idnits 2.17.1 draft-ietf-lisp-te-04.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 (April 11, 2019) is 1836 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RFC 6830 (Obsoleted by RFC 9300, RFC 9301) ** Obsolete normative reference: RFC 6833 (Obsoleted by RFC 9301) == Outdated reference: A later version (-19) exists of draft-ermagan-lisp-nat-traversal-15 Summary: 3 errors (**), 0 flaws (~~), 4 warnings (==), 1 comment (--).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: October 13, 2019 cisco Systems 6 P. Lahiri 7 April 11, 2019 9 LISP Traffic Engineering Use-Cases 10 draft-ietf-lisp-te-04 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 October 13, 2019. 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 . . . . . . . . . . . . . . . . . . . . . . . . 2 57 3. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 3 58 4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4 59 5. Explicit Locator Paths . . . . . . . . . . . . . . . . . . . 6 60 5.1. ELP Re-optimization . . . . . . . . . . . . . . . . . . . 7 61 5.2. Using Recursion . . . . . . . . . . . . . . . . . . . . . 8 62 5.3. ELP Selection based on Class of Service . . . . . . . . . 8 63 5.4. Packet Loop Avoidance . . . . . . . . . . . . . . . . . . 10 64 6. Service Chaining . . . . . . . . . . . . . . . . . . . . . . 10 65 7. RLOC Probing by RTRs . . . . . . . . . . . . . . . . . . . . 10 66 8. ELP Probing . . . . . . . . . . . . . . . . . . . . . . . . . 10 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 . . . . . . . . . . . . . . . . 15 76 B.1. Changes to draft-ietf-lisp-te-04 . . . . . . . . . . . . 15 77 B.2. Changes to draft-ietf-lisp-te-03 . . . . . . . . . . . . 15 78 B.3. Changes to draft-ietf-lisp-te-02 . . . . . . . . . . . . 16 79 B.4. Changes to draft-ietf-lisp-te-01 . . . . . . . . . . . . 16 80 B.5. Changes to draft-ietf-lisp-te-00 . . . . . . . . . . . . 16 81 B.6. Changes to draft-farinacci-lisp-te-02 through -12 . . . . 16 82 B.7. Changes to draft-farinacci-lisp-te-01.txt . . . . . . . . 16 83 B.8. Changes to draft-farinacci-lisp-te-00.txt . . . . . . . . 16 84 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 86 1. Requirements Language 88 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 89 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 90 document are to be interpreted as described in RFC 2119 [RFC2119]. 92 2. Introduction 94 This document describes the Locator/Identifier Separation Protocol 95 (LISP), which provides a set of functions for routers to exchange 96 information used to map from non globally routeable Endpoint 97 Identifiers (EIDs) to routeable Routing Locators (RLOCs). It also 98 defines a mechanism for these LISP routers to encapsulate IP packets 99 addressed with EIDs for transmission across the Internet that uses 100 RLOCs for routing and forwarding. 102 When LISP routers encapsulate packets to other LISP routers, the path 103 stretch is typically 1, meaning the packet travels on a direct path 104 from the encapsulating ITR to the decapsulating ETR at the 105 destination site. The direct path is determined by the underlying 106 routing protocol and metrics it uses to find the shortest path. 108 This specification will examine how reencapsulating tunnels [RFC6830] 109 can be used so a packet can take an adminstratively specified path, a 110 congestion avoidance path, a failure recovery path, or multiple load- 111 shared paths, as it travels from ITR to ETR. By introducing an 112 Explicit Locator Path (ELP) locator encoding [RFC8060], an ITR can 113 encapsulate a packet to a Reencapsulating Tunnel Router (RTR) which 114 decapsulates the packet, then encapsulates it to the next locator in 115 the ELP. 117 3. Definition of Terms 119 Endpoint ID (EID): An EID is a 32-bit (for IPv4) or 128-bit (for 120 IPv6) value used in the source and destination address fields of 121 the first (most inner) LISP header of a packet. The host obtains 122 a destination EID the same way it obtains an destination address 123 today, for example through a Domain Name System (DNS) [RFC1034] 124 lookup or Session Invitation Protocol (SIP) [RFC3261] exchange. 125 The source EID is obtained via existing mechanisms used to set a 126 host's "local" IP address. An EID used on the public Internet 127 must have the same properties as any other IP address used in that 128 manner; this means, among other things, that it must be globally 129 unique. An EID is allocated to a host from an EID-prefix block 130 associated with the site where the host is located. An EID can be 131 used by a host to refer to other hosts. EIDs MUST NOT be used as 132 LISP RLOCs. Note that EID blocks MAY be assigned in a 133 hierarchical manner, independent of the network topology, to 134 facilitate scaling of the mapping database. In addition, an EID 135 block assigned to a site may have site-local structure 136 (subnetting) for routing within the site; this structure is not 137 visible to the global routing system. In theory, the bit string 138 that represents an EID for one device can represent an RLOC for a 139 different device. As the architecture is realized, if a given bit 140 string is both an RLOC and an EID, it must refer to the same 141 entity in both cases. When used in discussions with other 142 Locator/ID separation proposals, a LISP EID will be called a 143 "LEID". Throughout this document, any references to "EID" refers 144 to an LEID. 146 Routing Locator (RLOC): A RLOC is an IPv4 [RFC0791] or IPv6 147 [RFC2460] address of an egress tunnel router (ETR). A RLOC is the 148 output of an EID-to-RLOC mapping lookup. An EID maps to one or 149 more RLOCs. Typically, RLOCs are numbered from topologically- 150 aggregatable blocks that are assigned to a site at each point to 151 which it attaches to the global Internet; where the topology is 152 defined by the connectivity of provider networks, RLOCs can be 153 thought of as PA addresses. Multiple RLOCs can be assigned to the 154 same ETR device or to multiple ETR devices at a site. 156 Reencapsulating Tunnel Router (RTR): An RTR is a router that acts 157 as an ETR (or PETR) by decapsulating packets where the destination 158 address in the "outer" IP header is one of its own RLOCs. Then 159 acts as an ITR (or PITR) by making a decision where to encapsulate 160 the packet based on the next locator in the ELP towards the final 161 destination ETR. 163 Explicit Locator Path (ELP): The ELP is an explicit list of RLOCs 164 for each RTR a packet must travel to along its path toward a final 165 destination ETR (or PETR). The list is a strict ordering where 166 each RLOC in the list is visited. However, the path from one RTR 167 to another is determined by the underlying routing protocol and 168 how the infrastructure assigns metrics and policies for the path. 170 Recursive Tunneling: Recursive tunneling occurs when a packet has 171 more than one LISP IP header. Additional layers of tunneling MAY 172 be employed to implement traffic engineering or other re-routing 173 as needed. When this is done, an additional "outer" LISP header 174 is added and the original RLOCs are preserved in the "inner" 175 header. Any references to tunnels in this specification refers to 176 dynamic encapsulating tunnels and they are never statically 177 configured. 179 Reencapsulating Tunnels: Reencapsulating tunneling occurs when an 180 ETR removes a LISP header, then acts as an ITR to prepend another 181 LISP header. Doing this allows a packet to be re-routed by the 182 reencapsulating router without adding the overhead of additional 183 tunnel headers. Any references to tunnels in this specification 184 refers to dynamic encapsulating tunnels and they are never 185 statically configured. When using multiple mapping database 186 systems, care must be taken to not create reencapsulation loops 187 through misconfiguration. 189 4. Overview 191 Typically, a packet's path from source EID to destination EID travels 192 through the locator core via the encapsulating ITR directly to the 193 decapsulating ETR as the following diagram illustrates: 195 Legend: 197 seid: Packet is originated by source EID 'seid'. 199 deid: Packet is consumed by destination EID 'deid'. 201 A,B,C,D : Core routers in different ASes. 203 ---> : The physical topological path between two routers. 205 ===> : A multi-hop LISP dynamic tunnel between LISP routers. 207 Core Network 208 Source site (----------------------------) Destination Site 209 +--------+ ( ) +---------+ 210 | \ ( ) / | 211 | seid ITR ---(---> A --> B --> C --> D ---)---> ETR deid | 212 | / || ( ) ^^ \ | 213 +--------+ || ( ) || +---------+ 214 || (----------------------------) || 215 || || 216 =========================================== 217 LISP Tunnel 219 Typical Data Path from ITR to ETR 221 Let's introduce RTRs 'X' and 'Y' so that, for example, if it is 222 desirable to route around the path from B to C, one could provide an 223 ELP of (X,Y,etr): 225 Core Network 226 Source site (----------------------------) Destination Site 227 +--------+ ( ) +---------+ 228 | \ ( ) / | 229 | seid ITR ---(---> A --> B --> C --> D ---)---> ETR deid | 230 | / || ( / ^ ) ^^ \ | 231 | / || ( | \ ) || \ | 232 +-------+ || ( v | ) || +--------+ 233 || ( X ======> Y ) || 234 || ( ^^ || ) || 235 || (--------||---------||-------) || 236 || || || || 237 ================= ================= 238 LISP Tunnel LISP Tunnel 240 ELP tunnel path ITR ==> X, then X ==> Y, and then Y ==> ETR 242 There are various reasons why the path from 'seid' to 'deid' may want 243 to avoid the path from B to C. To list a few: 245 o There may not be sufficient capacity provided by the networks that 246 connect B and C together. 248 o There may be a policy reason to avoid the ASes that make up the 249 path between B and C. 251 o There may be a failure on the path between B and C which makes the 252 path unreliable. 254 o There may be monitoring or traffic inspection resources close to 255 RTRs X and Y that do network accounting or measurement. 257 o There may be a chain of services performed at RTRs X and Y 258 regardless if the path from ITR to ETR is through B and C. 260 5. Explicit Locator Paths 262 The notation for a general formatted ELP is (x, y, etr) which 263 represents the list of RTRs a packet SHOULD travel through to reach 264 the final tunnel hop to the ETR. 266 The procedure for using an ELP at each tunnel hop is as follows: 268 1. The ITR will retrieve the ELP from the mapping database. 270 2. The ITR will encapsulate the packet to RLOC 'x'. 272 3. The RTR with RLOC 'x' will decapsulate the packet. It will use 273 the decapsulated packet's destination address as a lookup into 274 the mapping database to retrieve the ELP. 276 4. RTR 'x' will encapsulate the packet to RTR with RLOC 'y'. 278 5. The RTR with RLOC 'y' will decapsulate the packet. It will use 279 the decapsulated packet's destination address as a lookup into 280 the mapping database to retrieve the ELP. 282 6. RTR 'y' will encapsulate the packet on the final tunnel hop to 283 ETR with RLOC 'etr'. 285 7. The ETR will decapsulate the packet and deliver the packet to the 286 EID inside of its site. 288 The specific format for the ELP can be found in [RFC8060]. It is 289 defined that an ELP will appear as a single encoded locator in a 290 locator-set. Say for instance, we have a mapping entry for EID- 291 prefix 10.0.0.0/8 that is reachable via 4 locators. Two locators are 292 being used as active/active and the other two are used as active/ 293 active if the first two go unreachable (as noted by the priority 294 assignments below). This is what the mapping entry would look like: 296 EID-prefix: 10.0.0.0/8 297 Locator-set: ETR-A: priority 1, weight 50 298 ETR-B: priority 1, weight 50 299 ETR-C: priority 2, weight 50 300 ETR-D: priority 2, weight 50 302 If an ELP is going to be used to have a policy path to ETR-A and 303 possibly another policy path to ETR-B, the locator-set would be 304 encoded as follows: 306 EID-prefix: 10.0.0.0/8 307 Locator-set: (x, y, ETR-A): priority 1, weight 50 308 (q, r, ETR-B): priority 1, weight 50 309 ETR-C: priority 2, weight 50 310 ETR-D: priority 2, weight 50 312 The mapping entry with ELP locators is registered to the mapping 313 database system just like any other mapping entry would. The 314 registration is typically performed by the ETR(s) that are assigned 315 and own the EID-prefix. That is, the destination site makes the 316 choice of the RTRs in the ELP. However, it may be common practice 317 for a provisioning system to program the mapping database with ELPs. 319 Another case where a locator-set can be used for flow-based load- 320 sharing across multiple paths to the same destination site: 322 EID-prefix: 10.0.0.0/8 323 Locator-set: (x, y, ETR-A): priority 1, weight 75 324 (q, r, ETR-A): priority 1, weight 25 326 Using this mapping entry, an ITR would load split 75% of the EID 327 flows on the (x, y, ETR-A) ELP path and 25% of the EID flows on the 328 (q, r, ETR-A) ELP path. If any of the ELPs go down, then the other 329 can take 100% of the load. 331 5.1. ELP Re-optimization 333 ELP re-optimization is a process of changing the RLOCs of an ELP due 334 to underlying network change conditions. Just like when there is any 335 locator change for a locator-set, the procedures from the main LISP 336 specification [RFC6830] are followed. 338 When a RLOC from an ELP is changed, Map-Notify messages [RFC6833] can 339 be used to inform the existing RTRs in the ELP so they can do a 340 lookup to obtain the latest version of the ELP. Map-Notify messages 341 can also be sent to new RTRs in an ELP so they can get the ELP in 342 advance to receiving packets that will use the ELP. This can 343 minimize packet loss during mapping database lookups in RTRs. 345 5.2. Using Recursion 347 In the previous examples, we showed how an ITR encapsulates using an 348 ELP of (x, y, etr). When a packet is encapsulated by the ITR to RTR 349 'x', the RTR may want a policy path to RTR 'y' and run another level 350 of reencapsulating tunnels for packets destined to RTR 'y'. In this 351 case, RTR 'x' does not encapsulate packets to 'y' but rather performs 352 a mapping database lookup on the address 'y', requests the ELP for 353 RTR 'y', and encapsulates packets to the first-hop of the returned 354 ELP. This can be done when using a public or private mapping 355 database. The decision to use address 'y' as an encapsulation 356 address versus a lookup address is based on the L-bit setting for 'y' 357 in the ELP entry. The decision and policy of ELP encodings are local 358 to the entity which registers the EID-prefix associated with the ELP. 360 Another example of recursion is when the ITR uses the ELP (x, y, etr) 361 to first prepend a header with a destination RLOC of the ETR and then 362 prepend another header and encapsulate the packet to RTR 'x'. When 363 RTR 'x' decapsulates the packet, rather than doing a mapping database 364 lookup on RTR 'y' the last example showed, instead RTR 'x' does a 365 mapping database lookup on ETR 'etr'. In this scenario, RTR 'x' can 366 choose an ELP from the locator-set by considering the source RLOC 367 address of the ITR versus considering the source EID. 369 This additional level of recursion also brings advantages for the 370 provider of RTR 'x' to store less state. Since RTR 'x' does not need 371 to look at the inner most header, it does not need to store EID 372 state. It only stores an entry for RTR 'y' which many EID flows 373 could share for scaling benefits. The locator-set for entry 'y' 374 could either be a list of typical locators, a list of ELPs, or 375 combination of both. Another advantage is that packet load-splitting 376 can be accomplished by examining the source of a packet. If the 377 source is an ITR versus the source being the last-hop of an ELP the 378 last-hop selected, different forwarding paths can be used. 380 5.3. ELP Selection based on Class of Service 382 Paths to an ETR may want to be selected based on different classes of 383 service. Packets from a set of sources that have premium service can 384 use ELP paths that are less congested where normal sources use ELP 385 paths that compete for less resources or use longer paths for best 386 effort service. 388 Using source/destination lookups into the mapping database can yield 389 different ELPs. So for example, a premium service flow with 390 (source=1.1.1.1, dest=10.1.1.1) can be described by using the 391 following mapping entry: 393 EID-prefix: (1.0.0.0/8, 10.0.0.0/8) 394 Locator-set: (x, y, ETR-A): priority 1, weight 50 395 (q, r, ETR-A): priority 1, weight 50 397 And all other best-effort sources would use different mapping entry 398 described by: 400 EID-prefix: (0.0.0.0/0, 10.0.0.0/8) 401 Locator-set: (x, x', y, y', ETR-A): priority 1, weight 50 402 (q, q', r, r', ETR-A): priority 1, weight 50 404 If the source/destination lookup is coupled with recursive lookups, 405 then an ITR can encapsulate to the ETR, prepending a header that 406 selects source address ITR-1 based on the premium class of service 407 source, or selects source address ITR-2 for best-effort sources with 408 normal class of service. The ITR then does another lookup in the 409 mapping database on the prepended header using lookup key 410 (source=ITR-1, dest=10.1.1.1) that returns the following mapping 411 entry: 413 EID-prefix: (ITR-1, 10.0.0.0/8) 414 Locator-set: (x, y, ETR-A): priority 1, weight 50 415 (q, r, ETR-A): priority 1, weight 50 417 And all other sources would use different mapping entry with a lookup 418 key of (source=ITR-2, dest=10.1.1.1): 420 EID-prefix: (ITR-2, 10.0.0.0/8) 421 Locator-set: (x, x', y, y', ETR-A): priority 1, weight 50 422 (q, q', r, r', ETR-A): priority 1, weight 50 424 This will scale the mapping system better by having fewer source/ 425 destination combinations. Refer to the Source/Dest LCAF type 426 described in [RFC8060] for encoding EIDs in Map-Request and Map- 427 Register messages. 429 5.4. Packet Loop Avoidance 431 An ELP that is first used by an ITR must be inspected for encoding 432 loops. If any RLOC appears twice in the ELP, it MUST not be used. 434 Since it is expected that multiple mapping systems will be used, 435 there can be a loop across ELPs when registered in different mapping 436 systems. The TTL copying procedures for reencapsulating tunnels and 437 recursive tunnels in [RFC6830] MUST be followed. 439 6. Service Chaining 441 An ELP can be used to deploy services at each reencapsulation point 442 in the network. One example is to implement a scrubber service when 443 a destination EID is being DoS attacked. That is, when a DoS attack 444 is recognized when the encapsulation path is between ITR and ETR, an 445 ELP can be registered for a destination EID to the mapping database 446 system. The ELP can include an RTR so the ITR can encapsulate 447 packets to the RTR which will decapsulate and deliver packets to a 448 scrubber service device. The scrubber could decide if the offending 449 packets are dropped or allowed to be sent to the destination EID. In 450 which case, the scurbber delivers packets back to the RTR which 451 encapsulates to the ETR. 453 7. RLOC Probing by RTRs 455 Since an RTR knows the next tunnel hop to encapsulate to, it can 456 monitor the reachability of the next-hop RTR RLOC by doing RLOC- 457 probing according to the procedures in [RFC6830]. When the RLOC is 458 determined unreachable by the RLOC-probing mechanisms, the RTR can 459 use another locator in the locator-set. That could be the final ETR, 460 a RLOC of another RTR, or an ELP where it must search for itself and 461 use the next RLOC in the ELP list to encapsulate to. 463 RLOC-probing can also be used to measure delay on the path between 464 RTRs and when it is desirable switch to another lower delay ELP. 466 8. ELP Probing 468 Since an ELP-node knows the reachabiliy of the next ELP-node in a ELP 469 by using RLOC probing, the sum of reachability can determine the 470 reachability of the entire path. A head-end ITR/RTR/PITR can 471 determine the quality of a path and decide to select one path from 472 another based on the telemetry data gathered by RLOC-probing for each 473 encapsulation hop. 475 ELP-probing mechanism details can be found in [I-D.filyurin-lisp-elp- 476 probing]. 478 9. Interworking Considerations 480 [RFC6832] defines procedures for how non-LISP sites talk to LISP 481 sites. The network elements defined in the Interworking 482 specification, the proxy ITR (PITR) and proxy ETR (PETR) (as well as 483 their multicast counterparts defined in [RFC6831]) can participate in 484 LISP-TE. That is, a PITR and a PETR can appear in an ELP list and 485 act as an RTR. 487 Note when an RLOC appears in an ELP, it can be of any address-family. 488 There can be a mix of IPv4 and IPv6 locators present in the same ELP. 489 This can provide benefits where islands of one address-family or the 490 other are supported and connectivity across them is necessary. For 491 instance, an ELP can look like: 493 (x4, a46, b64, y4, etr) 495 Where an IPv4 ITR will encapsulate using an IPv4 RLOC 'x4' and 'x4' 496 could reach an IPv4 RLOC 'a46', but RTR 'a46' encapsulates to an IPv6 497 RLOC 'b64' when the network between them is IPv6-only. Then RTR 498 'b64' encapsulates to IPv4 RLOC 'y4' if the network between them is 499 dual-stack. 501 Note that RTRs can be used for NAT-traversal scenarios 502 [I-D.ermagan-lisp-nat-traversal] as well to reduce the state in both 503 an xTR that resides behind a NAT and the state the NAT needs to 504 maintain. In this case, the xTR only needs a default map-cache entry 505 pointing to the RTR for outbound traffic and all remote ITRs can 506 reach EIDs through the xTR behind a NAT via a single RTR (or a small 507 set RTRs for redundancy). 509 RTRs have some scaling features to reduce the number of locator-set 510 changes, the amount of state, and control packet overhead: 512 o When ITRs and PITRs are using a small set of RTRs for 513 encapsulating to "orders of magnitude" more EID-prefixes, the 514 probability of locator-set changes are limited to the RTR RLOC 515 changes versus the RLOC changes for the ETRs associated with the 516 EID-prefixes if the ITRs and PITRs were directly encapsulating to 517 the ETRs. This comes at an expense in packet stretch, but 518 depending on RTR placement, this expense can be mitigated. 520 o When RTRs are on-path between many pairwise EID flows, ITRs and 521 PITRs can store a small number of coarse EID-prefixes. 523 o RTRs can be used to help scale RLOC-probing. Instead of ITRs 524 RLOC-probing all ETRs for each destination site it has cached, the 525 ITRs can probe a smaller set of RTRs which in turn, probe the 526 destination sites. 528 10. Multicast Considerations 530 ELPs have application in multicast environments. Just like RTRs can 531 be used to provide connectivity across different address family 532 islands, RTRs can help concatenate a multicast region of the network 533 to one that does not support native multicast. 535 Note there are various combinations of connectivity that can be 536 accomplished with the deployment of RTRs and ELPs: 538 o Providing multicast forwarding between IPv4-only-unicast regions 539 and IPv4-multicast regions. 541 o Providing multicast forwarding between IPv6-only-unicast regions 542 and IPv6-multicast regions. 544 o Providing multicast forwarding between IPv4-only-unicast regions 545 and IPv6-multicast regions. 547 o Providing multicast forwarding between IPv6-only-unicast regions 548 and IPv4-multicast regions. 550 o Providing multicast forwarding between IPv4-multicast regions and 551 IPv6-multicast regions. 553 An ITR or PITR can do a (S-EID,G) lookup into the mapping database. 554 What can be returned is a typical locator-set that could be made up 555 of the various RLOC addresses: 557 Multicast EID key: (seid, G) 558 Locator-set: ETR-A: priority 1, weight 25 559 ETR-B: priority 1, weight 25 560 g1: priority 1, weight 25 561 g2: priority 1, weight 25 563 An entry for host 'seid' sending to application group 'G' 565 The locator-set above can be used as a replication list. That is 566 some RLOCs listed can be unicast RLOCs and some can be delivery group 567 RLOCs. A unicast RLOC in this case is used to encapsulate a 568 multicast packet originated by a multicast source EID into a unicast 569 packet for unicast delivery on the underlying network. ETR-A could 570 be a IPv4 unicast RLOC address and ETR-B could be a IPv6 unicast RLOC 571 address. 573 A delivery group address is used when a multicast packet originated 574 by a multicast source EID is encapsulated in a multicast packet for 575 multicast delivery on the underlying network. Group address 'g1' 576 could be a IPv4 delivery group RLOC and group address 'g2' could be 577 an IPv6 delivery group RLOC. 579 Flexibility for these various types of connectivity combinations can 580 be achieved and provided by the mapping database system. And the RTR 581 placement allows the connectivity to occur where the differences in 582 network functionality are located. 584 Extending this concept by allowing ELPs in locator-sets, one could 585 have this locator-set registered in the mapping database for (seid, 586 G). For example: 588 Multicast EID key: (seid, G) 589 Locator-set: (x, y, ETR-A): priority 1, weight 50 590 (a, g, b, ETR-B): priority 1, weight 50 592 Using ELPs for multicast flows 594 In the above situation, an ITR would encapsulate a multicast packet 595 originated by a multicast source EID to the RTR with unicast RLOC 596 'x'. Then RTR 'x' would decapsulate and unicast encapsulate to RTR 597 'y' ('x' or 'y' could be either IPv4 or IPv6 unicast RLOCs), which 598 would decapsulate and unicast encapsulate to the final RLOC 'ETR-A'. 599 The ETR 'ETR-A' would decapsulate and deliver the multicast packet 600 natively to all the receivers joined to application group 'G' inside 601 the LISP site. 603 Let's look at the ITR using the ELP (a, g, b, ETR-B). Here the 604 encapsulation path would be the ITR unicast encapsulates to unicast 605 RLOC 'a'. RTR 'a' multicast encapsulates to delivery group 'g'. The 606 packet gets to all ETRs that have joined delivery group 'g' so they 607 can deliver the multicast packet to joined receivers of application 608 group 'G' in their sites. RTR 'b' is also joined to delivery group 609 'g'. Since it is in the ELP, it will be the only RTR that unicast 610 encapsulates the multicast packet to ETR 'ETR-B'. Lastly, 'ETR-B' 611 decapsulates and delivers the multicast packet to joined receivers to 612 application group 'G' in its LISP site. 614 As one can see there are all sorts of opportunities to provide 615 multicast connectivity across a network with non-congruent support 616 for multicast and different address-families. One can also see how 617 using the mapping database can allow flexible forms of delivery 618 policy, rerouting, and congestion control management in multicast 619 environments. 621 11. Security Considerations 623 When an RTR receives a LISP encapsulated packet, it can look at the 624 outer source address to verify that RLOC is the one listed as the 625 previous hop in the ELP list. If the outer source RLOC address 626 appears before the RLOC which matches the outer destination RLOC 627 address, the decapsulating RTR (or ETR if last hop), MAY choose to 628 drop the packet. 630 12. IANA Considerations 632 At this time there are no requests for IANA. 634 13. References 636 13.1. Normative References 638 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 639 DOI 10.17487/RFC0791, September 1981, 640 . 642 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 643 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 644 . 646 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 647 Requirement Levels", BCP 14, RFC 2119, 648 DOI 10.17487/RFC2119, March 1997, 649 . 651 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 652 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, 653 December 1998, . 655 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 656 A., Peterson, J., Sparks, R., Handley, M., and E. 657 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 658 DOI 10.17487/RFC3261, June 2002, 659 . 661 [RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The 662 Locator/ID Separation Protocol (LISP)", RFC 6830, 663 DOI 10.17487/RFC6830, January 2013, 664 . 666 [RFC6831] Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas, "The 667 Locator/ID Separation Protocol (LISP) for Multicast 668 Environments", RFC 6831, DOI 10.17487/RFC6831, January 669 2013, . 671 [RFC6832] Lewis, D., Meyer, D., Farinacci, D., and V. Fuller, 672 "Interworking between Locator/ID Separation Protocol 673 (LISP) and Non-LISP Sites", RFC 6832, 674 DOI 10.17487/RFC6832, January 2013, 675 . 677 [RFC6833] Fuller, V. and D. Farinacci, "Locator/ID Separation 678 Protocol (LISP) Map-Server Interface", RFC 6833, 679 DOI 10.17487/RFC6833, January 2013, 680 . 682 [RFC8060] Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical 683 Address Format (LCAF)", RFC 8060, DOI 10.17487/RFC8060, 684 February 2017, . 686 13.2. Informative References 688 [I-D.ermagan-lisp-nat-traversal] 689 Ermagan, V., Farinacci, D., Lewis, D., Skriver, J., Maino, 690 F., and C. White, "NAT traversal for LISP", draft-ermagan- 691 lisp-nat-traversal-15 (work in progress), October 2018. 693 Appendix A. Acknowledgments 695 The authors would like to thank the following people for their ideas 696 and comments. They are Albert Cabellos, Khalid Raza, and Vina 697 Ermagan, Gregg Schudel, Yan Filyurin, Robert Raszuk, and Truman 698 Boyes. 700 Appendix B. Document Change Log 702 B.1. Changes to draft-ietf-lisp-te-04 704 o Posted April 2019. 706 o Update document timer and references. 708 B.2. Changes to draft-ietf-lisp-te-03 710 o Posted October 2018. 712 o Update document timer and references. 714 B.3. Changes to draft-ietf-lisp-te-02 716 o Posted April 2018. 718 o Update document timer and references. 720 B.4. Changes to draft-ietf-lisp-te-01 722 o Posted October 2017. 724 o Added section on ELP-probing that tells an ITR/RTR/PITR the 725 feasibility and reachability of an Explicit Lcoator Path. 727 B.5. Changes to draft-ietf-lisp-te-00 729 o Posted April 2017. 731 o Changed draft-farinacci-lisp-te-12 to working group document. 733 B.6. Changes to draft-farinacci-lisp-te-02 through -12 735 o Many postings from January 2013 through February 2017. 737 o Update references and document timer. 739 B.7. Changes to draft-farinacci-lisp-te-01.txt 741 o Posted July 2012. 743 o Add the Lookup bit to allow an ELP to be a list of encapsulation 744 and/or mapping database lookup addresses. 746 o Indicate that ELPs can be used for service chaining. 748 o Add text to indicate that Map-Notify messages can be sent to new 749 RTRs in a ELP so their map-caches can be pre-populated to avoid 750 mapping database lookup packet loss. 752 o Fixes to editorial comments from Gregg. 754 B.8. Changes to draft-farinacci-lisp-te-00.txt 756 o Initial draft posted March 2012. 758 Authors' Addresses 760 Dino Farinacci 761 lispers.net 762 San Jose, California 763 USA 765 Phone: 408-718-2001 766 Email: farinacci@gmail.com 768 Michael Kowal 769 cisco Systems 770 111 Wood Avenue South 771 ISELIN, NJ 772 USA 774 Email: mikowal@cisco.com 776 Parantap Lahiri 777 USA 779 Email: parantap.lahiri@gmail.com