idnits 2.17.1 draft-ietf-lisp-te-02.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 23, 2018) is 2189 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RFC 6830 (Obsoleted by RFC 9300, RFC 9301) ** Obsolete normative reference: RFC 6833 (Obsoleted by RFC 9301) == Outdated reference: A later version (-19) exists of draft-ermagan-lisp-nat-traversal-14 Summary: 3 errors (**), 0 flaws (~~), 4 warnings (==), 1 comment (--).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 25, 2018 cisco Systems 6 P. Lahiri 7 April 23, 2018 9 LISP Traffic Engineering Use-Cases 10 draft-ietf-lisp-te-02 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 25, 2018. 38 Copyright Notice 40 Copyright (c) 2018 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-02.txt . . . . . . . . . . 15 77 B.2. Changes to draft-ietf-lisp-te-01.txt . . . . . . . . . . 15 78 B.3. Changes to draft-ietf-lisp-te-00.txt . . . . . . . . . . 16 79 B.4. Changes to draft-farinacci-lisp-te-02 through -12 . . . . 16 80 B.5. Changes to draft-farinacci-lisp-te-01.txt . . . . . . . . 16 81 B.6. Changes to draft-farinacci-lisp-te-00.txt . . . . . . . . 16 82 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 84 1. Requirements Language 86 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 87 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 88 document are to be interpreted as described in RFC 2119 [RFC2119]. 90 2. Introduction 92 This document describes the Locator/Identifier Separation Protocol 93 (LISP), which provides a set of functions for routers to exchange 94 information used to map from non globally routeable Endpoint 95 Identifiers (EIDs) to routeable Routing Locators (RLOCs). It also 96 defines a mechanism for these LISP routers to encapsulate IP packets 97 addressed with EIDs for transmission across the Internet that uses 98 RLOCs for routing and forwarding. 100 When LISP routers encapsulate packets to other LISP routers, the path 101 stretch is typically 1, meaning the packet travels on a direct path 102 from the encapsulating ITR to the decapsulating ETR at the 103 destination site. The direct path is determined by the underlying 104 routing protocol and metrics it uses to find the shortest path. 106 This specification will examine how reencapsulating tunnels [RFC6830] 107 can be used so a packet can take an adminstratively specified path, a 108 congestion avoidance path, a failure recovery path, or multiple load- 109 shared paths, as it travels from ITR to ETR. By introducing an 110 Explicit Locator Path (ELP) locator encoding [RFC8060], an ITR can 111 encapsulate a packet to a Reencapsulating Tunnel Router (RTR) which 112 decapsulates the packet, then encapsulates it to the next locator in 113 the ELP. 115 3. Definition of Terms 117 Endpoint ID (EID): An EID is a 32-bit (for IPv4) or 128-bit (for 118 IPv6) value used in the source and destination address fields of 119 the first (most inner) LISP header of a packet. The host obtains 120 a destination EID the same way it obtains an destination address 121 today, for example through a Domain Name System (DNS) [RFC1034] 122 lookup or Session Invitation Protocol (SIP) [RFC3261] exchange. 123 The source EID is obtained via existing mechanisms used to set a 124 host's "local" IP address. An EID used on the public Internet 125 must have the same properties as any other IP address used in that 126 manner; this means, among other things, that it must be globally 127 unique. An EID is allocated to a host from an EID-prefix block 128 associated with the site where the host is located. An EID can be 129 used by a host to refer to other hosts. EIDs MUST NOT be used as 130 LISP RLOCs. Note that EID blocks MAY be assigned in a 131 hierarchical manner, independent of the network topology, to 132 facilitate scaling of the mapping database. In addition, an EID 133 block assigned to a site may have site-local structure 134 (subnetting) for routing within the site; this structure is not 135 visible to the global routing system. In theory, the bit string 136 that represents an EID for one device can represent an RLOC for a 137 different device. As the architecture is realized, if a given bit 138 string is both an RLOC and an EID, it must refer to the same 139 entity in both cases. When used in discussions with other 140 Locator/ID separation proposals, a LISP EID will be called a 141 "LEID". Throughout this document, any references to "EID" refers 142 to an LEID. 144 Routing Locator (RLOC): A RLOC is an IPv4 [RFC0791] or IPv6 145 [RFC2460] address of an egress tunnel router (ETR). A RLOC is the 146 output of an EID-to-RLOC mapping lookup. An EID maps to one or 147 more RLOCs. Typically, RLOCs are numbered from topologically- 148 aggregatable blocks that are assigned to a site at each point to 149 which it attaches to the global Internet; where the topology is 150 defined by the connectivity of provider networks, RLOCs can be 151 thought of as PA addresses. Multiple RLOCs can be assigned to the 152 same ETR device or to multiple ETR devices at a site. 154 Reencapsulating Tunnel Router (RTR): An RTR is a router that acts 155 as an ETR (or PETR) by decapsulating packets where the destination 156 address in the "outer" IP header is one of its own RLOCs. Then 157 acts as an ITR (or PITR) by making a decision where to encapsulate 158 the packet based on the next locator in the ELP towards the final 159 destination ETR. 161 Explicit Locator Path (ELP): The ELP is an explicit list of RLOCs 162 for each RTR a packet must travel to along its path toward a final 163 destination ETR (or PETR). The list is a strict ordering where 164 each RLOC in the list is visited. However, the path from one RTR 165 to another is determined by the underlying routing protocol and 166 how the infrastructure assigns metrics and policies for the path. 168 Recursive Tunneling: Recursive tunneling occurs when a packet has 169 more than one LISP IP header. Additional layers of tunneling MAY 170 be employed to implement traffic engineering or other re-routing 171 as needed. When this is done, an additional "outer" LISP header 172 is added and the original RLOCs are preserved in the "inner" 173 header. Any references to tunnels in this specification refers to 174 dynamic encapsulating tunnels and they are never statically 175 configured. 177 Reencapsulating Tunnels: Reencapsulating tunneling occurs when an 178 ETR removes a LISP header, then acts as an ITR to prepend another 179 LISP header. Doing this allows a packet to be re-routed by the 180 reencapsulating router without adding the overhead of additional 181 tunnel headers. Any references to tunnels in this specification 182 refers to dynamic encapsulating tunnels and they are never 183 statically configured. When using multiple mapping database 184 systems, care must be taken to not create reencapsulation loops 185 through misconfiguration. 187 4. Overview 189 Typically, a packet's path from source EID to destination EID travels 190 through the locator core via the encapsulating ITR directly to the 191 decapsulating ETR as the following diagram illustrates: 193 Legend: 195 seid: Packet is originated by source EID 'seid'. 197 deid: Packet is consumed by destination EID 'deid'. 199 A,B,C,D : Core routers in different ASes. 201 ---> : The physical topological path between two routers. 203 ===> : A multi-hop LISP dynamic tunnel between LISP routers. 205 Core Network 206 Source site (----------------------------) Destination Site 207 +--------+ ( ) +---------+ 208 | \ ( ) / | 209 | seid ITR ---(---> A --> B --> C --> D ---)---> ETR deid | 210 | / || ( ) ^^ \ | 211 +--------+ || ( ) || +---------+ 212 || (----------------------------) || 213 || || 214 =========================================== 215 LISP Tunnel 217 Typical Data Path from ITR to ETR 219 Let's introduce RTRs 'X' and 'Y' so that, for example, if it is 220 desirable to route around the path from B to C, one could provide an 221 ELP of (X,Y,etr): 223 Core Network 224 Source site (----------------------------) Destination Site 225 +--------+ ( ) +---------+ 226 | \ ( ) / | 227 | seid ITR ---(---> A --> B --> C --> D ---)---> ETR deid | 228 | / || ( / ^ ) ^^ \ | 229 | / || ( | \ ) || \ | 230 +-------+ || ( v | ) || +--------+ 231 || ( X ======> Y ) || 232 || ( ^^ || ) || 233 || (--------||---------||-------) || 234 || || || || 235 ================= ================= 236 LISP Tunnel LISP Tunnel 238 ELP tunnel path ITR ==> X, then X ==> Y, and then Y ==> ETR 240 There are various reasons why the path from 'seid' to 'deid' may want 241 to avoid the path from B to C. To list a few: 243 o There may not be sufficient capacity provided by the networks that 244 connect B and C together. 246 o There may be a policy reason to avoid the ASes that make up the 247 path between B and C. 249 o There may be a failure on the path between B and C which makes the 250 path unreliable. 252 o There may be monitoring or traffic inspection resources close to 253 RTRs X and Y that do network accounting or measurement. 255 o There may be a chain of services performed at RTRs X and Y 256 regardless if the path from ITR to ETR is through B and C. 258 5. Explicit Locator Paths 260 The notation for a general formatted ELP is (x, y, etr) which 261 represents the list of RTRs a packet SHOULD travel through to reach 262 the final tunnel hop to the ETR. 264 The procedure for using an ELP at each tunnel hop is as follows: 266 1. The ITR will retrieve the ELP from the mapping database. 268 2. The ITR will encapsulate the packet to RLOC 'x'. 270 3. The RTR with RLOC 'x' will decapsulate the packet. It will use 271 the decapsulated packet's destination address as a lookup into 272 the mapping database to retrieve the ELP. 274 4. RTR 'x' will encapsulate the packet to RTR with RLOC 'y'. 276 5. The RTR with RLOC 'y' will decapsulate the packet. It will use 277 the decapsulated packet's destination address as a lookup into 278 the mapping database to retrieve the ELP. 280 6. RTR 'y' will encapsulate the packet on the final tunnel hop to 281 ETR with RLOC 'etr'. 283 7. The ETR will decapsulate the packet and deliver the packet to the 284 EID inside of its site. 286 The specific format for the ELP can be found in [RFC8060]. It is 287 defined that an ELP will appear as a single encoded locator in a 288 locator-set. Say for instance, we have a mapping entry for EID- 289 prefix 10.0.0.0/8 that is reachable via 4 locators. Two locators are 290 being used as active/active and the other two are used as active/ 291 active if the first two go unreachable (as noted by the priority 292 assignments below). This is what the mapping entry would look like: 294 EID-prefix: 10.0.0.0/8 295 Locator-set: ETR-A: priority 1, weight 50 296 ETR-B: priority 1, weight 50 297 ETR-C: priority 2, weight 50 298 ETR-D: priority 2, weight 50 300 If an ELP is going to be used to have a policy path to ETR-A and 301 possibly another policy path to ETR-B, the locator-set would be 302 encoded as follows: 304 EID-prefix: 10.0.0.0/8 305 Locator-set: (x, y, ETR-A): priority 1, weight 50 306 (q, r, ETR-B): priority 1, weight 50 307 ETR-C: priority 2, weight 50 308 ETR-D: priority 2, weight 50 310 The mapping entry with ELP locators is registered to the mapping 311 database system just like any other mapping entry would. The 312 registration is typically performed by the ETR(s) that are assigned 313 and own the EID-prefix. That is, the destination site makes the 314 choice of the RTRs in the ELP. However, it may be common practice 315 for a provisioning system to program the mapping database with ELPs. 317 Another case where a locator-set can be used for flow-based load- 318 sharing across multiple paths to the same destination site: 320 EID-prefix: 10.0.0.0/8 321 Locator-set: (x, y, ETR-A): priority 1, weight 75 322 (q, r, ETR-A): priority 1, weight 25 324 Using this mapping entry, an ITR would load split 75% of the EID 325 flows on the (x, y, ETR-A) ELP path and 25% of the EID flows on the 326 (q, r, ETR-A) ELP path. If any of the ELPs go down, then the other 327 can take 100% of the load. 329 5.1. ELP Re-optimization 331 ELP re-optimization is a process of changing the RLOCs of an ELP due 332 to underlying network change conditions. Just like when there is any 333 locator change for a locator-set, the procedures from the main LISP 334 specification [RFC6830] are followed. 336 When a RLOC from an ELP is changed, Map-Notify messages [RFC6833] can 337 be used to inform the existing RTRs in the ELP so they can do a 338 lookup to obtain the latest version of the ELP. Map-Notify messages 339 can also be sent to new RTRs in an ELP so they can get the ELP in 340 advance to receiving packets that will use the ELP. This can 341 minimize packet loss during mapping database lookups in RTRs. 343 5.2. Using Recursion 345 In the previous examples, we showed how an ITR encapsulates using an 346 ELP of (x, y, etr). When a packet is encapsulated by the ITR to RTR 347 'x', the RTR may want a policy path to RTR 'y' and run another level 348 of reencapsulating tunnels for packets destined to RTR 'y'. In this 349 case, RTR 'x' does not encapsulate packets to 'y' but rather performs 350 a mapping database lookup on the address 'y', requests the ELP for 351 RTR 'y', and encapsulates packets to the first-hop of the returned 352 ELP. This can be done when using a public or private mapping 353 database. The decision to use address 'y' as an encapsulation 354 address versus a lookup address is based on the L-bit setting for 'y' 355 in the ELP entry. The decision and policy of ELP encodings are local 356 to the entity which registers the EID-prefix associated with the ELP. 358 Another example of recursion is when the ITR uses the ELP (x, y, etr) 359 to first prepend a header with a destination RLOC of the ETR and then 360 prepend another header and encapsulate the packet to RTR 'x'. When 361 RTR 'x' decapsulates the packet, rather than doing a mapping database 362 lookup on RTR 'y' the last example showed, instead RTR 'x' does a 363 mapping database lookup on ETR 'etr'. In this scenario, RTR 'x' can 364 choose an ELP from the locator-set by considering the source RLOC 365 address of the ITR versus considering the source EID. 367 This additional level of recursion also brings advantages for the 368 provider of RTR 'x' to store less state. Since RTR 'x' does not need 369 to look at the inner most header, it does not need to store EID 370 state. It only stores an entry for RTR 'y' which many EID flows 371 could share for scaling benefits. The locator-set for entry 'y' 372 could either be a list of typical locators, a list of ELPs, or 373 combination of both. Another advantage is that packet load-splitting 374 can be accomplished by examining the source of a packet. If the 375 source is an ITR versus the source being the last-hop of an ELP the 376 last-hop selected, different forwarding paths can be used. 378 5.3. ELP Selection based on Class of Service 380 Paths to an ETR may want to be selected based on different classes of 381 service. Packets from a set of sources that have premium service can 382 use ELP paths that are less congested where normal sources use ELP 383 paths that compete for less resources or use longer paths for best 384 effort service. 386 Using source/destination lookups into the mapping database can yield 387 different ELPs. So for example, a premium service flow with 388 (source=1.1.1.1, dest=10.1.1.1) can be described by using the 389 following mapping entry: 391 EID-prefix: (1.0.0.0/8, 10.0.0.0/8) 392 Locator-set: (x, y, ETR-A): priority 1, weight 50 393 (q, r, ETR-A): priority 1, weight 50 395 And all other best-effort sources would use different mapping entry 396 described by: 398 EID-prefix: (0.0.0.0/0, 10.0.0.0/8) 399 Locator-set: (x, x', y, y', ETR-A): priority 1, weight 50 400 (q, q', r, r', ETR-A): priority 1, weight 50 402 If the source/destination lookup is coupled with recursive lookups, 403 then an ITR can encapsulate to the ETR, prepending a header that 404 selects source address ITR-1 based on the premium class of service 405 source, or selects source address ITR-2 for best-effort sources with 406 normal class of service. The ITR then does another lookup in the 407 mapping database on the prepended header using lookup key 408 (source=ITR-1, dest=10.1.1.1) that returns the following mapping 409 entry: 411 EID-prefix: (ITR-1, 10.0.0.0/8) 412 Locator-set: (x, y, ETR-A): priority 1, weight 50 413 (q, r, ETR-A): priority 1, weight 50 415 And all other sources would use different mapping entry with a lookup 416 key of (source=ITR-2, dest=10.1.1.1): 418 EID-prefix: (ITR-2, 10.0.0.0/8) 419 Locator-set: (x, x', y, y', ETR-A): priority 1, weight 50 420 (q, q', r, r', ETR-A): priority 1, weight 50 422 This will scale the mapping system better by having fewer source/ 423 destination combinations. Refer to the Source/Dest LCAF type 424 described in [RFC8060] for encoding EIDs in Map-Request and Map- 425 Register messages. 427 5.4. Packet Loop Avoidance 429 An ELP that is first used by an ITR must be inspected for encoding 430 loops. If any RLOC appears twice in the ELP, it MUST not be used. 432 Since it is expected that multiple mapping systems will be used, 433 there can be a loop across ELPs when registered in different mapping 434 systems. The TTL copying procedures for reencapsulating tunnels and 435 recursive tunnels in [RFC6830] MUST be followed. 437 6. Service Chaining 439 An ELP can be used to deploy services at each reencapsulation point 440 in the network. One example is to implement a scrubber service when 441 a destination EID is being DoS attacked. That is, when a DoS attack 442 is recognized when the encapsulation path is between ITR and ETR, an 443 ELP can be registered for a destination EID to the mapping database 444 system. The ELP can include an RTR so the ITR can encapsulate 445 packets to the RTR which will decapsulate and deliver packets to a 446 scrubber service device. The scrubber could decide if the offending 447 packets are dropped or allowed to be sent to the destination EID. In 448 which case, the scurbber delivers packets back to the RTR which 449 encapsulates to the ETR. 451 7. RLOC Probing by RTRs 453 Since an RTR knows the next tunnel hop to encapsulate to, it can 454 monitor the reachability of the next-hop RTR RLOC by doing RLOC- 455 probing according to the procedures in [RFC6830]. When the RLOC is 456 determined unreachable by the RLOC-probing mechanisms, the RTR can 457 use another locator in the locator-set. That could be the final ETR, 458 a RLOC of another RTR, or an ELP where it must search for itself and 459 use the next RLOC in the ELP list to encapsulate to. 461 RLOC-probing can also be used to measure delay on the path between 462 RTRs and when it is desirable switch to another lower delay ELP. 464 8. ELP Probing 466 Since an ELP-node knows the reachabiliy of the next ELP-node in a ELP 467 by using RLOC probing, the sum of reachability can determine the 468 reachability of the entire path. A head-end ITR/RTR/PITR can 469 determine the quality of a path and decide to select one path from 470 another based on the telemetry data gathered by RLOC-probing for each 471 encapsulation hop. 473 ELP-probing mechanism details can be found in [I-D.filyurin-lisp-elp- 474 probing]. 476 9. Interworking Considerations 478 [RFC6832] defines procedures for how non-LISP sites talk to LISP 479 sites. The network elements defined in the Interworking 480 specification, the proxy ITR (PITR) and proxy ETR (PETR) (as well as 481 their multicast counterparts defined in [RFC6831]) can participate in 482 LISP-TE. That is, a PITR and a PETR can appear in an ELP list and 483 act as an RTR. 485 Note when an RLOC appears in an ELP, it can be of any address-family. 486 There can be a mix of IPv4 and IPv6 locators present in the same ELP. 487 This can provide benefits where islands of one address-family or the 488 other are supported and connectivity across them is necessary. For 489 instance, an ELP can look like: 491 (x4, a46, b64, y4, etr) 493 Where an IPv4 ITR will encapsulate using an IPv4 RLOC 'x4' and 'x4' 494 could reach an IPv4 RLOC 'a46', but RTR 'a46' encapsulates to an IPv6 495 RLOC 'b64' when the network between them is IPv6-only. Then RTR 496 'b64' encapsulates to IPv4 RLOC 'y4' if the network between them is 497 dual-stack. 499 Note that RTRs can be used for NAT-traversal scenarios 500 [I-D.ermagan-lisp-nat-traversal] as well to reduce the state in both 501 an xTR that resides behind a NAT and the state the NAT needs to 502 maintain. In this case, the xTR only needs a default map-cache entry 503 pointing to the RTR for outbound traffic and all remote ITRs can 504 reach EIDs through the xTR behind a NAT via a single RTR (or a small 505 set RTRs for redundancy). 507 RTRs have some scaling features to reduce the number of locator-set 508 changes, the amount of state, and control packet overhead: 510 o When ITRs and PITRs are using a small set of RTRs for 511 encapsulating to "orders of magnitude" more EID-prefixes, the 512 probability of locator-set changes are limited to the RTR RLOC 513 changes versus the RLOC changes for the ETRs associated with the 514 EID-prefixes if the ITRs and PITRs were directly encapsulating to 515 the ETRs. This comes at an expense in packet stretch, but 516 depending on RTR placement, this expense can be mitigated. 518 o When RTRs are on-path between many pairwise EID flows, ITRs and 519 PITRs can store a small number of coarse EID-prefixes. 521 o RTRs can be used to help scale RLOC-probing. Instead of ITRs 522 RLOC-probing all ETRs for each destination site it has cached, the 523 ITRs can probe a smaller set of RTRs which in turn, probe the 524 destination sites. 526 10. Multicast Considerations 528 ELPs have application in multicast environments. Just like RTRs can 529 be used to provide connectivity across different address family 530 islands, RTRs can help concatenate a multicast region of the network 531 to one that does not support native multicast. 533 Note there are various combinations of connectivity that can be 534 accomplished with the deployment of RTRs and ELPs: 536 o Providing multicast forwarding between IPv4-only-unicast regions 537 and IPv4-multicast regions. 539 o Providing multicast forwarding between IPv6-only-unicast regions 540 and IPv6-multicast regions. 542 o Providing multicast forwarding between IPv4-only-unicast regions 543 and IPv6-multicast regions. 545 o Providing multicast forwarding between IPv6-only-unicast regions 546 and IPv4-multicast regions. 548 o Providing multicast forwarding between IPv4-multicast regions and 549 IPv6-multicast regions. 551 An ITR or PITR can do a (S-EID,G) lookup into the mapping database. 552 What can be returned is a typical locator-set that could be made up 553 of the various RLOC addresses: 555 Multicast EID key: (seid, G) 556 Locator-set: ETR-A: priority 1, weight 25 557 ETR-B: priority 1, weight 25 558 g1: priority 1, weight 25 559 g2: priority 1, weight 25 561 An entry for host 'seid' sending to application group 'G' 563 The locator-set above can be used as a replication list. That is 564 some RLOCs listed can be unicast RLOCs and some can be delivery group 565 RLOCs. A unicast RLOC in this case is used to encapsulate a 566 multicast packet originated by a multicast source EID into a unicast 567 packet for unicast delivery on the underlying network. ETR-A could 568 be a IPv4 unicast RLOC address and ETR-B could be a IPv6 unicast RLOC 569 address. 571 A delivery group address is used when a multicast packet originated 572 by a multicast source EID is encapsulated in a multicast packet for 573 multicast delivery on the underlying network. Group address 'g1' 574 could be a IPv4 delivery group RLOC and group address 'g2' could be 575 an IPv6 delivery group RLOC. 577 Flexibility for these various types of connectivity combinations can 578 be achieved and provided by the mapping database system. And the RTR 579 placement allows the connectivity to occur where the differences in 580 network functionality are located. 582 Extending this concept by allowing ELPs in locator-sets, one could 583 have this locator-set registered in the mapping database for (seid, 584 G). For example: 586 Multicast EID key: (seid, G) 587 Locator-set: (x, y, ETR-A): priority 1, weight 50 588 (a, g, b, ETR-B): priority 1, weight 50 590 Using ELPs for multicast flows 592 In the above situation, an ITR would encapsulate a multicast packet 593 originated by a multicast source EID to the RTR with unicast RLOC 594 'x'. Then RTR 'x' would decapsulate and unicast encapsulate to RTR 595 'y' ('x' or 'y' could be either IPv4 or IPv6 unicast RLOCs), which 596 would decapsulate and unicast encapsulate to the final RLOC 'ETR-A'. 597 The ETR 'ETR-A' would decapsulate and deliver the multicast packet 598 natively to all the receivers joined to application group 'G' inside 599 the LISP site. 601 Let's look at the ITR using the ELP (a, g, b, ETR-B). Here the 602 encapsulation path would be the ITR unicast encapsulates to unicast 603 RLOC 'a'. RTR 'a' multicast encapsulates to delivery group 'g'. The 604 packet gets to all ETRs that have joined delivery group 'g' so they 605 can deliver the multicast packet to joined receivers of application 606 group 'G' in their sites. RTR 'b' is also joined to delivery group 607 'g'. Since it is in the ELP, it will be the only RTR that unicast 608 encapsulates the multicast packet to ETR 'ETR-B'. Lastly, 'ETR-B' 609 decapsulates and delivers the multicast packet to joined receivers to 610 application group 'G' in its LISP site. 612 As one can see there are all sorts of opportunities to provide 613 multicast connectivity across a network with non-congruent support 614 for multicast and different address-families. One can also see how 615 using the mapping database can allow flexible forms of delivery 616 policy, rerouting, and congestion control management in multicast 617 environments. 619 11. Security Considerations 621 When an RTR receives a LISP encapsulated packet, it can look at the 622 outer source address to verify that RLOC is the one listed as the 623 previous hop in the ELP list. If the outer source RLOC address 624 appears before the RLOC which matches the outer destination RLOC 625 address, the decapsulating RTR (or ETR if last hop), MAY choose to 626 drop the packet. 628 12. IANA Considerations 630 At this time there are no requests for IANA. 632 13. References 634 13.1. Normative References 636 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 637 DOI 10.17487/RFC0791, September 1981, 638 . 640 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 641 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 642 . 644 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 645 Requirement Levels", BCP 14, RFC 2119, 646 DOI 10.17487/RFC2119, March 1997, 647 . 649 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 650 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, 651 December 1998, . 653 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 654 A., Peterson, J., Sparks, R., Handley, M., and E. 655 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 656 DOI 10.17487/RFC3261, June 2002, 657 . 659 [RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The 660 Locator/ID Separation Protocol (LISP)", RFC 6830, 661 DOI 10.17487/RFC6830, January 2013, 662 . 664 [RFC6831] Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas, "The 665 Locator/ID Separation Protocol (LISP) for Multicast 666 Environments", RFC 6831, DOI 10.17487/RFC6831, January 667 2013, . 669 [RFC6832] Lewis, D., Meyer, D., Farinacci, D., and V. Fuller, 670 "Interworking between Locator/ID Separation Protocol 671 (LISP) and Non-LISP Sites", RFC 6832, 672 DOI 10.17487/RFC6832, January 2013, 673 . 675 [RFC6833] Fuller, V. and D. Farinacci, "Locator/ID Separation 676 Protocol (LISP) Map-Server Interface", RFC 6833, 677 DOI 10.17487/RFC6833, January 2013, 678 . 680 [RFC8060] Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical 681 Address Format (LCAF)", RFC 8060, DOI 10.17487/RFC8060, 682 February 2017, . 684 13.2. Informative References 686 [I-D.ermagan-lisp-nat-traversal] 687 Ermagan, V., Farinacci, D., Lewis, D., Skriver, J., Maino, 688 F., and C. White, "NAT traversal for LISP", draft-ermagan- 689 lisp-nat-traversal-14 (work in progress), April 2018. 691 Appendix A. Acknowledgments 693 The authors would like to thank the following people for their ideas 694 and comments. They are Albert Cabellos, Khalid Raza, and Vina 695 Ermagan, Gregg Schudel, Yan Filyurin, Robert Raszuk, and Truman 696 Boyes. 698 Appendix B. Document Change Log 700 B.1. Changes to draft-ietf-lisp-te-02.txt 702 o Posted April 2018. 704 o Update document timer and references. 706 B.2. Changes to draft-ietf-lisp-te-01.txt 708 o Posted October 2017. 710 o Added section on ELP-probing that tells an ITR/RTR/PITR the 711 feasibility and reachability of an Explicit Lcoator Path. 713 B.3. Changes to draft-ietf-lisp-te-00.txt 715 o Posted April 2017. 717 o Changed draft-farinacci-lisp-te-12 to working group document. 719 B.4. Changes to draft-farinacci-lisp-te-02 through -12 721 o Many postings from January 2013 through February 2017. 723 o Update references and document timer. 725 B.5. Changes to draft-farinacci-lisp-te-01.txt 727 o Posted July 2012. 729 o Add the Lookup bit to allow an ELP to be a list of encapsulation 730 and/or mapping database lookup addresses. 732 o Indicate that ELPs can be used for service chaining. 734 o Add text to indicate that Map-Notify messages can be sent to new 735 RTRs in a ELP so their map-caches can be pre-populated to avoid 736 mapping database lookup packet loss. 738 o Fixes to editorial comments from Gregg. 740 B.6. Changes to draft-farinacci-lisp-te-00.txt 742 o Initial draft posted March 2012. 744 Authors' Addresses 746 Dino Farinacci 747 lispers.net 748 San Jose, California 749 USA 751 Phone: 408-718-2001 752 Email: farinacci@gmail.com 753 Michael Kowal 754 cisco Systems 755 111 Wood Avenue South 756 ISELIN, NJ 757 USA 759 Email: mikowal@cisco.com 761 Parantap Lahiri 762 USA 764 Email: parantap.lahiri@gmail.com