Network Working Group C. Filsfils, Ed. Internet-Draft S. Previdi, Ed. Intended status: Standards Track A. Bashandy Expires: September 19, 2016 Cisco Systems, Inc. B. Decraene S. Litkowski Orange M. Horneffer Deutsche Telekom R. Shakir Jive Communications J. Tantsura Ericsson E. Crabbe Individual March 18, 2016 Segment Routing with MPLS data plane draft-ietf-spring-segment-routing-mpls-04 Abstract Segment Routing (SR) leverages the source routing paradigm. A node steers a packet through a controlled set of instructions, called segments, by prepending the packet with an SR header. A segment can represent any instruction, topological or service-based. SR allows to enforce a flow through any topological path and service chain while maintaining per-flow state only at the ingress node to the SR domain. Segment Routing can be directly applied to the MPLS architecture with no change in the forwarding plane. This drafts describes how Segment Routing operates on top of the MPLS data plane. 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 Filsfils, et al. Expires September 19, 2016 [Page 1] Internet-Draft Segment Routing with MPLS March 2016 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 September 19, 2016. Copyright Notice Copyright (c) 2016 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 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 . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Illustration . . . . . . . . . . . . . . . . . . . . . . . . 3 3. MPLS Instantiation of Segment Routing . . . . . . . . . . . . 4 4. IGP Segments Examples . . . . . . . . . . . . . . . . . . . . 6 4.1. Example 1 . . . . . . . . . . . . . . . . . . . . . . . . 7 4.2. Example 2 . . . . . . . . . . . . . . . . . . . . . . . . 8 4.3. Example 3 . . . . . . . . . . . . . . . . . . . . . . . . 8 4.4. Example 4 . . . . . . . . . . . . . . . . . . . . . . . . 8 4.5. Example 5 . . . . . . . . . . . . . . . . . . . . . . . . 8 5. Other Examples of MPLS Segments . . . . . . . . . . . . . . . 9 5.1. LDP LSP segment combined with IGP segments . . . . . . . 9 5.2. RSVP-TE LSP segment combined with IGP segments . . . . . 10 6. Segment List History . . . . . . . . . . . . . . . . . . . . 11 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 8. Manageability Considerations . . . . . . . . . . . . . . . . 11 9. Security Considerations . . . . . . . . . . . . . . . . . . . 11 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 11 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 12.1. Normative References . . . . . . . . . . . . . . . . . . 12 12.2. Informative References . . . . . . . . . . . . . . . . . 12 Filsfils, et al. Expires September 19, 2016 [Page 2] Internet-Draft Segment Routing with MPLS March 2016 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 1. Introduction The Segment Routing architecture [I-D.ietf-spring-segment-routing] can be directly applied to the MPLS architecture with no change in the MPLS forwarding plane. This drafts describes how Segment Routing operates on top of the MPLS data plane. The Segment Routing problem statement is described in [I-D.ietf-spring-problem-statement]. Link State protocol extensions for Segment Routing are described in [I-D.ietf-isis-segment-routing-extensions], [I-D.ietf-ospf-segment-routing-extensions] and [I-D.ietf-ospf-ospfv3-segment-routing-extensions]. 2. Illustration Segment Routing, applied to the MPLS data plane, offers the ability to tunnel services (VPN, VPLS, VPWS) from an ingress PE to an egress PE, without any other protocol than ISIS or OSPF ([I-D.ietf-isis-segment-routing-extensions] and [I-D.ietf-ospf-segment-routing-extensions]). LDP and RSVP-TE signaling protocols are not required. Note that [I-D.filsfils-spring-segment-routing-ldp-interop] documents SR co-existence and interworking with other MPLS signaling protocols, if present in the network during a migration, or in case of non- homogeneous deployments. The operator only needs to allocate one node segment per PE and the SR IGP control-plane automatically builds the required MPLS forwarding constructs from any PE to any PE. P1---P2 / \ A---CE1---PE1 PE2---CE2---Z \ / P3---P4 Figure 1: IGP-based MPLS Tunneling In Figure 1 above, the four nodes A, CE1, CE2 and Z are part of the same VPN. PE2 advertises (in the IGP) a host address 192.0.2.2/32 with its attached node segment 102. Filsfils, et al. Expires September 19, 2016 [Page 3] Internet-Draft Segment Routing with MPLS March 2016 CE2 advertises to PE2 a route to Z. PE2 binds a local label LZ to that route and propagates the route and its label via MPBGP to PE1 with nhop 192.0.2.2 (PE2 loopback address). PE1 installs the VPN prefix Z in the appropriate VRF and resolves the next-hop onto the node segment 102. Upon receiving a packet from A destined to Z, PE1 pushes two labels onto the packet: the top label is 102, the bottom label is LZ. 102 identifies the node segment to PE2 and hence transports the packet along the ECMP-aware shortest- path to PE2. PE2 then processes the VPN label LZ and forwards the packet to CE2. Supporting MPLS services (VPN, VPLS, VPWS) with SR has the following benefits: Simple operation: one single intra-domain protocol to operate: the IGP. No need to support IGP synchronization extensions as described in [RFC5443] and [RFC6138]. Excellent scaling: one Node-SID per PE. 3. MPLS Instantiation of Segment Routing MPLS instantiation of Segment Routing fits in the MPLS architecture as defined in [RFC3031] both from a control plane and forwarding plane perspective: o From a control plane perspective [RFC3031] does not mandate a single signaling protocol. Segment Routing proposes to use the Link State IGP as its use of information flooding fits very well with label stacking on ingress. o From a forwarding plane perspective, Segment Routing does not require any change to the forwarding plane. When applied to MPLS, a Segment is a LSP and the 20 right-most bits of the segment are encoded as a label. This implies that, in the MPLS instantiation, the SID values are allocated within a reduced 20-bit space out of the 32-bit SID space. The notion of indexed global segment fits the MPLS architecture [RFC3031] as the absolute value allocated to any segment (global or local) can be managed by a local allocation process (similarly to other MPLS signaling protocols). If present, SR can coexist and interworks with LDP and RSVP [I-D.filsfils-spring-segment-routing-ldp-interop]. Filsfils, et al. Expires September 19, 2016 [Page 4] Internet-Draft Segment Routing with MPLS March 2016 The source routing model described in [I-D.ietf-spring-segment-routing] is inherited from the ones proposed by [RFC1940] and [RFC2460]. The source routing model offers the support for explicit routing capability. Contrary to RSVP-based explicit routes where tunnel midpoints maintain states, SR-based explicit routes only require per-flow states at the ingress edge router where the traffic engineer policy is applied. Contrary to RSVP-based explicit routes which consist in non-ECMP circuits (similar to ATM/FR), SR-based explicit routes can be built as list of ECMP-aware node segments and hence ECMP-aware traffic engineering is natively supported by SR. When Segment Routing is instantiated over the MPLS data plane the following applies: o A list of segments is represented as a stack of labels. o The active segment is the top label. o The CONTINUE operation is implemented as an MPLS swap operation. The outgoing label value is computed as follows: * When the same Segment Routing Global Block (SRGB, defined in [I-D.ietf-spring-segment-routing] is used throughout the SR domain, the outgoing label value is equal to the incoming label value. * When different SRGBs are used, the outgoing label value is set as: [SRGB(next_hop)+index]. If the index can't be applied to the SRGB (i.e.: if the index points outside the SRGB of the next-hop or the next-hop has not advertised a valid SRGB), then no outgoing label value can be computed and the next-hop MUST be considered as not supporting the MPLS operations for that particular SID. o The NEXT operation is implemented as an MPLS pop operation. The NEXT operation does not require any mapping to an outgoing label hence the SRGB is irrelevant for this operation. o The PUSH operation is implemented as an MPLS push of a label stack. o The Segment Routing Global Block (SRGB) values MUST be greater than 15 in order to preserve values 0-15 as defined in [RFC3032]. Filsfils, et al. Expires September 19, 2016 [Page 5] Internet-Draft Segment Routing with MPLS March 2016 o As described in [I-D.ietf-spring-segment-routing], using the same SRGB on all nodes within the SR domain eases operations and troubleshooting and is expected to be a deployment guideline. In conclusion, there are no changes in the operations of the data- plane currently used in MPLS networks. 4. IGP Segments Examples Assuming the network diagram of Figure 2 and the IP address and IGP Segment allocation of Figure 3, the following examples can be constructed. +--------+ / \ R1-----R2----------R3-----R8 | \ / | | +--R4--+ | | | +-----R5-----+ Figure 2: IGP Segments - Illustration Filsfils, et al. Expires September 19, 2016 [Page 6] Internet-Draft Segment Routing with MPLS March 2016 +-----------------------------------------------------------+ | IP address allocated by the operator: | | 192.0.2.1/32 as a loopback of R1 | | 192.0.2.2/32 as a loopback of R2 | | 192.0.2.3/32 as a loopback of R3 | | 192.0.2.4/32 as a loopback of R4 | | 192.0.2.5/32 as a loopback of R5 | | 192.0.2.8/32 as a loopback of R8 | | 198.51.100.9/32 as an anycast loopback of R4 | | 198.51.100.9/32 as an anycast loopback of R5 | | | | SRGB defined by the operator as 1000-5000 | | | | Global IGP SID allocated by the operator: | | 1001 allocated to 192.0.2.1/32 | | 1002 allocated to 192.0.2.2/32 | | 1003 allocated to 192.0.2.3/32 | | 1004 allocated to 192.0.2.4/32 | | 1008 allocated to 192.0.2.8/32 | | 2009 allocated to 198.51.100.9/32 | | | | Local IGP SID allocated dynamically by R2 | | for its "north" adjacency to R3: 9001 | | for its "north" adjacency to R3: 9003 | | for its "south" adjacency to R3: 9002 | | for its "south" adjacency to R3: 9003 | +-----------------------------------------------------------+ Figure 3: IGP Address and Segment Allocation - Illustration 4.1. Example 1 R1 may send a packet P1 to R8 simply by pushing an SR header with segment list {1008}. 1008 is a global IGP segment attached to the IP prefix 192.0.2.8/32. Its semantic is global within the IGP domain: any router forwards a packet received with active segment 1008 to the next-hop along the ECMP-aware shortest-path to the related prefix. In conclusion, the path followed by P1 is R1-R2--R3-R8. The ECMP- awareness ensures that the traffic be load-shared between any ECMP path, in this case the two north and south links between R2 and R3. Filsfils, et al. Expires September 19, 2016 [Page 7] Internet-Draft Segment Routing with MPLS March 2016 4.2. Example 2 R1 may send a packet P2 to R8 by pushing an SR header with segment list {1002, 9001, 1008}. 1002 is a global IGP segment attached to the IP prefix 192.0.2.2/32. Its semantic is global within the IGP domain: any router forwards a packet received with active segment 1002 to the next-hop along the shortest-path to the related prefix. 9001 is a local IGP segment attached by node R2 to its north link to R3. Its semantic is local to node R2: R2 switches a packet received with active segment 9001 towards the north link to R3. In conclusion, the path followed by P2 is R1-R2-north-link-R3-R8. 4.3. Example 3 R1 may send a packet P3 along the same exact path as P1 using a different segment list {1002, 9003, 1008}. 9003 is a local IGP segment attached by node R2 to both its north and south links to R3. Its semantic is local to node R2: R2 switches a packet received with active segment 9003 towards either the north or south links to R3 (e.g. per-flow loadbalancing decision). In conclusion, the path followed by P3 is R1-R2-any-link-R3-R8. 4.4. Example 4 R1 may send a packet P4 to R8 while avoiding the links between R2 and R3 by pushing an SR header with segment list {1004, 1008}. 1004 is a global IGP segment attached to the IP prefix 192.0.2.4/32. Its semantic is global within the IGP domain: any router forwards a packet received with active segment 1004 to the next-hop along the shortest-path to the related prefix. In conclusion, the path followed by P4 is R1-R2-R4-R3-R8. 4.5. Example 5 R1 may send a packet P5 to R8 while avoiding the links between R2 and R3 while still benefitting from all the remaining shortest paths (via R4 and R5) by pushing an SR header with segment list {2009, 1008}. 2009 is a global IGP segment attached to the anycast IP prefix 198.51.100.9/32. Its semantic is global within the IGP domain: any Filsfils, et al. Expires September 19, 2016 [Page 8] Internet-Draft Segment Routing with MPLS March 2016 router forwards a packet received with active segment 2009 to the next-hop along the shortest-path to the related prefix. In conclusion, the path followed by P5 is either R1-R2-R4-R3-R8 or R1-R2-R5-R3-R8 . 5. Other Examples of MPLS Segments In addition to the IGP segments previously described, the SPRING source routing policy applied to MPLS can include MPLS LSP's signaled by LDP, RSVPTE and BGP. The list of examples is non exhaustive. Other form of segments combination can be instantiated through Segment Routing (e.g.: RSVP LSPs combined with LDP or IGP or BGP LSPs). 5.1. LDP LSP segment combined with IGP segments The example illustrates a segment-routing policy including IGP segments and LDP LSP segments. SL1---S2---SL3---L4---SL5---S6 | | +---------------+ Figure 4: LDP LSP segment combined with IGP segments We assume that: o All links have an IGP cost of 1 except SL3-S6 link which has cost 2. o All nodes are in the same IGP area. o Nodes SL1, S2, SL3, SL5 and S6 are IGP-SR capable. o SL3 and S6 have, respectively, index 3 and 6 assigned to them. o All SR nodes have the same SRGB consisting of: [1000, 1999] o SL1, SL3, L4 and SL5 are LDP capable. o SL1 has a directed LDP session with SL3 and is able to retrieve the SL3 local LDP mapping for FEC SL5: 35 o The following source-routed policy is defined in SL1 for the traffic destined to S6: use path SL1-S2-SL3-L4-SL5-S6 (instead of shortest-path SL1-S2-SL3-S6). Filsfils, et al. Expires September 19, 2016 [Page 9] Internet-Draft Segment Routing with MPLS March 2016 This is realized by programming the following segment-routing policy at SL1: for traffic destined to S6, push the ordered segment list: {1003, 35, 1006}, where: o 1003 gets the packets from SL1 to SL3 via S2. o 35 gets the packets from SL3 to SL5 via L4. o 1006 gets the packets from SL5 to S6. The above allows to steer the traffic into path SL1-S2-SL3-L4-SL5-S6 instead of the shortest path SL1-S2-SL3-S6. 5.2. RSVP-TE LSP segment combined with IGP segments The example illustrates a segment-routing policy including IGP segments and RSVP-TE LSP segments. S1---S2---RS3---R4---RS5---S6 | | +---------------+ Figure 5: RSVP-TE LSP segment combined with IGP segments We assume that: o All links have an IGP cost of 1 except link RS3-S6 which has cost 2. o All nodes are IGP-SR capable except R4. o RS3 and S6 have, respectively, index 3 and 6 assigned to them. o All SR nodes have the same SRGB consisting of: [1000, 1999] o RS3, R4 and RS5 are RSVP-TE capable. o An RSVP-TE LSP has been provisioned from RS3 to RS5 via R4. o RS3 allocates a binding SID (with value of 135) for this RSVP-TE LSP and signals it in the igp. o The following source-routed policy is defined at S1 for the traffic destined to S6: use path S1-S2-RS3-R4-RS5-S6 instead of shortest-path S1-S2-RS3-S6. Filsfils, et al. Expires September 19, 2016 [Page 10] Internet-Draft Segment Routing with MPLS March 2016 This is realized by programming the following segment-routing policy at S1: - for traffic destined to S6, push the ordered segment list: {1003, 135, 1006}, where: o 1003 gets the packets from S1 to RS3 via S2. o 135 gets the packets from RS3 into the RSVP-TE LSP to RS5 via R4. o 1006 gets the packets from RS5 to S6. The above allows to steer the traffic into path S1-S2-RS3-R4-RS5-S6 instead of the shortest path S1-S2-RS3-S6. 6. Segment List History In the abstract SR routing model [I-D.ietf-spring-segment-routing], any node N along the journey of the packet is able to determine where the packet P entered the SR domain and where it will exit. The intermediate node is also able to determine the paths from the ingress edge router to itself, and from itself to the egress edge router. In the MPLS instantiation, as the packet travels through the SR domain, the stack is depleted and the segment list history is gradually lost. 7. IANA Considerations This document doesn't introduce any codepoint. 8. Manageability Considerations TBD 9. Security Considerations TBD 10. Contributors The following contributors have substantially helped the definition and editing of the content of this document: Wim Henderickx Email: wim.henderickx@alcatel-lucent.com Igor Milojevic Email: milojevicigor@gmail.com Filsfils, et al. Expires September 19, 2016 [Page 11] Internet-Draft Segment Routing with MPLS March 2016 Saku Ytti Email: saku@ytti.fi 11. Acknowledgements The authors would like to thank Les Ginsberg and Shah Himanshu for their comments on this document. 12. References 12.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, December 1998, . [RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label Switching Architecture", RFC 3031, DOI 10.17487/RFC3031, January 2001, . [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001, . 12.2. Informative 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-06 (work in progress), December 2015. Filsfils, et al. Expires September 19, 2016 [Page 12] Internet-Draft Segment Routing with MPLS March 2016 [I-D.ietf-ospf-ospfv3-segment-routing-extensions] Psenak, P., Previdi, S., Filsfils, C., Gredler, H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPFv3 Extensions for Segment Routing", draft-ietf-ospf-ospfv3- segment-routing-extensions-04 (work in progress), December 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-06 (work in progress), December 2015. [I-D.ietf-spring-problem-statement] Previdi, S., Filsfils, C., Decraene, B., Litkowski, S., Horneffer, M., and R. Shakir, "SPRING Problem Statement and Requirements", draft-ietf-spring-problem-statement-07 (work in progress), March 2016. [I-D.ietf-spring-segment-routing] Filsfils, C., Previdi, S., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing Architecture", draft-ietf- spring-segment-routing-07 (work in progress), December 2015. [RFC1940] Estrin, D., Li, T., Rekhter, Y., Varadhan, K., and D. Zappala, "Source Demand Routing: Packet Format and Forwarding Specification (Version 1)", RFC 1940, DOI 10.17487/RFC1940, May 1996, . [RFC5443] Jork, M., Atlas, A., and L. Fang, "LDP IGP Synchronization", RFC 5443, DOI 10.17487/RFC5443, March 2009, . [RFC6138] Kini, S., Ed. and W. Lu, Ed., "LDP IGP Synchronization for Broadcast Networks", RFC 6138, DOI 10.17487/RFC6138, February 2011, . Authors' Addresses Clarence Filsfils (editor) Cisco Systems, Inc. Brussels BE Email: cfilsfil@cisco.com Filsfils, et al. Expires September 19, 2016 [Page 13] Internet-Draft Segment Routing with MPLS March 2016 Stefano Previdi (editor) Cisco Systems, Inc. Via Del Serafico, 200 Rome 00142 Italy Email: sprevidi@cisco.com Ahmed Bashandy Cisco Systems, Inc. 170, West Tasman Drive San Jose, CA 95134 US Email: bashandy@cisco.com Bruno Decraene Orange FR Email: bruno.decraene@orange.com Stephane Litkowski Orange FR Email: stephane.litkowski@orange.com Martin Horneffer Deutsche Telekom Hammer Str. 216-226 Muenster 48153 DE Email: Martin.Horneffer@telekom.de Rob Shakir Jive Communications, Inc. 1275 West 1600 North, Suite 100 Orem, UT 84057 Email: rjs@rob.sh Filsfils, et al. Expires September 19, 2016 [Page 14] Internet-Draft Segment Routing with MPLS March 2016 Jeff Tantsura Ericsson 300 Holger Way San Jose, CA 95134 US Email: Jeff.Tantsura@ericsson.com Edward Crabbe Individual Email: edward.crabbe@gmail.com Filsfils, et al. Expires September 19, 2016 [Page 15]