefix. The segments forwarding entries are learnt from its attached prefixes' egress information as described in [I-D.ietf-spring-segment-routing], where wrote: A node N attaching a Prefix-SID SID-R to its attached prefix R MUST maintain the following FIB entry: Incoming Active Segment: SID-R Ingress Operation: NEXT Egress interface: NULL A remote node M MUST maintain the following FIB entry for any learned Prefix-SID SID-R attached to IP prefix R: Incoming Active Segment: SID-R Ingress Operation: If the next-hop of R is the originator of R and instructed to remove the active segment: NEXT Else: CONTINUE Egress interface: the interface towards the next- hop along the shortest-path to prefix R. In some situations such as the SR need to be calculated as CSPF calculation, the path calculated is not the shortest path, so the SR needs to have the dependent topology. with the knowledge learnt from [I-D.ietf-spring-segment-routing], the SR node does not have the state about its neighbours. With the ldp interoperability as described in [I-D.filsfils-spring-segment-routing-ldp-interop] section 4.2, P6's next-hop for the IGP route "PE3" is not SR capable Liao, et al. Expires April 21, 2016 [Page 2] Internet-Draft SPRING SID Calculation October 2015 (P7 does not advertise the SR capability). However, P6 has an LDP label binding from that next-hop for the same FEC (e.g. LDP label 1037). Hence, P6 swaps 103 for 1037 and forwards to P7. The SR node needs to judge its neighbour is SR or LDP. So it is still necessary to maintain a SR topology to do the sid calculation. This draft describes a mechanism to do the sid calculation. 2. Conventions and Abbreviations 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] . The following notations and abbreviations are used throughout this draft. SID: Segment Identifiers. 3. Motivation As shown in the figure 1. +--+ +--+ +--+ ----|P1|---|P2|---|P3|---- / +--+ +--+ +--+ \ / \ +---+ +---+ +---+ +---+ |CE1|----|PE1| |PE2|----|CE2| +---+ +---+ +---+ +---+ \ / \ +--+ +--+ / ----|R5|----------|R6|---- +--+ +--+ Figure 1 Scenario 1 PE1\P1\P2\P3\PE2 are routers supporting mpls forwarding, while R5\R6 are routers do not enable mpls or occurred some error the mpls neighbour between R5\R6 is broken. Such as the SID assigned to PE1 10001, P1 10002, P2 10003, P3 10004 and PE2 10005. From PE1 to PE2, each link cost between the nodes is 1. So the shortest path is PE1-R5-R6-PE2, with SR forwarding, the next hop with the forwarding entry on PE1 to PE2 10005 is to R5 currently. It will causing the mpls encapsulation packets forwarding to R5 who does not support mpls forwarding, the packets will be dropped. Liao, et al. Expires April 21, 2016 [Page 3] Internet-Draft SPRING SID Calculation October 2015 +--+ +--+ +--+ +--+ ----|P1|---|P2|---|P3|---|P4|---- / sr +--+ sr+--+ sr+--+ sr+--+ sr \ / \ +---+ +---+ +---+ +---+ |CE1|----|PE1| |PE2|----|CE2| +---+ +---+ +---+ +---+ \ / \sr +--+ ldp +--+ igp +--+ igp/ ----|P5|------|P6|------|R7|---- +--+ +--+ +--+ Figure 2 Scenario 2 PE1\P1\P2\P3\P4\P5\P6\PE2 are routers supporting MPLS forwarding, Such as the SID assigned to PE1 10001, P1 10002, P2 10003, P3 10004, PE2 10005, P4 10006, P5 10007. While P5 and P6 is LDP neighbour, and P6 and R7 is LDP neighbour , R7 and PE2 is LDP neighbour, with some mistake, the LDP neighbour between P6-R7, R7-PE2 are off, and the IGP neighbour between P6-R7, R7-PE2 are still on. From PE1 to PE2, each link cost between the nodes is 1. So the shortest path is PE1-P5-P6-R7-PE2, with SR forwarding, the next hop with the forwarding entry on PE1 to PE2 10005 is to P5 currently. It will causing the MPLS encapsulation packets forwarding to P5 with the 10005 in the outer label, and switches to the LDP label which the P6 assigned to PE2, and the MPLS packet forwarding to P6, P6 accept the mpls packets, and find that the neighbour of the next hop is not ldp neighbour, so the packets will be dropped either. The problem in the SR dependent IGP topology is that the ingress nodes has not have the full information with all the nodes on the path. While the list includes nodes' information, all this nodes in the list is SR enabled nodes, but the nodes' information is not all the nodes on the path. So it is necessary to have the independent SR topology to support the mixed network. After all, the network where some nodes or links are not enabled mpls capabilities is commonly. 4. SID calculation In the proposed mechanism, the SR will be an independent topology, and the SID calculation will be calculated based in the topology. 4.1. SR independent topology The SR topology will be an independent topology based on the SR- Capabilities Sub-TLV (as described in [I-D.ietf-isis-segment-routing-extensions] and [I-D.ietf-ospf-segment-routing-extensions]. ) carried in each Liao, et al. Expires April 21, 2016 [Page 4] Internet-Draft SPRING SID Calculation October 2015 router's LSP. If SR node A accepted an lsp sending from node B, with the SR-Capabilities Sub-TLV carried in node B's LSP, the node A will know that the node B is a SR capable node, and in node A's LSDB, it will has an independent SR topology. 4.2. SID calculation With the independent SR topology, SID calculation will be calculated in the topology, and the SID forwarding entry will be maintained with SID calculation. As figure 1 described, PE1 will have an independent topology which includes the SID information of PE1\P1\P2\P3\PE2, and will not include the information of R5\R6, so when PE1 calculate the SID to 10005, even though the IGP shortest-path is through R5\R6, PE1 will calculate the path to 10005 only in the SR topology. 4.3. With SRMN or SRMS Optionally, If there are some SRMNs or SRMSes assigned by the NMS in the network, they assign SID to other SR or non-SR nodes, with the SR nodes, the SR nodes will sending out an TLV with it's SID and the SR- Capabilities Sub-TLV, then other nodes will learn which nodes are the SR nodes. With the non-SR nodes, this nodes can not sending out the SR-Capabilities Sub-TLV, but other SR nodes need to learn this SIDs' information, in this case, the SRMNs or SRMSes will sending an default label TLV extension out, using the default label to instruct the packet with the SID assigned to non-SR node forwarding to itself, and then it is responsible for sending the packet to the non-SR node. 4.3.1. Default label Optionally, the default label could either be an reserved and unused label, or be configured by the NMS and will be known by each SR node. 5. Security Considerations TBD. 6. Acknowledgements In progress. 7. IANA Considerations TBD. Liao, et al. Expires April 21, 2016 [Page 5] Internet-Draft SPRING SID Calculation October 2015 8. Normative References [I-D.filsfils-spring-segment-routing-ldp-interop] Filsfils, C., Previdi, S., Bashandy, A., Decraene, B., Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R., Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe, "Segment Routing interoperability with LDP", draft- filsfils-spring-segment-routing-ldp-interop-03 (work in progress), March 2015. [I-D.ietf-isis-segment-routing-extensions] Previdi, S., 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-05 (work in progress), June 2015. [I-D.ietf-ospf-segment-routing-extensions] Psenak, P., Previdi, S., Filsfils, C., Gredler, H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF Extensions for Segment Routing", draft-ietf-ospf-segment- routing-extensions-05 (work in progress), June 2015. [I-D.ietf-spring-segment-routing] Filsfils, C., Previdi, S., Decraene, B., Litkowski, S., and r. rjs@rob.sh, "Segment Routing Architecture", draft- ietf-spring-segment-routing-06 (work in progress), October 2015. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", RFC 4915, DOI 10.17487/RFC4915, June 2007, . [RFC4970] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and S. Shaffer, "Extensions to OSPF for Advertising Optional Router Capabilities", RFC 4970, DOI 10.17487/RFC4970, July 2007, . [RFC5250] Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The OSPF Opaque LSA Option", RFC 5250, DOI 10.17487/RFC5250, July 2008, . Liao, et al. Expires April 21, 2016 [Page 6] Internet-Draft SPRING SID Calculation October 2015 Authors' Addresses Ting Liao ZTE Corporation No.50 Software Avenue Nanjing, Jiangsu 210012 China Phone: +86 25 88016576 Email: liao.ting@zte.com.cn Ting Ao ZTE Corporation No.889 Bibo Rd Shanghai 201203 China Phone: +86 21 68896273 Email: ao.ting@zte.com.cn Fangwei Hu ZTE Corporation No.889 Bibo Rd Shanghai 201203 China Phone: +86 21 68896273 Email: hu.fangwei@zte.com.cn Liao, et al. Expires April 21, 2016 [Page 7]