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Saucez 5 Intended status: Standards Track INRIA Sophia Antipolis 6 Expires: February 17, 2020 O. Bonaventure 7 Universite catholique de Louvain 8 August 16, 2019 10 Locator/ID Separation Protocol (LISP) Map-Versioning 11 draft-ietf-lisp-6834bis-04 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 the 20 transport of such a version number in the LISP-specific header of 21 LISP-encapsulated packets. LISP Map-Versioning is particularly 22 useful to inform communicating Ingress Tunnel Routers (ITRs) and 23 Egress Tunnel Routers (ETRs) about modifications of the mappings used 24 to encapsulate packets. The mechanism is optional and transparent to 25 implementations not supporting this feature, since in the LISP- 26 specific header and in the Map Records, bits used for Map-Versioning 27 can be safely ignored by ITRs and ETRs that do not support or do not 28 want to use the mechanism. 30 This document obsoletes RFC 6834 "Locator/ID Separation Protocol 31 (LISP) Map-Versioning", which is the initial experimental 32 specifications of the mechanisms updated by this document. 34 Status of This Memo 36 This Internet-Draft is submitted in full conformance with the 37 provisions of BCP 78 and BCP 79. 39 Internet-Drafts are working documents of the Internet Engineering 40 Task Force (IETF). Note that other groups may also distribute 41 working documents as Internet-Drafts. The list of current Internet- 42 Drafts is at https://datatracker.ietf.org/drafts/current/. 44 Internet-Drafts are draft documents valid for a maximum of six months 45 and may be updated, replaced, or obsoleted by other documents at any 46 time. It is inappropriate to use Internet-Drafts as reference 47 material or to cite them other than as "work in progress." 48 This Internet-Draft will expire on February 17, 2020. 50 Copyright Notice 52 Copyright (c) 2019 IETF Trust and the persons identified as the 53 document authors. All rights reserved. 55 This document is subject to BCP 78 and the IETF Trust's Legal 56 Provisions Relating to IETF Documents 57 (https://trustee.ietf.org/license-info) in effect on the date of 58 publication of this document. Please review these documents 59 carefully, as they describe your rights and restrictions with respect 60 to this document. Code Components extracted from this document must 61 include Simplified BSD License text as described in Section 4.e of 62 the Trust Legal Provisions and are provided without warranty as 63 described in the Simplified BSD License. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 68 2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 4 69 3. Definitions of Terms . . . . . . . . . . . . . . . . . . . . 4 70 4. EID-to-RLOC Map-Version Number . . . . . . . . . . . . . . . 4 71 4.1. The Null Map-Version . . . . . . . . . . . . . . . . . . 5 72 5. Dealing with Map-Version Numbers . . . . . . . . . . . . . . 6 73 5.1. Handling Destination Map-Version Number . . . . . . . . . 7 74 5.2. Handling Source Map-Version Number . . . . . . . . . . . 9 75 6. LISP Header and Map-Version Numbers . . . . . . . . . . . . . 10 76 7. LISP Generic Protocol Encapsulation (GPE) Header and Map- 77 Version Numbers . . . . . . . . . . . . . . . . . . . . . . . 10 78 8. Map Record and Map-Version . . . . . . . . . . . . . . . . . 11 79 9. Benefits and Case Studies for Map-Versioning . . . . . . . . 12 80 9.1. Map-Versioning and Unidirectional Traffic . . . . . . . . 12 81 9.2. Map-Versioning and Interworking . . . . . . . . . . . . . 13 82 9.2.1. Map-Versioning and Proxy-ITRs . . . . . . . . . . . . 13 83 9.2.2. Map-Versioning and LISP-NAT . . . . . . . . . . . . . 14 84 9.2.3. Map-Versioning and Proxy-ETRs . . . . . . . . . . . . 14 85 9.3. RLOC Shutdown/Withdraw . . . . . . . . . . . . . . . . . 14 86 9.4. Map-Version Additional Use Cases . . . . . . . . . . . . 15 87 10. Security Considerations . . . . . . . . . . . . . . . . . . . 15 88 10.1. Map-Versioning against Traffic Disruption . . . . . . . 15 89 10.2. Map-Versioning against Reachability Information DoS . . 16 90 11. Deployment Considerations . . . . . . . . . . . . . . . . . . 16 91 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 92 13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18 93 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 94 14.1. Normative References . . . . . . . . . . . . . . . . . . 18 95 14.2. Informative References . . . . . . . . . . . . . . . . . 19 97 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 99 1. Introduction 101 This document describes the Map-Versioning mechanism used to provide 102 information on changes in the EID-to-RLOC (Endpoint ID to Routing 103 Locator) mappings used in the LISP (Locator/ID Separation Protocol 104 [I-D.ietf-lisp-rfc6830bis][I-D.ietf-lisp-rfc6833bis]) context to 105 perform packet encapsulation. The mechanism is totally transparent 106 to xTRs (Ingress and Egress Tunnel Routers) not supporting or not 107 using such functionality. 109 This document obsoletes [RFC6834], which is the initial experimental 110 specifications of the mechanisms updated by this document. 112 The basic mechanism is to associate a Map-Version number to each LISP 113 EID-to-RLOC mapping and transport such a version number in the LISP- 114 specific header. When a mapping changes, a new version number is 115 assigned to the updated mapping. A change in an EID-to-RLOC mapping 116 can be a change in the RLOCs set, by adding or removing one or more 117 RLOCs, but it can also be a change in the priority or weight of one 118 or more RLOCs. 120 When Map-Versioning is used, LISP-encapsulated data packets contain 121 the version number of the two mappings used to select the RLOCs in 122 the outer header (i.e., both source and destination). These version 123 numbers are encoded in the 24 low-order bits of the first longword of 124 the LISP header and indicated by a specific bit in the flags (first 8 125 high-order bits of the first longword of the LISP header). Note that 126 not all packets need to carry version numbers. 128 When an ITR (Ingress Tunnel Router) encapsulates a data packet, with 129 a LISP header containing the Map-Version numbers, it puts in the 130 LISP-specific header two version numbers: 132 1. The version number assigned to the mapping (contained in the EID- 133 to-RLOC Database) used to select the source RLOC. 135 2. The version number assigned to the mapping (contained in the EID- 136 to-RLOC Cache) used to select the destination RLOC. 138 This operation is two-fold. On the one hand, it enables the ETR 139 (Egress Tunnel Router) receiving the packet to know if the ITR is 140 using the latest mapping version that any ETR at the destination EID 141 site would provide to the ITR in a Map-Reply. If this is not the 142 case, the ETR can send to the ITR a Map-Request containing the 143 updated mapping or solicit a Map-Request from the ITR (both cases are 144 already defined in [I-D.ietf-lisp-rfc6833bis]). In this way, the ITR 145 can update its EID-to-RLOC Cache. On the other hand, it enables an 146 ETR receiving such a packet to know if it has in its EID-to-RLOC 147 Cache the latest mapping for the source EID. If this is not the 148 case, a Map-Request can be sent. 150 Considerations about the deployment of LISP Map-Versioning are 151 discussed in Section 11. 153 2. Requirements Notation 155 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 156 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 157 "OPTIONAL" in this document are to be interpreted as described in BCP 158 14 [RFC2119] [RFC8174] when, and only when, they appear in all 159 capitals, as shown here. 161 3. Definitions of Terms 163 This document uses terms already defined in the main LISP 164 specification (, [I-D.ietf-lisp-rfc6830bis] 165 [I-D.ietf-lisp-rfc6833bis]). Here, we define the terms that are 166 specific to the Map-Versioning mechanism. Throughout the whole 167 document, Big Endian bit ordering is used. 169 Map-Version number: An unsigned 12-bit integer is assigned to an 170 EID-to-RLOC mapping, not including the value 0 (0x000). 172 Null Map-Version: The 12-bit null value of 0 (0x000) is not used as 173 a Map-Version number. It is used to signal that no Map-Version 174 number is assigned to the EID-to-RLOC mapping. 176 Source Map-Version number: This Map-Version number of the EID-to- 177 RLOC mapping is used to select the source address (RLOC) of the 178 outer IP header of LISP-encapsulated packets. 180 Destination Map-Version number: This Map-Version number of the EID- 181 to-RLOC mapping is used to select the destination address (RLOC) of 182 the outer IP header of LISP-encapsulated packets. 184 4. EID-to-RLOC Map-Version Number 186 The EID-to-RLOC Map-Version number consists of an unsigned 12-bit 187 integer. The version number is assigned on a per-mapping basis, 188 meaning that different mappings have a different version number, 189 which is also updated independently. An update in the version number 190 (i.e., a newer version) consists of incrementing by one the older 191 version number. 193 The space of version numbers has a circular order where half of the 194 version numbers are greater (i.e., newer) than the current Map- 195 Version number and the other half of the version numbers are smaller 196 (i.e., older) than the current Map-Version number. In a more formal 197 way, assuming that we have two version numbers V1 and V2 and that the 198 numbers are expressed on N bits, the following steps MUST be 199 performed (in the same order as shown below) to strictly define their 200 order: 202 1. V1 = V2 : The Map-Version numbers are the same. 204 2. V2 > V1 : if and only if 206 V2 > V1 AND (V2 - V1) <= 2**(N-1) 208 OR 210 V1 > V2 AND (V1 - V2) > 2**(N-1) 212 3. V1 > V2 : otherwise. 214 Using 12 bits, as defined in this document, and assuming a Map- 215 Version value of 69, Map-Version numbers in the range [70; 69 + 2048] 216 are greater than 69, while Map-Version numbers in the range [69 + 217 2049; (69 + 4096) mod 4096] are smaller than 69. 219 Map-version numbers are assigned to mappings by configuration. The 220 initial Map-Version number of a new EID-to-RLOC mapping SHOULD be 221 assigned randomly, but it MUST NOT be set to the Null Map-Version 222 value (0x000), because the Null Map-Version number has a special 223 meaning (see Section 4.1). 225 Upon reboot, an ETR will use mappings configured in its EID-to-RLOC 226 Database. If those mappings have a Map-Version number, it will be 227 used according to the mechanisms described in this document. ETRs 228 MUST NOT automatically generate and assign Map-Version numbers to 229 mappings in the EID-to-RLOC Database. 231 4.1. The Null Map-Version 233 The value 0x000 (zero) is not a valid Map-Version number indicating 234 the version of the EID-to-RLOC mapping. Such a value is used for 235 special purposes and is named the Null Map-Version number. 237 The Null Map-Version MAY appear in the LISP-specific header as either 238 a Source Map-Version number (cf. Section 5.2) or a Destination Map- 239 Version number (cf. Section 5.1). When the Source Map-Version 240 number is set to the Null Map-Version value, it means that no map 241 version information is conveyed for the source site. This means that 242 if a mapping exists for the source EID in the EID-to-RLOC Cache, then 243 the ETR MUST NOT compare the received Null Map-Version with the 244 content of the EID-to-RLOC Cache. When the Destination Map-Version 245 number is set to the Null Map-Version value, it means that no map 246 version information is conveyed for the destination site. This means 247 that the ETR MUST NOT compare the value with the Map-Version number 248 of the mapping for the destination EID present in the EID-to-RLOC 249 Database. 251 The other use of the Null Map-Version number is in the Map Records, 252 which are part of the Map-Request, Map-Reply, and Map-Register 253 messages (defined in [I-D.ietf-lisp-rfc6833bis]). Map Records that 254 have a Null Map-Version number indicate that there is no Map-Version 255 number associated with the mapping. This means that LISP- 256 encapsulated packets destined to the EID-Prefix referred to by the 257 Map Record MUST either not contain any Map-Version numbers (V bit set 258 to 0) or, if they contain Map-Version numbers (V bit set to 1), then 259 the destination Map-Version number MUST be set to the Null Map- 260 Version number. Any value different from zero means that Map- 261 Versioning is supported and MAY be used. 263 The fact that the 0 value has a special meaning for the Map-Version 264 number implies that, when updating a Map-Version number because of a 265 change in the mapping, if the next value is 0, then the Map-Version 266 number MUST be incremented by 2 (i.e., set to 1, which is the next 267 valid value). 269 5. Dealing with Map-Version Numbers 271 The main idea of using Map-Version numbers is that whenever there is 272 a change in the mapping (e.g., adding/removing RLOCs, a change in the 273 weights due to Traffic Engineering policies, or a change in the 274 priorities) or a LISP site realizes that one or more of its own RLOCs 275 are not reachable anymore from a local perspective (e.g., through 276 IGP, or policy changes) the LISP site updates the mapping, also 277 assigning a new Map-Version number. 279 To each mapping, a version number is associated and changes each time 280 the mapping is changed. Note that Map-Versioning does not introduce 281 new problems concerning the coordination of different ETRs of a 282 domain. Indeed, ETRs belonging to the same LISP site must return for 283 a specific EID-prefix the same mapping, including the same Map- 284 Version number. This is orthogonal to whether or not Map-Versioning 285 is used. The synchronization problem and its implications on the 286 traffic are out of the scope of this document. 288 In order to announce in a data-driven fashion that the mapping has 289 been updated, Map-Version numbers used to create the outer IP header 290 of the LISP-encapsulated packet are embedded in the LISP-specific 291 header. This means that the header needs to contain two Map-Version 292 numbers: 294 o The Source Map-Version number of the EID-to-RLOC mapping in the 295 EID-to-RLOC Database used to select the source RLOC. 297 o The Destination Map-Version number of the EID-to-RLOC mapping in 298 the EID-to-RLOC Cache used to select the destination RLOC. 300 By embedding both the Source Map-Version number and the Destination 301 Map-Version number, an ETR receiving a LISP packet with Map-Version 302 numbers can perform the following checks: 304 1. The ITR that has sent the packet has an up-to-date mapping in its 305 EID-to-RLOC Cache for the destination EID and is performing 306 encapsulation correctly. 308 2. In the case of bidirectional traffic, the mapping in the local 309 ETR EID-to-RLOC Cache for the source EID is up to date. 311 If one or both of the above conditions do not hold, the ETR can send 312 a Map-Request either to make the ITR aware that a new mapping is 313 available (see Section 5.1) or to update the mapping in the local 314 EID-to-RLOC Cache (see Section 5.2). 316 5.1. Handling Destination Map-Version Number 318 When an ETR receives a packet, the Destination Map-Version number 319 relates to the mapping for the destination EID for which the ETR is 320 an RLOC. This mapping is part of the ETR EID-to-RLOC Database. 321 Since the ETR is authoritative for the mapping, it has the correct 322 and up-to-date Destination Map-Version number. A check on this 323 version number can be done, where the following cases can arise: 325 1. The packet arrives with the same Destination Map-Version number 326 stored in the EID-to-RLOC Database. This is the regular case. 327 The ITR sending the packet has in its EID-to-RLOC Cache an up-to- 328 date mapping. No further actions are needed. 330 2. The packet arrives with a Destination Map-Version number greater 331 (i.e., newer) than the one stored in the EID-to-RLOC Database. 332 Since the ETR is authoritative on the mapping, meaning that the 333 Map-Version number of its mapping is the correct one, this 334 implies that someone is not behaving correctly with respect to 335 the specifications. In this case, the packet carries a version 336 number that is not valid; otherwise, the ETR would have the same 337 number, and the packet SHOULD be silently dropped. 339 3. The packets arrive with a Destination Map-Version number smaller 340 (i.e., older) than the one stored in the EID-to-RLOC Database. 341 This means that the ITR sending the packet has an old mapping in 342 its EID-to-RLOC Cache containing stale information. The ETR MAY 343 choose to normally process the encapsulated datagram according to 344 [I-D.ietf-lisp-rfc6830bis]; however, the ITR sending the packet 345 has to be informed that a newer mapping is available. This is 346 done with a Map-Request message sent back to the ITR. The Map- 347 Request will either trigger a Map-Request back using the Solicit- 348 Map-Request (SMR) bit or it will piggyback the newer mapping. 349 These are not new mechanisms; how to use the SMR bit or how to 350 piggyback mappings in Map-Request messages is already described 351 in [I-D.ietf-lisp-rfc6833bis]. One feature introduced by Map- 352 Version numbers is the possibility of blocking traffic not using 353 the latest mapping. Indeed, after a certain number of retries, 354 if the Destination Map-Version number in the packets is not 355 updated, the ETR MAY drop packets with a stale Map-Version number 356 while strongly reducing the rate of Map-Request messages. This 357 is because either the ITR is refusing to use the mapping for 358 which the ETR is authoritative, or (worse) it might be some form 359 of attack. 361 The rule in the third case MAY be more restrictive. If the mapping 362 has been the same for a period of time as long as the Time To Live 363 (TTL) (defined in [I-D.ietf-lisp-rfc6833bis]) of the previous version 364 of the mapping, all packets arriving with an old Map-Version SHOULD 365 be silently dropped right away without issuing any Map-Request. Such 366 action is permitted because if the new mapping with the updated 367 version number has been unchanged for at least the same time as the 368 TTL of the older mapping, all the entries in the EID-to-RLOC Caches 369 of ITRs must have expired. Hence, all ITRs sending traffic should 370 have refreshed the mapping according to [I-D.ietf-lisp-rfc6833bis]. 371 If packets with old Map-Version numbers are still received, then 372 either someone has not respected the TTL or it is a form of spoof/ 373 attack. In both cases, this is not valid behavior with respect to 374 the specifications and the packet SHOULD be silently dropped. 376 LISP-encapsulated packets with the V-bit set, when the original 377 mapping in the EID-to-RLOC Database has the version number set to the 378 Null Map-Version value, MAY be silently dropped. As explained in 379 Section 4.1, if an EID-to-RLOC mapping has a Null Map-Version, it 380 means that ITRs, using the mapping for encapsulation, MUST NOT use a 381 Map-Version number in the LISP-specific header. 383 For LISP-encapsulated packets with the V-bit set, when the original 384 mapping in the EID-to-RLOC Database has the version number set to a 385 value different from the Null Map-Version value, a Destination Map- 386 Version number equal to the Null Map-Version value means that the 387 Destination Map-Version number MUST be ignored. 389 5.2. Handling Source Map-Version Number 391 When an ETR receives a packet, the Source Map-Version number relates 392 to the mapping for the source EID for which the ITR that sent the 393 packet is authoritative. If the ETR has an entry in its EID-to-RLOC 394 Cache for the source EID, then a check can be performed and the 395 following cases can arise: 397 1. The packet arrives with the same Source Map-Version number as 398 that stored in the EID-to-RLOC Cache. This is the correct 399 regular case. The ITR has in its EID-to-RLOC Cache an up-to-date 400 copy of the mapping. No further actions are needed. 402 2. The packet arrives with a Source Map-Version number greater 403 (i.e., newer) than the one stored in the local EID-to-RLOC Cache. 404 This means that the ETR has in its EID-to-RLOC Cache a mapping 405 that is stale and needs to be updated. A Map-Request SHOULD be 406 sent to get the new mapping for the source EID. This is a normal 407 Map-Request message sent through the mapping system and MUST 408 respect the specifications in [I-D.ietf-lisp-rfc6833bis], 409 including rate-limitation policies. 411 3. The packet arrives with a Source Map-Version number smaller 412 (i.e., older) than the one stored in the local EID-to-RLOC Cache. 413 Such a case is not valid with respect to the specifications. 414 Indeed, if the mapping is already present in the EID-to-RLOC 415 Cache, this means that an explicit Map-Request has been sent and 416 a Map-Reply has been received from an authoritative source. 417 Assuming that the mapping system is not corrupted, the Map- 418 Version in the EID-to-RLOC Cache is the correct one, while the 419 one carried by the packet is stale. In this situation, the 420 packet MAY be silently dropped. 422 If the ETR does not have an entry in the EID-to-RLOC Cache for the 423 source EID, then the Source Map-Version number can be ignored. 425 For LISP-encapsulated packets with the V-bit set, if the Source Map- 426 Version number is the Null Map-Version value, it means that the 427 Source Map-Version number MUST be ignored. 429 6. LISP Header and Map-Version Numbers 431 In order for the versioning approach to work, the LISP-specific 432 header has to carry both the Source Map-Version number and 433 Destination Map-Version number. This is done by setting the V-bit in 434 the LISP-specific header as defined in [I-D.ietf-lisp-rfc6830bis]. 435 When the V-bit is set and the P bit is reset (0), the low-order 24 436 bits of the first longword are used to transport both the source and 437 destination Map-Version numbers. In particular, the first 12 bits 438 are used for the Source Map-Version number and the second 12 bits for 439 the Destination Map-Version number. 441 Below is an example of a LISP header carrying version numbers. 443 0 1 2 3 444 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 1 445 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 446 / |N|L|E|V|I|P|K|K| Source Map-Version |Destination Map-Version| 447 LISP+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 448 \ | Instance ID/Locator Status Bits | 449 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 451 Source Map-Version number (12 bits): Map-Version of the mapping used 452 by the ITR to select the RLOC present in the "Source Routing 453 Locator" field. Section 5.2 describes how to set this value on 454 transmission and handle it on reception. 456 Destination Map-Version number (12 bits): Map-Version of the mapping 457 used by the ITR to select the RLOC present in the "Destination 458 Routing Locator" field. Section 5.1 describes how to set this 459 value on transmission and handle it on reception. 461 Not all of the LISP-encapsulated packets need to carry version 462 numbers. When Map-Version numbers are carried in these packets, the 463 V-bit MUST be set to 1. All permissible combinations of the flags 464 when the V-bit is set to 1 are described in 465 [I-D.ietf-lisp-rfc6830bis] and [I-D.ietf-lisp-gpe]. 467 7. LISP Generic Protocol Encapsulation (GPE) Header and Map-Version 468 Numbers 470 [I-D.ietf-lisp-gpe] extends the Locator/ID Separation Protocol (LISP) 471 Data-Plane, changing the LISP header, to support multi-protocol 472 encapsulation. A flag in the LISP header, called the P-bit, is used 473 to signal the presence of the Next Protocol field in the low-order 8 474 bits of the first longword. When the V-bit and P-bit are both set, 475 the middle-order 16 bits of the first longword are used to transport 476 both the source and destination Map-Version numbers. In particular, 477 the first 8 bits are used for the Source Map-Version number and the 478 second 8 bits for the Destination Map-Version number. 480 Below is an example of a LISP header carrying version numbers. 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 / |N|L|E|V|I|P|K|K|Src Map-Version|Dst Map-Version| Next Protocol | 486 LISP+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 487 \ | Instance ID/Locator Status Bits | 488 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 490 The Source Map-Version number and the Destination Map-Version number 491 are used exactly in the same way previously described. There are 492 only three differences: 494 o When filling the LISP-GPE-specific header only the low order 8 495 bits are copied in the Source and Destination Map-Version Number 496 (out of the original 12 bits). 498 o When comparing a Map-Version retrieved from the LISP-GPE-specific 499 header (either Source or Destination Map-Version number) with the 500 version number of a mapping (stored in the LISP Cache or LISP 501 Database) only the low-order 8 bits of the latter are used for the 502 comparison. 504 o When trimming a Map-Version number from 12 to 8 bits it may happen 505 that it is converted to a Null Map-Version number, which will 506 change the way Map-Version number is interpreted as described in 507 Section 4.1. To avoid such wrong behavior, Map-Version number 508 with the low-order 8 bits all equal to zero SHOULD be avoided on 509 xTRs using LISP-GPE. 511 8. Map Record and Map-Version 513 To accommodate the proposed mechanism, the Map Records that are 514 transported in Map-Request/Map-Reply/Map-Register messages need to 515 carry the Map-Version number as well. For this purpose, the 12 bits 516 before the EID-AFI field in the Record that describes a mapping are 517 used (see [I-D.ietf-lisp-rfc6833bis] and reported here as an example. 519 0 1 2 3 520 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 1 521 +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 522 | | Record TTL | 523 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 524 R | Locator Count | EID mask-len | ACT |A| Reserved | 525 e +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 526 c | Rsvd | Map-Version Number | EID-Prefix-AFI | 527 o +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 528 r | EID-Prefix | 529 d +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 530 | /| Priority | Weight | M Priority | M Weight | 531 | L +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 532 | o | Unused Flags |L|p|R| Loc-AFI | 533 | c +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 534 | \| Locator | 535 +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 537 Map-Version Number: Map-Version of the mapping contained in the 538 Record. As explained in Section 4.1, this field can be zero (0), 539 meaning that no Map-Version is associated to the mapping; hence, 540 packets that are LISP encapsulated using this mapping MUST NOT 541 contain Map-Version numbers in the LISP-specific header, and the 542 V-bit MUST be set to 0. 544 This packet format works perfectly with xTRs that do not support Map- 545 Versioning, since they can simply ignore those bits. 547 9. Benefits and Case Studies for Map-Versioning 549 In the following sections, we provide more discussion on various 550 aspects and uses of Map-Versioning. Security observations are 551 grouped in Section 10. 553 9.1. Map-Versioning and Unidirectional Traffic 555 When using Map-Versioning, the LISP-specific header carries two Map- 556 Version numbers, for both source and destination mappings. This can 557 raise the question on what will happen in the case of unidirectional 558 flows, for instance, in the case presented in Figure 1, since the 559 LISP specification does not mandate that the ETR have a mapping for 560 the source EID. 562 +-----------------+ +-----------------+ 563 | Domain A | | Domain B | 564 | +---------+ +---------+ | 565 | | ITR A |----------->| ETR B | | 566 | +---------+ +---------+ | 567 | | | | 568 +-----------------+ +-----------------+ 570 Figure 1: Unidirectional traffic between LISP domains. 572 In the case of the ITR, the ITR is able to put both the source and 573 destination version number in the LISP header, since the Source Map- 574 Version number is in the ITR's database, while the Destination Map- 575 Version number is in the ITR's cache. 577 In the case of the ETR, the ETR simply checks only the Destination 578 Map-Version number in the same way as that described in Section 5, 579 ignoring the Source Map-Version number. 581 9.2. Map-Versioning and Interworking 583 Map-Versioning is compatible with the LISP interworking between LISP 584 and non-LISP sites as defined in [RFC6832]. LISP interworking 585 defines three techniques to make LISP sites and non-LISP sites, 586 namely Proxy-ITR, LISP-NAT, and Proxy-ETR. The following text 587 describes how Map-Versioning relates to these three mechanisms. 589 9.2.1. Map-Versioning and Proxy-ITRs 591 The purpose of the Proxy-ITR (PITR) is to encapsulate traffic 592 originating in a non-LISP site in order to deliver the packet to one 593 of the ETRs of the LISP site (cf. Figure 2). This case is very 594 similar to the unidirectional traffic case described in Section 9.1; 595 hence, similar rules apply. 597 +----------+ +-------------+ 598 | LISP | | non-LISP | 599 | Domain A | | Domain B | 600 | +-------+ +-----------+ | | 601 | | ETR A |<-------| Proxy ITR |<-------| | 602 | +-------+ +-----------+ | | 603 | | | | 604 +----------+ +-------------+ 606 Figure 2: Unidirectional traffic from non-LISP domain to LISP domain. 608 The main difference is that a Proxy-ITR does not have any mapping, 609 since it just encapsulates packets arriving from the non-LISP site, 610 and thus cannot provide a Source Map-Version. In this case, the 611 proxy-ITR will just put the Null Map-Version value as the Source Map- 612 Version number, while the receiving ETR will ignore the field. 614 With this setup, LISP Domain A is able to check whether or not the 615 PITR is using the latest mapping. 617 9.2.2. Map-Versioning and LISP-NAT 619 The LISP-NAT mechanism is based on address translation from non- 620 routable EIDs to routable EIDs and does not involve any form of 621 encapsulation. As such, Map-Versioning does not apply in this case. 623 9.2.3. Map-Versioning and Proxy-ETRs 625 The purpose of the Proxy-ETR (PETR) is to decapsulate traffic 626 originating in a LISP site in order to deliver the packet to the non- 627 LISP site (cf. Figure 3). One of the main reasons to deploy PETRs 628 is to bypass uRPF (Unicast Reverse Path Forwarding) checks on the 629 provider edge. 631 +----------+ +-------------+ 632 | LISP | | non-LISP | 633 | Domain A | | Domain B | 634 | +-------+ +-----------+ | | 635 | | ITR A |------->| Proxy ETR |------->| | 636 | +-------+ +-----------+ | | 637 | | | | 638 +----------+ +-------------+ 640 Figure 3: Unidirectional traffic from LISP domain to non-LISP domain. 642 A Proxy-ETR does not have any mapping, since it just decapsulates 643 packets arriving from the LISP site. In this case, the ITR will just 644 put the Null Map-Version value as the Destination Map-Version number, 645 while the receiving Proxy-ETR will ignore the field. 647 With this setup, the Proxy-ETR is able to check whether or not the 648 mapping has changed. 650 9.3. RLOC Shutdown/Withdraw 652 Map-Versioning can also be used to perform a graceful shutdown or 653 withdraw of a specific RLOC. This is achieved by simply issuing a 654 new mapping, with an updated Map-Version number where the specific 655 RLOC to be shut down is withdrawn or announced as unreachable (via 656 the R bit in the Map Record; see [I-D.ietf-lisp-rfc6833bis]), but 657 without actually turning it off. 659 Once no more traffic is received by the RLOC, it can be shut down 660 gracefully, because all sites actively using the mapping have updated 661 it. 663 9.4. Map-Version Additional Use Cases 665 The use of Map-Versioning can help in developing a lightweight 666 implementation of LISP. However, this comes with the price of not 667 supporting the Loc-Status-Bit, which may be useful in some contexts. 669 In the current LISP specifications, the set of RLOCs must always be 670 maintained ordered and consistent with the content of the Loc Status 671 Bits ([I-D.ietf-lisp-rfc6830bis]). With Map-Versioning, such types 672 of mechanisms can be avoided. When a new RLOC is added to a mapping, 673 it is not necessary to "append" new locators to the existing ones as 674 explained in [I-D.ietf-lisp-rfc6830bis]. A new mapping with a new 675 Map-Version number will be issued, and since the old locators are 676 still valid, the transition will occur with no disruptions. The same 677 applies for the case where an RLOC is withdrawn. There is no need to 678 maintain holes in the list of locators, as is the case when using 679 Locator Status Bits, for sites that are not using the RLOC that has 680 been withdrawn; in this case, the transition will occur with no 681 disruptions. 683 All of these operations, as already stated, do not need to maintain 684 any consistency among Locator Status Bits and in the way that the 685 RLOCs are stored in the EID-to-RLOC Cache. 687 10. Security Considerations 689 Map-Versioning does not introduce any security issues concerning both 690 the data plane and the control plane. On the contrary, as described 691 below, if Map-Versioning may also be used to update mappings in the 692 case of change in the reachability information (i.e., instead of the 693 Locator Status Bits), it is possible to reduce the effects of some 694 DoS or spoofing attacks that can happen in an untrusted environment. 696 Robustness of the Map-Versioning mechanism leverages on a trusted 697 Mapping Distribution System. A thorough security analysis of LISP is 698 documented in [RFC7835]. 700 10.1. Map-Versioning against Traffic Disruption 702 An attacker can try to disrupt ongoing communications by creating 703 LISP-encapsulated packets with wrong Locator Status Bits. If the xTR 704 blindly trusts the Locator Status Bits, it will change the 705 encapsulation accordingly, which can result in traffic disruption. 707 This does not happen in the case of Map-Versioning. As described in 708 Section 5, upon a version number change the xTR first issues a Map- 709 Request. The assumption is that the mapping distribution system is 710 sufficiently secure that Map-Request and Map-Reply messages and their 711 content can be trusted. Security issues concerning specific mapping 712 distribution systems are out of the scope of this document. In the 713 case of Map-Versioning, the attacker should "guess" a valid version 714 number that triggers a Map-Request as described in Section 5; 715 otherwise, the packet is simply dropped. Nevertheless, guessing a 716 version number that generates a Map-Request is easy; hence, it is 717 important to follow the rate-limitation policies described in 718 [I-D.ietf-lisp-rfc6833bis] in order to avoid DoS attacks. 720 Note that a similar level of security can be obtained with Loc Status 721 Bits by simply making it mandatory to verify any change through a 722 Map-Request. However, in this case Locator Status Bits lose their 723 meaning, because it does not matter anymore which specific bits have 724 changed; the xTR will query the mapping system and trust the content 725 of the received Map-Reply. Furthermore, there is no way to perform 726 filtering as in Map-Versioning in order to drop packets that do not 727 carry a valid Map-Version number. In the case of Locator Status 728 Bits, any random change can trigger a Map-Request (unless rate 729 limitation is enabled, which raises another type of attack as 730 discussed in Section 10.2). 732 10.2. Map-Versioning against Reachability Information DoS 734 Attackers can try to trigger a large number of Map-Requests by simply 735 forging packets with random Map-Versions or random Locator Status 736 Bits. In both cases, the Map-Requests are rate-limited as described 737 in [I-D.ietf-lisp-rfc6833bis]. However, in contrast to the Locator 738 Status Bit, where there is no filtering possible, in the case of Map- 739 Versioning it is possible to filter invalid version numbers before 740 triggering a Map-Request, thus helping to reduce the effects of DoS 741 attacks. In other words, the use of Map-Versioning enables a fine 742 control on when to update a mapping or when to notify someone that a 743 mapping has been updated. 745 It is clear that Map-Versioning does not protect against DoS and DDoS 746 attacks, where an xTR loses processing power when doing checks on the 747 LISP header of packets sent by attackers. This is independent of 748 Map-Versioning and is the same for Loc Status Bits. 750 11. Deployment Considerations 752 Even without Map-Versioning, LISP requires ETRs to announce the same 753 mapping for the same EID-Prefix to a requester. Map-Versioning does 754 not require additional synchronization mechanisms as compared to the 755 normal functioning of LISP without Map-Versioning. Clearly, all the 756 ETRs have to reply with the same Map-Version number; otherwise, there 757 can be an inconsistency that creates additional control traffic, 758 instabilities, and traffic disruptions. It is the same without Map- 759 Versioning, with ETRs that have to reply with the same mapping; 760 otherwise, the same problems can arise. 762 There are two ways Map-Versioning is helpful with respect to the 763 synchronization problem. On the one hand, assigning version numbers 764 to mappings helps in debugging, since quick checks on the consistency 765 of the mappings on different ETRs can be done by looking at the Map- 766 Version number. On the other hand, Map-Versioning can be used to 767 control the traffic toward ETRs that announce the latest mapping. 769 As an example, let's consider the topology of Figure 4 where ITR A.1 770 of Domain A is sending unidirectional traffic to Domain B, while A.2 771 of Domain A exchanges bidirectional traffic with Domain B. In 772 particular, ITR A.2 sends traffic to ETR B, and ETR A.2 receives 773 traffic from ITR B. 775 +-----------------+ +-----------------+ 776 | Domain A | | Domain B | 777 | +---------+ | | 778 | | ITR A.1 |--- | | 779 | +---------+ \ +---------+ | 780 | | ------->| ETR B | | 781 | | ------->| | | 782 | +---------+ / | | | 783 | | ITR A.2 |--- -----| ITR B | | 784 | | | / +---------+ | 785 | | ETR A.2 |<----- | | 786 | +---------+ | | 787 | | | | 788 +-----------------+ +-----------------+ 790 Figure 4: Example topology. 792 Obviously, in the case of Map-Versioning, both ITR A.1 and ITR A.2 of 793 Domain A must use the same value; otherwise, the ETR of Domain B will 794 start to send Map-Requests. 796 The same problem can, however, arise without Map-Versioning, for 797 instance, if the two ITRs of Domain A send different Locator Status 798 Bits. In this case, either the traffic is disrupted if ETR B trusts 799 the Locator Status Bits, or if ETR B does not trust the Locator 800 Status Bits it will start sending Map-Requests to confirm each change 801 in reachability. 803 So far, LISP does not provide any specific synchronization mechanism 804 but assumes that synchronization is provided by configuring the 805 different xTRs consistently. The same applies for Map-Versioning. 806 If in the future any synchronization mechanism is provided, Map- 807 Versioning will take advantage of it automatically, since it is 808 included in the Record format, as described in Section 8. 810 12. IANA Considerations 812 This document includes no request to IANA. 814 13. Acknowledgments 816 This work benefited support from NewNet@Paris, Cisco's Chair 817 "Networks for the Future" at Telecom ParisTech 818 (http://newnet.telecom-paristech.fr). Any opinions, findings or 819 recommendations expressed in this material are those of the author(s) 820 and do not necessarily reflect the views of partners of the Chair. 822 14. References 824 14.1. Normative References 826 [I-D.ietf-lisp-gpe] 827 Maino, F., Lemon, J., Agarwal, P., Lewis, D., and M. 828 Smith, "LISP Generic Protocol Extension", draft-ietf-lisp- 829 gpe-06 (work in progress), September 2018. 831 [I-D.ietf-lisp-rfc6830bis] 832 Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A. 833 Cabellos-Aparicio, "The Locator/ID Separation Protocol 834 (LISP)", draft-ietf-lisp-rfc6830bis-27 (work in progress), 835 June 2019. 837 [I-D.ietf-lisp-rfc6833bis] 838 Farinacci, D., Maino, F., Fuller, V., and A. Cabellos- 839 Aparicio, "Locator/ID Separation Protocol (LISP) Control- 840 Plane", draft-ietf-lisp-rfc6833bis-25 (work in progress), 841 June 2019. 843 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 844 Requirement Levels", BCP 14, RFC 2119, 845 DOI 10.17487/RFC2119, March 1997, 846 . 848 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 849 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 850 May 2017, . 852 14.2. Informative References 854 [RFC6832] Lewis, D., Meyer, D., Farinacci, D., and V. Fuller, 855 "Interworking between Locator/ID Separation Protocol 856 (LISP) and Non-LISP Sites", RFC 6832, 857 DOI 10.17487/RFC6832, January 2013, 858 . 860 [RFC6834] Iannone, L., Saucez, D., and O. Bonaventure, "Locator/ID 861 Separation Protocol (LISP) Map-Versioning", RFC 6834, 862 DOI 10.17487/RFC6834, January 2013, 863 . 865 [RFC7835] Saucez, D., Iannone, L., and O. Bonaventure, "Locator/ID 866 Separation Protocol (LISP) Threat Analysis", RFC 7835, 867 DOI 10.17487/RFC7835, April 2016, 868 . 870 Authors' Addresses 872 Luigi Iannone 873 Telecom ParisTech 875 EMail: ggx@gigix.net 877 Damien Saucez 878 INRIA Sophia Antipolis 880 EMail: damien.saucez@inria.fr 882 Olivier Bonaventure 883 Universite catholique de Louvain 885 EMail: olivier.bonaventure@uclouvain.be