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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group V. Moreno 3 Internet-Draft Google LLC 4 Intended status: Experimental D. Farinacci 5 Expires: July 22, 2022 lispers.net 6 A. Rodriguez-Natal 7 M. Portoles-Comeras 8 F. Maino 9 S. Hooda 10 Cisco Systems 11 January 18, 2022 13 Uberlay Interconnection of Multiple LISP overlays 14 draft-moreno-lisp-uberlay-05 16 Abstract 18 This document describes the use of the Locator/ID Separation Protocol 19 (LISP) to interconnect multiple disparate and independent network 20 overlays by using a transit overlay. The transit overlay is referred 21 to as the "uberlay" and provides connectivity and control plane 22 abstraction between different overlays. Each network overlay may use 23 different control and data plane approaches and may be managed by a 24 different organization. Structuring the network into multiple 25 network overlays enables the interworking of different overlay 26 approaches to data and control plane methods. The different network 27 overlays are autonomous from a control and data plane perspective, 28 this in turn enables failure survivability across overlay domains. 29 This document specifies the mechanisms and procedures for the 30 distribution of control plane information across overlay sites and in 31 the uberlay as well as the lookup and forwarding procedures for 32 unicast and multicast traffic within and across overlays. The 33 specification also defines the procedures to support inter-overlay 34 mobility of EIDs and their integration with the intra-overlay EID 35 mobility procedures defined in draft-ietf-lisp-eid-mobility. 37 Requirements Language 39 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 40 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 41 document are to be interpreted as described in [RFC2119]. 43 Status of This Memo 45 This Internet-Draft is submitted in full conformance with the 46 provisions of BCP 78 and BCP 79. 48 Internet-Drafts are working documents of the Internet Engineering 49 Task Force (IETF). Note that other groups may also distribute 50 working documents as Internet-Drafts. The list of current Internet- 51 Drafts is at https://datatracker.ietf.org/drafts/current/. 53 Internet-Drafts are draft documents valid for a maximum of six months 54 and may be updated, replaced, or obsoleted by other documents at any 55 time. It is inappropriate to use Internet-Drafts as reference 56 material or to cite them other than as "work in progress." 58 This Internet-Draft will expire on July 22, 2022. 60 Copyright Notice 62 Copyright (c) 2022 IETF Trust and the persons identified as the 63 document authors. All rights reserved. 65 This document is subject to BCP 78 and the IETF Trust's Legal 66 Provisions Relating to IETF Documents 67 (https://trustee.ietf.org/license-info) in effect on the date of 68 publication of this document. Please review these documents 69 carefully, as they describe your rights and restrictions with respect 70 to this document. Code Components extracted from this document must 71 include Simplified BSD License text as described in Section 4.e of 72 the Trust Legal Provisions and are provided without warranty as 73 described in the Simplified BSD License. 75 Table of Contents 77 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 78 2. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 3 79 3. Interconnecting multiple LISP site-overlays via the Uberlay . 4 80 3.1. Logical Topology Considerations . . . . . . . . . . . . . 7 81 4. General Procedures . . . . . . . . . . . . . . . . . . . . . 9 82 4.1. Control Plane Procedures . . . . . . . . . . . . . . . . 10 83 4.1.1. Split-horizon at the Border xTRs . . . . . . . . . . 11 84 4.1.2. Border-xTR Resiliency . . . . . . . . . . . . . . . . 12 85 4.2. Resolution and Forwarding Procedures . . . . . . . . . . 12 86 4.2.1. Multi-overlay requests at border xTR . . . . . . . . 13 87 4.3. Default EID registration and treatment . . . . . . . . . 14 88 5. Multicast Specific Procedures . . . . . . . . . . . . . . . . 15 89 5.1. Inter-site-overlay Control Plane Procedures for Signal- 90 free multicast . . . . . . . . . . . . . . . . . . . . . 15 91 5.2. Border xTR Resolution and Forwarding procedures for 92 Signal-free multicast . . . . . . . . . . . . . . . . . . 16 93 6. Inter site-overlay Mobility Procedures . . . . . . . . . . . 16 94 7. Virtual Private Network (VPN) Considerations . . . . . . . . 18 95 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 96 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18 97 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 98 10.1. Normative References . . . . . . . . . . . . . . . . . . 18 99 10.2. Informative References . . . . . . . . . . . . . . . . . 19 100 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21 102 1. Introduction 104 The main motivation for this specification is to provide a 105 methodology for the interconnection of LISP domains that may use 106 disparate control and/or data plane approaches. For instance, one 107 domain may use native LISP encapsulation for its data plane and a DDT 108 based mapping system, while another domain may use VXLAN-GPE 109 encapsulation and a mapping system based on 110 [I-D.farinacci-lisp-decent]. Furthermore, one domain may use an IPv4 111 RLOC space and the other domain may use an IPv6 RLOC space and there 112 may not be connectivity between the domains at the RLOC level. We 113 propose a method to interconnect and enable interoperability between 114 these disparate LISP overlay networks by connecting them to a common 115 transit LISP overlay. 117 In order to provide interworking across implementations of overlays 118 that may use different control and data plane approaches, a LISP 119 network may be structured as a collection of site-overlays 120 interconnected by a transit area. Each site-overlay is a fully 121 functional overlay network and has its own set of Map Servers and Map 122 Resolvers. Site-overlays share a border xTR with a transit area. 123 Connectivity between site-overlays is provided via the transit area 124 which we will refer to as "The Uberlay". This specification 125 describes the Control Plane and Forwarding procedures for the 126 implementation of an Uberlay connected multi-overlay LISP network. 127 This approach to the structure of a LISP network may also enable 128 regional failure survivability and fault isolation. 130 2. Definition of Terms 132 LISP related terms, notably Map-Request, Map-Reply, Ingress Tunnel 133 Router (ITR), Egress Tunnel Router (ETR), Map-Server (MS) and Map- 134 Resolver (MR) are defined in the LISP specification [RFC6830]. 136 Terms defining interactions with the LISP Mapping System are defined 137 in [RFC6833]. 139 Terms related to the procedures for signal free multicast are defined 140 in [RFC8378]. 142 The following terms are here defined to facilitate the descriptions 143 and discussions within this particular document. 145 Site-Overlay - Overlay network at a specific area or domain. This 146 overlay network has a dedicated Mapping System. 148 Border-xTR - xTR that connects a site-overlay to one or more 149 uberlays. 151 xTR - LISP Tunnel Router as defined in [RFC6833]. An xTR connects 152 end-points to the site-overlay. 154 Local Mapping System - Mapping system of the site-overlay 156 Uberlay - Overlay network that interconnects different site-overlays 157 to each other. The Uberlay has a dedicated Mapping System and 158 creates an overlay amongst the border xTRs which connect different 159 site-overlays. 161 Uberlay Mapping System - Autonomous mapping system dedicated to the 162 uberlay. 164 Site-Overlay EIDs - Also referred to as local site-overlay EIDs, 165 these are the EIDs that are connected to xTRs in a particular site- 166 overlay and are registered in their own local site-overlay mapping 167 system. These EIDs will also be registered in the uberlay but not in 168 the remote site-overlay mapping systems. 170 Remote site-overlay EIDs - These are EIDs connected and registered in 171 site-overlays other than the local site-overlay. 173 Local site-overlay EIDs - These are EIDs connected and registered in 174 the local site-overlay. 176 3. Interconnecting multiple LISP site-overlays via the Uberlay 178 A LISP network can be structured as a collection of LISP site- 179 overlays that are interconnected by one or more LISP Uberlays. 181 A LISP site-overlay is an overlay network that has its own set of 182 xTRs, its own dedicated Mapping System and it may have a dedicated 183 RLOC space, separate from that of other site-overlays or the uberlay. 184 A LISP uberlay is also an overlay network with its own set of xTRs, 185 its own dedicated Mapping System and it may have its own dedicated 186 RLOC space. When the RLOC spaces are dedicated, RLOC routes in the 187 local underlay do not leak across to the underlay of other site- 188 overlays. 190 A site-overlay will have xTRs and Border xTRs. The xTRs provide 191 connectivity to the local site-overlay EIDs, which are the EIDs that 192 are locally connected to the overlay-site. The Border xTRs are Re- 193 encapsulating Tunnel Routers (RTRs) that connect the site-overlays to 194 the LISP Uberlay in the transit network. xTRs participate in one 195 site-overlay and one site-overlay only. Border xTRs participate in 196 the mapping system of the site-overlay it resides in and the mapping 197 system of the uberlay it connects the site-overlay to. Border xTRs 198 may be shared by more than one site-overlay. 200 The different site-overlays can be interconnected by an uberlay. The 201 uberlay consists of a dedicated Mapping System and the set of Border 202 xTRs that connect the participating site-overlays to the Uberlay and 203 the Uberlay Mapping System. 205 Each site-overlay will have its own set of Map Servers and Map 206 Resolvers (MS/MRs) which operate as an autonomous Mapping System. 207 The Uberlay Mapping System is also autonomous and includes all 208 necessary Map Servers and Map Resolvers. Any of the Mapping Systems, 209 in site-overlays or in the Uberlay, follow the control plane 210 specification in [RFC6833] and may be structured as a Distributed 211 Delegation Tree (DDT) per [RFC8111]for the purposes of horizontal 212 scaling or other optimizations within each Mapping System. 214 The MS/MRs can be co-located with the border-xTRs of the site-overlay 215 When a Border xTR services more than one site-overlay, and the MS/MRs 216 are instantiated on the Border xTR, logical instances of MS/MRs must 217 be dedicated to each site-overlay. 219 This specification defines the interaction between the Mapping 220 Systems of the site-overlays and the uberlay to deliver a multi- 221 overlay hierarchical network. The forwarding procedures relevant to 222 the border xTRs are also specified. Figure 1 illustrates the multi- 223 overlay network. 225 +-------------------------------+ 226 | +-----+ +-----+ +-----+ | 227 | | xTR | | xTR | | xTR | | 228 | +-----+ +-----+ +-----+ | 229 | | 230 | +-------+ | RLOC space 1 231 | Site Overlay 1 | MS/MR | | (underlay 1) 232 | +-------+ | 233 | | 234 | | 235 | +--------+ +--------+ | 236 +-----| Border |--| Border |----+ 237 +-----| xTR |--| xTR |----+ 238 | +--------+ +--------+ | 239 | | 240 | | 241 | | 242 | +-------+ | Uberlay 243 | Uberlay | MS/MR | | RLOC Space 244 | +-------+ | (Transit Underlay) 245 | | 246 | | 247 | +----------+ | 248 +---------| Border |----------+ 249 +---------| xTR |----------+ 250 | +----------+ | 251 | | 252 | +-------+ | RLOC space 2 253 | Site Overlay 2 | MS/MR | | (underlay 2) 254 | +-------+ | 255 | | 256 | +-----+ +-----+ +-----+ | 257 | | xTR | | xTR | | xTR | | 258 | +-----+ +-----+ +-----+ | 259 +-------------------------------+ 261 Figure 1. Site-overlays connected via Uberlay 263 Structuring the LISP network as multiple site-overlays interconnected 264 by an uberlay delivers the following benefits: 266 o Enable the interworking of diverse site-overlay implementations in 267 which different mapping systems and encapsulations may be used. 269 o Enhanced resiliency through regional failure survivability. 270 Failures in one site-overlay or failures in a portion of the 271 underlay should not affect other site-overlays. 273 o Reduce the state of the site-overlay control plane. The site- 274 overlay control plane will only maintain state for EIDs that are 275 connected to xTRs within the site-overlay These EIDs are referred 276 to as local site-overlay EIDs in this specification. Remote site- 277 overlay EIDs will not be explicitly registered within the site- 278 overlay. 280 o Separate the RLOC space of the different site-overlays as well as 281 the uberlay RLOC space. Each site-overlay will only need 282 reachability to its own RLOCs, making the RLOCs private to the 283 site-overlay Similarly, the uberlay RLOC space does not require 284 knowledge of site-overlay specific RLOCs. This simplifies the 285 underlay routing protocol structure and reduces the state that 286 must be handled and maintained by the underlay routing protocols. 288 o Reduced latency for local site-overlay EID registrations may be 289 achieved when xTRs and Map Servers are topologically close. 290 Topological proximity is expected when the RLOC spaces for the 291 different overlays are kept separate. 293 o Reduced latency for local site-overlay EID lookups may be achieved 294 when xTRs, Map Resolvers and Map Servers are topologically close. 295 Topological proximity is expected when the RLOC spaces for the 296 different overlays are kept separate. 298 o Creates a multicast replication hierarchy where the Border RTRs 299 serve as the points of multicast replication for multicast traffic 300 that spans multiple site-overlays. 302 o Creates a distributed structure of RTRs that can be leveraged for 303 the deployment of NAT traversal in the RLOC space. 305 o 307 3.1. Logical Topology Considerations 309 xTRs as defined in RFC6833bis connect a network to the LISP overlay 310 and register the EID prefixes from the connected network to the LISP 311 mapping system. Border xTRs, as defined in this document, will 312 connect site-overlays to the Uberlay and register the EID prefixes 313 that originate in a site-overlay in the Mapping System of the 314 Uberlay. Conversely, a border xTR may register EID prefixes present 315 in the Uberlay Mapping System into the Mapping System of a particular 316 site-overlay. Furthermore, border xTRs may connect Uberlays to each 317 other and register the EID prefixes from one Uberlay into the other. 318 There is no provision for the detection of registration loops when 319 concatenating site-overlays and Uberlays, thus any interconnection of 320 overlay domains (site-overlays or Uberlays) must be done in a loop 321 free topology. 323 A loop free topology is hereby defined for reference. This is a 324 general concept and is not encoded into any of the protocol messages 325 in LISP. A loop free topology limits the peerings between Uberlays 326 and/or overlays to a strict hierarchy. At the top of the hierarchy 327 is a single central Uberlay or Core Uberlay. The loop free topology 328 is defined by two simple rules: Uberlays must only connect to 329 Uberlays in the next consecutive level of hierarchy (no level 330 skipping) and uberlays within the same level of hierarchy must not 331 connect to each other. The loop-free topology hierarchy is 332 illustrated in Figure 2. 334 +----------------+ +----------------+ 335 | site-overlay 1 | | site-overlay 2 | 336 | (Level 2) | | (Level 2) | 337 +----------------+ +----------------+ 338 +---+ +---+ 339 |RTR| |RTR| 340 +---+ +---+ 341 +-----------+ +-----------+ 342 | Uberlay 1 | | Uberlay 2 | 343 | (Level 1) | | (Level 1) | 344 +-----------+ +-----------+ 345 +---+ +---+ 346 |RTR+---------+RTR| 347 +--++ ++--+ 348 | Core | 349 | Uberlay | 350 | (Level 0) | 351 +--++ ++--+ 352 |RTR+---------+RTR| 353 +---+ +---+ 354 +-----------+ +-----------+ 355 | Uberlay 3 | | Uberlay 4 | 356 | (Level 1) | | (Level 1) | 357 +-----------+ +-----------+ 358 +---+ +---+ 359 |RTR| |RTR| 360 +---+ +---+ 361 +----------------+ +----------------+ 362 | site-overlay 3 | | site-overlay 4 | 363 | (Level 2) | | (Level 2) | 364 +----------------+ +----------------+ 366 Figure 2. Loop-free topology hierarchy 368 4. General Procedures 370 A site-overlay maintains state only for its local site-overlay EIDs 371 and RLOCs. Tunnels never cross site-overlay or uberlay boundaries. 372 Remote site-overlay EIDs are reachable at the source site-overlay via 373 a default mapping which will steer all traffic destined to remote 374 site-overlay EIDs to the border xTRs where it can be handed off to 375 the uberlay. Traffic will be decapsulated at the border xTRs and a 376 lookup in the uberlay mapping system will determine the site-overlay 377 to which traffic is to be re-encapsulated. The uberlay maintains 378 state for the EIDs of all interconnected site-overlays and will steer 379 traffic from the source site-overlay to the destination site-overlay 380 by encapsulating the traffic from the source site-overlay border xTR 381 to the destination site-overlay border xTR. At the border xTR of the 382 destination site-overlay, traffic will be de-capsulated, a lookup in 383 the local destination site-overlay Mapping System will take place and 384 traffic will be re-encapsulated to the xTR that connects to the 385 destination EID. Thus, forwarding is achieved by concatenating 386 overlays and doing Re-encapsulation at the border xTRs to forward the 387 traffic from the Ingress site-overlay to the Egress site-overlay via 388 the Uberlay. 390 Traffic for non-LISP sites, or for EIDs not registered in any site- 391 overlay, will also be forwarded to the border xTR where it will be 392 forwarded or dropped as appropriate. 394 4.1. Control Plane Procedures 396 Local EIDs must be registered by the xTRs into the local Mapping 397 System of the site-overlay. Intra-site communication follows the 398 standard procedures of registration, resolution, caching and 399 encapsulation defined in [I-D.ietf-lisp-rfc6830bis] and 400 [I-D.ietf-lisp-rfc6833bis] amongst the xTRs within the local site- 401 overlay. 403 The border xTRs at a site-overlay should have a local site-overlay 404 RLOC-set and will also have an uberlay RLOC-set. The local site- 405 overlay RLOC-set is in the private site-overlay RLOC space and is 406 used by the border xTRs as the RLOC set for any mappings it may 407 register with the site-overlay Mapping System. The uberlay RLOC-set 408 for the border-xTRs of a particular site-overlay are the RLOCs to 409 reach the site-overlay in the uberlay RLOC space. The border xTR 410 will use the uberlay RLOC-set in any mappings it may register with 411 the uberlay Mapping System. It is possible for a deployment to 412 connect the RLOC spaces of the site-overlays and the uberlay, it is 413 also possible in the scenario of a common RLOC space for the uberlay 414 and local site-overlay RLOC sets to be one and the same. Any 415 implementation of this specification should support disjoint RLOC 416 spaces or joint RLOC spaces. 418 The border xTRs must register a default EID-prefix as specified in 419 Section 4.3 with the local site-overlay Mapping System. Remote EIDs 420 will be generally reachable by xTRs in a site-overlay using the 421 default EID mapping registered by the border xTRs. This is expected 422 to be the mapping used for most communications to remote site-overlay 423 EIDs. Remote site-overlay EIDs may be registered with the local 424 site-overlay Mapping System for the purposes of supporting inter- 425 overlay EID mobility as specified in Section 6, these mappings will 426 be preferred over the default EID mapping whenever present. 428 Local EIDs registered with the site-overlay mapping system must also 429 be registered with the Uberlay Mapping System. The registration of 430 the local site-overlay EIDs with the uberlay Mapping System is 431 originated by the Border xTRs. The local site-overlay EIDs SHOULD be 432 aggregated into the shortest covering prefix possible before being 433 registered with the uberlay Mapping System. How this aggregation is 434 achieved is implementation specific. 436 In order to be able to register the local site-overlay EIDs with the 437 uberlay Mapping System, the border xTRs must subscribe to all EIDs 438 registered in their local site-overlay Mapping System. This is a 439 subscription to 0.0.0.0/0 (or 0::/0) with the N-bit set as specified 440 in [I-D.ietf-lisp-pubsub]. The subscription populates all local 441 site-overlay EID mappings in the map-cache of the border xTRs. 443 Once received through the subscription, the local site-overlay EIDs 444 in the map-cache at the border xTRs must be registered by the border 445 xTRs with the uberlay Mapping System. The local site-overlay EIDs 446 will be registered using the 'uberlay' RLOC-set for the registering 447 border xTR. 449 Following [I-D.ietf-lisp-eid-mobility], the border xTRs will also 450 subscribe to any EID prefixes it registers with the uberlay Mapping 451 System. This allows the border xTRs to get Map Notify messages from 452 the uberlay Mapping System for EID prefixes that may move from their 453 local site-overlay to a remote site-overlay. 455 4.1.1. Split-horizon at the Border xTRs 457 Remote site-overlay EIDs may be learnt at a border xTR due to 458 resolution of a remote destination EID or due to a mobility event as 459 specified in Section 6. Remote site-overlay EIDs learnt from the 460 uberlay will be installed in the map-cache of the border xTR with the 461 corresponding remote uberlay RLOC-set for the remote border xTR. 462 When these remote site-overlay EIDs are learnt as a consequence of 463 the map-notify messages defined in the Inter-overlay mobility 464 procedures in Section 6, the EIDs will also be registered with the 465 local site-overlay mapping system using the local site-overlay RLOC- 466 set for the border-xTR. The remote site-overlay EIDs registered with 467 the local site-overlay mapping system will be learnt back at the 468 border xTR because of the border xTR's subscription to all local 469 site-overlay EIDs. This can cause the mapping for the remote EID 470 that is installed in the border xTR map-cache to flip flop between 471 the uberlay RLOC-set and the local site-overlay RLOC-set. 473 In order to avoid this flip flopping a split horizon procedure must 474 be implemented. When a mapping received at the border xTR (as part 475 of its subscription to all local site-overlay EID prefixes) has the 476 local site-overlay RLOC-set for the border xTR, the mapping received 477 in the subscription corresponds to a remote site-overlay EID and 478 should be ignored by the border xTR. The mapping should not be 479 installed in the map-cache of the border xTR and the EIDs in the 480 mapping should not be advertised to the uberlay. More robust split 481 horizon mechanisms can be proposed in future revisions of this 482 specification. 484 4.1.2. Border-xTR Resiliency 486 Redundancy at the border xTRs requires that border xTRs be logically 487 grouped so that the redundant array doesn't create a registration 488 loop. As border xTRs interconnect overlay domains, the border xTRs 489 will register the EID prefixes from one domain into the neighboring 490 domain. From the perspective of the border xTR, the EID prefixes to 491 be registered in one domain are learnt from a neighbor domain which 492 we will refer to as the "site-of-origin". The site-of-origin may be 493 an overlay-site, an Uberlay or an IP network. 495 Border xTRs should be logically grouped in Border Sets. A border set 496 is a group of border xTRs that register EID prefixes from the same 497 site-of-origin. Members of a border set will register the EIDs from 498 a particular site-of-origin into the neighboring overlay (site- 499 overlay or uberlay) using a common site-id. The use of the site-ID 500 namespace is locally significant to each overlay domain (site-overlay 501 or Uberlay) and does not require cross-domain synchronization or 502 dispersion. A border-xTR may be a member of multiple border sets to 503 allow different site-of-origin domains to be serviced by the border- 504 xTR. Note that not all site-of-origin domains will connect to the 505 same combination of border-xTRs. 507 EID Mappings will be tagged with a site-ID according to their site- 508 of-origin when they are registered by the border-xTR. The site-ID 509 must be maintained in the Mapping System as part of the registration 510 record. EID Mappings published and received at the border xTR must 511 include the site-ID for the EID Mapping. If the border-xTR receives 512 a mapping for an EID with a site-ID that matches the site-ID for one 513 of its border sets (site-of-origin), the Border xTR will not register 514 that information to the site-of-origin associated with that site-ID 515 and thus prevent any registration loops from occurring. 517 4.2. Resolution and Forwarding Procedures 519 Intra-site communication follows the standard procedures of 520 registration, resolution, caching and encapsulation defined in 521 [I-D.ietf-lisp-rfc6830bis] and [I-D.ietf-lisp-rfc6833bis] amongst the 522 xTRs within the local site-overlay. 524 Inter-site communication is achieved by encapsulating traffic 525 destined to remote site-overlay EIDs from the xTRs to the border 526 xTRs. Traffic will be decapsulated at the border xTRs and a lookup 527 in the uberlay mapping system will determine the site-overlay to 528 which traffic is to be re-encapsulated. The lookup should return the 529 uberlay RLOCs for the border xTRs of the site-overlay where the 530 destination EID is located. At the border xTR of the destination 531 overlay-site, traffic will be de-capsulated, and re-encapsulated to 532 the destination xTR, just like an RTR does. The border xTR already 533 has the destination EID in its cache per its subscription to all 534 local site-overlay EIDs. 536 When receiving encapsulated traffic, a border xTR will de-capsulate 537 the traffic and will do a lookup for the destination EID in its map 538 cache. If the destination EID is present in the map cache, the 539 traffic is forwarded and no lookup takes place. If the destination 540 EID is not present in the cache, the destination EID is not in any 541 local site-overlay connected to the border xTR, in which case the 542 border xTR will issue a map-request to all Uberlay Mapping Systems it 543 is connected to. The criteria to determine which Mapping Systems are 544 Uberlay Mapping Systems is simply to select those Mapping Systems 545 with which the border xTR doesn't hold a subscription to 0.0.0.0/0 546 (or 0::/0). 548 4.2.1. Multi-overlay requests at border xTR 550 A Border xTR may query all Mapping Systems in all uberlays it 551 participates in. The border xTR will then chose based on longest 552 prefix match the more specific EID mapping provided by any of the 553 Mapping Systems. This procedure could also include site-overlay 554 Mapping Systems, however those are not expected to be queried as the 555 border xTR subscribes to all EIDs in the site-overlays and the 556 presence of the mappings in the cache will prevent any lookups. The 557 processing of Map Requests following the multi-domain request logic 558 works as follows: 560 1. The Border xTR sends a map request for the prefix that it intends 561 to resolve to each of the uberlay Mapping Systems it participates 562 in. 564 2. The Border xTR receives Map Replies from each of the different 565 uberlay Mapping Systems it sent requests to. The Border xTR will 566 treat the replies differently depending on their contents: 568 * Negative Map Replies (NMR) are ignored and discarded unless 569 all Map Replies received are Negative, then the border xTR 570 follows the procedures specified in [RFC6833] for Negative Map 571 Replies. 573 * Map Replies with RLOCs that belong to the requesting border 574 xTR are ignored. 576 * Map Replies with EID prefixes that are not already in the map 577 cache of the border xTR are accepted and cached. 579 * If the EID prefix received in the Map-Reply already exists in 580 the cache/routing table, but the Map-Reply contains a 581 different RLOC-set than the one cached, the mappings are 582 merged so that the RLOCs received in the Map-Reply are added 583 to the RLOC-set previously cached for the EID prefix. 585 * If the EID prefix received in the Map-Reply is more specific 586 or less specific than an EID prefix already cached, the 587 mapping received MUST be cached. 589 It is expected that a deployment of the uberlay would include the 590 dynamic registration of default EIDs. It is also recommended that an 591 implementation adopts mechanisms for the dynamic resolution of 592 default EIDs. In an environment leveraging the dynamic registration 593 and resolution of default EIDs, the border xTR should not receive 594 Negative Map-Replies, but all replies (including those in response to 595 requests for destinations that are external to the EID space) will be 596 Map-replies with a non-zero locator count. Nevertheless, an 597 implementation could opt to not use dynamic default-EID handling. In 598 these cases, the border xTR will receive NMRs. The implementation of 599 the Border xTR should defer the decision on caching an NMR until all 600 relevant Map-replies are received. To this effect, the 601 implementation should implement mechanisms to ensure that sufficient 602 replies are received before programming the map-cache. The 603 mechanisms by which this is achieved are an implementation specific 604 matter and therefore not specified in this document. 606 When following these rules to process multi-domain requests, the 607 Border xTR guarantees proper discovery and use of destination 608 prefixes that will be associated with their corresponding overlay- 609 site. By ignoring the negative replies the procedure works 610 regardless of whether the Mapping Systems of multiple uberlays have 611 consistent configurations or operate individually without being aware 612 of the whole addressing space in the overlay fabric. 614 4.3. Default EID registration and treatment 616 Border xTRs will register a mapping to be used as a default mapping 617 to handle the forwarding of traffic destined to any EIDs that are not 618 explicitly registered. These mappings will be registered in the 619 local site-overlay Mapping System of each site-overlay. The RLOCs 620 for the mappings will be the site-overlay RLOCs of the border xTR. 622 This registration is intended to instruct the Mapping System to 623 follow the procedures in [RFC6833] for Negative Map Replies and 624 calculate the broadest non-registered EID prefix that includes the 625 requested destination EID and issue a map-reply with the calculated 626 EID and the RLOCs registered by the border xTRs. The map-reply for 627 this default mapping will have a shorter TTL to accommodate any 628 changes in the registrations. 630 The instruction to the Mapping System can be encoded as the 631 registration of an agreed upon distinguished name such as "Default". 632 The registration will contain the RLOC set desired for the default 633 handling. 635 5. Multicast Specific Procedures 637 This specification will focus on the procedures necessary to extend 638 signal-free multicast [RFC8378] across multiple site-overlays 639 interconnected with an uberlay. The specification will focus on the 640 extensions of the Sender and Receiver site procedures 642 5.1. Inter-site-overlay Control Plane Procedures for Signal-free 643 multicast 645 1. At the listener sites, xTRs with multicast listeners will follow 646 the receiver site procedures described in [RFC8378]. A 647 replication list will be built and registered on the site-overlay 648 Mapping System for the multicast channel being joined by the 649 listeners. 651 2. The Mapping System for the listener site-overlay will send Map- 652 Notify messages towards the multicast source or RP per [RFC8378]. 653 The multicast source or RP is reachable via the border-xTRs of 654 the listener site-overlay via the default EID mapping registered 655 in the listener site-overlay. 657 3. Upon reception of the Map-Notify in the previous step, the 658 listener site-overlay border-xTR will register the multicast EID 659 with the uberlay Mapping System using the uberlay RLOCs for its 660 site-overlay as the RLOC set for the mapping being registered. 661 Only one of the RLOCs in the set should be active in the 662 registration per the procedures in [RFC8378]. A replication tree 663 is built in the uberlay as specified in [RFC8378]. 665 4. After the listener site-overlay border-xTR registers the 666 multicast EID with the uberlay Mapping system, the uberlay MS 667 will send a Map-Notify toward the multicast source per [RFC8378] 669 5. Upon reception of the Map-Notify in the previous step, the border 670 xTR at the source site-overlay registers its interest in the 671 multicast EID with the source site-overlay Mapping System 672 following the procedures described in [RFC8378]. 674 5.2. Border xTR Resolution and Forwarding procedures for Signal-free 675 multicast 677 The mapping resolution procedures for multicast EIDs at border xTRs 678 fall within the scope of the mechanisms specified in Section 4. The 679 Map-replies obtained from the lookup will follow the behavior 680 specified in [RFC8378] for signal-free multicast. 682 Forwarding will also follow the General Procedures specified in 683 Section 4 without alteration. It is worth noting that the 684 concatenation of overlays between listener sites, uberlay and sender 685 site-overlays creates a convenient replication structure where the 686 border xTRs act as the replication points to form an optimized end- 687 to-end multi-level replication tree. 689 6. Inter site-overlay Mobility Procedures 691 The receiver and sender site procedures defined in 692 [I-D.ietf-lisp-eid-mobility] apply without change to each site- 693 overlay and to the uberlay. Border xTRs are connected to two or more 694 overlay networks which are following the mobility procedures. An 695 away table is defined at the border xTR for each overlay network it 696 participates in. In order to illustrate the procedures required, 697 this specification describes a scenario where a border xTR has one 698 local site-overlay away table and one uberlay facing away table. The 699 procedures for mobility described in this section are extensible to 700 border xTRs participating in more than two overlays. 702 When a map notify for an EID is received at an xTR, an away entry is 703 created on the receiving side table. Any away entries for the 704 specific EID in other tables on the same LISP node (xTR or RTR) must 705 be removed. This general rule addresses convergence necessary for a 706 first move as well as any subsequent moves (moves that take place 707 after the away tables are already populated with entries for the 708 moving EID due to previous moves). 710 The following set of procedures highlights any additions to the 711 mobility procedures defined in [I-D.ietf-lisp-eid-mobility]: 713 1. Detect the roaming EID per the mechanisms described in 714 [I-D.ietf-lisp-eid-mobility] and register the EID with the site- 715 overlay Mapping System at the landing site-overlay 717 2. The site-overlay Mapping System at the landing site-overlay must 718 send a Map-Notify to the last registrant xTR (if it is local to 719 the site-overlay) and to the border xTR as the border xTR 720 subscribes to all EIDs in the site-overlay. 722 3. The border xTR will install an entry for the moved host in the 723 local away table of the border xTR. 725 4. The border xTR from the landing site-overlay will register the 726 roaming EID with the uberlay Mapping System using the uberlay 727 RLOC-set for the landing site-overlay 729 5. The Uberlay Map Server will send Map-Notify messages to the 730 border xTRs at the departure site-overlay as specified in 731 [I-D.ietf-lisp-eid-mobility] (border xTR with the previously 732 registered RLOCs). 734 6. Upon reception of the Map-Notify, the border xTR must check if 735 the Map-Notify is for an EID-prefix that is covered by a broader 736 or equal EID-prefix that is locally registered. Local 737 registration is determined by the presence of the broader or 738 equal EID prefix in the map-cache of the border xTR. 740 7. If the roaming EID-prefix received in the Map-Notify is not 741 covered under a previously registered EID-prefix in the local 742 site-overlay, the EID-prefix is a newly registered prefix and no 743 further action is required. 745 8. If the roaming EID-prefix received in the Map-Notify is covered 746 under a registered EID-prefix, the Map-Notify is due to a move 747 event. In this case, the site-overlay border xTR must register 748 the roaming EID prefix in the site-overlay mapping system using 749 the site-overlay facing RLOC-set of the border-xTRs. The 750 roaming EID-prefix must also be installed in the uberlay facing 751 away table of the border xTR at the departure site-overlay. 753 9. The departure site-overlay Map-Server will send Map-Notify 754 messages to the xTRs at the departure site-overlay as specified 755 in [I-D.ietf-lisp-eid-mobility] (edge xTRs with the previously 756 registered RLOCs). 758 10. When the site-overlay xTR at the departure site-overlay receives 759 the Map-Notify from the border xTR, it will include the EID 760 prefix received in the Map-Notify in its away table per the 761 procedures described in [I-D.ietf-lisp-eid-mobility]. 763 11. Data triggered Solicit Map Requests (SMRs) will be initiated in 764 the different site-overlays and the uberlay as traffic matches 765 the different away tables. As specified in 766 [I-D.ietf-lisp-eid-mobility], these SMRs notify the different 767 ITRs involved in communications with the roaming EID that they 768 must issue a new Map-Request to the mapping system to renew 769 their mappings for the roaming EID. 771 7. Virtual Private Network (VPN) Considerations 773 When supporting multiple Instance IDs as specified in 774 [I-D.ietf-lisp-vpn] the Instance IDs range is divided in two sets. A 775 reuse-set that can be used in each site-overlay and a global-set used 776 across site-overlays and the uberlay. 778 Instance-IDs that are local to a site-overlay should only provide 779 intra-overlay connectivity and are in the site-overlay mapping system 780 only for VPN use for the xTRs in the site-overlay. When the VPN 781 reaches across site-overlays, then the global-set instance-IDs are in 782 the uberlay mapping system as well as each site-overlay mapping 783 system where the VPN members exist. 785 8. IANA Considerations 787 This document has no IANA implications 789 9. Acknowledgements 791 The authors want to thank Kedar Karamarkar, Prakash Jain and Vina 792 Ermagan for their insightful contribution to shaping the ideas in 793 this document. We would also like to acknowledge the valuable input 794 from the workgroup chairs Joel Halpern and Luigi Iannone in refining 795 the objectives of the document. 797 10. References 799 10.1. Normative References 801 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 802 Requirement Levels", BCP 14, RFC 2119, 803 DOI 10.17487/RFC2119, March 1997, 804 . 806 [RFC3618] Fenner, B., Ed. and D. Meyer, Ed., "Multicast Source 807 Discovery Protocol (MSDP)", RFC 3618, 808 DOI 10.17487/RFC3618, October 2003, 809 . 811 [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, 812 "Protocol Independent Multicast - Sparse Mode (PIM-SM): 813 Protocol Specification (Revised)", RFC 4601, 814 DOI 10.17487/RFC4601, August 2006, 815 . 817 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 818 IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, 819 . 821 10.2. Informative References 823 [I-D.farinacci-lisp-decent] 824 Farinacci, D. and C. Cantrell, "A Decent LISP Mapping 825 System (LISP-Decent)", draft-farinacci-lisp-decent-08 826 (work in progress), August 2021. 828 [I-D.ietf-lisp-eid-mobility] 829 Comeras, M. P., Ashtaputre, V., Moreno, V., Maino, F., and 830 D. Farinacci, "LISP L2/L3 EID Mobility Using a Unified 831 Control Plane", draft-ietf-lisp-eid-mobility-08 (work in 832 progress), July 2021. 834 [I-D.ietf-lisp-pubsub] 835 Rodriguez-Natal, A., Ermagan, V., Cabellos, A., Barkai, 836 S., and M. Boucadair, "Publish/Subscribe Functionality for 837 LISP", draft-ietf-lisp-pubsub-09 (work in progress), June 838 2021. 840 [I-D.ietf-lisp-rfc6830bis] 841 Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A. 842 Cabellos, "The Locator/ID Separation Protocol (LISP)", 843 draft-ietf-lisp-rfc6830bis-36 (work in progress), November 844 2020. 846 [I-D.ietf-lisp-rfc6833bis] 847 Farinacci, D., Maino, F., Fuller, V., and A. Cabellos, 848 "Locator/ID Separation Protocol (LISP) Control-Plane", 849 draft-ietf-lisp-rfc6833bis-30 (work in progress), November 850 2020. 852 [I-D.ietf-lisp-vpn] 853 Moreno, V. and D. Farinacci, "LISP Virtual Private 854 Networks (VPNs)", draft-ietf-lisp-vpn-08 (work in 855 progress), January 2022. 857 [RFC6407] Weis, B., Rowles, S., and T. Hardjono, "The Group Domain 858 of Interpretation", RFC 6407, DOI 10.17487/RFC6407, 859 October 2011, . 861 [RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The 862 Locator/ID Separation Protocol (LISP)", RFC 6830, 863 DOI 10.17487/RFC6830, January 2013, 864 . 866 [RFC6831] Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas, "The 867 Locator/ID Separation Protocol (LISP) for Multicast 868 Environments", RFC 6831, DOI 10.17487/RFC6831, January 869 2013, . 871 [RFC6833] Fuller, V. and D. Farinacci, "Locator/ID Separation 872 Protocol (LISP) Map-Server Interface", RFC 6833, 873 DOI 10.17487/RFC6833, January 2013, 874 . 876 [RFC7348] Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger, 877 L., Sridhar, T., Bursell, M., and C. Wright, "Virtual 878 eXtensible Local Area Network (VXLAN): A Framework for 879 Overlaying Virtualized Layer 2 Networks over Layer 3 880 Networks", RFC 7348, DOI 10.17487/RFC7348, August 2014, 881 . 883 [RFC8060] Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical 884 Address Format (LCAF)", RFC 8060, DOI 10.17487/RFC8060, 885 February 2017, . 887 [RFC8061] Farinacci, D. and B. Weis, "Locator/ID Separation Protocol 888 (LISP) Data-Plane Confidentiality", RFC 8061, 889 DOI 10.17487/RFC8061, February 2017, 890 . 892 [RFC8111] Fuller, V., Lewis, D., Ermagan, V., Jain, A., and A. 893 Smirnov, "Locator/ID Separation Protocol Delegated 894 Database Tree (LISP-DDT)", RFC 8111, DOI 10.17487/RFC8111, 895 May 2017, . 897 [RFC8378] Moreno, V. and D. Farinacci, "Signal-Free Locator/ID 898 Separation Protocol (LISP) Multicast", RFC 8378, 899 DOI 10.17487/RFC8378, May 2018, 900 . 902 Authors' Addresses 904 Victor Moreno 905 Google LLC 906 1600 Amphitheater Parkway 907 Mountain View, CA 94043 908 USA 910 Email: vimoreno@google.com 912 Dino Farinacci 913 lispers.net 914 San Jose, CA 95120 915 USA 917 Email: farinacci@gmail.com 919 Alberto Rodriguez-Natal 920 Cisco Systems 921 170 Tasman Drive 922 San Jose, California 95134 923 USA 925 Email: natal@cisco.com 927 Marc Portoles-Comeras 928 Cisco Systems 929 170 Tasman Drive 930 San Jose, California 95134 931 USA 933 Email: mportole@cisco.com 935 Fabio Maino 936 Cisco Systems 937 170 Tasman Drive 938 San Jose, California 95134 939 USA 941 Email: fmaino@cisco.com 942 Sanjay Hooda 943 Cisco Systems 944 170 Tasman Drive 945 San Jose, California 95134 946 USA 948 Email: shooda@cisco.com