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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group CY. Lee 3 Internet-Draft A. Farrel (Old Dog Consulting) 4 Expires: February 26, 2006 S. De Cnodder (Alcatel) 5 August 26, 2005 7 Exclude Routes - Extension to RSVP-TE 8 draft-ietf-ccamp-rsvp-te-exclude-route-05.txt 10 Status of this Memo 12 By submitting this Internet-Draft, each author represents that any 13 applicable patent or other IPR claims of which he or she is aware 14 have been or will be disclosed, and any of which he or she becomes 15 aware will be disclosed, in accordance with Section 6 of BCP 79. 17 Internet-Drafts are working documents of the Internet Engineering 18 Task Force (IETF), its areas, and its working groups. Note that 19 other groups may also distribute working documents as Internet- 20 Drafts. 22 Internet-Drafts are draft documents valid for a maximum of six months 23 and may be updated, replaced, or obsoleted by other documents at any 24 time. It is inappropriate to use Internet-Drafts as reference 25 material or to cite them other than as "work in progress." 27 The list of current Internet-Drafts can be accessed at 28 http://www.ietf.org/ietf/1id-abstracts.txt. 30 The list of Internet-Draft Shadow Directories can be accessed at 31 http://www.ietf.org/shadow.html. 33 This Internet-Draft will expire on February 26, 2006. 35 Copyright Notice 37 Copyright (C) The Internet Society (2005). 39 Abstract 41 The RSVP-TE specification, "RSVP-TE: Extensions to RSVP for LSP 42 Tunnels" (RFC 3209) and GMPLS extensions to RSVP-TE, "Generalized 43 Multi-Protocol Label Switching (GMPLS) Signaling Resource ReserVation 44 Protocol-Traffic Engineering (RSVP-TE) Extensions" (RFC 3473) allow 45 abstract nodes and resources to be explicitly included in a path 46 setup, but not to be explicitly excluded. 48 In some networks where precise explicit paths are not computed at the 49 head end it may be useful to specify and signal abstract nodes and 50 resources that are to be explicitly excluded from routes. These 51 exclusions may apply to the whole path, or to parts of a path between 52 two abstract nodes specified in an explicit path. How Shared Risk 53 Link Groups (SLRGs) can be excluded is also specified in this 54 document. 56 This document specifies ways to communicate route exclusions during 57 path setup using RSVP-TE. 59 Requirements notation 61 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 62 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 63 document are to be interpreted as described in [RFC2119]. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 68 1.1 Scope of Exclude Routes . . . . . . . . . . . . . . . . . 5 69 1.2 Relationship to MPLS TE MIB . . . . . . . . . . . . . . . 6 70 2. Shared Risk Link Groups . . . . . . . . . . . . . . . . . . . 6 71 2.1 SRLG ERO Subobject . . . . . . . . . . . . . . . . . . . . 6 72 3. Exclude Route List . . . . . . . . . . . . . . . . . . . . . . 7 73 3.1 Exclude Route Object (XRO) . . . . . . . . . . . . . . . . 7 74 3.1.1 IPv4 prefix Subobject . . . . . . . . . . . . . . . . 9 75 3.1.2 IPv6 Prefix Subobject . . . . . . . . . . . . . . . . 10 76 3.1.3 Unnumbered Interface ID Subobject . . . . . . . . . . 11 77 3.1.4 Autonomous System Number Subobject . . . . . . . . . . 12 78 3.1.5 SRLG Subobject . . . . . . . . . . . . . . . . . . . . 12 79 3.2 Processing Rules for the Exclude Route Object (XRO) . . . 12 80 4. Explicit Exclusion Route . . . . . . . . . . . . . . . . . . . 14 81 4.1 Explicit Exclusion Route Subobject (EXRS) . . . . . . . . 14 82 4.2 Processing Rules for the Explicit Exclusion Route 6 83 Subobject (EXRS) . . . . . . . . . . . . . . . . . . . . . 17 84 5. Processing of XRO together with EXRS . . . . . . . . . . . . . 16 85 6. Minimum compliance . . . . . . . . . . . . . . . . . . . . . . 17 86 7. Security Considerations . . . . . . . . . . . . . . . . . . . 17 87 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 88 8.1 New RSVP-TE Class Numbers . . . . . . . . . . . . . . . . 18 89 8.2 New ERO Subobject Type . . . . . . . . . . . . . . . . . . 18 90 8.3 New ERO and XRO Subobject Type . . . . . . . . . . . . . . 18 91 8.4 New Error Codes . . . . . . . . . . . . . . . . . . . . . 18 92 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18 93 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 94 10.1 Normative References . . . . . . . . . . . . . . . . . . . 19 95 10.2 Informational References . . . . . . . . . . . . . . . . . 19 96 11. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 20 97 Apendix A. Aplications . . . . . . . . . . . . . . . . . . . . . . 21 99 1. Introduction 101 The RSVP-TE specification [RFC3209] and GMPLS extensions [RFC3473] 102 allow abstract nodes and resources to be explicitly included in a 103 path setup, using the Explicit Route Object (ERO). 105 In some systems it may be useful to specify and signal abstract nodes 106 and resources that are to be explicitly excluded from routes. This 107 may be because loose hops or abstract nodes need to be prevented from 108 selecting a route through a specific resource. This is a special 109 case of distributed path calculation in the network. 111 Two types of exclusions are required: 113 1. Exclusion of certain abstract nodes or resources on the whole 114 path. This set of abstract nodes is referred to as the Exclude 115 Route list. 117 2. Exclusion of certain abstract nodes or resources between a 118 specific pair of abstract nodes present in an ERO. Such specific 119 exclusions are referred to as Explicit Exclusion Route. 121 To convey these constructs within the signaling protocol, a new RSVP 122 object and a new ERO subobject are introduced respectively. 124 - A new RSVP-TE object is introduced to convey the Exclude Route 125 list. This object is the Exclude Route Object (XRO). 127 - The second type of exclusion is achieved through a modification to 128 the existing ERO. A new ERO subobject type the Explicit Exclusion 129 Route Subobject (EXRS) is introduced to indicate an exclusion 130 between a pair of included abstract nodes. 132 The knowledge of SRLGs, as defined in [INTERAS-REQ], may be used to 133 compute diverse paths that can be used for protection. In systems 134 where it is useful to signal exclusions, it may be useful to signal 135 SRLGs to indicate groups of resources that should be excluded on the 136 whole path or between two abstract nodes specified in an explicit 137 path. 139 This document introduces an ERO subobject to indicate an SRLG to be 140 signaled in either of the two exclusion methods described above and 141 this document does not assume or preclude any other usage for this 142 subobject. This subobject might also be appropriate for use within 143 Explicit Routes or Record Routes, but this is outside the scope of 144 this document. 146 1.1 Scope of Exclude Routes 148 This document does not preclude a route exclusion from listing 149 arbitrary nodes or network elements to avoid. The intent is, 150 however, to indicate only the minimal number of subobjects to be 151 avoided. For instance it may be necessary to signal only the SRLGs 152 (or Shared Risk Groups) to avoid. 154 It is envisaged that most of the conventional inclusion subobjects 155 are specified in the signaled ERO only for the area where they are 156 pertinent. The number of subobjects to be avoided, specified in the 157 signaled XRO may be constant throughout the whole path setup, or the 158 subobjects to be avoided may be removed from the XRO as they become 159 irrelevant in the subsequent hops of the path setup. 161 For example, consider an LSP that traverses multiple computation 162 domains. A computation domain may be an area in the administrative 163 or IGP sense, or may be an arbitrary division of the network for 164 active management and path computational purposes. Let the primary 165 path be (Ingress, A1, A2, AB1, B1, B2, BC1, C1, C2, Egress) where: 167 - Xn denotes a node in domain X, and 169 - XYn denotes a node on the border of domain X and domain Y. 171 Note that Ingress is a node in domain A, and Egress is a node in 172 domain C. This is shown in Figure 1 where the domains correspond with 173 areas. 175 area A area B area C 176 <-------------------> <----------------> <------------------> 178 Ingress-----A1----A2----AB1----B1----B2----BC1----C1----C2----Egress 179 ^ \ / | \ / | \ / 180 | \ / | \ / | \ / 181 | A3----------A4--AB2--B3--------B4--BC2--C3----------C4 182 | ^ ^ 183 | | | 184 | | | 185 | | ERO: (C3-strict, C4-strict, 186 | | Egress-strict) 187 | | XRO: Not needed 188 | | 189 | ERO: (B3-strict, B4-strict, BC2-strict, Egress-loose) 190 | XRO: (BC1, C1, C2) 191 | 192 ERO: (A3-strict, A4-strict, AB2-strict, Egress-loose) 193 XRO: (AB1, B1, B2, BC1, C1, C2, Egress) 195 Figure 1 : Domains Corresponding to IGP Areas 197 Consider the establishment of a node-diverse protection path in the 198 example above. The protection path must avoid all nodes on the 199 primary path. The exclusions for area A are handled during 200 Constrained Shortest Path First (CSPF) computation at Ingress, so the 201 ERO and XRO signaled at Ingress could be (A3-strict, A4-strict, AB2- 202 strict, Egress-loose) and (AB1, B1, B2, BC1, C1, C2) respectively. 203 At AB2 the ERO and XRO could be (B3-strict, B4-strict, BC2-strict, 204 Egress-loose) and (BC1, C1, C2) respectively. At BC2 the ERO could 205 be (C3-strict, C4-strict, Egress-strict) and an XRO is not needed 206 from BC2 onwards. 208 In general, consideration SHOULD be given (as with explicit route) to 209 the size of signaled data and the impact on the signaling protocol. 211 1.2 Relationship to MPLS TE MIB 213 [RFC3812] defines managed objects for managing and modeling MPLS- 214 based traffic engineering. Included in [RFC3812] is a means to 215 configure explicit routes for use on specific LSPs. This 216 configuration allows the exclusion of certain resources. 218 In systems where the full explicit path is not computed at the 219 ingress (or at a path computation site for use at the ingress) it may 220 be necessary to signal those exclusions. This document offers a 221 means of doing this signaling. 223 2. Shared Risk Link Groups 225 The identifier of a SRLG is defined as a 32 bit quantity in [GMPLS- 226 RTG]. An SRLG ERO subobject is introduced such that it can be used 227 in the exclusion methods as described in the following sections. 228 This document does not assume or preclude any other usage for this 229 subobject. This subobject might also be appropriate for use within 230 Explicit Routes or Record Routes, but this is outside the scope of 231 this document. 233 2.1 SRLG ERO Subobject 235 The format of the ERO and its subobjects are defined in [RFC3209]. 236 The new SRLG subobject is defined by this document as follows. 238 0 1 2 3 239 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 1 241 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 242 |L| Type | Length | SRLG Id (4 bytes) | 243 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 244 | SRLG Id (continued) | Reserved | 245 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 247 L 249 The L bit is an attribute of the subobject. The L bit is set 250 if the subobject represents a loose hop in the explicit route. 251 If the bit is not set, the subobject represents a strict hop in 252 the explicit route. 254 For exclusions (as used by XRO and EXRS defined in this 255 document), the L bit SHOULD be set to zero and ignored. 257 Type 259 The type of the subobject [TBD by IANA]. 261 Length 263 The Length contains the total length of the subobject in bytes, 264 including the Type and Length fields. The Length is always 8. 266 SRLG Id 268 The 32 bit identifier of the SRLG. 270 Reserved 272 This field is reserved. It MUST be set to zero on transmission 273 and MUST be ignored on receipt. 275 3. Exclude Route List 277 The exclude route identifies a list of abstract nodes that should not 278 be traversed along the path of the LSP being established. It is 279 RECOMMENDED to limit size of the exlude route list to a value local 280 to the node originating the exclude route list. 282 3.1 Exclude Route Object (XRO) 284 Abstract nodes to be excluded from the path are specified via the 285 EXCLUDE_ROUTE object (XRO). The Exclude Route Class value is [TBD]. 287 Currently one C_Type is defined, Type 1 Exclude Route. The 288 EXCLUDE_ROUTE object has the following format: 290 Class = TBD by IANA, C_Type = 1 292 0 1 2 3 293 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 1 295 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 296 | | 297 // (Subobjects) // 298 | | 299 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 301 The contents of an EXCLUDE_ROUTE object are a series of variable- 302 length data items called subobjects. This specification adapts ERO 303 subojbects as defined in [RFC3209], [RFC3473], and [RFC3477] for 304 use in route exclusions. The SRLG ERO subobject as defined in 305 Section 2 of this document and its processing within ERO have not 306 been defined before. The SRLG ERO subobject is defined here for use 307 with route exclusions. 309 The following subobject types are supported. 311 Type Subobject 312 -------------+------------------------------- 313 1 IPv4 prefix 314 2 IPv6 prefix 315 4 Unnumbered Interface ID 317 32 Autonomous system number 318 TBD by IANA SRLG 320 The defined values for Type above are specified in [RFC3209] and in 321 this document. 323 The concept of loose or strict hops has no meaning in route 324 exclusion. The L bit, defined for ERO subobjects in [RFC3209], is 325 reused here to indicate that an abstract node MUST be avoided (value 326 0) or SHOULD be avoided (value 1). 328 Subobjects 1, 2, and 4 refer to an interface or a set of interfaces. 329 An Attribute octet is introduced in these subobjects to indicate the 330 attribute (e.g. interface, node, SRLG) associated with the interfaces 331 that should be excluded from the path. For instance, the attribute 332 node allows a whole node to be excluded from the path by specifying 333 an interface of that node in the XRO subobject, in contrast to the 334 attribute interface, which allows a specific interface (or multiple 335 interfaces) to be excluded from the path without excluding the whole 336 nodes. The attribute SRLG allows all SRLGs associated with an 337 interface to be excluded from the path. 339 3.1.1 IPv4 prefix Subobject 341 0 1 2 3 342 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 1 344 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 345 |L| Type | Length | IPv4 address (4 bytes) | 346 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 347 | IPv4 address (continued) | Prefix Length | Attribute | 348 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 350 L 352 0 indicates that the attribute specified MUST be excluded 354 1 indicates that the attribute specified SHOULD be avoided 356 Attribute 358 Interface attribute values 360 0 indicates that the interface or set of interfaces 361 associated with the IPv4 prefix should be excluded or avoided 362 node 364 Node attribute value 366 1 indicates that the node or set of nodes associated with 367 the IPv4 prefix should be excluded or avoided 369 SRLG attribute values 371 2 indicates that all the SRLGs associated with the IPv4 372 prefix should be excluded or avoided 374 The rest of the fields are as defined in [RFC3209]. 376 3.1.2 IPv6 Prefix Subobject 378 0 1 2 3 379 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 1 381 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 382 |L| Type | Length | IPv6 address (16 bytes) | 383 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 384 | IPv6 address (continued) | 385 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 386 | IPv6 address (continued) | 387 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 388 | IPv6 address (continued) | 389 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 390 | IPv6 address (continued) | Prefix Length | Attribute | 391 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 393 L 395 0 indicates that the attribute specified MUST be excluded 397 1 indicates that the attribute specified SHOULD be avoided 399 Attribute 401 Interface attribute value 403 0 indicates that the interface or set of interfaces associated 404 with the IPv6 prefix should be excluded or avoided 406 Node attribute value 408 1 indicates that the node or set of nodes associated with 409 the IPv6 prefix should be excluded or avoided 411 SRLG attribute value 413 2 indicates that all the SRLG associated with the IPv6 414 prefix should be excluded or avoided 416 The rest of the fields are as defined in [RFC3209]. 418 3.1.3 Unnumbered Interface ID Subobject 420 0 1 2 3 421 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 1 423 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 424 |L| Type | Length | Reserved | Attribute | 425 | | | |(must be zero) | | 426 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 427 | TE Router ID | 428 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 429 | Interface ID (32 bits) | 430 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 432 L 434 0 indicates that the attribute specified MUST be excluded 436 1 indicates that the attribute specified SHOULD be avoided 438 Attribute 440 Interface attribute value 442 0 indicates that the Interface ID specified should be 443 excluded or avoided 445 Node attribute value 447 1 indicates that the node with the Router ID should be 448 excluded or avoided (this can be achieved using IPv4/v6 449 subobject as well, but is included here because it may be 450 convenient to use information from subobjects of an RRO 451 as defined in [RFC3477], in specifying the exclusions). 453 SRLG attribute value 455 2 indicates that all the SRLGs associated with the 456 interface should be excluded or avoided 458 Reserved 460 This field is reserved. It MUST be set to zero on transmission 461 and MUST be ignored on receipt. 463 The rest of the fields are as defined in [RFC3477]. 465 3.1.4 Autonomous System Number Subobject 467 The meaning of the L bit is as follows: 469 0 indicates that the abstract node specified MUST be excluded 471 1 indicates that the abstract node specified SHOULD be avoided 473 The rest of the fields are as defined in [RFC3209]. There is no 474 Attribute octet defined. 476 3.1.5 SRLG Subobject 478 The meaning of the L bit is as follows: 480 0 indicates that the SRLG specified MUST be excluded 482 1 indicates that the SRLG specified SHOULD be avoided 484 The Attribute octet is not present. The rest of the fields are as 485 defined in the "SRLG ERO Subobject" section of this document. 487 3.2 Processing Rules for the Exclude Route Object (XRO) 489 The exclude route list is encoded as a series of subobjects con- 490 tained in an EXCLUDE_ROUTE object. Each subobject identifies an 491 abstract node in the exclude route list. 493 Each abstract node may be a precisely specified IP address belonging 494 to a node, or an IP address with prefix identifying interfaces of a 495 group of nodes, or an Autonomous System. 497 The Explicit Route and routing processing is unchanged from the 498 description in [RFC3209] with the following additions: 500 1. When a Path message is received at a node, the node MUST check 501 that it is not a member of any of the abstract nodes in the XRO 502 if it is present in the Path message. If the node is a member of 503 any of the abstract nodes in the XRO with the L-flag set to 504 "exclude", it SHOULD return a PathErr with the error code 505 "Routing Problem" and error value of "Local node in Exclude 506 Route". If there are SRLGs in the XRO, the node SHOULD check 507 that the resources the node uses are not part of any SRLG with 508 the L-flag set to "exclude" that is specified in the XRO. If it 509 is, it SHOULD return a PathErr with error code "Routing Problem" 510 and error value of "Local node in Exclude Route". 512 2. Each subobject MUST be consistent. If a subobject is not con- 513 sistent then the node SHOULDreturn a PathErr with error code 514 "Routing Problem" and error value "Inconsistent Subobject". An 515 example of an inconsistent subobject is an IPv4 Prefix subobject 516 containing the IP address of a node and the attribute field is 517 set to "interface" or "SRLG". 519 3. The subobjects in the ERO and XRO MUST NOT contradict each other. 520 If a Path message is received that contains contradicting ERO and 521 XRO subobjects, then: 523 - subobjects in the XRO with the L flag not set (zero) MUST take 524 precedence over the subobjects in the ERO - that is, a 525 mandatory exclusion expressed in the XRO MUST be honored and 526 an implementation MUST reject such a Path message. This means 527 that a PathErr with error code "Routing Problem" and error 528 value of "Route blocked by Exclude Route" is returned. 530 - subobjects in the XRO with the L flag set do not take 531 precedence over ERO subobjects - that is, an implementation 532 MAY choose to reject a Path message because of such a 533 contradiction, but MAY continue and set up the LSP (ignoring 534 the XRO subobjects contradicting the ERO subobjects). 536 4. When choosing a next hop or expanding an explicit route to 537 include additional subobjects, a node: 539 a. MUST NOT introduce an explicit node or an abstract node that 540 equals or is a member of any abstract node that is specified 541 in the Exclude Route Object with the L-flag set to "exclude". 542 The number of introduced explicit nodes or abstract nodes 543 with the L flag set to "avoid", which indicate that it is not 544 mandatory to be excluded but that it is less preferred, 545 SHOULD be minimised in the computed path. 547 b. MUST NOT introduce links, nodes or resources identified by 548 the SRLG Id specified in the SRLG subobjects(s). The number 549 of introduced SLRGs with the L flag set to "avoid" SHOULD be 550 minimised. 552 If these rules preclude further forwarding of the Path message, 553 the node SHOULD return a PathErr with the error code "Routing 554 Problem" and error value of "Route blocked by Exclude Route". 556 Note that the subobjects in the XRO is an unordered list of 557 subobjects. 559 The XRO Class-Num is of the form 11bbbbbb so that nodes which do not 560 support the XRO, forward it uninspected and do not apply the 561 extensions to ERO processing described above. This approach is 562 chosen to allow route exclusion to traverse parts of the network that 563 are not capable of parsing or handling the new function. Note that 564 Record Route may be used to allow computing nodes to observe 565 violations of route exclusion and attempt to re-route the LSP 566 accordingly. 568 If a node supports the XRO, but not a particular subobject or part of 569 that subobject, then that particular subobject is ignored. Examples 570 of a part of a subobject that can be supported are: (1) only prefix 571 32 of the IPv4 prefix subobject could be supported, or (2) a 572 particular subobject is supported but not the particular attribute 573 field. 575 When a node forwards a Path message, it can do the following three 576 operations related to XRO besides the processing rules mentioned 577 above: 579 1. If no XRO was present, an XRO may be included. 581 2. If an XRO was present, it may remove the XRO if it is sure that 582 the next nodes do not need this information anymore. An example 583 is where a node can expand the ERO to a full strict path towards 584 the destination. See Figure 1 where BC2 is removing the XRO from 585 the Path message. 587 3. If an XRO was present, the content of the XRO can be modified. 588 Subobjects can be added or removed. See Figure 1 for an example 589 where AB2 is stripping off some subobjects. 591 In any case, a node MUST NOT introduce any explicit or abstract node 592 in the XRO (irrespective of the value of the L flag) that it also has 593 introduced in the ERO. 595 4. Explicit Exclusion Route 597 The Explicit Exclusion Route defines abstract nodes or resources 598 (such as links, unnumbered interfaces or labels) that must not or 599 should not be used on the path between two inclusive abstract nodes 600 or resources in the explicit route. 602 4.1 Explicit Exclusion Route Subobject (EXRS) 604 A new ERO subobject type is defined. The Explicit Exclusion Route 605 Subobject (EXRS) has type [TBD by IANA]. Although the EXRS is an ERO 606 subobject and the XRO is reusing the ERO subobject, an EXRS MUST NOT 607 be present in an XRO. An EXRS is an ERO subobject, which contains 608 one or more subobjects in its own, called EXRS subobjects. 610 The format of the EXRS is as follows: 612 0 1 2 3 613 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 1 615 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 616 |L| Type | Length | Reserved | 617 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 618 | | 619 // one or more EXRS subobjects // 620 | | 621 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 623 L 625 It MUST be set to zero on transmission and MUST be ignored on 626 receipt. [Note: The L bit in an EXRS subobject is as defined 627 for the XRO subobjects] 629 Type 631 The type of the subobject, i.e. EXRS [TBD by IANA] 633 Reserved 635 This field is reserved. It MUST be set to zero on transmission 636 and MUST be ignored on receipt. 638 EXRS subobjects 640 An EXRS subobject indicates the abstract node or resource to be 641 excluded. The format of an EXRS subobject is exactly the same 642 as the format of a subobject in the XRO. An EXRS may include 643 all subobjects defined in this document for the XRO. 645 Thus, an EXRS for an IP hop may look as follows: 647 0 1 2 3 648 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 1 650 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 651 |L| Type | Length | Reserved | 652 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 653 |L| Type | Length | IPv4 address (4 bytes) | 654 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 655 | IPv4 address (continued) | Prefix Length | Attribute | 656 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 658 4.2 Processing Rules for the Explicit Exclusion Route Subobject (EXRS) 660 Each EXRS may carry multiple exclusions. The exclusion is encoded 661 exactly as for XRO subobjects and prefixed by an additional Type and 662 Length. 664 The scope of the exclusion is the step between the previous ERO 665 subobject that identifies an abstract node, and the subsequent ERO 666 subobject that identifies an abstract node. The processing rules of 667 the EXRS are the same as the processing rule of the XRO within this 668 scope. Multiple exclusions may be present between any pair of 669 abstract nodes. 671 Exclusions may indicate explicit nodes, abstract nodes or Autonomous 672 Systems that must not be traversed on the path to the next abstract 673 node indicated in the ERO. 675 Exclusions may also indicate resources (such as unnumbered 676 interfaces, link ids, labels) that must not be used on the path to 677 the next abstract node indicated in the ERO. 679 SRLGs may also be indicated for exclusion from the path to the next 680 abstract node in the ERO by the inclusion of an EXRS containing an 681 SRLG subobject. If the L-bit in the SRLG subobject is zero, the 682 resources (nodes, links, etc.) identified by the SRLG MUST NOT be 683 used on the path to the next abstract node indicated in the ERO. If 684 the L-bit is set, the resources identified by the SRLG SHOULD be 685 avoided. 687 If a node is called upon to process an EXRS and does not support 688 handling of exclusions it will behave as described in [RFC3209] when 689 an unrecognized ERO subobject is encountered. This means that this 690 node will return a PathErr with error code "Routing Error" and error 691 value "Bad Explicit Route Object" with the EXPLICIT_ROUTE object 692 inlcuded, truncated (on the left) to the offending EXRS. 694 If the presence of EXRS precludes further forwarding of the Path 695 message, the node SHOULD return a PathErr with the error code 696 "Routing Problem" and error value "Route blocked by Exclude Route". 698 5. Processing of XRO together with EXRS 700 When an LSR performs ERO expansion and finds both the XRO in the Path 701 message and EXRS in the ERO, it MUST exclude all the SRLGs, nodes, 702 links and resources listed in both places. Where some elements 703 appears in both lists it MUST be handled according to the stricter 704 exclusion request - that is, if one list says that an SRLG, node, 705 link or resource must be excluded and the other says only that it 706 should be avoided then the element MUST be excluded. 708 6. Minimum compliance 710 An implementation MUST be at least compliant with the following: 712 1. The XRO MUST be supported with the following restrictions: 714 - The IPv4 Prefix subobject MUST be supported with a prefix 715 length of 32, and an attribute value of "interface" and 716 "node". Other prefix values and attribute values MAY be 717 supported. 719 - The IPv6 Prefix subobject MUST be supported with a prefix 720 length of 128, and an attribute value of "interface" and 721 "node". Other prefix values and attribute values MAY be 722 supported. 724 2. The EXRS MAY be supported. If supported, the same restrictions 725 as for the XRO apply. 727 3. If XRO or EXRS are supported, the implementation MUST be 728 compliant with the processing rules of the supported, not 729 supported, or partially supported subobjects as specified within 730 this document. 732 7. Security Considerations 734 The new exclude route object poses no security exposures over and 735 above [RFC3209] and [RFC3473]. Note that any security concerns that 736 exist with Explicit Routes should be considered with regard to route 737 exclusions. 739 8. IANA Considerations 741 It might be considered that an alternative approach would be to 742 assign one of the bits of the ERO sub-object type field (perhaps the 743 top bit) to identify that a sub-object is intended for inclusion 744 rather than exclusion. However, [RFC3209] states that the type field 745 (seven bits) should be assigned as 0 - 63 through IETF consensus 746 action, 64 - 95 as first come first served, and 96 - 127 are reserved 747 for private use. It would not be acceptable to disrupt existing 748 implementations so the only option would be to split the IETF 749 consensus range leaving only 32 sub-object types. It is felt that 750 that would be an unacceptably small number for future expansion of 751 the protocol. 753 8.1 New RSVP-TE Class Numbers 755 One new class number is required for Exclude Route object (XRO) 756 defined in section "Exclude Route Object (XRO)". 758 EXCLUDE_ROUTE 759 Class-Num of type 11bbbbbb 760 Suggested value 232 761 Defined CType: 1 (Exclude Route) 763 Subobjects 1, 2, 4 and 32 as for Explicit Route Object. 764 Additional SRLG subobject as requested in "New ERO and XRO 765 Subobject Type" 767 8.2 New ERO Subobject Type 769 The Explicit Exclusion Route subobject (EXRS) is defined in section 770 "Explicit Exclusion Route Subobject (EXRS)". This subobject may be 771 present in the Explicit Route Object, but not in the Route Record 772 Object, nor in the new Exclude Route Object. 774 Suggested value 33 776 8.3 New ERO and XRO Subobject Type 778 The SRLG subobject is defined in section "SRLG ERO Subobject". This 779 subobject may be present in the Exclude Route Object or in the 780 Explicit Route Object, but not in the Route Record Object. 782 Suggested value 34 784 8.4 New Error Codes 786 New error values are needed for the error code 'Routing Problem' 787 (24). 789 Unsupported Exclude Route Subobject Type Suggested value 64 790 Inconsistent Subobject Suggested value 65 791 Local Node in Exclude Route Suggested value 66 792 Route Blocked by Exclude Route Suggested value 67 794 9. Acknowledgments 796 This document reuses text from [RFC3209] for the description of 797 EXCLUDE_ROUTE. 799 The authors would like to express their thanks to Lou Berger, Steffen 800 Brockmann, Igor Bryskin, Dimitri Papadimitriou, Cristel Pelsser, and 801 Richard Rabbat for their considered opinions on this draft. Also 802 thanks to Yakov Rekhter for reminding us about SRLGs! 804 10. References 806 10.1 Normative References 808 [GMPLS-RTG] 809 Kompella, K. and Y. Rekhter, "Routing Extensions in 810 Support of Generalized Multi-Protocol Label Switching", 811 draft-ietf-ccamp-gmpls-routing, work in progress. 813 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 814 Requirement Levels", BCP 14, RFC 2119, March 1997. 816 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., 817 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP 818 Tunnels", RFC 3209, December 2001. 820 [RFC3473] Berger, L., "Generalized Multi-Protocol Label Switching 821 (GMPLS) Signaling Resource ReserVation Protocol-Traffic 822 Engineering (RSVP-TE) Extensions", RFC 3473, January 2003. 824 [RFC3477] Kompella, K. and Y. Rekhter, "Signalling Unnumbered Links 825 in Resource ReSerVation Protocol - Traffic Engineering 826 (RSVP-TE)", RFC 3477, January 2003. 828 10.2 Informational References 830 [CRANKBACK] 831 Farrel, A., Satyanarayana, A., Iwata, A., Ash, G., and S. 832 Marshall-Unitt, "Crankback Signaling Extensions for MPLS 833 Signaling", draft-ietf-ccamp-crankback, work in progress. 835 [INTERAS] De Cnodder, S. and C. Pelsser, "Protection for inter-AS 836 MPLS tunnels", draft-decnodder-ccamp-interas-protection, 837 work in progress. 839 [INTERAS-REQ] 840 Zhang, R. and JP. Vasseur, "MPLS Inter-AS Traffic 841 Engineering requirements", 842 draft-ietf-tewg-interas-mpls-te-req, work in progress. 844 [MPLS-BUNDLE] 845 Kompella, K., Rekhter, Y., and L. Berger, "Link Bundling 846 in MPLS Traffic Engineering", draft-ietf-mpls-bundle, work 847 in progress. 849 [OVERLAY] Swallow, G., Drake, J., Ishimatsu, H., and Y. Rekhter, 850 "GMPLS UNI: RSVP Support for the Overlay Model", 851 draft-ietf-ccamp-gmpls-overlay, work in progress. 853 [RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering 854 (TE) Extensions to OSPF Version 2", RFC 3630, 855 September 2003. 857 [RFC3784] Smit, H. and T. Li, "Intermediate System to Intermediate 858 System (IS-IS) Extensions for Traffic Engineering (TE)", 859 RFC 3784, June 2004. 861 [RFC3812] Srinivasan, C., Viswanathan, A., and T. Nadeau, 862 "Multiprotocol Label Switching (MPLS) Traffic Engineering 863 (TE) Management Information Base (MIB)", RFC 3812, 864 June 2004. 866 11. Authors' Addresses 868 Cheng-Yin Lee 869 Email: leecy@sympatico.ca 871 Adrian Farrel 872 Old Dog Consulting 873 Phone: +44 (0) 1978 860944 874 Email: adrian@olddog.co.uk 876 Stefaan De Cnodder 877 Alcatel 878 Francis Wellesplein 1 879 B-2018 Antwerp 880 Belgium 881 Phone: +32 3 240 85 15 882 Email: stefaan.de_cnodder@alcatel.be 884 Appendix A. Applications 886 This section describes some applications that can make use of the 887 XRO. The intention is to show that the XRO is not an application 888 specific object, but that it can be used for multiple purposes. In a 889 few examples, other solutions might be possible for that particular 890 case but the intention is to show that a single object can be used 891 for all the examples, hence making the XRO a rather generic object 892 without having to define a solution and new objects for each new 893 application. 895 A.1 Inter-area LSP protection 897 One method to establish an inter-area LSP is where the ingress router 898 selects an ABR, and then the ingress router computes a path towards 899 this selected ABR such that the configured constraints of the LSP are 900 fulfilled. In the example of figure A.1, an LSP has to be 901 established from node A in area 1 to node C in area 2. If no loose 902 hops are con- figured, then the computed ERO at A could looks as 903 follows: (A1- strict, A2-strict, ABR1-strict, C-loose). When the 904 Path message arrives at ABR1, then the ERO is (ABR1-strict, C-loose) 905 and it can be expanded by ABR1 to (B1-strict, ABR3-strict, C-loose). 906 Similar, at ABR3 the received ERO is (ABR3-strict, C-loose) and it 907 can be expanded to (C1-strict, C2-strict, C-strict). If also a 908 backup LSP has to be established, then A takes another ABR (ABR2 in 909 this case) and computes a path towards this ABR that fulfills the 910 constraints of the LSP and such that is disjoint from the path of the 911 primary LSP. The ERO generated by A looks as follows for this 912 example: (A3-strict, A4-strict, ABR2-strict, C-loose). 914 In order to let ABR2 expand the ERO, it also needs to know the path 915 of the primary LSP to expand the ERO such that it is disjoint from 916 the path of the primary LSP. Therefore, A also includes an XRO that 917 at least contains (ABR1, B1, ABR3, C1, C2). Based on these con- 918 straints, ABR2 can expand the ERO such that it is disjoint from the 919 primary LSP. In this example, the ERO computed by ABR2 would be (B2- 920 strict, ABR4-strict, C-loose), and the XRO generated by B contains at 921 least (ABR3, C1, C2). The latter information is needed to let ABR4 922 to expand the ERO such that the path is disjoint from the primary LSP 923 in area 2. 925 Area 1 Area 0 Area 2 926 <---------------><--------------><---------------> 928 +---A1---A2----ABR1-----B1-----ABR3----C1---C2---+ 929 | | | | | 930 | | | | | 931 A | | | C 932 | | | | | 933 | | | | | 934 +---A3---A4----ABR2-----B2-----ABR4----C3---C4---+ 936 Figure A.1: Inter-area LSPs 938 In this example, a node performing the path computation, first 939 selects an ABR and then it computes a strict path towards this ABR. 940 For the backup LSP, all nodes of the primary LSP in the next areas 941 has to be put in the XRO (with the exception of the destination node 942 if node protection and no link protection is required). When an ABR 943 computes the next path segment, i.e. the path over the next area, it 944 may remove the nodes from the XRO that are located in that area with 945 the exception of the ABR where the primary LSP is exiting the area. 946 The latter information is still required because when the selected 947 ABR (ABR4 in this example) further expands the ERO, it has to exclude 948 the ABR on which the primary is entering that area (ABR3 in this 949 example). This means that when ABR2 generates an XRO, it may remove 950 the nodes in area 0 from the XRO but not ABR3. Note that not doing 951 this would not harm in this example because there is no path from 952 ABR4 to C via ABR3 in area2. If there is a link between ABR4- ABR3 953 and ABR3-C, then it is required to have ABR3 in the XRO gen- erated 954 by ABR2. 956 Discussion on the length of the XRO: when link or node protection is 957 requested, the length of the XRO is bounded by the length of the RRO 958 of the primary LSP. It can be made shorter by removing nodes by the 959 ingress node and the ABRs. In the example above, the RRO of the pri- 960 mary LSP contains 8 subobjects, while the maximum XRO length can be 961 bounded by 6 subobjects (nodes A1 and A2 do not have to be in the 962 XRO. For SRLG protection, the XRO has to list all SRLGs that are 963 crossed by the primary LSP. 965 A.2 Inter-AS LSP protection 967 When an inter-AS LSP is established, which has to be protected by a 968 backup LSP to provide link or node protection, the same method as for 969 the inter-area LSP case can be used. The difference is when the 970 backup LSP is not following the same AS-path as the primary LSP 971 because then the XRO should always contain the full path of the pri- 972 mary LSP. In case the backup LSP is following the same AS-path (but 973 with different ASBRs - at least in case of node protection), it is 974 similar to the inter-area case: ASBRs expanding the ERO over the next 975 AS may remove the XRO subobjects located in that AS. Note that this 976 can only be done by ingress ASBRs (the ASBR where the LSP is entering 977 the AS). 979 Discussion on the length of the XRO: the XRO is bounded by the length 980 of the RRO of the primary LSP. 982 Suppose that SRLG protection is required, and the ASs crossed by the 983 main LSP use a consistent way of allocating SRLG-ids to the links 984 (i.e. the ASs use a single SRLG space). In this case, the SRLG-ids 985 of each link used by the main LSP can be recorded by means of the 986 RRO, which are then used by the XRO. If the SRLG-ids are only 987 meaningfull local to the AS, putting SRLG-ids in the XRO crossing 988 many ASs makes no sense. More details on the method of providing 989 SRLG protection for inter-AS LSPs can be found in [INTERAS]. 990 Basically, the link IP address of the inter-AS link used by the 991 primary LSP is put into the XRO of the Path message of the detour LSP 992 or bypass tunnel. The ASBR where the detour LSP or bypass tunnel is 993 entering the AS can translate this into the list of SRLG-ids known to 994 the local AS. 996 Discussion on the length of the XRO: the XRO only contains 1 997 subobject, which contains the IP address of the inter-AS link 998 traversed by the primary LSP (assuming that the primary LSP and 999 detour LSP or bypass tunnel are leaving the AS in the same area, and 1000 they are also entering the next AS in the same area). 1002 A.3 Protection in the GMPLS overlay model 1004 When an edge-node wants to establish an LSP towards another edge-node 1005 over an optical core network as described in [OVERLAY] (see figure 1006 A.2), the XRO can be used for multiple purposes. 1008 Overlay Overlay 1009 Network +--------------------------------+ Network 1010 +----------+ | | +----------+ 1011 | +----+ | | +-----+ +-----+ +-----+ | | +----+ | 1012 | | | | | | | | | | | | | | | | 1013 | --+ EN1+-+-----+--+ CN1 +---+ CN2 +---+ CN3 +---+-----+-+ EN3+-- | 1014 | | | | +--+--+ | | | | +---+--+ | | | | 1015 | +----+ | | | +--+--+ +--+--+ +--+--+ | | | +----+ | 1016 | | | | | | | | | | | 1017 +----------+ | | | | | | | +----------+ 1018 | | | | | | | 1019 +----------+ | | | | | | | +----------+ 1020 | | | | +--+--+ | +--+--+ | | | | 1021 | +----+ | | | | | +------+ | | | | +----+ | 1022 | | +-+--+ | | CN4 +-------------+ CN5 | | +--+-+ | | 1023 | --+ EN2+-+-----+--+ | | +---+-----+-+ EN4+-- | 1024 | | | | | +-----+ +-----+ | | | | | 1025 | +----+ | | | | +----+ | 1026 | | +--------------------------------+ | | 1027 +----------+ Core Network +----------+ 1029 Overlay Overlay 1030 Network Network 1032 Legend: 1033 EN- Edge Node 1034 CN- Core Node 1036 Figure A.2 1038 A first application is where an edge-node wants to establish multiple 1039 LSPs towards the same destination edge-node, and these LSPs need to 1040 have as few or no SRLGs in common. In this case EN1 could establish 1041 an LSP towards EN3 and then it can establish a second LSP listing all 1042 links used by the first LSP with the indication to avoid the SRLGs of 1043 these links. This information can be used by CN1 to compute a path 1044 for the second LSP. If the core network consists of multiple areas, 1045 then the SRLG-ids have to be listed in the XRO. The same example 1046 applies to nodes and links. 1048 Another application is where the edge-node wants to set up a backup 1049 LSP that is also protecting the links between the edge-nodes and 1050 core-nodes. For instance, when EN2 establishes an LSP to EN4, it 1051 sends a Path message to CN4, which computes a path towards EN4 over 1052 for instance CN5. When EN2 gets back the RRO of that LSP, it can 1053 sig- nal a new LSP to CN1 with EN4 as destination and the XRO 1054 computed based on the RRO of the first LSP. Based on this 1055 information, CN1 can compute a path that has the requested diversity 1056 properties (e.g, a path going over CN2, CN3 and then to EN4). 1058 It is clear that in these examples, the core-node may not edit the 1059 RRO in a Resv message such that it includes only the subobjects from 1060 the egress core-node through the egress edge-node. 1062 A.4 LSP protection inside a single area 1064 The XRO can also be used inside a single area. Take for instance a 1065 network where the TE extensions of the IGPs as described in [RFC3630] 1066 and [RFC3784] are not used, and hence each node has to select a next- 1067 hop and possibly crankback [CRANKBACK] has to be used when there is 1068 no viable next-hop. In this case, when signaling a backup LSP, the 1069 XRO can be put in the Path message to exclude the links, nodes or 1070 SRLGs of the primary LSP. An alternative to provide this 1071 functionality would be to indicate in the Path message of the backup 1072 LSP, the primary LSP together with an indication which type of 1073 protection is required. This latter solution would work for link and 1074 node protec- tion, but not for SRLG protection. 1076 When link or node protection is requested, the XRO is of the same 1077 length as the RRO of the primary LSP. For SRLG protection, the XRO 1078 has to list all SRLGs that are crossed by the primary LSP. Note that 1079 for SRLG protection, the link IP address to reference the SRLGs of 1080 that link cannot be used since the TE extensions of the IGPs are not 1081 used in this example. Hence, a node cannot translate any link IP 1082 address located in that area to its SRLGs. 1084 Intellectual Property Statement 1086 The IETF takes no position regarding the validity or scope of any 1087 Intellectual Property Rights or other rights that might be claimed to 1088 pertain to the implementation or use of the technology described in 1089 this document or the extent to which any license under such rights 1090 might or might not be available; nor does it represent that it has 1091 made any independent effort to identify any such rights. 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