idnits 2.17.1 draft-ietf-spring-resiliency-use-cases-02.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** The document seems to lack a Security Considerations section. ** The document seems to lack an IANA Considerations section. (See Section 2.2 of https://www.ietf.org/id-info/checklist for how to handle the case when there are no actions for IANA.) ** The document seems to lack separate sections for Informative/Normative References. All references will be assumed normative when checking for downward references. ** The document seems to lack a both a reference to RFC 2119 and the recommended RFC 2119 boilerplate, even if it appears to use RFC 2119 keywords. RFC 2119 keyword, line 132: '... paths T1 and T2 MUST NOT benefit from...' RFC 2119 keyword, line 258: '... architecture SHOULD allow for the c...' Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (December 4, 2015) is 3064 days in the past. Is this intentional? -- Found something which looks like a code comment -- if you have code sections in the document, please surround them with '' and '' lines. Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-15) exists of draft-ietf-spring-segment-routing-06 Summary: 4 errors (**), 0 flaws (~~), 2 warnings (==), 2 comments (--).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 Clarence Filsfils 4 Intended status: Informational Cisco Systems, Inc. 5 Expires: June 6, 2016 Bruno Decraene 6 Orange 7 Rob Shakir 8 Jive Communications, Inc. 9 December 4, 2015 11 Use-cases for Resiliency in SPRING 12 draft-ietf-spring-resiliency-use-cases-02 14 Abstract 16 This document describes the use cases for resiliency in SPRING 17 networks. 19 Status of this Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at http://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on June 6, 2016. 36 Copyright Notice 38 Copyright (c) 2015 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (http://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 2. Path protection . . . . . . . . . . . . . . . . . . . . . . . . 4 55 3. Management free local protection . . . . . . . . . . . . . . . 4 56 3.1. Management free bypass protection . . . . . . . . . . . . . 5 57 3.2. Management-free shortest path based protection . . . . . . 5 58 4. Managed local protection . . . . . . . . . . . . . . . . . . . 6 59 4.1. Managed bypass protection . . . . . . . . . . . . . . . . . 6 60 4.2. Managed shortest path protection . . . . . . . . . . . . . 6 61 5. Co-existence . . . . . . . . . . . . . . . . . . . . . . . . . 7 62 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 63 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 65 1. Introduction 67 SPRING aims at providing a network architecture supporting services 68 with tight SLA guarantees [1]. This document reviews various use 69 cases for the protection of services in a SPRING network. Note that 70 these use cases are in particular applicable to existing LDP based 71 and pure IP networks. 73 Three key alternatives are described: path protection, local 74 protection without operator management and local protection with 75 operator management. 77 Path protection lets the ingress node be in charge of the failure 78 recovery, as discussed in Section 2. 80 The rest of the document focuses on approaches where protection is 81 performed by the node adjacent to the failed component, commonly 82 referred to as local protection techniques or Fast Reroute 83 techniques. 85 We discuss two different approaches to provide unmanaged local 86 protection, namely link/node bypass protection and shortest path 87 based protection, in Section 3. 89 A case is then made to allow the operator to manage the local 90 protection behavior in order to accommodate specific policies, in 91 Section 4. 93 The purpose of this document is to illustrate the different 94 approaches and explain how an operator could combine them in the same 95 network (see Section 5). Solutions are not defined in this document. 97 B------C------D------E 98 /| | \ / | \ / |\ 99 / | | \/ | \/ | \ 100 A | | /\ | /\ | Z 101 \ | | / \ | / \ | / 102 \| |/ \|/ \|/ 103 F------G------H------I 105 Figure 1: Reference topology 107 We use Figure 1 as a reference topology throughout the document. All 108 link metrics are equal to 1, with the exception of the links from/to 109 A and Z, which are configured with a metric of 100. 111 2. Path protection 113 A first protection strategy consists in excluding any local repair 114 but instead use end-to-end path protection. 116 For example, a Pseudo Wire (PW) from A to Z can be "path protected" 117 in the direction A to Z in the following manner: the operator 118 configures two SPRING paths T1 and T2 from A to Z. The two paths are 119 installed in the forwarding plane of A and hence are ready to forward 120 packets. The two paths are made disjoint using the SPRING 121 architecture. 123 T1 is established over path {AB, BC, CD, DE, EZ} and T2 over path 124 {AF, FG, GH, HI, IZ}. When T1 is up, the packets of the PW are sent 125 on T1. When T1 fails, the packets of the PW are sent on T2. When T1 126 comes back up, the operator either allows for an automated reversion 127 of the traffic onto T1 or selects an operator-driven reversion. The 128 solution to detect the end-to-end liveness of the path is out of the 129 scope of this document. 131 From a SPRING viewpoint, we would like to highlight the following 132 requirement: the two configured paths T1 and T2 MUST NOT benefit from 133 local protection. 135 3. Management free local protection 137 This section describes two alternatives to provide local protection 138 without requiring operator management, namely bypass protection and 139 shortest-path based protection. 141 For example, a demand from A to Z, transported over the shortest 142 paths provided by the SPRING architecture, benefits from management- 143 free local protection by having each node along the path 144 automatically pre-compute and pre-install a backup path for the 145 destination Z. Upon local detection of the failure, the traffic is 146 repaired over the backup path in sub-50msec. 148 The backup path computation should support the following 149 requirements: 151 o 100% link, node, and SRLG protection in any topology 152 o Automated computation by the IGP 153 o Selection of the backup path such as to minimize the chance for 154 transient congestion and/or delay during the protection period, as 155 reflected by the IGP metric configuration in the network. 157 3.1. Management free bypass protection 159 One way to provide local repair is to enforce a failover along the 160 shortest path around the failed component, ending at the protected 161 nexthop, so as to bypass the failed component and re-join the pre- 162 convergence path at the nexthop. In the case of node protection, 163 such bypass ends at the next-nexthop. 165 In our example, C protects Z, that it initially reaches via CD, by 166 enforcing the traffic over the bypass {CH, HD}. The resulting end- 167 to-end path between A and Z, upon recovery against the failure of 168 C-D, is depicted in Figure 2. 170 B * * *C------D * * *E 171 *| | * / * * / |* 172 * | | */ * */ | * 173 A | | /* * /* | Z 174 \ | | / * * / * | * 175 \| |/ **/ *|* 176 F------G------H------I 178 Figure 2: Bypass protection around link C-D 180 3.2. Management-free shortest path based protection 182 An alternative protection strategy consists in management-free local 183 protection, aiming at providing a repair for the destination based on 184 shortest path state for that destination. 186 In our example, C protects Z, that it initially reaches via CD, by 187 enforcing the traffic over its shortest path to Z, considering the 188 failure of the protected component. The resulting end-to-end path 189 between A and Z, upon recovery against the failure of C-D, is 190 depicted in Figure 3. 192 B * * *C------D------E 193 *| | * / | \ * |* 194 * | | */ | \* | * 195 A | | /* | *\ | Z 196 \ | | / * | * \ | * 197 \| |/ *|* \|* 198 F------G------H * * *I 200 Figure 3: Reference topology 202 4. Managed local protection 204 There may be cases where a management free repair does not fit the 205 policy of the operator. For example, in our illustration, the 206 operator may want to not have C-D and C-H used to protect each other, 207 in fear of a shared risk among the two links. 209 In this context, the protection mechanism must support the explicit 210 configuration of the backup path either under the form of high-level 211 constraints (end at the next-hop, end at the next-next-hop, minimize 212 this metric, avoid this SRLG...) or under the form of an explicit 213 path. 215 We discuss such aspects for both bypass and shortest path based 216 protection schemes. 218 4.1. Managed bypass protection 220 Let us illustrate the case using our reference example. For the 221 demand from A to B, the operator does not want to use the shortest 222 failover path to the nexthop, {CH, HD}, but rather the path 223 {CG,GH,HD}, as illustrated in Figure 4. 225 B * * *C------D * * *E 226 *| * \ / * * / |* 227 * | * \/ * */ | * 228 A | * /\ * /* | Z 229 \ | * / \ * / * | * 230 \| */ \*/ *|* 231 F------G * * *H------I 233 Figure 4: Managed bypass protection 235 4.2. Managed shortest path protection 237 In the case of shortest path protection, the case is the one of an 238 operator who does not want to use the shortest failover via link C-H, 239 but rather reach H via {CG, GH}. 241 The resulting end-to-end path upon activation of the protection is 242 illustrated in Figure 5. 244 B * * *C------D------E 245 *| * \ / | \ * |* 246 * | * \/ | \* | * 247 A | * /\ | *\ | Z 248 \ | * / \ | * \ | * 249 \| */ \|* \|* 250 F------G * * *H * * *I 252 Figure 5: Managed shortest path protection 254 5. Co-existence 256 The operator may want to support several very-different services on 257 the same packet-switching infrastructure. As a result, the SPRING 258 architecture SHOULD allow for the co-existence of the different use 259 cases listed in this document, in the same network. 261 Let us illustrate this with the following example. 263 o Flow F1 is supported over path {C, C-D, E} 264 o Flow F2 is supported over path {C, C-D, I) 265 o Flow F3 is supported over path {C, C-D, Z) 266 o Flow F4 is supported over path {C, C-D, Z} 267 o It should be possible for the operator to configure the network to 268 achieve path protection for F1, management free shortest path 269 local protection for F2, managed protection over path {C-G, G-H, 270 Z} for F3, and management free bypass protection for F4. 272 6. References 274 [1] Filsfils, C., Previdi, S., Decraene, B., Litkowski, S., and r. 275 rjs@rob.sh, "Segment Routing Architecture", 276 draft-ietf-spring-segment-routing-06 (work in progress), 277 October 2015. 279 Authors' Addresses 281 Pierre Francois 282 Cisco Systems, Inc. 283 Vimercate 284 IT 286 Email: pifranco@cisco.com 287 Clarence Filsfils 288 Cisco Systems, Inc. 289 Brussels 290 BE 292 Email: cfilsfil@cisco.com 294 Bruno Decraene 295 Orange 296 Issy-les-Moulineaux 297 FR 299 Email: bruno.decraene@orange.com 301 Rob Shakir 302 Jive Communications, Inc. 303 Orem 304 US 306 Email: rjs@rob.sh