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Checking references for intended status: Experimental ---------------------------------------------------------------------------- == Outdated reference: A later version (-24) exists of draft-ietf-lisp-15 == Outdated reference: A later version (-10) exists of draft-ietf-lisp-alt-08 == Outdated reference: A later version (-06) exists of draft-ietf-lisp-interworking-02 == Outdated reference: A later version (-16) exists of draft-ietf-lisp-ms-11 == Outdated reference: A later version (-15) exists of draft-ietf-lisp-threats-00 Summary: 0 errors (**), 0 flaws (~~), 6 warnings (==), 1 comment (--). 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: March 16, 2012 D. Saucez 6 O. Bonaventure 7 Universite catholique de Louvain 8 September 13, 2011 10 LISP Map-Versioning 11 draft-ietf-lisp-map-versioning-03.txt 13 Abstract 15 This document describes the LISP (Locator/ID Separation Protocol) 16 Map-Versioning mechanism, which provides in-packet information about 17 Endpoint-ID to Routing Locator (EID-to-RLOC) mappings used to 18 encapsulate LISP data packets. The proposed approach is based on 19 associating a version number to EID-to-RLOC mappings and transport 20 such a version number in the LISP specific header of LISP- 21 encapsulated packets. LISP Map-Versioning is particularly useful to 22 inform communicating Ingress Tunnel Routers (ITRs) and Egress Tunnel 23 Routers (ETRs) about modifications of the mappings used to 24 encapsulate packets. The mechanism is transparent to legacy 25 implementations, since in the LISP-specific header and in the Map 26 Records, bits used for Map-Versioning can be safely ignored by ITRs 27 and ETRs that do not support the mechanism. 29 Status of this Memo 31 This Internet-Draft is submitted in full conformance with the 32 provisions of BCP 78 and BCP 79. 34 Internet-Drafts are working documents of the Internet Engineering 35 Task Force (IETF). Note that other groups may also distribute 36 working documents as Internet-Drafts. The list of current Internet- 37 Drafts is at http://datatracker.ietf.org/drafts/current/. 39 Internet-Drafts are draft documents valid for a maximum of six months 40 and may be updated, replaced, or obsoleted by other documents at any 41 time. It is inappropriate to use Internet-Drafts as reference 42 material or to cite them other than as "work in progress." 44 This Internet-Draft will expire on March 16, 2012. 46 Copyright Notice 48 Copyright (c) 2011 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (http://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 64 2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 4 65 3. Definitions of Terms . . . . . . . . . . . . . . . . . . . . . 4 66 4. EID-to-RLOC Map-Version number . . . . . . . . . . . . . . . . 4 67 4.1. The Null Map-Version . . . . . . . . . . . . . . . . . . . 5 68 5. Dealing with Map-Version numbers . . . . . . . . . . . . . . . 6 69 5.1. Handling Destination Map-Version number . . . . . . . . . 7 70 5.2. Handling Source Map-Version number . . . . . . . . . . . . 8 71 6. LISP header and Map-Version numbers . . . . . . . . . . . . . 9 72 7. Map Record and Map-Version . . . . . . . . . . . . . . . . . . 10 73 8. Benefits and case studies for Map-Versioning . . . . . . . . . 11 74 8.1. Synchronization of different xTRs . . . . . . . . . . . . 11 75 8.2. Map-Versioning and unidirectional traffic . . . . . . . . 12 76 8.3. Map-Versioning and interworking . . . . . . . . . . . . . 13 77 8.3.1. Map-Versioning and Proxy-ITRs . . . . . . . . . . . . 13 78 8.3.2. Map-Versioning and LISP-NAT . . . . . . . . . . . . . 14 79 8.3.3. Map-Versioning and Proxy-ETRs . . . . . . . . . . . . 14 80 8.4. RLOC shutdown/withdraw . . . . . . . . . . . . . . . . . . 15 81 8.5. Map-Version for lightweight LISP implementation . . . . . 15 82 9. Incremental deployment and implementation status . . . . . . . 16 83 10. Security Considerations . . . . . . . . . . . . . . . . . . . 16 84 10.1. Map-Versioning against traffic disruption . . . . . . . . 16 85 10.2. Map-Versioning against reachability information DoS . . . 17 86 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 87 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17 88 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18 89 13.1. Normative References . . . . . . . . . . . . . . . . . . . 18 90 13.2. Informative References . . . . . . . . . . . . . . . . . . 18 91 Appendix A. Estimation of time before Map-Version wrap-around . . 18 92 Appendix B. Document Change Log . . . . . . . . . . . . . . . . . 19 93 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21 95 1. Introduction 97 This document describes the Map-Versioning mechanism used to provide 98 information on changes in the EID-to-RLOC mappings used in the LISP 99 ([I-D.ietf-lisp]) context to perform packet encapsulation. The 100 mechanism is totally transparent to xTRs not supporting such 101 functionality. It is not meant to replace any existing LISP 102 mechanism, but rather to complete them providing new functionalities. 103 The basic mechanism is to associate a Map-Version number to each LISP 104 EID-to-RLOC mapping and transport such a version number in the LISP- 105 specific header. When a mapping changes, a new version number is 106 assigned to the updated mapping. A change in an EID-to-RLOC mapping 107 can be a change in the RLOCs set, by adding or removing one or more 108 RLOCs, but it can also be a change in the priority or weight of one 109 or more RLOCs. 111 When Map-Versioning is used, LISP-encapsulated data packets contain 112 the version number of the two mappings used to select the RLOCs in 113 the outer header (i.e., both source and destination). These version 114 numbers are encoded in the 24 low-order bits of the first longword of 115 the LISP header and indicated by a specific bit in the flags (first 8 116 high-order bits of the first longword of the LISP header). Note that 117 not all packets need to carry version numbers. 119 When an ITR encapsulates a data packet, with a LISP header containing 120 the Map-Version numbers, it puts in the LISP-specific header two 121 version numbers: 123 1. The version number assigned to the mapping (contained in the EID- 124 to-RLOC Database) used to select the source RLOC. 126 2. The version number assigned to the mapping (contained in the EID- 127 to-RLOC Cache) used to select the destination RLOC. 129 This operation is two-fold. On the one hand, it enables the ETR 130 receiving the packet to know if the ITR has the latest version number 131 that any ETR at the destination EID site has provided to the ITR in a 132 Map-Reply. If it is not the case the ETR can send to the ITR a Map- 133 Request containing the updated mapping or soliciting a Map-Request 134 from the ITR (both cases are already defined in [I-D.ietf-lisp]). In 135 this way the ITR can update its cache. On the other hand, it enables 136 an ETR receiving such a packet to know if it has in its EID-to-RLOC 137 Cache the latest mapping for the source EID (in case of bidirectional 138 traffic). If it is not the case a Map-Request can be sent. 140 2. Requirements Notation 142 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 143 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 144 document are to be interpreted as described in [RFC2119]. 146 3. Definitions of Terms 148 The present document uses terms already defined in main LISP 149 specification [I-D.ietf-lisp]. Hereafter are defined only the terms 150 that are specific to the Map-Versioning mechanism. 152 Map-Version number: An unsigned 12-bits assigned to an EID-to-RLOC 153 mapping, not including the value 0 (0x000). 155 Null Map-Version: The 12-bits null value of 0 (0x000) is not used as 156 Map-Version number. It is used to signal that no Map-Version 157 number is assigned to the EID-to-RLOC mapping. 159 Source Map-Version number: Map-Version number of the EID-to-RLOC 160 mapping used to select the source address (RLOC) of the outer IP 161 header of LISP-encapsulated packets. 163 Destination Map-Version number: Map-Version number of the EID-to- 164 RLOC mapping used to select the destination address (RLOC) of the 165 outer IP header of LISP-encapsulated packets. 167 4. EID-to-RLOC Map-Version number 169 The EID-to-RLOC Map-Version number consists in an unsigned 12-bits 170 integer. The version number is assigned in a per-mapping fashion, 171 meaning that different mappings will have assigned a different 172 version number, which is also updated independently. An update in 173 the version number (i.e., a newer version) consist in incrementing by 174 one the older version number. Appendix A contains a rough estimation 175 of the wrap-around time for the Map-Version number. 177 The space of version numbers has a circular order where half of the 178 version numbers is greater than the current Map-Version number and 179 the other half is smaller than current Map-Version number. In a more 180 formal way, assuming we have two version numbers V1 and V2 and that 181 the numbers are expressed on N bits, the following three cases may 182 happen: 184 V1 = V2 : This is the exact match case. 186 V1 < V2 : True if and only if V1 < V2 < (V1 + 2**(N-1)). 188 V1 > V2 : True if and only if V1 > V2 > (V1 - 2**(N-1)). 190 Using 12 bits, as defined in this document, and assuming a Map- 191 Version value of 69, Map-Version numbers in the range [70; 69 + 2047] 192 are greater than 69, while Map-Version numbers in the range [69 + 193 2048; (69 + 4095) mod 4096] are smaller than 69. 195 The initial Map-Version number of a new EID-to-RLOC mapping SHOULD be 196 randomly generated. However, it MUST NOT be set to the Null Map- 197 Version value (0x000), because it has a special meaning (see 198 Section 4.1). 200 4.1. The Null Map-Version 202 The value 0x000 (zero) is not a valid Map-Version number indicating 203 the version of the EID-to-RLOC mapping. Such a value is used for 204 special purposes and is named the Null Map-Version number. 206 The Null Map-Version MAY appear in the LISP specific header as either 207 Source Map-Version number (cf. Section 5.2) or Destination Map- 208 Version number (cf. Section 5.1). When the Source Map-Version number 209 is set to the Null Map-version value it means that no map version 210 information is conveyed for the source site. This means that if a 211 mapping exists for the source EID in the EID-to-RLOC Cache, then the 212 ETR MUST NOT compare the received Null Map-Version with the content 213 of the EID-to-RLOC cache. When the Destination Map-version number is 214 set to the Null Map-version value it means that no map version 215 information is conveyed for the destination site. This means that 216 the ETR MUST NOT compare the value with the Map-Version number of the 217 mapping for the destination EID present in the EID-to-RLOC Database. 219 The other use of the Null Map-Version number is in the Map Records, 220 which are part of the Map-Request, Map-Reply and Map-Register 221 messages (defined in [I-D.ietf-lisp]). Map Records that have a Null 222 Map-Version number indicate that there is no Map-Version number 223 associated with the mapping. This means that LISP encapsulated 224 packets, destined to the EID-Prefix the Map Record refers to, MUST 225 either not contain any Map-Version numbers (V bit set to 0), or if it 226 contains Map-Version numbers (V bit set to 1) then the destination 227 Map-Version number MUST be set to the Null Map-Version number. Any 228 value different from zero means that Map-Versioning is supported and 229 MAY be used. 231 The fact that the 0 value has a special meaning for the Map-Version 232 number implies that, when updating a Map-Version number because of a 233 change in the mapping, if the next value is 0 then Map-Version number 234 MUST be incremented by 2 (i.e., set to 1, which is the next valid 235 value). 237 5. Dealing with Map-Version numbers 239 The main idea of using Map-Version numbers is that whenever there is 240 a change in the mapping (e.g., adding/removing RLOCs, a change in the 241 weights due to TE policies, or a change in the priorities) or an ISP 242 realizes that one or more of its own RLOCs are not reachable anymore 243 from a local perspective (e.g., through IGP, or policy changes) the 244 ISP updates the mapping also assigning a new Map-Version number. 246 To each mapping, a version number is associated and changes each time 247 the mapping is changed. Note that map-versioning does not introduce 248 new problems concerning the coordination of different ETRs of a 249 domain. Indeed, ETRs belonging to the same LISP site must return for 250 a specific EID-prefix the same mapping, including the same Map- 251 Version number. In principle this is orthogonal to whether or not 252 map-versioning is used. The synchronization problem is out of the 253 scope of this document. 255 In order to announce in a data-driven fashion that the mapping has 256 been updated, Map-Version numbers used to create the outer IP header 257 of the LISP-encapsulated packet are embedded in the LISP-specific 258 header. This means that the header needs to contain two Map-Version 259 numbers: 261 o The Source Map-Version number of the EID-to-RLOC mapping in the 262 EID-to-RLOC Database used to select the source RLOC. 264 o The Destination Map-Version number of the EID-to-RLOC mapping in 265 the EID-to-RLOC Cache used to select the destination RLOC. 267 By embedding both Source Map-Version number and Destination Map- 268 Version number an ETR receiving a LISP packet with Map-Version 269 numbers, can perform the following checks: 271 1. The ITR that has sent the packet has an up-to-date mapping in its 272 cache for the destination EID and is performing encapsulation 273 correctly. 275 2. In case of bidirectional traffic, the mapping in the local ETR 276 EID-to-RLOC cache for the source EID is up-to-date. 278 If one or both of the above conditions do not hold, the ETR can send 279 a Map-Request either to make the ITR aware that a new mapping is 280 available (see Section 5.1) or to update the mapping in the local 281 cache (see Section 5.2). 283 5.1. Handling Destination Map-Version number 285 When an ETR receives a packet, the Destination Map-Version number 286 relates to the mapping for the destination EID for which the ETR is a 287 RLOC. This mapping is part of the ETR EID-to-RLOC Database. Since 288 the ETR is authoritative for the mapping, it has the correct and up- 289 to-date Destination Map-Version number. A check on this version 290 number can be done, where the following cases can arise: 292 1. The packets arrive with the same Destination Map-Version number 293 stored in the EID-to-RLOC Database. This is the regular case. 294 The ITR sending the packet has in its EID-to-RLOC Cache an up-to- 295 date mapping. No further actions are needed. 297 2. The packet arrives with a Destination Map-Version number greater 298 (i.e., newer) than the one stored in the EID-to-RLOC Database. 299 Since the ETR is authoritative on the mapping, this means that 300 someone is not behaving correctly with respect to the 301 specifications, thus the packet carries a not valid version 302 number and SHOULD be silently dropped. 304 3. The packets arrive with a Destination Map-Version number smaller 305 (i.e., older) than the one stored in the EID-to-RLOC Database. 306 This means that the ITR sending the packet has an old mapping in 307 its EID-to-RLOC Cache containing stale information. The ITR 308 sending the packet has to be informed that a newer mapping is 309 available. This is done with a Map-Request message sent back to 310 the ITR. The Map-Request will either trigger a Map-Request back 311 using the Solicit-Map-Request (SMR) bit or it will piggyback the 312 newer mapping. These are not new mechanisms; how to SMR or 313 piggyback mappings in Map-Request messages is already described 314 in [I-D.ietf-lisp], while their security is discussed in 315 [I-D.ietf-lisp-threats]. These Map-Request messages should be 316 rate limited (rate limitation policies are also described in 317 [I-D.ietf-lisp]). The feature introduced by Map-Version numbers 318 is the possibility of blocking traffic not using the latest 319 mapping. Indeed, after a certain number of retries, if the 320 Destination Map-Version number in the packets is not updated, the 321 ETR MAY drop packets with a stale Map-Version number while 322 strongly reducing the rate of Map-Request messages. This because 323 either the ITR is refusing to use the mapping for which the ETR 324 is authoritative or (worse) it might be some form of attack. 325 Another case might be that the control-plane is experiencing 326 transient failures so the Map-Requests cannot reach that ITR. By 327 keeping sending Map-Requests at very low rate it is possible to 328 recover from this situation. 330 The rule in the third case MAY be more restrictive. If the mapping 331 has been the same for a period of time as long as the TTL (defined in 332 [I-D.ietf-lisp]) of the previous version of the mapping, all packets 333 arriving with an old Map-Version SHOULD be silently dropped right 334 away without issuing any Map-Request. The reason that allows such 335 action is the fact that if the new mapping with the updated version 336 number has been unchanged for at least the same time as the TTL of 337 the older mapping, all the entries in the caches of ITRs must have 338 expired. Hence, all ITRs sending traffic should have refreshed the 339 mapping according to [I-D.ietf-lisp]. If packets with old Map- 340 Version number are still received, then either someone has not 341 respected the TTL, or it is a form of spoof/attack. In both cases 342 this is not valid behavior with respect to the specifications and the 343 packet SHOULD be silently dropped. 345 LISP-encapsulated packets with the V-bit set, when the original 346 mapping in the EID-to-RLOC Database has version number set to the 347 Null Map-Version value, MAY be silently dropped. As explained in 348 Section 4.1, if an EID-to-RLOC mapping has a Null Map-Version, it 349 means that ITRs, using the mapping for encapsulation, MUST NOT use 350 Map-Version number in the LISP-specific header. 352 For LISP-encapsulated packets with the V-bit set, when the original 353 mapping in the EID-to-RLOC Database has version number set to a value 354 different from the Null Map-Version value, a Destination Map-Version 355 number equal to the Null Map-Version value means that the Destination 356 Map-Version number MUST be ignored. 358 5.2. Handling Source Map-Version number 360 When an ETR receives a packet, the Source Map-Version number relates 361 to the mapping for the source EID for which the ITR that sent the 362 packet is authoritative. If the ETR has an entry in its EID-to-RLOC 363 Cache for the source EID, then a check can be performed and the 364 following cases can arise: 366 1. The packet arrives with the same Source Map-Version number stored 367 in the EID-to-RLOC Cache. This is the correct regular case. The 368 ITR has in its cache an up-to-date copy of the mapping. No 369 further actions are needed. 371 2. The packet arrives with a Source Map-Version number greater 372 (i.e., newer) than the one stored in the local EID-to-RLOC Cache. 373 This means that ETR has in its cache a mapping that is stale and 374 needs to be updated. A Map-Request SHOULD be sent to get the new 375 mapping for the source EID. This is a normal Map-Request message 376 sent through the mapping system and MUST respect the 377 specifications in [I-D.ietf-lisp], including rate limitation 378 policies. 380 3. The packet arrives with a Source Map-Version number smaller 381 (i.e., older) than the one stored in the local EID-to-RLOC Cache. 382 Such a case is not valid with respect to the specifications. 383 Indeed, if the mapping is already present in the EID-to-RLOC 384 Cache, this means that an explicit Map-Request has been sent and 385 a Map-Reply has been received from an authoritative source. 386 Assuming that the mapping system is not corrupted anyhow, the 387 Map-Version in the EID-to-RLOC Cache is the correct one and the 388 packet MAY be silently dropped. 390 If the ETR does not have an entry in the EID-to-RLOC Cache for the 391 source EID (e.g., in case of unidirectional traffic) then the Source 392 Map-Version number can be safely ignored. 394 For LISP-encapsulated packets with the V-bit set, if the Source Map- 395 Version number is the Null Map-Version value, it means that the 396 Source Map-Version number MUST be ignored. 398 6. LISP header and Map-Version numbers 400 In order for the versioning approach to work, the LISP specific 401 header has to carry both Source Map-Version number and Destination 402 Map-Version number. This is done by setting the V-bit in the LISP 403 specific header as defined in [I-D.ietf-lisp] Section 5.3. When the 404 V-bit is set the low-order 24-bits of the first longword (which 405 usually contains the nonce) are used to transport both source and 406 destination Map-Version numbers. In particular the first 12 bits are 407 used for Source Map-Version number and the second 12 bits for the 408 Destination Map-Version number. 410 Hereafter is the example of LISP header carrying version numbers in 411 the case of IPv4-in-IPv4 encapsulation. The same setting can be used 412 for any other case (IPv4-in-IPv6, IPv6-in-IPv4, and IPv6-in-IPv6). 414 0 1 2 3 415 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 1 416 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 417 / |N|L|E|V|I|flags| Source Map-Version |Destination Map-Version| 418 LISP+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 419 \ | Instance ID/Locator Status Bits | 420 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 422 Source Map-Version number (12 bits): Map-Version of the mapping used 423 by the ITR to select the RLOC present in the "Source Routing 424 Locator" field. How to set on transmission and handle on 425 reception this value is described in Section 5.2. 427 Destination Map-Version number (12 bits): Map-Version of the mapping 428 used by the ITR to select the RLOC present in the "Destination 429 Routing Locator" field. How to set on transmission and handle on 430 reception this value is described in Section 5.1. 432 The present document just specifies how to use the low-order 24-bits 433 of the first longword of the LISP-specific header when the V-bit is 434 set to 1. All other cases, including the bit fields of the rest of 435 the LISP-specific header and the whole LISP packet format are 436 specified in [I-D.ietf-lisp]. Not all of the LISP encapsulated 437 packets need to carry version numbers. When Map-Version numbers are 438 carried the V-bit MUST be set to 1. All legal combinations of the 439 flags, when the V-bit is set to 1, are described in [I-D.ietf-lisp]. 441 7. Map Record and Map-Version 443 To accommodate the proposed mechanism, the Map Records that are 444 transported on Map-Request/Map-Reply/Map-Register messages need to 445 carry the Map-Version number as well. For this purpose the 12-bits 446 before the EID-AFI field in the Record that describe a mapping is 447 used. This is defined in [I-D.ietf-lisp] and reported here as 448 example. 450 0 1 2 3 451 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 1 452 +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 453 | | Record TTL | 454 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 455 R | Locator Count | EID mask-len | ACT |A| Reserved | 456 e +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 457 c | Rsvd | Map-Version Number | EID-AFI | 458 o +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 459 r | EID-prefix | 460 d +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 461 | /| Priority | Weight | M Priority | M Weight | 462 | L +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 463 | o | Unused Flags |L|p|R| Loc-AFI | 464 | c +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 465 | \| Locator | 466 +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 467 Map-Version Number: Map-Version of the mapping contained in the 468 Record. As explained in Section 4.1 this field can be zero (0), 469 meaning that no Map-Version is associated to the mapping, hence 470 packets that are LISP-encapsulated using this mapping MUST NOT 471 contain Map-Version numbers in the LISP specific header and the 472 V-bit MUST be set to 0. 474 This packet format works perfectly with xTRs that do not support Map- 475 Versioning, since they can simply ignore those bits. 477 8. Benefits and case studies for Map-Versioning 479 In the following sections we provide more discussion on various 480 aspects and use of the Map-Versioning. Security observations are 481 instead grouped in Section 10. 483 8.1. Synchronization of different xTRs 485 Map-Versioning does not require additional synchronization mechanism 486 compared to the normal functioning of LISP without Map-Versioning. 487 Clearly all the ETRs have to reply with the same Map-Version number, 488 otherwise there can be an inconsistency that creates additional 489 control traffic, instabilities, traffic disruptions. It is the same 490 without Map-Versioning, with ETRs that have to reply with the same 491 mapping, otherwise the same problems can arise. 493 As an example, let's consider the topology of Figure 1 where ITR A.1 494 of domain A is sending unidirectional traffic to the domain B, while 495 A.2 of domain A exchange bidirectional traffic with domain B. In 496 particular, ITR A.2 send traffic to ETR B and ETR A.2 receives 497 traffic from ITR B. 499 +-----------------+ +-----------------+ 500 | Domain A | | Domain B | 501 | +---------+ | | 502 | | ITR A.1 |--- | | 503 | +---------+ \ +---------+ | 504 | | ------->| ETR B | | 505 | | ------->| | | 506 | +---------+ / | | | 507 | | ITR A.2 |--- -----| ITR B | | 508 | | | / +---------+ | 509 | | ETR A.2 |<----- | | 510 | +---------+ | | 511 | | | | 512 +-----------------+ +-----------------+ 514 Figure 1 516 Obviously in the case of Map-Versioning both ITR A.1 and ITR A.2 of 517 domain A must use the same value otherwise the ETR of domain B will 518 start to send Map-Requests. 520 The same problem can, however, arise without Map-Versioning. For 521 instance, if the two ITRs of domain A send different Loc Status Bits. 522 In this case either the traffic is disrupted, if the ETR B trusts the 523 Locator Status Bits, or if ETR B does not trusts the Locator Status 524 Bits it will start sending Map-Requests to confirm the each change in 525 the reachability. 527 So far, LISP does not provide any specific synchronization mechanism, 528 but assumes that synchronization is provided by configuring the 529 different xTRs consistently. The same applies for Map-Versioning. 530 If in the future any synchronization mechanism is provided, Map- 531 Versioning will take advantage of it automatically since it is 532 included in the Record format, as described in Section 7. 534 8.2. Map-Versioning and unidirectional traffic 536 When using Map-Versioning the LISP specific header carries two Map- 537 Version numbers, for both source and destination mappings. This can 538 raise the question on what will happen in the case of unidirectional 539 flows, like for instance in the case presented in Figure 2, since 540 LISP specification do not mandate for ETR to have a mapping for the 541 source EID. 543 +-----------------+ +-----------------+ 544 | Domain A | | Domain B | 545 | +---------+ +---------+ | 546 | | ITR A |----------->| ETR B | | 547 | +---------+ +---------+ | 548 | | | | 549 +-----------------+ +-----------------+ 551 Figure 2 553 For what concerns the ITR, it is able to put both source and 554 destination version number in the LISP header since the Source Map- 555 Version number is in ITR's database, while the Destination Map- 556 Version number is in ITR's cache. 558 For what concerns the ETR, it simply checks only the Destination Map- 559 Version number in the same way as described in Section 5, ignoring 560 the Source Map-Version number. 562 8.3. Map-Versioning and interworking 564 Map-Versioning is compatible with the LISP interworking between LISP 565 and non-LISP sites as defined in [I-D.ietf-lisp-interworking]. LISP 566 interworking defines three techniques to make LISP sites and non-LISP 567 sites, namely Proxy-ITR, LISP-NAT, and Proxy-ETR. Hereafter it is 568 described how Map-Versioning relates to these three mechanisms. 570 8.3.1. Map-Versioning and Proxy-ITRs 572 The purpose of the Proxy-ITR (PITR) is to encapsulate traffic 573 originating in a non-LISP site in order to deliver the packet to one 574 of the ETRs of the LISP site (cf. Figure 3). This case is very 575 similar to the unidirectional traffic case described in Section 8.2, 576 hence similar rules apply. 578 +----------+ +-------------+ 579 | LISP | | non-LISP | 580 | Domain A | | Domain B | 581 | +-------+ +-----------+ | | 582 | | ETR A |<-------| Proxy ITR |<-------| | 583 | +-------+ +-----------+ | | 584 | | | | 585 +----------+ +-------------+ 587 Figure 3 589 The main difference is that a Proxy-ITR does not have any mapping, 590 since it just encapsulate packets arriving from non-LISP site, thus 591 cannot provide a Source Map-Version. In this case, the proxy-ITR 592 will just put the Null Map-Version value as Source Map-Version 593 number, while the receiving ETR will ignore the field. 595 With this setup the LISP Domain A is able to check whether or not the 596 PITR is using the latest mapping. If this is not the case the 597 mapping for LISP Domain A on the PITR can be updated using one of the 598 mechanisms defined in [I-D.ietf-lisp] and 599 [I-D.ietf-lisp-interworking]. 601 8.3.2. Map-Versioning and LISP-NAT 603 The LISP-NAT mechanism is based on address translation from non- 604 routable EIDs to routable EIDs and does not involve any form of 605 encapsulation. As such Map-Versioning does not apply in this case. 607 8.3.3. Map-Versioning and Proxy-ETRs 609 The purpose of the Proxy-ETR (PETR) is to decapsulate traffic 610 originating in a LISP site in order to deliver the packet to the non- 611 LISP site (cf. Figure 4). One of the main reasons of deploy PETRs is 612 to bypass uRPF (Unicast Reverse Path Forwarding) checks on the 613 provider edge. 615 +----------+ +-------------+ 616 | LISP | | non-LISP | 617 | Domain A | | Domain B | 618 | +-------+ +-----------+ | | 619 | | ITR A |------->| Proxy ETR |------->| | 620 | +-------+ +-----------+ | | 621 | | | | 622 +----------+ +-------------+ 624 Figure 4 626 A Proxy-ETR does not have any mapping, since it just decapsulates 627 packets arriving from LISP site. In this case, the ITR will just put 628 the Null Map-Version value as Destination Map-Version number, while 629 the receiving Proxy-ETR will ignore the field. 631 With this setup the Proxy-ETR is able to check whether or not the 632 mapping has changed. If this is the case the mapping for LISP Domain 633 A on the PETR can be updated using one of the mechanisms defined in 634 [I-D.ietf-lisp] and [I-D.ietf-lisp-interworking]. 636 8.4. RLOC shutdown/withdraw 638 Map-Versioning can be even used to perform a graceful shutdown or 639 withdraw of a specific RLOC. This is achieved by simply issuing a 640 new mapping, with an updated Map-Version number, where the specific 641 RLOC to be shut down is withdrawn or announced as unreachable (R bit 642 in the Map Record, see [I-D.ietf-lisp]), but without actually turning 643 it off. 645 Once no more traffic is received by the RLOC, it can be shut down 646 gracefully, because at least all sites actively using the mapping 647 have updated it. 649 It should be pointed out that for frequent up/down changes such a 650 mechanism should not be used since this can generate excessive load 651 on the Mapping System. 653 8.5. Map-Version for lightweight LISP implementation 655 The use of Map-Versioning can help in developing a lightweight 656 implementation of LISP. This comes with the price of not supporting 657 Loc-Status-Bit, which are useful in some contexts. 659 In the current LISP specifications the set of RLOCs must always be 660 maintained ordered and consistent with the content of the Loc Status 661 Bits (see section 6.5 of [I-D.ietf-lisp]). With Map-Versioning such 662 type of mechanisms can be avoided. When a new RLOC is added to a 663 mapping, it is not necessary to "append" new locators to the existing 664 ones as explained in Section 6.5 of [I-D.ietf-lisp]. A new mapping 665 with a new Map-Version number will be issued, and since the old 666 locators are still valid the transition will be with no disruptions. 667 The same applies for the case a RLOC is withdrawn. There is no need 668 to maintain holes in the list of locators, as is the case when using 669 Locator Status Bits, for sites that are not using the RLOC that has 670 been withdrawn the transition will be with no disruptions. 672 All of these operations, as already stated, do not need to maintain 673 any consistency among Locator Status Bits, and the way RLOC are 674 stored in the cache. 676 Further, Map-Version can be used to substitute the "clock sweep" 677 operation described in Section 6.5.1 of [I-D.ietf-lisp]. Indeed, 678 every LISP site communicating to a specific LISP site that has 679 updated the mapping will be informed of the available new mapping in 680 a data-driven manner. 682 Note that what is proposed in the present section is just an example 683 and MUST NOT be considered as specifications for a lightweight LISP 684 implementation. In case the IETF decides to undertake such a work, 685 it will be documented elsewhere. 687 9. Incremental deployment and implementation status 689 Map-Versioning can be incrementally deployed without any negative 690 impact on existing LISP elements (e.g., xTRs, Map-Servers, Proxy- 691 ITRs, etc). Any LISP element that does not support Map-Versioning 692 can safely ignore them. Further, there is no need of any specific 693 mechanism to discover if an xTR supports or not Map-Versioning. This 694 information is already included in the Map Record. 696 Map-Versioning is currently implemented in OpenLISP 697 [I-D.iannone-openlisp-implementation]. 699 Note that the reference document for LISP implementation and 700 interoperability tests remains [I-D.ietf-lisp]. 702 10. Security Considerations 704 Map-Versioning does not introduce any security issue concerning both 705 the data-plane and the control-plane. On the contrary, as described 706 in the following, if Map-Versioning may be used also to update 707 mappings in case of change in the reachability information (i.e., 708 instead of the Locator Status Bits) it is possible to reduce the 709 effects of some DoS or spoofing attacks that can happen in an 710 untrusted environment. 712 Robusteness of the Map-Versioning mechanism leverages on a trusted 713 Mapping Distribution System. A thorough security analysis of LISP is 714 documented in [I-D.ietf-lisp-threats]. 716 10.1. Map-Versioning against traffic disruption 718 An attacker can try to disrupt ongoing communications by creating 719 LISP encapsulated packets with wrong Locator Status Bits. If the xTR 720 blindly trusts the Locator Status Bits it will change the 721 encapsulation accordingly, which can result in traffic disruption. 723 This does not happen in the case of Map-Versioning. As described in 724 Section 5, upon a version number change the xTR first issues a Map- 725 Request. The assumption is that the mapping distribution system is 726 sufficiently secure that Map-Request and Map-Reply messages and their 727 content can be trusted. Security issues concerning specific mapping 728 distribution system are out of the scope of this document. In the 729 case of Map-Versioning the attacker should "guess" a valid version 730 number that triggers a Map-Request, as described in Section 5, 731 otherwise the packet is simply dropped. Nevertheless, guessing a 732 version number that generates a Map-Request is easy, hence it is 733 important to follow the rate limitations policies described in 734 [I-D.ietf-lisp] in order to avoid DoS attacks. 736 Note that a similar level of security can be obtained with Loc Status 737 Bits, by simply making mandatory to verify any change through a Map- 738 Request. However, in this case Locator Status Bits loose their 739 meaning, because, it does not matter anymore which specific bits has 740 changed, the xTR will query the mapping system and trust the content 741 of the received Map-Reply. Furthermore there is no way to perform 742 filtering as in the Map-Versioning in order to drop packets that do 743 not carry a valid Map-Version number. In the case of Locator Status 744 Bits, any random change can trigger a Map-Request (unless rate 745 limitation is enabled which raise another type of attack discussed in 746 Section 10.2). 748 10.2. Map-Versioning against reachability information DoS 750 Attackers can try to trigger a large amount of Map-Request by simply 751 forging packets with random Map-Version or random Locator Status 752 Bits. In both cases the Map-Requests are rate limited as described 753 in [I-D.ietf-lisp]. However, differently from Locator Status Bit 754 where there is no filtering possible, in the case of Map-Versioning 755 is possible to filter not valid version numbers before triggering a 756 Map-Request, thus helping in reducing the effects of DoS attacks. In 757 other words the use of Map-Versioning enables a fine control on when 758 to update a mapping or when to notify that a mapping has been 759 updated. 761 It is clear, that Map-Versioning does not protect against DoS and 762 DDoS attacks, where an xTR looses processing power doing checks on 763 the LISP header of packets sent by attackers. This is independent 764 from Map-Versioning and is the same for Loc Status Bits. 766 11. IANA Considerations 768 This document has no actions for IANA. 770 12. Acknowledgements 772 The authors would like to thank Alia Atlas, Jesper Skriver, Pierre 773 Francois, Noel Chiappa, Dino Farinacci for their comments and review. 775 This work has been partially supported by the INFSO-ICT-216372 776 TRILOGY Project (www.trilogy-project.org). 778 13. References 780 13.1. Normative References 782 [I-D.ietf-lisp] 783 Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, 784 "Locator/ID Separation Protocol (LISP)", 785 draft-ietf-lisp-15 (work in progress), July 2011. 787 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 788 Requirement Levels", BCP 14, RFC 2119, March 1997. 790 13.2. Informative References 792 [I-D.iannone-openlisp-implementation] 793 Iannone, L., Saucez, D., and O. Bonaventure, "OpenLISP 794 Implementation Report", 795 draft-iannone-openlisp-implementation-01 (work in 796 progress), July 2008. 798 [I-D.ietf-lisp-alt] 799 Fuller, V., Farinacci, D., Meyer, D., and D. Lewis, "LISP 800 Alternative Topology (LISP+ALT)", draft-ietf-lisp-alt-08 801 (work in progress), September 2011. 803 [I-D.ietf-lisp-interworking] 804 Lewis, D., Meyer, D., Farinacci, D., and V. Fuller, 805 "Interworking LISP with IPv4 and IPv6", 806 draft-ietf-lisp-interworking-02 (work in progress), 807 June 2011. 809 [I-D.ietf-lisp-ms] 810 Fuller, V. and D. Farinacci, "LISP Map Server", 811 draft-ietf-lisp-ms-11 (work in progress), August 2011. 813 [I-D.ietf-lisp-threats] 814 Saucez, D., Iannone, L., and O. Bonaventure, "LISP Threats 815 Analysis", draft-ietf-lisp-threats-00 (work in progress), 816 July 2011. 818 Appendix A. Estimation of time before Map-Version wrap-around 820 The present section proposes an estimation of the wrap-around time 821 for the proposed 12 bits size for the Map-Version number. Using a 822 granularity of seconds and assuming as worst-case that a new version 823 is issued each second, it takes slightly more than 1 hour before the 824 version wraps around. Note that the granularity of seconds is in 825 line with the rate limitation policy for Map-Request messages, as 826 proposed in the LISP main specifications ([I-D.ietf-lisp]). 827 Alternatively a granularity of minutes can also be used, as for the 828 TTL of the Map-Reply ([I-D.ietf-lisp]). In this case the worst 829 scenario is when a new version is issued every minute, leading to a 830 much longer time before wrap-around. In particular, when using 12 831 bits, the wrap-around time is almost 3 days. 833 For general information, hereafter there is a table with a rough 834 estimation of the time before wrap-around in the worst-case scenario, 835 considering different sizes (bits length) of the Map-Version number 836 and different time granularity. 838 +---------------+--------------------------------------------+ 839 |Version Number | Time before wrap around | 840 | Size (bits) +---------------------+----------------------+ 841 | |Granularity: Minutes | Granularity: Seconds | 842 | | (mapping changes | (mapping changes | 843 | | every 1 minute) | every 1 second) | 844 +-------------------------------------+----------------------+ 845 | 32 | 8171 Years | 136 Years | 846 | 30 | 2042 Years | 34 Years | 847 | 24 | 31 Years | 194 Days | 848 | 16 | 45 Days | 18 Hours | 849 | 15 | 22 Days | 9 Hours | 850 | 14 | 11 Days | 4 Hours | 851 | 13 | 5.6 Days | 2.2 Hours | 852 | 12 | 2.8 Days | 1.1 Hours | 853 +---------------+---------------------+----------------------+ 855 Figure 5: Estimation of time before wrap-around 857 Appendix B. Document Change Log 859 o Version 03 Posted September 2011. 861 * Added reference in Section 7 toward the main lisp documents 862 specifying the section, as requested by Jari Arkko. 864 * Fixed all typos and editorial issues pointed out by Jari Arkko. 866 * Added clarification in Section 8.4 as requested by Jari Arkko. 868 * Extentend all acronyms in the abstract as requested by Jari 869 Arkko. 871 * Clarified silent drop polocy in Section 5.2 as requested by 872 both Richard Barnes and Jari Arkko. 874 * Fixed typos pointed out by Richard Barnes. 876 o Version 02 Posted July 2011. 878 * Added text in Section 5 about ETR synchronization, as suggested 879 by Alia Atlas. 881 * Modified text in Section 8.5 concerning lightweight LISP 882 implementation, as suggested by Alia Atlas. 884 * Deleted text concerning old versions of [I-D.ietf-lisp-ms] and 885 [I-D.ietf-lisp-alt] in Section 7, as pointed out by Alia Atlas. 887 * Fixed section 4.1 to be less restrictive, as suggested by 888 Jesper Skriver. 890 o Version 01 Posted March 2011. 892 * Changed the wording from "Map-Version number 0" to "Null Map- 893 Version. 895 * Clarification of the use of the Null Map-Version value as 896 Source Map-Version Number and Destination Map-Version Number. 898 * Extended the section describing Map-Versioning and LISP 899 Interworking co-existence. 901 * Reduce packet format description to avoid double definitions 902 with the main specs. 904 o Version 00 Posted September 2010. 906 * Added Section "Definitions of Terms". 908 * Editorial polishing of all sections. 910 * Added clarifications in section "Dealing with Map-Version 911 numbers" for the case of the special Map-Version number 0. 913 * Rename of draft-iannone-mapping-versioning-02.txt. 915 Authors' Addresses 917 Luigi Iannone 918 TU Berlin - Deutsche Telekom Laboratories AG 919 Ernst-Reuter Platz 7 920 Berlin 921 Germany 923 Email: luigi@net.t-labs.tu-berlin.de 925 Damien Saucez 926 Universite catholique de Louvain 927 Place St. Barbe 2 928 Louvain-la-Neuve 929 Belgium 931 Email: damien.saucez@uclouvain.be 933 Olivier Bonaventure 934 Universite catholique de Louvain 935 Place St. Barbe 2 936 Louvain-la-Neuve 937 Belgium 939 Email: olivier.bonaventure@uclouvain.be