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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group B. Decraene 3 Internet Draft J.L. Le Roux 4 Document: draft-ietf-mpls-ldp-interarea-04.txt France Telecom 5 Intended status: Standards Track 6 Expiration Date: December 2008 I. Minei 7 Juniper Networks, Inc. 9 June 2008 11 LDP extension for Inter-Area LSP 13 Status of this Memo 15 By submitting this Internet-Draft, each author represents that any 16 applicable patent or other IPR claims of which he or she is aware 17 have been or will be disclosed, and any of which he or she becomes 18 aware will be disclosed, in accordance with Section 6 of BCP 79. 20 Internet-Drafts are working documents of the Internet Engineering 21 Task Force (IETF), its areas, and its working groups. Note that other 22 groups may also distribute working documents as Internet-Drafts. 24 Internet-Drafts are draft documents valid for a maximum of six months 25 and may be updated, replaced, or obsoleted by other documents at any 26 time. It is inappropriate to use Internet-Drafts as reference 27 material or to cite them other than as "work in progress." 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/ietf/1id-abstracts.txt 32 The list of Internet-Draft Shadow Directories can be accessed at 33 http://www.ietf.org/shadow.html. 35 Abstract 37 To facilitate the establishment of Label Switched Paths (LSP) that 38 would span multiple IGP areas in a given Autonomous System (AS), this 39 document describes a new optional Longest Match Label Mapping 40 Procedure for the Label Distribution Protocol (LDP). 42 This procedure allows the use of a label if the Forwarding 43 Equivalence Class (FEC) Element matches an entry in the routing table 44 (RIB). Matching is defined by an IP longest match search and does not 45 mandate an exact match. 47 Table of Contents 49 1. Conventions used in this document...........................2 50 2. Terminology.................................................2 51 3. Introduction................................................2 52 4. Problem statement...........................................3 53 5. Longest Match Label Mapping Message Procedure...............4 54 6. Application examples........................................6 55 6.1. Inter-area LSPs.............................................6 56 6.2. Use of static routes........................................7 57 7. Caveats for deployment......................................8 58 7.1. Deployment considerations...................................8 59 7.2. Routing convergence time considerations.....................8 60 8. Security Considerations.....................................9 61 9. IANA Considerations.........................................9 62 10. References..................................................9 63 10.1. Normative References........................................9 64 10.2. Informative References......................................9 65 11. Acknowledgments............................................10 66 12. Authors' Addresses.........................................11 68 1. Conventions used in this document 70 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 71 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 72 document are to be interpreted as described in [RFC 2119]. 74 2. Terminology 76 IGP Area: OSPF Area or IS-IS level 78 ABR: OSPF Area Border Router or IS-IS L1/L2 router 80 LSP: Label Switched Path 82 Intra-area LSP: LSP that does not traverse any IGP area boundary. 84 Inter-area LSP: LSP that traverses at least one IGP area boundary. 86 3. Introduction 88 Link state Interior Gateway Protocols (IGPs) such as OSPF [OSPFv2] 89 and IS-IS [IS-IS] allow the partition of an autonomous system into 90 areas or levels so as to increase routing scalability within a 91 routing domain. 93 However, [LDP] recommends that the IP address of the FEC Element 94 should *exactly* match an entry in the IP RIB: according to [LDP] 95 section 3.5.7.1 (Label Mapping Messages Procedures) "A Label 96 Switching Router (LSR) receiving a Label Mapping message from a 97 downstream LSR for a Prefix SHOULD NOT use the label for forwarding 98 unless its routing table contains an entry that exactly matches the 99 FEC Element.". 101 Therefore, MPLS LSPs between Label Edge Routers (LERs) in different 102 areas/levels are not setup unless the specific (e.g. /32 for IPv4) 103 loopback addresses of all the LERs are redistributed across all 104 areas. 106 The problem statement is discussed in section 4. Then, in section 5 107 we extend the Label Mapping Procedure defined in [LDP] so as to 108 support the setup of contiguous inter-area LSPs while maintaining IP 109 prefix aggregation on the ABRs. This consists of allowing for longest 110 match based Label Mapping. 112 4. Problem statement 114 Provider based MPLS (Multi Protocol Label Switching) networks are 115 expanding with the success of Layer 3 VPN (Virtual Private Networks 116 [L3-VPN]) and the new deployments of layer 2 VPNs ([VPLS-BGP], [VPLS- 117 LDP]). Service providers MPLS backbones are significantly growing 118 both in terms of density with the addition of Provider Edge (PE) 119 routers to connect new customers and in terms of footprint as 120 traditional layer two aggregation networks may be replaced by IP/MPLS 121 networks. 122 As a consequence many providers need to introduce IGP areas. Inter- 123 area LSPs, that is LSPs that traverse at least two IGP areas, are 124 required to ensure MPLS connectivity between PEs located in distinct 125 IGP areas. 127 To set up the required MPLS LSPs between PEs in different IGP areas, 128 service providers have currently three solutions: 1) LDP with IGP 129 route leaking, 2) BGP [MPLS-BGP] over LDP with MPLS hierarchy, and 3) 130 inter-area RSVP-TE (Resource Reservation Protocol-Traffic Engineering 131 [RSVP-TE]). 133 IGP route leaking consists in redistributing all specific PE loopback 134 addresses across area boundaries. As a result, LDP finds in the 135 Routing Information Base (RIB) an exact match for its FEC and sets up 136 the LSP. As a consequence, the potential benefits that a multi-area 137 domain may yield are significantly diminished since a lot of 138 addresses have to be redistributed by ABRs, and the number of IP 139 entries in the IGP Link State DataBase (LSDB), RIB and FIB maintained 140 by every LSR of the domain (whatever the area/level it belongs to) 141 cannot be minimized. 143 Service providers may also set up these inter-area LSPs by using MPLS 144 hierarchy with BGP [MPLS-BGP] as a label distribution protocol 145 between areas. The BGP next hop would typically be the ABRs and the 146 BGP-created LSPs would be nested within intra-area LSPs setup by LDP 147 between PEs and ABRs and between ABRs. 148 This solution is not adequate for service providers which don't want 149 to run BGP on their P routers as it requires BGP on all ABRs. In 150 addition, MPLS hierarchy does not allow locally protecting the LSP 151 against ABR failures (IP/LDP Fast Reroute), and hence ensuring sub- 152 50ms recovery upon ABR failure. The resulting convergence time may 153 not be acceptable for stringent Service Level Agreements (SLAs) 154 required for voice or mission critical applications. Finally, this 155 solution requires a significant migration effort for service 156 providers which started with LDP and IGP route leaking to quickly 157 set-up the first inter-area LSPs. 159 Service providers may also setup these inter-area LSPs by using 160 inter-area RSVP-TE [RSVP-TE]. This is a relevant solution when RSVP- 161 TE is already used for setting up intra-area LSPs, and inter-area 162 traffic engineering features are required. In return this is not a 163 desired solution when LDP is already used for setting up intra-area 164 LSPs, and inter-area traffic engineering features are not required. 166 To avoid the above drawbacks, there is a need for an LDP based 167 solution which allows setting up contiguous inter-area LSPs while 168 avoiding leaking of specific PE loopback addresses across area 169 boundaries, and hence keeping all the benefits of IGP hierarchy. 171 In that context, this document defines a new LDP Label Mapping 172 Procedure so as to support the setup of contiguous inter-area LSPs 173 while maintaining IP prefix aggregation on the ABRs. This procedure 174 is similar to the one defined in [LDP] but performs an IP longest 175 match when searching the FEC element in the RIB. 177 5. Longest Match Label Mapping Message Procedure 179 This document defines a new Label Mapping Procedure for [LDP]. It is 180 applicable to IPv4 and IPv6 prefix FEC elements (address families 1 181 and 2 as per [ASSIGNED_AF]). It SHOULD be possible to activate / 182 deactivate this procedure by configuration and it SHOULD be 183 deactivated by default. It MAY be possible to activate it on a per 184 prefix basis. 186 With this new Longest Match Label Mapping Procedure, an LSR receiving 187 a Label Mapping message from a neighbor LSR for a Prefix Address FEC 188 Element FEC1 SHOULD use the label for MPLS forwarding if its routing 189 table contains an entry that matches the FEC Element FEC1 and the 190 advertising LSR is a next hop to reach FEC1. If so, it SHOULD 191 advertise the received FEC Element FEC1 and a label to its LDP peers. 193 By "matching FEC Element", one should understand an IP longest match. 194 That is, either the LDP FEC element exactly matches an entry in the 195 IP RIB or the FEC element is a subset of an IP RIB entry. There is no 196 match for other cases such as the FEC element is a superset of a RIB 197 entry. 198 Note that LDP re-advertises to its peers the specific FEC element 199 FEC1, and not the aggregated prefix found in the IP RIB during the 200 longest match search. 202 Note that with this Longest Match Label Mapping Procedure, each LSP 203 established by LDP still strictly follows the shortest path(s) 204 defined by the IGP. 206 FECs selected by this Longest Match Label Mapping Procedure are 207 distributed in an ordered way. In case of LER failure, the removal of 208 reachability to the FEC occurs using LDP ordered label distribution 209 mode procedures. As defined in [LDP] in section A.1.5, the FEC will 210 be removed in an ordered way through the propagation of Label 211 Withdraw messages. The use of this (un)reachability information by 212 application layers using this MPLS LSP (e.g., [MP-BGP]) is outside 213 the scope of this document. 215 As per [LDP], LDP has already some interactions with the RIB. In 216 particular, it needs to be aware of the following events: 217 - prefix up when a new IP prefix appears in the RIB, 218 - prefix down when an existing IP prefix disappears, 219 - next hop change when an existing IP prefix has a new next hop 220 following a routing change. 222 With this Longest Match Label Mapping Message Procedure, multiple 223 FECs may be concerned by a single RIB prefix change. The LSR MUST 224 check all the FECs which are a subset of this RIB prefix. So some LDP 225 reactions following a RIB event are changed: 226 - When a new prefix appears in the RIB, the LSR MUST check if this 227 prefix is a better match for some existing FECs. E.g. the FEC 228 elements 192.0.2.1/32 and 192.0.2.2/32 used the IP RIB entry 229 192.0.2.0/24 and a new more specific IP RIB entry 192.0.2.0/26 230 appears. This may result in changing the LSR used as next hop 231 and hence the Next Hop Label Forwarding Entry (NHLFE) for this 232 FEC. 233 - When a prefix disappears in the RIB, the LSR MUST check all FEC 234 elements which are using this RIB prefix as best match. For each 235 FEC, if another RIB prefix is found as best match, LDP MUST use 236 it. This may result in changing the LSR used as next hop and 237 hence the NHLFE for this FEC. Otherwise, the LSR MUST remove the 238 FEC binding and send a Label Withdraw message. 239 - When the next hop of a RIB prefix changes, the LSR MUST change 240 the NHLFE of all the FEC elements using this prefix. 242 Future work may define new management objects to the MPLS LDP MIB 243 modules [LDP-MIB] to activate/deactivate this Longest Match Label 244 Mapping Message Procedure, possibly on a per prefix basis. 246 6. Application examples 248 6.1. Inter-area LSPs 250 Consider the following example of an autonomous system with one 251 backbone area and two edge areas: 253 Area "B" 255 Level 2 / Backbone area 257 +--------------------------+ 258 Area "A" | | Area "C" 259 | | 260 Level 1 | | Level 1 / area 261 | P1 | 262 +----------+ +-------------+ 263 | | P2 | PE1 | 192.0.2.1/32 264 | | | | 265 |PE4 ABR2 ABR1 PE2 | 192.0.2.2/32 266 | | P3 | | 267 | | | PE3 | 192.0.2.3/32 268 +----------+ +-------------+ 269 | | 270 +--------------------------+ 272 Figure 1: An IGP domain with two areas attached to the Backbone 273 Area. 275 Note that this applies equally to IS-IS and OSPF. An ABR refers here 276 either to an OSPF ABR or to an IS-IS L1/L2 node. 278 All routers are MPLS enabled and MPLS connectivity (i.e. an LSP) is 279 required between all PE routers. 281 In the "egress" area "C", the records available are: 282 IGP RIB LDP FEC elements: 283 192.0.2.1/32 192.0.2.1/32 284 192.0.2.2/32 192.0.2.2/32 285 192.0.2.3/32 192.0.2.3/32 287 The area border router ABR1 advertises in the backbone area: 288 - the aggregated IP prefix 192.0.2.0/26 in the IGP 289 - all the specific IP FEC elements (/32) in LDP 291 In the "backbone" area "B", the records available are: 292 IGP RIB LDP FEC elements: 293 192.0.2.0/26 192.0.2.1/32 294 192.0.2.2/32 295 192.0.2.3/32 297 The area border router ABR2 advertises in the area "A": 298 - an aggregated IP prefix 192.0.2.0/24 in the IGP 299 - all the individual IP FEC elements (/32) in LDP 301 In the "ingress" area "A", the records available are: 302 IGP RIB LDP FEC elements: 303 192.0.2.0/24 192.0.2.1/32 304 192.0.2.2/32 305 192.0.2.3/32 307 In this situation, one LSP is established between the ingress PE4 and 308 every egress PE of area C while maintaining IP prefix aggregation on 309 the ASBRs. 311 6.2. Use of static routes 313 Consider the following example where a LER is dual-connected to two 314 LSRs: 316 +--------LSR1---- 317 | | 318 LER | 319 | | 320 +--------LSR2---- 322 Figure 2: LER dual-connected to two LSRs. 324 In some situations, especially on the edge of the network, it is 325 valid to use static IP routes between the LER and the two LSRs. If 326 necessary, the BFD protocol ([BFD]) can be used to quickly detect 327 loss of connectivity. 329 The LDP specification defined in [LDP] would require on the ingress 330 LER the configuration and the maintenance of one IP route per egress 331 LER and per outgoing interface. 333 The Longest Match Label Mapping Procedure described in this document 334 only requires one IP route per outgoing interface. 336 7. Caveats for deployment 338 7.1. Deployment considerations 340 LSRs compliant with this document are backward compatible with LSRs 341 that comply with [LDP]. 343 For the successful establishment of end-to-end MPLS LSPs whose FEC 344 are aggregated in the RIB, this specification must be implemented on 345 all LSRs in all areas where IP aggregation is used. If an LSR on the 346 path does not support this procedure, then the LSP initiated on the 347 egress LSR stops at this non compliant LSR. There are no other 348 adverse effects. 350 This extension can be deployed incrementally: 351 - It can be deployed on a per area or routing domain basis and 352 does not necessarily require an AS wide deployment. For example, 353 if all specific IP prefixes are leaked in the IGP backbone area 354 and only stub areas use IP aggregation, LSRs in the backbone 355 area don't need to be compliant with this document. 356 - Within each routing area, LSRs can be upgraded independently, at 357 any time, in any order and without service disruption. During 358 deployment, if those LSPs are already used, one should only make 359 sure that ABRs keep advertising the specific IP prefixes in the 360 IGP until all LSR of this area are successfully upgraded. Then, 361 the ABRs can advertise the aggregated prefix only and stop 362 advertising the specific ones. 364 A service provider currently leaking specific LER's loopback 365 addresses in the IGP and now considering performing IP aggregation on 366 ABR should be aware that this may result in suboptimal routing as 367 discussed in [RFC 2966]. 369 7.2. Routing convergence time considerations 371 IP and MPLS traffic restoration time is based on two factors: the 372 Shortest Path First (SPF) calculation in the control plane and 373 Forwarding Information Base (FIB)/Label FIB (LFIB) update time in the 374 forwarding plane. The SPF calculation scales O(N*Log(N)) where N is 375 the number of Nodes. The FIB/LFIB update scales O(P) where P is the 376 number of modified prefixes. Currently, with most routers 377 implementations, the FIB/LFIB update is the dominant component [1] 378 and therefore the bottleneck that should be addressed in priority. 379 The solution documented in this draft reduces the link state database 380 size in the control plane and the number of FIB entries in the 381 forwarding plane. As such it solves the scaling of pure IP routers 382 sharing the IGP with MPLS routers. However, it does not decrease the 383 number of LFIB entries so is not sufficient to solve the scaling of 384 MPLS routers. For this, an additional mechanism is required (e.g. 385 introducing some MPLS hierarchy in LDP). This is out of scope of this 386 document. 388 Compared to [LDP], for all failures except LER failure (i.e. links, 389 Ps and ABRs nodes), the failure notification and the convergence is 390 unchanged. For LER failure, given that the IGP aggregates IP routes 391 on ABRs and no longer advertise specific prefixes, the control plane 392 and more specifically the routing convergence behavior of protocols 393 (e.g. [MP-BGP]) or applications (e.g. [L3-VPN]) may be changed in 394 case of failure of the egress LER node. For protocols and 395 applications which need to track egress LER availability, several 396 solutions can be used, for example: 397 - Rely on the LDP ordered label distribution control mode - as 398 defined in [LDP] - to know the availability of the LSP toward the 399 egress LER. The egress to ingress propagation time of that 400 unreachability information is expected to be comparable to the IGP 401 (but this may be implementation dependant). 402 - Advertise LER reachability in the IGP for the purpose of the 403 control plane in a way that do not create IP FIB entries in the 404 forwarding plane. 406 8. Security Considerations 408 The Longest Match Label Mapping procedure described in this document 409 does not introduce any change as far as the Security Consideration 410 section of [LDP] is concerned. 412 9. IANA Considerations 414 This document has no actions for IANA. 416 10. References 418 10.1. Normative References 420 [LDP] Andersson, L., Minei, I., Thomas, B., "LDP 421 Specification", RFC 5036, October 2007 423 [ASSIGNED_AF] http://www.iana.org/assignments/address-family- 424 numbers 426 [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate 427 Requirement Levels", RFC 2119, March 1997 429 10.2. Informative References 431 [L3-VPN] Rosen, E., Rekhter, Y. ," BGP/MPLS IP Virtual Private 432 Networks (VPNs) ", RFC 4374, February 2006 434 [MP-BGP] Bates, T., Chandra, R., Katz, D., Rekhter, Y., 435 "Multiprotocol Extensions for BGP-4", RFC 4760, January 2007 437 [MPLS-BGP] Rekhter, Y., Rosen, E., "Carrying Label Information in 438 BGP-4", RFC 3107, May 2001 440 [OSPFv2] Moy, J.,"OSPF Version 2", RFC 2328, April 1998 442 [IS-IS] Callon, R., "Use of OSI IS-IS for Routing in TCP/IP and 443 Dual Environments", RFC 1195, December 1990 445 [VPLS-BGP] Kompella, K., Rekhter, Y., "Virtual Private LAN Service 446 (VPLS) Using BGP for Auto-discovery and Signaling", RFC 4761, 447 January 2007. 449 [VPLS-LDP] Lasserre, M., Kompella, V., "Virtual Private LAN Service 450 (VPLS) Using Label Distribution Protocol (LDP) Signaling", RFC 451 4762, January 2007. 453 [RFC 2966] Li, T., Przygienda, T., Smit, H., "Domain-wide Prefix 454 Distribution with Two-Level IS-IS", RFC 2966, October 2000. 456 [RSVP-TE] Farrel, Ayyangar, Vasseur, "Inter domain MPLS and GMPLS 457 Traffic Engineering - RSVP-TE extensions", RFC 5151, February 458 2008. 460 [LDP-MIB] Cucchiara, J., Sjostrand, H., Luciani, J., "Definitions 461 of Managed Objects for the Multiprotocol Label Switching 462 (MPLS), Label Distribution Protocol (LDP)", RFC 3815, June 463 2004. 465 [BFD] Katz, D., Ward, D., "Bidirectional Forwarding Detection", 466 draft-ietf-bfd-base-08.txt, March 2008. 468 [1] Francois, P., Filsfils, C., and Evans, J. 2005. "Achieving sub- 469 second IGP convergence in large IP networks". ACM SIGCOMM 470 Computer Communications Review, July 2005 472 11. Acknowledgments 474 Authors would like to thank Yakov Rekhter, Stefano Previdi, Vach 475 Kompella, Bob Thomas, Clarence Filsfils, Kireeti Kompella, Luca 476 Martini, Sina Mirtorabi, Dave McDysan, Benoit Fondeviole, Gilles 477 Bourdon and Christian Jacquenet for the useful discussions on this 478 subject, their review and comments. 480 12. Authors' Addresses 482 Bruno Decraene 483 France Telecom 484 38 rue du General Leclerc 485 92794 Issy Moulineaux cedex 9 486 France 488 EMail: bruno.decraene@orange-ftgroup.com 490 Jean-Louis Le Roux 491 France Telecom 492 2, avenue Pierre-Marzin 493 22307 Lannion Cedex 494 France 496 EMail: jeanlouis.leroux@orange-ftgroup.com 498 Ina Minei 499 Juniper Networks 500 1194 N. 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