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Saucez 5 Intended status: Standards Track INRIA Sophia Antipolis 6 Expires: March 9, 2019 O. Bonaventure 7 Universite catholique de Louvain 8 September 5, 2018 10 Locator/ID Separation Protocol (LISP) Map-Versioning 11 draft-ietf-lisp-6834bis-01 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 Protocl 31 (LISP) Map-Versionin", 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 March 9, 2019. 50 Copyright Notice 52 Copyright (c) 2018 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 . . . . . . . 16 89 10.2. Map-Versioning against Reachability Information DoS . . 16 90 11. Considerations . . . . . . . . . . . . . . . . . . . . . . . 17 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 (in the case of 148 bidirectional traffic). If this is not the case, a Map-Request can 149 be sent. 151 Considerations about the deployment of LISP Map-Versioning for 152 Internet traffic are discussed in Section 11. 154 2. Requirements Notation 156 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 157 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 158 "OPTIONAL" in this document are to be interpreted as described in BCP 159 14 [RFC2119] [RFC8174] when, and only when, they appear in all 160 capitals, as shown here. 162 3. Definitions of Terms 164 This document uses terms already defined in the main LISP 165 specification (, [I-D.ietf-lisp-rfc6830bis] 166 [I-D.ietf-lisp-rfc6833bis]). Here, we define the terms that are 167 specific to the Map-Versioning mechanism. Throughout the whole 168 document, Big Endian bit ordering is used. 170 Map-Version number: An unsigned 12-bit integer is assigned to an 171 EID-to-RLOC mapping, not including the value 0 (0x000). 173 Null Map-Version: The 12-bit null value of 0 (0x000) is not used as 174 a Map-Version number. It is used to signal that no Map-Version 175 number is assigned to the EID-to-RLOC mapping. 177 Source Map-Version number: This Map-Version number of the EID-to- 178 RLOC mapping is used to select the source address (RLOC) of the 179 outer IP header of LISP-encapsulated packets. 181 Destination Map-Version number: This Map-Version number of the EID- 182 to-RLOC mapping is used to select the destination address (RLOC) of 183 the outer IP header of LISP-encapsulated packets. 185 4. EID-to-RLOC Map-Version Number 187 The EID-to-RLOC Map-Version number consists of an unsigned 12-bit 188 integer. The version number is assigned on a per-mapping basis, 189 meaning that different mappings have a different version number, 190 which is also updated independently. An update in the version number 191 (i.e., a newer version) consists of incrementing by one the older 192 version number. 194 The space of version numbers has a circular order where half of the 195 version numbers are greater (i.e., newer) than the current Map- 196 Version number and the other half of the version numbers are smaller 197 (i.e., older) than the current Map-Version number. In a more formal 198 way, assuming that we have two version numbers V1 and V2 and that the 199 numbers are expressed in N bits, the following steps MUST be 200 performed (in the same order as shown below) to strictly define their 201 order: 203 1. V1 = V2 : The map-version numbers are the same. 205 2. V2 > V1 : if and only if 207 V2 > V1 AND (V2 - V1) <= 2**(N-1) 209 OR 211 V1 > V2 AND (V1 - V2) > 2**(N-1) 213 3. V1 > V2 : otherwise. 215 Using 12 bits, as defined in this document, and assuming a Map- 216 Version value of 69, Map-Version numbers in the range [70; 69 + 2048] 217 are greater than 69, while Map-Version numbers in the range [69 + 218 2049; (69 + 4096) mod 4096] are smaller than 69. 220 Map-version numbers are assigned to mappings by configuration. The 221 initial Map-Version number of a new EID-to-RLOC mapping SHOULD be 222 assigned randomly, but it MUST NOT be set to the Null Map-Version 223 value (0x000), because the Null Map-Version number has a special 224 meaning (see Section 4.1). 226 Upon reboot, an ETR will use mappings configured in its EID-to-RLOC 227 Database. If those mappings have a Map-Version number, it will be 228 used according to the mechanisms described in this document. ETRs 229 MUST NOT automatically generate and assign Map-Version numbers to 230 mappings in the EID-to-RLOC Database. 232 4.1. The Null Map-Version 234 The value 0x000 (zero) is not a valid Map-Version number indicating 235 the version of the EID-to-RLOC mapping. Such a value is used for 236 special purposes and is named the Null Map-Version number. 238 The Null Map-Version MAY appear in the LISP-specific header as either 239 a Source Map-Version number (cf. Section 5.2) or a Destination Map- 240 Version number (cf. Section 5.1). When the Source Map-Version 241 number is set to the Null Map-version value, it means that no map 242 version information is conveyed for the source site. This means that 243 if a mapping exists for the source EID in the EID-to-RLOC Cache, then 244 the ETR MUST NOT compare the received Null Map-Version with the 245 content of the EID-to-RLOC Cache. When the Destination Map-version 246 number is set to the Null Map-version value, it means that no map 247 version information is conveyed for the destination site. This means 248 that the ETR MUST NOT compare the value with the Map-Version number 249 of the mapping for the destination EID present in the EID-to-RLOC 250 Database. 252 The other use of the Null Map-Version number is in the Map Records, 253 which are part of the Map-Request, Map-Reply, and Map-Register 254 messages (defined in [I-D.ietf-lisp-rfc6833bis]). Map Records that 255 have a Null Map-Version number indicate that there is no Map-Version 256 number associated with the mapping. This means that LISP- 257 encapsulated packets destined to the EID-Prefix referred to by the 258 Map Record MUST either not contain any Map-Version numbers (V bit set 259 to 0) or, if they contain Map-Version numbers (V bit set to 1), then 260 the destination Map-Version number MUST be set to the Null Map- 261 Version number. Any value different from zero means that Map- 262 Versioning is supported and MAY be used. 264 The fact that the 0 value has a special meaning for the Map-Version 265 number implies that, when updating a Map-Version number because of a 266 change in the mapping, if the next value is 0, then the Map-Version 267 number MUST be incremented by 2 (i.e., set to 1, which is the next 268 valid value). 270 5. Dealing with Map-Version Numbers 272 The main idea of using Map-Version numbers is that whenever there is 273 a change in the mapping (e.g., adding/removing RLOCs, a change in the 274 weights due to Traffic Engineering policies, or a change in the 275 priorities) or a LISP site realizes that one or more of its own RLOCs 276 are not reachable anymore from a local perspective (e.g., through 277 IGP, or policy changes) the LISP site updates the mapping, also 278 assigning a new Map-Version number. 280 To each mapping, a version number is associated and changes each time 281 the mapping is changed. Note that Map-Versioning does not introduce 282 new problems concerning the coordination of different ETRs of a 283 domain. Indeed, ETRs belonging to the same LISP site must return for 284 a specific EID-prefix the same mapping, including the same Map- 285 Version number. This is orthogonal to whether or not Map-Versioning 286 is used. The synchronization problem and its implications on the 287 traffic are out of the scope of this document. 289 In order to announce in a data-driven fashion that the mapping has 290 been updated, Map-Version numbers used to create the outer IP header 291 of the LISP-encapsulated packet are embedded in the LISP-specific 292 header. This means that the header needs to contain two Map-Version 293 numbers: 295 o The Source Map-Version number of the EID-to-RLOC mapping in the 296 EID-to-RLOC Database used to select the source RLOC. 298 o The Destination Map-Version number of the EID-to-RLOC mapping in 299 the EID-to-RLOC Cache used to select the destination RLOC. 301 By embedding both the Source Map-Version number and the Destination 302 Map-Version number, an ETR receiving a LISP packet with Map-Version 303 numbers can perform the following checks: 305 1. The ITR that has sent the packet has an up-to-date mapping in its 306 EID-to-RLOC Cache for the destination EID and is performing 307 encapsulation correctly. 309 2. In the case of bidirectional traffic, the mapping in the local 310 ETR EID-to-RLOC Cache for the source EID is up to date. 312 If one or both of the above conditions do not hold, the ETR can send 313 a Map-Request either to make the ITR aware that a new mapping is 314 available (see Section 5.1) or to update the mapping in the local 315 EID-to-RLOC Cache (see Section 5.2). 317 5.1. Handling Destination Map-Version Number 319 When an ETR receives a packet, the Destination Map-Version number 320 relates to the mapping for the destination EID for which the ETR is 321 an RLOC. This mapping is part of the ETR EID-to-RLOC Database. 322 Since the ETR is authoritative for the mapping, it has the correct 323 and up-to-date Destination Map-Version number. A check on this 324 version number can be done, where the following cases can arise: 326 1. The packet arrives with the same Destination Map-Version number 327 stored in the EID-to-RLOC Database. This is the regular case. 328 The ITR sending the packet has in its EID-to-RLOC Cache an up-to- 329 date mapping. No further actions are needed. 331 2. The packet arrives with a Destination Map-Version number greater 332 (i.e., newer) than the one stored in the EID-to-RLOC Database. 333 Since the ETR is authoritative on the mapping, meaning that the 334 Map-Version number of its mapping is the correct one, this 335 implies that someone is not behaving correctly with respect to 336 the specifications. In this case, the packet carries a version 337 number that is not valid; otherwise, the ETR would have the same 338 number, and the packet SHOULD be silently dropped. 340 3. The packets arrive with a Destination Map-Version number smaller 341 (i.e., older) than the one stored in the EID-to-RLOC Database. 342 This means that the ITR sending the packet has an old mapping in 343 its EID-to-RLOC Cache containing stale information. The ETR MAY 344 choose to normally process the encapsulated datagram according to 345 [I-D.ietf-lisp-rfc6830bis]; however, the ITR sending the packet 346 has to be informed that a newer mapping is available. This is 347 done with a Map-Request message sent back to the ITR. The Map- 348 Request will either trigger a Map-Request back using the Solicit- 349 Map-Request (SMR) bit or it will piggyback the newer mapping. 350 These are not new mechanisms; how to use the SMR bit or how to 351 piggyback mappings in Map-Request messages is already described 352 in [I-D.ietf-lisp-rfc6833bis]. One feature introduced by Map- 353 Version numbers is the possibility of blocking traffic not using 354 the latest mapping. Indeed, after a certain number of retries, 355 if the Destination Map-Version number in the packets is not 356 updated, the ETR MAY drop packets with a stale Map-Version number 357 while strongly reducing the rate of Map-Request messages. This 358 is because either the ITR is refusing to use the mapping for 359 which the ETR is authoritative, or (worse) it might be some form 360 of attack. 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 Time To Live 364 (TTL) (defined in [I-D.ietf-lisp-rfc6833bis]) of the previous version 365 of the mapping, all packets arriving with an old Map-Version SHOULD 366 be silently dropped right away without issuing any Map-Request. Such 367 action is permitted because if the new mapping with the updated 368 version number has been unchanged for at least the same time as the 369 TTL of the older mapping, all the entries in the EID-to-RLOC Caches 370 of ITRs must have expired. Hence, all ITRs sending traffic should 371 have refreshed the mapping according to [I-D.ietf-lisp-rfc6833bis]. 372 If packets with old Map-Version numbers are still received, then 373 either someone has not respected the TTL or it is a form of spoof/ 374 attack. In both cases, this is not valid behavior with respect to 375 the specifications 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 the 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 a 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 the version number set to a 386 value different from the Null Map-Version value, a Destination Map- 387 Version number equal to the Null Map-Version value means that the 388 Destination 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 as 399 that stored in the EID-to-RLOC Cache. This is the correct 400 regular case. The ITR has in its EID-to-RLOC Cache an up-to-date 401 copy of the 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 the ETR has in its EID-to-RLOC Cache a mapping 406 that is stale and needs to be updated. A Map-Request SHOULD be 407 sent to get the new mapping for the source EID. This is a normal 408 Map-Request message sent through the mapping system and MUST 409 respect the specifications in [I-D.ietf-lisp-rfc6833bis], 410 including rate-limitation 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, the Map- 419 Version in the EID-to-RLOC Cache is the correct one, while the 420 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, then the Source Map-Version number can be safely ignored. 426 For LISP-encapsulated packets with the V-bit set, if the Source Map- 427 Version number is the Null Map-Version value, it means that the 428 Source Map-Version number MUST be ignored. 430 6. LISP Header and Map-Version Numbers 432 In order for the versioning approach to work, the LISP-specific 433 header has to carry both the Source Map-Version number and 434 Destination Map-Version number. This is done by setting the V-bit in 435 the LISP-specific header as defined in [I-D.ietf-lisp-rfc6830bis]. 436 When the V-bit is set and the P bit is reset (0), the low-order 24 437 bits of the first longword are used to transport both the source and 438 destination Map-Version numbers. In particular, the first 12 bits 439 are used for the Source Map-Version number and the second 12 bits for 440 the Destination Map-Version number. 442 Below is an example of a LISP header carrying version numbers. 444 0 1 2 3 445 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 1 446 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 447 / |N|L|E|V|I|P|K|K| Source Map-Version |Destination Map-Version| 448 LISP+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 449 \ | Instance ID/Locator Status Bits | 450 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 452 Source Map-Version number (12 bits): Map-Version of the mapping used 453 by the ITR to select the RLOC present in the "Source Routing 454 Locator" field. Section 5.2 describes how to set this value on 455 transmission and handle it on reception. 457 Destination Map-Version number (12 bits): Map-Version of the mapping 458 used by the ITR to select the RLOC present in the "Destination 459 Routing Locator" field. Section 5.1 describes how to set this 460 value on transmission and handle it on reception. 462 Not all of the LISP-encapsulated packets need to carry version 463 numbers. When Map-Version numbers are carried in these packets, the 464 V-bit MUST be set to 1. All permissible combinations of the flags 465 when the V-bit is set to 1 are described in 466 [I-D.ietf-lisp-rfc6830bis] and [I-D.ietf-lisp-gpe]. 468 7. LISP Generic Protocol Encapsulation (GPE) Header and Map-Version 469 Numbers 471 [I-D.ietf-lisp-gpe] extends the Locator/ID Separation Protocol (LISP) 472 Data-Plane, changing the LISP header, to support multi-protocol 473 encapsulation. A flag in the LISP header, called the P-bit, is used 474 to signal the presence of the Next Protocol field in the low-order 8 475 bits of the first longword. When the V-bit and P-bit are both set, 476 the middle-order 16 bits of the first longword are used to transport 477 both the source and destination Map-Version numbers. In particular, 478 the first 8 bits are used for the Source Map-Version number and the 479 second 8 bits for the Destination Map-Version number. 481 Below is an example of a LISP header carrying version numbers. 483 0 1 2 3 484 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 1 485 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 486 / |N|L|E|V|I|P|K|K|Src Map-Version|Dst Map-Version| Next Protocol | 487 LISP+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 488 \ | Instance ID/Locator Status Bits | 489 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 491 The Source Map-Version number and the Destination Map-Version number 492 are used exactly in the same way previously described. There are 493 only three differences: 495 o When filling the LISP-GPE-specific header only the low order 8 496 bits are copied in the Source and Destination Map-Version Number 497 (out of the original 12 bits). 499 o When comparing a Map-Version retrieved from the LISP-GPE-specific 500 header (either Source or Destination Map-Version number) with the 501 version number of a mapping (stored in the LISP Cache or LISP 502 Database) only the low-order 8 bits of the latter are used for the 503 comparison. 505 o When trimming a Map-Version number from 12 to 8 bits it may happen 506 that it is converted to a Null Map-Version number, which will 507 change the way Map-Version number is interpreted as described in 508 Section 4.1. To avoid such wrong behavior, Map-Version number 509 with the low-order 8 bits all equal to zero SHOULD be avoided on 510 xTRs using LISP-GPE. 512 8. Map Record and Map-Version 514 To accommodate the proposed mechanism, the Map Records that are 515 transported in Map-Request/Map-Reply/Map-Register messages need to 516 carry the Map-Version number as well. For this purpose, the 12 bits 517 before the EID-AFI field in the Record that describes a mapping are 518 used (see [I-D.ietf-lisp-rfc6833bis] and reported here as an example. 520 0 1 2 3 521 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 1 522 +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 523 | | Record TTL | 524 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 525 R | Locator Count | EID mask-len | ACT |A| Reserved | 526 e +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 527 c | Rsvd | Map-Version Number | EID-Prefix-AFI | 528 o +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 529 r | EID-Prefix | 530 d +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 531 | /| Priority | Weight | M Priority | M Weight | 532 | L +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 533 | o | Unused Flags |L|p|R| Loc-AFI | 534 | c +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 535 | \| Locator | 536 +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 538 Map-Version Number: Map-Version of the mapping contained in the 539 Record. As explained in Section 4.1, this field can be zero (0), 540 meaning that no Map-Version is associated to the mapping; hence, 541 packets that are LISP encapsulated using this mapping MUST NOT 542 contain Map-Version numbers in the LISP-specific header, and the 543 V-bit MUST be set to 0. 545 This packet format works perfectly with xTRs that do not support Map- 546 Versioning, since they can simply ignore those bits. 548 9. Benefits and Case Studies for Map-Versioning 550 In the following sections, we provide more discussion on various 551 aspects and uses of Map-Versioning. Security observations are 552 grouped in Section 10. 554 9.1. Map-Versioning and Unidirectional Traffic 556 When using Map-Versioning, the LISP-specific header carries two Map- 557 Version numbers, for both source and destination mappings. This can 558 raise the question on what will happen in the case of unidirectional 559 flows, for instance, in the case presented in Figure 1, since the 560 LISP specification does not mandate that the ETR have a mapping for 561 the source EID. 563 +-----------------+ +-----------------+ 564 | Domain A | | Domain B | 565 | +---------+ +---------+ | 566 | | ITR A |----------->| ETR B | | 567 | +---------+ +---------+ | 568 | | | | 569 +-----------------+ +-----------------+ 571 Figure 1: Unidirectional traffic between LISP domains. 573 In the case of the ITR, the ITR is able to put both the source and 574 destination version number in the LISP header, since the Source Map- 575 Version number is in the ITR's database, while the Destination Map- 576 Version number is in the ITR's cache. 578 In the case of the ETR, the ETR simply checks only the Destination 579 Map-Version number in the same way as that described in Section 5, 580 ignoring the Source Map-Version number. 582 9.2. Map-Versioning and Interworking 584 Map-Versioning is compatible with the LISP interworking between LISP 585 and non-LISP sites as defined in [RFC6832]. LISP interworking 586 defines three techniques to make LISP sites and non-LISP sites, 587 namely Proxy-ITR, LISP-NAT, and Proxy-ETR. The following text 588 describes how Map-Versioning relates to these three mechanisms. 590 9.2.1. Map-Versioning and Proxy-ITRs 592 The purpose of the Proxy-ITR (PITR) is to encapsulate traffic 593 originating in a non-LISP site in order to deliver the packet to one 594 of the ETRs of the LISP site (cf. Figure 2). This case is very 595 similar to the unidirectional traffic case described in Section 9.1; 596 hence, similar rules apply. 598 +----------+ +-------------+ 599 | LISP | | non-LISP | 600 | Domain A | | Domain B | 601 | +-------+ +-----------+ | | 602 | | ETR A |<-------| Proxy ITR |<-------| | 603 | +-------+ +-----------+ | | 604 | | | | 605 +----------+ +-------------+ 607 Figure 2: Unidirectional traffic from non-LISP domain to LISP domain. 609 The main difference is that a Proxy-ITR does not have any mapping, 610 since it just encapsulates packets arriving from the non-LISP site, 611 and thus cannot provide a Source Map-Version. In this case, the 612 proxy-ITR will just put the Null Map-Version value as the Source Map- 613 Version number, while the receiving ETR will ignore the field. 615 With this setup, LISP Domain A is able to check whether or not the 616 PITR is using the latest mapping. 618 9.2.2. Map-Versioning and LISP-NAT 620 The LISP-NAT mechanism is based on address translation from non- 621 routable EIDs to routable EIDs and does not involve any form of 622 encapsulation. As such, Map-Versioning does not apply in this case. 624 9.2.3. Map-Versioning and Proxy-ETRs 626 The purpose of the Proxy-ETR (PETR) is to decapsulate traffic 627 originating in a LISP site in order to deliver the packet to the non- 628 LISP site (cf. Figure 3). One of the main reasons to deploy PETRs 629 is to bypass uRPF (Unicast Reverse Path Forwarding) checks on the 630 provider edge. 632 +----------+ +-------------+ 633 | LISP | | non-LISP | 634 | Domain A | | Domain B | 635 | +-------+ +-----------+ | | 636 | | ITR A |------->| Proxy ETR |------->| | 637 | +-------+ +-----------+ | | 638 | | | | 639 +----------+ +-------------+ 641 Figure 3: Unidirectional traffic from LISP domain to non-LISP domain. 643 A Proxy-ETR does not have any mapping, since it just decapsulates 644 packets arriving from the LISP site. In this case, the ITR will just 645 put the Null Map-Version value as the Destination Map-Version number, 646 while the receiving Proxy-ETR will ignore the field. 648 With this setup, the Proxy-ETR is able to check whether or not the 649 mapping has changed. 651 9.3. RLOC Shutdown/Withdraw 653 Map-Versioning can also be used to perform a graceful shutdown or 654 withdraw of a specific RLOC. This is achieved by simply issuing a 655 new mapping, with an updated Map-Version number where the specific 656 RLOC to be shut down is withdrawn or announced as unreachable (via 657 the R bit in the Map Record; see [I-D.ietf-lisp-rfc6833bis]), but 658 without actually turning it off. 660 Once no more traffic is received by the RLOC, it can be shut down 661 gracefully, because all sites actively using the mapping have updated 662 it. 664 9.4. Map-Version Additional Use Cases 666 The use of Map-Versioning can help in developing a lightweight 667 implementation of LISP. However, this comes with the price of not 668 supporting the Loc-Status-Bit, which is useful in some contexts. 670 In the current LISP specifications, the set of RLOCs must always be 671 maintained ordered and consistent with the content of the Loc Status 672 Bits ([I-D.ietf-lisp-rfc6830bis]). With Map-Versioning, such types 673 of mechanisms can be avoided. When a new RLOC is added to a mapping, 674 it is not necessary to "append" new locators to the existing ones as 675 explained in [I-D.ietf-lisp-rfc6830bis]. A new mapping with a new 676 Map-Version number will be issued, and since the old locators are 677 still valid, the transition will occur with no disruptions. The same 678 applies for the case where an RLOC is withdrawn. There is no need to 679 maintain holes in the list of locators, as is the case when using 680 Locator Status Bits, for sites that are not using the RLOC that has 681 been withdrawn; in this case, the transition will occur with no 682 disruptions. 684 All of these operations, as already stated, do not need to maintain 685 any consistency among Locator Status Bits and in the way that the 686 RLOCs are stored in the EID-to-RLOC Cache. 688 Map-Versioning can be used as a substitute for the "clock sweep" 689 operation described in Section 6.6.1 of [I-D.ietf-lisp-rfc6833bis]. 690 Indeed, every LISP site communicating to a specific LISP site that 691 has updated the mapping will be informed of the available new mapping 692 in a data-driven manner. 694 10. Security Considerations 696 Map-Versioning does not introduce any security issues concerning both 697 the data plane and the control plane. On the contrary, as described 698 below, if Map-Versioning may also be used to update mappings in the 699 case of change in the reachability information (i.e., instead of the 700 Locator Status Bits), it is possible to reduce the effects of some 701 DoS or spoofing attacks that can happen in an untrusted environment. 703 Robustness of the Map-Versioning mechanism leverages on a trusted 704 Mapping Distribution System. A thorough security analysis of LISP is 705 documented in [RFC7835]. 707 10.1. Map-Versioning against Traffic Disruption 709 An attacker can try to disrupt ongoing communications by creating 710 LISP-encapsulated packets with wrong Locator Status Bits. If the xTR 711 blindly trusts the Locator Status Bits, it will change the 712 encapsulation accordingly, which can result in traffic disruption. 714 This does not happen in the case of Map-Versioning. As described in 715 Section 5, upon a version number change the xTR first issues a Map- 716 Request. The assumption is that the mapping distribution system is 717 sufficiently secure that Map-Request and Map-Reply messages and their 718 content can be trusted. Security issues concerning specific mapping 719 distribution systems are out of the scope of this document. In the 720 case of Map-Versioning, the attacker should "guess" a valid version 721 number that triggers a Map-Request as described in Section 5; 722 otherwise, the packet is simply dropped. Nevertheless, guessing a 723 version number that generates a Map-Request is easy; hence, it is 724 important to follow the rate-limitation policies described in 725 [I-D.ietf-lisp-rfc6833bis] in order to avoid DoS attacks. 727 Note that a similar level of security can be obtained with Loc Status 728 Bits by simply making it mandatory to verify any change through a 729 Map-Request. However, in this case Locator Status Bits lose their 730 meaning, because it does not matter anymore which specific bits have 731 changed; the xTR will query the mapping system and trust the content 732 of the received Map-Reply. Furthermore, there is no way to perform 733 filtering as in Map-Versioning in order to drop packets that do not 734 carry a valid Map-Version number. In the case of Locator Status 735 Bits, any random change can trigger a Map-Request (unless rate 736 limitation is enabled, which raises another type of attack as 737 discussed in Section 10.2). 739 10.2. Map-Versioning against Reachability Information DoS 741 Attackers can try to trigger a large number of Map-Requests by simply 742 forging packets with random Map-Versions or random Locator Status 743 Bits. In both cases, the Map-Requests are rate-limited as described 744 in [I-D.ietf-lisp-rfc6833bis]. However, in contrast to the Locator 745 Status Bit, where there is no filtering possible, in the case of Map- 746 Versioning it is possible to filter invalid version numbers before 747 triggering a Map-Request, thus helping to reduce the effects of DoS 748 attacks. In other words, the use of Map-Versioning enables a fine 749 control on when to update a mapping or when to notify someone that a 750 mapping has been updated. 752 It is clear that Map-Versioning does not protect against DoS and DDoS 753 attacks, where an xTR loses processing power when doing checks on the 754 LISP header of packets sent by attackers. This is independent of 755 Map-Versioning and is the same for Loc Status Bits. 757 11. Considerations 759 Even without Map-Versioning, LISP requires ETRs to announce the same 760 mapping for the same EID-Prefix to a requester. The implications 761 that a temporary lack of synchronization may have on the traffic are 762 yet to be fully explored. 764 Map-Versioning does not require additional synchronization mechanisms 765 as compared to the normal functioning of LISP without Map-Versioning. 766 Clearly, all the ETRs have to reply with the same Map-Version number; 767 otherwise, there can be an inconsistency that creates additional 768 control traffic, instabilities, and traffic disruptions. It is the 769 same without Map-Versioning, with ETRs that have to reply with the 770 same mapping; otherwise, the same problems can arise. 772 There are two ways Map-Versioning is helpful with respect to the 773 synchronization problem. On the one hand, assigning version numbers 774 to mappings helps in debugging, since quick checks on the consistency 775 of the mappings on different ETRs can be done by looking at the Map- 776 Version number. On the other hand, Map-Versioning can be used to 777 control the traffic toward ETRs that announce the latest mapping. 779 As an example, let's consider the topology of Figure 4 where ITR A.1 780 of Domain A is sending unidirectional traffic to Domain B, while A.2 781 of Domain A exchanges bidirectional traffic with Domain B. In 782 particular, ITR A.2 sends traffic to ETR B, and ETR A.2 receives 783 traffic from ITR B. 785 +-----------------+ +-----------------+ 786 | Domain A | | Domain B | 787 | +---------+ | | 788 | | ITR A.1 |--- | | 789 | +---------+ \ +---------+ | 790 | | ------->| ETR B | | 791 | | ------->| | | 792 | +---------+ / | | | 793 | | ITR A.2 |--- -----| ITR B | | 794 | | | / +---------+ | 795 | | ETR A.2 |<----- | | 796 | +---------+ | | 797 | | | | 798 +-----------------+ +-----------------+ 800 Figure 4: Example topology. 802 Obviously, in the case of Map-Versioning, both ITR A.1 and ITR A.2 of 803 Domain A must use the same value; otherwise, the ETR of Domain B will 804 start to send Map-Requests. 806 The same problem can, however, arise without Map-Versioning, for 807 instance, if the two ITRs of Domain A send different Locator Status 808 Bits. In this case, either the traffic is disrupted if ETR B trusts 809 the Locator Status Bits, or if ETR B does not trust the Locator 810 Status Bits it will start sending Map-Requests to confirm each change 811 in reachability. 813 So far, LISP does not provide any specific synchronization mechanism 814 but assumes that synchronization is provided by configuring the 815 different xTRs consistently. The same applies for Map-Versioning. 816 If in the future any synchronization mechanism is provided, Map- 817 Versioning will take advantage of it automatically, since it is 818 included in the Record format, as described in Section 8. 820 12. IANA Considerations 822 This document includes no request to IANA. 824 13. Acknowledgments 826 This work benefited support from NewNet@Paris, Cisco's Chair 827 "Networks for the Future" at Telecom ParisTech 828 (http://newnet.telecom-paristech.fr). Any opinions, findings or 829 recommendations expressed in this material are those of the author(s) 830 and do not necessarily reflect the views of partners of the Chair. 832 14. References 834 14.1. Normative References 836 [I-D.ietf-lisp-gpe] 837 Maino, F., Lemon, J., Agarwal, P., Lewis, D., and M. 838 Smith, "LISP Generic Protocol Extension", draft-ietf-lisp- 839 gpe-05 (work in progress), August 2018. 841 [I-D.ietf-lisp-rfc6830bis] 842 Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A. 843 Cabellos-Aparicio, "The Locator/ID Separation Protocol 844 (LISP)", draft-ietf-lisp-rfc6830bis-16 (work in progress), 845 August 2018. 847 [I-D.ietf-lisp-rfc6833bis] 848 Fuller, V., Farinacci, D., and A. Cabellos-Aparicio, 849 "Locator/ID Separation Protocol (LISP) Control-Plane", 850 draft-ietf-lisp-rfc6833bis-13 (work in progress), August 851 2018. 853 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 854 Requirement Levels", BCP 14, RFC 2119, 855 DOI 10.17487/RFC2119, March 1997, 856 . 858 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 859 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 860 May 2017, . 862 14.2. Informative References 864 [RFC6832] Lewis, D., Meyer, D., Farinacci, D., and V. Fuller, 865 "Interworking between Locator/ID Separation Protocol 866 (LISP) and Non-LISP Sites", RFC 6832, 867 DOI 10.17487/RFC6832, January 2013, 868 . 870 [RFC6834] Iannone, L., Saucez, D., and O. Bonaventure, "Locator/ID 871 Separation Protocol (LISP) Map-Versioning", RFC 6834, 872 DOI 10.17487/RFC6834, January 2013, 873 . 875 [RFC7835] Saucez, D., Iannone, L., and O. Bonaventure, "Locator/ID 876 Separation Protocol (LISP) Threat Analysis", RFC 7835, 877 DOI 10.17487/RFC7835, April 2016, 878 . 880 Authors' Addresses 882 Luigi Iannone 883 Telecom ParisTech 885 EMail: ggx@gigix.net 887 Damien Saucez 888 INRIA Sophia Antipolis 890 EMail: damien.saucez@inria.fr 891 Olivier Bonaventure 892 Universite catholique de Louvain 894 EMail: olivier.bonaventure@uclouvain.be