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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. -- The document has examples using IPv4 documentation addresses according to RFC6890, but does not use any IPv6 documentation addresses. Maybe there should be IPv6 examples, too? Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (June 30, 2011) is 4683 days in the past. Is this intentional? Checking references for intended status: Experimental ---------------------------------------------------------------------------- == Unused Reference: 'LISP-MS' is defined on line 756, but no explicit reference was found in the text == Unused Reference: 'RFC4632' is defined on line 763, but no explicit reference was found in the text == Outdated reference: A later version (-24) exists of draft-ietf-lisp-14 == Outdated reference: A later version (-10) exists of draft-ietf-lisp-alt-07 == Outdated reference: A later version (-16) exists of draft-ietf-lisp-ms-09 -- Obsolete informational reference (is this intentional?): RFC 2434 (Obsoleted by RFC 5226) Summary: 0 errors (**), 0 flaws (~~), 8 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group D. Lewis 3 Internet-Draft D. Meyer 4 Intended status: Experimental D. Farinacci 5 Expires: January 2, 2012 V. Fuller 6 Cisco Systems, Inc. 7 June 30, 2011 9 Interworking LISP with IPv4 and IPv6 10 draft-ietf-lisp-interworking-02.txt 12 Abstract 14 This document describes techniques for allowing sites running the 15 Locator/ID Separation Protocol (LISP) to interoperate with Internet 16 sites (which may be using either IPv4, IPv6, or both) but which are 17 not running LISP. A fundamental property of LISP speaking sites is 18 that they use Endpoint Identifiers (EIDs), rather than traditional IP 19 addresses, in the source and destination fields of all traffic they 20 emit or receive. While EIDs are syntactically identical to IPv4 or 21 IPv6 addresses, normally routes to them are not carried in the global 22 routing system so an interoperability mechanism is needed for non- 23 LISP-speaking sites to exchange traffic with LISP-speaking sites. 24 This document introduces three such mechanisms. The first uses a new 25 network element, the LISP Proxy Ingress Tunnel Routers (PITR) 26 (Section 5) to act as a intermediate LISP Ingress Tunnel Router (ITR) 27 for non-LISP-speaking hosts. Second the document adds Network 28 Address Translation (NAT) functionality to LISP Ingress and LISP 29 Egress Tunnel Routers (xTRs) to substitute routable IP addresses for 30 non-routable EIDs. Finally, this document introduces a Proxy Egress 31 Tunnel Router (PETR) to handle cases where a LISP ITR cannot send 32 packets to non-LISP sites without encapsulation. 34 Status of this Memo 36 This Internet-Draft is submitted in full conformance with the 37 provisions of BCP 78 and BCP 79. 39 Internet-Drafts are working documents of the Internet Engineering 40 Task Force (IETF). Note that other groups may also distribute 41 working documents as Internet-Drafts. The list of current Internet- 42 Drafts is at http://datatracker.ietf.org/drafts/current/. 44 Internet-Drafts are draft documents valid for a maximum of six months 45 and may be updated, replaced, or obsoleted by other documents at any 46 time. It is inappropriate to use Internet-Drafts as reference 47 material or to cite them other than as "work in progress." 48 This Internet-Draft will expire on January 2, 2012. 50 Copyright Notice 52 Copyright (c) 2011 IETF Trust and the persons identified as the 53 document authors. All rights reserved. 55 This document is subject to BCP 78 and the IETF Trust's Legal 56 Provisions Relating to IETF Documents 57 (http://trustee.ietf.org/license-info) in effect on the date of 58 publication of this document. Please review these documents 59 carefully, as they describe your rights and restrictions with respect 60 to this document. Code Components extracted from this document must 61 include Simplified BSD License text as described in Section 4.e of 62 the Trust Legal Provisions and are provided without warranty as 63 described in the Simplified BSD License. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 68 2. LISP Interworking Models . . . . . . . . . . . . . . . . . . . 6 69 3. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 8 70 4. Routable EIDs . . . . . . . . . . . . . . . . . . . . . . . . 9 71 4.1. Impact on Routing Table . . . . . . . . . . . . . . . . . 9 72 4.2. Requirement for using BGP . . . . . . . . . . . . . . . . 9 73 4.3. Limiting the Impact of Routable EIDs . . . . . . . . . . . 9 74 4.4. Use of Routable EIDs for sites transitioning to LISP . . . 9 75 5. Proxy Ingress Tunnel Routers . . . . . . . . . . . . . . . . . 11 76 5.1. PITR EID announcements . . . . . . . . . . . . . . . . . . 11 77 5.2. Packet Flow with PITRs . . . . . . . . . . . . . . . . . . 11 78 5.3. Scaling PITRs . . . . . . . . . . . . . . . . . . . . . . 12 79 5.4. Impact of the PITRs placement in the network . . . . . . . 13 80 5.5. Benefit to Networks Deploying PITRs . . . . . . . . . . . 13 81 6. LISP-NAT . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 82 6.1. Using LISP-NAT with LISP-NR EIDs . . . . . . . . . . . . . 14 83 6.2. LISP Sites with Hosts using RFC 1918 Addresses Sending 84 to non-LISP Sites . . . . . . . . . . . . . . . . . . . . 15 85 6.3. LISP Sites with Hosts using RFC 1918 Addresses 86 Sending Packets to Other LISP Sites . . . . . . . . . . . 15 87 6.4. LISP-NAT and multiple EIDs . . . . . . . . . . . . . . . . 16 88 6.5. When LISP-NAT and PITRs used by the same LISP Site . . . . 16 89 7. Proxy Egress Tunnel Routers . . . . . . . . . . . . . . . . . 17 90 7.1. Packet Flow with Proxy Egress Tunnel Routers . . . . . . . 17 91 8. Discussion of Proxy ITRs (PITRs), LISP-NAT, and Proxy-ETRs 92 (PETRs) . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 93 8.1. How Proxy-ITRs and Proxy-ETRs Interact . . . . . . . . . . 19 94 9. Security Considerations . . . . . . . . . . . . . . . . . . . 20 95 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21 96 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22 97 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23 98 12.1. Normative References . . . . . . . . . . . . . . . . . . . 23 99 12.2. Informative References . . . . . . . . . . . . . . . . . . 23 100 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24 102 1. Introduction 104 This document describes interoperation between LISP [LISP] sites 105 which use non-globally-routed EIDs, and non-LISP sites. The first is 106 the use of Proxy Ingress Tunnel router (PITRs), which originate 107 highly-aggregated routes to EID prefixes for non-LISP sites to use. 108 It also describes the use of NAT by LISP ITRs when sending packets to 109 non-LISP hosts. Finally, it describes Proxy Egress Tunnel routers 110 (PETRs) LISP for sites relying on PITRs, and which are faced with 111 certain restrictions. 113 A key behavior of the separation of Locators and End-Point-IDs is 114 that EID prefixes are normally not advertised into the Internet's 115 Default Free Zone (DFZ). Specifically, only RLOCs are carried in the 116 Internet's DFZ. Existing Internet sites (and their hosts) which do 117 not run in the LISP protocol must still be able to reach sites 118 numbered from LISP EID space. This draft describes three mechanisms 119 that can be used to provide reachability between sites that are LISP- 120 capable and those that are not. 122 The first mechanism uses a new network element, the LISP Proxy 123 Ingress Tunnel Router (PITR) to act as a intermediate LISP Ingress 124 Tunnel Router (ITR) for non-LISP-speaking hosts. The second 125 mechanism adds a form of Network Address Translation (NAT) 126 functionality to Tunnel Routers (xTRs), to substitute routable IP 127 addresses for non-routable EIDs. The final network element is the 128 LISP Proxy Egress Tunnel Routers (PETR), which act as an intermediate 129 Egress Tunnel Router (ETR) for LISP sites which need to encapsulate 130 packets LISP packets destined to non-LISP sites. 132 More detailed descriptions of these mechanisms and the network 133 elements involved may be found in the following sections: 135 - Section 2 describes the different cases where interworking 136 mechanisms are needed 138 - Section 3 defines terms used throughout the document 140 - Section 4 describes the relationship between the new EID prefix 141 space and the IP address space used by the current Internet 143 - Section 5 introduces and describes the operation of Proxy-ITRs 145 - Section 6 defines how NAT is used by ETRs to translate non-routable 146 EIDs into routable IP addresses. 148 - Section 7 introduces and describes the operations of Proxy-ETRs 149 - Section 8 describes the relationship between asymmetric and 150 Symmetric interworking mechanisms (Proxy-ITRs and Proxy-ETRs vs LISP- 151 NAT) 153 Note that any successful interworking model should be independent of 154 any particular EID-to-RLOC mapping algorithm. This document does not 155 comment on the value of any of the particular LISP mapping systems. 157 2. LISP Interworking Models 159 There are 4 unicast connectivity cases which describe how sites can 160 send packets to each other: 162 1. Non-LISP site to Non-LISP site 164 2. LISP site to LISP site 166 3. LISP site to Non-LISP site 168 4. Non-LISP site to LISP site 170 Note that while Cases 3 and 4 seem similar, there are subtle 171 differences due to the way packets are originated. 173 The first case is the Internet as we know it today and as such will 174 not be discussed further here. The second case is documented in 175 [LISP] and there are no new interworking requirements because there 176 are no new protocol requirements placed on intermediate non- LISP 177 routers. 179 In case 3, LISP site to Non-LISP site, a LISP site can (in most 180 cases) send packets to a non-LISP site because the non-LISP site 181 prefixes are routable. The non-LISP site need not do anything new to 182 receive packets. The only action the LISP site needs (with two 183 possible caveats introduced below) to take is to know when not to 184 LISP-encapsulate packets. This can be achieved by using one of two 185 mechanisms: 187 1. At the ITR in the source site, if the destination of an IP packet 188 is found to match a prefix from the BGP routing table, then the 189 site is directly reachable by the BGP core that exists and 190 operates today. 192 2. Second, if (from the perspective of the ITR at the source site) 193 the packet's destination IP address is not found in the EID-to- 194 RLOC mapping database, then the ITR could infer that it is not a 195 LISP-capable site. An ITR can also know explicitly that the 196 destination is non-LISP if the destination IP address matches a 197 Negative Map Reply found in its Map Cache. 199 3. In either of the two exceptions mentioned above there could be 200 some situations where (unencapsulated) packets originated by a 201 LISP site may not be forwarded to a non-LISP site. These cases 202 are reviewed in section 7, (Proxy-Egress Tunnel Routers). 204 Case 4, typically the most challenging, occurs when a host at a non- 205 LISP site wishes to send traffic to a host at a LISP site. If the 206 source host uses a (non-globally-routable) EID as the destination IP 207 address, the packet is forwarded inside the source site until it 208 reaches a router which cannot forward it (due to lack of a default 209 route), at which point the traffic is dropped. For traffic not to be 210 dropped, either some mechanism to make this destination EID routable 211 must be in place. Section 5 (PITRs) and Section 6 (LISP-NAT) 212 describe two such mechanisms. 214 Case 4 also applies to packets returning to the LISP site, in Case 3. 216 3. Definition of Terms 218 LISP Routable (LISP-R) Site: A LISP site whose addresses are used as 219 both globally routable IP addresses and LISP EIDs. 221 LISP Non-Routable (LISP-NR) Site: A LISP site whose addresses are 222 EIDs only, these EIDs are not found in the legacy Internet routing 223 table. 225 LISP Proxy Ingress Tunnel Router (PITR): PITRs are used to provide 226 interconnectivity between sites which use LISP EIDs and those 227 which do not. They act as gateways between those parts of the 228 Internet which are not using LISP (the legacy Internet) A given 229 PITR advertises one or more highly aggregated EID prefixes into 230 the public Internet and acts as the ITR for traffic received from 231 the public Internet. LISP Proxy Ingress Tunnel Routers are 232 described in Section 5. 234 LISP Network Address Translation (LISP-NAT): Network Address 235 Translation between EID space assigned to a site and RLOC space 236 also assigned to that site. LISP Network Address Translation is 237 described in Section 6. 239 LISP Proxy Egress Tunnel Router (PETR): PETRs provide a LISP 240 (Routable or Non-Routable EID) site's ITRs the ability to send 241 packets to non-LISP sites in cases where unencapsualted packets 242 (the default mechanism) would fail to be delivered. PETRs are 243 function by having an ITR encapsulate all non-LISP destined 244 traffic to a pre-configured PETR. LISP Proxy Egress Tunnel 245 Routers are described in Section 7. 247 EID Sub Namespace: A power-of-two block of aggregatable locators 248 set aside for LISP interworking. 250 For definitions of other terms, notably Map-Request, Map-Reply, 251 Ingress Tunnel Router (ITR), and Egress Tunnel Router (ETR), please 252 consult the LISP specification [LISP]. 254 4. Routable EIDs 256 An obvious way to achieve interworking between LISP and non-LISP 257 hosts is for a LISP site to simply announce EID prefixes into the 258 DFZ, much like the current routing system, effectively treating them 259 as "Provider Independent (PI)" prefixes. Having a site do this is 260 undesirable as it defeats one of the primary goals of LISP - to 261 reduce global routing system state. 263 4.1. Impact on Routing Table 265 If EID prefixes are announced into the DFZ, the impact is similar to 266 the case in which LISP has not been deployed, because these EID 267 prefixes will be no more aggregatable than existing PI addressing. 268 Such a mechanism is not viewed as a viable long term solution, but 269 may be a viable short term way for a site to transition a portion of 270 its address space to EID space without changing its existing routing 271 policy. 273 4.2. Requirement for using BGP 275 Non-LISP sites today use BGP to, among other things, enable ingress 276 traffic engineering. Relaxing this requirement is another primary 277 design goal of LISP. 279 4.3. Limiting the Impact of Routable EIDs 281 Two schemes are proposed to limit the impact of having EIDs announced 282 in the current global Internet routing table: 284 1. Section 5 discusses the LISP Proxy Tunnel Router, an approach 285 that provides ITR functionality to bridge LISP-capable and non- 286 LISP-capable sites. 288 2. Section 6 discusses another approach, LISP-NAT, in which NAT 289 [RFC2993] is combined with ITR functionality to limit the impact 290 of routable EIDs on the Internet routing infrastructure. 292 4.4. Use of Routable EIDs for sites transitioning to LISP 294 A primary design goal for LISP (and other Locator/ID separation 295 proposals) is to facilitate topological aggregation of namespace used 296 by the path computation, and, thus, decrease global routing system 297 overhead. Another goal is to achieve the benefits of improved 298 aggregation as soon as possible. Individual sites advertising their 299 own routes for LISP EID prefixes into the global routing system is 300 therefore not recommended. 302 That being said, single homed sites (or multi-homed sites that are 303 not leaking more specific exceptions) and that are already using 304 provider-aggregated prefixes can use these prefixes as LISP EIDs 305 without adding state to the routing system. In other words, such 306 sites do not cause additional prefixes to be advertised. For such 307 sites, connectivity to a non-LISP sites does not require interworking 308 machinery because the "PA" EIDs are already routable (they are 309 effectively LISP-R type sites). Their EIDs are found in the LISP 310 mapping system, and their (aggregate) PA prefix(es) are found in the 311 DFZ Internet. 313 The continued announcements of an existing site's Provider 314 Independent (or "PI") prefix(es) is of course under control of that 315 site. Some period of transition, where a site is found both in the 316 LISP mapping system, and as a discrete prefix in the Internet routing 317 system, may be a viable transition strategy. Care should be taken 318 not to advertise additional more specific LISP EID prefixes into the 319 DFZ. 321 5. Proxy Ingress Tunnel Routers 323 Proxy Ingress Tunnel Routers (PITRs) allow for non-LISP sites to send 324 packets to LISP-NR sites. A PITR is a new network element that 325 shares many characteristics with the LISP ITR. PITRs allow non-LISP 326 sites to send packets to LISP-NR sites without any changes to 327 protocols or equipment at the non-LISP site. PITRs have two primary 328 functions: 330 Originating EID Advertisements: PITRs advertise highly aggregated 331 EID-prefix space on behalf of LISP sites to so that non-LISP sites 332 can reach them. 334 Encapsulating Legacy Internet Traffic: PITRs also encapsulate non- 335 LISP Internet traffic into LISP packets and route them towards 336 their destination RLOCs. 338 5.1. PITR EID announcements 340 A key part of PITR functionality is to advertise routes for highly- 341 aggregated EID prefixes into part of the global routing system. 342 Aggressive aggregation is performed to minimize the number of new 343 announced routes. In addition, careful placement of PITRs can 344 greatly reduce the advertised scope of these new routes. To this 345 end, PITRs should be deployed close to non-LISP-speaking rather than 346 close to LISP sites. Such deployment not only limits the scope of 347 EID-prefix route advertisements, it also allows traffic forwarding 348 load to be spread among many PITRs. 350 5.2. Packet Flow with PITRs 352 What follows is an example of the path a packet would take when using 353 a PITR. In this example, the LISP-NR site is given the EID prefix 354 240.0.0.0/24. For the purposes of this example, this prefix and no 355 covering aggregate is present in the global routing system. In other 356 words, without the Proxy-ITR announcing 240.0.0.0/24, a packet with 357 this destination were to reach a router in the "Default Free Zone", 358 it would be dropped. 360 A full protocol exchange example follows: 362 1. The source host makes a DNS lookup EID for destination, and gets 363 240.1.1.1 in return. 365 2. The source host has a default route to customer Edge (CE) router 366 and forwards the packet to the CE. 368 3. The CE has a default route to its Provider Edge (PE) router, and 369 forwards the packet to the PE. 371 4. The PE has route to 240.0.0.0/24 and the next hop is the PITR. 373 5. The PITR has or acquires a mapping for 240.1.1.1 and LISP 374 encapsulates the packet. The outer IP header now has a 375 destination address of one of the destination EID's RLOCs. The 376 outer source address of this encapsulated packet is the PITR's 377 RLOC. 379 6. The PITR looks up the RLOC, and forwards LISP packet to the next 380 hop, after which, it is forwarded by other routers to the ETR's 381 RLOC. 383 7. The ETR decapsulates the packet and delivers the packet to the 384 240.1.1.1 host in the destination LISP site. 386 8. Packets from host 240.1.1.1 will flow back through the LISP 387 site's ITR. Such packets are not encapsulated because the ITR 388 knows that the destination (the original source) is a non-LISP 389 site. The ITR knows this because it can check the LISP mapping 390 database for the destination EID, and on a failure determine that 391 the destination site is not LISP enabled. 393 9. Packets are then routed natively and directly to the destination 394 (original source) site. 396 Note that in this example the return path is asymmetric, so return 397 traffic will not go back through the PITR. This is because the 398 LISP-NR site's ITR will discover that the originating site is not a 399 LISP site, and not encapsulate the returning packet (see [LISP] for 400 details of ITR behavior). 402 The asymmetric nature of traffic flows allows the PITR to be 403 relatively simple - it will only have to encapsulate LISP packets. 405 5.3. Scaling PITRs 407 PITRs attract traffic by announcing the LISP EID namespace into parts 408 of the non-LISP-speaking global routing system. There are several 409 ways that a network could control how traffic reaches a particular 410 PITR to prevent it from receiving more traffic than it can handle: 412 1. The PITR's aggregate routes might be selectively announced, 413 giving a coarse way to control the quantity of traffic attracted 414 by that PITR. For example, some of the routes being announced 415 might be tagged with a BGP community and their scope of 416 announcement limited by the routing policy of the provider. 418 2. The same address might be announced by multiple PITRs in order to 419 share the traffic using IP Anycast. The asymmetric nature of 420 traffic flows through the Proxy ITR means that operationally, 421 deploying a set PITRs would be very similar to existing Anycasted 422 services like DNS caches. Multiple Proxy ITRs could advertise 423 the same BGP Next Hop IP address as their RLOC, and traffic would 424 be attracted to the nearest Next Hop according to the network's 425 IGP. 427 5.4. Impact of the PITRs placement in the network 429 There are several approaches that a network could take in placing 430 PITRs. Placing the PITR near the source of traffic allows for the 431 communication between the non-LISP site and the LISP site to have the 432 least "stretch" (i.e. the least number of forwarding hops when 433 compared to an optimal path between the sites). 435 Some proposals, for example CRIO [CRIO], have suggested grouping 436 PITRs near an arbitrary subset of ETRs and announcing a 'local' 437 subset of EID space. This model cannot guarantee minimum stretch if 438 the EID prefix route advertisement points are changed (such a change 439 might occur if a site adds, removes, or replaces one or more of its 440 ISP connections). 442 5.5. Benefit to Networks Deploying PITRs 444 When packets destined for LISP-NR sites arrive and are encapsulated 445 at a Proxy-ITR, a new LISP packet header is pre-pended. This causes 446 the packet's destination to be set to the destination ETRs RLOC. 447 Because packets are thus routed towards RLOCs, it can potentially 448 better follow the Proxy-ITR network's traffic engineering policies 449 (such as closest exit routing). This also means that providers which 450 are not default-free and do not deploy Proxy-ITRs end up sending more 451 traffic to expensive transit links (assuming their upstreams have 452 deployed Proxy-ITRs) rather than to the ETR's RLOC addresses, to 453 which they may well have cheaper and closer connectivity to (via, for 454 example, settlement-free peering). A corollary to this would be that 455 large transit providers, deploying PITRs may attract more traffic, 456 and therefore more revenue, from their customers. 458 6. LISP-NAT 460 LISP Network Address Translation (LISP-NAT) is a limited form of NAT 461 [RFC2993]. LISP-NAT is designed to enable the interworking of non- 462 LISP sites and LISP-NR sites by ensuring that the LISP-NR's site 463 addresses are always routable. LISP-NAT accomplishes this by 464 translating a host's source address from an 'inner' (LISP-NR EID) 465 value to an 'outer' (LISP-R) value and keeping this translation in a 466 table that it can reference for subsequent packets. 468 In addition, existing RFC 1918 [RFC1918] sites can use LISP-NAT to 469 talk to both LISP or non-LISP sites. 471 The basic concept of LISP-NAT is that when transmitting a packet, the 472 ITR replaces a non-routable EID source address with a routable source 473 address, which enables packets to return to the site. 475 There are two main cases that involve LISP-NAT: 477 1. Hosts at LISP sites that use non-routable global EIDs speaking to 478 non-LISP sites using global addresses. 480 2. Hosts at LISP sites that use RFC 1918 private EIDs speaking to 481 other sites, who may be either LISP or non-LISP. 483 Note that LISP-NAT is not needed in the case of LISP-R (routable 484 global EIDs) sources. This case occurs when a site is announcing its 485 prefix into both the LISP mapping system as well as the Internet DFZ. 486 This is because the LISP-R source's address is routable, and return 487 packets will be able to natively reach the site. 489 6.1. Using LISP-NAT with LISP-NR EIDs 491 LISP-NAT allows a host with a LISP-NR EID to send packets to non-LISP 492 hosts by translating the LISP-NR EID to a globally unique address (a 493 LISP-R EID). This globally unique address may be a either a PI or PA 494 address. 496 An example of this translation follows. For this example, a site has 497 been assigned a LISP-NR EID of 220.1.1.0/24. In order to utilize 498 LISP-NAT, the site has also been provided the PA EID of 499 128.200.1.0/24, and uses the first address (128.200.1.1) as the 500 site's RLOC. The rest of this PA space (128.200.1.2 to 501 128.200.1.254) is used as a translation pool for this site's hosts 502 who need to send packets to non-LISP hosts. 504 The translation table might look like the following: 506 Site NR-EID Site R-EID Site's RLOC Translation Pool 507 ============================================================== 508 220.1.1.0/24 128.200.1.0/24 128.200.1.1 128.200.1.2-254 510 Figure 1: Example Translation Table 512 The Host 220.1.1.2 sends a packet (which, for the purposes of this 513 example is destined for a non-LISP site) to its default route (the 514 ITR). The ITR receives the packet, and determines that the 515 destination is not a LISP site. How the ITR makes this determination 516 is up to the ITRs implementation of the EID-to-RLOC mapping system 517 used (see, for example [LISP-ALT]). 519 The ITR then rewrites the source address of the packet from 220.1.1.2 520 to 128.200.1.2, which is the first available address in the LISP-R 521 EID space available to it. The ITR keeps this translation in a table 522 in order to reverse this process when receiving packets destined to 523 128.200.1.2. 525 Finally, when the ITR forwards this packet without encapsulating it, 526 it uses the entry in its LISP-NAT table to translate the returning 527 packets' destination IPs to the proper host. 529 6.2. LISP Sites with Hosts using RFC 1918 Addresses Sending to non-LISP 530 Sites 532 In the case where hosts using RFC 1918 addresses desire to send 533 packets to non-LISP hosts, the LISP-NAT implementation acts much like 534 an existing IPv4 NAT device. The ITR providing the NAT service must 535 use LISP-R EIDs for its global address pool as well as providing all 536 the standard NAT functions required today. 538 The source of the packet must be translated to a LISP-R EID in a 539 manner similar to Section 6, and this packet must be forwarded to the 540 ITR's next hop for the destination, without LISP encapsulation. 542 6.3. LISP Sites with Hosts using RFC 1918 Addresses Sending Packets 543 to Other LISP Sites 545 LISP-NAT allows a host with an RFC 1918 address to send packets to 546 LISP hosts by translating the RFC 1918 address to a LISP EID. After 547 translation, the communication between source and destination ITR and 548 ETRs continues as described in [LISP]. 550 An example of this translation and encapsulation follows. For this 551 example, a host has been assigned a RFC 1918 address of 192.168.1.2. 552 In order to utilize LISP-NAT, the site also has been provided the 553 LISP-R EID prefix of 192.0.2.0/24, and uses the first address 554 (192.0.2.1) as the site's RLOC. The rest of this PA space (192.0.2.2 555 to 192.0.2.254) is used as a translation pool for this site's hosts 556 who need to send packets to both non-LISP and LISP hosts. 558 The Host 192.168.1.2 sends a packet destined for a non-LISP site to 559 its default route (the ITR). The ITR receives the packet and 560 determines that the destination is a LISP site. How the ITR makes 561 this determination is up to the ITRs implementation of the EID/RLOC 562 mapping system. 564 The ITR then rewrites the source address of the packet from 565 192.168.1.2 to 192.0.2.2, which is the first available address in the 566 LISP EID space available to it. The ITR keeps this translation in a 567 table in order to reverse this process when receiving packets 568 destined to 192.0.2.2. 570 The ITR then LISP encapsulates this packet (see [LISP] for details). 571 The ITR uses the site's RLOC as the LISP outer header's source and 572 the translation address as the LISP inner header's source. Once it 573 decapsulates returning traffic, it uses the entry in its LISP-NAT 574 table to translate the returning packet's destination IP address and 575 then forward to the proper host. 577 6.4. LISP-NAT and multiple EIDs 579 When a site has two addresses that a host might use for global 580 reachability, care must be chosen on which EID is found in DNS. For 581 example, whether applications such as DNS use the LISP-R EID or the 582 LISP-NR EID. This problem exists for NAT in general, but the 583 specific issue described above is unique to LISP. Using PITRs can 584 mitigate this problem, since the LISP-NR EID can be reached in all 585 cases. 587 6.5. When LISP-NAT and PITRs used by the same LISP Site 589 With LISP-NAT, there are two EIDs possible for a given host, the 590 LISP-R EID and the LISP-NR EID. When a site has two addresses that a 591 host might use for global reachability, name-to-address directories 592 may need to be modified. 594 This problem, global vs. local addressability, exists for NAT in 595 general, but the specific issue described above is unique to 596 location/identity separation schemes. Some of these have suggested 597 running a separate DNS instance for new types of EIDs. This solves 598 the problem but introduces complexity for the site. Alternatively, 599 using PITRs can mitigate this problem, because the LISP-NR EID can be 600 reached in all cases. 602 7. Proxy Egress Tunnel Routers 604 Proxy Egress Tunnel Routers (PETRs) allow for LISP sites to send 605 packets to non-LISP sites in the case where the access network does 606 not allow for the LISP site send packets with the source address of 607 the site's EID(s). A PETR is a new network element that, 608 conceptually, acts as an ETR for traffic destined to non-LISP sites. 609 This also has the effect of allowing an ITR avoid having to decide 610 whether to encapsulate packets or not - it can always encapsulate 611 packets. An ITR would encapsulate packets destined for LISP sites 612 (no change here) and these would be routed directly to the 613 corespondent site's ETR. All other packets (those destined to non- 614 LISP sites) will be sent to the originating site's PETR. 616 There are two primary reasons why sites would want to utilize a PETR: 618 Avoiding strict uRPF failures: Some provider's access networks 619 require the source of the packets emitted to be within the 620 addressing scope of the access networks. (see section 9) 622 Traversing a different IP Protocol: A LISP site may want to transmit 623 packets to a non-LISP site where some of the intermediate network 624 does not support the particular IP protocol desired (v4 or v6). 625 PETRs can allow this LISP site's data to 'hop over' this by 626 utilizing LISP's support for mixed protocol encapsulation. 628 7.1. Packet Flow with Proxy Egress Tunnel Routers 630 Packets from a LISP site can reach a non-LISP site with the aid of a 631 Proxy-ETR (or PETR). An ITR is simply configured to send all non- 632 LISP traffic, which it normally would have forwarded natively (non- 633 encapsulated), to a PETR. In the case where the ITR uses a Map- 634 Resolver(s), the ITR will encapsulate packets that match the received 635 Negative Map-Cache to the configured Proxy-ETR(s). In the case where 636 the ITR is connected to the mapping system directly it would 637 encapsulate all packets to the configured Proxy-ETR that are cache 638 misses. Note that this outer encapsulation to the Proxy-ETR may be 639 in an IP protocol other than the (inner) encapsulated data. Routers 640 then use the LISP (outer) header's destination address to route the 641 packets toward the configured Proxy-ETR. 643 A PETR should verify the (inner) source EID of the packet at time of 644 decapsulation in order to verify that this is from a configured LISP 645 site. This is to prevent spoofed inner sources from being 646 encapsulated through the Proxy-ETR. 648 What follows is an example of the path a packet would take when using 649 a PETR. In this example, the LISP-NR (or LISP-R) site is given the 650 EID prefix 240.2.0.0/24, and it is trying to reach host at a non-LISP 651 site with the IP prefix of 192.0.2.0/24. For the purposes of this 652 example, the destination is a non-LISP site and 192.0.2.0/24 is found 653 in the Internet's routing system. 655 A full protocol exchange example follows: 657 1. The source host makes a DNS lookup for the destination, and gets 658 192.0.2.100 (a host in a non-LISP site) in return. 660 2. The source host has a default route to customer Edge (CE) router 661 and forwards the packet towards the CE. 663 3. The CE is a LISP ITR, and is configured to encapsulate traffic 664 destined for non-LISP sites to a Proxy-ETR. 666 4. The Proxy ETR decapsulates the LISP packet and forwards the 667 original packet to its next hop. 669 5. The packet is then routed natively and directly to the 670 destination (non-LISP) site 192.0.2.0/24. 672 Note that in this example the return path is asymmetric, so return 673 traffic will not go back through the Proxy-ETR. This means that in 674 order to reach LISP-NR sites, non-LISP sites must still use Proxy 675 ITRs. 677 8. Discussion of Proxy ITRs (PITRs), LISP-NAT, and Proxy-ETRs (PETRs) 679 In summary, there are three mechanisms for interworking LISP with 680 non-LISP Sites (for both IPv4 and IPv6). In the LISP-NAT option the 681 LISP site can manage and control the interworking on its own. In the 682 PITR case, the site is not required to manage the advertisement of 683 it's EID prefix into the DFZ, with the cost of potentially adding 684 stretch to the connections of non-LISP sites sending packets to the 685 LISP site. The third option is Proxy-ETRs, which are optionally used 686 by sites relying on PITRs case to mitigate two caveats for LISP sites 687 sending packets to non-LISP sites. This means Proxy-ETRs are not 688 usually expected to be deployed by themselves, rather they will be 689 used to assist LISP-NR sites which are already using PITRs. 691 8.1. How Proxy-ITRs and Proxy-ETRs Interact 693 There is a subtle difference between Symmetrical (LISP-NAT) vs 694 Asymmetrical (Proxy-ITR and Proxy-ETR) Interworking techniques. 695 Operationally, Proxy-ITRs (PITRs) and Proxy-ETRs (PETRs) can (and 696 likely should) be decoupled since Proxy-ITRs are best deployed 697 closest to non-LISP sites, and Proxy-ETRs are best located close to 698 the LISP sites they are decapsulating for. This asymmetric placement 699 of the two network elements minimizes the stretch imposed on each 700 direction of the packet flow, while still allowing for coarsely 701 aggregated announcements of EIDs into the Internet's routing table. 703 9. Security Considerations 705 Like any router or LISP ITR, PITRs will have the opportunity to 706 inspect traffic at the time that they encapsulate. The location of 707 these devices in the network can have implications for discarding 708 malicious traffic on behalf of ETRs which request this behavior (via 709 the drop action bit in Map-Reply packets for an EID or EID prefix). 711 As with traditional NAT, LISP-NAT will obscure the actual host 712 LISP-NR EID behind the LISP-R addresses used as the NAT pool. 714 When LISP sites send packets to non-LISP sites (these non-LISP sites 715 rely on PITRs to enable Interworking), packets will have the Site's 716 EID as its source IP address. These EIDs may not be recognized by 717 their Internet Service Provider's Unicast Reverse Path Forwarding 718 (uRPF) rules enabled on the Provider Edge Router. Several options 719 are available to the service provider. For example they could enable 720 a less strict version of uRPF, where they only look for the existence 721 of the EID prefix in the routing table. Another, more secure, option 722 is to add a static route for the customer on the PE router, but not 723 redistribute this route into the provider's routing table. Finally, 724 Proxy-ETRs can enable LISP sites to bypass this uRPF check by 725 encapsulating all of their egressing traffic destined to non-LISP 726 sites to the Proxy-ETR (thus ensuring the outer IP source address is 727 the site's RLOC). 729 10. Acknowledgments 731 Thanks goes to Christian Vogt, Lixia Zhang, Robin Whittle, Michael 732 Menth, and Xuewei Wang, and Noel Chiappa who have made insightful 733 comments with respect to LISP Interworking and transition mechanisms. 735 A special thanks goes to Scott Brim for his initial brainstorming of 736 these ideas and also for his careful review. 738 11. IANA Considerations 740 This document creates no new requirements on IANA namespaces 741 [RFC2434]. 743 12. References 745 12.1. Normative References 747 [LISP] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, 748 "Locator/ID Separation Protocol (LISP)", 749 draft-ietf-lisp-14 (work in progress), June 2011. 751 [LISP-ALT] 752 Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "LISP 753 Alternative Topology (LISP+ALT)", 754 draft-ietf-lisp-alt-07.txt (work in progress), June 2011. 756 [LISP-MS] Farinacci, D. and V. Fuller, "LISP Map Server", 757 draft-ietf-lisp-ms-09.txt (work in progress), June 2011. 759 [RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and 760 E. Lear, "Address Allocation for Private Internets", 761 BCP 5, RFC 1918, February 1996. 763 [RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing 764 (CIDR): The Internet Address Assignment and Aggregation 765 Plan", BCP 122, RFC 4632, August 2006. 767 12.2. Informative References 769 [CRIO] Zhang, X., Francis, P., Wang, J., and K. Yoshida, "CRIO: 770 Scaling IP Routing with the Core Router-Integrated 771 Overlay", January 2006. 773 [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an 774 IANA Considerations Section in RFCs", BCP 26, RFC 2434, 775 October 1998. 777 [RFC2993] Hain, T., "Architectural Implications of NAT", RFC 2993, 778 November 2000. 780 Authors' Addresses 782 Darrel Lewis 783 Cisco Systems, Inc. 785 Email: darlewis@cisco.com 787 David Meyer 788 Cisco Systems, Inc. 790 Email: dmm@cisco.com 792 Dino Farinacci 793 Cisco Systems, Inc. 795 Email: dino@cisco.com 797 Vince Fuller 798 Cisco Systems, Inc. 800 Email: vaf@cisco.com