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Summary: 4 errors (**), 0 flaws (~~), 1 warning (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group Pierre Francois 3 Internet-Draft IMDEA Networks Institute 4 Intended status: Informational Clarence Filsfils 5 Expires: November 13, 2014 Cisco Systems, Inc. 6 Bruno Decraene 7 Orange 8 Rob Shakir 9 BT 10 May 12, 2014 12 Use-cases for Resiliency in SPRING 13 draft-ietf-spring-resiliency-use-cases-00 15 Abstract 17 This document describes the use cases for resiliency in SPRING 18 networks. 20 Status of this Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at http://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on November 13, 2014. 37 Copyright Notice 39 Copyright (c) 2014 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (http://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 55 2. Path protection . . . . . . . . . . . . . . . . . . . . . . . . 4 56 3. Management free local protection . . . . . . . . . . . . . . . 4 57 3.1. Management free bypass protection . . . . . . . . . . . . . 5 58 3.2. Management-free shortest path based protection . . . . . . 5 59 4. Managed local protection . . . . . . . . . . . . . . . . . . . 6 60 4.1. Managed bypass protection . . . . . . . . . . . . . . . . . 6 61 4.2. Managed shortest path protection . . . . . . . . . . . . . 6 62 5. Co-existence . . . . . . . . . . . . . . . . . . . . . . . . . 7 63 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 64 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 66 1. Introduction 68 SPRING aims at providing a network architecture supporting services 69 with tight SLA guarantees [1]. This document reviews various use 70 cases for the protection of services in a SPRING network. Note that 71 these use cases are in particular applicable to existing LDP based 72 and pure IP networks. 74 Three key alternatives are described: path protection, local 75 protection without operator management and local protection with 76 operator management. 78 Path protection lets the ingress node be in charge of the failure 79 recovery, as discussed in Section 2. 81 The rest of the document focuses on approaches where protection is 82 performed by the node adjacent to the failed component, commonly 83 referred to as local protection techniques or Fast Reroute 84 techniques. 86 We discuss two different approaches to provide unmanaged local 87 protection, namely link/node bypass protection and shortest path 88 based protection, in Section 3. 90 A case is then made to allow the operator to manage the local 91 protection behavior in order to accommodate specific policies, in 92 Section 4. 94 The purpose of this document is to illustrate the different 95 approaches and explain how an operator could combine them in the same 96 network (see Section 5). Solutions are not defined in this document. 98 B------C------D------E 99 /| | \ / | \ / |\ 100 / | | \/ | \/ | \ 101 A | | /\ | /\ | Z 102 \ | | / \ | / \ | / 103 \| |/ \|/ \|/ 104 F------G------H------I 106 Figure 1: Reference topology 108 We use Figure 1 as a reference topology throughout the document. All 109 link metrics are equal to 1, with the exception of the links from/to 110 A and Z, which are configured with a metric of 100. 112 2. Path protection 114 A first protection strategy consists in excluding any local repair 115 but instead use end-to-end path protection. 117 For example, a Pseudo Wire (PW) from A to Z can be "path protected" 118 in the direction A to Z in the following manner: the operator 119 configures two SPRING paths T1 and T2 from A to Z. The two paths are 120 installed in the forwarding plane of A and hence are ready to forward 121 packets. The two paths are made disjoint using the SPRING 122 architecture. 124 T1 is established over path {AB, BC, CD, DE, EZ} and T2 over path 125 {AF, FG, GH, HI, IZ}. When T1 is up, the packets of the PW are sent 126 on T1. When T1 fails, the packets of the PW are sent on T2. When T1 127 comes back up, the operator either allows for an automated reversion 128 of the traffic onto T1 or selects an operator-driven reversion. The 129 solution to detect the end-to-end liveness of the path is out of the 130 scope of this document. 132 From a SPRING viewpoint, we would like to highlight the following 133 requirement: the two configured paths T1 and T2 MUST NOT benefit from 134 local protection. 136 3. Management free local protection 138 This section describes two alternatives to provide local protection 139 without requiring operator management, namely bypass protection and 140 shortest-path based protection. 142 For example, a demand from A to Z, transported over the shortest 143 paths provided by the SPRING architecture, benefits from management- 144 free local protection by having each node along the path 145 automatically pre-compute and pre-install a backup path for the 146 destination Z. Upon local detection of the failure, the traffic is 147 repaired over the backup path in sub-50msec. 149 The backup path computation should support the following 150 requirements: 152 o 100% link, node, and SRLG protection in any topology 153 o Automated computation by the IGP 154 o Selection of the backup path such as to minimize the chance for 155 transient congestion and/or delay during the protection period, as 156 reflected by the IGP metric configuration in the network. 158 3.1. Management free bypass protection 160 One way to provide local repair is to enforce a failover along the 161 shortest path around the failed component, ending at the protected 162 nexthop, so as to bypass the failed component and re-join the pre- 163 convergence path at the nexthop. In the case of node protection, 164 such bypass ends at the next-nexthop. 166 In our example, C protects Z, that it initially reaches via CD, by 167 enforcing the traffic over the bypass {CH, HD}. The resulting end- 168 to-end path between A and Z, upon recovery against the failure of 169 C-D, is depicted in Figure 2. 171 B * * *C------D * * *E 172 *| | * / * * / |* 173 * | | */ * */ | * 174 A | | /* * /* | Z 175 \ | | / * * / * | * 176 \| |/ **/ *|* 177 F------G------H------I 179 Figure 2: Bypass protection around link C-D 181 3.2. Management-free shortest path based protection 183 An alternative protection strategy consists in management-free local 184 protection, aiming at providing a repair for the destination based on 185 shortest path state for that destination. 187 In our example, C protects Z, that it initially reaches via CD, by 188 enforcing the traffic over its shortest path to Z, considering the 189 failure of the protected component. The resulting end-to-end path 190 between A and Z, upon recovery against the failure of C-D, is 191 depicted in Figure 3. 193 B * * *C------D------E 194 *| | * / | \ * |* 195 * | | */ | \* | * 196 A | | /* | *\ | Z 197 \ | | / * | * \ | * 198 \| |/ *|* \|* 199 F------G------H * * *I 201 Figure 3: Reference topology 203 4. Managed local protection 205 There may be cases where a management free repair does not fit the 206 policy of the operator. For example, in our illustration, the 207 operator may want to not have C-D and C-H used to protect each other, 208 in fear of a shared risk among the two links. 210 In this context, the protection mechanism must support the explicit 211 configuration of the backup path either under the form of high-level 212 constraints (end at the next-hop, end at the next-next-hop, minimize 213 this metric, avoid this SRLG...) or under the form of an explicit 214 path. 216 We discuss such aspects for both bypass and shortest path based 217 protection schemes. 219 4.1. Managed bypass protection 221 Let us illustrate the case using our reference example. For the 222 demand from A to B, the operator does not want to use the shortest 223 failover path to the nexthop, {CH, HD}, but rather the path 224 {CG,GH,HD}, as illustrated in Figure 4. 226 B * * *C------D * * *E 227 *| * \ / * * / |* 228 * | * \/ * */ | * 229 A | * /\ * /* | Z 230 \ | * / \ * / * | * 231 \| */ \*/ *|* 232 F------G * * *H------I 234 Figure 4: Managed bypass protection 236 4.2. Managed shortest path protection 238 In the case of shortest path protection, the case is the one of an 239 operator who does not want to use the shortest failover via link C-H, 240 but rather reach H via {CG, GH}. 242 The resulting end-to-end path upon activation of the protection is 243 illustrated in Figure 5. 245 B * * *C------D------E 246 *| * \ / | \ * |* 247 * | * \/ | \* | * 248 A | * /\ | *\ | Z 249 \ | * / \ | * \ | * 250 \| */ \|* \|* 251 F------G * * *H * * *I 253 Figure 5: Managed shortest path protection 255 5. Co-existence 257 The operator may want to support several very-different services on 258 the same packet-switching infrastructure. As a result, the SPRING 259 architecture SHOULD allow for the co-existence of the different use 260 cases listed in this document, in the same network. 262 Let us illustrate this with the following example. 264 o Flow F1 is supported over path {C, C-D, E} 265 o Flow F2 is supported over path {C, C-D, I) 266 o Flow F3 is supported over path {C, C-D, Z) 267 o Flow F4 is supported over path {C, C-D, Z} 268 o It should be possible for the operator to configure the network to 269 achieve path protection for F1, management free shortest path 270 local protection for F2, managed protection over path {C-G, G-H, 271 Z} for F3, and management free bypass protection for F4. 273 6. References 275 [1] Filsfils, C., Previdi, S., Bashandy, A., Decraene, B., 276 Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R., Ytti, 277 S., Henderickx, W., Tantsura, J., and E. Crabbe, "Segment 278 Routing Architecture", draft-filsfils-rtgwg-segment-routing-01 279 (work in progress), October 2013. 281 Authors' Addresses 283 Pierre Francois 284 IMDEA Networks Institute 285 Leganes 286 ES 288 Email: pierre.francois@imdea.org 289 Clarence Filsfils 290 Cisco Systems, Inc. 291 Brussels 292 BE 294 Email: cfilsfil@cisco.com 296 Bruno Decraene 297 Orange 298 Issy-les-Moulineaux 299 FR 301 Email: bruno.decraene@orange.com 303 Rob Shakir 304 BT 305 London 306 UK 308 Email: rob.shakir@bt.com