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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group D. Farinacci 3 Internet-Draft V. Fuller 4 Intended status: Standards Track D. Meyer 5 Expires: October 13, 2017 D. Lewis 6 Cisco Systems 7 A. Cabellos (Ed.) 8 UPC/BarcelonaTech 9 April 11, 2017 11 The Locator/ID Separation Protocol (LISP) 12 draft-ietf-lisp-rfc6830bis-02 14 Abstract 16 This document describes the data-plane protocol for the Locator/ID 17 Separation Protocol (LISP). LISP defines two namespaces, End-point 18 Identifiers (EIDs) that identify end-hosts and Routing Locators 19 (RLOCs) that identify network attachment points. With this, LISP 20 effectively separates control from data, and allows routers to create 21 overlay networks. LISP-capable routers exchange encapsulated packets 22 according to EID-to-RLOC mappings stored in a local map-cache. The 23 map-cache is populated by the LISP Control-Plane protocol 24 [I-D.ietf-lisp-rfc6833bis]. 26 LISP requires no change to either host protocol stacks or to underlay 27 routers and offers Traffic Engineering, multihoming and mobility, 28 among other features. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at http://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on October 13, 2017. 47 Copyright Notice 49 Copyright (c) 2017 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (http://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 65 2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 4 66 3. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 4 67 4. Basic Overview . . . . . . . . . . . . . . . . . . . . . . . 9 68 4.1. Packet Flow Sequence . . . . . . . . . . . . . . . . . . 11 69 5. LISP Encapsulation Details . . . . . . . . . . . . . . . . . 13 70 5.1. LISP IPv4-in-IPv4 Header Format . . . . . . . . . . . . . 14 71 5.2. LISP IPv6-in-IPv6 Header Format . . . . . . . . . . . . . 15 72 5.3. Tunnel Header Field Descriptions . . . . . . . . . . . . 16 73 6. LISP EID-to-RLOC Map-Cache . . . . . . . . . . . . . . . . . 20 74 7. Dealing with Large Encapsulated Packets . . . . . . . . . . . 20 75 7.1. A Stateless Solution to MTU Handling . . . . . . . . . . 21 76 7.2. A Stateful Solution to MTU Handling . . . . . . . . . . . 22 77 8. Using Virtualization and Segmentation with LISP . . . . . . . 22 78 9. Routing Locator Selection . . . . . . . . . . . . . . . . . . 23 79 10. Routing Locator Reachability . . . . . . . . . . . . . . . . 24 80 10.1. Echo Nonce Algorithm . . . . . . . . . . . . . . . . . . 27 81 10.2. RLOC-Probing Algorithm . . . . . . . . . . . . . . . . . 28 82 11. EID Reachability within a LISP Site . . . . . . . . . . . . . 29 83 12. Routing Locator Hashing . . . . . . . . . . . . . . . . . . . 30 84 13. Changing the Contents of EID-to-RLOC Mappings . . . . . . . . 31 85 13.1. Clock Sweep . . . . . . . . . . . . . . . . . . . . . . 32 86 13.2. Solicit-Map-Request (SMR) . . . . . . . . . . . . . . . 32 87 13.3. Database Map-Versioning . . . . . . . . . . . . . . . . 34 88 14. Multicast Considerations . . . . . . . . . . . . . . . . . . 34 89 15. Router Performance Considerations . . . . . . . . . . . . . . 35 90 16. Mobility Considerations . . . . . . . . . . . . . . . . . . . 36 91 16.1. Slow Mobility . . . . . . . . . . . . . . . . . . . . . 36 92 16.2. Fast Mobility . . . . . . . . . . . . . . . . . . . . . 36 93 16.3. LISP Mobile Node Mobility . . . . . . . . . . . . . . . 37 94 17. LISP xTR Placement and Encapsulation Methods . . . . . . . . 38 95 17.1. First-Hop/Last-Hop xTRs . . . . . . . . . . . . . . . . 39 96 17.2. Border/Edge xTRs . . . . . . . . . . . . . . . . . . . . 39 97 17.3. ISP Provider Edge (PE) xTRs . . . . . . . . . . . . . . 40 98 17.4. LISP Functionality with Conventional NATs . . . . . . . 40 99 17.5. Packets Egressing a LISP Site . . . . . . . . . . . . . 41 100 18. Traceroute Considerations . . . . . . . . . . . . . . . . . . 41 101 18.1. IPv6 Traceroute . . . . . . . . . . . . . . . . . . . . 42 102 18.2. IPv4 Traceroute . . . . . . . . . . . . . . . . . . . . 42 103 18.3. Traceroute Using Mixed Locators . . . . . . . . . . . . 43 104 19. Security Considerations . . . . . . . . . . . . . . . . . . . 43 105 20. Network Management Considerations . . . . . . . . . . . . . . 44 106 21. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 44 107 21.1. LISP ACT and Flag Fields . . . . . . . . . . . . . . . . 44 108 21.2. LISP Address Type Codes . . . . . . . . . . . . . . . . 45 109 21.3. LISP UDP Port Numbers . . . . . . . . . . . . . . . . . 45 110 21.4. LISP Key ID Numbers . . . . . . . . . . . . . . . . . . 45 111 22. References . . . . . . . . . . . . . . . . . . . . . . . . . 45 112 22.1. Normative References . . . . . . . . . . . . . . . . . . 45 113 22.2. Informative References . . . . . . . . . . . . . . . . . 48 114 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 52 115 Appendix B. Document Change Log . . . . . . . . . . . . . . . . 52 116 B.1. Changes to draft-ietf-lisp-rfc6830bis-02 . . . . . . . . 53 117 B.2. Changes to draft-ietf-lisp-rfc6830bis-01 . . . . . . . . 53 118 B.3. Changes to draft-ietf-lisp-rfc6830bis-00 . . . . . . . . 53 119 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 53 121 1. Introduction 123 This document describes the Locator/Identifier Separation Protocol 124 (LISP). LISP is an encapsulation protocol built around the 125 fundamental idea of separating the topological location of a network 126 attachment point from the node's identity [CHIAPPA]. As a result 127 LISP creates two namespaces: Endpoint Identifiers (EIDs), that are 128 used to identify end-hosts (e.g., nodes or Virtual Machines) and 129 routable Routing Locators (RLOCs), used to identify network 130 attachment points. LISP then defines functions for mapping between 131 the two namespaces and for encapsulating traffic originated by 132 devices using non-routable EIDs for transport across a network 133 infrastructure that routes and forwards using RLOCs. 135 LISP is an overlay protocol that separates control from data-plane, 136 this document specifies the data-plane, how LISP-capable routers 137 (Tunnel Routers) exchange packets by encapsulating them to the 138 appropriate location. Tunnel routers are equipped with a cache, 139 called map-cache, that contains EID-to-RLOC mappings. The map-cache 140 is populated using the LISP Control-Plane protocol 141 [I-D.ietf-lisp-rfc6833bis]. 143 LISP does not require changes to either host protocol stack or to 144 underlay routers. By separating the EID from the RLOC space, LISP 145 offers native Traffic Engineering, multihoming and mobility, among 146 other features. 148 Creation of LISP was initially motivated by discussions during the 149 IAB-sponsored Routing and Addressing Workshop held in Amsterdam in 150 October 2006 (see [RFC4984]) 152 This document specifies the LISP data-plane encapsulation and other 153 LISP forwarding node functionality while [I-D.ietf-lisp-rfc6833bis] 154 specifies the LISP control plane. LISP deployment guidelines can be 155 found in [RFC7215] and [RFC6835] describes considerations for network 156 operational management. Finally, [I-D.ietf-lisp-introduction] 157 describes the LISP architecture. 159 2. Requirements Notation 161 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 162 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 163 document are to be interpreted as described in [RFC2119]. 165 3. Definition of Terms 167 Provider-Independent (PI) Addresses: PI addresses are an address 168 block assigned from a pool where blocks are not associated with 169 any particular location in the network (e.g., from a particular 170 service provider) and are therefore not topologically aggregatable 171 in the routing system. 173 Provider-Assigned (PA) Addresses: PA addresses are an address block 174 assigned to a site by each service provider to which a site 175 connects. Typically, each block is a sub-block of a service 176 provider Classless Inter-Domain Routing (CIDR) [RFC4632] block and 177 is aggregated into the larger block before being advertised into 178 the global Internet. Traditionally, IP multihoming has been 179 implemented by each multihomed site acquiring its own globally 180 visible prefix. LISP uses only topologically assigned and 181 aggregatable address blocks for RLOCs, eliminating this 182 demonstrably non-scalable practice. 184 Routing Locator (RLOC): An RLOC is an IPv4 [RFC0791] or IPv6 185 [RFC2460] address of an Egress Tunnel Router (ETR). An RLOC is 186 the output of an EID-to-RLOC mapping lookup. An EID maps to one 187 or more RLOCs. Typically, RLOCs are numbered from topologically 188 aggregatable blocks that are assigned to a site at each point to 189 which it attaches to the global Internet; where the topology is 190 defined by the connectivity of provider networks, RLOCs can be 191 thought of as PA addresses. Multiple RLOCs can be assigned to the 192 same ETR device or to multiple ETR devices at a site. 194 Endpoint ID (EID): An EID is a 32-bit (for IPv4) or 128-bit (for 195 IPv6) value used in the source and destination address fields of 196 the first (most inner) LISP header of a packet. The host obtains 197 a destination EID the same way it obtains a destination address 198 today, for example, through a Domain Name System (DNS) [RFC1034] 199 lookup or Session Initiation Protocol (SIP) [RFC3261] exchange. 200 The source EID is obtained via existing mechanisms used to set a 201 host's "local" IP address. An EID used on the public Internet 202 must have the same properties as any other IP address used in that 203 manner; this means, among other things, that it must be globally 204 unique. An EID is allocated to a host from an EID-Prefix block 205 associated with the site where the host is located. An EID can be 206 used by a host to refer to other hosts. EIDs MUST NOT be used as 207 LISP RLOCs. Note that EID blocks MAY be assigned in a 208 hierarchical manner, independent of the network topology, to 209 facilitate scaling of the mapping database. In addition, an EID 210 block assigned to a site may have site-local structure 211 (subnetting) for routing within the site; this structure is not 212 visible to the global routing system. In theory, the bit string 213 that represents an EID for one device can represent an RLOC for a 214 different device. As the architecture is realized, if a given bit 215 string is both an RLOC and an EID, it must refer to the same 216 entity in both cases. When used in discussions with other 217 Locator/ID separation proposals, a LISP EID will be called an 218 "LEID". Throughout this document, any references to "EID" refer 219 to an LEID. 221 EID-Prefix: An EID-Prefix is a power-of-two block of EIDs that are 222 allocated to a site by an address allocation authority. EID- 223 Prefixes are associated with a set of RLOC addresses that make up 224 a "database mapping". EID-Prefix allocations can be broken up 225 into smaller blocks when an RLOC set is to be associated with the 226 larger EID-Prefix block. A globally routed address block (whether 227 PI or PA) is not inherently an EID-Prefix. A globally routed 228 address block MAY be used by its assignee as an EID block. The 229 converse is not supported. That is, a site that receives an 230 explicitly allocated EID-Prefix may not use that EID-Prefix as a 231 globally routed prefix. This would require coordination and 232 cooperation with the entities managing the mapping infrastructure. 233 Once this has been done, that block could be removed from the 234 globally routed IP system, if other suitable transition and access 235 mechanisms are in place. Discussion of such transition and access 236 mechanisms can be found in [RFC6832] and [RFC7215]. 238 End-system: An end-system is an IPv4 or IPv6 device that originates 239 packets with a single IPv4 or IPv6 header. The end-system 240 supplies an EID value for the destination address field of the IP 241 header when communicating globally (i.e., outside of its routing 242 domain). An end-system can be a host computer, a switch or router 243 device, or any network appliance. 245 Ingress Tunnel Router (ITR): An ITR is a router that resides in a 246 LISP site. Packets sent by sources inside of the LISP site to 247 destinations outside of the site are candidates for encapsulation 248 by the ITR. The ITR treats the IP destination address as an EID 249 and performs an EID-to-RLOC mapping lookup. The router then 250 prepends an "outer" IP header with one of its globally routable 251 RLOCs in the source address field and the result of the mapping 252 lookup in the destination address field. Note that this 253 destination RLOC MAY be an intermediate, proxy device that has 254 better knowledge of the EID-to-RLOC mapping closer to the 255 destination EID. In general, an ITR receives IP packets from site 256 end-systems on one side and sends LISP-encapsulated IP packets 257 toward the Internet on the other side. 259 Specifically, when a service provider prepends a LISP header for 260 Traffic Engineering purposes, the router that does this is also 261 regarded as an ITR. The outer RLOC the ISP ITR uses can be based 262 on the outer destination address (the originating ITR's supplied 263 RLOC) or the inner destination address (the originating host's 264 supplied EID). 266 TE-ITR: A TE-ITR is an ITR that is deployed in a service provider 267 network that prepends an additional LISP header for Traffic 268 Engineering purposes. 270 Egress Tunnel Router (ETR): An ETR is a router that accepts an IP 271 packet where the destination address in the "outer" IP header is 272 one of its own RLOCs. The router strips the "outer" header and 273 forwards the packet based on the next IP header found. In 274 general, an ETR receives LISP-encapsulated IP packets from the 275 Internet on one side and sends decapsulated IP packets to site 276 end-systems on the other side. ETR functionality does not have to 277 be limited to a router device. A server host can be the endpoint 278 of a LISP tunnel as well. 280 TE-ETR: A TE-ETR is an ETR that is deployed in a service provider 281 network that strips an outer LISP header for Traffic Engineering 282 purposes. 284 xTR: An xTR is a reference to an ITR or ETR when direction of data 285 flow is not part of the context description. "xTR" refers to the 286 router that is the tunnel endpoint and is used synonymously with 287 the term "Tunnel Router". For example, "An xTR can be located at 288 the Customer Edge (CE) router" indicates both ITR and ETR 289 functionality at the CE router. 291 LISP Router: A LISP router is a router that performs the functions 292 of any or all of the following: ITR, ETR, Proxy-ITR (PITR), or 293 Proxy-ETR (PETR). 295 EID-to-RLOC Map-Cache: The EID-to-RLOC map-cache is a short-lived, 296 on-demand table in an ITR that stores, tracks, and is responsible 297 for timing out and otherwise validating EID-to-RLOC mappings. 298 This cache is distinct from the full "database" of EID-to-RLOC 299 mappings; it is dynamic, local to the ITR(s), and relatively 300 small, while the database is distributed, relatively static, and 301 much more global in scope. 303 EID-to-RLOC Database: The EID-to-RLOC Database is a global 304 distributed database that contains all known EID-Prefix-to-RLOC 305 mappings. Each potential ETR typically contains a small piece of 306 the database: the EID-to-RLOC mappings for the EID-Prefixes 307 "behind" the router. These map to one of the router's own 308 globally visible IP addresses. The same database mapping entries 309 MUST be configured on all ETRs for a given site. In a steady 310 state, the EID-Prefixes for the site and the Locator-Set for each 311 EID-Prefix MUST be the same on all ETRs. Procedures to enforce 312 and/or verify this are outside the scope of this document. Note 313 that there MAY be transient conditions when the EID-Prefix for the 314 site and Locator-Set for each EID-Prefix may not be the same on 315 all ETRs. This has no negative implications, since a partial set 316 of Locators can be used. 318 Recursive Tunneling: Recursive Tunneling occurs when a packet has 319 more than one LISP IP header. Additional layers of tunneling MAY 320 be employed to implement Traffic Engineering or other re-routing 321 as needed. When this is done, an additional "outer" LISP header 322 is added, and the original RLOCs are preserved in the "inner" 323 header. Any references to tunnels in this specification refer to 324 dynamic encapsulating tunnels; they are never statically 325 configured. 327 Re-encapsulating Tunnels: Re-encapsulating Tunneling occurs when an 328 ETR removes a LISP header, then acts as an ITR to prepend another 329 LISP header. Doing this allows a packet to be re-routed by the 330 re-encapsulating router without adding the overhead of additional 331 tunnel headers. Any references to tunnels in this specification 332 refer to dynamic encapsulating tunnels; they are never statically 333 configured. When using multiple mapping database systems, care 334 must be taken to not create re-encapsulation loops through 335 misconfiguration. 337 LISP Header: LISP header is a term used in this document to refer 338 to the outer IPv4 or IPv6 header, a UDP header, and a LISP- 339 specific 8-octet header that follow the UDP header and that an ITR 340 prepends or an ETR strips. 342 Address Family Identifier (AFI): AFI is a term used to describe an 343 address encoding in a packet. An address family currently 344 pertains to an IPv4 or IPv6 address. See [AFN] and [RFC3232] for 345 details. An AFI value of 0 used in this specification indicates 346 an unspecified encoded address where the length of the address is 347 0 octets following the 16-bit AFI value of 0. 349 Negative Mapping Entry: A negative mapping entry, also known as a 350 negative cache entry, is an EID-to-RLOC entry where an EID-Prefix 351 is advertised or stored with no RLOCs. That is, the Locator-Set 352 for the EID-to-RLOC entry is empty or has an encoded Locator count 353 of 0. This type of entry could be used to describe a prefix from 354 a non-LISP site, which is explicitly not in the mapping database. 355 There are a set of well-defined actions that are encoded in a 356 Negative Map-Reply. 358 Data-Probe: A Data-Probe is a LISP-encapsulated data packet where 359 the inner-header destination address equals the outer-header 360 destination address used to trigger a Map-Reply by a decapsulating 361 ETR. In addition, the original packet is decapsulated and 362 delivered to the destination host if the destination EID is in the 363 EID-Prefix range configured on the ETR. Otherwise, the packet is 364 discarded. A Data-Probe is used in some of the mapping database 365 designs to "probe" or request a Map-Reply from an ETR; in other 366 cases, Map-Requests are used. See each mapping database design 367 for details. When using Data-Probes, by sending Map-Requests on 368 the underlying routing system, EID-Prefixes must be advertised. 369 However, this is discouraged if the core is to scale by having 370 less EID-Prefixes stored in the core router's routing tables. 372 Proxy-ITR (PITR): A PITR is defined and described in [RFC6832]. A 373 PITR acts like an ITR but does so on behalf of non-LISP sites that 374 send packets to destinations at LISP sites. 376 Proxy-ETR (PETR): A PETR is defined and described in [RFC6832]. A 377 PETR acts like an ETR but does so on behalf of LISP sites that 378 send packets to destinations at non-LISP sites. 380 Route-returnability: Route-returnability is an assumption that the 381 underlying routing system will deliver packets to the destination. 383 When combined with a nonce that is provided by a sender and 384 returned by a receiver, this limits off-path data insertion. A 385 route-returnability check is verified when a message is sent with 386 a nonce, another message is returned with the same nonce, and the 387 destination of the original message appears as the source of the 388 returned message. 390 LISP site: LISP site is a set of routers in an edge network that are 391 under a single technical administration. LISP routers that reside 392 in the edge network are the demarcation points to separate the 393 edge network from the core network. 395 Client-side: Client-side is a term used in this document to indicate 396 a connection initiation attempt by an EID. The ITR(s) at the LISP 397 site are the first to get involved in obtaining database Map-Cache 398 entries by sending Map-Request messages. 400 Server-side: Server-side is a term used in this document to indicate 401 that a connection initiation attempt is being accepted for a 402 destination EID. The ETR(s) at the destination LISP site are the 403 first to send Map-Replies to the source site initiating the 404 connection. The ETR(s) at this destination site can obtain 405 mappings by gleaning information from Map-Requests, Data-Probes, 406 or encapsulated packets. 408 Locator-Status-Bits (LSBs): Locator-Status-Bits are present in the 409 LISP header. They are used by ITRs to inform ETRs about the up/ 410 down status of all ETRs at the local site. These bits are used as 411 a hint to convey up/down router status and not path reachability 412 status. The LSBs can be verified by use of one of the Locator 413 reachability algorithms described in Section 10. 415 Anycast Address: Anycast Address is a term used in this document to 416 refer to the same IPv4 or IPv6 address configured and used on 417 multiple systems at the same time. An EID or RLOC can be an 418 anycast address in each of their own address spaces. 420 4. Basic Overview 422 One key concept of LISP is that end-systems operate the same way they 423 do today. The IP addresses that hosts use for tracking sockets and 424 connections, and for sending and receiving packets, do not change. 425 In LISP terminology, these IP addresses are called Endpoint 426 Identifiers (EIDs). 428 Routers continue to forward packets based on IP destination 429 addresses. When a packet is LISP encapsulated, these addresses are 430 referred to as Routing Locators (RLOCs). Most routers along a path 431 between two hosts will not change; they continue to perform routing/ 432 forwarding lookups on the destination addresses. For routers between 433 the source host and the ITR as well as routers from the ETR to the 434 destination host, the destination address is an EID. For the routers 435 between the ITR and the ETR, the destination address is an RLOC. 437 Another key LISP concept is the "Tunnel Router". A Tunnel Router 438 prepends LISP headers on host-originated packets and strips them 439 prior to final delivery to their destination. The IP addresses in 440 this "outer header" are RLOCs. During end-to-end packet exchange 441 between two Internet hosts, an ITR prepends a new LISP header to each 442 packet, and an ETR strips the new header. The ITR performs EID-to- 443 RLOC lookups to determine the routing path to the ETR, which has the 444 RLOC as one of its IP addresses. 446 Some basic rules governing LISP are: 448 o End-systems only send to addresses that are EIDs. They don't know 449 that addresses are EIDs versus RLOCs but assume that packets get 450 to their intended destinations. In a system where LISP is 451 deployed, LISP routers intercept EID-addressed packets and assist 452 in delivering them across the network core where EIDs cannot be 453 routed. The procedure a host uses to send IP packets does not 454 change. 456 o EIDs are typically IP addresses assigned to hosts. 458 o Other types of EID are supported by LISP, see [RFC8060] for 459 further information. 461 o LISP routers mostly deal with Routing Locator addresses. See 462 details in Section 4.1 to clarify what is meant by "mostly". 464 o RLOCs are always IP addresses assigned to routers, preferably 465 topologically oriented addresses from provider CIDR (Classless 466 Inter-Domain Routing) blocks. 468 o When a router originates packets, it may use as a source address 469 either an EID or RLOC. When acting as a host (e.g., when 470 terminating a transport session such as Secure SHell (SSH), 471 TELNET, or the Simple Network Management Protocol (SNMP)), it may 472 use an EID that is explicitly assigned for that purpose. An EID 473 that identifies the router as a host MUST NOT be used as an RLOC; 474 an EID is only routable within the scope of a site. A typical BGP 475 configuration might demonstrate this "hybrid" EID/RLOC usage where 476 a router could use its "host-like" EID to terminate iBGP sessions 477 to other routers in a site while at the same time using RLOCs to 478 terminate eBGP sessions to routers outside the site. 480 o Packets with EIDs in them are not expected to be delivered end-to- 481 end in the absence of an EID-to-RLOC mapping operation. They are 482 expected to be used locally for intra-site communication or to be 483 encapsulated for inter-site communication. 485 o EID-Prefixes are likely to be hierarchically assigned in a manner 486 that is optimized for administrative convenience and to facilitate 487 scaling of the EID-to-RLOC mapping database. The hierarchy is 488 based on an address allocation hierarchy that is independent of 489 the network topology. 491 o EIDs may also be structured (subnetted) in a manner suitable for 492 local routing within an Autonomous System (AS). 494 An additional LISP header MAY be prepended to packets by a TE-ITR 495 when re-routing of the path for a packet is desired. A potential 496 use-case for this would be an ISP router that needs to perform 497 Traffic Engineering for packets flowing through its network. In such 498 a situation, termed "Recursive Tunneling", an ISP transit acts as an 499 additional ITR, and the RLOC it uses for the new prepended header 500 would be either a TE-ETR within the ISP (along an intra-ISP traffic 501 engineered path) or a TE-ETR within another ISP (an inter-ISP traffic 502 engineered path, where an agreement to build such a path exists). 504 In order to avoid excessive packet overhead as well as possible 505 encapsulation loops, this document mandates that a maximum of two 506 LISP headers can be prepended to a packet. For initial LISP 507 deployments, it is assumed that two headers is sufficient, where the 508 first prepended header is used at a site for Location/Identity 509 separation and the second prepended header is used inside a service 510 provider for Traffic Engineering purposes. 512 Tunnel Routers can be placed fairly flexibly in a multi-AS topology. 513 For example, the ITR for a particular end-to-end packet exchange 514 might be the first-hop or default router within a site for the source 515 host. Similarly, the ETR might be the last-hop router directly 516 connected to the destination host. Another example, perhaps for a 517 VPN service outsourced to an ISP by a site, the ITR could be the 518 site's border router at the service provider attachment point. 519 Mixing and matching of site-operated, ISP-operated, and other Tunnel 520 Routers is allowed for maximum flexibility. 522 4.1. Packet Flow Sequence 524 This section provides an example of the unicast packet flow, 525 including also control-plane information as specified in 526 [I-D.ietf-lisp-rfc6833bis]. The example also assumes the following 527 conditions: 529 o Source host "host1.abc.example.com" is sending a packet to 530 "host2.xyz.example.com", exactly what host1 would do if the site 531 was not using LISP. 533 o Each site is multihomed, so each Tunnel Router has an address 534 (RLOC) assigned from the service provider address block for each 535 provider to which that particular Tunnel Router is attached. 537 o The ITR(s) and ETR(s) are directly connected to the source and 538 destination, respectively, but the source and destination can be 539 located anywhere in the LISP site. 541 o Map-Requests are sent to the mapping database system by using the 542 LISP control-plane protocol documented in 543 [I-D.ietf-lisp-rfc6833bis]. A Map-Request is sent for an external 544 destination when the destination is not found in the forwarding 545 table or matches a default route. 547 o Map-Replies are sent on the underlying routing system topology 548 using the [I-D.ietf-lisp-rfc6833bis] control-plane protocol. 550 Client host1.abc.example.com wants to communicate with server 551 host2.xyz.example.com: 553 1. host1.abc.example.com wants to open a TCP connection to 554 host2.xyz.example.com. It does a DNS lookup on 555 host2.xyz.example.com. An A/AAAA record is returned. This 556 address is the destination EID. The locally assigned address of 557 host1.abc.example.com is used as the source EID. An IPv4 or IPv6 558 packet is built and forwarded through the LISP site as a normal 559 IP packet until it reaches a LISP ITR. 561 2. The LISP ITR must be able to map the destination EID to an RLOC 562 of one of the ETRs at the destination site. The specific method 563 used to do this is not described in this example. See 564 [I-D.ietf-lisp-rfc6833bis] for further information. 566 3. The ITR sends a LISP Map-Request as specified in 567 [I-D.ietf-lisp-rfc6833bis]. Map-Requests SHOULD be rate-limited. 569 4. The mapping system helps forwarding the Map-Request to the 570 corresponding ETR. When the Map-Request arrives at one of the 571 ETRs at the destination site, it will process the packet as a 572 control message. 574 5. The ETR looks at the destination EID of the Map-Request and 575 matches it against the prefixes in the ETR's configured EID-to- 576 RLOC mapping database. This is the list of EID-Prefixes the ETR 577 is supporting for the site it resides in. If there is no match, 578 the Map-Request is dropped. Otherwise, a LISP Map-Reply is 579 returned to the ITR. 581 6. The ITR receives the Map-Reply message, parses the message (to 582 check for format validity), and stores the mapping information 583 from the packet. This information is stored in the ITR's EID-to- 584 RLOC map-cache. Note that the map-cache is an on-demand cache. 585 An ITR will manage its map-cache in such a way that optimizes for 586 its resource constraints. 588 7. Subsequent packets from host1.abc.example.com to 589 host2.xyz.example.com will have a LISP header prepended by the 590 ITR using the appropriate RLOC as the LISP header destination 591 address learned from the ETR. Note that the packet MAY be sent 592 to a different ETR than the one that returned the Map-Reply due 593 to the source site's hashing policy or the destination site's 594 Locator-Set policy. 596 8. The ETR receives these packets directly (since the destination 597 address is one of its assigned IP addresses), checks the validity 598 of the addresses, strips the LISP header, and forwards packets to 599 the attached destination host. 601 9. In order to defer the need for a mapping lookup in the reverse 602 direction, an ETR can OPTIONALLY create a cache entry that maps 603 the source EID (inner-header source IP address) to the source 604 RLOC (outer-header source IP address) in a received LISP packet. 605 Such a cache entry is termed a "gleaned" mapping and only 606 contains a single RLOC for the EID in question. More complete 607 information about additional RLOCs SHOULD be verified by sending 608 a LISP Map-Request for that EID. Both the ITR and the ETR may 609 also influence the decision the other makes in selecting an RLOC. 611 5. LISP Encapsulation Details 613 Since additional tunnel headers are prepended, the packet becomes 614 larger and can exceed the MTU of any link traversed from the ITR to 615 the ETR. It is RECOMMENDED in IPv4 that packets do not get 616 fragmented as they are encapsulated by the ITR. Instead, the packet 617 is dropped and an ICMP Unreachable/Fragmentation-Needed message is 618 returned to the source. 620 This specification RECOMMENDS that implementations provide support 621 for one of the proposed fragmentation and reassembly schemes. Two 622 existing schemes are detailed in Section 7. 624 Since IPv4 or IPv6 addresses can be either EIDs or RLOCs, the LISP 625 architecture supports IPv4 EIDs with IPv6 RLOCs (where the inner 626 header is in IPv4 packet format and the outer header is in IPv6 627 packet format) or IPv6 EIDs with IPv4 RLOCs (where the inner header 628 is in IPv6 packet format and the outer header is in IPv4 packet 629 format). The next sub-sections illustrate packet formats for the 630 homogeneous case (IPv4-in-IPv4 and IPv6-in-IPv6), but all 4 631 combinations MUST be supported. Additional types of EIDs are defined 632 in [RFC8060]. 634 5.1. LISP IPv4-in-IPv4 Header Format 636 0 1 2 3 637 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 638 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 639 / |Version| IHL |Type of Service| Total Length | 640 / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 641 | | Identification |Flags| Fragment Offset | 642 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 643 OH | Time to Live | Protocol = 17 | Header Checksum | 644 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 645 | | Source Routing Locator | 646 \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 647 \ | Destination Routing Locator | 648 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 649 / | Source Port = xxxx | Dest Port = 4341 | 650 UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 651 \ | UDP Length | UDP Checksum | 652 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 653 L |N|L|E|V|I|R|K|K| Nonce/Map-Version | 654 I \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 655 S / | Instance ID/Locator-Status-Bits | 656 P +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 657 / |Version| IHL |Type of Service| Total Length | 658 / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 659 | | Identification |Flags| Fragment Offset | 660 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 661 IH | Time to Live | Protocol | Header Checksum | 662 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 663 | | Source EID | 664 \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 665 \ | Destination EID | 666 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 668 IHL = IP-Header-Length 670 5.2. LISP IPv6-in-IPv6 Header Format 672 0 1 2 3 673 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 674 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 675 / |Version| Traffic Class | Flow Label | 676 / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 677 | | Payload Length | Next Header=17| Hop Limit | 678 v +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 679 | | 680 O + + 681 u | | 682 t + Source Routing Locator + 683 e | | 684 r + + 685 | | 686 H +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 687 d | | 688 r + + 689 | | 690 ^ + Destination Routing Locator + 691 | | | 692 \ + + 693 \ | | 694 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 695 / | Source Port = xxxx | Dest Port = 4341 | 696 UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 697 \ | UDP Length | UDP Checksum | 698 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 699 L |N|L|E|V|I|R|K|K| Nonce/Map-Version | 700 I \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 701 S / | Instance ID/Locator-Status-Bits | 702 P +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 703 / |Version| Traffic Class | Flow Label | 704 / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 705 / | Payload Length | Next Header | Hop Limit | 706 v +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 707 | | 708 I + + 709 n | | 710 n + Source EID + 711 e | | 712 r + + 713 | | 714 H +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 715 d | | 716 r + + 717 | | 719 ^ + Destination EID + 720 \ | | 721 \ + + 722 \ | | 723 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 725 5.3. Tunnel Header Field Descriptions 727 Inner Header (IH): The inner header is the header on the datagram 728 received from the originating host. The source and destination IP 729 addresses are EIDs [RFC0791] [RFC2460]. 731 Outer Header: (OH) The outer header is a new header prepended by an 732 ITR. The address fields contain RLOCs obtained from the ingress 733 router's EID-to-RLOC Cache. The IP protocol number is "UDP (17)" 734 from [RFC0768]. The setting of the Don't Fragment (DF) bit 735 'Flags' field is according to rules listed in Sections 7.1 and 736 7.2. 738 UDP Header: The UDP header contains an ITR selected source port when 739 encapsulating a packet. See Section 12 for details on the hash 740 algorithm used to select a source port based on the 5-tuple of the 741 inner header. The destination port MUST be set to the well-known 742 IANA-assigned port value 4341. 744 UDP Checksum: The 'UDP Checksum' field SHOULD be transmitted as zero 745 by an ITR for either IPv4 [RFC0768] or IPv6 encapsulation 746 [RFC6935] [RFC6936]. When a packet with a zero UDP checksum is 747 received by an ETR, the ETR MUST accept the packet for 748 decapsulation. When an ITR transmits a non-zero value for the UDP 749 checksum, it MUST send a correctly computed value in this field. 750 When an ETR receives a packet with a non-zero UDP checksum, it MAY 751 choose to verify the checksum value. If it chooses to perform 752 such verification, and the verification fails, the packet MUST be 753 silently dropped. If the ETR chooses not to perform the 754 verification, or performs the verification successfully, the 755 packet MUST be accepted for decapsulation. The handling of UDP 756 checksums for all tunneling protocols, including LISP, is under 757 active discussion within the IETF. When that discussion 758 concludes, any necessary changes will be made to align LISP with 759 the outcome of the broader discussion. 761 UDP Length: The 'UDP Length' field is set for an IPv4-encapsulated 762 packet to be the sum of the inner-header IPv4 Total Length plus 763 the UDP and LISP header lengths. For an IPv6-encapsulated packet, 764 the 'UDP Length' field is the sum of the inner-header IPv6 Payload 765 Length, the size of the IPv6 header (40 octets), and the size of 766 the UDP and LISP headers. 768 N: The N-bit is the nonce-present bit. When this bit is set to 1, 769 the low-order 24 bits of the first 32 bits of the LISP header 770 contain a Nonce. See Section 10.1 for details. Both N- and 771 V-bits MUST NOT be set in the same packet. If they are, a 772 decapsulating ETR MUST treat the 'Nonce/Map-Version' field as 773 having a Nonce value present. 775 L: The L-bit is the 'Locator-Status-Bits' field enabled bit. When 776 this bit is set to 1, the Locator-Status-Bits in the second 777 32 bits of the LISP header are in use. 779 x 1 x x 0 x x x 780 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 781 |N|L|E|V|I|R|K|K| Nonce/Map-Version | 782 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 783 | Locator-Status-Bits | 784 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 786 E: The E-bit is the echo-nonce-request bit. This bit MUST be ignored 787 and has no meaning when the N-bit is set to 0. When the N-bit is 788 set to 1 and this bit is set to 1, an ITR is requesting that the 789 nonce value in the 'Nonce' field be echoed back in LISP- 790 encapsulated packets when the ITR is also an ETR. See 791 Section 10.1 for details. 793 V: The V-bit is the Map-Version present bit. When this bit is set to 794 1, the N-bit MUST be 0. Refer to Section 13.3 for more details. 795 This bit indicates that the LISP header is encoded in this 796 case as: 798 0 x 0 1 x x x x 799 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 800 |N|L|E|V|I|R|K|K| Source Map-Version | Dest Map-Version | 801 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 802 | Instance ID/Locator-Status-Bits | 803 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 805 I: The I-bit is the Instance ID bit. See Section 8 for more details. 806 When this bit is set to 1, the 'Locator-Status-Bits' field is 807 reduced to 8 bits and the high-order 24 bits are used as an 808 Instance ID. If the L-bit is set to 0, then the low-order 8 bits 809 are transmitted as zero and ignored on receipt. The format of the 810 LISP header would look like this: 812 x x x x 1 x x x 813 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 814 |N|L|E|V|I|R|K|K| Nonce/Map-Version | 815 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 816 | Instance ID | LSBs | 817 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 819 R: The R-bit is a Reserved bit for future use. It MUST be set to 0 820 on transmit and MUST be ignored on receipt. 822 KK: The KK-bits are a 2-bit field used when encapsualted packets are 823 encrypted. The field is set to 00 when the packet is not 824 encrypted. See [RFC8061] for further information. 826 LISP Nonce: The LISP 'Nonce' field is a 24-bit value that is 827 randomly generated by an ITR when the N-bit is set to 1. Nonce 828 generation algorithms are an implementation matter but are 829 required to generate different nonces when sending to different 830 destinations. However, the same nonce can be used for a period of 831 time to the same destination. The nonce is also used when the 832 E-bit is set to request the nonce value to be echoed by the other 833 side when packets are returned. When the E-bit is clear but the 834 N-bit is set, a remote ITR is either echoing a previously 835 requested echo-nonce or providing a random nonce. See 836 Section 10.1 for more details. 838 LISP Locator-Status-Bits (LSBs): When the L-bit is also set, the 839 'Locator-Status-Bits' field in the LISP header is set by an ITR to 840 indicate to an ETR the up/down status of the Locators in the 841 source site. Each RLOC in a Map-Reply is assigned an ordinal 842 value from 0 to n-1 (when there are n RLOCs in a mapping entry). 843 The Locator-Status-Bits are numbered from 0 to n-1 from the least 844 significant bit of the field. The field is 32 bits when the I-bit 845 is set to 0 and is 8 bits when the I-bit is set to 1. When a 846 Locator-Status-Bit is set to 1, the ITR is indicating to the ETR 847 that the RLOC associated with the bit ordinal has up status. See 848 Section 10 for details on how an ITR can determine the status of 849 the ETRs at the same site. When a site has multiple EID-Prefixes 850 that result in multiple mappings (where each could have a 851 different Locator-Set), the Locator-Status-Bits setting in an 852 encapsulated packet MUST reflect the mapping for the EID-Prefix 853 that the inner-header source EID address matches. If the LSB for 854 an anycast Locator is set to 1, then there is at least one RLOC 855 with that address, and the ETR is considered 'up'. 857 When doing ITR/PITR encapsulation: 859 o The outer-header 'Time to Live' field (or 'Hop Limit' field, in 860 the case of IPv6) SHOULD be copied from the inner-header 'Time to 861 Live' field. 863 o The outer-header 'Type of Service' field (or the 'Traffic Class' 864 field, in the case of IPv6) SHOULD be copied from the inner-header 865 'Type of Service' field (with one exception; see below). 867 When doing ETR/PETR decapsulation: 869 o The inner-header 'Time to Live' field (or 'Hop Limit' field, in 870 the case of IPv6) SHOULD be copied from the outer-header 'Time to 871 Live' field, when the Time to Live value of the outer header is 872 less than the Time to Live value of the inner header. Failing to 873 perform this check can cause the Time to Live of the inner header 874 to increment across encapsulation/decapsulation cycles. This 875 check is also performed when doing initial encapsulation, when a 876 packet comes to an ITR or PITR destined for a LISP site. 878 o The inner-header 'Type of Service' field (or the 'Traffic Class' 879 field, in the case of IPv6) SHOULD be copied from the outer-header 880 'Type of Service' field (with one exception; see below). 882 Note that if an ETR/PETR is also an ITR/PITR and chooses to re- 883 encapsulate after decapsulating, the net effect of this is that the 884 new outer header will carry the same Time to Live as the old outer 885 header minus 1. 887 Copying the Time to Live (TTL) serves two purposes: first, it 888 preserves the distance the host intended the packet to travel; 889 second, and more importantly, it provides for suppression of looping 890 packets in the event there is a loop of concatenated tunnels due to 891 misconfiguration. See Section 18.3 for TTL exception handling for 892 traceroute packets. 894 The Explicit Congestion Notification ('ECN') field occupies bits 6 895 and 7 of both the IPv4 'Type of Service' field and the IPv6 'Traffic 896 Class' field [RFC3168]. The 'ECN' field requires special treatment 897 in order to avoid discarding indications of congestion [RFC3168]. 898 ITR encapsulation MUST copy the 2-bit 'ECN' field from the inner 899 header to the outer header. Re-encapsulation MUST copy the 2-bit 900 'ECN' field from the stripped outer header to the new outer header. 901 If the 'ECN' field contains a congestion indication codepoint (the 902 value is '11', the Congestion Experienced (CE) codepoint), then ETR 903 decapsulation MUST copy the 2-bit 'ECN' field from the stripped outer 904 header to the surviving inner header that is used to forward the 905 packet beyond the ETR. These requirements preserve CE indications 906 when a packet that uses ECN traverses a LISP tunnel and becomes 907 marked with a CE indication due to congestion between the tunnel 908 endpoints. 910 6. LISP EID-to-RLOC Map-Cache 912 ITRs and PITRs maintain an on-demand cache, referred as LISP EID-to- 913 RLOC Map-Cache, that contains mappings from EID-prefixes to locator 914 sets. The cache is used to encapsulate packets from the EID space to 915 the corresponding RLOC network attachment point. 917 When an ITR/PITR receives a packet from inside of the LISP site to 918 destinations outside of the site a longest-prefix match lookup of the 919 EID is done to the map-cache. 921 When the lookup succeeds, the locator-set retrieved from the map- 922 cache is used to send the packet to the EID's topological location. 924 If the lookup fails, the ITR/PITR needs to retrieve the mapping using 925 the LISP control-plane protocol [I-D.ietf-lisp-rfc6833bis]. The 926 mapping is then stored in the local map-cache to forward subsequent 927 packets addressed to the same EID-prefix. 929 The map-cache is a local cache of mappings, entries are expired based 930 on the associated Time to live. In addition, entries can be updated 931 with more current information, see Section 13 for further information 932 on this. Finally, the map-cache also contains reachability 933 information about EIDs and RLOCs, and uses LISP reachability 934 information mechanisms to determine the reachability of RLOCs, see 935 Section 10 for the specific mechanisms. 937 7. Dealing with Large Encapsulated Packets 939 This section proposes two mechanisms to deal with packets that exceed 940 the path MTU between the ITR and ETR. 942 It is left to the implementor to decide if the stateless or stateful 943 mechanism should be implemented. Both or neither can be used, since 944 it is a local decision in the ITR regarding how to deal with MTU 945 issues, and sites can interoperate with differing mechanisms. 947 Both stateless and stateful mechanisms also apply to Re-encapsulating 948 and Recursive Tunneling, so any actions below referring to an ITR 949 also apply to a TE-ITR. 951 7.1. A Stateless Solution to MTU Handling 953 An ITR stateless solution to handle MTU issues is described as 954 follows: 956 1. Define H to be the size, in octets, of the outer header an ITR 957 prepends to a packet. This includes the UDP and LISP header 958 lengths. 960 2. Define L to be the size, in octets, of the maximum-sized packet 961 an ITR can send to an ETR without the need for the ITR or any 962 intermediate routers to fragment the packet. 964 3. Define an architectural constant S for the maximum size of a 965 packet, in octets, an ITR must receive from the source so the 966 effective MTU can be met. That is, L = S + H. 968 When an ITR receives a packet from a site-facing interface and adds H 969 octets worth of encapsulation to yield a packet size greater than L 970 octets (meaning the received packet size was greater than S octets 971 from the source), it resolves the MTU issue by first splitting the 972 original packet into 2 equal-sized fragments. A LISP header is then 973 prepended to each fragment. The size of the encapsulated fragments 974 is then (S/2 + H), which is less than the ITR's estimate of the path 975 MTU between the ITR and its correspondent ETR. 977 When an ETR receives encapsulated fragments, it treats them as two 978 individually encapsulated packets. It strips the LISP headers and 979 then forwards each fragment to the destination host of the 980 destination site. The two fragments are reassembled at the 981 destination host into the single IP datagram that was originated by 982 the source host. Note that reassembly can happen at the ETR if the 983 encapsulated packet was fragmented at or after the ITR. 985 This behavior is performed by the ITR when the source host originates 986 a packet with the 'DF' field of the IP header set to 0. When the 987 'DF' field of the IP header is set to 1, or the packet is an IPv6 988 packet originated by the source host, the ITR will drop the packet 989 when the size is greater than L and send an ICMP Unreachable/ 990 Fragmentation-Needed message to the source with a value of S, where S 991 is (L - H). 993 When the outer-header encapsulation uses an IPv4 header, an 994 implementation SHOULD set the DF bit to 1 so ETR fragment reassembly 995 can be avoided. An implementation MAY set the DF bit in such headers 996 to 0 if it has good reason to believe there are unresolvable path MTU 997 issues between the sending ITR and the receiving ETR. 999 This specification RECOMMENDS that L be defined as 1500. 1001 7.2. A Stateful Solution to MTU Handling 1003 An ITR stateful solution to handle MTU issues is described as follows 1004 and was first introduced in [OPENLISP]: 1006 1. The ITR will keep state of the effective MTU for each Locator per 1007 Map-Cache entry. The effective MTU is what the core network can 1008 deliver along the path between the ITR and ETR. 1010 2. When an IPv6-encapsulated packet, or an IPv4-encapsulated packet 1011 with the DF bit set to 1, exceeds what the core network can 1012 deliver, one of the intermediate routers on the path will send an 1013 ICMP Unreachable/Fragmentation-Needed message to the ITR. The 1014 ITR will parse the ICMP message to determine which Locator is 1015 affected by the effective MTU change and then record the new 1016 effective MTU value in the Map-Cache entry. 1018 3. When a packet is received by the ITR from a source inside of the 1019 site and the size of the packet is greater than the effective MTU 1020 stored with the Map-Cache entry associated with the destination 1021 EID the packet is for, the ITR will send an ICMP Unreachable/ 1022 Fragmentation-Needed message back to the source. The packet size 1023 advertised by the ITR in the ICMP Unreachable/Fragmentation- 1024 Needed message is the effective MTU minus the LISP encapsulation 1025 length. 1027 Even though this mechanism is stateful, it has advantages over the 1028 stateless IP fragmentation mechanism, by not involving the 1029 destination host with reassembly of ITR fragmented packets. 1031 8. Using Virtualization and Segmentation with LISP 1033 When multiple organizations inside of a LISP site are using private 1034 addresses [RFC1918] as EID-Prefixes, their address spaces MUST remain 1035 segregated due to possible address duplication. An Instance ID in 1036 the address encoding can aid in making the entire AFI-based address 1037 unique. See IANA Considerations (Section 21.2) for details on 1038 possible address encodings. 1040 An Instance ID can be carried in a LISP-encapsulated packet. An ITR 1041 that prepends a LISP header will copy a 24-bit value used by the LISP 1042 router to uniquely identify the address space. The value is copied 1043 to the 'Instance ID' field of the LISP header, and the I-bit is set 1044 to 1. 1046 When an ETR decapsulates a packet, the Instance ID from the LISP 1047 header is used as a table identifier to locate the forwarding table 1048 to use for the inner destination EID lookup. 1050 For example, an 802.1Q VLAN tag or VPN identifier could be used as a 1051 24-bit Instance ID. 1053 The Instance ID that is stored in the mapping database when LISP-DDT 1054 [I-D.ietf-lisp-ddt] is used is 32 bits in length. That means the 1055 control-plane can store more instances than a given data-plane can 1056 use. Multiple data-planes can use the same 32-bit space as long as 1057 the low-order 24 bits don't overlap among xTRs. 1059 9. Routing Locator Selection 1061 Both the client-side and server-side may need control over the 1062 selection of RLOCs for conversations between them. This control is 1063 achieved by manipulating the 'Priority' and 'Weight' fields in EID- 1064 to-RLOC Map-Reply messages. Alternatively, RLOC information MAY be 1065 gleaned from received tunneled packets or EID-to-RLOC Map-Request 1066 messages. 1068 The following are different scenarios for choosing RLOCs and the 1069 controls that are available: 1071 o The server-side returns one RLOC. The client-side can only use 1072 one RLOC. The server-side has complete control of the selection. 1074 o The server-side returns a list of RLOCs where a subset of the list 1075 has the same best Priority. The client can only use the subset 1076 list according to the weighting assigned by the server-side. In 1077 this case, the server-side controls both the subset list and load- 1078 splitting across its members. The client-side can use RLOCs 1079 outside of the subset list if it determines that the subset list 1080 is unreachable (unless RLOCs are set to a Priority of 255). Some 1081 sharing of control exists: the server-side determines the 1082 destination RLOC list and load distribution while the client-side 1083 has the option of using alternatives to this list if RLOCs in the 1084 list are unreachable. 1086 o The server-side sets a Weight of 0 for the RLOC subset list. In 1087 this case, the client-side can choose how the traffic load is 1088 spread across the subset list. Control is shared by the server- 1089 side determining the list and the client determining load 1090 distribution. Again, the client can use alternative RLOCs if the 1091 server-provided list of RLOCs is unreachable. 1093 o Either side (more likely the server-side ETR) decides not to send 1094 a Map-Request. For example, if the server-side ETR does not send 1095 Map-Requests, it gleans RLOCs from the client-side ITR, giving the 1096 client-side ITR responsibility for bidirectional RLOC reachability 1097 and preferability. Server-side ETR gleaning of the client-side 1098 ITR RLOC is done by caching the inner-header source EID and the 1099 outer-header source RLOC of received packets. The client-side ITR 1100 controls how traffic is returned and can alternate using an outer- 1101 header source RLOC, which then can be added to the list the 1102 server-side ETR uses to return traffic. Since no Priority or 1103 Weights are provided using this method, the server-side ETR MUST 1104 assume that each client-side ITR RLOC uses the same best Priority 1105 with a Weight of zero. In addition, since EID-Prefix encoding 1106 cannot be conveyed in data packets, the EID-to-RLOC Cache on 1107 Tunnel Routers can grow to be very large. 1109 o A "gleaned" Map-Cache entry, one learned from the source RLOC of a 1110 received encapsulated packet, is only stored and used for a few 1111 seconds, pending verification. Verification is performed by 1112 sending a Map-Request to the source EID (the inner-header IP 1113 source address) of the received encapsulated packet. A reply to 1114 this "verifying Map-Request" is used to fully populate the Map- 1115 Cache entry for the "gleaned" EID and is stored and used for the 1116 time indicated from the 'TTL' field of a received Map-Reply. When 1117 a verified Map-Cache entry is stored, data gleaning no longer 1118 occurs for subsequent packets that have a source EID that matches 1119 the EID-Prefix of the verified entry. This "gleaning" mechanism 1120 is OPTIONAL. 1122 RLOCs that appear in EID-to-RLOC Map-Reply messages are assumed to be 1123 reachable when the R-bit for the Locator record is set to 1. When 1124 the R-bit is set to 0, an ITR or PITR MUST NOT encapsulate to the 1125 RLOC. Neither the information contained in a Map-Reply nor that 1126 stored in the mapping database system provides reachability 1127 information for RLOCs. Note that reachability is not part of the 1128 mapping system and is determined using one or more of the Routing 1129 Locator reachability algorithms described in the next section. 1131 10. Routing Locator Reachability 1133 Several mechanisms for determining RLOC reachability are currently 1134 defined: 1136 1. An ETR may examine the Locator-Status-Bits in the LISP header of 1137 an encapsulated data packet received from an ITR. If the ETR is 1138 also acting as an ITR and has traffic to return to the original 1139 ITR site, it can use this status information to help select an 1140 RLOC. 1142 2. An ITR may receive an ICMP Network Unreachable or Host 1143 Unreachable message for an RLOC it is using. This indicates that 1144 the RLOC is likely down. Note that trusting ICMP messages may 1145 not be desirable, but neither is ignoring them completely. 1146 Implementations are encouraged to follow current best practices 1147 in treating these conditions. 1149 3. An ITR that participates in the global routing system can 1150 determine that an RLOC is down if no BGP Routing Information Base 1151 (RIB) route exists that matches the RLOC IP address. 1153 4. An ITR may receive an ICMP Port Unreachable message from a 1154 destination host. This occurs if an ITR attempts to use 1155 interworking [RFC6832] and LISP-encapsulated data is sent to a 1156 non-LISP-capable site. 1158 5. An ITR may receive a Map-Reply from an ETR in response to a 1159 previously sent Map-Request. The RLOC source of the Map-Reply is 1160 likely up, since the ETR was able to send the Map-Reply to the 1161 ITR. 1163 6. When an ETR receives an encapsulated packet from an ITR, the 1164 source RLOC from the outer header of the packet is likely up. 1166 7. An ITR/ETR pair can use the Locator reachability algorithms 1167 described in this section, namely Echo-Noncing or RLOC-Probing. 1169 When determining Locator up/down reachability by examining the 1170 Locator-Status-Bits from the LISP-encapsulated data packet, an ETR 1171 will receive up-to-date status from an encapsulating ITR about 1172 reachability for all ETRs at the site. CE-based ITRs at the source 1173 site can determine reachability relative to each other using the site 1174 IGP as follows: 1176 o Under normal circumstances, each ITR will advertise a default 1177 route into the site IGP. 1179 o If an ITR fails or if the upstream link to its PE fails, its 1180 default route will either time out or be withdrawn. 1182 Each ITR can thus observe the presence or lack of a default route 1183 originated by the others to determine the Locator-Status-Bits it sets 1184 for them. 1186 RLOCs listed in a Map-Reply are numbered with ordinals 0 to n-1. The 1187 Locator-Status-Bits in a LISP-encapsulated packet are numbered from 0 1188 to n-1 starting with the least significant bit. For example, if an 1189 RLOC listed in the 3rd position of the Map-Reply goes down (ordinal 1190 value 2), then all ITRs at the site will clear the 3rd least 1191 significant bit (xxxx x0xx) of the 'Locator-Status-Bits' field for 1192 the packets they encapsulate. 1194 When an ETR decapsulates a packet, it will check for any change in 1195 the 'Locator-Status-Bits' field. When a bit goes from 1 to 0, the 1196 ETR, if acting also as an ITR, will refrain from encapsulating 1197 packets to an RLOC that is indicated as down. It will only resume 1198 using that RLOC if the corresponding Locator-Status-Bit returns to a 1199 value of 1. Locator-Status-Bits are associated with a Locator-Set 1200 per EID-Prefix. Therefore, when a Locator becomes unreachable, the 1201 Locator-Status-Bit that corresponds to that Locator's position in the 1202 list returned by the last Map-Reply will be set to zero for that 1203 particular EID-Prefix. 1205 When ITRs at the site are not deployed in CE routers, the IGP can 1206 still be used to determine the reachability of Locators, provided 1207 they are injected into the IGP. This is typically done when a /32 1208 address is configured on a loopback interface. 1210 When ITRs receive ICMP Network Unreachable or Host Unreachable 1211 messages as a method to determine unreachability, they will refrain 1212 from using Locators that are described in Locator lists of Map- 1213 Replies. However, using this approach is unreliable because many 1214 network operators turn off generation of ICMP Destination Unreachable 1215 messages. 1217 If an ITR does receive an ICMP Network Unreachable or Host 1218 Unreachable message, it MAY originate its own ICMP Destination 1219 Unreachable message destined for the host that originated the data 1220 packet the ITR encapsulated. 1222 Also, BGP-enabled ITRs can unilaterally examine the RIB to see if a 1223 locator address from a Locator-Set in a mapping entry matches a 1224 prefix. If it does not find one and BGP is running in the Default- 1225 Free Zone (DFZ), it can decide to not use the Locator even though the 1226 Locator-Status-Bits indicate that the Locator is up. In this case, 1227 the path from the ITR to the ETR that is assigned the Locator is not 1228 available. More details are in [I-D.meyer-loc-id-implications]. 1230 Optionally, an ITR can send a Map-Request to a Locator, and if a Map- 1231 Reply is returned, reachability of the Locator has been determined. 1232 Obviously, sending such probes increases the number of control 1233 messages originated by Tunnel Routers for active flows, so Locators 1234 are assumed to be reachable when they are advertised. 1236 This assumption does create a dependency: Locator unreachability is 1237 detected by the receipt of ICMP Host Unreachable messages. When a 1238 Locator has been determined to be unreachable, it is not used for 1239 active traffic; this is the same as if it were listed in a Map-Reply 1240 with Priority 255. 1242 The ITR can test the reachability of the unreachable Locator by 1243 sending periodic Requests. Both Requests and Replies MUST be rate- 1244 limited. Locator reachability testing is never done with data 1245 packets, since that increases the risk of packet loss for end-to-end 1246 sessions. 1248 When an ETR decapsulates a packet, it knows that it is reachable from 1249 the encapsulating ITR because that is how the packet arrived. In 1250 most cases, the ETR can also reach the ITR but cannot assume this to 1251 be true, due to the possibility of path asymmetry. In the presence 1252 of unidirectional traffic flow from an ITR to an ETR, the ITR SHOULD 1253 NOT use the lack of return traffic as an indication that the ETR is 1254 unreachable. Instead, it MUST use an alternate mechanism to 1255 determine reachability. 1257 10.1. Echo Nonce Algorithm 1259 When data flows bidirectionally between Locators from different 1260 sites, a data-plane mechanism called "nonce echoing" can be used to 1261 determine reachability between an ITR and ETR. When an ITR wants to 1262 solicit a nonce echo, it sets the N- and E-bits and places a 24-bit 1263 nonce [RFC4086] in the LISP header of the next encapsulated data 1264 packet. 1266 When this packet is received by the ETR, the encapsulated packet is 1267 forwarded as normal. When the ETR next sends a data packet to the 1268 ITR, it includes the nonce received earlier with the N-bit set and 1269 E-bit cleared. The ITR sees this "echoed nonce" and knows that the 1270 path to and from the ETR is up. 1272 The ITR will set the E-bit and N-bit for every packet it sends while 1273 in the echo-nonce-request state. The time the ITR waits to process 1274 the echoed nonce before it determines the path is unreachable is 1275 variable and is a choice left for the implementation. 1277 If the ITR is receiving packets from the ETR but does not see the 1278 nonce echoed while being in the echo-nonce-request state, then the 1279 path to the ETR is unreachable. This decision may be overridden by 1280 other Locator reachability algorithms. Once the ITR determines that 1281 the path to the ETR is down, it can switch to another Locator for 1282 that EID-Prefix. 1284 Note that "ITR" and "ETR" are relative terms here. Both devices MUST 1285 be implementing both ITR and ETR functionality for the echo nonce 1286 mechanism to operate. 1288 The ITR and ETR may both go into the echo-nonce-request state at the 1289 same time. The number of packets sent or the time during which echo 1290 nonce requests are sent is an implementation-specific setting. 1291 However, when an ITR is in the echo-nonce-request state, it can echo 1292 the ETR's nonce in the next set of packets that it encapsulates and 1293 subsequently continue sending echo-nonce-request packets. 1295 This mechanism does not completely solve the forward path 1296 reachability problem, as traffic may be unidirectional. That is, the 1297 ETR receiving traffic at a site may not be the same device as an ITR 1298 that transmits traffic from that site, or the site-to-site traffic is 1299 unidirectional so there is no ITR returning traffic. 1301 The echo-nonce algorithm is bilateral. That is, if one side sets the 1302 E-bit and the other side is not enabled for echo-noncing, then the 1303 echoing of the nonce does not occur and the requesting side may 1304 erroneously consider the Locator unreachable. An ITR SHOULD only set 1305 the E-bit in an encapsulated data packet when it knows the ETR is 1306 enabled for echo-noncing. This is conveyed by the E-bit in the Map- 1307 Reply message. 1309 Note that other Locator reachability mechanisms are being researched 1310 and can be used to compliment or even override the echo nonce 1311 algorithm. See the next section for an example of control-plane 1312 probing. 1314 10.2. RLOC-Probing Algorithm 1316 RLOC-Probing is a method that an ITR or PITR can use to determine the 1317 reachability status of one or more Locators that it has cached in a 1318 Map-Cache entry. The probe-bit of the Map-Request and Map-Reply 1319 messages is used for RLOC-Probing. 1321 RLOC-Probing is done in the control plane on a timer basis, where an 1322 ITR or PITR will originate a Map-Request destined to a locator 1323 address from one of its own locator addresses. A Map-Request used as 1324 an RLOC-probe is NOT encapsulated and NOT sent to a Map-Server or to 1325 the mapping database system as one would when soliciting mapping 1326 data. The EID record encoded in the Map-Request is the EID-Prefix of 1327 the Map-Cache entry cached by the ITR or PITR. The ITR may include a 1328 mapping data record for its own database mapping information that 1329 contains the local EID-Prefixes and RLOCs for its site. RLOC-probes 1330 are sent periodically using a jittered timer interval. 1332 When an ETR receives a Map-Request message with the probe-bit set, it 1333 returns a Map-Reply with the probe-bit set. The source address of 1334 the Map-Reply is set according to the procedure described in 1335 [I-D.ietf-lisp-rfc6833bis]. The Map-Reply SHOULD contain mapping 1336 data for the EID-Prefix contained in the Map-Request. This provides 1337 the opportunity for the ITR or PITR that sent the RLOC-probe to get 1338 mapping updates if there were changes to the ETR's database mapping 1339 entries. 1341 There are advantages and disadvantages of RLOC-Probing. The greatest 1342 benefit of RLOC-Probing is that it can handle many failure scenarios 1343 allowing the ITR to determine when the path to a specific Locator is 1344 reachable or has become unreachable, thus providing a robust 1345 mechanism for switching to using another Locator from the cached 1346 Locator. RLOC-Probing can also provide rough Round-Trip Time (RTT) 1347 estimates between a pair of Locators, which can be useful for network 1348 management purposes as well as for selecting low delay paths. The 1349 major disadvantage of RLOC-Probing is in the number of control 1350 messages required and the amount of bandwidth used to obtain those 1351 benefits, especially if the requirement for failure detection times 1352 is very small. 1354 Continued research and testing will attempt to characterize the 1355 tradeoffs of failure detection times versus message overhead. 1357 11. EID Reachability within a LISP Site 1359 A site may be multihomed using two or more ETRs. The hosts and 1360 infrastructure within a site will be addressed using one or more EID- 1361 Prefixes that are mapped to the RLOCs of the relevant ETRs in the 1362 mapping system. One possible failure mode is for an ETR to lose 1363 reachability to one or more of the EID-Prefixes within its own site. 1364 When this occurs when the ETR sends Map-Replies, it can clear the 1365 R-bit associated with its own Locator. And when the ETR is also an 1366 ITR, it can clear its Locator-Status-Bit in the encapsulation data 1367 header. 1369 It is recognized that there are no simple solutions to the site 1370 partitioning problem because it is hard to know which part of the 1371 EID-Prefix range is partitioned and which Locators can reach any sub- 1372 ranges of the EID-Prefixes. This problem is under investigation with 1373 the expectation that experiments will tell us more. Note that this 1374 is not a new problem introduced by the LISP architecture. The 1375 problem exists today when a multihomed site uses BGP to advertise its 1376 reachability upstream. 1378 12. Routing Locator Hashing 1380 When an ETR provides an EID-to-RLOC mapping in a Map-Reply message to 1381 a requesting ITR, the Locator-Set for the EID-Prefix may contain 1382 different Priority values for each locator address. When more than 1383 one best Priority Locator exists, the ITR can decide how to load- 1384 share traffic against the corresponding Locators. 1386 The following hash algorithm may be used by an ITR to select a 1387 Locator for a packet destined to an EID for the EID-to-RLOC mapping: 1389 1. Either a source and destination address hash or the traditional 1390 5-tuple hash can be used. The traditional 5-tuple hash includes 1391 the source and destination addresses; source and destination TCP, 1392 UDP, or Stream Control Transmission Protocol (SCTP) port numbers; 1393 and the IP protocol number field or IPv6 next-protocol fields of 1394 a packet that a host originates from within a LISP site. When a 1395 packet is not a TCP, UDP, or SCTP packet, the source and 1396 destination addresses only from the header are used to compute 1397 the hash. 1399 2. Take the hash value and divide it by the number of Locators 1400 stored in the Locator-Set for the EID-to-RLOC mapping. 1402 3. The remainder will yield a value of 0 to "number of Locators 1403 minus 1". Use the remainder to select the Locator in the 1404 Locator-Set. 1406 Note that when a packet is LISP encapsulated, the source port number 1407 in the outer UDP header needs to be set. Selecting a hashed value 1408 allows core routers that are attached to Link Aggregation Groups 1409 (LAGs) to load-split the encapsulated packets across member links of 1410 such LAGs. Otherwise, core routers would see a single flow, since 1411 packets have a source address of the ITR, for packets that are 1412 originated by different EIDs at the source site. A suggested setting 1413 for the source port number computed by an ITR is a 5-tuple hash 1414 function on the inner header, as described above. 1416 Many core router implementations use a 5-tuple hash to decide how to 1417 balance packet load across members of a LAG. The 5-tuple hash 1418 includes the source and destination addresses of the packet and the 1419 source and destination ports when the protocol number in the packet 1420 is TCP or UDP. For this reason, UDP encoding is used for LISP 1421 encapsulation. 1423 13. Changing the Contents of EID-to-RLOC Mappings 1425 Since the LISP architecture uses a caching scheme to retrieve and 1426 store EID-to-RLOC mappings, the only way an ITR can get a more up-to- 1427 date mapping is to re-request the mapping. However, the ITRs do not 1428 know when the mappings change, and the ETRs do not keep track of 1429 which ITRs requested its mappings. For scalability reasons, we want 1430 to maintain this approach but need to provide a way for ETRs to 1431 change their mappings and inform the sites that are currently 1432 communicating with the ETR site using such mappings. 1434 When adding a new Locator record in lexicographic order to the end of 1435 a Locator-Set, it is easy to update mappings. We assume that new 1436 mappings will maintain the same Locator ordering as the old mapping 1437 but will just have new Locators appended to the end of the list. So, 1438 some ITRs can have a new mapping while other ITRs have only an old 1439 mapping that is used until they time out. When an ITR has only an 1440 old mapping but detects bits set in the Locator-Status-Bits that 1441 correspond to Locators beyond the list it has cached, it simply 1442 ignores them. However, this can only happen for locator addresses 1443 that are lexicographically greater than the locator addresses in the 1444 existing Locator-Set. 1446 When a Locator record is inserted in the middle of a Locator-Set, to 1447 maintain lexicographic order, the SMR procedure in Section 13.2 is 1448 used to inform ITRs and PITRs of the new Locator-Status-Bit mappings. 1450 When a Locator record is removed from a Locator-Set, ITRs that have 1451 the mapping cached will not use the removed Locator because the xTRs 1452 will set the Locator-Status-Bit to 0. So, even if the Locator is in 1453 the list, it will not be used. For new mapping requests, the xTRs 1454 can set the Locator AFI to 0 (indicating an unspecified address), as 1455 well as setting the corresponding Locator-Status-Bit to 0. This 1456 forces ITRs with old or new mappings to avoid using the removed 1457 Locator. 1459 If many changes occur to a mapping over a long period of time, one 1460 will find empty record slots in the middle of the Locator-Set and new 1461 records appended to the Locator-Set. At some point, it would be 1462 useful to compact the Locator-Set so the Locator-Status-Bit settings 1463 can be efficiently packed. 1465 We propose here three approaches for Locator-Set compaction: one 1466 operational mechanism and two protocol mechanisms. The operational 1467 approach uses a clock sweep method. The protocol approaches use the 1468 concept of Solicit-Map-Requests and Map-Versioning. 1470 13.1. Clock Sweep 1472 The clock sweep approach uses planning in advance and the use of 1473 count-down TTLs to time out mappings that have already been cached. 1474 The default setting for an EID-to-RLOC mapping TTL is 24 hours. So, 1475 there is a 24-hour window to time out old mappings. The following 1476 clock sweep procedure is used: 1478 1. 24 hours before a mapping change is to take effect, a network 1479 administrator configures the ETRs at a site to start the clock 1480 sweep window. 1482 2. During the clock sweep window, ETRs continue to send Map-Reply 1483 messages with the current (unchanged) mapping records. The TTL 1484 for these mappings is set to 1 hour. 1486 3. 24 hours later, all previous cache entries will have timed out, 1487 and any active cache entries will time out within 1 hour. During 1488 this 1-hour window, the ETRs continue to send Map-Reply messages 1489 with the current (unchanged) mapping records with the TTL set to 1490 1 minute. 1492 4. At the end of the 1-hour window, the ETRs will send Map-Reply 1493 messages with the new (changed) mapping records. So, any active 1494 caches can get the new mapping contents right away if not cached, 1495 or in 1 minute if they had the mapping cached. The new mappings 1496 are cached with a TTL equal to the TTL in the Map-Reply. 1498 13.2. Solicit-Map-Request (SMR) 1500 Soliciting a Map-Request is a selective way for ETRs, at the site 1501 where mappings change, to control the rate they receive requests for 1502 Map-Reply messages. SMRs are also used to tell remote ITRs to update 1503 the mappings they have cached. 1505 Since the ETRs don't keep track of remote ITRs that have cached their 1506 mappings, they do not know which ITRs need to have their mappings 1507 updated. As a result, an ETR will solicit Map-Requests (called an 1508 SMR message) from those sites to which it has been sending 1509 encapsulated data for the last minute. In particular, an ETR will 1510 send an SMR to an ITR to which it has recently sent encapsulated 1511 data. 1513 An SMR message is simply a bit set in a Map-Request message. An ITR 1514 or PITR will send a Map-Request when they receive an SMR message. 1515 Both the SMR sender and the Map-Request responder MUST rate-limit 1516 these messages. Rate-limiting can be implemented as a global rate- 1517 limiter or one rate-limiter per SMR destination. 1519 The following procedure shows how an SMR exchange occurs when a site 1520 is doing Locator-Set compaction for an EID-to-RLOC mapping: 1522 1. When the database mappings in an ETR change, the ETRs at the site 1523 begin to send Map-Requests with the SMR bit set for each Locator 1524 in each Map-Cache entry the ETR caches. 1526 2. A remote ITR that receives the SMR message will schedule sending 1527 a Map-Request message to the source locator address of the SMR 1528 message or to the mapping database system. A newly allocated 1529 random nonce is selected, and the EID-Prefix used is the one 1530 copied from the SMR message. If the source Locator is the only 1531 Locator in the cached Locator-Set, the remote ITR SHOULD send a 1532 Map-Request to the database mapping system just in case the 1533 single Locator has changed and may no longer be reachable to 1534 accept the Map-Request. 1536 3. The remote ITR MUST rate-limit the Map-Request until it gets a 1537 Map-Reply while continuing to use the cached mapping. When 1538 Map-Versioning as described in Section 13.3 is used, an SMR 1539 sender can detect if an ITR is using the most up-to-date database 1540 mapping. 1542 4. The ETRs at the site with the changed mapping will reply to the 1543 Map-Request with a Map-Reply message that has a nonce from the 1544 SMR-invoked Map-Request. The Map-Reply messages SHOULD be rate- 1545 limited. This is important to avoid Map-Reply implosion. 1547 5. The ETRs at the site with the changed mapping record the fact 1548 that the site that sent the Map-Request has received the new 1549 mapping data in the Map-Cache entry for the remote site so the 1550 Locator-Status-Bits are reflective of the new mapping for packets 1551 going to the remote site. The ETR then stops sending SMR 1552 messages. 1554 For security reasons, an ITR MUST NOT process unsolicited Map- 1555 Replies. To avoid Map-Cache entry corruption by a third party, a 1556 sender of an SMR-based Map-Request MUST be verified. If an ITR 1557 receives an SMR-based Map-Request and the source is not in the 1558 Locator-Set for the stored Map-Cache entry, then the responding Map- 1559 Request MUST be sent with an EID destination to the mapping database 1560 system. Since the mapping database system is a more secure way to 1561 reach an authoritative ETR, it will deliver the Map-Request to the 1562 authoritative source of the mapping data. 1564 When an ITR receives an SMR-based Map-Request for which it does not 1565 have a cached mapping for the EID in the SMR message, it MAY not send 1566 an SMR-invoked Map-Request. This scenario can occur when an ETR 1567 sends SMR messages to all Locators in the Locator-Set it has stored 1568 in its map-cache but the remote ITRs that receive the SMR may not be 1569 sending packets to the site. There is no point in updating the ITRs 1570 until they need to send, in which case they will send Map-Requests to 1571 obtain a Map-Cache entry. 1573 13.3. Database Map-Versioning 1575 When there is unidirectional packet flow between an ITR and ETR, and 1576 the EID-to-RLOC mappings change on the ETR, it needs to inform the 1577 ITR so encapsulation to a removed Locator can stop and can instead be 1578 started to a new Locator in the Locator-Set. 1580 An ETR, when it sends Map-Reply messages, conveys its own Map-Version 1581 Number. This is known as the Destination Map-Version Number. ITRs 1582 include the Destination Map-Version Number in packets they 1583 encapsulate to the site. When an ETR decapsulates a packet and 1584 detects that the Destination Map-Version Number is less than the 1585 current version for its mapping, the SMR procedure described in 1586 Section 13.2 occurs. 1588 An ITR, when it encapsulates packets to ETRs, can convey its own Map- 1589 Version Number. This is known as the Source Map-Version Number. 1590 When an ETR decapsulates a packet and detects that the Source Map- 1591 Version Number is greater than the last Map-Version Number sent in a 1592 Map-Reply from the ITR's site, the ETR will send a Map-Request to one 1593 of the ETRs for the source site. 1595 A Map-Version Number is used as a sequence number per EID-Prefix, so 1596 values that are greater are considered to be more recent. A value of 1597 0 for the Source Map-Version Number or the Destination Map-Version 1598 Number conveys no versioning information, and an ITR does no 1599 comparison with previously received Map-Version Numbers. 1601 A Map-Version Number can be included in Map-Register messages as 1602 well. This is a good way for the Map-Server to assure that all ETRs 1603 for a site registering to it will be synchronized according to Map- 1604 Version Number. 1606 See [RFC6834] for a more detailed analysis and description of 1607 Database Map-Versioning. 1609 14. Multicast Considerations 1611 A multicast group address, as defined in the original Internet 1612 architecture, is an identifier of a grouping of topologically 1613 independent receiver host locations. The address encoding itself 1614 does not determine the location of the receiver(s). The multicast 1615 routing protocol, and the network-based state the protocol creates, 1616 determine where the receivers are located. 1618 In the context of LISP, a multicast group address is both an EID and 1619 a Routing Locator. Therefore, no specific semantic or action needs 1620 to be taken for a destination address, as it would appear in an IP 1621 header. Therefore, a group address that appears in an inner IP 1622 header built by a source host will be used as the destination EID. 1623 The outer IP header (the destination Routing Locator address), 1624 prepended by a LISP router, can use the same group address as the 1625 destination Routing Locator, use a multicast or unicast Routing 1626 Locator obtained from a Mapping System lookup, or use other means to 1627 determine the group address mapping. 1629 With respect to the source Routing Locator address, the ITR prepends 1630 its own IP address as the source address of the outer IP header. 1631 Just like it would if the destination EID was a unicast address. 1632 This source Routing Locator address, like any other Routing Locator 1633 address, MUST be globally routable. 1635 There are two approaches for LISP-Multicast, one that uses native 1636 multicast routing in the underlay with no support from the Mapping 1637 System and the other that uses only unicast routing in the underlay 1638 with support from the Mapping System. See [RFC6831] and 1639 [I-D.ietf-lisp-signal-free-multicast], respectively, for details. 1640 Details for LISP-Multicast and interworking with non-LISP sites are 1641 described in [RFC6831] and [RFC6832]. 1643 15. Router Performance Considerations 1645 LISP is designed to be very "hardware-based forwarding friendly". A 1646 few implementation techniques can be used to incrementally implement 1647 LISP: 1649 o When a tunnel-encapsulated packet is received by an ETR, the outer 1650 destination address may not be the address of the router. This 1651 makes it challenging for the control plane to get packets from the 1652 hardware. This may be mitigated by creating special Forwarding 1653 Information Base (FIB) entries for the EID-Prefixes of EIDs served 1654 by the ETR (those for which the router provides an RLOC 1655 translation). These FIB entries are marked with a flag indicating 1656 that control-plane processing should be performed. The forwarding 1657 logic of testing for particular IP protocol number values is not 1658 necessary. There are a few proven cases where no changes to 1659 existing deployed hardware were needed to support the LISP data- 1660 plane. 1662 o On an ITR, prepending a new IP header consists of adding more 1663 octets to a MAC rewrite string and prepending the string as part 1664 of the outgoing encapsulation procedure. Routers that support 1665 Generic Routing Encapsulation (GRE) tunneling [RFC2784] or 6to4 1666 tunneling [RFC3056] may already support this action. 1668 o A packet's source address or interface the packet was received on 1669 can be used to select VRF (Virtual Routing/Forwarding). The VRF's 1670 routing table can be used to find EID-to-RLOC mappings. 1672 For performance issues related to map-cache management, see 1673 Section 19. 1675 16. Mobility Considerations 1677 There are several kinds of mobility, of which only some might be of 1678 concern to LISP. Essentially, they are as follows. 1680 16.1. Slow Mobility 1682 A site wishes to change its attachment points to the Internet, and 1683 its LISP Tunnel Routers will have new RLOCs when it changes upstream 1684 providers. Changes in EID-to-RLOC mappings for sites are expected to 1685 be handled by configuration, outside of LISP. 1687 An individual endpoint wishes to move but is not concerned about 1688 maintaining session continuity. Renumbering is involved. LISP can 1689 help with the issues surrounding renumbering [RFC4192] [LISA96] by 1690 decoupling the address space used by a site from the address spaces 1691 used by its ISPs [RFC4984]. 1693 16.2. Fast Mobility 1695 Fast endpoint mobility occurs when an endpoint moves relatively 1696 rapidly, changing its IP-layer network attachment point. Maintenance 1697 of session continuity is a goal. This is where the Mobile IPv4 1698 [RFC5944] and Mobile IPv6 [RFC6275] [RFC4866] mechanisms are used and 1699 primarily where interactions with LISP need to be explored, such as 1700 the mechanisms in [I-D.portoles-lisp-eid-mobility] when the EID moves 1701 but the RLOC is in the network infrastructure. 1703 In LISP, one possibility is to "glean" information. When a packet 1704 arrives, the ETR could examine the EID-to-RLOC mapping and use that 1705 mapping for all outgoing traffic to that EID. It can do this after 1706 performing a route-returnability check, to ensure that the new 1707 network location does have an internal route to that endpoint. 1708 However, this does not cover the case where an ITR (the node assigned 1709 the RLOC) at the mobile-node location has been compromised. 1711 Mobile IP packet exchange is designed for an environment in which all 1712 routing information is disseminated before packets can be forwarded. 1713 In order to allow the Internet to grow to support expected future 1714 use, we are moving to an environment where some information may have 1715 to be obtained after packets are in flight. Modifications to IP 1716 mobility should be considered in order to optimize the behavior of 1717 the overall system. Anything that decreases the number of new EID- 1718 to-RLOC mappings needed when a node moves, or maintains the validity 1719 of an EID-to-RLOC mapping for a longer time, is useful. 1721 In addition to endpoints, a network can be mobile, possibly changing 1722 xTRs. A "network" can be as small as a single router and as large as 1723 a whole site. This is different from site mobility in that it is 1724 fast and possibly short-lived, but different from endpoint mobility 1725 in that a whole prefix is changing RLOCs. However, the mechanisms 1726 are the same, and there is no new overhead in LISP. A map request 1727 for any endpoint will return a binding for the entire mobile prefix. 1729 If mobile networks become a more common occurrence, it may be useful 1730 to revisit the design of the mapping service and allow for dynamic 1731 updates of the database. 1733 The issue of interactions between mobility and LISP needs to be 1734 explored further. Specific improvements to the entire system will 1735 depend on the details of mapping mechanisms. Mapping mechanisms 1736 should be evaluated on how well they support session continuity for 1737 mobile nodes. See [I-D.farinacci-lisp-predictive-rlocs] for more 1738 recent mechanisms which can provide near-zero packet loss during 1739 handoffs. 1741 16.3. LISP Mobile Node Mobility 1743 A mobile device can use the LISP infrastructure to achieve mobility 1744 by implementing the LISP encapsulation and decapsulation functions 1745 and acting as a simple ITR/ETR. By doing this, such a "LISP mobile 1746 node" can use topologically independent EID IP addresses that are not 1747 advertised into and do not impose a cost on the global routing 1748 system. These EIDs are maintained at the edges of the mapping system 1749 in LISP Map-Servers and Map-Resolvers) and are provided on demand to 1750 only the correspondents of the LISP mobile node. 1752 Refer to [I-D.meyer-lisp-mn] for more details for when the EID and 1753 RLOC are co-located in the roaming node. 1755 17. LISP xTR Placement and Encapsulation Methods 1757 This section will explore how and where ITRs and ETRs can be placed 1758 in the network and will discuss the pros and cons of each scenario. 1759 For a more detailed networkd design deployment recommendation, refer 1760 to [RFC7215]. 1762 There are two basic deployment tradeoffs to consider: centralized 1763 versus distributed caches; and flat, Recursive, or Re-encapsulating 1764 Tunneling. When deciding on centralized versus distributed caching, 1765 the following issues should be considered: 1767 o Are the xTRs spread out so that the caches are spread across all 1768 the memories of each router? A centralized cache is when an ITR 1769 keeps a cache for all the EIDs it is encapsulating to. The packet 1770 takes a direct path to the destination Locator. A distributed 1771 cache is when an ITR needs help from other Re-Encapsulating Tunnel 1772 Routers (RTRs) because it does not store all the cache entries for 1773 the EIDs it is encapsulating to. So, the packet takes a path 1774 through RTRs that have a different set of cache entries. 1776 o Should management "touch points" be minimized by only choosing a 1777 few xTRs, just enough for redundancy? 1779 o In general, using more ITRs doesn't increase management load, 1780 since caches are built and stored dynamically. On the other hand, 1781 using more ETRs does require more management, since EID-Prefix-to- 1782 RLOC mappings need to be explicitly configured. 1784 When deciding on flat, Recursive, or Re-Encapsulating Tunneling, the 1785 following issues should be considered: 1787 o Flat tunneling implements a single encapsulation path between the 1788 source site and destination site. This generally offers better 1789 paths between sources and destinations with a single encapsulation 1790 path. 1792 o Recursive Tunneling is when encapsulated traffic is again further 1793 encapsulated in another tunnel, either to implement VPNs or to 1794 perform Traffic Engineering. When doing VPN-based tunneling, the 1795 site has some control, since the site is prepending a new 1796 encapsulation header. In the case of TE-based tunneling, the site 1797 may have control if it is prepending a new tunnel header, but if 1798 the site's ISP is doing the TE, then the site has no control. 1799 Recursive Tunneling generally will result in suboptimal paths but 1800 with the benefit of steering traffic to parts of the network that 1801 have more resources available. 1803 o The technique of Re-Encapsulation ensures that packets only 1804 require one encapsulation header. So, if a packet needs to be re- 1805 routed, it is first decapsulated by the RTR and then Re- 1806 Encapsulated with a new encapsulation header using a new RLOC. 1808 The next sub-sections will examine where xTRs and RTRs can reside in 1809 the network. 1811 17.1. First-Hop/Last-Hop xTRs 1813 By locating xTRs close to hosts, the EID-Prefix set is at the 1814 granularity of an IP subnet. So, at the expense of more EID-Prefix- 1815 to-RLOC sets for the site, the caches in each xTR can remain 1816 relatively small. But caches always depend on the number of non- 1817 aggregated EID destination flows active through these xTRs. 1819 With more xTRs doing encapsulation, the increase in control traffic 1820 grows as well: since the EID granularity is greater, more Map- 1821 Requests and Map-Replies are traveling between more routers. 1823 The advantage of placing the caches and databases at these stub 1824 routers is that the products deployed in this part of the network 1825 have better price-memory ratios than their core router counterparts. 1826 Memory is typically less expensive in these devices, and fewer routes 1827 are stored (only IGP routes). These devices tend to have excess 1828 capacity, both for forwarding and routing states. 1830 LISP functionality can also be deployed in edge switches. These 1831 devices generally have layer-2 ports facing hosts and layer-3 ports 1832 facing the Internet. Spare capacity is also often available in these 1833 devices. 1835 17.2. Border/Edge xTRs 1837 Using Customer Edge (CE) routers for xTR placement allows the EID 1838 space associated with a site to be reachable via a small set of RLOCs 1839 assigned to the CE-based xTRs for that site. 1841 This offers the opposite benefit of the first-hop/last-hop xTR 1842 scenario: the number of mapping entries and network management touch 1843 points is reduced, allowing better scaling. 1845 One disadvantage is that fewer network resources are used to reach 1846 host endpoints, thereby centralizing the point-of-failure domain and 1847 creating network choke points at the CE xTR. 1849 Note that more than one CE xTR at a site can be configured with the 1850 same IP address. In this case, an RLOC is an anycast address. This 1851 allows resilience between the CE xTRs. That is, if a CE xTR fails, 1852 traffic is automatically routed to the other xTRs using the same 1853 anycast address. However, this comes with the disadvantage where the 1854 site cannot control the entrance point when the anycast route is 1855 advertised out from all border routers. Another disadvantage of 1856 using anycast Locators is the limited advertisement scope of /32 (or 1857 /128 for IPv6) routes. 1859 17.3. ISP Provider Edge (PE) xTRs 1861 The use of ISP PE routers as xTRs is not the typical deployment 1862 scenario envisioned in this specification. This section attempts to 1863 capture some of the reasoning behind this preference for implementing 1864 LISP on CE routers. 1866 The use of ISP PE routers for xTR placement gives an ISP, rather than 1867 a site, control over the location of the ETRs. That is, the ISP can 1868 decide whether the xTRs are in the destination site (in either CE 1869 xTRs or last-hop xTRs within a site) or at other PE edges. The 1870 advantage of this case is that two encapsulation headers can be 1871 avoided. By having the PE be the first router on the path to 1872 encapsulate, it can choose a TE path first, and the ETR can 1873 decapsulate and Re-Encapsulate for a new encapsuluation path to the 1874 destination end site. 1876 An obvious disadvantage is that the end site has no control over 1877 where its packets flow or over the RLOCs used. Other disadvantages 1878 include difficulty in synchronizing path liveness updates between CE 1879 and PE routers. 1881 As mentioned in earlier sections, a combination of these scenarios is 1882 possible at the expense of extra packet header overhead; if both site 1883 and provider want control, then Recursive or Re-Encapsulating Tunnels 1884 are used. 1886 17.4. LISP Functionality with Conventional NATs 1888 LISP routers can be deployed behind Network Address Translator (NAT) 1889 devices to provide the same set of packet services hosts have today 1890 when they are addressed out of private address space. 1892 It is important to note that a locator address in any LISP control 1893 message MUST be a globally routable address and therefore SHOULD NOT 1894 contain [RFC1918] addresses. If a LISP xTR is configured with 1895 private RLOC addresses, they MUST be used only in the outer IP header 1896 so the NAT device can translate properly. Otherwise, EID addresses 1897 MUST be translated before encapsulation is performed when LISP VPNs 1898 are not in use. Both NAT translation and LISP encapsulation 1899 functions could be co-located in the same device. 1901 17.5. Packets Egressing a LISP Site 1903 When a LISP site is using two ITRs for redundancy, the failure of one 1904 ITR will likely shift outbound traffic to the second. This second 1905 ITR's cache may not be populated with the same EID-to-RLOC mapping 1906 entries as the first. If this second ITR does not have these 1907 mappings, traffic will be dropped while the mappings are retrieved 1908 from the mapping system. The retrieval of these messages may 1909 increase the load of requests being sent into the mapping system. 1911 18. Traceroute Considerations 1913 When a source host in a LISP site initiates a traceroute to a 1914 destination host in another LISP site, it is highly desirable for it 1915 to see the entire path. Since packets are encapsulated from the ITR 1916 to the ETR, the hop across the tunnel could be viewed as a single 1917 hop. However, LISP traceroute will provide the entire path so the 1918 user can see 3 distinct segments of the path from a source LISP host 1919 to a destination LISP host: 1921 Segment 1 (in source LISP site based on EIDs): 1923 source host ---> first hop ... next hop ---> ITR 1925 Segment 2 (in the core network based on RLOCs): 1927 ITR ---> next hop ... next hop ---> ETR 1929 Segment 3 (in the destination LISP site based on EIDs): 1931 ETR ---> next hop ... last hop ---> destination host 1933 For segment 1 of the path, ICMP Time Exceeded messages are returned 1934 in the normal manner as they are today. The ITR performs a TTL 1935 decrement and tests for 0 before encapsulating. Therefore, the ITR's 1936 hop is seen by the traceroute source as having an EID address (the 1937 address of the site-facing interface). 1939 For segment 2 of the path, ICMP Time Exceeded messages are returned 1940 to the ITR because the TTL decrement to 0 is done on the outer 1941 header, so the destinations of the ICMP messages are the ITR RLOC 1942 address and the source RLOC address of the encapsulated traceroute 1943 packet. The ITR looks inside of the ICMP payload to inspect the 1944 traceroute source so it can return the ICMP message to the address of 1945 the traceroute client and also retain the core router IP address in 1946 the ICMP message. This is so the traceroute client can display the 1947 core router address (the RLOC address) in the traceroute output. The 1948 ETR returns its RLOC address and responds to the TTL decrement to 0, 1949 as the previous core routers did. 1951 For segment 3, the next-hop router downstream from the ETR will be 1952 decrementing the TTL for the packet that was encapsulated, sent into 1953 the core, decapsulated by the ETR, and forwarded because it isn't the 1954 final destination. If the TTL is decremented to 0, any router on the 1955 path to the destination of the traceroute, including the next-hop 1956 router or destination, will send an ICMP Time Exceeded message to the 1957 source EID of the traceroute client. The ICMP message will be 1958 encapsulated by the local ITR and sent back to the ETR in the 1959 originated traceroute source site, where the packet will be delivered 1960 to the host. 1962 18.1. IPv6 Traceroute 1964 IPv6 traceroute follows the procedure described above, since the 1965 entire traceroute data packet is included in the ICMP Time Exceeded 1966 message payload. Therefore, only the ITR needs to pay special 1967 attention to forwarding ICMP messages back to the traceroute source. 1969 18.2. IPv4 Traceroute 1971 For IPv4 traceroute, we cannot follow the above procedure, since IPv4 1972 ICMP Time Exceeded messages only include the invoking IP header and 1973 8 octets that follow the IP header. Therefore, when a core router 1974 sends an IPv4 Time Exceeded message to an ITR, all the ITR has in the 1975 ICMP payload is the encapsulated header it prepended, followed by a 1976 UDP header. The original invoking IP header, and therefore the 1977 identity of the traceroute source, is lost. 1979 The solution we propose to solve this problem is to cache traceroute 1980 IPv4 headers in the ITR and to match them up with corresponding IPv4 1981 Time Exceeded messages received from core routers and the ETR. The 1982 ITR will use a circular buffer for caching the IPv4 and UDP headers 1983 of traceroute packets. It will select a 16-bit number as a key to 1984 find them later when the IPv4 Time Exceeded messages are received. 1985 When an ITR encapsulates an IPv4 traceroute packet, it will use the 1986 16-bit number as the UDP source port in the encapsulating header. 1987 When the ICMP Time Exceeded message is returned to the ITR, the UDP 1988 header of the encapsulating header is present in the ICMP payload, 1989 thereby allowing the ITR to find the cached headers for the 1990 traceroute source. The ITR puts the cached headers in the payload 1991 and sends the ICMP Time Exceeded message to the traceroute source 1992 retaining the source address of the original ICMP Time Exceeded 1993 message (a core router or the ETR of the site of the traceroute 1994 destination). 1996 The signature of a traceroute packet comes in two forms. The first 1997 form is encoded as a UDP message where the destination port is 1998 inspected for a range of values. The second form is encoded as an 1999 ICMP message where the IP identification field is inspected for a 2000 well-known value. 2002 18.3. Traceroute Using Mixed Locators 2004 When either an IPv4 traceroute or IPv6 traceroute is originated and 2005 the ITR encapsulates it in the other address family header, one 2006 cannot get all 3 segments of the traceroute. Segment 2 of the 2007 traceroute cannot be conveyed to the traceroute source, since it is 2008 expecting addresses from intermediate hops in the same address format 2009 for the type of traceroute it originated. Therefore, in this case, 2010 segment 2 will make the tunnel look like one hop. All the ITR has to 2011 do to make this work is to not copy the inner TTL to the outer, 2012 encapsulating header's TTL when a traceroute packet is encapsulated 2013 using an RLOC from a different address family. This will cause no 2014 TTL decrement to 0 to occur in core routers between the ITR and ETR. 2016 19. Security Considerations 2018 Security considerations for LISP are discussed in [RFC7833], in 2019 addition [I-D.ietf-lisp-sec] provides authentication and integrity to 2020 LISP mappings. 2022 A complete LISP threat analysis can be found in [RFC7835], in what 2023 follows we provide a summary. 2025 The optional mechanisms of gleaning is offered to directly obtain a 2026 mapping from the LISP encapsulated packets. Specifically, an xTR can 2027 learn the EID-to-RLOC mapping by inspecting the source RLOC and 2028 source EID of an encapsulated packet, and insert this new mapping 2029 into its map-cache. An off-path attacker can spoof the source EID 2030 address to divert the traffic sent to the victim's spoofed EID. If 2031 the attacker spoofs the source RLOC, it can mount a DoS attack by 2032 redirecting traffic to the spoofed victim;s RLOC, potentially 2033 overloading it. 2035 The LISP Data-Plane defines several mechanisms to monitor RLOC data- 2036 plane reachability, in this context Locator-Status Bits, Nonce- 2037 Present and Echo-Nonce bits of the LISP encapsulation header can be 2038 manipulated by an attacker to mount a DoS attack. An off-path 2039 attacker able to spoof the RLOC of a victim's xTR can manipulate such 2040 mechanisms to declare a set of RLOCs unreachable. This can be used 2041 also, for instance, to declare only one RLOC reachable with the aim 2042 of overload it. 2044 Map-Versioning is a data-plane mechanism used to signal a peering xTR 2045 that a local EID-to-RLOC mapping has been updated, so that the 2046 peering xTR uses LISP Control-Plane signaling message to retrieve a 2047 fresh mapping. This can be used by an attacker to forge the map- 2048 versioning field of a LISP encapsulated header and force an excessive 2049 amount of signaling between xTRs that may overload them. 2051 Most of the attack vectors can be mitigated with careful deployment 2052 and configuration, information learned opportunistically (such as LSB 2053 or gleaning) should be verified with other reachability mechanisms. 2054 In addition, systematic rate-limitation and filtering is an effective 2055 technique to mitigate attacks that aim to overload the control-plane. 2057 20. Network Management Considerations 2059 Considerations for network management tools exist so the LISP 2060 protocol suite can be operationally managed. These mechanisms can be 2061 found in [RFC7052] and [RFC6835]. 2063 21. IANA Considerations 2065 This section provides guidance to the Internet Assigned Numbers 2066 Authority (IANA) regarding registration of values related to the LISP 2067 specification, in accordance with BCP 26 [RFC5226]. 2069 There are four namespaces (listed in the sub-sections below) in LISP 2070 that have been registered. 2072 o LISP IANA registry allocations should not be made for purposes 2073 unrelated to LISP routing or transport protocols. 2075 o The following policies are used here with the meanings defined in 2076 BCP 26: "Specification Required", "IETF Review", "Experimental 2077 Use", and "First Come First Served". 2079 21.1. LISP ACT and Flag Fields 2081 New ACT values [I-D.ietf-lisp-rfc6833bis] can be allocated through 2082 IETF review or IESG approval. Four values have already been 2083 allocated by this specification [I-D.ietf-lisp-rfc6833bis]. 2085 In addition, LISP has a number of flag fields and reserved fields, 2086 such as the LISP header flags field (Section 5.3). New bits for 2087 flags in these fields can be implemented after IETF review or IESG 2088 approval, but these need not be managed by IANA. 2090 21.2. LISP Address Type Codes 2092 LISP Canonical Address Format (LCAF) [RFC8060] is an 8-bit field that 2093 defines LISP-specific encodings for AFI value 16387. LCAF encodings 2094 are used for specific use-cases where different address types for 2095 EID-records and RLOC-records are required. 2097 The IANA registry "LISP Canonical Address Format (LCAF) Types" is 2098 used for LCAF types, the registry for LCAF types use the 2099 Specification Required policy [RFC5226]. Initial values for the 2100 registry as well as further information can be found in [RFC8060]. 2102 21.3. LISP UDP Port Numbers 2104 The IANA registry has allocated UDP port numbers 4341 and 4342 for 2105 lisp-data and lisp-control operation, respectively. IANA has updated 2106 the description for UDP ports 4341 and 4342 as follows: 2108 lisp-data 4341 udp LISP Data Packets 2109 lisp-control 4342 udp LISP Control Packets 2111 21.4. LISP Key ID Numbers 2113 The following Key ID values are defined by this specification as used 2114 in any packet type that references a 'Key ID' field: 2116 Name Number Defined in 2117 ----------------------------------------------- 2118 None 0 n/a 2119 HMAC-SHA-1-96 1 [RFC2404] 2120 HMAC-SHA-256-128 2 [RFC4868] 2122 Number values are in the range of 0 to 65535. The allocation of 2123 values is on a first come first served basis. 2125 22. References 2127 22.1. Normative References 2129 [I-D.ietf-lisp-ddt] 2130 Fuller, V., Lewis, D., Ermagan, V., Jain, A., and A. 2131 Smirnov, "LISP Delegated Database Tree", draft-ietf-lisp- 2132 ddt-09 (work in progress), January 2017. 2134 [I-D.ietf-lisp-introduction] 2135 Cabellos-Aparicio, A. and D. Saucez, "An Architectural 2136 Introduction to the Locator/ID Separation Protocol 2137 (LISP)", draft-ietf-lisp-introduction-13 (work in 2138 progress), April 2015. 2140 [I-D.ietf-lisp-rfc6833bis] 2141 Fuller, V., Farinacci, D., and A. Cabellos-Aparicio, 2142 "Locator/ID Separation Protocol (LISP) Control-Plane", 2143 draft-ietf-lisp-rfc6833bis-01 (work in progress), March 2144 2017. 2146 [I-D.ietf-lisp-sec] 2147 Maino, F., Ermagan, V., Cabellos-Aparicio, A., and D. 2148 Saucez, "LISP-Security (LISP-SEC)", draft-ietf-lisp-sec-12 2149 (work in progress), November 2016. 2151 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 2152 DOI 10.17487/RFC0768, August 1980, 2153 . 2155 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 2156 DOI 10.17487/RFC0791, September 1981, 2157 . 2159 [RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G., 2160 and E. Lear, "Address Allocation for Private Internets", 2161 BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996, 2162 . 2164 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2165 Requirement Levels", BCP 14, RFC 2119, 2166 DOI 10.17487/RFC2119, March 1997, 2167 . 2169 [RFC2404] Madson, C. and R. Glenn, "The Use of HMAC-SHA-1-96 within 2170 ESP and AH", RFC 2404, DOI 10.17487/RFC2404, November 2171 1998, . 2173 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2174 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, 2175 December 1998, . 2177 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 2178 of Explicit Congestion Notification (ECN) to IP", 2179 RFC 3168, DOI 10.17487/RFC3168, September 2001, 2180 . 2182 [RFC3232] Reynolds, J., Ed., "Assigned Numbers: RFC 1700 is Replaced 2183 by an On-line Database", RFC 3232, DOI 10.17487/RFC3232, 2184 January 2002, . 2186 [RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker, 2187 "Randomness Requirements for Security", BCP 106, RFC 4086, 2188 DOI 10.17487/RFC4086, June 2005, 2189 . 2191 [RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing 2192 (CIDR): The Internet Address Assignment and Aggregation 2193 Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August 2194 2006, . 2196 [RFC4868] Kelly, S. and S. Frankel, "Using HMAC-SHA-256, HMAC-SHA- 2197 384, and HMAC-SHA-512 with IPsec", RFC 4868, 2198 DOI 10.17487/RFC4868, May 2007, 2199 . 2201 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 2202 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 2203 DOI 10.17487/RFC5226, May 2008, 2204 . 2206 [RFC5496] Wijnands, IJ., Boers, A., and E. Rosen, "The Reverse Path 2207 Forwarding (RPF) Vector TLV", RFC 5496, 2208 DOI 10.17487/RFC5496, March 2009, 2209 . 2211 [RFC5944] Perkins, C., Ed., "IP Mobility Support for IPv4, Revised", 2212 RFC 5944, DOI 10.17487/RFC5944, November 2010, 2213 . 2215 [RFC6115] Li, T., Ed., "Recommendation for a Routing Architecture", 2216 RFC 6115, DOI 10.17487/RFC6115, February 2011, 2217 . 2219 [RFC6275] Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility 2220 Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July 2221 2011, . 2223 [RFC6834] Iannone, L., Saucez, D., and O. Bonaventure, "Locator/ID 2224 Separation Protocol (LISP) Map-Versioning", RFC 6834, 2225 DOI 10.17487/RFC6834, January 2013, 2226 . 2228 [RFC6836] Fuller, V., Farinacci, D., Meyer, D., and D. Lewis, 2229 "Locator/ID Separation Protocol Alternative Logical 2230 Topology (LISP+ALT)", RFC 6836, DOI 10.17487/RFC6836, 2231 January 2013, . 2233 [RFC7052] Schudel, G., Jain, A., and V. Moreno, "Locator/ID 2234 Separation Protocol (LISP) MIB", RFC 7052, 2235 DOI 10.17487/RFC7052, October 2013, 2236 . 2238 [RFC7214] Andersson, L. and C. Pignataro, "Moving Generic Associated 2239 Channel (G-ACh) IANA Registries to a New Registry", 2240 RFC 7214, DOI 10.17487/RFC7214, May 2014, 2241 . 2243 [RFC7215] Jakab, L., Cabellos-Aparicio, A., Coras, F., Domingo- 2244 Pascual, J., and D. Lewis, "Locator/Identifier Separation 2245 Protocol (LISP) Network Element Deployment 2246 Considerations", RFC 7215, DOI 10.17487/RFC7215, April 2247 2014, . 2249 [RFC7833] Howlett, J., Hartman, S., and A. Perez-Mendez, Ed., "A 2250 RADIUS Attribute, Binding, Profiles, Name Identifier 2251 Format, and Confirmation Methods for the Security 2252 Assertion Markup Language (SAML)", RFC 7833, 2253 DOI 10.17487/RFC7833, May 2016, 2254 . 2256 [RFC7835] Saucez, D., Iannone, L., and O. Bonaventure, "Locator/ID 2257 Separation Protocol (LISP) Threat Analysis", RFC 7835, 2258 DOI 10.17487/RFC7835, April 2016, 2259 . 2261 [RFC8061] Farinacci, D. and B. Weis, "Locator/ID Separation Protocol 2262 (LISP) Data-Plane Confidentiality", RFC 8061, 2263 DOI 10.17487/RFC8061, February 2017, 2264 . 2266 22.2. Informative References 2268 [AFN] IANA, "Address Family Numbers", August 2016, 2269 . 2271 [CHIAPPA] Chiappa, J., "Endpoints and Endpoint names: A Proposed", 2272 1999, 2273 . 2275 [I-D.farinacci-lisp-predictive-rlocs] 2276 Farinacci, D. and P. Pillay-Esnault, "LISP Predictive 2277 RLOCs", draft-farinacci-lisp-predictive-rlocs-01 (work in 2278 progress), November 2016. 2280 [I-D.ietf-lisp-signal-free-multicast] 2281 Moreno, V. and D. Farinacci, "Signal-Free LISP Multicast", 2282 draft-ietf-lisp-signal-free-multicast-02 (work in 2283 progress), October 2016. 2285 [I-D.meyer-lisp-mn] 2286 Farinacci, D., Lewis, D., Meyer, D., and C. White, "LISP 2287 Mobile Node", draft-meyer-lisp-mn-16 (work in progress), 2288 December 2016. 2290 [I-D.meyer-loc-id-implications] 2291 Meyer, D. and D. Lewis, "Architectural Implications of 2292 Locator/ID Separation", draft-meyer-loc-id-implications-01 2293 (work in progress), January 2009. 2295 [I-D.portoles-lisp-eid-mobility] 2296 Portoles-Comeras, M., Ashtaputre, V., Moreno, V., Maino, 2297 F., and D. Farinacci, "LISP L2/L3 EID Mobility Using a 2298 Unified Control Plane", draft-portoles-lisp-eid- 2299 mobility-02 (work in progress), April 2017. 2301 [LISA96] Lear, E., Tharp, D., Katinsky, J., and J. Coffin, 2302 "Renumbering: Threat or Menace?", Usenix Tenth System 2303 Administration Conference (LISA 96), October 1996. 2305 [OPENLISP] 2306 Iannone, L., Saucez, D., and O. Bonaventure, "OpenLISP 2307 Implementation Report", Work in Progress, July 2008. 2309 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 2310 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 2311 . 2313 [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. 2314 Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, 2315 DOI 10.17487/RFC2784, March 2000, 2316 . 2318 [RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains 2319 via IPv4 Clouds", RFC 3056, DOI 10.17487/RFC3056, February 2320 2001, . 2322 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 2323 A., Peterson, J., Sparks, R., Handley, M., and E. 2324 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 2325 DOI 10.17487/RFC3261, June 2002, 2326 . 2328 [RFC4107] Bellovin, S. and R. Housley, "Guidelines for Cryptographic 2329 Key Management", BCP 107, RFC 4107, DOI 10.17487/RFC4107, 2330 June 2005, . 2332 [RFC4192] Baker, F., Lear, E., and R. Droms, "Procedures for 2333 Renumbering an IPv6 Network without a Flag Day", RFC 4192, 2334 DOI 10.17487/RFC4192, September 2005, 2335 . 2337 [RFC4866] Arkko, J., Vogt, C., and W. Haddad, "Enhanced Route 2338 Optimization for Mobile IPv6", RFC 4866, 2339 DOI 10.17487/RFC4866, May 2007, 2340 . 2342 [RFC4984] Meyer, D., Ed., Zhang, L., Ed., and K. Fall, Ed., "Report 2343 from the IAB Workshop on Routing and Addressing", 2344 RFC 4984, DOI 10.17487/RFC4984, September 2007, 2345 . 2347 [RFC6480] Lepinski, M. and S. Kent, "An Infrastructure to Support 2348 Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480, 2349 February 2012, . 2351 [RFC6518] Lebovitz, G. and M. Bhatia, "Keying and Authentication for 2352 Routing Protocols (KARP) Design Guidelines", RFC 6518, 2353 DOI 10.17487/RFC6518, February 2012, 2354 . 2356 [RFC6831] Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas, "The 2357 Locator/ID Separation Protocol (LISP) for Multicast 2358 Environments", RFC 6831, DOI 10.17487/RFC6831, January 2359 2013, . 2361 [RFC6832] Lewis, D., Meyer, D., Farinacci, D., and V. Fuller, 2362 "Interworking between Locator/ID Separation Protocol 2363 (LISP) and Non-LISP Sites", RFC 6832, 2364 DOI 10.17487/RFC6832, January 2013, 2365 . 2367 [RFC6835] Farinacci, D. and D. Meyer, "The Locator/ID Separation 2368 Protocol Internet Groper (LIG)", RFC 6835, 2369 DOI 10.17487/RFC6835, January 2013, 2370 . 2372 [RFC6837] Lear, E., "NERD: A Not-so-novel Endpoint ID (EID) to 2373 Routing Locator (RLOC) Database", RFC 6837, 2374 DOI 10.17487/RFC6837, January 2013, 2375 . 2377 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 2378 UDP Checksums for Tunneled Packets", RFC 6935, 2379 DOI 10.17487/RFC6935, April 2013, 2380 . 2382 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 2383 for the Use of IPv6 UDP Datagrams with Zero Checksums", 2384 RFC 6936, DOI 10.17487/RFC6936, April 2013, 2385 . 2387 [RFC8060] Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical 2388 Address Format (LCAF)", RFC 8060, DOI 10.17487/RFC8060, 2389 February 2017, . 2391 Appendix A. Acknowledgments 2393 An initial thank you goes to Dave Oran for planting the seeds for the 2394 initial ideas for LISP. His consultation continues to provide value 2395 to the LISP authors. 2397 A special and appreciative thank you goes to Noel Chiappa for 2398 providing architectural impetus over the past decades on separation 2399 of location and identity, as well as detailed reviews of the LISP 2400 architecture and documents, coupled with enthusiasm for making LISP a 2401 practical and incremental transition for the Internet. 2403 The authors would like to gratefully acknowledge many people who have 2404 contributed discussions and ideas to the making of this proposal. 2405 They include Scott Brim, Andrew Partan, John Zwiebel, Jason Schiller, 2406 Lixia Zhang, Dorian Kim, Peter Schoenmaker, Vijay Gill, Geoff Huston, 2407 David Conrad, Mark Handley, Ron Bonica, Ted Seely, Mark Townsley, 2408 Chris Morrow, Brian Weis, Dave McGrew, Peter Lothberg, Dave Thaler, 2409 Eliot Lear, Shane Amante, Ved Kafle, Olivier Bonaventure, Luigi 2410 Iannone, Robin Whittle, Brian Carpenter, Joel Halpern, Terry 2411 Manderson, Roger Jorgensen, Ran Atkinson, Stig Venaas, Iljitsch van 2412 Beijnum, Roland Bless, Dana Blair, Bill Lynch, Marc Woolward, Damien 2413 Saucez, Damian Lezama, Attilla De Groot, Parantap Lahiri, David 2414 Black, Roque Gagliano, Isidor Kouvelas, Jesper Skriver, Fred Templin, 2415 Margaret Wasserman, Sam Hartman, Michael Hofling, Pedro Marques, Jari 2416 Arkko, Gregg Schudel, Srinivas Subramanian, Amit Jain, Xu Xiaohu, 2417 Dhirendra Trivedi, Yakov Rekhter, John Scudder, John Drake, Dimitri 2418 Papadimitriou, Ross Callon, Selina Heimlich, Job Snijders, Vina 2419 Ermagan, Fabio Maino, Victor Moreno, Chris White, Clarence Filsfils, 2420 Alia Atlas, Florin Coras and Alberto Rodriguez. 2422 This work originated in the Routing Research Group (RRG) of the IRTF. 2423 An individual submission was converted into the IETF LISP working 2424 group document that became this RFC. 2426 The LISP working group would like to give a special thanks to Jari 2427 Arkko, the Internet Area AD at the time that the set of LISP 2428 documents were being prepared for IESG last call, and for his 2429 meticulous reviews and detailed commentaries on the 7 working group 2430 last call documents progressing toward standards-track RFCs. 2432 Appendix B. Document Change Log 2434 [RFC Editor: Please delete this section on publication as RFC.] 2436 B.1. Changes to draft-ietf-lisp-rfc6830bis-02 2438 o Posted April 2017. 2440 o Reflect some editorial comments from Damien Sausez. 2442 B.2. Changes to draft-ietf-lisp-rfc6830bis-01 2444 o Posted March 2017. 2446 o Include references to new RFCs published. 2448 o Change references from RFC6833 to RFC6833bis. 2450 o Clarified LCAF text in the IANA section. 2452 o Remove references to "experimental". 2454 B.3. Changes to draft-ietf-lisp-rfc6830bis-00 2456 o Posted December 2016. 2458 o Created working group document from draft-farinacci-lisp 2459 -rfc6830-00 individual submission. No other changes made. 2461 Authors' Addresses 2463 Dino Farinacci 2464 Cisco Systems 2465 Tasman Drive 2466 San Jose, CA 95134 2467 USA 2469 EMail: farinacci@gmail.com 2471 Vince Fuller 2472 Cisco Systems 2473 Tasman Drive 2474 San Jose, CA 95134 2475 USA 2477 EMail: vince.fuller@gmail.com 2478 Dave Meyer 2479 Cisco Systems 2480 170 Tasman Drive 2481 San Jose, CA 2482 USA 2484 EMail: dmm@1-4-5.net 2486 Darrel Lewis 2487 Cisco Systems 2488 170 Tasman Drive 2489 San Jose, CA 2490 USA 2492 EMail: darlewis@cisco.com 2494 Albert Cabellos 2495 UPC/BarcelonaTech 2496 Campus Nord, C. Jordi Girona 1-3 2497 Barcelona, Catalunya 2498 Spain 2500 EMail: acabello@ac.upc.edu