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Checking references for intended status: Experimental ---------------------------------------------------------------------------- == Outdated reference: A later version (-24) exists of draft-ietf-lisp-19 == Outdated reference: A later version (-06) exists of draft-ietf-lisp-interworking-02 == Outdated reference: A later version (-16) exists of draft-ietf-lisp-ms-15 == Outdated reference: A later version (-15) exists of draft-ietf-lisp-threats-00 Summary: 0 errors (**), 0 flaws (~~), 5 warnings (==), 1 comment (--).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 Telekom Innovation Laboratories 4 Intended status: Experimental D. Saucez 5 Expires: July 22, 2012 INRIA Sophia Antipolis 6 O. Bonaventure 7 Universite catholique de Louvain 8 January 19, 2012 10 LISP Map-Versioning 11 draft-ietf-lisp-map-versioning-07.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 implementations 25 not supporting this feature, since in the LISP-specific header and in 26 the Map Records, bits used for Map-Versioning can be safely ignored 27 by ITRs 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 July 22, 2012. 46 Copyright Notice 48 Copyright (c) 2012 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 . . . . . . . . . . . . 9 71 6. LISP header and Map-Version numbers . . . . . . . . . . . . . 10 72 7. Map Record and Map-Version . . . . . . . . . . . . . . . . . . 11 73 8. Benefits and case studies for Map-Versioning . . . . . . . . . 11 74 8.1. Map-Versioning and unidirectional traffic . . . . . . . . 12 75 8.2. Map-Versioning and interworking . . . . . . . . . . . . . 12 76 8.2.1. Map-Versioning and Proxy-ITRs . . . . . . . . . . . . 12 77 8.2.2. Map-Versioning and LISP-NAT . . . . . . . . . . . . . 13 78 8.2.3. Map-Versioning and Proxy-ETRs . . . . . . . . . . . . 13 79 8.3. RLOC shutdown/withdraw . . . . . . . . . . . . . . . . . . 14 80 8.4. Map-Version for lightweight LISP implementation . . . . . 14 81 9. Incremental deployment and implementation status . . . . . . . 15 82 10. Security Considerations . . . . . . . . . . . . . . . . . . . 15 83 10.1. Map-Versioning against traffic disruption . . . . . . . . 15 84 10.2. Map-Versioning against reachability information DoS . . . 16 85 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 86 12. Open Issues and Considerations . . . . . . . . . . . . . . . . 17 87 12.1. Lack of Synchronization among ETRs . . . . . . . . . . . . 17 88 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18 89 14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19 90 14.1. Normative References . . . . . . . . . . . . . . . . . . . 19 91 14.2. Informative References . . . . . . . . . . . . . . . . . . 19 92 Appendix A. Estimation of time before Map-Version wrap-around . . 19 93 Appendix B. Document Change Log . . . . . . . . . . . . . . . . . 20 94 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23 96 1. Introduction 98 This document describes the Map-Versioning mechanism used to provide 99 information on changes in the EID-to-RLOC (Endsystem ID to Routing 100 LOCator) mappings used in the LISP (Locator/Id Separation Protocol 101 [I-D.ietf-lisp]) context to perform packet encapsulation. The 102 mechanism is totally transparent to xTRs (Ingress and Egress Tunnel 103 Routers) not supporting such functionality. It is not meant to 104 replace any existing LISP mechanism, but rather to extend them 105 providing new functionalities. If for any unforseen reason a 106 normative conflict between the present document and the LISP main 107 specifications is found, the latter ([I-D.ietf-lisp]) has precedence 108 on the present document. 110 The basic mechanism is to associate a Map-Version number to each LISP 111 EID-to-RLOC mapping and transport such a version number in the LISP- 112 specific header. When a mapping changes, a new version number is 113 assigned to the updated mapping. A change in an EID-to-RLOC mapping 114 can be a change in the RLOCs set, by adding or removing one or more 115 RLOCs, but it can also be a change in the priority or weight of one 116 or more RLOCs. 118 When Map-Versioning is used, LISP-encapsulated data packets contain 119 the version number of the two mappings used to select the RLOCs in 120 the outer header (i.e., both source and destination). These version 121 numbers are encoded in the 24 low-order bits of the first longword of 122 the LISP header and indicated by a specific bit in the flags (first 8 123 high-order bits of the first longword of the LISP header). Note that 124 not all packets need to carry version numbers. 126 When an ITR (Ingress Tunnel Router) encapsulates a data packet, with 127 a LISP header containing the Map-Version numbers, it puts in the 128 LISP-specific header two version numbers: 130 1. The version number assigned to the mapping (contained in the EID- 131 to-RLOC Database) used to select the source RLOC. 133 2. The version number assigned to the mapping (contained in the EID- 134 to-RLOC Cache) used to select the destination RLOC. 136 This operation is two-fold. On the one hand, it enables the ETR 137 (Egress Tunnel Router) receiving the packet to know if the ITR has 138 the latest version number that any ETR at the destination EID site 139 has provided to the ITR in a Map-Reply. If it is not the case the 140 ETR can send to the ITR a Map-Request containing the updated mapping 141 or soliciting a Map-Request from the ITR (both cases are already 142 defined in [I-D.ietf-lisp]). In this way the ITR can update its EID- 143 to-RLOC Cache. On the other hand, it enables an ETR receiving such a 144 packet to know if it has in its EID-to-RLOC Cache the latest mapping 145 for the source EID (in case of bidirectional traffic). If it is not 146 the case a Map-Request can be sent. 148 Issues and concerns about the deployment of LISP for Internet traffic 149 are discussed in [I-D.ietf-lisp]. Section 12 provides additional 150 issues and concerns raised by this document. In particular, 151 Section 12.1 provides details about the ETRs' synchronization issue 152 in the context of Map-Versioning. 154 2. Requirements Notation 156 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 157 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 158 document are to be interpreted as described in [RFC2119]. 160 3. Definitions of Terms 162 The present document uses terms already defined in main LISP 163 specification [I-D.ietf-lisp]. Hereafter are defined only the terms 164 that are specific to the Map-Versioning mechanism. Throughout the 165 whole document Big Endian bit ordering is used. 167 Map-Version number: An unsigned 12-bits assigned to an EID-to-RLOC 168 mapping, not including the value 0 (0x000). 170 Null Map-Version: The 12-bits null value of 0 (0x000) is not used as 171 Map-Version number. It is used to signal that no Map-Version 172 number is assigned to the EID-to-RLOC mapping. 174 Source Map-Version number: Map-Version number of the EID-to-RLOC 175 mapping used to select the source address (RLOC) of the outer IP 176 header of LISP-encapsulated packets. 178 Destination Map-Version number: Map-Version number of the EID-to- 179 RLOC mapping used to select the destination address (RLOC) of the 180 outer IP header of LISP-encapsulated packets. 182 4. EID-to-RLOC Map-Version number 184 The EID-to-RLOC Map-Version number consists in an unsigned 12-bits 185 integer. The version number is assigned on a per-mapping basis, 186 meaning that different mappings have a different version number, 187 which is also updated independently. An update in the version number 188 (i.e., a newer version) consists in incrementing by one the older 189 version number. Appendix A contains a rough estimation of the wrap- 190 around time for the Map-Version number. 192 The space of version numbers has a circular order where half of the 193 version numbers is greater(i.e., newer) than the current Map-Version 194 number and the other half is smaller (i.e., older) than current Map- 195 Version number. In a more formal way, assuming we have two version 196 numbers V1 and V2 and that the numbers are expressed on N bits, the 197 following steps MUST be performed (in the same order as hereafter) to 198 strictly define their order: 200 1. V1 = V2 : The map-version number are the same. 202 2. V2 > V1 : if and only if 204 V2 > V1 AND (V2 - V1) <= 2**(N-1) 206 OR 208 V1 > V2 AND (V1 - V2) > 2**(N-1) 210 3. V1 > V2 : otherwise. 212 Using 12 bits, as defined in this document, and assuming a Map- 213 Version value of 69, Map-Version numbers in the range [70; 69 + 2048] 214 are greater than 69, while Map-Version numbers in the range [69 + 215 2049; (69 + 4096) mod 4096] are smaller than 69. 217 Map-version number are assigned to mappings by configuration. The 218 initial Map-Version number of a new EID-to-RLOC mapping SHOULD be 219 assigned randomly, but it MUST NOT be set to the Null Map-Version 220 value (0x000), because it has a special meaning (see Section 4.1). 222 Upon reboot, an ETR will use mappings configured in its EID-to-RLOC 223 Database. If those mappings have a Map-Version number, it will be 224 used according to the mechnisms described in this document. ETRs 225 MUST NOT automatically generate and assign Map-Version numbers to 226 mappings in the EID-to-RLOC Database. 228 4.1. The Null Map-Version 230 The value 0x000 (zero) is not a valid Map-Version number indicating 231 the version of the EID-to-RLOC mapping. Such a value is used for 232 special purposes and is named the Null Map-Version number. 234 The Null Map-Version MAY appear in the LISP specific header as either 235 Source Map-Version number (cf. Section 5.2) or Destination Map- 236 Version number (cf. Section 5.1). When the Source Map-Version number 237 is set to the Null Map-version value it means that no map version 238 information is conveyed for the source site. This means that if a 239 mapping exists for the source EID in the EID-to-RLOC Cache, then the 240 ETR MUST NOT compare the received Null Map-Version with the content 241 of the EID-to-RLOC Cache. When the Destination Map-version number is 242 set to the Null Map-version value it means that no map version 243 information is conveyed for the destination site. This means that 244 the ETR MUST NOT compare the value with the Map-Version number of the 245 mapping for the destination EID present in the EID-to-RLOC Database. 247 The other use of the Null Map-Version number is in the Map Records, 248 which are part of the Map-Request, Map-Reply and Map-Register 249 messages (defined in [I-D.ietf-lisp]). Map Records that have a Null 250 Map-Version number indicate that there is no Map-Version number 251 associated with the mapping. This means that LISP encapsulated 252 packets, destined to the EID-Prefix the Map Record refers to, MUST 253 either not contain any Map-Version numbers (V bit set to 0), or if it 254 contains Map-Version numbers (V bit set to 1) then the destination 255 Map-Version number MUST be set to the Null Map-Version number. Any 256 value different from zero means that Map-Versioning is supported and 257 MAY be used. 259 The fact that the 0 value has a special meaning for the Map-Version 260 number implies that, when updating a Map-Version number because of a 261 change in the mapping, if the next value is 0 then Map-Version number 262 MUST be incremented by 2 (i.e., set to 1, which is the next valid 263 value). 265 5. Dealing with Map-Version numbers 267 The main idea of using Map-Version numbers is that whenever there is 268 a change in the mapping (e.g., adding/removing RLOCs, a change in the 269 weights due to TE policies, or a change in the priorities) or a LISP 270 site realizes that one or more of its own RLOCs are not reachable 271 anymore from a local perspective (e.g., through IGP, or policy 272 changes) the LISP site updates the mapping also assigning a new Map- 273 Version number. 275 To each mapping, a version number is associated and changes each time 276 the mapping is changed. Note that map-versioning does not introduce 277 new problems concerning the coordination of different ETRs of a 278 domain. Indeed, ETRs belonging to the same LISP site must return for 279 a specific EID-prefix the same mapping, including the same Map- 280 Version number. In principle this is orthogonal to whether or not 281 map-versioning is used. The synchronization problem and its 282 implication on the traffic is out of the scope of this document (see 283 Section 12). 285 In order to announce in a data-driven fashion that the mapping has 286 been updated, Map-Version numbers used to create the outer IP header 287 of the LISP-encapsulated packet are embedded in the LISP-specific 288 header. This means that the header needs to contain two Map-Version 289 numbers: 291 o The Source Map-Version number of the EID-to-RLOC mapping in the 292 EID-to-RLOC Database used to select the source RLOC. 294 o The Destination Map-Version number of the EID-to-RLOC mapping in 295 the EID-to-RLOC Cache used to select the destination RLOC. 297 By embedding both Source Map-Version number and Destination Map- 298 Version number an ETR receiving a LISP packet with Map-Version 299 numbers, can perform the following checks: 301 1. The ITR that has sent the packet has an up-to-date mapping in its 302 EID-to-RLOC Cache for the destination EID and is performing 303 encapsulation correctly. 305 2. In case of bidirectional traffic, the mapping in the local ETR 306 EID-to-RLOC Cache for the source EID is up-to-date. 308 If one or both of the above conditions do not hold, the ETR can send 309 a Map-Request either to make the ITR aware that a new mapping is 310 available (see Section 5.1) or to update the mapping in the local 311 EID-to-RLOC Cache (see Section 5.2). 313 5.1. Handling Destination Map-Version number 315 When an ETR receives a packet, the Destination Map-Version number 316 relates to the mapping for the destination EID for which the ETR is a 317 RLOC. This mapping is part of the ETR EID-to-RLOC Database. Since 318 the ETR is authoritative for the mapping, it has the correct and up- 319 to-date Destination Map-Version number. A check on this version 320 number can be done, where the following cases can arise: 322 1. The packets arrive with the same Destination Map-Version number 323 stored in the EID-to-RLOC Database. This is the regular case. 324 The ITR sending the packet has in its EID-to-RLOC Cache an up-to- 325 date mapping. No further actions are needed. 327 2. The packet arrives with a Destination Map-Version number greater 328 (i.e., newer) than the one stored in the EID-to-RLOC Database. 329 Since the ETR is authoritative on the mapping, meaning that the 330 Map-Version number of its mapping is the correct one, this 331 implies that someone is not behaving correctly with respect to 332 the specifications. In this case the packet carries a version 333 number that is not valid, otherwise the ETR would have the same, 334 and SHOULD be silently dropped. 336 3. The packets arrive with a Destination Map-Version number smaller 337 (i.e., older) than the one stored in the EID-to-RLOC Database. 338 This means that the ITR sending the packet has an old mapping in 339 its EID-to-RLOC Cache containing stale information. The ITR 340 sending the packet has to be informed that a newer mapping is 341 available. This is done with a Map-Request message sent back to 342 the ITR. The Map-Request will either trigger a Map-Request back 343 using the Solicit-Map-Request (SMR) bit or it will piggyback the 344 newer mapping. These are not new mechanisms; how to SMR or 345 piggyback mappings in Map-Request messages is already described 346 in [I-D.ietf-lisp], while their security is discussed in 347 [I-D.ietf-lisp-threats]. These Map-Request messages should be 348 rate limited (rate limitation policies are also described in 349 [I-D.ietf-lisp]). The feature introduced by Map-Version numbers 350 is the possibility of blocking traffic not using the latest 351 mapping. Indeed, after a certain number of retries, if the 352 Destination Map-Version number in the packets is not updated, the 353 ETR MAY drop packets with a stale Map-Version number while 354 strongly reducing the rate of Map-Request messages. This because 355 either the ITR is refusing to use the mapping for which the ETR 356 is authoritative or (worse) it might be some form of attack. 357 Another case might be that the control-plane is experiencing 358 transient failures so the Map-Requests cannot reach that ITR. By 359 keeping sending Map-Requests at very low rate it is possible to 360 recover from this situation. 362 The rule in the third case MAY be more restrictive. If the mapping 363 has been the same for a period of time as long as the TTL (defined in 364 [I-D.ietf-lisp]) of the previous version of the mapping, all packets 365 arriving with an old Map-Version SHOULD be silently dropped right 366 away without issuing any Map-Request. The reason that allows such 367 action is the fact that if the new mapping with the updated version 368 number has been unchanged for at least the same time as the TTL of 369 the older mapping, all the entries in the EID-to-RLOC Caches of ITRs 370 must have expired. Hence, all ITRs sending traffic should have 371 refreshed the mapping according to [I-D.ietf-lisp]. If packets with 372 old Map-Version number are still received, then either someone has 373 not respected the TTL, or it is a form of spoof/attack. In both 374 cases this is not valid behavior with respect to the specifications 375 and the packet SHOULD be silently dropped. 377 LISP-encapsulated packets with the V-bit set, when the original 378 mapping in the EID-to-RLOC Database has version number set to the 379 Null Map-Version value, MAY be silently dropped. As explained in 380 Section 4.1, if an EID-to-RLOC mapping has a Null Map-Version, it 381 means that ITRs, using the mapping for encapsulation, MUST NOT use 382 Map-Version number in the LISP-specific header. 384 For LISP-encapsulated packets with the V-bit set, when the original 385 mapping in the EID-to-RLOC Database has version number set to a value 386 different from the Null Map-Version value, a Destination Map-Version 387 number equal to the Null Map-Version value means that the Destination 388 Map-Version number MUST be ignored. 390 5.2. Handling Source Map-Version number 392 When an ETR receives a packet, the Source Map-Version number relates 393 to the mapping for the source EID for which the ITR that sent the 394 packet is authoritative. If the ETR has an entry in its EID-to-RLOC 395 Cache for the source EID, then a check can be performed and the 396 following cases can arise: 398 1. The packet arrives with the same Source Map-Version number stored 399 in the EID-to-RLOC Cache. This is the correct regular case. The 400 ITR has in its EID-to-RLOC Cache an up-to-date copy of the 401 mapping. No further actions are needed. 403 2. The packet arrives with a Source Map-Version number greater 404 (i.e., newer) than the one stored in the local EID-to-RLOC Cache. 405 This means that ETR has in its EID-to-RLOC Cache a mapping that 406 is stale and needs to be updated. A Map-Request SHOULD be sent 407 to get the new mapping for the source EID. This is a normal Map- 408 Request message sent through the mapping system and MUST respect 409 the specifications in [I-D.ietf-lisp], including rate limitation 410 policies. 412 3. The packet arrives with a Source Map-Version number smaller 413 (i.e., older) than the one stored in the local EID-to-RLOC Cache. 414 Such a case is not valid with respect to the specifications. 415 Indeed, if the mapping is already present in the EID-to-RLOC 416 Cache, this means that an explicit Map-Request has been sent and 417 a Map-Reply has been received from an authoritative source. 418 Assuming that the mapping system is not corrupted anyhow, the 419 Map-Version in the EID-to-RLOC Cache is the correct one, while 420 the one carried by the packet is stale. In this situation the 421 packet MAY be silently dropped. 423 If the ETR does not have an entry in the EID-to-RLOC Cache for the 424 source EID (e.g., in case of unidirectional traffic) then the Source 425 Map-Version number can be safely ignored. 427 For LISP-encapsulated packets with the V-bit set, if the Source Map- 428 Version number is the Null Map-Version value, it means that the 429 Source Map-Version number MUST be ignored. 431 6. LISP header and Map-Version numbers 433 In order for the versioning approach to work, the LISP specific 434 header has to carry both Source Map-Version number and Destination 435 Map-Version number. This is done by setting the V-bit in the LISP 436 specific header as defined in [I-D.ietf-lisp] Section 5.3. When the 437 V-bit is set the low-order 24-bits of the first longword are used to 438 transport both source and destination Map-Version numbers. In 439 particular the first 12 bits are used for Source Map-Version number 440 and the second 12 bits for the Destination Map-Version number. 442 Hereafter is the example of LISP header carrying version numbers in 443 the case of IPv4-in-IPv4 encapsulation. The same setting can be used 444 for any other case (IPv4-in-IPv6, IPv6-in-IPv4, and IPv6-in-IPv6). 446 0 1 2 3 447 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 1 448 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 449 / |N|L|E|V|I|flags| Source Map-Version |Destination Map-Version| 450 LISP+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 451 \ | Instance ID/Locator Status Bits | 452 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 454 Source Map-Version number (12 bits): Map-Version of the mapping used 455 by the ITR to select the RLOC present in the "Source Routing 456 Locator" field. How to set on transmission and handle on 457 reception this value is described in Section 5.2. 459 Destination Map-Version number (12 bits): Map-Version of the mapping 460 used by the ITR to select the RLOC present in the "Destination 461 Routing Locator" field. How to set on transmission and handle on 462 reception this value is described in Section 5.1. 464 The present document just specifies how to use the low-order 24-bits 465 of the first longword of the LISP-specific header when the V-bit is 466 set to 1. All other cases, including the bit fields of the rest of 467 the LISP-specific header and the whole LISP packet format are 468 specified in [I-D.ietf-lisp]. Not all of the LISP encapsulated 469 packets need to carry version numbers. When Map-Version numbers are 470 carried the V-bit MUST be set to 1. All legal combinations of the 471 flags, when the V-bit is set to 1, are described in [I-D.ietf-lisp]. 473 7. Map Record and Map-Version 475 To accommodate the proposed mechanism, the Map Records that are 476 transported on Map-Request/Map-Reply/Map-Register messages need to 477 carry the Map-Version number as well. For this purpose the 12-bits 478 before the EID-AFI field in the Record that describe a mapping is 479 used. This is defined in Section 6.1.4 of [I-D.ietf-lisp] and 480 reported here as example. 482 0 1 2 3 483 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 1 484 +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 485 | | Record TTL | 486 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 487 R | Locator Count | EID mask-len | ACT |A| Reserved | 488 e +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 489 c | Rsvd | Map-Version Number | EID-prefix-AFI | 490 o +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 491 r | EID-prefix | 492 d +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 493 | /| Priority | Weight | M Priority | M Weight | 494 | L +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 495 | o | Unused Flags |L|p|R| Loc-AFI | 496 | c +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 497 | \| Locator | 498 +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 500 Map-Version Number: Map-Version of the mapping contained in the 501 Record. As explained in Section 4.1 this field can be zero (0), 502 meaning that no Map-Version is associated to the mapping, hence 503 packets that are LISP-encapsulated using this mapping MUST NOT 504 contain Map-Version numbers in the LISP specific header and the 505 V-bit MUST be set to 0. 507 This packet format works perfectly with xTRs that do not support Map- 508 Versioning, since they can simply ignore those bits. 510 8. Benefits and case studies for Map-Versioning 512 In the following sections we provide more discussion on various 513 aspects and use of the Map-Versioning. Security observations are 514 instead grouped in Section 10. 516 8.1. Map-Versioning and unidirectional traffic 518 When using Map-Versioning the LISP specific header carries two Map- 519 Version numbers, for both source and destination mappings. This can 520 raise the question on what will happen in the case of unidirectional 521 flows, like for instance in the case presented in Figure 1, since 522 LISP specification do not mandate for ETR to have a mapping for the 523 source EID. 525 +-----------------+ +-----------------+ 526 | Domain A | | Domain B | 527 | +---------+ +---------+ | 528 | | ITR A |----------->| ETR B | | 529 | +---------+ +---------+ | 530 | | | | 531 +-----------------+ +-----------------+ 533 Figure 1 535 For what concerns the ITR, it is able to put both source and 536 destination version number in the LISP header since the Source Map- 537 Version number is in ITR's database, while the Destination Map- 538 Version number is in ITR's cache. 540 For what concerns the ETR, it simply checks only the Destination Map- 541 Version number in the same way as described in Section 5, ignoring 542 the Source Map-Version number. 544 8.2. Map-Versioning and interworking 546 Map-Versioning is compatible with the LISP interworking between LISP 547 and non-LISP sites as defined in [I-D.ietf-lisp-interworking]. LISP 548 interworking defines three techniques to make LISP sites and non-LISP 549 sites, namely Proxy-ITR, LISP-NAT, and Proxy-ETR. Hereafter it is 550 described how Map-Versioning relates to these three mechanisms. 552 8.2.1. Map-Versioning and Proxy-ITRs 554 The purpose of the Proxy-ITR (PITR) is to encapsulate traffic 555 originating in a non-LISP site in order to deliver the packet to one 556 of the ETRs of the LISP site (cf. Figure 2). This case is very 557 similar to the unidirectional traffic case described in Section 8.1, 558 hence similar rules apply. 560 +----------+ +-------------+ 561 | LISP | | non-LISP | 562 | Domain A | | Domain B | 563 | +-------+ +-----------+ | | 564 | | ETR A |<-------| Proxy ITR |<-------| | 565 | +-------+ +-----------+ | | 566 | | | | 567 +----------+ +-------------+ 569 Figure 2 571 The main difference is that a Proxy-ITR does not have any mapping, 572 since it just encapsulate packets arriving from non-LISP site, thus 573 cannot provide a Source Map-Version. In this case, the proxy-ITR 574 will just put the Null Map-Version value as Source Map-Version 575 number, while the receiving ETR will ignore the field. 577 With this setup the LISP Domain A is able to check whether or not the 578 PITR is using the latest mapping. If this is not the case the 579 mapping for LISP Domain A on the PITR can be updated using one of the 580 mechanisms defined in [I-D.ietf-lisp] and 581 [I-D.ietf-lisp-interworking]. 583 8.2.2. Map-Versioning and LISP-NAT 585 The LISP-NAT mechanism is based on address translation from non- 586 routable EIDs to routable EIDs and does not involve any form of 587 encapsulation. As such Map-Versioning does not apply in this case. 589 8.2.3. Map-Versioning and Proxy-ETRs 591 The purpose of the Proxy-ETR (PETR) is to decapsulate traffic 592 originating in a LISP site in order to deliver the packet to the non- 593 LISP site (cf. Figure 3). One of the main reasons of deploy PETRs is 594 to bypass uRPF (Unicast Reverse Path Forwarding) checks on the 595 provider edge. 597 +----------+ +-------------+ 598 | LISP | | non-LISP | 599 | Domain A | | Domain B | 600 | +-------+ +-----------+ | | 601 | | ITR A |------->| Proxy ETR |------->| | 602 | +-------+ +-----------+ | | 603 | | | | 604 +----------+ +-------------+ 606 Figure 3 608 A Proxy-ETR does not have any mapping, since it just decapsulates 609 packets arriving from LISP site. In this case, the ITR will just put 610 the Null Map-Version value as Destination Map-Version number, while 611 the receiving Proxy-ETR will ignore the field. 613 With this setup the Proxy-ETR is able to check whether or not the 614 mapping has changed. If this is the case the mapping for LISP Domain 615 A on the PETR can be updated using one of the mechanisms defined in 616 [I-D.ietf-lisp] and [I-D.ietf-lisp-interworking]. 618 8.3. RLOC shutdown/withdraw 620 Map-Versioning can be even used to perform a graceful shutdown or 621 withdraw of a specific RLOC. This is achieved by simply issuing a 622 new mapping, with an updated Map-Version number, where the specific 623 RLOC to be shut down is withdrawn or announced as unreachable (R bit 624 in the Map Record, see [I-D.ietf-lisp]), but without actually turning 625 it off. 627 Once no more traffic is received by the RLOC, it can be shut down 628 gracefully, because at least all sites actively using the mapping 629 have updated it. 631 It should be pointed out that for frequent up/down changes such a 632 mechanism should not be used since this can generate excessive load 633 on the Mapping System. 635 8.4. Map-Version for lightweight LISP implementation 637 The use of Map-Versioning can help in developing a lightweight 638 implementation of LISP. This comes with the price of not supporting 639 Loc-Status-Bit, which are useful in some contexts. 641 In the current LISP specifications the set of RLOCs must always be 642 maintained ordered and consistent with the content of the Loc Status 643 Bits (see section 6.5 of [I-D.ietf-lisp]). With Map-Versioning such 644 type of mechanisms can be avoided. When a new RLOC is added to a 645 mapping, it is not necessary to "append" new locators to the existing 646 ones as explained in Section 6.5 of [I-D.ietf-lisp]. A new mapping 647 with a new Map-Version number will be issued, and since the old 648 locators are still valid the transition will be with no disruptions. 649 The same applies for the case a RLOC is withdrawn. There is no need 650 to maintain holes in the list of locators, as is the case when using 651 Locator Status Bits, for sites that are not using the RLOC that has 652 been withdrawn the transition will be with no disruptions. 654 All of these operations, as already stated, do not need to maintain 655 any consistency among Locator Status Bits, and the way RLOC are 656 stored in the EID-to-RLOC Cache. 658 Further, Map-Version can be used to substitute the "clock sweep" 659 operation described in Section 6.5.1 of [I-D.ietf-lisp]. Indeed, 660 every LISP site communicating to a specific LISP site that has 661 updated the mapping will be informed of the available new mapping in 662 a data-driven manner. 664 Note that what is proposed in the present section is just an example 665 and MUST NOT be considered as specifications for a lightweight LISP 666 implementation. In case the IETF decides to undertake such a work, 667 it will be documented elsewhere. 669 9. Incremental deployment and implementation status 671 Map-Versioning can be incrementally deployed without any negative 672 impact on existing LISP elements (e.g., xTRs, Map-Servers, Proxy- 673 ITRs, etc). Any LISP element that does not support Map-Versioning 674 can safely ignore them. Further, there is no need of any specific 675 mechanism to discover if an xTR supports or not Map-Versioning. This 676 information is already included in the Map Record. 678 Map-Versioning is currently implemented in OpenLISP 679 [I-D.iannone-openlisp-implementation]. 681 Note that the reference document for LISP implementation and 682 interoperability tests remains [I-D.ietf-lisp]. 684 10. Security Considerations 686 Map-Versioning does not introduce any security issue concerning both 687 the data-plane and the control-plane. On the contrary, as described 688 in the following, if Map-Versioning may be used also to update 689 mappings in case of change in the reachability information (i.e., 690 instead of the Locator Status Bits) it is possible to reduce the 691 effects of some DoS or spoofing attacks that can happen in an 692 untrusted environment. 694 Robustness of the Map-Versioning mechanism leverages on a trusted 695 Mapping Distribution System. A thorough security analysis of LISP is 696 documented in [I-D.ietf-lisp-threats]. 698 10.1. Map-Versioning against traffic disruption 700 An attacker can try to disrupt ongoing communications by creating 701 LISP encapsulated packets with wrong Locator Status Bits. If the xTR 702 blindly trusts the Locator Status Bits it will change the 703 encapsulation accordingly, which can result in traffic disruption. 705 This does not happen in the case of Map-Versioning. As described in 706 Section 5, upon a version number change the xTR first issues a Map- 707 Request. The assumption is that the mapping distribution system is 708 sufficiently secure that Map-Request and Map-Reply messages and their 709 content can be trusted. Security issues concerning specific mapping 710 distribution system are out of the scope of this document. In the 711 case of Map-Versioning the attacker should "guess" a valid version 712 number that triggers a Map-Request, as described in Section 5, 713 otherwise the packet is simply dropped. Nevertheless, guessing a 714 version number that generates a Map-Request is easy, hence it is 715 important to follow the rate limitations policies described in 716 [I-D.ietf-lisp] in order to avoid DoS attacks. 718 Note that a similar level of security can be obtained with Loc Status 719 Bits, by simply making mandatory to verify any change through a Map- 720 Request. However, in this case Locator Status Bits loose their 721 meaning, because, it does not matter anymore which specific bits has 722 changed, the xTR will query the mapping system and trust the content 723 of the received Map-Reply. Furthermore there is no way to perform 724 filtering as in the Map-Versioning in order to drop packets that do 725 not carry a valid Map-Version number. In the case of Locator Status 726 Bits, any random change can trigger a Map-Request (unless rate 727 limitation is enabled which raise another type of attack discussed in 728 Section 10.2). 730 10.2. Map-Versioning against reachability information DoS 732 Attackers can try to trigger a large amount of Map-Request by simply 733 forging packets with random Map-Version or random Locator Status 734 Bits. In both cases the Map-Requests are rate limited as described 735 in [I-D.ietf-lisp]. However, differently from Locator Status Bit 736 where there is no filtering possible, in the case of Map-Versioning 737 is possible to filter not valid version numbers before triggering a 738 Map-Request, thus helping in reducing the effects of DoS attacks. In 739 other words the use of Map-Versioning enables a fine control on when 740 to update a mapping or when to notify that a mapping has been 741 updated. 743 It is clear, that Map-Versioning does not protect against DoS and 744 DDoS attacks, where an xTR looses processing power doing checks on 745 the LISP header of packets sent by attackers. This is independent 746 from Map-Versioning and is the same for Loc Status Bits. 748 11. IANA Considerations 750 This document has no actions for IANA. 752 12. Open Issues and Considerations 754 There are a number of implications of the use of Map-Versioning that 755 are not yet completely explored. Among these are: 757 o Performance of the convergence time when an EID-to-RLOC mapping 758 changes, i.e., how much time is needed to update mappings in the 759 EID-to-RLOC Cache of the ITRs currently sending traffic to ETRs 760 for the EID whose mapping has been changed. 762 o Support to ETR synchronization.The implications that a temporary 763 lack of synchronization may have on the traffic is yet to be fully 764 explored. Details on how to keep synchronization are presented in 765 Section 6.6 of [I-D.ietf-lisp]. Section 12.1 hereafter discusses 766 the issue in further details with respect to the Map-Versioning 767 mechanism. 769 The authors expect that experimentation will help assess the 770 performance and the limitations of the Map-Versioning mechanism. 771 Issues and concerns about the deployment of LISP for Internet traffic 772 are discussed in [I-D.ietf-lisp]. 774 12.1. Lack of Synchronization among ETRs 776 Even without Map-Versioning, LISP ([I-D.ietf-lisp]) requires ETRs to 777 announce the same mapping for the same EID-Prefix to a requester. 778 The implications that a temporary lack of synchronization may have on 779 the traffic is yet to be fully explored. 781 Map-Versioning does not require additional synchronization mechanism 782 compared to the normal functioning of LISP without Map-Versioning. 783 Clearly all the ETRs have to reply with the same Map-Version number, 784 otherwise there can be an inconsistency that creates additional 785 control traffic, instabilities, traffic disruptions. It is the same 786 without Map-Versioning, with ETRs that have to reply with the same 787 mapping, otherwise the same problems can arise. 789 There are two ways Map-Versioning is helpful with respect to the 790 synchronization problem. On the one hand, assigning version numbers 791 to mappings helps in debugging, since quick checks on the consistency 792 of the mappings on different ETRs can be done by looking at the Map- 793 Version number. On the other hand, Map-Versioning can be used to 794 control the traffic toward ETRs that announce the latest mapping. 796 As an example, let's consider the topology of Figure 4 where ITR A.1 797 of domain A is sending unidirectional traffic to the domain B, while 798 A.2 of domain A exchange bidirectional traffic with domain B. In 799 particular, ITR A.2 send traffic to ETR B and ETR A.2 receives 800 traffic from ITR B. 802 +-----------------+ +-----------------+ 803 | Domain A | | Domain B | 804 | +---------+ | | 805 | | ITR A.1 |--- | | 806 | +---------+ \ +---------+ | 807 | | ------->| ETR B | | 808 | | ------->| | | 809 | +---------+ / | | | 810 | | ITR A.2 |--- -----| ITR B | | 811 | | | / +---------+ | 812 | | ETR A.2 |<----- | | 813 | +---------+ | | 814 | | | | 815 +-----------------+ +-----------------+ 817 Figure 4 819 Obviously in the case of Map-Versioning both ITR A.1 and ITR A.2 of 820 domain A must use the same value otherwise the ETR of domain B will 821 start to send Map-Requests. 823 The same problem can, however, arise without Map-Versioning. For 824 instance, if the two ITRs of domain A send different Loc Status Bits. 825 In this case either the traffic is disrupted, if the ETR B trusts the 826 Locator Status Bits, or if ETR B does not trusts the Locator Status 827 Bits it will start sending Map-Requests to confirm the each change in 828 the reachability. 830 So far, LISP does not provide any specific synchronization mechanism, 831 but assumes that synchronization is provided by configuring the 832 different xTRs consistently (see Section 6.6 in [I-D.ietf-lisp]). 833 The same applies for Map-Versioning. If in the future any 834 synchronization mechanism is provided, Map-Versioning will take 835 advantage of it automatically since it is included in the Record 836 format, as described in Section 7. 838 13. Acknowledgements 840 The authors would like to thank Alia Atlas, Jesper Skriver, Pierre 841 Francois, Noel Chiappa, Dino Farinacci for their comments and review. 843 This work has been partially supported by the INFSO-ICT-216372 844 TRILOGY Project (www.trilogy-project.org). 846 14. References 848 14.1. Normative References 850 [I-D.ietf-lisp] 851 Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, 852 "Locator/ID Separation Protocol (LISP)", 853 draft-ietf-lisp-19 (work in progress), January 2012. 855 [I-D.ietf-lisp-interworking] 856 Lewis, D., Meyer, D., Farinacci, D., and V. Fuller, 857 "Interworking LISP with IPv4 and IPv6", 858 draft-ietf-lisp-interworking-02 (work in progress), 859 June 2011. 861 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 862 Requirement Levels", BCP 14, RFC 2119, March 1997. 864 14.2. Informative References 866 [I-D.iannone-openlisp-implementation] 867 Iannone, L., Saucez, D., and O. Bonaventure, "OpenLISP 868 Implementation Report", 869 draft-iannone-openlisp-implementation-01 (work in 870 progress), July 2008. 872 [I-D.ietf-lisp-alt] 873 Fuller, V., Farinacci, D., Meyer, D., and D. Lewis, "LISP 874 Alternative Topology (LISP+ALT)", draft-ietf-lisp-alt-10 875 (work in progress), December 2011. 877 [I-D.ietf-lisp-ms] 878 Fuller, V. and D. Farinacci, "LISP Map Server Interface", 879 draft-ietf-lisp-ms-15 (work in progress), January 2012. 881 [I-D.ietf-lisp-threats] 882 Saucez, D., Iannone, L., and O. Bonaventure, "LISP Threats 883 Analysis", draft-ietf-lisp-threats-00 (work in progress), 884 July 2011. 886 Appendix A. Estimation of time before Map-Version wrap-around 888 The present section proposes an estimation of the wrap-around time 889 for the proposed 12 bits size for the Map-Version number. Using a 890 granularity of seconds and assuming as worst-case that a new version 891 is issued each second, it takes slightly more than 1 hour before the 892 version wraps around. Note that the granularity of seconds is in 893 line with the rate limitation policy for Map-Request messages, as 894 proposed in the LISP main specifications ([I-D.ietf-lisp]). 895 Alternatively a granularity of minutes can also be used, as for the 896 TTL of the Map-Reply ([I-D.ietf-lisp]). In this case the worst 897 scenario is when a new version is issued every minute, leading to a 898 much longer time before wrap-around. In particular, when using 12 899 bits, the wrap-around time is almost 3 days. 901 For general information, hereafter there is a table with a rough 902 estimation of the time before wrap-around in the worst-case scenario, 903 considering different sizes (bits length) of the Map-Version number 904 and different time granularity. 906 +---------------+--------------------------------------------+ 907 |Version Number | Time before wrap around | 908 | Size (bits) +---------------------+----------------------+ 909 | |Granularity: Minutes | Granularity: Seconds | 910 | | (mapping changes | (mapping changes | 911 | | every 1 minute) | every 1 second) | 912 +-------------------------------------+----------------------+ 913 | 32 | 8171 Years | 136 Years | 914 | 30 | 2042 Years | 34 Years | 915 | 24 | 31 Years | 194 Days | 916 | 16 | 45 Days | 18 Hours | 917 | 15 | 22 Days | 9 Hours | 918 | 14 | 11 Days | 4 Hours | 919 | 13 | 5.6 Days | 2.2 Hours | 920 | 12 | 2.8 Days | 1.1 Hours | 921 +---------------+---------------------+----------------------+ 923 Figure 5: Estimation of time before wrap-around 925 Appendix B. Document Change Log 927 o Version 07 Posted January 2012. 929 * Moved Subsection 8.1 in Section 12 as requested by R. Bonica. 931 * Added explicit reference to the discussion about ETR 932 synchronization at the end of the Introduction, as requested by 933 R. Bonica. 935 * Added cross-reference to Section 6.6 in [I-D.ietf-lisp] as 936 requested by R. Bonica. 938 * Moved [I-D.ietf-lisp-interworking] as normative reference as 939 requested by R. Droms. 941 * Added long version of all acronyms in the Introduction as 942 requested by S. Bryant. 944 o Version 06 Posted October 2011. 946 * Added disclaimer in the Introduction about general issues 947 concerning LISP as requested by A. Farrel. 949 * Fixed sentence about legacy systems in the abstract as 950 requested by A. Farrel. 952 * Added Section 12 as requested by A. Farrel. 954 o Version 05 Posted October 2011. 956 * Added sentence in Section 3 on the use of Big Endian, as for 957 comment of P. Resnick. 959 * Extended the end of Section 4 in order to clarify that Map- 960 Version numbers are assigned to mappings by configuration and 961 not automatically generated by ETRs, as for comments of R. 962 Sparks 964 * Changed formal definition of Map-Version order (greater vs. 965 smaller) in Section 4 as for comments from R. Housley and R. 966 Sparks. 968 * Added disclaimer in Section 1 stating that in case of unforseen 969 conflict with the main spec the base document has precedence on 970 the present one, as for comment from Sthephen Farrell. 972 o Version 04 Posted September 2011. 974 * Added clarifications in Section 1, Section 4, Section 5.2, and 975 Section 5.1 to address Stephen Farrell's comments. 977 * Used the term LISP Site instead of ISP in Section 5 as 978 suggested by Stephen Farrell. 980 * Deleted "(usually contains the nonce)" from Section 6 because 981 confusing, as suggested by Stephen Farrell. 983 * Fixed several typos pointed out by Stephen Farrell. 985 o Version 03 Posted September 2011. 987 * Added reference in Section 7 toward the main lisp documents 988 specifying the section, as requested by Jari Arkko. 990 * Fixed all typos and editorial issues pointed out by Jari Arkko. 992 * Added clarification in Section 8.3 as requested by Jari Arkko. 994 * Extentend all acronyms in the abstract as requested by Jari 995 Arkko. 997 * Clarified silent drop polocy in Section 5.2 as requested by 998 both Richard Barnes and Jari Arkko. 1000 * Fixed typos pointed out by Richard Barnes. 1002 o Version 02 Posted July 2011. 1004 * Added text in Section 5 about ETR synchronization, as suggested 1005 by Alia Atlas. 1007 * Modified text in Section 8.4 concerning lightweight LISP 1008 implementation, as suggested by Alia Atlas. 1010 * Deleted text concerning old versions of [I-D.ietf-lisp-ms] and 1011 [I-D.ietf-lisp-alt] in Section 7, as pointed out by Alia Atlas. 1013 * Fixed section 4.1 to be less restrictive, as suggested by 1014 Jesper Skriver. 1016 o Version 01 Posted March 2011. 1018 * Changed the wording from "Map-Version number 0" to "Null Map- 1019 Version. 1021 * Clarification of the use of the Null Map-Version value as 1022 Source Map-Version Number and Destination Map-Version Number. 1024 * Extended the section describing Map-Versioning and LISP 1025 Interworking co-existence. 1027 * Reduce packet format description to avoid double definitions 1028 with the main specs. 1030 o Version 00 Posted September 2010. 1032 * Added Section "Definitions of Terms". 1034 * Editorial polishing of all sections. 1036 * Added clarifications in section "Dealing with Map-Version 1037 numbers" for the case of the special Map-Version number 0. 1039 * Rename of draft-iannone-mapping-versioning-02.txt. 1041 Authors' Addresses 1043 Luigi Iannone 1044 Telekom Innovation Laboratories 1045 Ernst-Reuter Platz 7 1046 Berlin 1047 Germany 1049 Email: luigi@net.t-labs.tu-berlin.de 1051 Damien Saucez 1052 INRIA Sophia Antipolis 1053 2004 route des Lucioles - BP 93 1054 Sophia Antipolis 1055 France 1057 Email: damien.saucez@inria.fr 1059 Olivier Bonaventure 1060 Universite catholique de Louvain 1061 Place St. Barbe 2 1062 Louvain-la-Neuve 1063 Belgium 1065 Email: olivier.bonaventure@uclouvain.be