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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network working group X. Xu 2 Internet Draft M. Chen 3 Category: Standard Track Huawei 5 Expires: January 2014 July 11, 2013 7 Advertising Global Labels Using IGP 9 draft-xu-rtgwg-global-label-adv-00 11 Abstract 13 Segment Routing (SR) [SR-ARCH] is a new MPLS paradigm in which each 14 SR-capable router is required to independently advertise global MPLS 15 labels for its attached prefixes using IGP [SR-ISIS-EXT][SR-OSPF-EXT]. 16 One major challenge associated with such label advertisement 17 mechanism is how to avoid a given global MPLS label from being 18 allocated by different routers to different prefixes. Although manual 19 allocation can address such label allocation collision problem, it is 20 error-prone and therefore may not be suitable for large SR network 21 environments. This document proposes an alternative approach for 22 advertising global labels without any risk of label allocation 23 collision. 25 Status of this Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at http://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on January 11, 2014. 42 Copyright Notice 44 Copyright (c) 2013 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (http://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Conventions used in this document 59 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 60 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 61 document are to be interpreted as described in RFC-2119 [RFC2119]. 63 Table of Contents 65 1. Introduction ................................................ 3 66 2. Terminology ................................................. 3 67 3. Advertising Label Bindings for Prefixes ..................... 3 68 3.1. Extension to ISIS ...................................... 3 69 3.2. Extension to OSPFv2 .................................... 4 70 3.3. Extension to OSPFv3 .................................... 6 71 4. Requesting Label Bindings for Prefixes ...................... 6 72 4.1. Extension to ISIS ...................................... 6 73 4.2. Extension to OSPFv2 .................................... 7 74 4.3. Extension to OSPFv3 .................................... 7 75 5. Mapping Server Redundancy and Election ...................... 7 76 5.1. Extension to ISIS ...................................... 8 77 5.2. Extension to OSPFv2 .................................... 8 78 5.3. Extension to OSPFv3 .................................... 8 79 6. Security Considerations ..................................... 9 80 7. IANA Considerations ......................................... 9 81 8. Acknowledgements ............................................ 9 82 9. References .................................................. 9 83 9.1. Normative References ................................... 9 84 9.2. Informative References ................................. 9 85 Authors' Addresses ............................................ 10 87 1. Introduction 89 Segment Routing (SR) [SR-ARCH] is a new MPLS paradigm in which each 90 SR-capable router is required to independently advertise global MPLS 91 labels for its attached prefixes using IGP [SR-ISIS-EXT][SR-OSPF-EXT]. 92 One major challenge associated with such label advertisement 93 mechanism is how to avoid a given global MPLS label from being 94 allocated by different routers to different prefixes. Although manual 95 allocation can address such label allocation collision problem, it is 96 error-prone therefore may not be suitable for large SR network 97 environments. 99 This document proposes an alternative approach for advertising global 100 labels without any risk of label allocation collision. The basic idea 101 of this approach is that a single mapping server would, on behalf of 102 all SR-capable routers within an IGP domain, allocate global labels 103 for prefixes attached to those SR-capable routers and then advertise 104 the label bindings in the IGP domain scope. Those prefixes which need 105 to be allocated with global labels can be manually configured on the 106 mapping servers or be advertised by the corresponding SR-capable 107 routers to which those prefixes are attached. In the multi-area/level 108 scenario where route summary between areas/levels is required, the IP 109 longest-match algorithm SHOULD be used by SR-capable routers when 110 processing label bindings advertised by the mapping server. 112 As for the scenario where the scope of label advertisement is set to 113 area/level-scoped, it will be discussed in a future version of this 114 document. 116 2. Terminology 118 This memo makes use of the terms defined in [RFC1195] [RFC2328] [SR- 119 ARCH]. 121 3. Advertising Label Bindings for Prefixes 123 3.1. Extension to ISIS 125 A mapping server could uses one or more of the following TLVs to 126 advertise global labels for those prefixes which need to be allocated 127 with global labels: 129 TLV-135 (IPv4) [RFC5305] 131 TLV-235 (MT-IPv4) [RFC5120] 132 TLV-236 (IPv6) [RFC5308] 134 TLV-237 (MT-IPv6) [RFC5120] 136 A Label Binding Sub-TLV (TBD) as shown below is associated with a 137 prefix which is contained in one of the above TLVs: 139 0 1 2 3 140 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 141 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 142 | Type=TBD | Length | 143 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 144 |P| Reserved | MPLS Label (20 bit) | 145 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 147 Type: TBD 149 Length: 4 151 P-Flag: if set, the penultimate hop router MUST perform PHP 152 action on the allocated MPLS label. For a given prefix, the P- 153 Flag in the Label Binding Sub-TLV MUST be set to the same value 154 as that of the P-Flag in the Label Request Sub-TLV if a label 155 request message (see section 4 of this document) for that prefix 156 is received by the mapping server. 158 MPLS Label: a global label for the prefix which is carried in the 159 TLV containing this sub-TLV. 161 Since the mapping server uses these TLVs for label binding 162 advertisement purpose other than building the normal IP routing table, 163 the Metric field MUST be set to a value larger than MAX_PATH_METRIC 164 (i.e., 0xFE000000). 166 3.2. Extension to OSPFv2 168 A new Opaque LSA [RFC5250] of type 11 (with domain-wide flooding 169 scope), referred to as Prefix Opaque LSA, is defined. The opaque type 170 of this Prefix Opaque LSA is TBD. A mapping server could use one or 171 more Prefix Opaque LSAs to advertise label bindings for those 172 prefixes which need to be allocated with global labels. 174 One or more Prefix TLV (type code=TBD) as shown below could be 175 contained in a Prefix Opaque LSA. 177 0 1 2 3 178 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 180 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 181 | Type=TBD | Length | 182 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 183 | MT-ID | Prefix-Len | Sub-TLV-Len | Reserved | 184 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 185 | IPv4 Prefix (0-4 octets) | 186 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 187 // Sub-TLVs (Variable) // 188 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 190 ? 191 | MT-ID | Prefix-Len | Sub-TLV-Len | Reserved | 192 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 193 | IPv4 Prefix (0-4 octets) | 194 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 195 // Sub-TLVs (Variable) // 196 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 198 Type: TBD. 200 Length: Variable. 202 MT-ID: Multi-Topology ID as defined in [RFC4915]. 204 Prefix-Len: the length of the prefix in bits (i.e., 0-32). 206 Sub-TLV-Len: the length of Sub-TLVs. 208 IPv4 Prefix: the prefix is encoded in the minimal number of 209 octets (i.e., 0-4) for the given number of significant bits. 211 A Label Binding Sub-TLV (type code=TBD) as shown below is associated 212 with a prefix which is contained in the Prefix TLV. 214 0 1 2 3 215 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 216 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 217 | Type=TBD | Length | 218 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 219 |P| Reserved | MPLS Label (20 bit) | 220 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 222 Type: TBD. 224 Length: 4. 226 P-Flag: if set, the penultimate hop router MUST perform PHP 227 action on the allocated MPLS label. For a given prefix, the P- 228 Flag in the Label Binding Sub-TLV MUST be set to the same value 229 as that of the P-Flag in the Label Request Sub-TLV if a label 230 request message (see section 4 of this document) for that prefix 231 is received by the mapping server. 233 MPLS Label: a global label which is allocated to the prefix which 234 is contained in the Prefix TLV. 236 3.3. Extension to OSPFv3 238 TBD. 240 4. Requesting Label Bindings for Prefixes 242 4.1. Extension to ISIS 244 When advertising IP reachability information by using one of the 245 Extended IP Reachability TLVs (i.e., TLV-135, TLV-235, TLV-236 and 246 TLV-237), SR-capable ISIS routers SHOULD mark those among their 247 attached prefixes which need to be allocated with a global label by 248 associating each of these prefixes with a Label Request sub-TLV (type 249 code=TBD) as shown below. 251 0 1 2 3 252 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 253 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 254 | Type=TBD | Length | 255 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 256 |P| Reserved | 257 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 259 Type: TBD 261 Length: 4 263 P-Flag: if set, the penultimate hop router MUST perform PHP 264 action on the required label. 266 In the multi-level scenario where route summary between levels is 267 required, separate Extended IP Reachability TLVs other than those for 268 IP reachability advertisement purpose SHOULD be used for label 269 binding advertisement purpose. Since these separate TLVs are not used 270 for the purpose of building the normal IP routing table, the Metric 271 field MUST be set to a value larger than MAX_PATH_METRIC (i.e., 272 0xFE000000). 274 4.2. Extension to OSPFv2 276 SR-capable OSPF routers could use one or more Prefix Opaque LSAs as 277 defined in section 3.2 of this document to advertise those among 278 their attached prefixes which need to be allocated with global labels. 280 A new Sub-TLV of the Prefix TLV, referred to as Label Request Sub-TLV 281 (type code=TBD) as shown below is associated with a prefix which is 282 contained in a Prefix TLV. 284 0 1 2 3 285 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 286 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 287 | Type=TBD | Length | 288 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 289 |P| Reserved | 290 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 292 Type: TBD 294 Length: 4 296 P-Flag: if set, the penultimate hop router MUST perform PHP 297 action. 299 4.3. Extension to OSPFv3 301 TBD. 303 5. Mapping Server Redundancy and Election 305 For redundancy purpose, more than one router could be configured as 306 candidates for mapping servers. Each candidate for mapping servers 307 SHOULD advertise its capability of being a mapping servers by using 308 IS-IS or OSPF Router Capability TLV. The one with the highest 309 priority SHOULD be elected as the primary mapping server which is 310 eligible to allocate and advertise global labels for prefixes on 311 behalf of SR-capable routers. The comparison of Router ID of ISIS or 312 OSPF routers breaks the tie between two or more candidates with the 313 same highest priority. Meanwhile, the one with the second highest 314 priority SHOULD be elected as a backup mapping server. This backup 315 mapping server is responsible for advertising the same label bindings 316 as those advertised by the primary mapping server. In this way, it's 317 possible to avoid unnecessary changes to the data plane (i.e., MPLS 318 forwarding table) of SR-capable routers in the event of mapping 319 server failover. 321 5.1. Extension to ISIS 323 Each candidate mapping server SHOULD advertise its capability of 324 being a mapping server and the corresponding priority for mapping 325 server election by attaching a Mapping Server Capability Sub-TLV 326 (type code=TBD) shown as below to an IS-IS Router Capability TLV 327 [RFC4971] with the S flag set (with domain-wide flooding scope). 329 0 1 2 3 330 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 331 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 332 | Type | Length | Priority | 333 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 335 Type: TBD 337 Length: 1 339 Priority: the priority for mapping server election. 341 5.2. Extension to OSPFv2 343 Each candidate mapping server SHOULD advertise its capability of 344 being mapping servers by using an OSPF Router Informational 345 Capabilities TLV [RFC4970] contained in an Opaque LSA of type 11 346 (with domain-wide flooding scope). One of the unreserved OSPF Router 347 Informational Capabilities Bits is reserved for this purpose. 348 Furthermore, a sub-TLV (type code=TBD) as shown below is used to 349 convey the priority value for mapping server election. 351 0 1 2 3 352 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 353 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 354 | Type | Length | 355 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 356 | Priority | 357 +-+-+-+-+-+-+-+-+ 359 Type: TBD 361 Length: 1 363 Priority: the priority for mapping server election. 365 5.3. Extension to OSPFv3 367 TBD. 369 6. Security Considerations 371 TBD. 373 7. IANA Considerations 375 TBD. 377 8. Acknowledgements 379 Thanks to. 381 9. References 383 9.1. Normative References 385 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 386 Requirement Levels", BCP 14, RFC 2119, March 1997. 388 9.2. Informative References 390 [SR-ARCH] Filsfils, C., Previdi, S., Bashandy, A., Decraene, B., 391 Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R., 392 Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe, 393 "Segment Routing Architecture", draft-filsfils-rtgwg- 394 segment-routing-00 (work in progress), June 2013. 396 [SR-ISIS-EXT] Previdi, S., Filsfils, C., and A. Bashandy, "IS-IS 397 Segment Routing Extensions", May 2013. 399 [SR-OSPF-EXT] Psenak, P. and S. Previdi, "OSPF Segment Routing 400 Extensions", May 2013. 402 [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and 403 dual environments", RFC 1195, December 1990. 405 [RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308, 406 October 2008. 408 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 409 Engineering", RFC 5305, October 2008. 411 [RFC4971] Vasseur, J-P., Ed., Shen, N., Ed., and R. Aggarwal, Ed., 412 "Intermediate System to Intermediate System (IS-IS) 413 Extensions for Advertising Router Information", RFC 4971, 414 July 2007. 416 [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi 417 Topology (MT) Routing in Intermediate System to 418 Intermediate Systems (IS-ISs)", RFC 5120, February 2008. 420 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998. 422 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, 423 "OSPF for IPv6", RFC 5340, July 2008. 425 [RFC5250] Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The 426 OSPF Opaque LSA Option", RFC 5250, July 2008. 428 [RFC4970] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 429 S. Shaffer, "Extensions to OSPF for Advertising Optional 430 Router Capabilities", RFC 4970, July 2007. 432 [RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. 433 Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", 434 RFC 4915, June 2007. 436 Authors' Addresses 438 Xiaohu Xu 439 Huawei Technologies, 440 Beijing, China 441 Phone: +86-10-60610041 442 Email: xuxiaohu@huawei.com 444 Mach(Guoyi) Chen 445 Huawei Technologies, 446 Beijing, China 447 Phone: +86-10-60610041 448 Email: mach.chen@huawei.com