Network Working Group Anil Kumar S N INTERNET-DRAFT Gaurav Agrawal Intended Status: Standard Track Vinod Kumar S Expires: April 11, 2016 Huawei Technologies India October 9, 2015 Maximally Redundant Trees in Segment Routing draft-agv-rtgwg-spring-segment-routing-mrt-01 Abstract This document presents a Fast Reroute (FRR) approach aimed at providing link and node protection of node and adjacency segments within the Segment Routing (SR) framework. This FRR behavior builds on Maximally Redundant Trees (MRT) FRR algorithm [I-D.atlas-rtgwg- mrt-mc-arch]. Fast-Reroute with Maximally Redundant Trees (MRT-FRR) using Segment routing is a technology that gives link-protection and node- protection with 100% coverage in any network topology that is still connected after the failure. MRT is computational efficient. For any router in the network, the MRT computation is less than the LFA computation for a node with three or more neighbors in SR domain (Ex: Topology Independent Fast Reroute). Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html AGV Expires April 11, 2016 [Page 1] INTERNET DRAFT MRT in Segment Routing October 9, 2015 Copyright and License 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 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 1.1 Standard Terminology . . . . . . . . . . . . . . . . . . . . 3 2. Draft Specific Terminology . . . . . . . . . . . . . . . . . . 3 3. Overview of SR Signaling for MRT . . . . . . . . . . . . . . . 5 4. Protecting segments . . . . . . . . . . . . . . . . . . . . . . 5 4.1. The top segment is a node segment . . . . . . . . . . . . . 5 4.1. The top segment is an adjacency segment . . . . . . . . . . 5 5. Requirements for SR MRT implementation . . . . . . . . . . . . 6 3 Security Considerations . . . . . . . . . . . . . . . . . . . . 6 4 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 5 References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5.1 Normative References . . . . . . . . . . . . . . . . . . . 7 5.2. Informative References . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8 AGV Expires April 11, 2016 [Page 2] INTERNET DRAFT MRT in Segment Routing October 9, 2015 1 Introduction SR MRT FRR is one among the local repair mechanisms for Segment routing network. Another well known local repair mechanism for SR is Topology Independent Fast Reroute which is also capable of restoring end-to-end connectivity in case of a failure of a link or a node, with guaranteed coverage properties. MRT also provides 100% network failure coverage. The advantage of MRT over TI-LFA would be the computation complexities involved in MRT is much lesser then TI-LFA. MRT is best suited for access/aggregate ring network or low end devices which has low computing capacity. 1.1 Standard Terminology 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]. 2. Draft Specific Terminology For ease of reading, some of the terminology defined in [I-D.ietf- rtgwg-mrt-frr-architecture] is repeated here. Redundant Trees (RT): A pair of trees where the path from any node X to the root R along the first tree is node-disjoint with the path from the same node X to the root along the second tree. These can be computed in 2-connected graphs. Maximally Redundant Trees (MRT): A pair of trees where the path from any node X to the root R along the first tree and the path from the same node X to the root along the second tree share the minimum number of nodes and the minimum number of links. Each such shared node is a cut-vertex. Any shared links are cut-links. Any RT is an MRT but many MRTs are not RTs. The two MRTs are referred to as MRT- Blue and MRT-Red. MRT-Red: MRT-Red is used to describe one of the two MRTs; it is used to described the associated forwarding topology and MT-ID. Specifically, MRT-Red is the decreasing MRT where links in the GADAG are taken in the direction from a higher topologically ordered node to a lower one. MRT-Blue: MRT-Blue is used to describe one of the two MRTs; it is used to described the associated forwarding topology and MT-ID. Specifically, MRT-Blue is the increasing MRT where links in the GADAG are taken in the direction from a lower topologically ordered node to a higher one. AGV Expires April 11, 2016 [Page 3] INTERNET DRAFT MRT in Segment Routing October 9, 2015 Rainbow MRT MT-ID: It is useful to have an MT-ID that refers to the multiple MRT topologies and to the default topology. This is referred to as the Rainbow MRT MT-ID and is used by LDP to reduce signaling and permit the same label to always be advertised to all peers for the same (MT-ID, Prefix). MRT Island: From the computing router, the set of routers that support a particular MRT profile and are connected via MRT- eligible links. Island Border Router (IBR): A router in the MRT Island that is connected to a router not in the MRT Island and both routers are in a common area or level. Island Neighbor (IN): A router that is not in the MRT Island but is adjacent to an IBR and in the same area/level as the IBR.. AGV Expires April 11, 2016 [Page 4] INTERNET DRAFT MRT in Segment Routing October 9, 2015 3. Overview of SR Signaling for MRT To extend MRT support to Segment routing following requirement need to be achieved : 1. SR MRT Capabilities must be advertised using IGP extension for SR MRT. Also SR MRT capabilities must be in sync with IGP specific MRT capabilities advertisement. If the peer has not advertised the SR MRT capability, then it indicates that LSR does not support MRT procedures. 2. As specified in MRT Architecture draft-ietf-rtgwg-mrt-frr- architecture, both Option 1A and Option 1B can be used for the implementation of SR MRT. For Option 1A, two additional Prefix SID's/Label for RED and BLUE MT must be advertised in addition to default prefix SID/Label. The IGP extension carrying prefix SID for RED and BLUE MT must have corresponding MT-ID allocated by IANA for default MRT profile. For Option 1B, Global Unique Context SID/Label for Red & Blue as topology identifier must be used. 4. Protecting segments In this section, we explain how a protecting router processes the label stack of a packet upon the failure of its interface. The behavior depends on the type of top segment in SR label stack to be protected. Its assumed the MRT algorithm is run prior to interface failure and alternate is selected as per the algorithm. The alternate segment could be MRT-RED label or MRT Blue label of Next/Next-to-Next Hop depending on the scenario. 4.1. The top segment is a node segment The current SR Label Stack is kept intact. The alternate segment is pushed at the top of SR label stack and continue forwarding the packet as per updated label stack. 4.1. The top segment is an adjacency segment The top adjacency label in the SR label stack representing the failed interface is popped & the alternate segment is pushed at the top of SR Label stack and contineu forwarding the packet as per updated label stack. AGV Expires April 11, 2016 [Page 5] INTERNET DRAFT MRT in Segment Routing October 9, 2015 5. Requirements for SR MRT implementation REQ1 : IGP Extension to carry the Segment Routing Node MRT Capability in addition to exiting IGP extension carrying IGP MRT Capability REQ2 : IGP Extension to carry Red & Blue MRT SR Segments in addition to existing Default SR Segment 3 Security Considerations None of the security consideration are identified 4 IANA Considerations None of the IANA consideration are identified AGV Expires April 11, 2016 [Page 6] INTERNET DRAFT MRT in Segment Routing October 9, 2015 5 References 5.1 Normative References [I-D.ietf-rtgwg-mrt-frr-algorithm] Envedi, G., Csaszar, A., Atlas, A., Bowers, C., and A. Gopalan, "Algorithms for computing Maximally Redundant Trees for IP/LDP Fast- Reroute", draft-ietf-rtgwg-mrt-frr- algorithm-05 (work in progress), July 2015. [I-D.ietf-rtgwg-mrt-frr-architecture] Atlas, A., Kebler, R., Bowers, C., Envedi, G., Csaszar, A., Tantsura, J., and R. White, "An Architecture for IP/ LDP Fast-Reroute Using Maximally Redundant Trees", draft- ietf-rtgwg-mrt-frr-architecture-05 (work in progress), January 2015. [RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed., "LDP Specification", RFC 5036, DOI 10.17487/RFC5036, October 2007, . [RFC5561] Thomas, B., Raza, K., Aggarwal, S., Aggarwal, R., and JL. Le Roux, "LDP Capabilities", RFC 5561, DOI 10.17487/RFC5561, July 2009, . [RFC6420] Cai, Y. and H. Ou, "PIM Multi-Topology ID (MT-ID) Join Attribute", RFC 6420, DOI 10.17487/RFC6420, November 2011, . [RFC7307] Zhao, Q., Raza, K., Zhou, C., Fang, L., Li, L., and D. King, "LDP Extensions for Multi-Topology", RFC 7307, DOI 10.17487/RFC7307, July 2014, . AGV Expires April 11, 2016 [Page 7] INTERNET DRAFT MRT in Segment Routing October 9, 2015 5.2. Informative References [I-D.atlas-rtgwg-mrt-mc-arch] Atlas, A., Kebler, R., Wijnands, I., Csaszar, A., and G. Envedi, "An Architecture for Multicast Protection Using Maximally Redundant Trees", draft-atlas-rtgwg-mrt-mc- arch-02 (work in progress), July 2013. [I-D.ietf-isis-mrt] Li, Z., Wu, N., Zhao, Q., Atlas, A., Bowers, C., and J. Tantsura, "Intermediate System to Intermediate System (IS- IS) Extensions for Maximally Redundant Trees (MRT)", draft-ietf-isis-mrt-00 (work in progress), February 2015. [I-D.ietf-ospf-mrt] Atlas, A., Hegde, S., Bowers, C., Tantsura, J., and Z. Li, "OSPF Extensions to Support Maximally Redundant Trees", draft-ietf-ospf-mrt-00 (work in progress), January 2015. [I-D.wijnands-mpls-mldp-node-protection] Wijnands, I., Rosen, E., Raza, K., Tantsura, J., Atlas, A., and Q. Zhao, "mLDP Node Protection", draft-wijnands- mpls-mldp-node-protection-04 (work in progress), June 2013. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . Authors' Addresses Anil Kumar S N Huawei Technologies India Pvt. Ltd, Near EPIP Industrial Area, Kundalahalli Village, Whitefield, Bangalore - 560037 EMail: anil.sn@huawei.com Gaurav Agrawal AGV Expires April 11, 2016 [Page 8] INTERNET DRAFT MRT in Segment Routing October 9, 2015 Huawei Technologies India Pvt. Ltd, Near EPIP Industrial Area, Kundalahalli Village, Whitefield, Bangalore - 560037 EMail: gaurav.agrawal@huawei.com Vinod Kumar S Huawei Technologies India Pvt. Ltd, Near EPIP Industrial Area, Kundalahalli Village, Whitefield, Bangalore - 560037 EMail: vinods.kumar@huawei.com AGV Expires April 11, 2016 [Page 9]