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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group L. Iannone 3 Internet-Draft TU Berlin - Deutsche Telekom 4 Intended status: Experimental Laboratories AG 5 Expires: January 13, 2011 D. Saucez 6 O. Bonaventure 7 Universite catholique de Louvain 8 July 12, 2010 10 LISP Map-Versioning 11 draft-iannone-lisp-mapping-versioning-02.txt 13 Abstract 15 This document describes the LISP Map-Versioning mechanism. This is 16 mechanism to provide in-packet information about EID-to-RLOC mappings 17 used to encapsulate LISP data packets. The proposed approach is 18 based on associating a version number to EID-to-RLOC mappings and 19 transport such a version number in the LISP specific header of LISP- 20 encapsulated packets. LISP Map-Versioning is particularly useful to 21 inform communicating xTRs about modification of the mappings used to 22 encapsulate packets. Note that, in the LISP encapsulation and in the 23 Map Records, bits used for Map-Versioning can be safely ignored by 24 xTRs that do not support the mechanism. 26 Status of this Memo 28 This Internet-Draft is submitted to IETF in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF), its areas, and its working groups. Note that 33 other groups may also distribute working documents as Internet- 34 Drafts. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 The list of current Internet-Drafts can be accessed at 42 http://www.ietf.org/ietf/1id-abstracts.txt. 44 The list of Internet-Draft Shadow Directories can be accessed at 45 http://www.ietf.org/shadow.html. 47 This Internet-Draft will expire on January 13, 2011. 49 Copyright Notice 51 Copyright (c) 2010 IETF Trust and the persons identified as the 52 document authors. All rights reserved. 54 This document is subject to BCP 78 and the IETF Trust's Legal 55 Provisions Relating to IETF Documents 56 (http://trustee.ietf.org/license-info) in effect on the date of 57 publication of this document. Please review these documents 58 carefully, as they describe your rights and restrictions with respect 59 to this document. Code Components extracted from this document must 60 include Simplified BSD License text as described in Section 4.e of 61 the Trust Legal Provisions and are provided without warranty as 62 described in the BSD License. 64 Table of Contents 66 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 67 2. Requirements notation . . . . . . . . . . . . . . . . . . . . 3 68 3. EID-to-RLOC Map-Version number . . . . . . . . . . . . . . . . 4 69 3.1. The special Map-Version 0 . . . . . . . . . . . . . . . . 4 70 4. Dealing with Map-Version numbers . . . . . . . . . . . . . . . 5 71 4.1. Handling Destination Map-Version Number . . . . . . . . . 5 72 4.2. Handling Source Map-Version Number . . . . . . . . . . . . 6 73 5. LISP header and Map-Version numbers . . . . . . . . . . . . . 7 74 6. Map Record and Map-Version . . . . . . . . . . . . . . . . . . 9 75 7. Benefits and case studies for Map-Versioning . . . . . . . . . 10 76 7.1. Synchronization of different xTRs . . . . . . . . . . . . 10 77 7.2. Map-Versioning and unidirectional traffic . . . . . . . . 11 78 7.3. Map-Versioning and interworking . . . . . . . . . . . . . 11 79 7.4. Graceful RLOC shutdown/withdraw . . . . . . . . . . . . . 12 80 7.5. Map-Version for lightweight LISP implementation . . . . . 12 81 8. Incremental deployment and implementation status . . . . . . . 13 82 9. Security Considerations . . . . . . . . . . . . . . . . . . . 13 83 9.1. Map-Versioning against traffic disruption . . . . . . . . 13 84 9.2. Map-Versioning against reachability information DoS . . . 14 85 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14 86 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 87 11.1. Normative References . . . . . . . . . . . . . . . . . . . 14 88 11.2. Informative References . . . . . . . . . . . . . . . . . . 15 89 Appendix A. Map-Version wrap-around . . . . . . . . . . . . . . . 15 90 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16 92 1. Introduction 94 This document describes the Map-Versioning mechanism used to provide 95 information on changes in the EID-to-RLOC mappings used in the LISP 96 ([I-D.ietf-lisp]) context to perform encapsulation. The mechanism is 97 totally transparent to xTRs not supporting such a functionality. It 98 is not meant to replace any existing LISP mechanism, but rather to 99 complete them providing new functionalities. The basic mechanism is 100 to associate Map-Version numbers to each LISP mapping and transport 101 such a version number in the LISP specific header. When a mapping 102 changes, a new version number is assigned to the updated mapping. A 103 change in an EID-to-RLOC mapping can be a change in the RLOCs set, by 104 adding or removing one or more RLOCs, but it can also be a change in 105 the priority or weight of one or more RLOCs. 107 When Map-Versioning is used, LISP-encapsulated data packets contain 108 the version number of the mappings used to select the RLOCs in the 109 outer header (both source and destination). These version numbers 110 are encoded in the 24 low-order bits of the first longword of the 111 LISP header and indicated by a specific bit in the flags (first 8 112 high-order bits of the first longword of the LISP header). Note that 113 not all packets need to carry version numbers. 115 When an ITR encapsulates a data packet, with a LISP header containing 116 the Map-Versions, it puts in the LISP-specific header two version 117 numbers: 118 1. The version number assigned to the mapping (contained in the EID- 119 to-RLOC Database) used to select the source RLOC. 120 2. The version number assigned to the mapping (contained in the EID- 121 to-RLOC Cache) used to select the destination RLOC. 122 This operation is two-fold. On the one hand it enables the ETR 123 receiving the packet to know if the ITR that sent it is using the 124 latest mapping for the destination EID. If it is not the case the 125 eTR can send to the ITR a Map-Request containing the updated mapping 126 or invoking a Map-Request from the ITR (both cases are already 127 defined in [I-D.ietf-lisp]). In this way the ITR can update its 128 cache. On the other hand, it enables an xTR receiving such a packet 129 to know if it has in its cache the latest mapping for the source EID 130 (in case of bidirectional traffic). If it is not the case a Map- 131 Request can be send. 133 2. Requirements notation 135 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 136 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 137 document are to be interpreted as described in [RFC2119]. 139 3. EID-to-RLOC Map-Version number 141 The EID-to-RLOC Map-Version number consists in an unsigned 12-bits 142 integer. The version number is assigned in a per-mapping fashion, 143 meaning that different mappings will have assigned a different 144 version number, which is also updated independently. An update in 145 the version number (i.e., a newer version) consist in incrementing by 146 one the older version number. Appendix A contains a rough estimation 147 of the wrap-around time for the Map Version number. 149 The space of version numbers has a circular order where half of the 150 version numbers is greater than the current Map-Version number and 151 the other half is smaller than current Map-Version number. In a more 152 formal way, assuming we have two version numbers V1 and V2 and that 153 the numbers are expressed on N bits, the following three cases may 154 happen: 156 V1 = V2 : This is the exact match case. 157 V1 < V2 : True if and only if V1 < V2 < (V1 + 2**(N-1)). 158 V1 > V2 : True if and only if V1 > V2 > (V1 - 2**(N-1)). 160 Using 12 bits, as defined in this document, and assuming a Map- 161 Version value of 69, Map-Versions in [70; 69 + 2047] are greater and 162 versions in [69 + 2048; (69 + 4095) mod 4096] are smaller. 164 The initial Map-Version number of a new mapping can be randomly 165 generated. However, it MUST NOT be zero (0) because it has a special 166 meaning (see section Section 3.1). 168 3.1. The special Map-Version 0 170 The value 0 (zero) is not a valid Map-Version Number. The only valid 171 use of Map-Version number equal to 0 is in the Map Records. Map 172 Records that have Map-Version number equal 0 indicate that there is 173 no Map-Version number associated with the mapping. This means that 174 LISP encapsulated packets, destined to the EID-Prefix the Map Record 175 refers to, MUST never contain Map-Version number (i.e., V bit MUST 176 always be 0). In other words, Map-Version number equal to 0 signal 177 to the requester of the mapping that the Map-Versioning is not 178 supported, or even if supported it must not be used for that specific 179 EID-Prefix. Any value different from zero means that Map-Versionig 180 is supported and can be used. 182 For LISP encapsulated packets with the V-bit set, if the Source Map- 183 Version is 0, it means that the version number must be ignored and no 184 checks (described in Section 4) need to be performed. 186 The fact that the 0 value has a special meaning for the Map-Version 187 number implies that, when updating a Map-Version number because of a 188 change in the mapping, if the next value is 0 then Map-Version number 189 must be incremented by 2 (i.e., set to 1, the next valid value). 191 4. Dealing with Map-Version numbers 193 The main idea of using Map-Version numbers is that whenever there is 194 a change in the mapping (e.g., adding/removing RLOCs, a change in the 195 weights due to TE policies, or a change in the priorities) or an ISP 196 realizes that one or more of its own RLOCs are not reachable anymore 197 from a local perspective (e.g., through IGP, or policy changes) the 198 ISP updates the mapping with a new Map-Version number. 200 In order to announce in a data-driven fashion that the mapping has 201 been updated, Map-Version numbers used to create the outer IP header 202 of the LISP encapsulated packet are embedded in the LISP specific 203 header. This means that the header needs to contain two Map-Version 204 numbers: 205 o A first one from the EID-to-RLOC mapping in the EID-to-RLOC 206 Database used to select the source RLOC, and called Source Map- 207 Version Number. 208 o A second one from the EID-to-RLOC mapping in the EID-to-RLOC Cache 209 used to select the destination RLOC, and called Destination Map- 210 Version Number. 211 By embedding both Source Map-Version Number and Destination Map- 212 Version Number an ETR can perform the following checks: 213 1. The ITR has an up-to-date mapping in its cache for the 214 destination EID and is performing encapsulation correctly. 215 2. In case of bedirectional traffic, the mapping in the local xTR 216 cache for the source EID is up-to-date. 217 If one or both of the above conditions do not hold, the xTR can send 218 a Map-Request either to make the ITR aware that a new mapping is 219 available (see Section 4.1) or to updated local mapping in the cache 220 (see section Section 4.2). 222 4.1. Handling Destination Map-Version Number 224 When an ETR receives a packet, the Destination Map Version number 225 relates to the mapping for the destination EID for which the ETR is a 226 RLOC. This mapping is part of the ETR LISP Database. Since the ETR 227 is authoritative for the mapping, it has the correct and up-to-date 228 Destination Map-Version number. A check on this version number is 229 done, where the following cases can arise: 230 o The packets arrive with the same Destination Map Version number 231 stored in the EID-to-RLOC Database. This is the regular case. 232 The ITR sending the packet has in its EID-to-RLOC Cache an up-to- 233 date mapping. No further actions are needed. 235 o The packet arrives with a Destination Map-Version number greater 236 (i.e., newer) than the one stored in the EID-to-RLOC Database. 237 Since the ETR is authoritative on the mapping, this means that 238 someone is not behaving correctly w.r.t. the specifications, thus 239 the packets carries a not valid version number and can be silently 240 dropped. 241 o The packets arrive with an Destination Map-Version number smaller 242 (i.e., older) than the one stored in the EID-to-RLOC Database. 243 This means that the ITR sending the packet has an old mapping in 244 its EID-to-RLOC Cache containing stale information. Further 245 actions are needed. The ITR sending the packet must be informed 246 that a newer mapping is available. This is done with a Map- 247 Request message sent back to the ITR. The Map-Request will either 248 trigger a Map-Request back using the SMR bit or it will piggy-back 249 the newer mapping. These are not new mechanisms; how to SMR or 250 piggy-back mappings in Map-Request messages is already described 251 in [I-D.ietf-lisp], while their security is discussed in 252 [I-D.saucez-lisp-security]. These Map-Request message should be 253 rate limited (rate limitation policies are also described in 254 [I-D.ietf-lisp]). The gain introduced by Map-Version Numbers is 255 that after a certain number of retries, if the Destination Map- 256 Version Number in the packets is not updated, packet can be 257 silently dropped because either the ITR is refusing to use the 258 mapping for which the ETR is authoritative or it might be some 259 form of attack. Note that the rule can be even more restrictive. 260 If the mapping has been the same for a period of time as long as 261 the TTL (defined in LISP [I-D.ietf-lisp]) of the previous version 262 of the mapping, all packets arriving with an old Map-Version 263 should be silently dropped right away without issuing any Map- 264 Request. Indeed, if the new mapping with the updated version 265 number has been stable for at least the same time as the TTL of 266 the older mapping, all the entries in the caches of ITRs must have 267 expired. If packets with old Map-Version number are still 268 received, the reason is that either someone has not respected the 269 TTL, or it is a form of spoof/attack. In both cases this is not 270 valid behavior w.r.t. the specifications and the packet can be 271 silently dropped. 273 4.2. Handling Source Map-Version Number 275 When an xTR receives a packet, the Source Map-Version Number relates 276 to the mapping for the source EID for which the ITR is authoritative. 277 If the xTR has an entry in its LISP Cache a check is performed and 278 the following cases can arise: 279 o The packet arrives with the same Source Map-Version number stored 280 in the LISP Cache. This is the correct regular case. The xTR has 281 in its cache an up-to-date copy of the mapping. No further 282 actions are needed. 284 o The packet arrives with a Source Map-Version number greater (i.e., 285 newer) than the one stored in the local LISP Cache. This means 286 that xTR has in its cache a mapping that is stale and needs to be 287 updated. The packet is considered valid but further actions are 288 needed. In particular a Map-Request must be sent to get the new 289 mapping for the source EID. This is a normal Map-Request message 290 sent through the mapping system and must respect the 291 specifications in [I-D.ietf-lisp], including rate limitation 292 policies. 293 o The packet arrives with a Source Map-Version number smaller (i.e., 294 older) than the one stored in the local LISP Cache. Such a case 295 is not valid w.r.t. the specifications. Indeed, if the mapping is 296 already present in the LISP Cache, this means that an explicit 297 Map-Request has been sent and a Map-Reply has been received from 298 an authoritative source. Assuming that the mapping system is not 299 corrupted anyhow, the Map-Version in the LISP Cache is the correct 300 one, hence the packet is not valid and can be silently dropped. 302 Otherwise, if the xTR does not have an entry in its cache (e.g. 303 unidirectional traffic) the Source Map-Version can be safely ignored. 305 5. LISP header and Map-Version numbers 307 In order for the versioning approach to work, the LISP specific 308 header has to carry both Source Map-Version Number and Destination 309 Map-Version Number. This is done by setting the V-bit in the LISP 310 specific header. When the V-bit is set the low-order 24-bits of the 311 first longword (which usually contains the nonce) are used transport 312 both source and destination Map-Versions. In particular the first 12 313 bits are used for Source Map-Version and the second 12 bits for the 314 Destination Map-Version. 316 Hereafter is the example of LISP header carrying version numbers in 317 the case of IPv4-in-IPv4 encapsulation. The same setting can be used 318 for any other case (IPv4-in-IPv6, IPv6-in-IPv4, IPv6-in-IPv6). The 319 authoritative document for LISP packet format is [I-D.ietf-lisp], the 320 following example is proposed only for explanation purposes. 322 0 1 2 3 323 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 1 324 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 325 /|Version| IHL |Type of Service| Total Length | 326 / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 327 / | Identification |Flags| Fragment Offset | 328 / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 329 OH | Time to Live | Protocol = 17 | Header Checksum | 330 \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 331 \ | Source Routing Locator | 332 \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 333 \| Destination Routing Locator | 334 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 335 / | Source Port = xxxx | Dest Port = 4341 | 336 UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 337 \ | UDP Length | UDP Checksum | 338 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 339 / |N|L|E|V|I|flags| Source Map-Version |Destination Map-Version| 340 LISP+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 341 \ | Instance ID/Locator Status Bits | 342 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 343 /|Version| IHL |Type of Service| Total Length | 344 / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 345 / | Identification |Flags| Fragment Offset | 346 / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 347 IH | Time to Live | Protocol | Header Checksum | 348 \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 349 \ | Source EID | 350 \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 351 \| Destination EID | 352 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 354 V: this is the Map-Version bit as defined in [I-D.ietf-lisp]. When 355 this bit is set to 1 the low-order 24-bits of the first longword 356 of the LISP header contain Map-Version numbers. 357 Source Map-Version number (12 bits): Map-Version of the mapping used 358 by the ITR to select the RLOC present in the "Source Routing 359 Locator" field. Note that the mapping used for such a selection 360 is determined by the Source EID through a search in the LISP 361 Database of the ITR. 362 Destination Map-Version Number (12 bits): Map-Version of the mapping 363 used by the ITR to select the RLOC present in the "Destination 364 Routing Locator" field. Note that the mapping used for such a 365 selection is determined by the Destination EID, used as lookup key 366 in the LISP Cache of the ITR. 368 Not all of the LISP encapsulated packets need to carry version 369 numbers. When Map-Version number are carried the V bit must be set 370 to 1. All legal combination of the flags, when the V-bit is set to 1 371 are described in [I-D.ietf-lisp]. As a recall and in summary, Map- 372 Version cannot be used with the Echo-Nonce feature (E = 1) and the 373 Nonce feature (N = 1), since they use the same bitfield. 375 6. Map Record and Map-Version 377 To accommodate the proposed mechanism, the Map Records that are 378 transported on Map-Request/Map-Reply messages need to carry the Map- 379 Version number as well. For this purpose the 12-bits before the EID- 380 AFI field in the Record that describe a mapping is used. This is 381 defined in [I-D.ietf-lisp] and reported here as example. 383 0 1 2 3 384 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 1 385 +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 386 | | Record TTL | 387 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 388 R | Locator Count | EID mask-len | ACT |A| Reserved | 389 e +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 390 c | Rsvd | Map-Version Number | EID-AFI | 391 o +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 392 r | EID-prefix | 393 d +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 394 | /| Priority | Weight | M Priority | M Weight | 395 | L +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 396 | o | Unused Flags |L|p|R| Loc-AFI | 397 | c +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 398 | \| Locator | 399 +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 401 Map-Version Number: Map-Version of the mapping contained in the 402 Record. As explained in Section 3.1 this field can be zero (0), 403 meaning that no Map-Version is associated to the mapping, hence 404 LISP encapsulated packet must not contain Map-Version in the LISP 405 specific header. 407 Note that this packet format works perfectly with xTRs that do not 408 support Map-Versioning, since they can simply ignore those bits. 409 Furthermore, existing and future mapping distribution protocol (e.g., 410 ALT [I-D.ietf-lisp-alt]) are able to carry version numbers without 411 needing any modification. The same applies to the LISP Map Server 412 ([I-D.ietf-lisp-ms]) which will still work without any change since 413 reserved bits are simply ignored. 415 7. Benefits and case studies for Map-Versioning 417 In the following sections we provide more discussion on various 418 aspects and use of the Map-Versioning. Security observations are 419 instead grouped in Section 9. 421 7.1. Synchronization of different xTRs 423 Map-Versioning does not require additional synchronization mechanism 424 compared to the normal functioning of LISP without Map-Versioning. 425 Clearly all the ETRs have to reply with the same Map-Version number, 426 otherwise there can be an inconsistency that creates additional 427 control traffic, instabilities, traffic disruptions. 429 As an example, let's consider the topology of Figure 1 where ITR A.1 430 of domain A is sending unidirectional traffic to the xTR B of domain 431 B, while xTR A.2 of domain A and xTR B of domain B exchange 432 bidirectional traffic. 434 +-----------------+ +-----------------+ 435 | Domain A | | Domain B | 436 | +---------+ | | 437 | | xTR A.1 |--- | | 438 | +---------+ \ +---------+ | 439 | | -------->| xTR B | | 440 | | -------->| | | 441 | +---------+ / +---------+ | 442 | | xTR A.2 |<-- | | 443 | +---------+ | | 444 | | | | 445 +-----------------+ +-----------------+ 447 Figure 1 449 Obviously in the case of Map-Versioning both xTRs of domain A must 450 use the same value otherwise the xTR of domain B will start to send 451 Map-Requests. 453 The same problem can, however, arise without Map-Versioning. For 454 instance if the two xTRs of domain A send different Loc Status Bits. 455 In this case either the traffic is disrupted, if the xTR B trusts the 456 Locator Status Bits, or it xTR B will start sending Map-Requests to 457 confirm the each change in the reachability. 459 So far, LISP does not provide any specific synchronization mechanism, 460 but assumes that synchronization is provided by configuring the 461 different xTRs consistently. The same applies for Map-Versioning. 463 If in the future any synchronization mechanism is provided, Map- 464 Versioning will take advantage of it automatically since it is 465 included in the Record format, as described in Section 6. 467 7.2. Map-Versioning and unidirectional traffic 469 When using Map-Versioning the LISP specific header carries two Map- 470 Version numbers, for both source and destination mapping. This can 471 raise the question on what will happen in the case of unidirectional 472 flows, like for instance in the case presented in Figure 2, since 473 LISP specification do not mandate for ETR to have a mapping for the 474 source EID. 476 +-----------------+ +-----------------+ 477 | Domain A | | Domain B | 478 | +---------+ +---------+ | 479 | | ITR A |----------->| ETR B | | 480 | +---------+ +---------+ | 481 | | | | 482 +-----------------+ +-----------------+ 484 Figure 2 486 For what concerns the ITR, it is able to put both source and 487 destination version number in the LISP header since the Source Map- 488 Version number is in ITR's database, while the Destination Map- 489 Version number is in ITR's cache. 491 For what concerns the ETR, it simply checks only the Destination Map- 492 Version number in the same way as described in Section 4, ignoring 493 the Source Map-Version number. 495 7.3. Map-Versioning and interworking 497 Map-Versioning works in the context of interworking between LISP and 498 IPv4 and IPv6 ([I-D.ietf-lisp-interworking]) in the following way. 500 The case of proxy-ITR encapsulating packet for LISP sites is 501 basically the same as the unidirectional traffic case presented in 502 the previous section. The same rules can be applied. The only 503 difference that arises is the fact that a proxy-ITR does not have any 504 mapping, since it just encapsulate packets arriving from non-LISP 505 site, thus it has no Source Map-Version. In this case, the proxy-ITR 506 will just put the special value 0 (zero) as Source Map-Version 507 number, while the receiving ETR will ignore the field. 509 7.4. Graceful RLOC shutdown/withdraw 511 Map-Versioning can be even used to perform a graceful shutdown or 512 withdraw of a specific RLOC. This is achieved by simply issuing a 513 new mapping, with an updated Map-Version number, where the specific 514 RLOC to be shut down is withdrawn or announced as unreachable (R bit 515 in the Map Record, see [I-D.ietf-lisp]), but without actually turning 516 it off. 518 Once no more traffic is received by the RLOC, because all sites have 519 updated the mapping, it can be shut down safely. 521 7.5. Map-Version for lightweight LISP implementation 523 The use of Map-Versioning can help in simplifying the implementation 524 of LISP. This comes with the price of not supporting Loc-Status-Bit, 525 which are useful in some contexts. 527 In the current LISP specifications the set of RLOCs must always be 528 maintained ordered and consistent with the content of the Loc Status 529 Bits (see section 6.5 of [I-D.ietf-lisp]). With Map-Versioning such 530 type of mechanisms can be avoided. When a new RLOC is added to a 531 mapping, it is not necessary to "append" new locators to the existing 532 ones as explained in Section 6.5 of [I-D.ietf-lisp]. A new mapping 533 with a new Map-Version number will be issued, and since the old 534 locators are still valid the transition will be disruptionless. The 535 same applies for the case a RLOC is withdrawn. There is no need to 536 maintain holes in the list of locators, as is the case when using 537 Locator Status Bits, for sites that are not using the RLOC that has 538 been withdrawn the transition will be disruptionless. 540 All of these operations, as already stated, do not need to maintain 541 any consistency among Locator Status Bits, and the way RLOC are 542 stored in the cache. This eases implementation. 544 Further, Map-Version can be used to substitute the "clock sweep" 545 operation described in Section 6.5.1 of [I-D.ietf-lisp]. Indeed, 546 every LISP site communicating to a specific LISP site that has 547 updated the mapping will be informed of the available new mapping in 548 a data-driven manner. 550 Note that what proposed in the present section is just a case study 551 and MUST NOT be considered as specification for a lightweight LISP 552 implementation. 554 8. Incremental deployment and implementation status 556 Map-Versioning can be incrementally deployed without any negative 557 impact on existing LISP xTRs. Any LISP element that does not support 558 Map-Versioning can safely ignore them. Further, there is no need of 559 any specific mechanism to discover if an xTR supports or not Map- 560 Versioning. This information is already included in the Map Record. 562 Map-Versioning is currently implemented in OpenLISP 563 [I-D.iannone-openlisp-implementation]. 565 Note that the reference document for LISP implementation and 566 interoperability tests remains [I-D.ietf-lisp]. 568 9. Security Considerations 570 Map-Versioning does not introduces any new security issue concerning 571 both the data-plane and the control-plane. On the contrary, as 572 described in the following, if Map-Versioning is used also to update 573 mappings in case of change in the reachability information (i.e., 574 instead of the Locator Status Bits) it is possible to reduce the 575 effects of some DoS or spoofing attacks that can happen in an 576 untrusted environment. 578 A thorough security analysis of LISP is documented in 579 [I-D.saucez-lisp-security]. 581 9.1. Map-Versioning against traffic disruption 583 An attacker can try to disrupt ongoing communications by creating 584 LISP encapsulated packets with wrong Locator Status Bits. If the xTR 585 blindly trusts the Locator Status Bits it will change the 586 encapsulation accordingly, which can result in traffic disruption. 588 This does not happen in the case of Map-Versioning. As described in 589 Section 4, upon a version number change the xTR first issues a Map- 590 Request. The assumption is that the mapping distribution system is 591 sufficiently secure that Map-Request and Map-Reply messages and their 592 content can be trusted. Security issues concerning specific mapping 593 distribution system are out of the scope of this document. Note also 594 that in the case of Map-Versioning the attacker should "guess" a 595 valid version number that triggers a Map-Request, as described in 596 Section 4, otherwise the packet is simply dropped. 598 Note that a similar level of security can be obtained with Loc Status 599 Bits, by simply making mandatory to verify any change through a Map- 600 Request. However, in this case Locator Status Bits loose their 601 meaning, because, it does not matter anymore which specific bits has 602 changed, the xTR will query the mapping system and trust the content 603 of the received Map-Reply. Furthermore there is no way to perform 604 filtering as in the Map-Versioning in order to drop packets that do 605 not carry a valid Map-Version number. In the case of Locator Status 606 Bits, any random change can trigger a Map-Request (unless rate 607 limitation is enabled which raise another type of attack discussed in 608 Section 9.2). 610 9.2. Map-Versioning against reachability information DoS 612 Attackers can try to trigger a large amount of Map-Request by simply 613 forging packets with random Map-Version or random Locator Status 614 Bits. In both cases the Map-Requests are rate limited as described 615 in [I-D.ietf-lisp]. However, differently from Locator Status Bit 616 where there is no filtering possible, in the case of Map-Versioning 617 is possible to filter not valid version numbers before triggering a 618 Map-Request, thus helping in reducing the effects of DoS attacks. In 619 other words the use of Map-Versioning enables a fine control on when 620 to update a mapping or when to notify that a mapping has been 621 updated. 623 It is clear, that Map-Versioning does not protect against DoS and 624 DDoS attacks, where an xTR looses processing power doing checks on 625 the LISP header of packets sent by attackers. This is independent 626 from Map-Versioning and is the same for Loc Status Bits. 628 10. Acknowledgements 630 The authors would like to thank Pierre Francois, Noel Chiappa, Dino 631 Farinacci for their comments and review. 633 This work has been partially supported by the INFSO-ICT-216372 634 TRILOGY Project (www.trilogy-project.org). 636 11. References 638 11.1. Normative References 640 [I-D.ietf-lisp] 641 Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, 642 "Locator/ID Separation Protocol (LISP)", 643 draft-ietf-lisp-07 (work in progress), April 2010. 645 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 646 Requirement Levels", BCP 14, RFC 2119, March 1997. 648 11.2. Informative References 650 [I-D.iannone-openlisp-implementation] 651 Iannone, L., Saucez, D., and O. Bonaventure, "OpenLISP 652 Implementation Report", 653 draft-iannone-openlisp-implementation-01 (work in 654 progress), July 2008. 656 [I-D.ietf-lisp-alt] 657 Fuller, V., Farinacci, D., Meyer, D., and D. Lewis, "LISP 658 Alternative Topology (LISP+ALT)", draft-ietf-lisp-alt-04 659 (work in progress), April 2010. 661 [I-D.ietf-lisp-interworking] 662 Lewis, D., Meyer, D., Farinacci, D., and V. Fuller, 663 "Interworking LISP with IPv4 and IPv6", 664 draft-ietf-lisp-interworking-00 (work in progress), 665 May 2009. 667 [I-D.ietf-lisp-ms] 668 Fuller, V. and D. Farinacci, "LISP Map Server", 669 draft-ietf-lisp-ms-05 (work in progress), April 2010. 671 [I-D.saucez-lisp-security] 672 Saucez, D., Iannone, L., and O. Bonaventure, "Notes on 673 LISP Security Threats and Requirements", 674 draft-saucez-lisp-security-00 (work in progress), 675 October 2009. 677 Appendix A. Map-Version wrap-around 679 The present section proposes an estimation of the wrap-around time 680 for proposed 12 bits size for the Map-Version Number. Using a 681 granularity of seconds and assuming as worst case that a new version 682 is issued each second, it takes slightly more than 1 hour before the 683 version wraps around. Note that the granularity of seconds is in 684 line with the rate limitation policy for Map-Request messages, as 685 proposed in the LISP main specifications ([I-D.ietf-lisp]). 686 Alternatively a granularity of minutes can also be used, as for the 687 TTL of the Map-Reply ([I-D.ietf-lisp]). Using a granularity of 688 minutes leads to a much longer time before wrap-around. In 689 particular, when using 12 bits, the wrap-around time is almost 3 690 days. 692 For general information, hereafter there is a table with a rough 693 estimation of the time before wrap-around happens considering 694 different sizes of the Map-Version Number and different time 695 granularity. 697 +---------------+--------------------------------------------+ 698 |Version Number | Time before wrap around | 699 | Size (bits) +--------------------------------------------+ 700 | |Granularity: Minutes | Granularity: Seconds | 701 +------------------------------------------------------------+ 702 | 32 | 8171 Years | 136 Years | 703 | 30 | 2042 Years | 34 Years | 704 | 24 | 31 Years | 194 Days | 705 | 16 | 45 Days | 18 Hours | 706 | 15 | 22 Days | 9 Hours | 707 | 14 | 11 Days | 4 Hours | 708 | 13 | 5.6 Days | 2.2 Hours | 709 | 12 | 2.8 Days | 1.1 Hours | 710 +---------------+---------------------+----------------------+ 712 Figure 3: Estimation of time before wrap-around 714 Authors' Addresses 716 Luigi Iannone 717 TU Berlin - Deutsche Telekom Laboratories AG 718 Ernst-Reuter Platz 7 719 Berlin 720 Germany 722 Email: luigi@net.t-labs.tu-berlin.de 724 Damien Saucez 725 Universite catholique de Louvain 726 Place St. Barbe 2 727 Louvain la Neuve 728 Belgium 730 Email: damien.saucez@uclouvain.be 732 Olivier Bonaventure 733 Universite catholique de Louvain 734 Place St. Barbe 2 735 Louvain la Neuve 736 Belgium 738 Email: olivier.bonaventure@uclouvain.be