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Iannone 3 Internet-Draft TU Berlin - Deutsche Telekom 4 Intended status: Experimental Laboratories AG 5 Expires: September 12, 2011 D. Saucez 6 O. Bonaventure 7 Universite catholique de Louvain 8 March 11, 2011 10 LISP Map-Versioning 11 draft-ietf-lisp-map-versioning-01.txt 13 Abstract 15 This document describes the LISP Map-Versioning mechanism, which 16 provides in-packet information about EID-to-RLOC mappings used to 17 encapsulate LISP data packets. The proposed approach is based on 18 associating a version number to EID-to-RLOC mappings and transport 19 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 modifications of the mappings used to 22 encapsulate packets. The mechanism is transparent to legacy 23 implementations, since in the LISP-specific header and in the Map 24 Records, bits used for Map-Versioning can be safely ignored by xTRs 25 that do not support the mechanism. 27 Status of this Memo 29 This Internet-Draft is submitted to IETF in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF), its areas, and its working groups. Note that 34 other groups may also distribute working documents as Internet- 35 Drafts. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 The list of current Internet-Drafts can be accessed at 43 http://www.ietf.org/ietf/1id-abstracts.txt. 45 The list of Internet-Draft Shadow Directories can be accessed at 46 http://www.ietf.org/shadow.html. 48 This Internet-Draft will expire on September 12, 2011. 50 Copyright Notice 52 Copyright (c) 2011 IETF Trust and the persons identified as the 53 document authors. All rights reserved. 55 This document is subject to BCP 78 and the IETF Trust's Legal 56 Provisions Relating to IETF Documents 57 (http://trustee.ietf.org/license-info) in effect on the date of 58 publication of this document. Please review these documents 59 carefully, as they describe your rights and restrictions with respect 60 to this document. Code Components extracted from this document must 61 include Simplified BSD License text as described in Section 4.e of 62 the Trust Legal Provisions and are provided without warranty as 63 described in the BSD License. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 68 2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 5 69 3. Definitions of Terms . . . . . . . . . . . . . . . . . . . . . 5 70 4. EID-to-RLOC Map-Version number . . . . . . . . . . . . . . . . 5 71 4.1. The Null Map-Version . . . . . . . . . . . . . . . . . . . 6 72 5. Dealing with Map-Version numbers . . . . . . . . . . . . . . . 7 73 5.1. Handling Destination Map-Version number . . . . . . . . . 7 74 5.2. Handling Source Map-Version number . . . . . . . . . . . . 9 75 6. LISP header and Map-Version numbers . . . . . . . . . . . . . 10 76 7. Map Record and Map-Version . . . . . . . . . . . . . . . . . . 11 77 8. Benefits and case studies for Map-Versioning . . . . . . . . . 12 78 8.1. Synchronization of different xTRs . . . . . . . . . . . . 12 79 8.2. Map-Versioning and unidirectional traffic . . . . . . . . 13 80 8.3. Map-Versioning and interworking . . . . . . . . . . . . . 13 81 8.3.1. Map-Versioning and Proxy-ITRs . . . . . . . . . . . . 14 82 8.3.2. Map-Versioning and LISP-NAT . . . . . . . . . . . . . 14 83 8.3.3. Map-Versioning and Proxy-ETRs . . . . . . . . . . . . 14 84 8.4. RLOC shutdown/withdraw . . . . . . . . . . . . . . . . . . 15 85 8.5. Map-Version for lightweight LISP implementation . . . . . 15 86 9. Incremental deployment and implementation status . . . . . . . 16 87 10. Security Considerations . . . . . . . . . . . . . . . . . . . 16 88 10.1. Map-Versioning against traffic disruption . . . . . . . . 17 89 10.2. Map-Versioning against reachability information DoS . . . 17 90 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 91 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18 92 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18 93 13.1. Normative References . . . . . . . . . . . . . . . . . . . 18 94 13.2. Informative References . . . . . . . . . . . . . . . . . . 18 95 Appendix A. Estimation of time before Map-Version wrap-around . . 19 96 Appendix B. Document Change Log . . . . . . . . . . . . . . . . . 20 97 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21 99 1. Introduction 101 This document describes the Map-Versioning mechanism used to provide 102 information on changes in the EID-to-RLOC mappings used in the LISP 103 ([I-D.ietf-lisp]) context to perform packet encapsulation. The 104 mechanism is totally transparent to xTRs not supporting such 105 functionality. It is not meant to replace any existing LISP 106 mechanism, but rather to complete them providing new functionalities. 107 The basic mechanism is to associate a Map-Version number to each LISP 108 EID-to-RLOC mapping and transport such a version number in the LISP- 109 specific header. When a mapping changes, a new version number is 110 assigned to the updated mapping. A change in an EID-to-RLOC mapping 111 can be a change in the RLOCs set, by adding or removing one or more 112 RLOCs, but it can also be a change in the priority or weight of one 113 or more RLOCs. 115 When Map-Versioning is used, LISP-encapsulated data packets contain 116 the version number of the two mappings used to select the RLOCs in 117 the outer header (i.e., both source and destination). These version 118 numbers are encoded in the 24 low-order bits of the first longword of 119 the LISP header and indicated by a specific bit in the flags (first 8 120 high-order bits of the first longword of the LISP header). Note that 121 not all packets need to carry version numbers. 123 When an ITR encapsulates a data packet, with a LISP header containing 124 the Map-Version numbers, it puts in the LISP-specific header two 125 version numbers: 127 1. The version number assigned to the mapping (contained in the EID- 128 to-RLOC Database) used to select the source RLOC. 130 2. The version number assigned to the mapping (contained in the EID- 131 to-RLOC Cache) used to select the destination RLOC. 133 This operation is two-fold. On the one hand, it enables the ETR 134 receiving the packet to know if the ITR has the latest version number 135 that any ETR at the destination EID site has provided to the ITR in a 136 Map-Reply. If it is not the case the ETR can send to the ITR a Map- 137 Request containing the updated mapping or soliciting a Map-Request 138 from the ITR (both cases are already defined in [I-D.ietf-lisp]). In 139 this way the ITR can update its cache. On the other hand, it enables 140 an ETR receiving such a packet to know if it has in its EID-to-RLOC 141 Cache the latest mapping for the source EID (in case of bidirectional 142 traffic). If it is not the case a Map-Request can be send. 144 2. Requirements Notation 146 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 147 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 148 document are to be interpreted as described in [RFC2119]. 150 3. Definitions of Terms 152 The present document uses terms already defined in main LISP 153 specification [I-D.ietf-lisp]. Hereafter are defined only the terms 154 that are specific to the Map-Versioning mechanism. 156 Map-Version number: An unsigned 12-bits assigned to an EID-to-RLOC 157 mapping, not including the value 0 (0x000). 159 Null Map-Version: The 12-bits null value of 0 (0x000) is not used as 160 Map-Version number. It is used to signal that no Map-Version 161 number is assigned to the EID-to-RLOC mapping. 163 Source Map-Version number: Map-Version number of the EID-to-RLOC 164 mapping used to select the source address (RLOC) of the outer IP 165 header of LISP-encapsulated packets. 167 Destination Map-Version number: Map-Version number of the EID-to- 168 RLOC mapping used to select the destination address (RLOC) of the 169 outer IP header of LISP-encapsulated packets. 171 4. EID-to-RLOC Map-Version number 173 The EID-to-RLOC Map-Version number consists in an unsigned 12-bits 174 integer. The version number is assigned in a per-mapping fashion, 175 meaning that different mappings will have assigned a different 176 version number, which is also updated independently. An update in 177 the version number (i.e., a newer version) consist in incrementing by 178 one the older version number. Appendix A contains a rough estimation 179 of the wrap-around time for the Map-Version number. 181 The space of version numbers has a circular order where half of the 182 version numbers is greater than the current Map-Version number and 183 the other half is smaller than current Map-Version number. In a more 184 formal way, assuming we have two version numbers V1 and V2 and that 185 the numbers are expressed on N bits, the following three cases may 186 happen: 188 V1 = V2 : This is the exact match case. 190 V1 < V2 : True if and only if V1 < V2 < (V1 + 2**(N-1)). 192 V1 > V2 : True if and only if V1 > V2 > (V1 - 2**(N-1)). 194 Using 12 bits, as defined in this document, and assuming a Map- 195 Version value of 69, Map-Version numbers in the range [70; 69 + 2047] 196 are greater than 69, while Map-Version numbers in the range [69 + 197 2048; (69 + 4095) mod 4096] are smaller than 69. 199 The initial Map-Version number of a new EID-to-RLOC mapping SHOULD be 200 randomly generated. However, it MUST NOT be set to the Null Map- 201 Version value (0x000), because it has a special meaning (see 202 Section 4.1). 204 4.1. The Null Map-Version 206 The value 0x000 (zero) is not a valid Map-Version number indicating 207 the version of the EID-to-RLOC mapping. Such a value is used for 208 special purposes and is named the Null Map-Version number. 210 The Null Map-Version MAY appear in the LISP specific header as either 211 Source Map-Version number (cf. Section 5.2) or Destination Map- 212 Version number (cf. Section 5.1). When the Source Map-Version number 213 is set to the Null Map-version value it means that no map version 214 information is conveyed for the source site. This means that if a 215 mapping exists for the source EID in the EID-to-RLOC Cache, then the 216 ETR MUST NOT compare the received Null Map-Version with the content 217 of the EID-to-RLOC cache. When the Destination Map-version number is 218 set to the Null Map-version value it means that no map version 219 information is conveyed for the destination site. This means that 220 the ETR MUST NOT compare the value with the Map-Version number of the 221 mapping for the destination EID present in the EID-to-RLOC Database. 223 The other use of the Null Map-Version number is in the Map Records, 224 which are part of the Map-Request, Map-Reply and Map-Register 225 messages (defined in [I-D.ietf-lisp]). Map Records that have a Null 226 Map-Version number indicate that there is no Map-Version number 227 associated with the mapping. This means that LISP encapsulated 228 packets, destined to the EID-Prefix the Map Record refers to, MUST 229 NOT contain Map-Version numbers (i.e., V bit MUST always be 0). In 230 other words, the Null Map-Version number signals to the ITR using the 231 mapping that the Map-Versioning is not supported, or even if 232 supported it MUST NOT be used for that specific EID-Prefix. Any 233 value different from zero means that Map-Versioning is supported and 234 MAY be used. 236 The fact that the 0 value has a special meaning for the Map-Version 237 number implies that, when updating a Map-Version number because of a 238 change in the mapping, if the next value is 0 then Map-Version number 239 MUST be incremented by 2 (i.e., set to 1, which is the next valid 240 value). 242 5. Dealing with Map-Version numbers 244 The main idea of using Map-Version numbers is that whenever there is 245 a change in the mapping (e.g., adding/removing RLOCs, a change in the 246 weights due to TE policies, or a change in the priorities) or an ISP 247 realizes that one or more of its own RLOCs are not reachable anymore 248 from a local perspective (e.g., through IGP, or policy changes) the 249 ISP updates the mapping also assigning a new Map-Version number. 251 In order to announce in a data-driven fashion that the mapping has 252 been updated, Map-Version numbers used to create the outer IP header 253 of the LISP-encapsulated packet are embedded in the LISP-specific 254 header. This means that the header needs to contain two Map-Version 255 numbers: 257 o The Source Map-Version number of the EID-to-RLOC mapping in the 258 EID-to-RLOC Database used to select the source RLOC. 260 o The Destination Map-Version number of the EID-to-RLOC mapping in 261 the EID-to-RLOC Cache used to select the destination RLOC. 263 By embedding both Source Map-Version number and Destination Map- 264 Version number an ETR receiving a LISP packet with Map-Version 265 numbers, can perform the following checks: 267 1. The ITR that has sent the packet has an up-to-date mapping in its 268 cache for the destination EID and is performing encapsulation 269 correctly. 271 2. In case of bidirectional traffic, the mapping in the local ETR 272 EID-to-RLOC cache for the source EID is up-to-date. 274 If one or both of the above conditions do not hold, the ETR can send 275 a Map-Request either to make the ITR aware that a new mapping is 276 available (see Section 5.1) or to update the mapping in the local 277 cache (see Section 5.2). 279 5.1. Handling Destination Map-Version number 281 When an ETR receives a packet, the Destination Map-Version number 282 relates to the mapping for the destination EID for which the ETR is a 283 RLOC. This mapping is part of the ETR EID-to-RLOC Database. Since 284 the ETR is authoritative for the mapping, it has the correct and up- 285 to-date Destination Map-Version number. A check on this version 286 number can be done, where the following cases can arise: 288 1. The packets arrive with the same Destination Map-Version number 289 stored in the EID-to-RLOC Database. This is the regular case. 290 The ITR sending the packet has in its EID-to-RLOC Cache an up-to- 291 date mapping. No further actions are needed. 293 2. The packet arrives with a Destination Map-Version number greater 294 (i.e., newer) than the one stored in the EID-to-RLOC Database. 295 Since the ETR is authoritative on the mapping, this means that 296 someone is not behaving correctly w.r.t. the specifications, thus 297 the packet carries a not valid version number and SHOULD be 298 silently dropped. 300 3. The packets arrive with a Destination Map-Version number smaller 301 (i.e., older) than the one stored in the EID-to-RLOC Database. 302 This means that the ITR sending the packet has an old mapping in 303 its EID-to-RLOC Cache containing stale information. The ITR 304 sending the packet has to be informed that a newer mapping is 305 available. This is done with a Map-Request message sent back to 306 the ITR. The Map-Request will either trigger a Map-Request back 307 using the SMR bit or it will piggyback the newer mapping. These 308 are not new mechanisms; how to SMR or piggyback mappings in Map- 309 Request messages is already described in [I-D.ietf-lisp], while 310 their security is discussed in [I-D.saucez-lisp-security]. These 311 Map-Request messages should be rate limited (rate limitation 312 policies are also described in [I-D.ietf-lisp]). The feature 313 introduced by Map-Version numbers is the possibility of blocking 314 traffic from ITRs not using the latest mapping. Indeed, after a 315 certain number of retries, if the Destination Map-Version number 316 in the packets is not updated, the ETR MAY silently drop packets 317 with a stale Map-Version number. This because either the ITR is 318 refusing to use the mapping for which the ETR is authoritative or 319 (worse) it might be some form of attack. 321 The rule in the third case MAY be more restrictive. If the mapping 322 has been the same for a period of time as long as the TTL (defined in 323 [I-D.ietf-lisp]) of the previous version of the mapping, all packets 324 arriving with an old Map-Version SHOULD be silently dropped right 325 away without issuing any Map-Request. The reason that allows such 326 action is the fact that if the new mapping with the updated version 327 number has been unchanged for at least the same time as the TTL of 328 the older mapping, all the entries in the caches of ITRs must have 329 expired. Hence, all ITRs sending traffic should have refreshed the 330 mapping according to [I-D.ietf-lisp]. If packets with old Map- 331 Version number are still received, then either someone has not 332 respected the TTL, or it is a form of spoof/attack. In both cases 333 this is not valid behavior w.r.t. the specifications and the packet 334 SHOULD be silently dropped. 336 LISP-encapsulated packets with the V-bit set, when the original 337 mapping in the EID-to-RLOC Database has version number set to the 338 Null Map-Version value, MAY be silently dropped. As explained in 339 Section 4.1, if an EID-to-RLOC mapping has a Null Map-Version, it 340 means that ITRs, using the mapping for encapsulation, MUST NOT use 341 Map-Version number in the LISP-specific header. 343 For LISP-encapsulated packets with the V-bit set, when the original 344 mapping in the EID-to-RLOC Database has version number set to a value 345 different from the Null Map-Version value, a Destination Map-Version 346 number equal to the Null Map-Version value means that the Destination 347 Map-Version number MUST be ignored. 349 5.2. Handling Source Map-Version number 351 When an ETR receives a packet, the Source Map-Version number relates 352 to the mapping for the source EID for which the ITR that sent the 353 packet is authoritative. If the ETR has an entry in its EID-to-RLOC 354 Cache for the source EID, then a check can be performed and the 355 following cases can arise: 357 1. The packet arrives with the same Source Map-Version number stored 358 in the EID-to-RLOC Cache. This is the correct regular case. The 359 ITR has in its cache an up-to-date copy of the mapping. No 360 further actions are needed. 362 2. The packet arrives with a Source Map-Version number greater 363 (i.e., newer) than the one stored in the local EID-to-RLOC Cache. 364 This means that ETR has in its cache a mapping that is stale and 365 needs to be updated. A Map-Request SHOULD be sent to get the new 366 mapping for the source EID. This is a normal Map-Request message 367 sent through the mapping system and MUST respect the 368 specifications in [I-D.ietf-lisp], including rate limitation 369 policies. 371 3. The packet arrives with a Source Map-Version number smaller 372 (i.e., older) than the one stored in the local EID-to-RLOC Cache. 373 Such a case is not valid w.r.t. the specifications. Indeed, if 374 the mapping is already present in the EID-to-RLOC Cache, this 375 means that an explicit Map-Request has been sent and a Map-Reply 376 has been received from an authoritative source. Assuming that 377 the mapping system is not corrupted anyhow, the Map-Version in 378 the EID-to-RLOC Cache is the correct one and the packet MAY be 379 silently dropped. 381 If the ETR does not have an entry in the EID-to-RLOC Cache for the 382 source EID (e.g., in case of unidirectional traffic) then the Source 383 Map-Version number can be safely ignored. 385 For LISP-encapsulated packets with the V-bit set, if the Source Map- 386 Version number is the Null Map-Version value, it means that the 387 Source Map-Version number MUST be ignored. 389 6. LISP header and Map-Version numbers 391 In order for the versioning approach to work, the LISP specific 392 header has to carry both Source Map-Version number and Destination 393 Map-Version number. This is done by setting the V-bit in the LISP 394 specific header. When the V-bit is set the low-order 24-bits of the 395 first longword (which usually contains the nonce) are used to 396 transport both source and destination Map-Version numbers. In 397 particular the first 12 bits are used for Source Map-Version number 398 and the second 12 bits for the Destination Map-Version number. 400 Hereafter is the example of LISP header carrying version numbers in 401 the case of IPv4-in-IPv4 encapsulation. The same setting can be used 402 for any other case (IPv4-in-IPv6, IPv6-in-IPv4, and IPv6-in-IPv6). 404 0 1 2 3 405 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 1 406 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 407 / |N|L|E|V|I|flags| Source Map-Version |Destination Map-Version| 408 LISP+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 409 \ | Instance ID/Locator Status Bits | 410 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 412 Source Map-Version number (12 bits): Map-Version of the mapping used 413 by the ITR to select the RLOC present in the "Source Routing 414 Locator" field. How to set on transmission and handle on 415 reception this value is described in Section 5.2. 417 Destination Map-Version number (12 bits): Map-Version of the mapping 418 used by the ITR to select the RLOC present in the "Destination 419 Routing Locator" field. How to set on transmission and handle on 420 reception this value is described in Section 5.1. 422 The present document just specifies how to use the low-order 24-bits 423 of the first longword of the LISP-specific header when the V-bit is 424 set to 1. All other cases, including the bit fields of the rest of 425 the LISP-specific header and the whole LISP packet format are 426 specified in [I-D.ietf-lisp]. Not all of the LISP encapsulated 427 packets need to carry version numbers. When Map-Version numbers are 428 carried the V-bit MUST be set to 1. All legal combinations of the 429 flags, when the V-bit is set to 1, are described in [I-D.ietf-lisp]. 431 7. Map Record and Map-Version 433 To accommodate the proposed mechanism, the Map Records that are 434 transported on Map-Request/Map-Reply/Map-Register messages need to 435 carry the Map-Version number as well. For this purpose the 12-bits 436 before the EID-AFI field in the Record that describe a mapping is 437 used. This is defined in [I-D.ietf-lisp] and reported here as 438 example. 440 0 1 2 3 441 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 1 442 +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 443 | | Record TTL | 444 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 445 R | Locator Count | EID mask-len | ACT |A| Reserved | 446 e +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 447 c | Rsvd | Map-Version Number | EID-AFI | 448 o +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 449 r | EID-prefix | 450 d +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 451 | /| Priority | Weight | M Priority | M Weight | 452 | L +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 453 | o | Unused Flags |L|p|R| Loc-AFI | 454 | c +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 455 | \| Locator | 456 +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 458 Map-Version Number: Map-Version of the mapping contained in the 459 Record. As explained in Section 4.1 this field can be zero (0), 460 meaning that no Map-Version is associated to the mapping, hence 461 packets that are LISP-encapsulated using this mapping MUST NOT 462 contain Map-Version numbers in the LISP specific header and the 463 V-bit MUST be set to 0. 465 This packet format works perfectly with xTRs that do not support Map- 466 Versioning, since they can simply ignore those bits. Furthermore, 467 existing and future mapping distribution protocol (e.g., ALT 468 [I-D.ietf-lisp-alt]) are able to carry version numbers without 469 needing any modification. The same applies to the LISP Map Server 470 ([I-D.ietf-lisp-ms]), which will still work without any change since 471 reserved bits are simply ignored. 473 8. Benefits and case studies for Map-Versioning 475 In the following sections we provide more discussion on various 476 aspects and use of the Map-Versioning. Security observations are 477 instead grouped in Section 10. 479 8.1. Synchronization of different xTRs 481 Map-Versioning does not require additional synchronization mechanism 482 compared to the normal functioning of LISP without Map-Versioning. 483 Clearly all the ETRs have to reply with the same Map-Version number, 484 otherwise there can be an inconsistency that creates additional 485 control traffic, instabilities, traffic disruptions. It is the same 486 without Map-Versioning, with ETRs that have to reply with the same 487 mapping, otherwise the same problems can arise. 489 As an example, let's consider the topology of Figure 1 where ITR A.1 490 of domain A is sending unidirectional traffic to the domain B, while 491 A.2 of domain A exchange bidirectional traffic with domain B. In 492 particular, ITR A.2 send traffic to ETR B and ETR A.2 receives 493 traffic from ITR B. 495 +-----------------+ +-----------------+ 496 | Domain A | | Domain B | 497 | +---------+ | | 498 | | ITR A.1 |--- | | 499 | +---------+ \ +---------+ | 500 | | ------->| ETR B | | 501 | | ------->| | | 502 | +---------+ / | | | 503 | | ITR A.2 |--- -----| ITR B | | 504 | | | / +---------+ | 505 | | ETR A.2 |<----- | | 506 | +---------+ | | 507 | | | | 508 +-----------------+ +-----------------+ 510 Figure 1 512 Obviously in the case of Map-Versioning both ITR A.1 and ITR A.2 of 513 domain A must use the same value otherwise the ETR of domain B will 514 start to send Map-Requests. 516 The same problem can, however, arise without Map-Versioning. For 517 instance, if the two ITRs of domain A send different Loc Status Bits. 518 In this case either the traffic is disrupted, if the ETR B trusts the 519 Locator Status Bits, or if ETR B does not trusts the Locator Status 520 Bits it will start sending Map-Requests to confirm the each change in 521 the reachability. 523 So far, LISP does not provide any specific synchronization mechanism, 524 but assumes that synchronization is provided by configuring the 525 different xTRs consistently. The same applies for Map-Versioning. 526 If in the future any synchronization mechanism is provided, Map- 527 Versioning will take advantage of it automatically since it is 528 included in the Record format, as described in Section 7. 530 8.2. Map-Versioning and unidirectional traffic 532 When using Map-Versioning the LISP specific header carries two Map- 533 Version numbers, for both source and destination mappings. This can 534 raise the question on what will happen in the case of unidirectional 535 flows, like for instance in the case presented in Figure 2, since 536 LISP specification do not mandate for ETR to have a mapping for the 537 source EID. 539 +-----------------+ +-----------------+ 540 | Domain A | | Domain B | 541 | +---------+ +---------+ | 542 | | ITR A |----------->| ETR B | | 543 | +---------+ +---------+ | 544 | | | | 545 +-----------------+ +-----------------+ 547 Figure 2 549 For what concerns the ITR, it is able to put both source and 550 destination version number in the LISP header since the Source Map- 551 Version number is in ITR's database, while the Destination Map- 552 Version number is in ITR's cache. 554 For what concerns the ETR, it simply checks only the Destination Map- 555 Version number in the same way as described in Section 5, ignoring 556 the Source Map-Version number. 558 8.3. Map-Versioning and interworking 560 Map-Versioning is compatible with the LISP interworking between LISP 561 and non-LISP sites as defined in [I-D.ietf-lisp-interworking]. LISP 562 interworking defines three techniques to make LISP sites and non-LISP 563 sites, namely Proxy-ITR, LISP-NAT, and Proxy-ETR. Hereafter it is 564 described how Map-Versioning relates to these three mechanisms. 566 8.3.1. Map-Versioning and Proxy-ITRs 568 The purpose of the Proxy-ITR (PITR) is to encapsulate traffic 569 originating in a non-LISP site in order to deliver the packet to one 570 of the ETRs of the LISP site (cf. Figure 3). This case is very 571 similar to the unidirectional traffic case described in Section 8.2, 572 hence similar rules apply. 574 +----------+ +-------------+ 575 | LISP | | non-LISP | 576 | Domain A | | Domain B | 577 | +-------+ +-----------+ | | 578 | | ETR A |<-------| Proxy ITR |<-------| | 579 | +-------+ +-----------+ | | 580 | | | | 581 +----------+ +-------------+ 583 Figure 3 585 The main difference is that a Proxy-ITR does not have any mapping, 586 since it just encapsulate packets arriving from non-LISP site, thus 587 cannot provide a Source Map-Version. In this case, the proxy-ITR 588 will just put the Null Map-Version value as Source Map-Version 589 number, while the receiving ETR will ignore the field. 591 With this setup the LISP Domain A is able to check whether or not the 592 PITR is using the latest mapping. If this is not the case the 593 mapping for LISP Domain A on the PITR can be updated using one of the 594 mechanisms defined in [I-D.ietf-lisp] and 595 [I-D.ietf-lisp-interworking]. 597 8.3.2. Map-Versioning and LISP-NAT 599 The LISP-NAT mechanism is based on address translation from non- 600 routable EIDs to routable EIDs and does not involve any form of 601 encapsulation. As such Map-Versioning does not apply in this case. 603 8.3.3. Map-Versioning and Proxy-ETRs 605 The purpose of the Proxy-ETR (PETR) is to decapsulate traffic 606 originating in a LISP site in order to deliver the packet to the non- 607 LISP site (cf. Figure 4). One of the main reasons of deploy PETRs is 608 to bypass uRPF (Unicast Reverse Path Forwarding) checks on the 609 provider edge. 611 +----------+ +-------------+ 612 | LISP | | non-LISP | 613 | Domain A | | Domain B | 614 | +-------+ +-----------+ | | 615 | | ITR A |------->| Proxy ETR |------->| | 616 | +-------+ +-----------+ | | 617 | | | | 618 +----------+ +-------------+ 620 Figure 4 622 A Proxy-ETR does not have any mapping, since it just decapsulate 623 packets arriving from LISP site. In this case, the ITR will just put 624 the Null Map-Version value as Destination Map-Version number, while 625 the receiving Proxy-ETR will ignore the field. 627 With this setup the Proxy-ETR is able to check whether or not the 628 mapping has changed. If this is the case the mapping for LISP Domain 629 A on the PETR can be updated using one of the mechanisms defined in 630 [I-D.ietf-lisp] and [I-D.ietf-lisp-interworking]. 632 8.4. RLOC shutdown/withdraw 634 Map-Versioning can be even used to perform a graceful shutdown or 635 withdraw of a specific RLOC. This is achieved by simply issuing a 636 new mapping, with an updated Map-Version number, where the specific 637 RLOC to be shut down is withdrawn or announced as unreachable (R bit 638 in the Map Record, see [I-D.ietf-lisp]), but without actually turning 639 it off. 641 Once no more traffic is received by the RLOC, because all sites have 642 updated the mapping, it can be shut down safely. 644 It should be pointed out that for frequent up/down changes such a 645 mechanism should not be used since this can generate excessive load 646 on the Mapping System. 648 8.5. Map-Version for lightweight LISP implementation 650 The use of Map-Versioning can help in developing a lightweight 651 implementation of LISP. This comes with the price of not supporting 652 Loc-Status-Bit, which are useful in some contexts. 654 In the current LISP specifications the set of RLOCs must always be 655 maintained ordered and consistent with the content of the Loc Status 656 Bits (see section 6.5 of [I-D.ietf-lisp]). With Map-Versioning such 657 type of mechanisms can be avoided. When a new RLOC is added to a 658 mapping, it is not necessary to "append" new locators to the existing 659 ones as explained in Section 6.5 of [I-D.ietf-lisp]. A new mapping 660 with a new Map-Version number will be issued, and since the old 661 locators are still valid the transition will be with no disruptions. 662 The same applies for the case a RLOC is withdrawn. There is no need 663 to maintain holes in the list of locators, as is the case when using 664 Locator Status Bits, for sites that are not using the RLOC that has 665 been withdrawn the transition will be with no disruptions. 667 All of these operations, as already stated, do not need to maintain 668 any consistency among Locator Status Bits, and the way RLOC are 669 stored in the cache. 671 Further, Map-Version can be used to substitute the "clock sweep" 672 operation described in Section 6.5.1 of [I-D.ietf-lisp]. Indeed, 673 every LISP site communicating to a specific LISP site that has 674 updated the mapping will be informed of the available new mapping in 675 a data-driven manner. 677 Note that what proposed in the present section is just a case study 678 and MUST NOT be considered as specification for a lightweight LISP 679 implementation. 681 9. Incremental deployment and implementation status 683 Map-Versioning can be incrementally deployed without any negative 684 impact on existing LISP elements (e.g., xTRs, Map-Servers, Proxy- 685 ITRs, etc). Any LISP element that does not support Map-Versioning 686 can safely ignore them. Further, there is no need of any specific 687 mechanism to discover if an xTR supports or not Map-Versioning. This 688 information is already included in the Map Record. 690 Map-Versioning is currently implemented in OpenLISP 691 [I-D.iannone-openlisp-implementation]. 693 Note that the reference document for LISP implementation and 694 interoperability tests remains [I-D.ietf-lisp]. 696 10. Security Considerations 698 Map-Versioning does not introduce any new security issue concerning 699 both the data-plane and the control-plane. On the contrary, as 700 described in the following, if Map-Versioning may be used also to 701 update mappings in case of change in the reachability information 702 (i.e., instead of the Locator Status Bits) it is possible to reduce 703 the effects of some DoS or spoofing attacks that can happen in an 704 untrusted environment. 706 A thorough security analysis of LISP is documented in 707 [I-D.saucez-lisp-security]. 709 10.1. Map-Versioning against traffic disruption 711 An attacker can try to disrupt ongoing communications by creating 712 LISP encapsulated packets with wrong Locator Status Bits. If the xTR 713 blindly trusts the Locator Status Bits it will change the 714 encapsulation accordingly, which can result in traffic disruption. 716 This does not happen in the case of Map-Versioning. As described in 717 Section 5, upon a version number change the xTR first issues a Map- 718 Request. The assumption is that the mapping distribution system is 719 sufficiently secure that Map-Request and Map-Reply messages and their 720 content can be trusted. Security issues concerning specific mapping 721 distribution system are out of the scope of this document. In the 722 case of Map-Versioning the attacker should "guess" a valid version 723 number that triggers a Map-Request, as described in Section 5, 724 otherwise the packet is simply dropped. Nevertheless, guessing a 725 version number that generates a Map-Request is easy, hence it is 726 important to follow the rate limitations policies described in 727 [I-D.ietf-lisp] in order to avoid DoS attacks. 729 Note that a similar level of security can be obtained with Loc Status 730 Bits, by simply making mandatory to verify any change through a Map- 731 Request. However, in this case Locator Status Bits loose their 732 meaning, because, it does not matter anymore which specific bits has 733 changed, the xTR will query the mapping system and trust the content 734 of the received Map-Reply. Furthermore there is no way to perform 735 filtering as in the Map-Versioning in order to drop packets that do 736 not carry a valid Map-Version number. In the case of Locator Status 737 Bits, any random change can trigger a Map-Request (unless rate 738 limitation is enabled which raise another type of attack discussed in 739 Section 10.2). 741 10.2. Map-Versioning against reachability information DoS 743 Attackers can try to trigger a large amount of Map-Request by simply 744 forging packets with random Map-Version or random Locator Status 745 Bits. In both cases the Map-Requests are rate limited as described 746 in [I-D.ietf-lisp]. However, differently from Locator Status Bit 747 where there is no filtering possible, in the case of Map-Versioning 748 is possible to filter not valid version numbers before triggering a 749 Map-Request, thus helping in reducing the effects of DoS attacks. In 750 other words the use of Map-Versioning enables a fine control on when 751 to update a mapping or when to notify that a mapping has been 752 updated. 754 It is clear, that Map-Versioning does not protect against DoS and 755 DDoS attacks, where an xTR looses processing power doing checks on 756 the LISP header of packets sent by attackers. This is independent 757 from Map-Versioning and is the same for Loc Status Bits. 759 11. IANA Considerations 761 This document has no actions for IANA. 763 12. Acknowledgements 765 The authors would like to thank Pierre Francois, Noel Chiappa, Dino 766 Farinacci for their comments and review. 768 This work has been partially supported by the INFSO-ICT-216372 769 TRILOGY Project (www.trilogy-project.org). 771 13. References 773 13.1. Normative References 775 [I-D.ietf-lisp] 776 Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, 777 "Locator/ID Separation Protocol (LISP)", 778 draft-ietf-lisp-10 (work in progress), March 2011. 780 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 781 Requirement Levels", BCP 14, RFC 2119, March 1997. 783 13.2. Informative References 785 [I-D.iannone-openlisp-implementation] 786 Iannone, L., Saucez, D., and O. Bonaventure, "OpenLISP 787 Implementation Report", 788 draft-iannone-openlisp-implementation-01 (work in 789 progress), July 2008. 791 [I-D.ietf-lisp-alt] 792 Fuller, V., Farinacci, D., Meyer, D., and D. Lewis, "LISP 793 Alternative Topology (LISP+ALT)", draft-ietf-lisp-alt-06 794 (work in progress), March 2011. 796 [I-D.ietf-lisp-interworking] 797 Lewis, D., Meyer, D., Farinacci, D., and V. Fuller, 798 "Interworking LISP with IPv4 and IPv6", 799 draft-ietf-lisp-interworking-02 (work in progress), 800 March 2011. 802 [I-D.ietf-lisp-ms] 803 Fuller, V. and D. Farinacci, "LISP Map Server", 804 draft-ietf-lisp-ms-07 (work in progress), March 2011. 806 [I-D.saucez-lisp-security] 807 Saucez, D., Iannone, L., and O. Bonaventure, "LISP 808 Security Threats", draft-saucez-lisp-security-03 (work in 809 progress), March 2011. 811 Appendix A. Estimation of time before Map-Version wrap-around 813 The present section proposes an estimation of the wrap-around time 814 for the proposed 12 bits size for the Map-Version number. Using a 815 granularity of seconds and assuming as worst-case that a new version 816 is issued each second, it takes slightly more than 1 hour before the 817 version wraps around. Note that the granularity of seconds is in 818 line with the rate limitation policy for Map-Request messages, as 819 proposed in the LISP main specifications ([I-D.ietf-lisp]). 820 Alternatively a granularity of minutes can also be used, as for the 821 TTL of the Map-Reply ([I-D.ietf-lisp]). In this case the worst 822 scenario is when a new version is issued every minute, leading to a 823 much longer time before wrap-around. In particular, when using 12 824 bits, the wrap-around time is almost 3 days. 826 For general information, hereafter there is a table with a rough 827 estimation of the time before wrap-around in the worst-case scenario, 828 considering different sizes (bits length) of the Map-Version number 829 and different time granularity. 831 +---------------+--------------------------------------------+ 832 |Version Number | Time before wrap around | 833 | Size (bits) +---------------------+----------------------+ 834 | |Granularity: Minutes | Granularity: Seconds | 835 | | (mapping changes | (mapping changes | 836 | | every 1 minute) | every 1 second) | 837 +-------------------------------------+----------------------+ 838 | 32 | 8171 Years | 136 Years | 839 | 30 | 2042 Years | 34 Years | 840 | 24 | 31 Years | 194 Days | 841 | 16 | 45 Days | 18 Hours | 842 | 15 | 22 Days | 9 Hours | 843 | 14 | 11 Days | 4 Hours | 844 | 13 | 5.6 Days | 2.2 Hours | 845 | 12 | 2.8 Days | 1.1 Hours | 846 +---------------+---------------------+----------------------+ 848 Figure 5: Estimation of time before wrap-around 850 Appendix B. Document Change Log 852 o Version 01 Posted March 2011. 854 * Changed the wording from "Map-Version number 0" to "Null Map- 855 Version. 857 * Clarification of the use of the Null Map-Version value as 858 Source Map-Version Number and Destination Map-Version Number. 860 * Extended the section describing Map-Versioning and LISP 861 Interworking co-existence. 863 * Reduce packet format description to avoid double definitions 864 with the main specs. 866 o Version 00 Posted September 2010. 868 * Added Section "Definitions of Terms". 870 * Editorial polishing of all sections. 872 * Added clarifications in section "Dealing with Map-Version 873 numbers" for the case of the special Map-Version number 0. 875 * Rename of draft-iannone-mapping-versioning-02.txt. 877 Authors' Addresses 879 Luigi Iannone 880 TU Berlin - Deutsche Telekom Laboratories AG 881 Ernst-Reuter Platz 7 882 Berlin 883 Germany 885 Email: luigi@net.t-labs.tu-berlin.de 887 Damien Saucez 888 Universite catholique de Louvain 889 Place St. Barbe 2 890 Louvain la Neuve 891 Belgium 893 Email: damien.saucez@uclouvain.be 895 Olivier Bonaventure 896 Universite catholique de Louvain 897 Place St. Barbe 2 898 Louvain la Neuve 899 Belgium 901 Email: olivier.bonaventure@uclouvain.be