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Bonaventure 7 Universite catholique de Louvain 8 March 24, 2021 10 Locator/ID Separation Protocol (LISP) Map-Versioning 11 draft-ietf-lisp-6834bis-08 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 September 25, 2021. 50 Copyright Notice 52 Copyright (c) 2021 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 . . . . . . . . . . . . . 9 76 7. Map Record and Map-Version . . . . . . . . . . . . . . . . . 10 77 8. Benefits and Case Studies for Map-Versioning . . . . . . . . 11 78 8.1. Map-Versioning and Unidirectional Traffic . . . . . . . . 11 79 8.2. Map-Versioning and Interworking . . . . . . . . . . . . . 12 80 8.2.1. Map-Versioning and Proxy-ITRs . . . . . . . . . . . . 12 81 8.2.2. Map-Versioning and LISP-NAT . . . . . . . . . . . . . 13 82 8.2.3. Map-Versioning and Proxy-ETRs . . . . . . . . . . . . 13 83 8.3. RLOC Shutdown/Withdraw . . . . . . . . . . . . . . . . . 13 84 8.4. Map-Version Additional Use Cases . . . . . . . . . . . . 14 85 9. Security Considerations . . . . . . . . . . . . . . . . . . . 14 86 10. Deployment Considerations . . . . . . . . . . . . . . . . . . 14 87 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 88 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 89 12.1. Normative References . . . . . . . . . . . . . . . . . . 16 90 12.2. Informative References . . . . . . . . . . . . . . . . . 16 91 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 93 1. Introduction 95 This document describes the Map-Versioning mechanism used to provide 96 information on changes in the EID-to-RLOC (Endpoint ID to Routing 97 Locator) mappings used in the LISP (Locator/ID Separation Protocol 98 [I-D.ietf-lisp-rfc6830bis][I-D.ietf-lisp-rfc6833bis]) context to 99 perform packet encapsulation. The mechanism is totally transparent 100 to xTRs (Ingress and Egress Tunnel Routers) not supporting or not 101 using such functionality. 103 This document obsoletes [RFC6834], which is the initial experimental 104 specifications of the mechanisms updated by this document. 106 The basic mechanism is to associate a Map-Version number to each LISP 107 EID-to-RLOC mapping and transport such a version number in the LISP- 108 specific header. When a mapping changes, a new version number is 109 assigned to the updated mapping. A change in an EID-to-RLOC mapping 110 can be a change in the RLOCs set, by adding or removing one or more 111 RLOCs, but it can also be a change in the priority or weight of one 112 or more RLOCs. 114 When Map-Versioning is used, LISP-encapsulated data packets contain 115 the version number of the two mappings used to select the RLOCs in 116 the outer header (i.e., both source and destination RLOCs). These 117 version numbers are encoded in the 24 low-order bits of the first 118 longword of the LISP header and indicated by a specific bit in the 119 flags (first 8 high-order bits of the first longword of the LISP 120 header). Note that not all packets need to carry version numbers. 122 When an ITR (Ingress Tunnel Router) encapsulates a data packet, with 123 a LISP header containing the Map-Version numbers, it puts in the 124 LISP-specific header two version numbers: 126 1. The version number assigned to the mapping used to select the 127 source RLOC (contained in the EID-to-RLOC Database). 129 2. The version number assigned to the mapping used to select the 130 destination RLOC (contained in the EID-to-RLOC Map-Cache). 132 This operation is two-fold. On the one hand, it enables the ETR 133 (Egress Tunnel Router) receiving the packet to know if the ITR is 134 using the latest mapping version that any ETR at the destination EID 135 site would provide to the ITR in a Map-Reply. If this is not the 136 case, the ETR can send to the ITR a Map-Request containing the 137 updated mapping or solicit a Map-Request from the ITR (both cases are 138 already defined in [I-D.ietf-lisp-rfc6833bis]). In this way, the ITR 139 can update its EID-to-RLOC Map-Cache. On the other hand, it enables 140 an ETR receiving such a packet to know if it has in its EID-to-RLOC 141 Map-Cache the latest mapping for the source EID. If this is not the 142 case, a Map-Request can be sent. 144 Considerations about the deployment of LISP Map-Versioning are 145 discussed in Section 10. 147 2. Requirements Notation 149 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 150 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 151 "OPTIONAL" in this document are to be interpreted as described in BCP 152 14 [RFC2119] [RFC8174] when, and only when, they appear in all 153 capitals, as shown here. 155 3. Definitions of Terms 157 This document uses terms already defined in the main LISP 158 specification ([I-D.ietf-lisp-rfc6830bis], 159 [I-D.ietf-lisp-rfc6833bis]). Here, we define the terms that are 160 specific to the Map-Versioning mechanism. Throughout the whole 161 document, Big Endian bit ordering is used. 163 Map-Version number: An unsigned 12-bit integer is assigned to an 164 EID-to-RLOC mapping, not including the value 0 (0x000). 166 Null Map-Version: The 12-bit null value of 0 (0x000) is not used as 167 a Map-Version number. It is used to signal that no Map-Version 168 number is assigned to the EID-to-RLOC mapping. 170 Source Map-Version number: This Map-Version number of the EID-to- 171 RLOC mapping is used to select the source address (RLOC) of the 172 outer IP header of LISP-encapsulated packets. 174 Destination Map-Version number: This Map-Version number of the EID- 175 to-RLOC mapping is used to select the destination address (RLOC) of 176 the outer IP header of LISP-encapsulated packets. 178 4. EID-to-RLOC Map-Version Number 180 The EID-to-RLOC Map-Version number consists of an unsigned 12-bit 181 integer. The version number is assigned on a per-mapping basis, 182 meaning that different mappings have a different version number, 183 which is also updated independently. An update in the version number 184 (i.e., a newer version) consists of incrementing by one the older 185 version number. 187 The space of version numbers has a circular order where half of the 188 version numbers are greater (i.e., newer) than the current Map- 189 Version number and the other half of the version numbers are smaller 190 (i.e., older) than the current Map-Version number. In a more formal 191 way, assuming that we have two version numbers V1 and V2 and that the 192 numbers are expressed on N bits, the following steps MUST be 193 performed (in the same order as shown below) to strictly define their 194 order: 196 1. V1 = V2 : The Map-Version numbers are the same. 198 2. V2 > V1 : if and only if 200 V2 > V1 AND (V2 - V1) <= 2**(N-1) 202 OR 204 V1 > V2 AND (V1 - V2) > 2**(N-1) 206 3. V1 > V2 : otherwise. 208 Using 12 bits, as defined in this document, and assuming a Map- 209 Version value of 69, Map-Version numbers in the range [70; 69 + 2048] 210 are greater than 69, while Map-Version numbers in the range [69 + 211 2049; (69 + 4096) mod 4096] are smaller than 69. 213 Map-version numbers are assigned to mappings by configuration. The 214 initial Map-Version number of a new EID-to-RLOC mapping SHOULD be 215 assigned randomly, but it MUST NOT be set to the Null Map-Version 216 value (0x000), because the Null Map-Version number has a special 217 meaning (see Section 4.1). 219 Upon reboot, an ETR will use mappings configured in its EID-to-RLOC 220 Database. If those mappings have a Map-Version number, it will be 221 used according to the mechanisms described in this document. ETRs 222 MUST NOT automatically generate and assign Map-Version numbers to 223 mappings in the EID-to-RLOC Database. 225 4.1. The Null Map-Version 227 The value 0x000 (zero) is not a valid Map-Version number indicating 228 the version of the EID-to-RLOC mapping. Such a value is used for 229 special purposes and is named the Null Map-Version number. 231 The Null Map-Version MAY appear in the LISP-specific header as either 232 a Source Map-Version number (cf. Section 5.2) or a Destination Map- 233 Version number (cf. Section 5.1). When the Source Map-Version 234 number is set to the Null Map-Version value, it means that no map 235 version information is conveyed for the source site. This means that 236 if a mapping exists for the source EID in the EID-to-RLOC Map-Cache, 237 then the ETR MUST NOT compare the received Null Map-Version with the 238 content of the EID-to-RLOC Map-Cache. When the Destination Map- 239 Version number is set to the Null Map-Version value, it means that no 240 map version information is conveyed for the destination site. This 241 means that the ETR MUST NOT compare the value with the Map-Version 242 number of the mapping for the destination EID present in the EID-to- 243 RLOC Database. 245 The other use of the Null Map-Version number is in the Map Records, 246 which are part of the Map-Request, Map-Reply, and Map-Register 247 messages (defined in [I-D.ietf-lisp-rfc6833bis]). Map Records that 248 have a Null Map-Version number indicate that there is no Map-Version 249 number associated with the mapping. This means that LISP- 250 encapsulated packets destined to the EID-Prefix referred to by the 251 Map Record MUST either not contain any Map-Version numbers (V bit set 252 to 0) or, if they contain Map-Version numbers (V bit set to 1), then 253 the destination Map-Version number MUST be set to the Null Map- 254 Version number. Any value different from zero means that Map- 255 Versioning is supported and MAY be used. 257 The fact that the 0 value has a special meaning for the Map-Version 258 number implies that, when updating a Map-Version number because of a 259 change in the mapping, if the next value is 0, then the Map-Version 260 number MUST be incremented by 2 (i.e., set to 1 (0x001), which is the 261 next valid value). 263 5. Dealing with Map-Version Numbers 265 The main idea of using Map-Version numbers is that whenever there is 266 a change in the mapping (e.g., adding/removing RLOCs, a change in the 267 weights due to Traffic Engineering policies, or a change in the 268 priorities) or a LISP site realizes that one or more of its own RLOCs 269 are not reachable anymore from a local perspective (e.g., through 270 IGP, or policy changes) the LISP site updates the mapping, also 271 assigning a new Map-Version number. 273 To each mapping, a version number is associated and changes each time 274 the mapping is changed. Note that Map-Versioning does not introduce 275 new problems concerning the coordination of different ETRs of a 276 domain. Indeed, ETRs belonging to the same LISP site must return for 277 a specific EID-prefix the same mapping, including the same Map- 278 Version number. This is orthogonal to whether or not Map-Versioning 279 is used. The synchronization problem and its implications on the 280 traffic are out of the scope of this document. 282 In order to announce in a data-driven fashion that the mapping has 283 been updated, Map-Version numbers used to create the outer IP header 284 of the LISP-encapsulated packet are embedded in the LISP-specific 285 header. This means that the header needs to contain two Map-Version 286 numbers: 288 o The Source Map-Version number of the EID-to-RLOC mapping in the 289 EID-to-RLOC Database used to select the source RLOC. 291 o The Destination Map-Version number of the EID-to-RLOC mapping in 292 the EID-to-RLOC Map-Cache used to select the destination RLOC. 294 By embedding both the Source Map-Version number and the Destination 295 Map-Version number, an ETR receiving a LISP packet with Map-Version 296 numbers can perform the following checks: 298 1. The ITR that has sent the packet has an up-to-date mapping in its 299 EID-to-RLOC Map-Cache for the destination EID and is performing 300 encapsulation correctly. 302 2. In the case of bidirectional traffic, the mapping in the local 303 ETR EID-to-RLOC Map-Cache for the source EID is up to date. 305 If one or both of the above conditions do not hold, the ETR can send 306 a Map-Request either to make the ITR aware that a new mapping is 307 available (see Section 5.1) or to update the mapping in the local 308 EID-to-RLOC Map-Cache (see Section 5.2). 310 5.1. Handling Destination Map-Version Number 312 When an ETR receives a packet, the Destination Map-Version number 313 relates to the mapping for the destination EID for which the ETR is 314 an RLOC. This mapping is part of the ETR EID-to-RLOC Database. 315 Since the ETR is authoritative for the mapping, it has the correct 316 and up-to-date Destination Map-Version number. A check on this 317 version number can be done, where the following cases can arise: 319 1. The packet arrives with the same Destination Map-Version number 320 stored in the EID-to-RLOC Database. This is the regular case. 321 The ITR sending the packet has in its EID-to-RLOC Map-Cache an 322 up-to-date mapping. No further actions are needed. 324 2. The packet arrives with a Destination Map-Version number greater 325 (i.e., newer) than the one stored in the EID-to-RLOC Database. 326 Since the ETR is authoritative on the mapping, meaning that the 327 Map-Version number of its mapping is the correct one, this 328 implies that someone is not behaving correctly with respect to 329 the specifications. In this case, the packet carries a version 330 number that is not valid; otherwise, the ETR would have the same 331 number, and the packet SHOULD be silently dropped. 333 3. The packets arrive with a Destination Map-Version number smaller 334 (i.e., older) than the one stored in the EID-to-RLOC Database. 335 This means that the ITR sending the packet has an old mapping in 336 its EID-to-RLOC Map-Cache containing stale information. The ETR 337 MAY choose to normally process the encapsulated datagram 338 according to [I-D.ietf-lisp-rfc6830bis]; however, the ITR sending 339 the packet has to be informed that a newer mapping is available. 340 This is done with a Map-Request message sent back to the ITR. 341 The Map-Request will either trigger a Map-Request back using the 342 Solicit-Map-Request (SMR) bit or it will piggyback the newer 343 mapping. These are not new mechanisms; how to use the SMR bit or 344 how to piggyback mappings in Map-Request messages is already 345 described in [I-D.ietf-lisp-rfc6833bis]. One feature introduced 346 by Map-Version numbers is the possibility of blocking traffic not 347 using the latest mapping. Indeed, after a certain number of 348 retries, if the Destination Map-Version number in the packets is 349 not updated, the ETR MAY drop packets with a stale Map-Version 350 number while limiting the rate of Map-Request messages. This is 351 because either the ITR is refusing to use the mapping for which 352 the ETR is authoritative, or (worse) it might be some form of 353 attack. 355 The rule in the third case MAY be more restrictive. If the mapping 356 has been the same for a period of time as long as the Time To Live 357 (TTL) (defined in [I-D.ietf-lisp-rfc6833bis]) of the previous version 358 of the mapping, all packets arriving with an old Map-Version SHOULD 359 be silently dropped right away without issuing any Map-Request. Such 360 action is permitted because if the new mapping with the updated 361 version number has been unchanged for at least the same time as the 362 TTL of the older mapping, all the entries in the EID-to-RLOC Map- 363 Caches of ITRs must have expired. Hence, all ITRs sending traffic 364 should have refreshed the mapping according to 365 [I-D.ietf-lisp-rfc6833bis]. If packets with old Map-Version numbers 366 are still received, then either someone has not respected the TTL or 367 it is a form of spoof/attack. In both cases, this is not valid 368 behavior with respect to the specifications and the packet SHOULD be 369 silently dropped. 371 LISP-encapsulated packets with the V-bit set, when the original 372 mapping in the EID-to-RLOC Database has the version number set to the 373 Null Map-Version value, MAY be silently dropped. As explained in 374 Section 4.1, if an EID-to-RLOC mapping has a Null Map-Version, it 375 means that ITRs, using the mapping for encapsulation, MUST NOT use a 376 Map-Version number in the LISP-specific header. 378 For LISP-encapsulated packets with the V-bit set, when the original 379 mapping in the EID-to-RLOC Database has the version number set to a 380 value different from the Null Map-Version value, a Destination Map- 381 Version number equal to the Null Map-Version value means that the 382 Destination Map-Version number MUST be ignored. 384 5.2. Handling Source Map-Version Number 386 When an ETR receives a packet, the Source Map-Version number relates 387 to the mapping for the source EID for which the ITR that sent the 388 packet is authoritative. If the ETR has an entry in its EID-to-RLOC 389 Map-Cache for the source EID, then a check can be performed and the 390 following cases can arise: 392 1. The packet arrives with the same Source Map-Version number as 393 that stored in the EID-to-RLOC Map-Cache. This is the correct 394 regular case. The ITR has in its EID-to-RLOC Map-Cache an up-to- 395 date copy of the mapping. No further actions are needed. 397 2. The packet arrives with a Source Map-Version number greater 398 (i.e., newer) than the one stored in the local EID-to-RLOC Map- 399 Cache. This means that the ETR has in its EID-to-RLOC Map-Cache 400 a mapping that is stale and needs to be updated. A Map-Request 401 SHOULD be sent to get the new mapping for the source EID. This 402 is a normal Map-Request message sent through the mapping system 403 and MUST respect the specifications in 404 [I-D.ietf-lisp-rfc6833bis], including rate-limitation policies. 406 3. The packet arrives with a Source Map-Version number smaller 407 (i.e., older) than the one stored in the local EID-to-RLOC Map- 408 Cache. Such a case is not valid with respect to the 409 specifications. Indeed, if the mapping is already present in the 410 EID-to-RLOC Map-Cache, this means that an explicit Map-Request 411 has been sent and a Map-Reply has been received from an 412 authoritative source. Assuming that the mapping system is not 413 corrupted, the Map-Version in the EID-to-RLOC Map-Cache is the 414 correct one, while the one carried by the packet is stale. In 415 this situation, the packet MAY be silently dropped. 417 If the ETR does not have an entry in the EID-to-RLOC Map-Cache for 418 the source EID, then the Source Map-Version number can be ignored. 420 For LISP-encapsulated packets with the V-bit set, if the Source Map- 421 Version number is the Null Map-Version value, it means that the 422 Source Map-Version number MUST be ignored. 424 6. LISP Header and Map-Version Numbers 426 In order for the versioning approach to work, the LISP-specific 427 header has to carry both the Source Map-Version number and 428 Destination Map-Version number. This is done by setting the V-bit in 429 the LISP-specific header as specified in [I-D.ietf-lisp-rfc6830bis]. 430 When the V-bit is set and the N bit is reset (0), the low-order 24 431 bits of the first longword are used to transport both the source and 432 destination Map-Version numbers. In particular, the first 12 bits 433 are used for the Source Map-Version number and the second 12 bits for 434 the Destination Map-Version number. 436 Below is an example of a LISP header carrying version numbers. 438 0 1 2 3 439 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 1 440 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 441 / |N|L|E|V|I|R|K|K| Source Map-Version |Destination Map-Version| 442 LISP+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 443 \ | Instance ID/Locator Status Bits | 444 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 446 Source Map-Version number (12 bits): Map-Version of the mapping used 447 by the ITR to select the RLOC present in the "Source Routing 448 Locator" field. Section 5.2 describes how to set this value on 449 transmission and handle it on reception. 451 Destination Map-Version number (12 bits): Map-Version of the mapping 452 used by the ITR to select the RLOC present in the "Destination 453 Routing Locator" field. Section 5.1 describes how to set this 454 value on transmission and handle it on reception. 456 Not all of the LISP-encapsulated packets need to carry version 457 numbers. When Map-Version numbers are carried, the V-bit MUST be set 458 to 1. All permissible combinations of the flags when the V-bit is 459 set to 1 are described in [I-D.ietf-lisp-rfc6830bis]. 461 7. Map Record and Map-Version 463 To accommodate the proposed mechanism, the Map Records that are 464 transported in Map-Request/Map-Reply/Map-Register messages need to 465 carry the Map-Version number as well. For this purpose, the 12 bits 466 before the EID-AFI field in the Record that describes a mapping are 467 used (see [I-D.ietf-lisp-rfc6833bis] and reported here as an example. 469 0 1 2 3 470 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 1 471 +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 472 | | Record TTL | 473 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 474 R | Locator Count | EID mask-len | ACT |A| Reserved | 475 e +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 476 c | Rsvd | Map-Version Number | EID-Prefix-AFI | 477 o +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 478 r | EID-Prefix | 479 d +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 480 | /| Priority | Weight | M Priority | M Weight | 481 | L +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 482 | o | Unused Flags |L|p|R| Loc-AFI | 483 | c +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 484 | \| Locator | 485 +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 487 Map-Version Number: Map-Version of the mapping contained in the 488 Record. As explained in Section 4.1, this field can be zero (0), 489 meaning that no Map-Version is associated to the mapping; hence, 490 packets that are LISP encapsulated using this mapping MUST NOT 491 contain Map-Version numbers in the LISP-specific header, and the 492 V-bit MUST be set to 0. 494 This packet format works perfectly with xTRs that do not support Map- 495 Versioning, since they can simply ignore those bits. 497 8. Benefits and Case Studies for Map-Versioning 499 In the following sections, we provide more discussion on various 500 aspects and uses of Map-Versioning. Security observations are 501 grouped in Section 9. 503 8.1. Map-Versioning and Unidirectional Traffic 505 When using Map-Versioning, the LISP-specific header carries two Map- 506 Version numbers, for both source and destination mappings. This can 507 raise the question on what will happen in the case of unidirectional 508 flows, for instance, in the case presented in Figure 1, since the 509 LISP specification does not mandate that the ETR have a mapping for 510 the source EID. 512 +-----------------+ +-----------------+ 513 | Domain A | | Domain B | 514 | +---------+ +---------+ | 515 | | ITR A |----------->| ETR B | | 516 | +---------+ +---------+ | 517 | | | | 518 +-----------------+ +-----------------+ 520 Figure 1: Unidirectional traffic between LISP domains. 522 In the case of the ITR, the ITR is able to put both the source and 523 destination version number in the LISP header, since the Source Map- 524 Version number is in the ITR's database, while the Destination Map- 525 Version number is in the ITR's cache. 527 In the case of the ETR, the ETR simply checks only the Destination 528 Map-Version number in the same way as that described in Section 5, 529 ignoring the Source Map-Version number. 531 8.2. Map-Versioning and Interworking 533 Map-Versioning is compatible with the LISP interworking between LISP 534 and non-LISP sites as defined in [RFC6832]. LISP interworking 535 defines three techniques to make LISP sites and non-LISP sites, 536 namely Proxy-ITR, LISP-NAT, and Proxy-ETR. The following text 537 describes how Map-Versioning relates to these three mechanisms. 539 8.2.1. Map-Versioning and Proxy-ITRs 541 The purpose of the Proxy-ITR (PITR) is to encapsulate traffic 542 originating in a non-LISP site in order to deliver the packet to one 543 of the ETRs of the LISP site (cf. Figure 2). This case is very 544 similar to the unidirectional traffic case described in Section 8.1; 545 hence, similar rules apply. 547 +----------+ +-------------+ 548 | LISP | | non-LISP | 549 | Domain A | | Domain B | 550 | +-------+ +-----------+ | | 551 | | ETR A |<-------| Proxy ITR |<-------| | 552 | +-------+ +-----------+ | | 553 | | | | 554 +----------+ +-------------+ 556 Figure 2: Unidirectional traffic from non-LISP domain to LISP domain. 558 The main difference is that a Proxy-ITR does not have any mapping, 559 since it just encapsulates packets arriving from the non-LISP site, 560 and thus cannot provide a Source Map-Version. In this case, the 561 proxy-ITR will just put the Null Map-Version value as the Source Map- 562 Version number, while the receiving ETR will ignore the field. 564 With this setup, LISP Domain A is able to check whether or not the 565 PITR is using the latest mapping. 567 8.2.2. Map-Versioning and LISP-NAT 569 The LISP-NAT mechanism is based on address translation from non- 570 routable EIDs to routable EIDs and does not involve any form of 571 encapsulation. As such, Map-Versioning does not apply in this case. 573 8.2.3. Map-Versioning and Proxy-ETRs 575 The purpose of the Proxy-ETR (PETR) is to decapsulate traffic 576 originating in a LISP site in order to deliver the packet to the non- 577 LISP site (cf. Figure 3). One of the main reasons to deploy PETRs 578 is to bypass uRPF (Unicast Reverse Path Forwarding) checks on the 579 provider edge. 581 +----------+ +-------------+ 582 | LISP | | non-LISP | 583 | Domain A | | Domain B | 584 | +-------+ +-----------+ | | 585 | | ITR A |------->| Proxy ETR |------->| | 586 | +-------+ +-----------+ | | 587 | | | | 588 +----------+ +-------------+ 590 Figure 3: Unidirectional traffic from LISP domain to non-LISP domain. 592 A Proxy-ETR does not have any mapping, since it just decapsulates 593 packets arriving from the LISP site. In this case, the ITR will just 594 put the Null Map-Version value as the Destination Map-Version number, 595 while the receiving Proxy-ETR will ignore the field. 597 With this setup, the Proxy-ETR is able to check whether or not the 598 mapping has changed. 600 8.3. RLOC Shutdown/Withdraw 602 Map-Versioning can also be used to perform a graceful shutdown or 603 withdraw of a specific RLOC. This is achieved by simply issuing a 604 new mapping, with an updated Map-Version number where the specific 605 RLOC to be shut down is withdrawn or announced as unreachable (via 606 the R bit in the Map Record; see [I-D.ietf-lisp-rfc6833bis]), but 607 without actually turning it off. 609 Once no more traffic is received by the RLOC, it can be shut down 610 gracefully, because all sites actively using the mapping have updated 611 it. 613 8.4. Map-Version Additional Use Cases 615 The use of Map-Versioning can help in developing a lightweight 616 implementation of LISP. However, this comes with the price of not 617 supporting the Loc Status Bit, which may be useful in some contexts. 619 In the current LISP specifications, the set of RLOCs must always be 620 maintained ordered and consistent with the content of the Loc Status 621 Bits ([I-D.ietf-lisp-rfc6830bis]). . When a new RLOC is added to a 622 mapping, a new mapping with a new Map-Version number will be issued, 623 and since the old locators are still valid, the transition will occur 624 with no disruptions. The same applies for the case where an RLOC is 625 withdrawn. The use of Map-Versioning allows to avoiding using the 626 "use-LSB" timer (cf. [I-D.ietf-lisp-rfc6830bis]) since it allows to 627 check whether or not the mapping has been updated. 629 9. Security Considerations 631 Attackers can try to trigger a large number of Map-Requests by simply 632 forging packets with random Map-Versions. The Map-Requests are rate- 633 limited as described in [I-D.ietf-lisp-rfc6833bis]. With Map- 634 Versioning it is possible to filter invalid version numbers before 635 triggering a Map-Request, thus helping to reduce the effects of DoS 636 attacks. However, it might not be enough to really protect from a 637 DDoS attack. 639 Robustness of the Map-Versioning mechanism leverages on a trusted 640 Mapping Distribution System. A thorough security analysis of LISP is 641 documented in [RFC7835]. 643 As specified in [I-D.ietf-lisp-rfc6830bis], Map-Versioning MUST NOT 644 be used over the public Internet and SHOULD only be used in trusted 645 and closed deployments. 647 10. Deployment Considerations 649 Even without Map-Versioning, LISP requires ETRs to announce the same 650 mapping for the same EID-Prefix to a requester. Map-Versioning does 651 not require additional synchronization mechanisms as compared to the 652 normal functioning of LISP without Map-Versioning. Clearly, all the 653 ETRs have to reply with the same Map-Version number; otherwise, there 654 can be an inconsistency that creates additional control traffic, 655 instabilities, and traffic disruptions. It is the same without Map- 656 Versioning, with ETRs that have to reply with the same mapping; 657 otherwise, the same problems arise. 659 There are two ways Map-Versioning is helpful with respect to the 660 synchronization problem. On the one hand, assigning version numbers 661 to mappings helps in debugging, since quick checks on the consistency 662 of the mappings on different ETRs can be done by looking at the Map- 663 Version number. On the other hand, Map-Versioning can be used to 664 control the traffic toward ETRs that announce the latest mapping. 666 As an example, let's consider the topology of Figure 4 where ITR A.1 667 of Domain A is sending unidirectional traffic to Domain B, while A.2 668 of Domain A exchanges bidirectional traffic with Domain B. In 669 particular, ITR A.2 sends traffic to ETR B, and ETR A.2 receives 670 traffic from ITR B. 672 +-----------------+ +-----------------+ 673 | Domain A | | Domain B | 674 | +---------+ | | 675 | | ITR A.1 |--- | | 676 | +---------+ \ +---------+ | 677 | | ------->| ETR B | | 678 | | ------->| | | 679 | +---------+ / | | | 680 | | ITR A.2 |--- -----| ITR B | | 681 | | | / +---------+ | 682 | | ETR A.2 |<----- | | 683 | +---------+ | | 684 | | | | 685 +-----------------+ +-----------------+ 687 Figure 4: Example topology. 689 Obviously, in the case of Map-Versioning, both ITR A.1 and ITR A.2 of 690 Domain A must use the same value; otherwise, the ETR of Domain B will 691 start to send Map-Requests. 693 The same problem can, however, arise without Map-Versioning, for 694 instance, if the two ITRs of Domain A send different Locator Status 695 Bits. In this case, either the traffic is disrupted if ETR B trusts 696 the Locator Status Bits, or if ETR B does not trust the Locator 697 Status Bits it will start sending Map-Requests to confirm each change 698 in reachability. 700 So far, LISP does not provide any specific synchronization mechanism 701 but assumes that synchronization is provided by configuring the 702 different xTRs consistently. The same applies for Map-Versioning. 703 If in the future any synchronization mechanism is provided, Map- 704 Versioning will take advantage of it automatically, since it is 705 included in the Record format, as described in Section 7. 707 11. IANA Considerations 709 This document includes no request to IANA. 711 12. References 713 12.1. Normative References 715 [I-D.ietf-lisp-rfc6830bis] 716 Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A. 717 Cabellos-Aparicio, "The Locator/ID Separation Protocol 718 (LISP)", draft-ietf-lisp-rfc6830bis-36 (work in progress), 719 November 2020. 721 [I-D.ietf-lisp-rfc6833bis] 722 Farinacci, D., Maino, F., Fuller, V., and A. Cabellos- 723 Aparicio, "Locator/ID Separation Protocol (LISP) Control- 724 Plane", draft-ietf-lisp-rfc6833bis-30 (work in progress), 725 November 2020. 727 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 728 Requirement Levels", BCP 14, RFC 2119, 729 DOI 10.17487/RFC2119, March 1997, 730 . 732 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 733 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 734 May 2017, . 736 12.2. Informative References 738 [RFC6832] Lewis, D., Meyer, D., Farinacci, D., and V. Fuller, 739 "Interworking between Locator/ID Separation Protocol 740 (LISP) and Non-LISP Sites", RFC 6832, 741 DOI 10.17487/RFC6832, January 2013, 742 . 744 [RFC6834] Iannone, L., Saucez, D., and O. Bonaventure, "Locator/ID 745 Separation Protocol (LISP) Map-Versioning", RFC 6834, 746 DOI 10.17487/RFC6834, January 2013, 747 . 749 [RFC7835] Saucez, D., Iannone, L., and O. Bonaventure, "Locator/ID 750 Separation Protocol (LISP) Threat Analysis", RFC 7835, 751 DOI 10.17487/RFC7835, April 2016, 752 . 754 Authors' Addresses 756 Luigi Iannone 757 Huawei Technologies France S.A.S.U 759 EMail: luigi.iannone@huawei.com 761 Damien Saucez 762 INRIA 764 EMail: damien.saucez@inria.fr 766 Olivier Bonaventure 767 Universite catholique de Louvain 769 EMail: olivier.bonaventure@uclouvain.be