idnits 2.17.1 draft-ietf-lisp-te-09.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- == There are 8 instances of lines with private range IPv4 addresses in the document. If these are generic example addresses, they should be changed to use any of the ranges defined in RFC 6890 (or successor): 192.0.2.x, 198.51.100.x or 203.0.113.x. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'MUST not' in this paragraph: An ELP that is first used by an ITR must be inspected for encoding loops. If any RLOC appears twice in the ELP, it MUST not be used. -- The document date (September 19, 2021) is 943 days in the past. Is this intentional? Checking references for intended status: Experimental ---------------------------------------------------------------------------- ** Obsolete normative reference: RFC 2460 (Obsoleted by RFC 8200) ** Obsolete normative reference: RFC 6830 (Obsoleted by RFC 9300, RFC 9301) ** Obsolete normative reference: RFC 6833 (Obsoleted by RFC 9301) Summary: 3 errors (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force D. Farinacci 3 Internet-Draft lispers.net 4 Intended status: Experimental M. Kowal 5 Expires: March 23, 2022 cisco Systems 6 P. Lahiri 7 September 19, 2021 9 LISP Traffic Engineering Use-Cases 10 draft-ietf-lisp-te-09 12 Abstract 14 This document describes how LISP reencapsulating tunnels can be used 15 for Traffic Engineering purposes. The mechanisms described in this 16 document require no LISP protocol changes but do introduce a new 17 locator (RLOC) encoding. The Traffic Engineering features provided 18 by these LISP mechanisms can span intra-domain, inter-domain, or 19 combination of both. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at https://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on March 23, 2022. 38 Copyright Notice 40 Copyright (c) 2021 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (https://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Requirements Language . . . . . . . . . . . . . . . . . . . . 2 56 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 57 3. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 3 58 4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5 59 5. Explicit Locator Paths . . . . . . . . . . . . . . . . . . . 6 60 5.1. ELP Re-optimization . . . . . . . . . . . . . . . . . . . 8 61 5.2. Using Recursion . . . . . . . . . . . . . . . . . . . . . 8 62 5.3. ELP Selection based on Class of Service . . . . . . . . . 9 63 5.4. Packet Loop Avoidance . . . . . . . . . . . . . . . . . . 10 64 6. Service Chaining . . . . . . . . . . . . . . . . . . . . . . 10 65 7. RLOC Probing by RTRs . . . . . . . . . . . . . . . . . . . . 10 66 8. ELP Probing . . . . . . . . . . . . . . . . . . . . . . . . . 11 67 9. Interworking Considerations . . . . . . . . . . . . . . . . . 11 68 10. Multicast Considerations . . . . . . . . . . . . . . . . . . 12 69 11. Security Considerations . . . . . . . . . . . . . . . . . . . 14 70 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 71 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 72 13.1. Normative References . . . . . . . . . . . . . . . . . . 14 73 13.2. Informative References . . . . . . . . . . . . . . . . . 15 74 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 15 75 Appendix B. Document Change Log . . . . . . . . . . . . . . . . 16 76 B.1. Changes to draft-ietf-lisp-te-09 . . . . . . . . . . . . 16 77 B.2. Changes to draft-ietf-lisp-te-08 . . . . . . . . . . . . 16 78 B.3. Changes to draft-ietf-lisp-te-07 . . . . . . . . . . . . 16 79 B.4. Changes to draft-ietf-lisp-te-06 . . . . . . . . . . . . 16 80 B.5. Changes to draft-ietf-lisp-te-05 . . . . . . . . . . . . 16 81 B.6. Changes to draft-ietf-lisp-te-04 . . . . . . . . . . . . 16 82 B.7. Changes to draft-ietf-lisp-te-03 . . . . . . . . . . . . 16 83 B.8. Changes to draft-ietf-lisp-te-02 . . . . . . . . . . . . 17 84 B.9. Changes to draft-ietf-lisp-te-01 . . . . . . . . . . . . 17 85 B.10. Changes to draft-ietf-lisp-te-00 . . . . . . . . . . . . 17 86 B.11. Changes to draft-farinacci-lisp-te-02 through -12 . . . . 17 87 B.12. Changes to draft-farinacci-lisp-te-01.txt . . . . . . . . 17 88 B.13. Changes to draft-farinacci-lisp-te-00.txt . . . . . . . . 17 89 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 91 1. Requirements Language 93 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 94 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 95 document are to be interpreted as described in RFC 2119 [RFC2119]. 97 2. Introduction 99 This document describes the Locator/Identifier Separation Protocol 100 (LISP), which provides a set of functions for routers to exchange 101 information used to map from non globally routeable Endpoint 102 Identifiers (EIDs) to routeable Routing Locators (RLOCs). It also 103 defines a mechanism for these LISP routers to encapsulate IP packets 104 addressed with EIDs for transmission across the Internet that uses 105 RLOCs for routing and forwarding. 107 When LISP routers encapsulate packets to other LISP routers, the path 108 stretch is typically 1, meaning the packet travels on a direct path 109 from the encapsulating ITR to the decapsulating ETR at the 110 destination site. The direct path is determined by the underlying 111 routing protocol and metrics it uses to find the shortest path. 113 This specification will examine how reencapsulating tunnels [RFC6830] 114 can be used so a packet can take an adminstratively specified path, a 115 congestion avoidance path, a failure recovery path, or multiple load- 116 shared paths, as it travels from ITR to ETR. By introducing an 117 Explicit Locator Path (ELP) locator encoding [RFC8060], an ITR can 118 encapsulate a packet to a Reencapsulating Tunnel Router (RTR) which 119 decapsulates the packet, then encapsulates it to the next locator in 120 the ELP. 122 3. Definition of Terms 124 Endpoint ID (EID): An EID is a 32-bit (for IPv4) or 128-bit (for 125 IPv6) value used in the source and destination address fields of 126 the first (most inner) LISP header of a packet. The host obtains 127 a destination EID the same way it obtains an destination address 128 today, for example through a Domain Name System (DNS) [RFC1034] 129 lookup or Session Invitation Protocol (SIP) [RFC3261] exchange. 130 The source EID is obtained via existing mechanisms used to set a 131 host's "local" IP address. An EID used on the public Internet 132 must have the same properties as any other IP address used in that 133 manner; this means, among other things, that it must be globally 134 unique. An EID is allocated to a host from an EID-prefix block 135 associated with the site where the host is located. An EID can be 136 used by a host to refer to other hosts. EIDs MUST NOT be used as 137 LISP RLOCs. Note that EID blocks MAY be assigned in a 138 hierarchical manner, independent of the network topology, to 139 facilitate scaling of the mapping database. In addition, an EID 140 block assigned to a site may have site-local structure 141 (subnetting) for routing within the site; this structure is not 142 visible to the global routing system. In theory, the bit string 143 that represents an EID for one device can represent an RLOC for a 144 different device. As the architecture is realized, if a given bit 145 string is both an RLOC and an EID, it must refer to the same 146 entity in both cases. When used in discussions with other 147 Locator/ID separation proposals, a LISP EID will be called a 148 "LEID". Throughout this document, any references to "EID" refers 149 to an LEID. 151 Routing Locator (RLOC): A RLOC is an IPv4 [RFC0791] or IPv6 152 [RFC2460] address of an egress tunnel router (ETR). A RLOC is the 153 output of an EID-to-RLOC mapping lookup. An EID maps to one or 154 more RLOCs. Typically, RLOCs are numbered from topologically- 155 aggregatable blocks that are assigned to a site at each point to 156 which it attaches to the global Internet; where the topology is 157 defined by the connectivity of provider networks, RLOCs can be 158 thought of as PA addresses. Multiple RLOCs can be assigned to the 159 same ETR device or to multiple ETR devices at a site. 161 Reencapsulating Tunnel Router (RTR): An RTR is a router that acts 162 as an ETR (or PETR) by decapsulating packets where the destination 163 address in the "outer" IP header is one of its own RLOCs. Then 164 acts as an ITR (or PITR) by making a decision where to encapsulate 165 the packet based on the next locator in the ELP towards the final 166 destination ETR. 168 Explicit Locator Path (ELP): The ELP is an explicit list of RLOCs 169 for each RTR a packet must travel to along its path toward a final 170 destination ETR (or PETR). The list is a strict ordering where 171 each RLOC in the list is visited. However, the path from one RTR 172 to another is determined by the underlying routing protocol and 173 how the infrastructure assigns metrics and policies for the path. 175 Recursive Tunneling: Recursive tunneling occurs when a packet has 176 more than one LISP IP header. Additional layers of tunneling MAY 177 be employed to implement traffic engineering or other re-routing 178 as needed. When this is done, an additional "outer" LISP header 179 is added and the original RLOCs are preserved in the "inner" 180 header. Any references to tunnels in this specification refers to 181 dynamic encapsulating tunnels and they are never statically 182 configured. 184 Reencapsulating Tunnels: Reencapsulating tunneling occurs when an 185 ETR removes a LISP header, then acts as an ITR to prepend another 186 LISP header. Doing this allows a packet to be re-routed by the 187 reencapsulating router without adding the overhead of additional 188 tunnel headers. Any references to tunnels in this specification 189 refers to dynamic encapsulating tunnels and they are never 190 statically configured. When using multiple mapping database 191 systems, care must be taken to not create reencapsulation loops 192 through misconfiguration. 194 4. Overview 196 Typically, a packet's path from source EID to destination EID travels 197 through the locator core via the encapsulating ITR directly to the 198 decapsulating ETR as the following diagram illustrates: 200 Legend: 202 seid: Packet is originated by source EID 'seid'. 204 deid: Packet is consumed by destination EID 'deid'. 206 A,B,C,D : Core routers in different ASes. 208 ---> : The physical topological path between two routers. 210 ===> : A multi-hop LISP dynamic tunnel between LISP routers. 212 Core Network 213 Source site (----------------------------) Destination Site 214 +--------+ ( ) +---------+ 215 | \ ( ) / | 216 | seid ITR ---(---> A --> B --> C --> D ---)---> ETR deid | 217 | / || ( ) ^^ \ | 218 +--------+ || ( ) || +---------+ 219 || (----------------------------) || 220 || || 221 =========================================== 222 LISP Tunnel 224 Typical Data Path from ITR to ETR 226 Let's introduce RTRs 'X' and 'Y' so that, for example, if it is 227 desirable to route around the path from B to C, one could provide an 228 ELP of (X,Y,etr): 230 Core Network 231 Source site (----------------------------) Destination Site 232 +--------+ ( ) +---------+ 233 | \ ( ) / | 234 | seid ITR ---(---> A --> B --> C --> D ---)---> ETR deid | 235 | / || ( / ^ ) ^^ \ | 236 | / || ( | \ ) || \ | 237 +-------+ || ( v | ) || +--------+ 238 || ( X ======> Y ) || 239 || ( ^^ || ) || 240 || (--------||---------||-------) || 241 || || || || 242 ================= ================= 243 LISP Tunnel LISP Tunnel 245 ELP tunnel path ITR ==> X, then X ==> Y, and then Y ==> ETR 247 There are various reasons why the path from 'seid' to 'deid' may want 248 to avoid the path from B to C. To list a few: 250 o There may not be sufficient capacity provided by the networks that 251 connect B and C together. 253 o There may be a policy reason to avoid the ASes that make up the 254 path between B and C. 256 o There may be a failure on the path between B and C which makes the 257 path unreliable. 259 o There may be monitoring or traffic inspection resources close to 260 RTRs X and Y that do network accounting or measurement. 262 o There may be a chain of services performed at RTRs X and Y 263 regardless if the path from ITR to ETR is through B and C. 265 5. Explicit Locator Paths 267 The notation for a general formatted ELP is (x, y, etr) which 268 represents the list of RTRs a packet SHOULD travel through to reach 269 the final tunnel hop to the ETR. 271 The procedure for using an ELP at each tunnel hop is as follows: 273 1. The ITR will retrieve the ELP from the mapping database. 275 2. The ITR will encapsulate the packet to RLOC 'x'. 277 3. The RTR with RLOC 'x' will decapsulate the packet. It will use 278 the decapsulated packet's destination address as a lookup into 279 the mapping database to retrieve the ELP. 281 4. RTR 'x' will encapsulate the packet to RTR with RLOC 'y'. 283 5. The RTR with RLOC 'y' will decapsulate the packet. It will use 284 the decapsulated packet's destination address as a lookup into 285 the mapping database to retrieve the ELP. 287 6. RTR 'y' will encapsulate the packet on the final tunnel hop to 288 ETR with RLOC 'etr'. 290 7. The ETR will decapsulate the packet and deliver the packet to the 291 EID inside of its site. 293 The specific format for the ELP can be found in [RFC8060]. It is 294 defined that an ELP will appear as a single encoded locator in a 295 locator-set. Say for instance, we have a mapping entry for EID- 296 prefix 10.0.0.0/8 that is reachable via 4 locators. Two locators are 297 being used as active/active and the other two are used as active/ 298 active if the first two go unreachable (as noted by the priority 299 assignments below). This is what the mapping entry would look like: 301 EID-prefix: 10.0.0.0/8 302 Locator-set: ETR-A: priority 1, weight 50 303 ETR-B: priority 1, weight 50 304 ETR-C: priority 2, weight 50 305 ETR-D: priority 2, weight 50 307 If an ELP is going to be used to have a policy path to ETR-A and 308 possibly another policy path to ETR-B, the locator-set would be 309 encoded as follows: 311 EID-prefix: 10.0.0.0/8 312 Locator-set: (x, y, ETR-A): priority 1, weight 50 313 (q, r, ETR-B): priority 1, weight 50 314 ETR-C: priority 2, weight 50 315 ETR-D: priority 2, weight 50 317 The mapping entry with ELP locators is registered to the mapping 318 database system just like any other mapping entry would. The 319 registration is typically performed by the ETR(s) that are assigned 320 and own the EID-prefix. That is, the destination site makes the 321 choice of the RTRs in the ELP. However, it may be common practice 322 for a provisioning system to program the mapping database with ELPs. 324 Another case where a locator-set can be used for flow-based load- 325 sharing across multiple paths to the same destination site: 327 EID-prefix: 10.0.0.0/8 328 Locator-set: (x, y, ETR-A): priority 1, weight 75 329 (q, r, ETR-A): priority 1, weight 25 331 Using this mapping entry, an ITR would load split 75% of the EID 332 flows on the (x, y, ETR-A) ELP path and 25% of the EID flows on the 333 (q, r, ETR-A) ELP path. If any of the ELPs go down, then the other 334 can take 100% of the load. 336 5.1. ELP Re-optimization 338 ELP re-optimization is a process of changing the RLOCs of an ELP due 339 to underlying network change conditions. Just like when there is any 340 locator change for a locator-set, the procedures from the main LISP 341 specification [RFC6830] are followed. 343 When a RLOC from an ELP is changed, Map-Notify messages [RFC6833] can 344 be used to inform the existing RTRs in the ELP so they can do a 345 lookup to obtain the latest version of the ELP. Map-Notify messages 346 can also be sent to new RTRs in an ELP so they can get the ELP in 347 advance to receiving packets that will use the ELP. This can 348 minimize packet loss during mapping database lookups in RTRs. 350 5.2. Using Recursion 352 In the previous examples, we showed how an ITR encapsulates using an 353 ELP of (x, y, etr). When a packet is encapsulated by the ITR to RTR 354 'x', the RTR may want a policy path to RTR 'y' and run another level 355 of reencapsulating tunnels for packets destined to RTR 'y'. In this 356 case, RTR 'x' does not encapsulate packets to 'y' but rather performs 357 a mapping database lookup on the address 'y', requests the ELP for 358 RTR 'y', and encapsulates packets to the first-hop of the returned 359 ELP. This can be done when using a public or private mapping 360 database. The decision to use address 'y' as an encapsulation 361 address versus a lookup address is based on the L-bit setting for 'y' 362 in the ELP entry. The decision and policy of ELP encodings are local 363 to the entity which registers the EID-prefix associated with the ELP. 365 Another example of recursion is when the ITR uses the ELP (x, y, etr) 366 to first prepend a header with a destination RLOC of the ETR and then 367 prepend another header and encapsulate the packet to RTR 'x'. When 368 RTR 'x' decapsulates the packet, rather than doing a mapping database 369 lookup on RTR 'y' the last example showed, instead RTR 'x' does a 370 mapping database lookup on ETR 'etr'. In this scenario, RTR 'x' can 371 choose an ELP from the locator-set by considering the source RLOC 372 address of the ITR versus considering the source EID. 374 This additional level of recursion also brings advantages for the 375 provider of RTR 'x' to store less state. Since RTR 'x' does not need 376 to look at the inner most header, it does not need to store EID 377 state. It only stores an entry for RTR 'y' which many EID flows 378 could share for scaling benefits. The locator-set for entry 'y' 379 could either be a list of typical locators, a list of ELPs, or 380 combination of both. Another advantage is that packet load-splitting 381 can be accomplished by examining the source of a packet. If the 382 source is an ITR versus the source being the last-hop of an ELP the 383 last-hop selected, different forwarding paths can be used. 385 5.3. ELP Selection based on Class of Service 387 Paths to an ETR may want to be selected based on different classes of 388 service. Packets from a set of sources that have premium service can 389 use ELP paths that are less congested where normal sources use ELP 390 paths that compete for less resources or use longer paths for best 391 effort service. 393 Using source/destination lookups into the mapping database can yield 394 different ELPs. So for example, a premium service flow with 395 (source=1.1.1.1, dest=10.1.1.1) can be described by using the 396 following mapping entry: 398 EID-prefix: (1.0.0.0/8, 10.0.0.0/8) 399 Locator-set: (x, y, ETR-A): priority 1, weight 50 400 (q, r, ETR-A): priority 1, weight 50 402 And all other best-effort sources would use different mapping entry 403 described by: 405 EID-prefix: (0.0.0.0/0, 10.0.0.0/8) 406 Locator-set: (x, x', y, y', ETR-A): priority 1, weight 50 407 (q, q', r, r', ETR-A): priority 1, weight 50 409 If the source/destination lookup is coupled with recursive lookups, 410 then an ITR can encapsulate to the ETR, prepending a header that 411 selects source address ITR-1 based on the premium class of service 412 source, or selects source address ITR-2 for best-effort sources with 413 normal class of service. The ITR then does another lookup in the 414 mapping database on the prepended header using lookup key 415 (source=ITR-1, dest=10.1.1.1) that returns the following mapping 416 entry: 418 EID-prefix: (ITR-1, 10.0.0.0/8) 419 Locator-set: (x, y, ETR-A): priority 1, weight 50 420 (q, r, ETR-A): priority 1, weight 50 422 And all other sources would use different mapping entry with a lookup 423 key of (source=ITR-2, dest=10.1.1.1): 425 EID-prefix: (ITR-2, 10.0.0.0/8) 426 Locator-set: (x, x', y, y', ETR-A): priority 1, weight 50 427 (q, q', r, r', ETR-A): priority 1, weight 50 429 This will scale the mapping system better by having fewer source/ 430 destination combinations. Refer to the Source/Dest LCAF type 431 described in [RFC8060] for encoding EIDs in Map-Request and Map- 432 Register messages. 434 5.4. Packet Loop Avoidance 436 An ELP that is first used by an ITR must be inspected for encoding 437 loops. If any RLOC appears twice in the ELP, it MUST not be used. 439 Since it is expected that multiple mapping systems will be used, 440 there can be a loop across ELPs when registered in different mapping 441 systems. The TTL copying procedures for reencapsulating tunnels and 442 recursive tunnels in [RFC6830] MUST be followed. 444 6. Service Chaining 446 An ELP can be used to deploy services at each reencapsulation point 447 in the network. One example is to implement a scrubber service when 448 a destination EID is being DoS attacked. That is, when a DoS attack 449 is recognized when the encapsulation path is between ITR and ETR, an 450 ELP can be registered for a destination EID to the mapping database 451 system. The ELP can include an RTR so the ITR can encapsulate 452 packets to the RTR which will decapsulate and deliver packets to a 453 scrubber service device. The scrubber could decide if the offending 454 packets are dropped or allowed to be sent to the destination EID. In 455 which case, the scurbber delivers packets back to the RTR which 456 encapsulates to the ETR. 458 7. RLOC Probing by RTRs 460 Since an RTR knows the next tunnel hop to encapsulate to, it can 461 monitor the reachability of the next-hop RTR RLOC by doing RLOC- 462 probing according to the procedures in [RFC6830]. When the RLOC is 463 determined unreachable by the RLOC-probing mechanisms, the RTR can 464 use another locator in the locator-set. That could be the final ETR, 465 a RLOC of another RTR, or an ELP where it must search for itself and 466 use the next RLOC in the ELP list to encapsulate to. 468 RLOC-probing can also be used to measure delay on the path between 469 RTRs and when it is desirable switch to another lower delay ELP. 471 8. ELP Probing 473 Since an ELP-node knows the reachabiliy of the next ELP-node in a ELP 474 by using RLOC probing, the sum of reachability can determine the 475 reachability of the entire path. A head-end ITR/RTR/PITR can 476 determine the quality of a path and decide to select one path from 477 another based on the telemetry data gathered by RLOC-probing for each 478 encapsulation hop. 480 ELP-probing mechanism details can be found in [I-D.filyurin-lisp-elp- 481 probing]. 483 9. Interworking Considerations 485 [RFC6832] defines procedures for how non-LISP sites talk to LISP 486 sites. The network elements defined in the Interworking 487 specification, the proxy ITR (PITR) and proxy ETR (PETR) (as well as 488 their multicast counterparts defined in [RFC6831]) can participate in 489 LISP-TE. That is, a PITR and a PETR can appear in an ELP list and 490 act as an RTR. 492 Note when an RLOC appears in an ELP, it can be of any address-family. 493 There can be a mix of IPv4 and IPv6 locators present in the same ELP. 494 This can provide benefits where islands of one address-family or the 495 other are supported and connectivity across them is necessary. For 496 instance, an ELP can look like: 498 (x4, a46, b64, y4, etr) 500 Where an IPv4 ITR will encapsulate using an IPv4 RLOC 'x4' and 'x4' 501 could reach an IPv4 RLOC 'a46', but RTR 'a46' encapsulates to an IPv6 502 RLOC 'b64' when the network between them is IPv6-only. Then RTR 503 'b64' encapsulates to IPv4 RLOC 'y4' if the network between them is 504 dual-stack. 506 Note that RTRs can be used for NAT-traversal scenarios 507 [I-D.ermagan-lisp-nat-traversal] as well to reduce the state in both 508 an xTR that resides behind a NAT and the state the NAT needs to 509 maintain. In this case, the xTR only needs a default map-cache entry 510 pointing to the RTR for outbound traffic and all remote ITRs can 511 reach EIDs through the xTR behind a NAT via a single RTR (or a small 512 set RTRs for redundancy). 514 RTRs have some scaling features to reduce the number of locator-set 515 changes, the amount of state, and control packet overhead: 517 o When ITRs and PITRs are using a small set of RTRs for 518 encapsulating to "orders of magnitude" more EID-prefixes, the 519 probability of locator-set changes are limited to the RTR RLOC 520 changes versus the RLOC changes for the ETRs associated with the 521 EID-prefixes if the ITRs and PITRs were directly encapsulating to 522 the ETRs. This comes at an expense in packet stretch, but 523 depending on RTR placement, this expense can be mitigated. 525 o When RTRs are on-path between many pairwise EID flows, ITRs and 526 PITRs can store a small number of coarse EID-prefixes. 528 o RTRs can be used to help scale RLOC-probing. Instead of ITRs 529 RLOC-probing all ETRs for each destination site it has cached, the 530 ITRs can probe a smaller set of RTRs which in turn, probe the 531 destination sites. 533 10. Multicast Considerations 535 ELPs have application in multicast environments. Just like RTRs can 536 be used to provide connectivity across different address family 537 islands, RTRs can help concatenate a multicast region of the network 538 to one that does not support native multicast. 540 Note there are various combinations of connectivity that can be 541 accomplished with the deployment of RTRs and ELPs: 543 o Providing multicast forwarding between IPv4-only-unicast regions 544 and IPv4-multicast regions. 546 o Providing multicast forwarding between IPv6-only-unicast regions 547 and IPv6-multicast regions. 549 o Providing multicast forwarding between IPv4-only-unicast regions 550 and IPv6-multicast regions. 552 o Providing multicast forwarding between IPv6-only-unicast regions 553 and IPv4-multicast regions. 555 o Providing multicast forwarding between IPv4-multicast regions and 556 IPv6-multicast regions. 558 An ITR or PITR can do a (S-EID,G) lookup into the mapping database. 559 What can be returned is a typical locator-set that could be made up 560 of the various RLOC addresses: 562 Multicast EID key: (seid, G) 563 Locator-set: ETR-A: priority 1, weight 25 564 ETR-B: priority 1, weight 25 565 g1: priority 1, weight 25 566 g2: priority 1, weight 25 568 An entry for host 'seid' sending to application group 'G' 570 The locator-set above can be used as a replication list. That is 571 some RLOCs listed can be unicast RLOCs and some can be delivery group 572 RLOCs. A unicast RLOC in this case is used to encapsulate a 573 multicast packet originated by a multicast source EID into a unicast 574 packet for unicast delivery on the underlying network. ETR-A could 575 be a IPv4 unicast RLOC address and ETR-B could be a IPv6 unicast RLOC 576 address. 578 A delivery group address is used when a multicast packet originated 579 by a multicast source EID is encapsulated in a multicast packet for 580 multicast delivery on the underlying network. Group address 'g1' 581 could be a IPv4 delivery group RLOC and group address 'g2' could be 582 an IPv6 delivery group RLOC. 584 Flexibility for these various types of connectivity combinations can 585 be achieved and provided by the mapping database system. And the RTR 586 placement allows the connectivity to occur where the differences in 587 network functionality are located. 589 Extending this concept by allowing ELPs in locator-sets, one could 590 have this locator-set registered in the mapping database for (seid, 591 G). For example: 593 Multicast EID key: (seid, G) 594 Locator-set: (x, y, ETR-A): priority 1, weight 50 595 (a, g, b, ETR-B): priority 1, weight 50 597 Using ELPs for multicast flows 599 In the above situation, an ITR would encapsulate a multicast packet 600 originated by a multicast source EID to the RTR with unicast RLOC 601 'x'. Then RTR 'x' would decapsulate and unicast encapsulate to RTR 602 'y' ('x' or 'y' could be either IPv4 or IPv6 unicast RLOCs), which 603 would decapsulate and unicast encapsulate to the final RLOC 'ETR-A'. 604 The ETR 'ETR-A' would decapsulate and deliver the multicast packet 605 natively to all the receivers joined to application group 'G' inside 606 the LISP site. 608 Let's look at the ITR using the ELP (a, g, b, ETR-B). Here the 609 encapsulation path would be the ITR unicast encapsulates to unicast 610 RLOC 'a'. RTR 'a' multicast encapsulates to delivery group 'g'. The 611 packet gets to all ETRs that have joined delivery group 'g' so they 612 can deliver the multicast packet to joined receivers of application 613 group 'G' in their sites. RTR 'b' is also joined to delivery group 614 'g'. Since it is in the ELP, it will be the only RTR that unicast 615 encapsulates the multicast packet to ETR 'ETR-B'. Lastly, 'ETR-B' 616 decapsulates and delivers the multicast packet to joined receivers to 617 application group 'G' in its LISP site. 619 As one can see there are all sorts of opportunities to provide 620 multicast connectivity across a network with non-congruent support 621 for multicast and different address-families. One can also see how 622 using the mapping database can allow flexible forms of delivery 623 policy, rerouting, and congestion control management in multicast 624 environments. 626 11. Security Considerations 628 When an RTR receives a LISP encapsulated packet, it can look at the 629 outer source address to verify that RLOC is the one listed as the 630 previous hop in the ELP list. If the outer source RLOC address 631 appears before the RLOC which matches the outer destination RLOC 632 address, the decapsulating RTR (or ETR if last hop), MAY choose to 633 drop the packet. 635 12. IANA Considerations 637 At this time there are no requests for IANA. 639 13. References 641 13.1. Normative References 643 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 644 DOI 10.17487/RFC0791, September 1981, 645 . 647 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 648 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 649 . 651 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 652 Requirement Levels", BCP 14, RFC 2119, 653 DOI 10.17487/RFC2119, March 1997, 654 . 656 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 657 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, 658 December 1998, . 660 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 661 A., Peterson, J., Sparks, R., Handley, M., and E. 662 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 663 DOI 10.17487/RFC3261, June 2002, 664 . 666 [RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The 667 Locator/ID Separation Protocol (LISP)", RFC 6830, 668 DOI 10.17487/RFC6830, January 2013, 669 . 671 [RFC6831] Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas, "The 672 Locator/ID Separation Protocol (LISP) for Multicast 673 Environments", RFC 6831, DOI 10.17487/RFC6831, January 674 2013, . 676 [RFC6832] Lewis, D., Meyer, D., Farinacci, D., and V. Fuller, 677 "Interworking between Locator/ID Separation Protocol 678 (LISP) and Non-LISP Sites", RFC 6832, 679 DOI 10.17487/RFC6832, January 2013, 680 . 682 [RFC6833] Fuller, V. and D. Farinacci, "Locator/ID Separation 683 Protocol (LISP) Map-Server Interface", RFC 6833, 684 DOI 10.17487/RFC6833, January 2013, 685 . 687 [RFC8060] Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical 688 Address Format (LCAF)", RFC 8060, DOI 10.17487/RFC8060, 689 February 2017, . 691 13.2. Informative References 693 [I-D.ermagan-lisp-nat-traversal] 694 Ermagan, V., Farinacci, D., Lewis, D., Maino, F., Comeras, 695 M. P., Skriver, J., White, C., Lopez, A., and A. Cabellos, 696 "NAT traversal for LISP", draft-ermagan-lisp-nat- 697 traversal-19 (work in progress), May 2021. 699 Appendix A. Acknowledgments 701 The authors would like to thank the following people for their ideas 702 and comments. They are Albert Cabellos, Khalid Raza, and Vina 703 Ermagan, Gregg Schudel, Yan Filyurin, Robert Raszuk, and Truman 704 Boyes. 706 Appendix B. Document Change Log 708 B.1. Changes to draft-ietf-lisp-te-09 710 o Posted September 2021. 712 o Update document timer and references. 714 B.2. Changes to draft-ietf-lisp-te-08 716 o Posted March 2021. 718 o Update document timer and references. 720 B.3. Changes to draft-ietf-lisp-te-07 722 o Posted October 2020. 724 o Update document timer and references. 726 B.4. Changes to draft-ietf-lisp-te-06 728 o Posted April 2020. 730 o Update document timer and references. 732 B.5. Changes to draft-ietf-lisp-te-05 734 o Posted October 2019. 736 o Update document timer and references. 738 B.6. Changes to draft-ietf-lisp-te-04 740 o Posted April 2019. 742 o Update document timer and references. 744 B.7. Changes to draft-ietf-lisp-te-03 746 o Posted October 2018. 748 o Update document timer and references. 750 B.8. Changes to draft-ietf-lisp-te-02 752 o Posted April 2018. 754 o Update document timer and references. 756 B.9. Changes to draft-ietf-lisp-te-01 758 o Posted October 2017. 760 o Added section on ELP-probing that tells an ITR/RTR/PITR the 761 feasibility and reachability of an Explicit Lcoator Path. 763 B.10. Changes to draft-ietf-lisp-te-00 765 o Posted April 2017. 767 o Changed draft-farinacci-lisp-te-12 to working group document. 769 B.11. Changes to draft-farinacci-lisp-te-02 through -12 771 o Many postings from January 2013 through February 2017. 773 o Update references and document timer. 775 B.12. Changes to draft-farinacci-lisp-te-01.txt 777 o Posted July 2012. 779 o Add the Lookup bit to allow an ELP to be a list of encapsulation 780 and/or mapping database lookup addresses. 782 o Indicate that ELPs can be used for service chaining. 784 o Add text to indicate that Map-Notify messages can be sent to new 785 RTRs in a ELP so their map-caches can be pre-populated to avoid 786 mapping database lookup packet loss. 788 o Fixes to editorial comments from Gregg. 790 B.13. Changes to draft-farinacci-lisp-te-00.txt 792 o Initial draft posted March 2012. 794 Authors' Addresses 796 Dino Farinacci 797 lispers.net 798 San Jose, California 799 USA 801 Phone: 408-718-2001 802 Email: farinacci@gmail.com 804 Michael Kowal 805 cisco Systems 806 111 Wood Avenue South 807 ISELIN, NJ 808 USA 810 Email: mikowal@cisco.com 812 Parantap Lahiri 813 USA 815 Email: parantap.lahiri@gmail.com