idnits 2.17.1 draft-ietf-lisp-te-05.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 (October 7, 2019) is 1663 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RFC 6830 (Obsoleted by RFC 9300, RFC 9301) ** Obsolete normative reference: RFC 6833 (Obsoleted by RFC 9301) == Outdated reference: A later version (-19) exists of draft-ermagan-lisp-nat-traversal-16 Summary: 3 errors (**), 0 flaws (~~), 4 warnings (==), 1 comment (--).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: April 9, 2020 cisco Systems 6 P. Lahiri 7 October 7, 2019 9 LISP Traffic Engineering Use-Cases 10 draft-ietf-lisp-te-05 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 April 9, 2020. 38 Copyright Notice 40 Copyright (c) 2019 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-05 . . . . . . . . . . . . 16 77 B.2. Changes to draft-ietf-lisp-te-04 . . . . . . . . . . . . 16 78 B.3. Changes to draft-ietf-lisp-te-03 . . . . . . . . . . . . 16 79 B.4. Changes to draft-ietf-lisp-te-02 . . . . . . . . . . . . 16 80 B.5. Changes to draft-ietf-lisp-te-01 . . . . . . . . . . . . 16 81 B.6. Changes to draft-ietf-lisp-te-00 . . . . . . . . . . . . 16 82 B.7. Changes to draft-farinacci-lisp-te-02 through -12 . . . . 16 83 B.8. Changes to draft-farinacci-lisp-te-01.txt . . . . . . . . 17 84 B.9. Changes to draft-farinacci-lisp-te-00.txt . . . . . . . . 17 85 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 87 1. Requirements Language 89 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 90 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 91 document are to be interpreted as described in RFC 2119 [RFC2119]. 93 2. Introduction 95 This document describes the Locator/Identifier Separation Protocol 96 (LISP), which provides a set of functions for routers to exchange 97 information used to map from non globally routeable Endpoint 98 Identifiers (EIDs) to routeable Routing Locators (RLOCs). It also 99 defines a mechanism for these LISP routers to encapsulate IP packets 100 addressed with EIDs for transmission across the Internet that uses 101 RLOCs for routing and forwarding. 103 When LISP routers encapsulate packets to other LISP routers, the path 104 stretch is typically 1, meaning the packet travels on a direct path 105 from the encapsulating ITR to the decapsulating ETR at the 106 destination site. The direct path is determined by the underlying 107 routing protocol and metrics it uses to find the shortest path. 109 This specification will examine how reencapsulating tunnels [RFC6830] 110 can be used so a packet can take an adminstratively specified path, a 111 congestion avoidance path, a failure recovery path, or multiple load- 112 shared paths, as it travels from ITR to ETR. By introducing an 113 Explicit Locator Path (ELP) locator encoding [RFC8060], an ITR can 114 encapsulate a packet to a Reencapsulating Tunnel Router (RTR) which 115 decapsulates the packet, then encapsulates it to the next locator in 116 the ELP. 118 3. Definition of Terms 120 Endpoint ID (EID): An EID is a 32-bit (for IPv4) or 128-bit (for 121 IPv6) value used in the source and destination address fields of 122 the first (most inner) LISP header of a packet. The host obtains 123 a destination EID the same way it obtains an destination address 124 today, for example through a Domain Name System (DNS) [RFC1034] 125 lookup or Session Invitation Protocol (SIP) [RFC3261] exchange. 126 The source EID is obtained via existing mechanisms used to set a 127 host's "local" IP address. An EID used on the public Internet 128 must have the same properties as any other IP address used in that 129 manner; this means, among other things, that it must be globally 130 unique. An EID is allocated to a host from an EID-prefix block 131 associated with the site where the host is located. An EID can be 132 used by a host to refer to other hosts. EIDs MUST NOT be used as 133 LISP RLOCs. Note that EID blocks MAY be assigned in a 134 hierarchical manner, independent of the network topology, to 135 facilitate scaling of the mapping database. In addition, an EID 136 block assigned to a site may have site-local structure 137 (subnetting) for routing within the site; this structure is not 138 visible to the global routing system. In theory, the bit string 139 that represents an EID for one device can represent an RLOC for a 140 different device. As the architecture is realized, if a given bit 141 string is both an RLOC and an EID, it must refer to the same 142 entity in both cases. When used in discussions with other 143 Locator/ID separation proposals, a LISP EID will be called a 144 "LEID". Throughout this document, any references to "EID" refers 145 to an LEID. 147 Routing Locator (RLOC): A RLOC is an IPv4 [RFC0791] or IPv6 148 [RFC2460] address of an egress tunnel router (ETR). A RLOC is the 149 output of an EID-to-RLOC mapping lookup. An EID maps to one or 150 more RLOCs. Typically, RLOCs are numbered from topologically- 151 aggregatable blocks that are assigned to a site at each point to 152 which it attaches to the global Internet; where the topology is 153 defined by the connectivity of provider networks, RLOCs can be 154 thought of as PA addresses. Multiple RLOCs can be assigned to the 155 same ETR device or to multiple ETR devices at a site. 157 Reencapsulating Tunnel Router (RTR): An RTR is a router that acts 158 as an ETR (or PETR) by decapsulating packets where the destination 159 address in the "outer" IP header is one of its own RLOCs. Then 160 acts as an ITR (or PITR) by making a decision where to encapsulate 161 the packet based on the next locator in the ELP towards the final 162 destination ETR. 164 Explicit Locator Path (ELP): The ELP is an explicit list of RLOCs 165 for each RTR a packet must travel to along its path toward a final 166 destination ETR (or PETR). The list is a strict ordering where 167 each RLOC in the list is visited. However, the path from one RTR 168 to another is determined by the underlying routing protocol and 169 how the infrastructure assigns metrics and policies for the path. 171 Recursive Tunneling: Recursive tunneling occurs when a packet has 172 more than one LISP IP header. Additional layers of tunneling MAY 173 be employed to implement traffic engineering or other re-routing 174 as needed. When this is done, an additional "outer" LISP header 175 is added and the original RLOCs are preserved in the "inner" 176 header. Any references to tunnels in this specification refers to 177 dynamic encapsulating tunnels and they are never statically 178 configured. 180 Reencapsulating Tunnels: Reencapsulating tunneling occurs when an 181 ETR removes a LISP header, then acts as an ITR to prepend another 182 LISP header. Doing this allows a packet to be re-routed by the 183 reencapsulating router without adding the overhead of additional 184 tunnel headers. Any references to tunnels in this specification 185 refers to dynamic encapsulating tunnels and they are never 186 statically configured. When using multiple mapping database 187 systems, care must be taken to not create reencapsulation loops 188 through misconfiguration. 190 4. Overview 192 Typically, a packet's path from source EID to destination EID travels 193 through the locator core via the encapsulating ITR directly to the 194 decapsulating ETR as the following diagram illustrates: 196 Legend: 198 seid: Packet is originated by source EID 'seid'. 200 deid: Packet is consumed by destination EID 'deid'. 202 A,B,C,D : Core routers in different ASes. 204 ---> : The physical topological path between two routers. 206 ===> : A multi-hop LISP dynamic tunnel between LISP routers. 208 Core Network 209 Source site (----------------------------) Destination Site 210 +--------+ ( ) +---------+ 211 | \ ( ) / | 212 | seid ITR ---(---> A --> B --> C --> D ---)---> ETR deid | 213 | / || ( ) ^^ \ | 214 +--------+ || ( ) || +---------+ 215 || (----------------------------) || 216 || || 217 =========================================== 218 LISP Tunnel 220 Typical Data Path from ITR to ETR 222 Let's introduce RTRs 'X' and 'Y' so that, for example, if it is 223 desirable to route around the path from B to C, one could provide an 224 ELP of (X,Y,etr): 226 Core Network 227 Source site (----------------------------) Destination Site 228 +--------+ ( ) +---------+ 229 | \ ( ) / | 230 | seid ITR ---(---> A --> B --> C --> D ---)---> ETR deid | 231 | / || ( / ^ ) ^^ \ | 232 | / || ( | \ ) || \ | 233 +-------+ || ( v | ) || +--------+ 234 || ( X ======> Y ) || 235 || ( ^^ || ) || 236 || (--------||---------||-------) || 237 || || || || 238 ================= ================= 239 LISP Tunnel LISP Tunnel 241 ELP tunnel path ITR ==> X, then X ==> Y, and then Y ==> ETR 243 There are various reasons why the path from 'seid' to 'deid' may want 244 to avoid the path from B to C. To list a few: 246 o There may not be sufficient capacity provided by the networks that 247 connect B and C together. 249 o There may be a policy reason to avoid the ASes that make up the 250 path between B and C. 252 o There may be a failure on the path between B and C which makes the 253 path unreliable. 255 o There may be monitoring or traffic inspection resources close to 256 RTRs X and Y that do network accounting or measurement. 258 o There may be a chain of services performed at RTRs X and Y 259 regardless if the path from ITR to ETR is through B and C. 261 5. Explicit Locator Paths 263 The notation for a general formatted ELP is (x, y, etr) which 264 represents the list of RTRs a packet SHOULD travel through to reach 265 the final tunnel hop to the ETR. 267 The procedure for using an ELP at each tunnel hop is as follows: 269 1. The ITR will retrieve the ELP from the mapping database. 271 2. The ITR will encapsulate the packet to RLOC 'x'. 273 3. The RTR with RLOC 'x' will decapsulate the packet. It will use 274 the decapsulated packet's destination address as a lookup into 275 the mapping database to retrieve the ELP. 277 4. RTR 'x' will encapsulate the packet to RTR with RLOC 'y'. 279 5. The RTR with RLOC 'y' will decapsulate the packet. It will use 280 the decapsulated packet's destination address as a lookup into 281 the mapping database to retrieve the ELP. 283 6. RTR 'y' will encapsulate the packet on the final tunnel hop to 284 ETR with RLOC 'etr'. 286 7. The ETR will decapsulate the packet and deliver the packet to the 287 EID inside of its site. 289 The specific format for the ELP can be found in [RFC8060]. It is 290 defined that an ELP will appear as a single encoded locator in a 291 locator-set. Say for instance, we have a mapping entry for EID- 292 prefix 10.0.0.0/8 that is reachable via 4 locators. Two locators are 293 being used as active/active and the other two are used as active/ 294 active if the first two go unreachable (as noted by the priority 295 assignments below). This is what the mapping entry would look like: 297 EID-prefix: 10.0.0.0/8 298 Locator-set: ETR-A: priority 1, weight 50 299 ETR-B: priority 1, weight 50 300 ETR-C: priority 2, weight 50 301 ETR-D: priority 2, weight 50 303 If an ELP is going to be used to have a policy path to ETR-A and 304 possibly another policy path to ETR-B, the locator-set would be 305 encoded as follows: 307 EID-prefix: 10.0.0.0/8 308 Locator-set: (x, y, ETR-A): priority 1, weight 50 309 (q, r, ETR-B): priority 1, weight 50 310 ETR-C: priority 2, weight 50 311 ETR-D: priority 2, weight 50 313 The mapping entry with ELP locators is registered to the mapping 314 database system just like any other mapping entry would. The 315 registration is typically performed by the ETR(s) that are assigned 316 and own the EID-prefix. That is, the destination site makes the 317 choice of the RTRs in the ELP. However, it may be common practice 318 for a provisioning system to program the mapping database with ELPs. 320 Another case where a locator-set can be used for flow-based load- 321 sharing across multiple paths to the same destination site: 323 EID-prefix: 10.0.0.0/8 324 Locator-set: (x, y, ETR-A): priority 1, weight 75 325 (q, r, ETR-A): priority 1, weight 25 327 Using this mapping entry, an ITR would load split 75% of the EID 328 flows on the (x, y, ETR-A) ELP path and 25% of the EID flows on the 329 (q, r, ETR-A) ELP path. If any of the ELPs go down, then the other 330 can take 100% of the load. 332 5.1. ELP Re-optimization 334 ELP re-optimization is a process of changing the RLOCs of an ELP due 335 to underlying network change conditions. Just like when there is any 336 locator change for a locator-set, the procedures from the main LISP 337 specification [RFC6830] are followed. 339 When a RLOC from an ELP is changed, Map-Notify messages [RFC6833] can 340 be used to inform the existing RTRs in the ELP so they can do a 341 lookup to obtain the latest version of the ELP. Map-Notify messages 342 can also be sent to new RTRs in an ELP so they can get the ELP in 343 advance to receiving packets that will use the ELP. This can 344 minimize packet loss during mapping database lookups in RTRs. 346 5.2. Using Recursion 348 In the previous examples, we showed how an ITR encapsulates using an 349 ELP of (x, y, etr). When a packet is encapsulated by the ITR to RTR 350 'x', the RTR may want a policy path to RTR 'y' and run another level 351 of reencapsulating tunnels for packets destined to RTR 'y'. In this 352 case, RTR 'x' does not encapsulate packets to 'y' but rather performs 353 a mapping database lookup on the address 'y', requests the ELP for 354 RTR 'y', and encapsulates packets to the first-hop of the returned 355 ELP. This can be done when using a public or private mapping 356 database. The decision to use address 'y' as an encapsulation 357 address versus a lookup address is based on the L-bit setting for 'y' 358 in the ELP entry. The decision and policy of ELP encodings are local 359 to the entity which registers the EID-prefix associated with the ELP. 361 Another example of recursion is when the ITR uses the ELP (x, y, etr) 362 to first prepend a header with a destination RLOC of the ETR and then 363 prepend another header and encapsulate the packet to RTR 'x'. When 364 RTR 'x' decapsulates the packet, rather than doing a mapping database 365 lookup on RTR 'y' the last example showed, instead RTR 'x' does a 366 mapping database lookup on ETR 'etr'. In this scenario, RTR 'x' can 367 choose an ELP from the locator-set by considering the source RLOC 368 address of the ITR versus considering the source EID. 370 This additional level of recursion also brings advantages for the 371 provider of RTR 'x' to store less state. Since RTR 'x' does not need 372 to look at the inner most header, it does not need to store EID 373 state. It only stores an entry for RTR 'y' which many EID flows 374 could share for scaling benefits. The locator-set for entry 'y' 375 could either be a list of typical locators, a list of ELPs, or 376 combination of both. Another advantage is that packet load-splitting 377 can be accomplished by examining the source of a packet. If the 378 source is an ITR versus the source being the last-hop of an ELP the 379 last-hop selected, different forwarding paths can be used. 381 5.3. ELP Selection based on Class of Service 383 Paths to an ETR may want to be selected based on different classes of 384 service. Packets from a set of sources that have premium service can 385 use ELP paths that are less congested where normal sources use ELP 386 paths that compete for less resources or use longer paths for best 387 effort service. 389 Using source/destination lookups into the mapping database can yield 390 different ELPs. So for example, a premium service flow with 391 (source=1.1.1.1, dest=10.1.1.1) can be described by using the 392 following mapping entry: 394 EID-prefix: (1.0.0.0/8, 10.0.0.0/8) 395 Locator-set: (x, y, ETR-A): priority 1, weight 50 396 (q, r, ETR-A): priority 1, weight 50 398 And all other best-effort sources would use different mapping entry 399 described by: 401 EID-prefix: (0.0.0.0/0, 10.0.0.0/8) 402 Locator-set: (x, x', y, y', ETR-A): priority 1, weight 50 403 (q, q', r, r', ETR-A): priority 1, weight 50 405 If the source/destination lookup is coupled with recursive lookups, 406 then an ITR can encapsulate to the ETR, prepending a header that 407 selects source address ITR-1 based on the premium class of service 408 source, or selects source address ITR-2 for best-effort sources with 409 normal class of service. The ITR then does another lookup in the 410 mapping database on the prepended header using lookup key 411 (source=ITR-1, dest=10.1.1.1) that returns the following mapping 412 entry: 414 EID-prefix: (ITR-1, 10.0.0.0/8) 415 Locator-set: (x, y, ETR-A): priority 1, weight 50 416 (q, r, ETR-A): priority 1, weight 50 418 And all other sources would use different mapping entry with a lookup 419 key of (source=ITR-2, dest=10.1.1.1): 421 EID-prefix: (ITR-2, 10.0.0.0/8) 422 Locator-set: (x, x', y, y', ETR-A): priority 1, weight 50 423 (q, q', r, r', ETR-A): priority 1, weight 50 425 This will scale the mapping system better by having fewer source/ 426 destination combinations. Refer to the Source/Dest LCAF type 427 described in [RFC8060] for encoding EIDs in Map-Request and Map- 428 Register messages. 430 5.4. Packet Loop Avoidance 432 An ELP that is first used by an ITR must be inspected for encoding 433 loops. If any RLOC appears twice in the ELP, it MUST not be used. 435 Since it is expected that multiple mapping systems will be used, 436 there can be a loop across ELPs when registered in different mapping 437 systems. The TTL copying procedures for reencapsulating tunnels and 438 recursive tunnels in [RFC6830] MUST be followed. 440 6. Service Chaining 442 An ELP can be used to deploy services at each reencapsulation point 443 in the network. One example is to implement a scrubber service when 444 a destination EID is being DoS attacked. That is, when a DoS attack 445 is recognized when the encapsulation path is between ITR and ETR, an 446 ELP can be registered for a destination EID to the mapping database 447 system. The ELP can include an RTR so the ITR can encapsulate 448 packets to the RTR which will decapsulate and deliver packets to a 449 scrubber service device. The scrubber could decide if the offending 450 packets are dropped or allowed to be sent to the destination EID. In 451 which case, the scurbber delivers packets back to the RTR which 452 encapsulates to the ETR. 454 7. RLOC Probing by RTRs 456 Since an RTR knows the next tunnel hop to encapsulate to, it can 457 monitor the reachability of the next-hop RTR RLOC by doing RLOC- 458 probing according to the procedures in [RFC6830]. When the RLOC is 459 determined unreachable by the RLOC-probing mechanisms, the RTR can 460 use another locator in the locator-set. That could be the final ETR, 461 a RLOC of another RTR, or an ELP where it must search for itself and 462 use the next RLOC in the ELP list to encapsulate to. 464 RLOC-probing can also be used to measure delay on the path between 465 RTRs and when it is desirable switch to another lower delay ELP. 467 8. ELP Probing 469 Since an ELP-node knows the reachabiliy of the next ELP-node in a ELP 470 by using RLOC probing, the sum of reachability can determine the 471 reachability of the entire path. A head-end ITR/RTR/PITR can 472 determine the quality of a path and decide to select one path from 473 another based on the telemetry data gathered by RLOC-probing for each 474 encapsulation hop. 476 ELP-probing mechanism details can be found in [I-D.filyurin-lisp-elp- 477 probing]. 479 9. Interworking Considerations 481 [RFC6832] defines procedures for how non-LISP sites talk to LISP 482 sites. The network elements defined in the Interworking 483 specification, the proxy ITR (PITR) and proxy ETR (PETR) (as well as 484 their multicast counterparts defined in [RFC6831]) can participate in 485 LISP-TE. That is, a PITR and a PETR can appear in an ELP list and 486 act as an RTR. 488 Note when an RLOC appears in an ELP, it can be of any address-family. 489 There can be a mix of IPv4 and IPv6 locators present in the same ELP. 490 This can provide benefits where islands of one address-family or the 491 other are supported and connectivity across them is necessary. For 492 instance, an ELP can look like: 494 (x4, a46, b64, y4, etr) 496 Where an IPv4 ITR will encapsulate using an IPv4 RLOC 'x4' and 'x4' 497 could reach an IPv4 RLOC 'a46', but RTR 'a46' encapsulates to an IPv6 498 RLOC 'b64' when the network between them is IPv6-only. Then RTR 499 'b64' encapsulates to IPv4 RLOC 'y4' if the network between them is 500 dual-stack. 502 Note that RTRs can be used for NAT-traversal scenarios 503 [I-D.ermagan-lisp-nat-traversal] as well to reduce the state in both 504 an xTR that resides behind a NAT and the state the NAT needs to 505 maintain. In this case, the xTR only needs a default map-cache entry 506 pointing to the RTR for outbound traffic and all remote ITRs can 507 reach EIDs through the xTR behind a NAT via a single RTR (or a small 508 set RTRs for redundancy). 510 RTRs have some scaling features to reduce the number of locator-set 511 changes, the amount of state, and control packet overhead: 513 o When ITRs and PITRs are using a small set of RTRs for 514 encapsulating to "orders of magnitude" more EID-prefixes, the 515 probability of locator-set changes are limited to the RTR RLOC 516 changes versus the RLOC changes for the ETRs associated with the 517 EID-prefixes if the ITRs and PITRs were directly encapsulating to 518 the ETRs. This comes at an expense in packet stretch, but 519 depending on RTR placement, this expense can be mitigated. 521 o When RTRs are on-path between many pairwise EID flows, ITRs and 522 PITRs can store a small number of coarse EID-prefixes. 524 o RTRs can be used to help scale RLOC-probing. Instead of ITRs 525 RLOC-probing all ETRs for each destination site it has cached, the 526 ITRs can probe a smaller set of RTRs which in turn, probe the 527 destination sites. 529 10. Multicast Considerations 531 ELPs have application in multicast environments. Just like RTRs can 532 be used to provide connectivity across different address family 533 islands, RTRs can help concatenate a multicast region of the network 534 to one that does not support native multicast. 536 Note there are various combinations of connectivity that can be 537 accomplished with the deployment of RTRs and ELPs: 539 o Providing multicast forwarding between IPv4-only-unicast regions 540 and IPv4-multicast regions. 542 o Providing multicast forwarding between IPv6-only-unicast regions 543 and IPv6-multicast regions. 545 o Providing multicast forwarding between IPv4-only-unicast regions 546 and IPv6-multicast regions. 548 o Providing multicast forwarding between IPv6-only-unicast regions 549 and IPv4-multicast regions. 551 o Providing multicast forwarding between IPv4-multicast regions and 552 IPv6-multicast regions. 554 An ITR or PITR can do a (S-EID,G) lookup into the mapping database. 555 What can be returned is a typical locator-set that could be made up 556 of the various RLOC addresses: 558 Multicast EID key: (seid, G) 559 Locator-set: ETR-A: priority 1, weight 25 560 ETR-B: priority 1, weight 25 561 g1: priority 1, weight 25 562 g2: priority 1, weight 25 564 An entry for host 'seid' sending to application group 'G' 566 The locator-set above can be used as a replication list. That is 567 some RLOCs listed can be unicast RLOCs and some can be delivery group 568 RLOCs. A unicast RLOC in this case is used to encapsulate a 569 multicast packet originated by a multicast source EID into a unicast 570 packet for unicast delivery on the underlying network. ETR-A could 571 be a IPv4 unicast RLOC address and ETR-B could be a IPv6 unicast RLOC 572 address. 574 A delivery group address is used when a multicast packet originated 575 by a multicast source EID is encapsulated in a multicast packet for 576 multicast delivery on the underlying network. Group address 'g1' 577 could be a IPv4 delivery group RLOC and group address 'g2' could be 578 an IPv6 delivery group RLOC. 580 Flexibility for these various types of connectivity combinations can 581 be achieved and provided by the mapping database system. And the RTR 582 placement allows the connectivity to occur where the differences in 583 network functionality are located. 585 Extending this concept by allowing ELPs in locator-sets, one could 586 have this locator-set registered in the mapping database for (seid, 587 G). For example: 589 Multicast EID key: (seid, G) 590 Locator-set: (x, y, ETR-A): priority 1, weight 50 591 (a, g, b, ETR-B): priority 1, weight 50 593 Using ELPs for multicast flows 595 In the above situation, an ITR would encapsulate a multicast packet 596 originated by a multicast source EID to the RTR with unicast RLOC 597 'x'. Then RTR 'x' would decapsulate and unicast encapsulate to RTR 598 'y' ('x' or 'y' could be either IPv4 or IPv6 unicast RLOCs), which 599 would decapsulate and unicast encapsulate to the final RLOC 'ETR-A'. 600 The ETR 'ETR-A' would decapsulate and deliver the multicast packet 601 natively to all the receivers joined to application group 'G' inside 602 the LISP site. 604 Let's look at the ITR using the ELP (a, g, b, ETR-B). Here the 605 encapsulation path would be the ITR unicast encapsulates to unicast 606 RLOC 'a'. RTR 'a' multicast encapsulates to delivery group 'g'. The 607 packet gets to all ETRs that have joined delivery group 'g' so they 608 can deliver the multicast packet to joined receivers of application 609 group 'G' in their sites. RTR 'b' is also joined to delivery group 610 'g'. Since it is in the ELP, it will be the only RTR that unicast 611 encapsulates the multicast packet to ETR 'ETR-B'. Lastly, 'ETR-B' 612 decapsulates and delivers the multicast packet to joined receivers to 613 application group 'G' in its LISP site. 615 As one can see there are all sorts of opportunities to provide 616 multicast connectivity across a network with non-congruent support 617 for multicast and different address-families. One can also see how 618 using the mapping database can allow flexible forms of delivery 619 policy, rerouting, and congestion control management in multicast 620 environments. 622 11. Security Considerations 624 When an RTR receives a LISP encapsulated packet, it can look at the 625 outer source address to verify that RLOC is the one listed as the 626 previous hop in the ELP list. If the outer source RLOC address 627 appears before the RLOC which matches the outer destination RLOC 628 address, the decapsulating RTR (or ETR if last hop), MAY choose to 629 drop the packet. 631 12. IANA Considerations 633 At this time there are no requests for IANA. 635 13. References 637 13.1. Normative References 639 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 640 DOI 10.17487/RFC0791, September 1981, 641 . 643 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 644 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 645 . 647 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 648 Requirement Levels", BCP 14, RFC 2119, 649 DOI 10.17487/RFC2119, March 1997, 650 . 652 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 653 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, 654 December 1998, . 656 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 657 A., Peterson, J., Sparks, R., Handley, M., and E. 658 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 659 DOI 10.17487/RFC3261, June 2002, 660 . 662 [RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The 663 Locator/ID Separation Protocol (LISP)", RFC 6830, 664 DOI 10.17487/RFC6830, January 2013, 665 . 667 [RFC6831] Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas, "The 668 Locator/ID Separation Protocol (LISP) for Multicast 669 Environments", RFC 6831, DOI 10.17487/RFC6831, January 670 2013, . 672 [RFC6832] Lewis, D., Meyer, D., Farinacci, D., and V. Fuller, 673 "Interworking between Locator/ID Separation Protocol 674 (LISP) and Non-LISP Sites", RFC 6832, 675 DOI 10.17487/RFC6832, January 2013, 676 . 678 [RFC6833] Fuller, V. and D. Farinacci, "Locator/ID Separation 679 Protocol (LISP) Map-Server Interface", RFC 6833, 680 DOI 10.17487/RFC6833, January 2013, 681 . 683 [RFC8060] Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical 684 Address Format (LCAF)", RFC 8060, DOI 10.17487/RFC8060, 685 February 2017, . 687 13.2. Informative References 689 [I-D.ermagan-lisp-nat-traversal] 690 Ermagan, V., Farinacci, D., Lewis, D., Maino, F., 691 Portoles-Comeras, M., Skriver, J., and C. White, "NAT 692 traversal for LISP", draft-ermagan-lisp-nat-traversal-16 693 (work in progress), June 2019. 695 Appendix A. Acknowledgments 697 The authors would like to thank the following people for their ideas 698 and comments. They are Albert Cabellos, Khalid Raza, and Vina 699 Ermagan, Gregg Schudel, Yan Filyurin, Robert Raszuk, and Truman 700 Boyes. 702 Appendix B. Document Change Log 704 B.1. Changes to draft-ietf-lisp-te-05 706 o Posted October 2019. 708 o Update document timer and references. 710 B.2. Changes to draft-ietf-lisp-te-04 712 o Posted April 2019. 714 o Update document timer and references. 716 B.3. Changes to draft-ietf-lisp-te-03 718 o Posted October 2018. 720 o Update document timer and references. 722 B.4. Changes to draft-ietf-lisp-te-02 724 o Posted April 2018. 726 o Update document timer and references. 728 B.5. Changes to draft-ietf-lisp-te-01 730 o Posted October 2017. 732 o Added section on ELP-probing that tells an ITR/RTR/PITR the 733 feasibility and reachability of an Explicit Lcoator Path. 735 B.6. Changes to draft-ietf-lisp-te-00 737 o Posted April 2017. 739 o Changed draft-farinacci-lisp-te-12 to working group document. 741 B.7. Changes to draft-farinacci-lisp-te-02 through -12 743 o Many postings from January 2013 through February 2017. 745 o Update references and document timer. 747 B.8. Changes to draft-farinacci-lisp-te-01.txt 749 o Posted July 2012. 751 o Add the Lookup bit to allow an ELP to be a list of encapsulation 752 and/or mapping database lookup addresses. 754 o Indicate that ELPs can be used for service chaining. 756 o Add text to indicate that Map-Notify messages can be sent to new 757 RTRs in a ELP so their map-caches can be pre-populated to avoid 758 mapping database lookup packet loss. 760 o Fixes to editorial comments from Gregg. 762 B.9. Changes to draft-farinacci-lisp-te-00.txt 764 o Initial draft posted March 2012. 766 Authors' Addresses 768 Dino Farinacci 769 lispers.net 770 San Jose, California 771 USA 773 Phone: 408-718-2001 774 Email: farinacci@gmail.com 776 Michael Kowal 777 cisco Systems 778 111 Wood Avenue South 779 ISELIN, NJ 780 USA 782 Email: mikowal@cisco.com 784 Parantap Lahiri 785 USA 787 Email: parantap.lahiri@gmail.com