idnits 2.17.1 draft-ietf-lisp-rfc6830bis-18.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (September 17, 2018) is 2047 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-14) exists of draft-ietf-lisp-6834bis-02 == Outdated reference: A later version (-31) exists of draft-ietf-lisp-rfc6833bis-14 == Outdated reference: A later version (-15) exists of draft-ietf-lisp-introduction-13 == Outdated reference: A later version (-12) exists of draft-ietf-lisp-vpn-02 Summary: 0 errors (**), 0 flaws (~~), 5 warnings (==), 1 comment (--). 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 Obsoletes: 6830 (if approved) D. Meyer 5 Intended status: Standards Track D. Lewis 6 Expires: March 21, 2019 Cisco Systems 7 A. Cabellos (Ed.) 8 UPC/BarcelonaTech 9 September 17, 2018 11 The Locator/ID Separation Protocol (LISP) 12 draft-ietf-lisp-rfc6830bis-18 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. 24 LISP requires no change to either host protocol stacks or to underlay 25 routers and offers Traffic Engineering, multihoming and mobility, 26 among other features. 28 This document obsoletes RFC 6830. 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 https://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 March 21, 2019. 47 Copyright Notice 49 Copyright (c) 2018 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 (https://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 . . . . . . . . . . . . . . . . . . . . . . . 8 68 4.1. Packet Flow Sequence . . . . . . . . . . . . . . . . . . 10 69 5. LISP Encapsulation Details . . . . . . . . . . . . . . . . . 12 70 5.1. LISP IPv4-in-IPv4 Header Format . . . . . . . . . . . . . 13 71 5.2. LISP IPv6-in-IPv6 Header Format . . . . . . . . . . . . . 14 72 5.3. Tunnel Header Field Descriptions . . . . . . . . . . . . 15 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 . . . . . . . . . . . . . . . . 25 80 10.1. Echo Nonce Algorithm . . . . . . . . . . . . . . . . . . 26 81 11. EID Reachability within a LISP Site . . . . . . . . . . . . . 27 82 12. Routing Locator Hashing . . . . . . . . . . . . . . . . . . . 28 83 13. Changing the Contents of EID-to-RLOC Mappings . . . . . . . . 29 84 13.1. Database Map-Versioning . . . . . . . . . . . . . . . . 30 85 14. Multicast Considerations . . . . . . . . . . . . . . . . . . 31 86 15. Router Performance Considerations . . . . . . . . . . . . . . 31 87 16. Security Considerations . . . . . . . . . . . . . . . . . . . 32 88 17. Network Management Considerations . . . . . . . . . . . . . . 33 89 18. Changes since RFC 6830 . . . . . . . . . . . . . . . . . . . 33 90 19. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33 91 19.1. LISP UDP Port Numbers . . . . . . . . . . . . . . . . . 34 92 20. References . . . . . . . . . . . . . . . . . . . . . . . . . 34 93 20.1. Normative References . . . . . . . . . . . . . . . . . . 34 94 20.2. Informative References . . . . . . . . . . . . . . . . . 35 96 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 39 97 Appendix B. Document Change Log . . . . . . . . . . . . . . . . 39 98 B.1. Changes to draft-ietf-lisp-rfc6830bis-18 . . . . . . . . 40 99 B.2. Changes to draft-ietf-lisp-rfc6830bis-17 . . . . . . . . 40 100 B.3. Changes to draft-ietf-lisp-rfc6830bis-16 . . . . . . . . 40 101 B.4. Changes to draft-ietf-lisp-rfc6830bis-15 . . . . . . . . 40 102 B.5. Changes to draft-ietf-lisp-rfc6830bis-14 . . . . . . . . 40 103 B.6. Changes to draft-ietf-lisp-rfc6830bis-13 . . . . . . . . 40 104 B.7. Changes to draft-ietf-lisp-rfc6830bis-12 . . . . . . . . 41 105 B.8. Changes to draft-ietf-lisp-rfc6830bis-11 . . . . . . . . 41 106 B.9. Changes to draft-ietf-lisp-rfc6830bis-10 . . . . . . . . 41 107 B.10. Changes to draft-ietf-lisp-rfc6830bis-09 . . . . . . . . 41 108 B.11. Changes to draft-ietf-lisp-rfc6830bis-08 . . . . . . . . 42 109 B.12. Changes to draft-ietf-lisp-rfc6830bis-07 . . . . . . . . 42 110 B.13. Changes to draft-ietf-lisp-rfc6830bis-06 . . . . . . . . 42 111 B.14. Changes to draft-ietf-lisp-rfc6830bis-05 . . . . . . . . 42 112 B.15. Changes to draft-ietf-lisp-rfc6830bis-04 . . . . . . . . 43 113 B.16. Changes to draft-ietf-lisp-rfc6830bis-03 . . . . . . . . 43 114 B.17. Changes to draft-ietf-lisp-rfc6830bis-02 . . . . . . . . 43 115 B.18. Changes to draft-ietf-lisp-rfc6830bis-01 . . . . . . . . 43 116 B.19. Changes to draft-ietf-lisp-rfc6830bis-00 . . . . . . . . 43 117 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 43 119 1. Introduction 121 This document describes the Locator/Identifier Separation Protocol 122 (LISP). LISP is an encapsulation protocol built around the 123 fundamental idea of separating the topological location of a network 124 attachment point from the node's identity [CHIAPPA]. As a result 125 LISP creates two namespaces: Endpoint Identifiers (EIDs), that are 126 used to identify end-hosts (e.g., nodes or Virtual Machines) and 127 routable Routing Locators (RLOCs), used to identify network 128 attachment points. LISP then defines functions for mapping between 129 the two namespaces and for encapsulating traffic originated by 130 devices using non-routable EIDs for transport across a network 131 infrastructure that routes and forwards using RLOCs. LISP 132 encapsulation uses a dynamic form of tunneling where no static 133 provisioning is required or necessary. 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 This document obsoletes RFC 6830. 161 2. Requirements Notation 163 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 164 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 165 document are to be interpreted as described in [RFC2119] and 166 [RFC8174]. 168 3. Definition of Terms 170 Address Family Identifier (AFI): AFI is a term used to describe an 171 address encoding in a packet. An address family that pertains to 172 the Data-Plane. See [AFN] and [RFC3232] for details. An AFI 173 value of 0 used in this specification indicates an unspecified 174 encoded address where the length of the address is 0 octets 175 following the 16-bit AFI value of 0. 177 Anycast Address: Anycast Address is a term used in this document to 178 refer to the same IPv4 or IPv6 address configured and used on 179 multiple systems at the same time. An EID or RLOC can be an 180 anycast address in each of their own address spaces. 182 Client-side: Client-side is a term used in this document to indicate 183 a connection initiation attempt by an end-system represented by an 184 EID. 186 Data-Probe: A Data-Probe is a LISP-encapsulated data packet where 187 the inner-header destination address equals the outer-header 188 destination address used to trigger a Map-Reply by a decapsulating 189 ETR. In addition, the original packet is decapsulated and 190 delivered to the destination host if the destination EID is in the 191 EID-Prefix range configured on the ETR. Otherwise, the packet is 192 discarded. A Data-Probe is used in some of the mapping database 193 designs to "probe" or request a Map-Reply from an ETR; in other 194 cases, Map-Requests are used. See each mapping database design 195 for details. When using Data-Probes, by sending Map-Requests on 196 the underlying routing system, EID-Prefixes must be advertised. 198 Egress Tunnel Router (ETR): An ETR is a router that accepts an IP 199 packet where the destination address in the "outer" IP header is 200 one of its own RLOCs. The router strips the "outer" header and 201 forwards the packet based on the next IP header found. In 202 general, an ETR receives LISP-encapsulated IP packets from the 203 Internet on one side and sends decapsulated IP packets to site 204 end-systems on the other side. ETR functionality does not have to 205 be limited to a router device. A server host can be the endpoint 206 of a LISP tunnel as well. 208 EID-to-RLOC Database: The EID-to-RLOC Database is a global 209 distributed database that contains all known EID-Prefix-to-RLOC 210 mappings. Each potential ETR typically contains a small piece of 211 the database: the EID-to-RLOC mappings for the EID-Prefixes 212 "behind" the router. These map to one of the router's own 213 globally visible IP addresses. Note that there MAY be transient 214 conditions when the EID-Prefix for the site and Locator-Set for 215 each EID-Prefix may not be the same on all ETRs. This has no 216 negative implications, since a partial set of Locators can be 217 used. 219 EID-to-RLOC Map-Cache: The EID-to-RLOC Map-Cache is generally 220 short-lived, on-demand table in an ITR that stores, tracks, and is 221 responsible for timing out and otherwise validating EID-to-RLOC 222 mappings. This cache is distinct from the full "database" of EID- 223 to-RLOC mappings; it is dynamic, local to the ITR(s), and 224 relatively small, while the database is distributed, relatively 225 static, and much more global in scope. 227 EID-Prefix: An EID-Prefix is a power-of-two block of EIDs that are 228 allocated to a site by an address allocation authority. EID- 229 Prefixes are associated with a set of RLOC addresses. EID-Prefix 230 allocations can be broken up into smaller blocks when an RLOC set 231 is to be associated with the larger EID-Prefix block. 233 End-System: An end-system is an IPv4 or IPv6 device that originates 234 packets with a single IPv4 or IPv6 header. The end-system 235 supplies an EID value for the destination address field of the IP 236 header when communicating globally (i.e., outside of its routing 237 domain). An end-system can be a host computer, a switch or router 238 device, or any network appliance. 240 Endpoint ID (EID): An EID is a 32-bit (for IPv4) or 128-bit (for 241 IPv6) value used in the source and destination address fields of 242 the first (most inner) LISP header of a packet. The host obtains 243 a destination EID the same way it obtains a destination address 244 today, for example, through a Domain Name System (DNS) [RFC1034] 245 lookup or Session Initiation Protocol (SIP) [RFC3261] exchange. 246 The source EID is obtained via existing mechanisms used to set a 247 host's "local" IP address. An EID used on the public Internet 248 MUST have the same properties as any other IP address used in that 249 manner; this means, among other things, that it MUST be globally 250 unique. An EID is allocated to a host from an EID-Prefix block 251 associated with the site where the host is located. An EID can be 252 used by a host to refer to other hosts. Note that EID blocks MAY 253 be assigned in a hierarchical manner, independent of the network 254 topology, to facilitate scaling of the mapping database. In 255 addition, an EID block assigned to a site MAY have site-local 256 structure (subnetting) for routing within the site; this structure 257 is not visible to the global routing system. In theory, the bit 258 string that represents an EID for one device can represent an RLOC 259 for a different device. When used in discussions with other 260 Locator/ID separation proposals, a LISP EID will be called an 261 "LEID". Throughout this document, any references to "EID" refer 262 to an LEID. 264 Ingress Tunnel Router (ITR): An ITR is a router that resides in a 265 LISP site. Packets sent by sources inside of the LISP site to 266 destinations outside of the site are candidates for encapsulation 267 by the ITR. The ITR treats the IP destination address as an EID 268 and performs an EID-to-RLOC mapping lookup. The router then 269 prepends an "outer" IP header with one of its routable RLOCs (in 270 the RLOC space) in the source address field and the result of the 271 mapping lookup in the destination address field. Note that this 272 destination RLOC MAY be an intermediate, proxy device that has 273 better knowledge of the EID-to-RLOC mapping closer to the 274 destination EID. In general, an ITR receives IP packets from site 275 end-systems on one side and sends LISP-encapsulated IP packets 276 toward the Internet on the other side. 278 Specifically, when a service provider prepends a LISP header for 279 Traffic Engineering purposes, the router that does this is also 280 regarded as an ITR. The outer RLOC the ISP ITR uses can be based 281 on the outer destination address (the originating ITR's supplied 282 RLOC) or the inner destination address (the originating host's 283 supplied EID). 285 LISP Header: LISP header is a term used in this document to refer 286 to the outer IPv4 or IPv6 header, a UDP header, and a LISP- 287 specific 8-octet header that follow the UDP header and that an ITR 288 prepends or an ETR strips. 290 LISP Router: A LISP router is a router that performs the functions 291 of any or all of the following: ITR, ETR, RTR, Proxy-ITR (PITR), 292 or Proxy-ETR (PETR). 294 LISP Site: LISP site is a set of routers in an edge network that are 295 under a single technical administration. LISP routers that reside 296 in the edge network are the demarcation points to separate the 297 edge network from the core network. 299 Locator-Status-Bits (LSBs): Locator-Status-Bits are present in the 300 LISP header. They are used by ITRs to inform ETRs about the up/ 301 down status of all ETRs at the local site. These bits are used as 302 a hint to convey up/down router status and not path reachability 303 status. The LSBs can be verified by use of one of the Locator 304 reachability algorithms described in Section 10. 306 Negative Mapping Entry: A negative mapping entry, also known as a 307 negative cache entry, is an EID-to-RLOC entry where an EID-Prefix 308 is advertised or stored with no RLOCs. That is, the Locator-Set 309 for the EID-to-RLOC entry is empty or has an encoded Locator count 310 of 0. This type of entry could be used to describe a prefix from 311 a non-LISP site, which is explicitly not in the mapping database. 312 There are a set of well-defined actions that are encoded in a 313 Negative Map-Reply. 315 Proxy-ETR (PETR): A PETR is defined and described in [RFC6832]. A 316 PETR acts like an ETR but does so on behalf of LISP sites that 317 send packets to destinations at non-LISP sites. 319 Proxy-ITR (PITR): A PITR is defined and described in [RFC6832]. A 320 PITR acts like an ITR but does so on behalf of non-LISP sites that 321 send packets to destinations at LISP sites. 323 Recursive Tunneling: Recursive Tunneling occurs when a packet has 324 more than one LISP IP header. Additional layers of tunneling MAY 325 be employed to implement Traffic Engineering or other re-routing 326 as needed. When this is done, an additional "outer" LISP header 327 is added, and the original RLOCs are preserved in the "inner" 328 header. 330 Re-Encapsulating Tunneling Router (RTR): An RTR acts like an ETR to 331 remove a LISP header, then acts as an ITR to prepend a new LISP 332 header. This is known as Re-encapsulating Tunneling. Doing this 333 allows a packet to be re-routed by the RTR without adding the 334 overhead of additional tunnel headers. When using multiple 335 mapping database systems, care must be taken to not create re- 336 encapsulation loops through misconfiguration. 338 Route-Returnability: Route-returnability is an assumption that the 339 underlying routing system will deliver packets to the destination. 340 When combined with a nonce that is provided by a sender and 341 returned by a receiver, this limits off-path data insertion. A 342 route-returnability check is verified when a message is sent with 343 a nonce, another message is returned with the same nonce, and the 344 destination of the original message appears as the source of the 345 returned message. 347 Routing Locator (RLOC): An RLOC is an IPv4 [RFC0791] or IPv6 348 [RFC8200] address of an Egress Tunnel Router (ETR). An RLOC is 349 the output of an EID-to-RLOC mapping lookup. An EID maps to zero 350 or more RLOCs. Typically, RLOCs are numbered from blocks that are 351 assigned to a site at each point to which it attaches to the 352 underlay network; where the topology is defined by the 353 connectivity of provider networks. Multiple RLOCs can be assigned 354 to the same ETR device or to multiple ETR devices at a site. 356 Server-side: Server-side is a term used in this document to indicate 357 that a connection initiation attempt is being accepted for a 358 destination EID. 360 TE-ETR: A TE-ETR is an ETR that is deployed in a service provider 361 network that strips an outer LISP header for Traffic Engineering 362 purposes. 364 TE-ITR: A TE-ITR is an ITR that is deployed in a service provider 365 network that prepends an additional LISP header for Traffic 366 Engineering purposes. 368 xTR: An xTR is a reference to an ITR or ETR when direction of data 369 flow is not part of the context description. "xTR" refers to the 370 router that is the tunnel endpoint and is used synonymously with 371 the term "Tunnel Router". For example, "An xTR can be located at 372 the Customer Edge (CE) router" indicates both ITR and ETR 373 functionality at the CE router. 375 4. Basic Overview 377 One key concept of LISP is that end-systems operate the same way they 378 do today. The IP addresses that hosts use for tracking sockets and 379 connections, and for sending and receiving packets, do not change. 380 In LISP terminology, these IP addresses are called Endpoint 381 Identifiers (EIDs). 383 Routers continue to forward packets based on IP destination 384 addresses. When a packet is LISP encapsulated, these addresses are 385 referred to as Routing Locators (RLOCs). Most routers along a path 386 between two hosts will not change; they continue to perform routing/ 387 forwarding lookups on the destination addresses. For routers between 388 the source host and the ITR as well as routers from the ETR to the 389 destination host, the destination address is an EID. For the routers 390 between the ITR and the ETR, the destination address is an RLOC. 392 Another key LISP concept is the "Tunnel Router". A Tunnel Router 393 prepends LISP headers on host-originated packets and strips them 394 prior to final delivery to their destination. The IP addresses in 395 this "outer header" are RLOCs. During end-to-end packet exchange 396 between two Internet hosts, an ITR prepends a new LISP header to each 397 packet, and an ETR strips the new header. The ITR performs EID-to- 398 RLOC lookups to determine the routing path to the ETR, which has the 399 RLOC as one of its IP addresses. 401 Some basic rules governing LISP are: 403 o End-systems only send to addresses that are EIDs. EIDs are 404 typically IP addresses assigned to hosts (other types of EID are 405 supported by LISP, see [RFC8060] for further information). End- 406 systems don't know that addresses are EIDs versus RLOCs but assume 407 that packets get to their intended destinations. In a system 408 where LISP is deployed, LISP routers intercept EID-addressed 409 packets and assist in delivering them across the network core 410 where EIDs cannot be routed. The procedure a host uses to send IP 411 packets does not change. 413 o LISP routers mostly deal with Routing Locator addresses. See 414 details in Section 4.1 to clarify what is meant by "mostly". 416 o RLOCs are always IP addresses assigned to routers, preferably 417 topologically oriented addresses from provider CIDR (Classless 418 Inter-Domain Routing) blocks. 420 o When a router originates packets, it MAY use as a source address 421 either an EID or RLOC. When acting as a host (e.g., when 422 terminating a transport session such as Secure SHell (SSH), 423 TELNET, or the Simple Network Management Protocol (SNMP)), it MAY 424 use an EID that is explicitly assigned for that purpose. An EID 425 that identifies the router as a host MUST NOT be used as an RLOC; 426 an EID is only routable within the scope of a site. A typical BGP 427 configuration might demonstrate this "hybrid" EID/RLOC usage where 428 a router could use its "host-like" EID to terminate iBGP sessions 429 to other routers in a site while at the same time using RLOCs to 430 terminate eBGP sessions to routers outside the site. 432 o Packets with EIDs in them are not expected to be delivered end-to- 433 end in the absence of an EID-to-RLOC mapping operation. They are 434 expected to be used locally for intra-site communication or to be 435 encapsulated for inter-site communication. 437 o EIDs MAY also be structured (subnetted) in a manner suitable for 438 local routing within an Autonomous System (AS). 440 An additional LISP header MAY be prepended to packets by a TE-ITR 441 when re-routing of the path for a packet is desired. A potential 442 use-case for this would be an ISP router that needs to perform 443 Traffic Engineering for packets flowing through its network. In such 444 a situation, termed "Recursive Tunneling", an ISP transit acts as an 445 additional ITR, and the RLOC it uses for the new prepended header 446 would be either a TE-ETR within the ISP (along an intra-ISP traffic 447 engineered path) or a TE-ETR within another ISP (an inter-ISP traffic 448 engineered path, where an agreement to build such a path exists). 450 In order to avoid excessive packet overhead as well as possible 451 encapsulation loops, this document recommends that a maximum of two 452 LISP headers can be prepended to a packet. For initial LISP 453 deployments, it is assumed that two headers is sufficient, where the 454 first prepended header is used at a site for Location/Identity 455 separation and the second prepended header is used inside a service 456 provider for Traffic Engineering purposes. 458 Tunnel Routers can be placed fairly flexibly in a multi-AS topology. 459 For example, the ITR for a particular end-to-end packet exchange 460 might be the first-hop or default router within a site for the source 461 host. Similarly, the ETR might be the last-hop router directly 462 connected to the destination host. Another example, perhaps for a 463 VPN service outsourced to an ISP by a site, the ITR could be the 464 site's border router at the service provider attachment point. 465 Mixing and matching of site-operated, ISP-operated, and other Tunnel 466 Routers is allowed for maximum flexibility. 468 4.1. Packet Flow Sequence 470 This section provides an example of the unicast packet flow, 471 including also Control-Plane information as specified in 472 [I-D.ietf-lisp-rfc6833bis]. The example also assumes the following 473 conditions: 475 o Source host "host1.abc.example.com" is sending a packet to 476 "host2.xyz.example.com", exactly what host1 would do if the site 477 was not using LISP. 479 o Each site is multihomed, so each Tunnel Router has an address 480 (RLOC) assigned from the service provider address block for each 481 provider to which that particular Tunnel Router is attached. 483 o The ITR(s) and ETR(s) are directly connected to the source and 484 destination, respectively, but the source and destination can be 485 located anywhere in the LISP site. 487 o A Map-Request is sent for an external destination when the 488 destination is not found in the forwarding table or matches a 489 default route. Map-Requests are sent to the mapping database 490 system by using the LISP Control-Plane protocol documented in 491 [I-D.ietf-lisp-rfc6833bis]. 493 o Map-Replies are sent on the underlying routing system topology 494 using the [I-D.ietf-lisp-rfc6833bis] Control-Plane protocol. 496 Client host1.abc.example.com wants to communicate with server 497 host2.xyz.example.com: 499 1. host1.abc.example.com wants to open a TCP connection to 500 host2.xyz.example.com. It does a DNS lookup on 501 host2.xyz.example.com. An A/AAAA record is returned. This 502 address is the destination EID. The locally assigned address of 503 host1.abc.example.com is used as the source EID. An IPv4 or IPv6 504 packet is built and forwarded through the LISP site as a normal 505 IP packet until it reaches a LISP ITR. 507 2. The LISP ITR must be able to map the destination EID to an RLOC 508 of one of the ETRs at the destination site. The specific method 509 used to do this is not described in this example. See 510 [I-D.ietf-lisp-rfc6833bis] for further information. 512 3. The ITR sends a LISP Map-Request as specified in 513 [I-D.ietf-lisp-rfc6833bis]. Map-Requests SHOULD be rate-limited. 515 4. The mapping system helps forwarding the Map-Request to the 516 corresponding ETR. When the Map-Request arrives at one of the 517 ETRs at the destination site, it will process the packet as a 518 control message. 520 5. The ETR looks at the destination EID of the Map-Request and 521 matches it against the prefixes in the ETR's configured EID-to- 522 RLOC mapping database. This is the list of EID-Prefixes the ETR 523 is supporting for the site it resides in. If there is no match, 524 the Map-Request is dropped. Otherwise, a LISP Map-Reply is 525 returned to the ITR. 527 6. The ITR receives the Map-Reply message, parses the message (to 528 check for format validity), and stores the mapping information 529 from the packet. This information is stored in the ITR's EID-to- 530 RLOC Map-Cache. Note that the Map-Cache is an on-demand cache. 531 An ITR will manage its Map-Cache in such a way that optimizes for 532 its resource constraints. 534 7. Subsequent packets from host1.abc.example.com to 535 host2.xyz.example.com will have a LISP header prepended by the 536 ITR using the appropriate RLOC as the LISP header destination 537 address learned from the ETR. Note that the packet MAY be sent 538 to a different ETR than the one that returned the Map-Reply due 539 to the source site's hashing policy or the destination site's 540 Locator-Set policy. 542 8. The ETR receives these packets directly (since the destination 543 address is one of its assigned IP addresses), checks the validity 544 of the addresses, strips the LISP header, and forwards packets to 545 the attached destination host. 547 9. In order to defer the need for a mapping lookup in the reverse 548 direction, an ETR can OPTIONALLY create a cache entry that maps 549 the source EID (inner-header source IP address) to the source 550 RLOC (outer-header source IP address) in a received LISP packet. 551 Such a cache entry is termed a "glean mapping" and only contains 552 a single RLOC for the EID in question. More complete information 553 about additional RLOCs SHOULD be verified by sending a LISP Map- 554 Request for that EID. Both the ITR and the ETR MAY also 555 influence the decision the other makes in selecting an RLOC. 557 5. LISP Encapsulation Details 559 Since additional tunnel headers are prepended, the packet becomes 560 larger and can exceed the MTU of any link traversed from the ITR to 561 the ETR. It is RECOMMENDED in IPv4 that packets do not get 562 fragmented as they are encapsulated by the ITR. Instead, the packet 563 is dropped and an ICMP Unreachable/Fragmentation-Needed message is 564 returned to the source. 566 In the case when fragmentation is needed, this specification 567 RECOMMENDS that implementations provide support for one of the 568 proposed fragmentation and reassembly schemes. Two existing schemes 569 are detailed in Section 7. 571 Since IPv4 or IPv6 addresses can be either EIDs or RLOCs, the LISP 572 architecture supports IPv4 EIDs with IPv6 RLOCs (where the inner 573 header is in IPv4 packet format and the outer header is in IPv6 574 packet format) or IPv6 EIDs with IPv4 RLOCs (where the inner header 575 is in IPv6 packet format and the outer header is in IPv4 packet 576 format). The next sub-sections illustrate packet formats for the 577 homogeneous case (IPv4-in-IPv4 and IPv6-in-IPv6), but all 4 578 combinations MUST be supported. Additional types of EIDs are defined 579 in [RFC8060]. 581 As LISP uses UDP encapsulation to carry traffic between xTRs across 582 the Internet, implementors should be aware of the provisions of 583 [RFC8085], especially those given in section 3.1.11 on congestion 584 control for UDP tunneling. 586 Implementors are encouraged to consider UDP checksum usage guidelines 587 in section 3.4 of [RFC8085] when it is desirable to protect UDP and 588 LISP headers against corruption. 590 5.1. LISP IPv4-in-IPv4 Header Format 591 0 1 2 3 592 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 1 593 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 594 / |Version| IHL | DSCP |ECN| Total Length | 595 / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 596 | | Identification |Flags| Fragment Offset | 597 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 598 OH | Time to Live | Protocol = 17 | Header Checksum | 599 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 600 | | Source Routing Locator | 601 \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 602 \ | Destination Routing Locator | 603 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 604 / | Source Port = xxxx | Dest Port = 4341 | 605 UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 606 \ | UDP Length | UDP Checksum | 607 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 608 L |N|L|E|V|I|R|K|K| Nonce/Map-Version | 609 I \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 610 S / | Instance ID/Locator-Status-Bits | 611 P +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 612 / |Version| IHL | DSCP |ECN| Total Length | 613 / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 614 | | Identification |Flags| Fragment Offset | 615 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 616 IH | Time to Live | Protocol | Header Checksum | 617 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 618 | | Source EID | 619 \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 620 \ | Destination EID | 621 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 623 IHL = IP-Header-Length 625 5.2. LISP IPv6-in-IPv6 Header Format 627 0 1 2 3 628 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 1 629 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 630 / |Version| DSCP |ECN| Flow Label | 631 / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 632 | | Payload Length | Next Header=17| Hop Limit | 633 v +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 634 | | 635 O + + 636 u | | 637 t + Source Routing Locator + 638 e | | 639 r + + 640 | | 641 H +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 642 d | | 643 r + + 644 | | 645 ^ + Destination Routing Locator + 646 | | | 647 \ + + 648 \ | | 649 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 650 / | Source Port = xxxx | Dest Port = 4341 | 651 UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 652 \ | UDP Length | UDP Checksum | 653 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 654 L |N|L|E|V|I|R|K|K| Nonce/Map-Version | 655 I \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 656 S / | Instance ID/Locator-Status-Bits | 657 P +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 658 / |Version| DSCP |ECN| Flow Label | 659 / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 660 / | Payload Length | Next Header | Hop Limit | 661 v +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 662 | | 663 I + + 664 n | | 665 n + Source EID + 666 e | | 667 r + + 668 | | 669 H +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 670 d | | 671 r + + 672 | | 673 ^ + Destination EID + 674 \ | | 675 \ + + 676 \ | | 677 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 679 5.3. Tunnel Header Field Descriptions 681 Inner Header (IH): The inner header is the header on the 682 datagram received from the originating host [RFC0791] [RFC8200] 683 [RFC2474]. The source and destination IP addresses are EIDs. 685 Outer Header: (OH) The outer header is a new header prepended by an 686 ITR. The address fields contain RLOCs obtained from the ingress 687 router's EID-to-RLOC Cache. The IP protocol number is "UDP (17)" 688 from [RFC0768]. The setting of the Don't Fragment (DF) bit 689 'Flags' field is according to rules listed in Sections 7.1 and 690 7.2. 692 UDP Header: The UDP header contains an ITR selected source port when 693 encapsulating a packet. See Section 12 for details on the hash 694 algorithm used to select a source port based on the 5-tuple of the 695 inner header. The destination port MUST be set to the well-known 696 IANA-assigned port value 4341. 698 UDP Checksum: The 'UDP Checksum' field SHOULD be transmitted as zero 699 by an ITR for either IPv4 [RFC0768] and IPv6 encapsulation 700 [RFC6935] [RFC6936]. When a packet with a zero UDP checksum is 701 received by an ETR, the ETR MUST accept the packet for 702 decapsulation. When an ITR transmits a non-zero value for the UDP 703 checksum, it MUST send a correctly computed value in this field. 704 When an ETR receives a packet with a non-zero UDP checksum, it MAY 705 choose to verify the checksum value. If it chooses to perform 706 such verification, and the verification fails, the packet MUST be 707 silently dropped. If the ETR chooses not to perform the 708 verification, or performs the verification successfully, the 709 packet MUST be accepted for decapsulation. The handling of UDP 710 zero checksums over IPv6 for all tunneling protocols, including 711 LISP, is subject to the applicability statement in [RFC6936]. 713 UDP Length: The 'UDP Length' field is set for an IPv4-encapsulated 714 packet to be the sum of the inner-header IPv4 Total Length plus 715 the UDP and LISP header lengths. For an IPv6-encapsulated packet, 716 the 'UDP Length' field is the sum of the inner-header IPv6 Payload 717 Length, the size of the IPv6 header (40 octets), and the size of 718 the UDP and LISP headers. 720 N: The N-bit is the nonce-present bit. When this bit is set to 1, 721 the low-order 24 bits of the first 32 bits of the LISP header 722 contain a Nonce. See Section 10.1 for details. Both N- and 723 V-bits MUST NOT be set in the same packet. If they are, a 724 decapsulating ETR MUST treat the 'Nonce/Map-Version' field as 725 having a Nonce value present. 727 L: The L-bit is the 'Locator-Status-Bits' field enabled bit. When 728 this bit is set to 1, the Locator-Status-Bits in the second 729 32 bits of the LISP header are in use. 731 x 1 x x 0 x x x 732 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 733 |N|L|E|V|I|R|K|K| Nonce/Map-Version | 734 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 735 | Locator-Status-Bits | 736 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 738 E: The E-bit is the echo-nonce-request bit. This bit MUST be ignored 739 and has no meaning when the N-bit is set to 0. When the N-bit is 740 set to 1 and this bit is set to 1, an ITR is requesting that the 741 nonce value in the 'Nonce' field be echoed back in LISP- 742 encapsulated packets when the ITR is also an ETR. See 743 Section 10.1 for details. 745 V: The V-bit is the Map-Version present bit. When this bit is set to 746 1, the N-bit MUST be 0. Refer to Section 13.1 for more details. 747 This bit indicates that the LISP header is encoded in this 748 case as: 750 0 x 0 1 x x x x 751 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 752 |N|L|E|V|I|R|K|K| Source Map-Version | Dest Map-Version | 753 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 754 | Instance ID/Locator-Status-Bits | 755 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 757 I: The I-bit is the Instance ID bit. See Section 8 for more details. 758 When this bit is set to 1, the 'Locator-Status-Bits' field is 759 reduced to 8 bits and the high-order 24 bits are used as an 760 Instance ID. If the L-bit is set to 0, then the low-order 8 bits 761 are transmitted as zero and ignored on receipt. The format of the 762 LISP header would look like this: 764 x x x x 1 x x x 765 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 766 |N|L|E|V|I|R|K|K| Nonce/Map-Version | 767 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 768 | Instance ID | LSBs | 769 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 771 R: The R-bit is a Reserved bit for future use. It MUST be set to 0 772 on transmit and MUST be ignored on receipt. 774 KK: The KK-bits are a 2-bit field used when encapsulated packets are 775 encrypted. The field is set to 00 when the packet is not 776 encrypted. See [RFC8061] for further information. 778 LISP Nonce: The LISP 'Nonce' field is a 24-bit value that is 779 randomly generated by an ITR when the N-bit is set to 1. Nonce 780 generation algorithms are an implementation matter but are 781 required to generate different nonces when sending to different 782 RLOCs. However, the same nonce can be used for a period of time 783 when encapsulating to the same ETR. The nonce is also used when 784 the E-bit is set to request the nonce value to be echoed by the 785 other side when packets are returned. When the E-bit is clear but 786 the N-bit is set, a remote ITR is either echoing a previously 787 requested echo-nonce or providing a random nonce. See 788 Section 10.1 for more details. 790 LISP Locator-Status-Bits (LSBs): When the L-bit is also set, the 791 'Locator-Status-Bits' field in the LISP header is set by an ITR to 792 indicate to an ETR the up/down status of the Locators in the 793 source site. Each RLOC in a Map-Reply is assigned an ordinal 794 value from 0 to n-1 (when there are n RLOCs in a mapping entry). 795 The Locator-Status-Bits are numbered from 0 to n-1 from the least 796 significant bit of the field. The field is 32 bits when the I-bit 797 is set to 0 and is 8 bits when the I-bit is set to 1. When a 798 Locator-Status-Bit is set to 1, the ITR is indicating to the ETR 799 that the RLOC associated with the bit ordinal has up status. See 800 Section 10 for details on how an ITR can determine the status of 801 the ETRs at the same site. When a site has multiple EID-Prefixes 802 that result in multiple mappings (where each could have a 803 different Locator-Set), the Locator-Status-Bits setting in an 804 encapsulated packet MUST reflect the mapping for the EID-Prefix 805 that the inner-header source EID address matches. If the LSB for 806 an anycast Locator is set to 1, then there is at least one RLOC 807 with that address, and the ETR is considered 'up'. 809 When doing ITR/PITR encapsulation: 811 o The outer-header 'Time to Live' field (or 'Hop Limit' field, in 812 the case of IPv6) SHOULD be copied from the inner-header 'Time to 813 Live' field. 815 o The outer-header 'Differentiated Services Code Point' (DSCP) field 816 (or the 'Traffic Class' field, in the case of IPv6) SHOULD be 817 copied from the inner-header DSCP field ('Traffic Class' field, in 818 the case of IPv6) considering the exception listed below. 820 o The 'Explicit Congestion Notification' (ECN) field (bits 6 and 7 821 of the IPv6 'Traffic Class' field) requires special treatment in 822 order to avoid discarding indications of congestion [RFC3168]. 823 ITR encapsulation MUST copy the 2-bit 'ECN' field from the inner 824 header to the outer header. Re-encapsulation MUST copy the 2-bit 825 'ECN' field from the stripped outer header to the new outer 826 header. 828 When doing ETR/PETR decapsulation: 830 o The inner-header 'Time to Live' field (or 'Hop Limit' field, in 831 the case of IPv6) SHOULD be copied from the outer-header 'Time to 832 Live' field, when the Time to Live value of the outer header is 833 less than the Time to Live value of the inner header. Failing to 834 perform this check can cause the Time to Live of the inner header 835 to increment across encapsulation/decapsulation cycles. This 836 check is also performed when doing initial encapsulation, when a 837 packet comes to an ITR or PITR destined for a LISP site. 839 o The inner-header 'Differentiated Services Code Point' (DSCP) field 840 (or the 'Traffic Class' field, in the case of IPv6) SHOULD be 841 copied from the outer-header DSCP field ('Traffic Class' field, in 842 the case of IPv6) to the inner-header. 844 o The 'Explicit Congestion Notification' (ECN) field (bits 6 and 7 845 of the IPv6 'Traffic Class' field) requires special treatment in 846 order to avoid discarding indications of congestion [RFC6040]. If 847 the 'ECN' field contains a congestion indication codepoint (the 848 value is '11', the Congestion Experienced (CE) codepoint), then 849 ETR decapsulation MUST copy the 2-bit 'ECN' field from the 850 stripped outer header to the surviving inner header that is used 851 to forward the packet beyond the ETR. These requirements preserve 852 CE indications when a packet that uses ECN traverses a LISP tunnel 853 and becomes marked with a CE indication due to congestion between 854 the tunnel endpoints. Implementations exist that copy the 'ECN' 855 field from the outer header to the inner header even though 856 [RFC6040] does not recommend this behavior. It is RECOMMENDED 857 that implementations change to support the behavior in [RFC6040]. 859 Note that if an ETR/PETR is also an ITR/PITR and chooses to re- 860 encapsulate after decapsulating, the net effect of this is that the 861 new outer header will carry the same Time to Live as the old outer 862 header minus 1. 864 Copying the Time to Live (TTL) serves two purposes: first, it 865 preserves the distance the host intended the packet to travel; 866 second, and more importantly, it provides for suppression of looping 867 packets in the event there is a loop of concatenated tunnels due to 868 misconfiguration. 870 The Explicit Congestion Notification ('ECN') field occupies bits 6 871 and 7 of both the IPv4 'Type of Service' field and the IPv6 'Traffic 872 Class' field [RFC6040]. The 'ECN' field requires special treatment 873 in order to avoid discarding indications of congestion [RFC6040]. An 874 ITR/PITR encapsulation MUST copy the 2-bit 'ECN' field from the inner 875 header to the outer header. Re-encapsulation MUST copy the 2-bit 876 'ECN' field from the stripped outer header to the new outer header. 877 If the 'ECN' field contains a congestion indication codepoint (the 878 value is '11', the Congestion Experienced (CE) codepoint), then ETR/ 879 PETR decapsulation MUST copy the 2-bit 'ECN' field from the stripped 880 outer header to the surviving inner header that is used to forward 881 the packet beyond the ETR. These requirements preserve CE 882 indications when a packet that uses ECN traverses a LISP tunnel and 883 becomes marked with a CE indication due to congestion between the 884 tunnel endpoints. 886 6. LISP EID-to-RLOC Map-Cache 888 ITRs and PITRs maintain an on-demand cache, referred as LISP EID-to- 889 RLOC Map-Cache, that contains mappings from EID-prefixes to locator 890 sets. The cache is used to encapsulate packets from the EID space to 891 the corresponding RLOC network attachment point. 893 When an ITR/PITR receives a packet from inside of the LISP site to 894 destinations outside of the site a longest-prefix match lookup of the 895 EID is done to the Map-Cache. 897 When the lookup succeeds, the Locator-Set retrieved from the Map- 898 Cache is used to send the packet to the EID's topological location. 900 If the lookup fails, the ITR/PITR needs to retrieve the mapping using 901 the LISP Control-Plane protocol [I-D.ietf-lisp-rfc6833bis]. The 902 mapping is then stored in the local Map-Cache to forward subsequent 903 packets addressed to the same EID-prefix. 905 The Map-Cache is a local cache of mappings, entries are expired based 906 on the associated Time to live. In addition, entries can be updated 907 with more current information, see Section 13 for further information 908 on this. Finally, the Map-Cache also contains reachability 909 information about EIDs and RLOCs, and uses LISP reachability 910 information mechanisms to determine the reachability of RLOCs, see 911 Section 10 for the specific mechanisms. 913 7. Dealing with Large Encapsulated Packets 915 This section proposes two mechanisms to deal with packets that exceed 916 the path MTU between the ITR and ETR. 918 It is left to the implementor to decide if the stateless or stateful 919 mechanism SHOULD be implemented. Both or neither can be used, since 920 it is a local decision in the ITR regarding how to deal with MTU 921 issues, and sites can interoperate with differing mechanisms. 923 Both stateless and stateful mechanisms also apply to Re-encapsulating 924 and Recursive Tunneling, so any actions below referring to an ITR 925 also apply to a TE-ITR. 927 7.1. A Stateless Solution to MTU Handling 929 An ITR stateless solution to handle MTU issues is described as 930 follows: 932 1. Define H to be the size, in octets, of the outer header an ITR 933 prepends to a packet. This includes the UDP and LISP header 934 lengths. 936 2. Define L to be the size, in octets, of the maximum-sized packet 937 an ITR can send to an ETR without the need for the ITR or any 938 intermediate routers to fragment the packet. 940 3. Define an architectural constant S for the maximum size of a 941 packet, in octets, an ITR MUST receive from the source so the 942 effective MTU can be met. That is, L = S + H. 944 When an ITR receives a packet from a site-facing interface and adds H 945 octets worth of encapsulation to yield a packet size greater than L 946 octets (meaning the received packet size was greater than S octets 947 from the source), it resolves the MTU issue by first splitting the 948 original packet into 2 equal-sized fragments. A LISP header is then 949 prepended to each fragment. The size of the encapsulated fragments 950 is then (S/2 + H), which is less than the ITR's estimate of the path 951 MTU between the ITR and its correspondent ETR. 953 When an ETR receives encapsulated fragments, it treats them as two 954 individually encapsulated packets. It strips the LISP headers and 955 then forwards each fragment to the destination host of the 956 destination site. The two fragments are reassembled at the 957 destination host into the single IP datagram that was originated by 958 the source host. Note that reassembly can happen at the ETR if the 959 encapsulated packet was fragmented at or after the ITR. 961 This behavior MAY be performed by the ITR only when the source host 962 originates a packet with the 'DF' field of the IP header set to 0. 963 When the 'DF' field of the IP header is set to 1, or the packet is an 964 IPv6 packet originated by the source host, the ITR will drop the 965 packet when the size is greater than L and send an ICMP Unreachable/ 966 Fragmentation-Needed message to the source with a value of S, where S 967 is (L - H). 969 When the outer-header encapsulation uses an IPv4 header, an 970 implementation SHOULD set the DF bit to 1 so ETR fragment reassembly 971 can be avoided. An implementation MAY set the DF bit in such headers 972 to 0 if it has good reason to believe there are unresolvable path MTU 973 issues between the sending ITR and the receiving ETR. 975 This specification RECOMMENDS that L be defined as 1500. 977 7.2. A Stateful Solution to MTU Handling 979 An ITR stateful solution to handle MTU issues is described as follows 980 and was first introduced in [OPENLISP]: 982 1. The ITR will keep state of the effective MTU for each Locator per 983 Map-Cache entry. The effective MTU is what the core network can 984 deliver along the path between the ITR and ETR. 986 2. When an IPv6-encapsulated packet, or an IPv4-encapsulated packet 987 with the DF bit set to 1, exceeds what the core network can 988 deliver, one of the intermediate routers on the path will send an 989 ICMPv6 "Packet Too Big" message or an ICMPv4 Unreachable/ 990 Fragmentation-Needed to the ITR, respectively. The ITR will 991 parse the ICMP message to determine which Locator is affected by 992 the effective MTU change and then record the new effective MTU 993 value in the Map-Cache entry. 995 3. When a packet is received by the ITR from a source inside of the 996 site and the size of the packet is greater than the effective MTU 997 stored with the Map-Cache entry associated with the destination 998 EID the packet is for, the ITR will send an ICMPv4 ICMP 999 Unreachable/Fragmentation-Needed or ICMPv6 "Packet Too Big" 1000 message back to the source. The packet size advertised by the 1001 ITR in the ICMP message is the effective MTU minus the LISP 1002 encapsulation length. 1004 Even though this mechanism is stateful, it has advantages over the 1005 stateless IP fragmentation mechanism, by not involving the 1006 destination host with reassembly of ITR fragmented packets. 1008 8. Using Virtualization and Segmentation with LISP 1010 There are several cases where segregation is needed at the EID level. 1011 For instance, this is the case for deployments containing overlapping 1012 addresses, traffic isolation policies or multi-tenant virtualization. 1013 For these and other scenarios where segregation is needed, Instance 1014 IDs are used. 1016 An Instance ID can be carried in a LISP-encapsulated packet. An ITR 1017 that prepends a LISP header will copy a 24-bit value used by the LISP 1018 router to uniquely identify the address space. The value is copied 1019 to the 'Instance ID' field of the LISP header, and the I-bit is set 1020 to 1. 1022 When an ETR decapsulates a packet, the Instance ID from the LISP 1023 header is used as a table identifier to locate the forwarding table 1024 to use for the inner destination EID lookup. 1026 For example, an 802.1Q VLAN tag or VPN identifier could be used as a 1027 24-bit Instance ID. See [I-D.ietf-lisp-vpn] for LISP VPN use-case 1028 details. 1030 The Instance ID that is stored in the mapping database when LISP-DDT 1031 [RFC8111] is used is 32 bits in length. That means the Control-Plane 1032 can store more instances than a given Data-Plane can use. Multiple 1033 Data-Planes can use the same 32-bit space as long as the low-order 24 1034 bits don't overlap among xTRs. 1036 9. Routing Locator Selection 1038 The Map-Cache contains the state used by ITRs and PITRs to 1039 encapsulate packets. When an ITR/PITR receives a packet from inside 1040 the LISP site to a destination outside of the site a longest-prefix 1041 match lookup of the EID is done to the Map-Cache (see Section 6). 1042 The lookup returns a single Locator-Set containing a list of RLOCs 1043 corresponding to the EID's topological location. Each RLOC in the 1044 Locator-Set is associated with a 'Priority' and 'Weight', this 1045 information is used to select the RLOC to encapsulate. 1047 The RLOC with the lowest 'Priority' is selected. An RLOC with 1048 'Priority' 255 means that MUST NOT be used for forwarding. When 1049 multiple RLOC have the same 'Priority' then the 'Weight' states how 1050 to load balance traffic among them. The value of the 'Weight' 1051 represents the relative weight of the total packets that match the 1052 maping entry. 1054 The following are different scenarios for choosing RLOCs and the 1055 controls that are available: 1057 o The server-side returns one RLOC. The client-side can only use 1058 one RLOC. The server-side has complete control of the selection. 1060 o The server-side returns a list of RLOCs where a subset of the list 1061 has the same best Priority. The client can only use the subset 1062 list according to the weighting assigned by the server-side. In 1063 this case, the server-side controls both the subset list and load- 1064 splitting across its members. The client-side can use RLOCs 1065 outside of the subset list if it determines that the subset list 1066 is unreachable (unless RLOCs are set to a Priority of 255). Some 1067 sharing of control exists: the server-side determines the 1068 destination RLOC list and load distribution while the client-side 1069 has the option of using alternatives to this list if RLOCs in the 1070 list are unreachable. 1072 o The server-side sets a Weight of zero for the RLOC subset list. 1073 In this case, the client-side can choose how the traffic load is 1074 spread across the subset list. Control is shared by the server- 1075 side determining the list and the client-side determining load 1076 distribution. Again, the client can use alternative RLOCs if the 1077 server-provided list of RLOCs is unreachable. 1079 o Either side (more likely the server-side ETR) decides not to send 1080 a Map-Request. For example, if the server-side ETR does not send 1081 Map-Requests, it gleans RLOCs from the client-side ITR, giving the 1082 client-side ITR responsibility for bidirectional RLOC reachability 1083 and preferability. Server-side ETR gleaning of the client-side 1084 ITR RLOC is done by caching the inner-header source EID and the 1085 outer-header source RLOC of received packets. The client-side ITR 1086 controls how traffic is returned and can alternate using an outer- 1087 header source RLOC, which then can be added to the list the 1088 server-side ETR uses to return traffic. Since no Priority or 1089 Weights are provided using this method, the server-side ETR MUST 1090 assume that each client-side ITR RLOC uses the same best Priority 1091 with a Weight of zero. In addition, since EID-Prefix encoding 1092 cannot be conveyed in data packets, the EID-to-RLOC Cache on 1093 Tunnel Routers can grow to be very large. 1095 Alternatively, RLOC information MAY be gleaned from received tunneled 1096 packets or EID-to-RLOC Map-Request messages. A "gleaned" Map-Cache 1097 entry, one learned from the source RLOC of a received encapsulated 1098 packet, is only stored and used for a few seconds, pending 1099 verification. Verification is performed by sending a Map-Request to 1100 the source EID (the inner-header IP source address) of the received 1101 encapsulated packet. A reply to this "verifying Map-Request" is used 1102 to fully populate the Map-Cache entry for the "gleaned" EID and is 1103 stored and used for the time indicated from the 'TTL' field of a 1104 received Map-Reply. When a verified Map-Cache entry is stored, data 1105 gleaning no longer occurs for subsequent packets that have a source 1106 EID that matches the EID-Prefix of the verified entry. This 1107 "gleaning" mechanism is OPTIONAL, refer to Section 16 for security 1108 issues regarding this mechanism. 1110 RLOCs that appear in EID-to-RLOC Map-Reply messages are assumed to be 1111 reachable when the R-bit for the Locator record is set to 1. When 1112 the R-bit is set to 0, an ITR or PITR MUST NOT encapsulate to the 1113 RLOC. Neither the information contained in a Map-Reply nor that 1114 stored in the mapping database system provides reachability 1115 information for RLOCs. Note that reachability is not part of the 1116 mapping system and is determined using one or more of the Routing 1117 Locator reachability algorithms described in the next section. 1119 10. Routing Locator Reachability 1121 Several Data-Plane mechanisms for determining RLOC reachability are 1122 currently defined. Please note that additional Control-Plane based 1123 reachability mechanisms are defined in [I-D.ietf-lisp-rfc6833bis]. 1125 1. An ETR MAY examine the Locator-Status-Bits in the LISP header of 1126 an encapsulated data packet received from an ITR. If the ETR is 1127 also acting as an ITR and has traffic to return to the original 1128 ITR site, it can use this status information to help select an 1129 RLOC. 1131 2. When an ETR receives an encapsulated packet from an ITR, the 1132 source RLOC from the outer header of the packet is likely up. 1134 3. An ITR/ETR pair can use the 'Echo-Noncing' Locator reachability 1135 algorithms described in this section. 1137 When determining Locator up/down reachability by examining the 1138 Locator-Status-Bits from the LISP-encapsulated data packet, an ETR 1139 will receive up-to-date status from an encapsulating ITR about 1140 reachability for all ETRs at the site. CE-based ITRs at the source 1141 site can determine reachability relative to each other using the site 1142 IGP as follows: 1144 o Under normal circumstances, each ITR will advertise a default 1145 route into the site IGP. 1147 o If an ITR fails or if the upstream link to its PE fails, its 1148 default route will either time out or be withdrawn. 1150 Each ITR can thus observe the presence or lack of a default route 1151 originated by the others to determine the Locator-Status-Bits it sets 1152 for them. 1154 When ITRs at the site are not deployed in CE routers, the IGP can 1155 still be used to determine the reachability of Locators, provided 1156 they are injected into the IGP. This is typically done when a /32 1157 address is configured on a loopback interface. 1159 RLOCs listed in a Map-Reply are numbered with ordinals 0 to n-1. The 1160 Locator-Status-Bits in a LISP-encapsulated packet are numbered from 0 1161 to n-1 starting with the least significant bit. For example, if an 1162 RLOC listed in the 3rd position of the Map-Reply goes down (ordinal 1163 value 2), then all ITRs at the site will clear the 3rd least 1164 significant bit (xxxx x0xx) of the 'Locator-Status-Bits' field for 1165 the packets they encapsulate. 1167 When an ETR decapsulates a packet, it will check for any change in 1168 the 'Locator-Status-Bits' field. When a bit goes from 1 to 0, the 1169 ETR, if acting also as an ITR, will refrain from encapsulating 1170 packets to an RLOC that is indicated as down. It will only resume 1171 using that RLOC if the corresponding Locator-Status-Bit returns to a 1172 value of 1. Locator-Status-Bits are associated with a Locator-Set 1173 per EID-Prefix. Therefore, when a Locator becomes unreachable, the 1174 Locator-Status-Bit that corresponds to that Locator's position in the 1175 list returned by the last Map-Reply will be set to zero for that 1176 particular EID-Prefix. Refer to Section 16 for security related 1177 issues regarding Locator-Status-Bits. 1179 When an ETR decapsulates a packet, it knows that it is reachable from 1180 the encapsulating ITR because that is how the packet arrived. In 1181 most cases, the ETR can also reach the ITR but cannot assume this to 1182 be true, due to the possibility of path asymmetry. In the presence 1183 of unidirectional traffic flow from an ITR to an ETR, the ITR SHOULD 1184 NOT use the lack of return traffic as an indication that the ETR is 1185 unreachable. Instead, it MUST use an alternate mechanism to 1186 determine reachability. 1188 10.1. Echo Nonce Algorithm 1190 When data flows bidirectionally between Locators from different 1191 sites, a Data-Plane mechanism called "nonce echoing" can be used to 1192 determine reachability between an ITR and ETR. When an ITR wants to 1193 solicit a nonce echo, it sets the N- and E-bits and places a 24-bit 1194 nonce [RFC4086] in the LISP header of the next encapsulated data 1195 packet. 1197 When this packet is received by the ETR, the encapsulated packet is 1198 forwarded as normal. When the ETR next sends a data packet to the 1199 ITR, it includes the nonce received earlier with the N-bit set and 1200 E-bit cleared. The ITR sees this "echoed nonce" and knows that the 1201 path to and from the ETR is up. 1203 The ITR will set the E-bit and N-bit for every packet it sends while 1204 in the echo-nonce-request state. The time the ITR waits to process 1205 the echoed nonce before it determines the path is unreachable is 1206 variable and is a choice left for the implementation. 1208 If the ITR is receiving packets from the ETR but does not see the 1209 nonce echoed while being in the echo-nonce-request state, then the 1210 path to the ETR is unreachable. This decision MAY be overridden by 1211 other Locator reachability algorithms. Once the ITR determines that 1212 the path to the ETR is down, it can switch to another Locator for 1213 that EID-Prefix. 1215 Note that "ITR" and "ETR" are relative terms here. Both devices MUST 1216 be implementing both ITR and ETR functionality for the echo nonce 1217 mechanism to operate. 1219 The ITR and ETR MAY both go into the echo-nonce-request state at the 1220 same time. The number of packets sent or the time during which echo 1221 nonce requests are sent is an implementation-specific setting. 1222 However, when an ITR is in the echo-nonce-request state, it can echo 1223 the ETR's nonce in the next set of packets that it encapsulates and 1224 subsequently continue sending echo-nonce-request packets. 1226 This mechanism does not completely solve the forward path 1227 reachability problem, as traffic may be unidirectional. That is, the 1228 ETR receiving traffic at a site MAY not be the same device as an ITR 1229 that transmits traffic from that site, or the site-to-site traffic is 1230 unidirectional so there is no ITR returning traffic. 1232 The echo-nonce algorithm is bilateral. That is, if one side sets the 1233 E-bit and the other side is not enabled for echo-noncing, then the 1234 echoing of the nonce does not occur and the requesting side may 1235 erroneously consider the Locator unreachable. An ITR SHOULD only set 1236 the E-bit in an encapsulated data packet when it knows the ETR is 1237 enabled for echo-noncing. This is conveyed by the E-bit in the RLOC- 1238 probe Map-Reply message. 1240 11. EID Reachability within a LISP Site 1242 A site MAY be multihomed using two or more ETRs. The hosts and 1243 infrastructure within a site will be addressed using one or more EID- 1244 Prefixes that are mapped to the RLOCs of the relevant ETRs in the 1245 mapping system. One possible failure mode is for an ETR to lose 1246 reachability to one or more of the EID-Prefixes within its own site. 1247 When this occurs when the ETR sends Map-Replies, it can clear the 1248 R-bit associated with its own Locator. And when the ETR is also an 1249 ITR, it can clear its Locator-Status-Bit in the encapsulation data 1250 header. 1252 It is recognized that there are no simple solutions to the site 1253 partitioning problem because it is hard to know which part of the 1254 EID-Prefix range is partitioned and which Locators can reach any sub- 1255 ranges of the EID-Prefixes. Note that this is not a new problem 1256 introduced by the LISP architecture. The problem exists today when a 1257 multihomed site uses BGP to advertise its reachability upstream. 1259 12. Routing Locator Hashing 1261 When an ETR provides an EID-to-RLOC mapping in a Map-Reply message 1262 that is stored in the Map-Cache of a requesting ITR, the Locator-Set 1263 for the EID-Prefix MAY contain different Priority and Weight values 1264 for each locator address. When more than one best Priority Locator 1265 exists, the ITR can decide how to load-share traffic against the 1266 corresponding Locators. 1268 The following hash algorithm MAY be used by an ITR to select a 1269 Locator for a packet destined to an EID for the EID-to-RLOC mapping: 1271 1. Either a source and destination address hash or the traditional 1272 5-tuple hash can be used. The traditional 5-tuple hash includes 1273 the source and destination addresses; source and destination TCP, 1274 UDP, or Stream Control Transmission Protocol (SCTP) port numbers; 1275 and the IP protocol number field or IPv6 next-protocol fields of 1276 a packet that a host originates from within a LISP site. When a 1277 packet is not a TCP, UDP, or SCTP packet, the source and 1278 destination addresses only from the header are used to compute 1279 the hash. 1281 2. Take the hash value and divide it by the number of Locators 1282 stored in the Locator-Set for the EID-to-RLOC mapping. 1284 3. The remainder will yield a value of 0 to "number of Locators 1285 minus 1". Use the remainder to select the Locator in the 1286 Locator-Set. 1288 Note that when a packet is LISP encapsulated, the source port number 1289 in the outer UDP header needs to be set. Selecting a hashed value 1290 allows core routers that are attached to Link Aggregation Groups 1291 (LAGs) to load-split the encapsulated packets across member links of 1292 such LAGs. Otherwise, core routers would see a single flow, since 1293 packets have a source address of the ITR, for packets that are 1294 originated by different EIDs at the source site. A suggested setting 1295 for the source port number computed by an ITR is a 5-tuple hash 1296 function on the inner header, as described above. The source port 1297 SHOULD be the same for all packets belonging to the same flow. 1299 Many core router implementations use a 5-tuple hash to decide how to 1300 balance packet load across members of a LAG. The 5-tuple hash 1301 includes the source and destination addresses of the packet and the 1302 source and destination ports when the protocol number in the packet 1303 is TCP or UDP. For this reason, UDP encoding is used for LISP 1304 encapsulation. 1306 13. Changing the Contents of EID-to-RLOC Mappings 1308 Since the LISP architecture uses a caching scheme to retrieve and 1309 store EID-to-RLOC mappings, the only way an ITR can get a more up-to- 1310 date mapping is to re-request the mapping. However, the ITRs do not 1311 know when the mappings change, and the ETRs do not keep track of 1312 which ITRs requested its mappings. For scalability reasons, it is 1313 desirable to maintain this approach but need to provide a way for 1314 ETRs to change their mappings and inform the sites that are currently 1315 communicating with the ETR site using such mappings. 1317 This section defines a Data-Plane mechanism for updating EID-to-RLOC 1318 mappings. Additionally, the Solicit-Map Request (SMR) Control-Plane 1319 updating mechanism is specified in [I-D.ietf-lisp-rfc6833bis]. 1321 When adding a new Locator record in lexicographic order to the end of 1322 a Locator-Set, it is easy to update mappings. We assume that new 1323 mappings will maintain the same Locator ordering as the old mapping 1324 but will just have new Locators appended to the end of the list. So, 1325 some ITRs can have a new mapping while other ITRs have only an old 1326 mapping that is used until they time out. When an ITR has only an 1327 old mapping but detects bits set in the Locator-Status-Bits that 1328 correspond to Locators beyond the list it has cached, it simply 1329 ignores them. However, this can only happen for locator addresses 1330 that are lexicographically greater than the locator addresses in the 1331 existing Locator-Set. 1333 When a Locator record is inserted in the middle of a Locator-Set, to 1334 maintain lexicographic order, SMR procedure 1335 [I-D.ietf-lisp-rfc6833bis] is used to inform ITRs and PITRs of the 1336 new Locator-Status-Bit mappings. 1338 When a Locator record is removed from a Locator-Set, ITRs that have 1339 the mapping cached will not use the removed Locator because the xTRs 1340 will set the Locator-Status-Bit to 0. So, even if the Locator is in 1341 the list, it will not be used. For new mapping requests, the xTRs 1342 can set the Locator AFI to 0 (indicating an unspecified address), as 1343 well as setting the corresponding Locator-Status-Bit to 0. This 1344 forces ITRs with old or new mappings to avoid using the removed 1345 Locator. 1347 If many changes occur to a mapping over a long period of time, one 1348 will find empty record slots in the middle of the Locator-Set and new 1349 records appended to the Locator-Set. At some point, it would be 1350 useful to compact the Locator-Set so the Locator-Status-Bit settings 1351 can be efficiently packed. 1353 We propose here a Data-Plane mechanism (Map-Versioning specified in 1354 [I-D.ietf-lisp-6834bis]) to update the contents of EID-to-RLOC 1355 mappings. Please note that in addition the Solicit-Map Request 1356 (specified in [I-D.ietf-lisp-rfc6833bis]) is a Control-Plane 1357 mechanisms that can be used to update EID-to-RLOC mappings. 1359 13.1. Database Map-Versioning 1361 When there is unidirectional packet flow between an ITR and ETR, and 1362 the EID-to-RLOC mappings change on the ETR, it needs to inform the 1363 ITR so encapsulation to a removed Locator can stop and can instead be 1364 started to a new Locator in the Locator-Set. 1366 An ETR, when it sends Map-Reply messages, conveys its own Map-Version 1367 Number. This is known as the Destination Map-Version Number. ITRs 1368 include the Destination Map-Version Number in packets they 1369 encapsulate to the site. When an ETR decapsulates a packet and 1370 detects that the Destination Map-Version Number is less than the 1371 current version for its mapping, the SMR procedure described in 1372 [I-D.ietf-lisp-rfc6833bis] occurs. 1374 An ITR, when it encapsulates packets to ETRs, can convey its own Map- 1375 Version Number. This is known as the Source Map-Version Number. 1376 When an ETR decapsulates a packet and detects that the Source Map- 1377 Version Number is greater than the last Map-Version Number sent in a 1378 Map-Reply from the ITR's site, the ETR will send a Map-Request to one 1379 of the ETRs for the source site. 1381 A Map-Version Number is used as a sequence number per EID-Prefix, so 1382 values that are greater are considered to be more recent. A value of 1383 0 for the Source Map-Version Number or the Destination Map-Version 1384 Number conveys no versioning information, and an ITR does no 1385 comparison with previously received Map-Version Numbers. 1387 A Map-Version Number can be included in Map-Register messages as 1388 well. This is a good way for the Map-Server to assure that all ETRs 1389 for a site registering to it will be synchronized according to Map- 1390 Version Number. 1392 See [I-D.ietf-lisp-6834bis] for a more detailed analysis and 1393 description of Database Map-Versioning. 1395 14. Multicast Considerations 1397 A multicast group address, as defined in the original Internet 1398 architecture, is an identifier of a grouping of topologically 1399 independent receiver host locations. The address encoding itself 1400 does not determine the location of the receiver(s). The multicast 1401 routing protocol, and the network-based state the protocol creates, 1402 determine where the receivers are located. 1404 In the context of LISP, a multicast group address is both an EID and 1405 a Routing Locator. Therefore, no specific semantic or action needs 1406 to be taken for a destination address, as it would appear in an IP 1407 header. Therefore, a group address that appears in an inner IP 1408 header built by a source host will be used as the destination EID. 1409 The outer IP header (the destination Routing Locator address), 1410 prepended by a LISP router, can use the same group address as the 1411 destination Routing Locator, use a multicast or unicast Routing 1412 Locator obtained from a Mapping System lookup, or use other means to 1413 determine the group address mapping. 1415 With respect to the source Routing Locator address, the ITR prepends 1416 its own IP address as the source address of the outer IP header. 1417 Just like it would if the destination EID was a unicast address. 1418 This source Routing Locator address, like any other Routing Locator 1419 address, MUST be globally routable. 1421 There are two approaches for LISP-Multicast, one that uses native 1422 multicast routing in the underlay with no support from the Mapping 1423 System and the other that uses only unicast routing in the underlay 1424 with support from the Mapping System. See [RFC6831] and [RFC8378], 1425 respectively, for details. Details for LISP-Multicast and 1426 interworking with non-LISP sites are described in [RFC6831] and 1427 [RFC6832]. 1429 15. Router Performance Considerations 1431 LISP is designed to be very "hardware-based forwarding friendly". A 1432 few implementation techniques can be used to incrementally implement 1433 LISP: 1435 o When a tunnel-encapsulated packet is received by an ETR, the outer 1436 destination address may not be the address of the router. This 1437 makes it challenging for the control plane to get packets from the 1438 hardware. This may be mitigated by creating special Forwarding 1439 Information Base (FIB) entries for the EID-Prefixes of EIDs served 1440 by the ETR (those for which the router provides an RLOC 1441 translation). These FIB entries are marked with a flag indicating 1442 that Control-Plane processing SHOULD be performed. The forwarding 1443 logic of testing for particular IP protocol number values is not 1444 necessary. There are a few proven cases where no changes to 1445 existing deployed hardware were needed to support the LISP Data- 1446 Plane. 1448 o On an ITR, prepending a new IP header consists of adding more 1449 octets to a MAC rewrite string and prepending the string as part 1450 of the outgoing encapsulation procedure. Routers that support 1451 Generic Routing Encapsulation (GRE) tunneling [RFC2784] or 6to4 1452 tunneling [RFC3056] may already support this action. 1454 o A packet's source address or interface the packet was received on 1455 can be used to select VRF (Virtual Routing/Forwarding). The VRF's 1456 routing table can be used to find EID-to-RLOC mappings. 1458 For performance issues related to Map-Cache management, see 1459 Section 16. 1461 16. Security Considerations 1463 Security considerations for LISP are discussed in [RFC7833]. 1465 A complete LISP threat analysis can be found in [RFC7835], in what 1466 follows we provide a summary. 1468 The optional mechanisms of gleaning is offered to directly obtain a 1469 mapping from the LISP encapsulated packets. Specifically, an xTR can 1470 learn the EID-to-RLOC mapping by inspecting the source RLOC and 1471 source EID of an encapsulated packet, and insert this new mapping 1472 into its Map-Cache. An off-path attacker can spoof the source EID 1473 address to divert the traffic sent to the victim's spoofed EID. If 1474 the attacker spoofs the source RLOC, it can mount a DoS attack by 1475 redirecting traffic to the spoofed victim's RLOC, potentially 1476 overloading it. 1478 The LISP Data-Plane defines several mechanisms to monitor RLOC Data- 1479 Plane reachability, in this context Locator-Status Bits, Nonce- 1480 Present and Echo-Nonce bits of the LISP encapsulation header can be 1481 manipulated by an attacker to mount a DoS attack. An off-path 1482 attacker able to spoof the RLOC of a victim's xTR can manipulate such 1483 mechanisms to declare a set of RLOCs unreachable. This can be used 1484 also, for instance, to declare only one RLOC reachable with the aim 1485 of overload it. 1487 Map-Versioning is a Data-Plane mechanism used to signal a peering xTR 1488 that a local EID-to-RLOC mapping has been updated, so that the 1489 peering xTR uses LISP Control-Plane signaling message to retrieve a 1490 fresh mapping. This can be used by an attacker to forge the map- 1491 versioning field of a LISP encapsulated header and force an excessive 1492 amount of signaling between xTRs that may overload them. 1494 Most of the attack vectors can be mitigated with careful deployment 1495 and configuration, information learned opportunistically (such as LSB 1496 or gleaning) SHOULD be verified with other reachability mechanisms. 1497 In addition, systematic rate-limitation and filtering is an effective 1498 technique to mitigate attacks that aim to overload the Control-Plane. 1500 17. Network Management Considerations 1502 Considerations for network management tools exist so the LISP 1503 protocol suite can be operationally managed. These mechanisms can be 1504 found in [RFC7052] and [RFC6835]. 1506 18. Changes since RFC 6830 1508 For implementation considerations, the following changes have been 1509 made to this document since RFC 6830 was published: 1511 o It is no longer mandated that a maximum number of 2 LISP headers 1512 be prepended to a packet. If there is a application need for more 1513 than 2 LISP headers, an implementation can support more. However, 1514 it is RECOMMENDED that a maximum of two LISP headers can be 1515 prepended to a packet. 1517 o The 3 reserved flag bits in the LISP header have been allocated 1518 for [RFC8061]. The low-order 2 bits of the 3-bit field (now named 1519 the KK bits) are used as a key identifier. The 1 remaining bit is 1520 still documented as reserved. 1522 o Data-Plane gleaning for creating map-cache entries has been made 1523 optional. If any ITR implementations depend or assume the remote 1524 ETR is gleaning should not do so. This does not create any 1525 interoperability problems since the control-plane map-cache 1526 population procedures are unilateral and are the typical method 1527 for map-cache population. 1529 o The bulk of the changes to this document which reduces its length 1530 are due to moving the LISP control-plane messaging and procedures 1531 to [I-D.ietf-lisp-rfc6833bis]. 1533 19. IANA Considerations 1535 This section provides guidance to the Internet Assigned Numbers 1536 Authority (IANA) regarding registration of values related to this 1537 Data-Plane LISP specification, in accordance with BCP 26 [RFC8126]. 1539 19.1. LISP UDP Port Numbers 1541 The IANA registry has allocated UDP port number 4341 for the LISP 1542 Data-Plane. IANA has updated the description for UDP port 4341 as 1543 follows: 1545 lisp-data 4341 udp LISP Data Packets 1547 20. References 1549 20.1. Normative References 1551 [I-D.ietf-lisp-6834bis] 1552 Iannone, L., Saucez, D., and O. Bonaventure, "Locator/ID 1553 Separation Protocol (LISP) Map-Versioning", draft-ietf- 1554 lisp-6834bis-02 (work in progress), September 2018. 1556 [I-D.ietf-lisp-rfc6833bis] 1557 Fuller, V., Farinacci, D., and A. Cabellos-Aparicio, 1558 "Locator/ID Separation Protocol (LISP) Control-Plane", 1559 draft-ietf-lisp-rfc6833bis-14 (work in progress), 1560 September 2018. 1562 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 1563 DOI 10.17487/RFC0768, August 1980, 1564 . 1566 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 1567 DOI 10.17487/RFC0791, September 1981, 1568 . 1570 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1571 Requirement Levels", BCP 14, RFC 2119, 1572 DOI 10.17487/RFC2119, March 1997, 1573 . 1575 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 1576 "Definition of the Differentiated Services Field (DS 1577 Field) in the IPv4 and IPv6 Headers", RFC 2474, 1578 DOI 10.17487/RFC2474, December 1998, 1579 . 1581 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 1582 of Explicit Congestion Notification (ECN) to IP", 1583 RFC 3168, DOI 10.17487/RFC3168, September 2001, 1584 . 1586 [RFC6040] Briscoe, B., "Tunnelling of Explicit Congestion 1587 Notification", RFC 6040, DOI 10.17487/RFC6040, November 1588 2010, . 1590 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1591 Writing an IANA Considerations Section in RFCs", BCP 26, 1592 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1593 . 1595 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1596 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1597 May 2017, . 1599 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1600 (IPv6) Specification", STD 86, RFC 8200, 1601 DOI 10.17487/RFC8200, July 2017, 1602 . 1604 20.2. Informative References 1606 [AFN] IANA, "Address Family Numbers", August 2016, 1607 . 1609 [CHIAPPA] Chiappa, J., "Endpoints and Endpoint names: A Proposed", 1610 1999, 1611 . 1613 [I-D.ietf-lisp-introduction] 1614 Cabellos-Aparicio, A. and D. Saucez, "An Architectural 1615 Introduction to the Locator/ID Separation Protocol 1616 (LISP)", draft-ietf-lisp-introduction-13 (work in 1617 progress), April 2015. 1619 [I-D.ietf-lisp-vpn] 1620 Moreno, V. and D. Farinacci, "LISP Virtual Private 1621 Networks (VPNs)", draft-ietf-lisp-vpn-02 (work in 1622 progress), May 2018. 1624 [OPENLISP] 1625 Iannone, L., Saucez, D., and O. Bonaventure, "OpenLISP 1626 Implementation Report", Work in Progress, July 2008. 1628 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 1629 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 1630 . 1632 [RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G., 1633 and E. Lear, "Address Allocation for Private Internets", 1634 BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996, 1635 . 1637 [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. 1638 Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, 1639 DOI 10.17487/RFC2784, March 2000, 1640 . 1642 [RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains 1643 via IPv4 Clouds", RFC 3056, DOI 10.17487/RFC3056, February 1644 2001, . 1646 [RFC3232] Reynolds, J., Ed., "Assigned Numbers: RFC 1700 is Replaced 1647 by an On-line Database", RFC 3232, DOI 10.17487/RFC3232, 1648 January 2002, . 1650 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 1651 A., Peterson, J., Sparks, R., Handley, M., and E. 1652 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 1653 DOI 10.17487/RFC3261, June 2002, 1654 . 1656 [RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker, 1657 "Randomness Requirements for Security", BCP 106, RFC 4086, 1658 DOI 10.17487/RFC4086, June 2005, 1659 . 1661 [RFC4984] Meyer, D., Ed., Zhang, L., Ed., and K. Fall, Ed., "Report 1662 from the IAB Workshop on Routing and Addressing", 1663 RFC 4984, DOI 10.17487/RFC4984, September 2007, 1664 . 1666 [RFC6831] Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas, "The 1667 Locator/ID Separation Protocol (LISP) for Multicast 1668 Environments", RFC 6831, DOI 10.17487/RFC6831, January 1669 2013, . 1671 [RFC6832] Lewis, D., Meyer, D., Farinacci, D., and V. Fuller, 1672 "Interworking between Locator/ID Separation Protocol 1673 (LISP) and Non-LISP Sites", RFC 6832, 1674 DOI 10.17487/RFC6832, January 2013, 1675 . 1677 [RFC6835] Farinacci, D. and D. Meyer, "The Locator/ID Separation 1678 Protocol Internet Groper (LIG)", RFC 6835, 1679 DOI 10.17487/RFC6835, January 2013, 1680 . 1682 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 1683 UDP Checksums for Tunneled Packets", RFC 6935, 1684 DOI 10.17487/RFC6935, April 2013, 1685 . 1687 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 1688 for the Use of IPv6 UDP Datagrams with Zero Checksums", 1689 RFC 6936, DOI 10.17487/RFC6936, April 2013, 1690 . 1692 [RFC7052] Schudel, G., Jain, A., and V. Moreno, "Locator/ID 1693 Separation Protocol (LISP) MIB", RFC 7052, 1694 DOI 10.17487/RFC7052, October 2013, 1695 . 1697 [RFC7215] Jakab, L., Cabellos-Aparicio, A., Coras, F., Domingo- 1698 Pascual, J., and D. Lewis, "Locator/Identifier Separation 1699 Protocol (LISP) Network Element Deployment 1700 Considerations", RFC 7215, DOI 10.17487/RFC7215, April 1701 2014, . 1703 [RFC7833] Howlett, J., Hartman, S., and A. Perez-Mendez, Ed., "A 1704 RADIUS Attribute, Binding, Profiles, Name Identifier 1705 Format, and Confirmation Methods for the Security 1706 Assertion Markup Language (SAML)", RFC 7833, 1707 DOI 10.17487/RFC7833, May 2016, 1708 . 1710 [RFC7835] Saucez, D., Iannone, L., and O. Bonaventure, "Locator/ID 1711 Separation Protocol (LISP) Threat Analysis", RFC 7835, 1712 DOI 10.17487/RFC7835, April 2016, 1713 . 1715 [RFC8060] Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical 1716 Address Format (LCAF)", RFC 8060, DOI 10.17487/RFC8060, 1717 February 2017, . 1719 [RFC8061] Farinacci, D. and B. Weis, "Locator/ID Separation Protocol 1720 (LISP) Data-Plane Confidentiality", RFC 8061, 1721 DOI 10.17487/RFC8061, February 2017, 1722 . 1724 [RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage 1725 Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085, 1726 March 2017, . 1728 [RFC8111] Fuller, V., Lewis, D., Ermagan, V., Jain, A., and A. 1729 Smirnov, "Locator/ID Separation Protocol Delegated 1730 Database Tree (LISP-DDT)", RFC 8111, DOI 10.17487/RFC8111, 1731 May 2017, . 1733 [RFC8378] Moreno, V. and D. Farinacci, "Signal-Free Locator/ID 1734 Separation Protocol (LISP) Multicast", RFC 8378, 1735 DOI 10.17487/RFC8378, May 2018, 1736 . 1738 Appendix A. Acknowledgments 1740 An initial thank you goes to Dave Oran for planting the seeds for the 1741 initial ideas for LISP. His consultation continues to provide value 1742 to the LISP authors. 1744 A special and appreciative thank you goes to Noel Chiappa for 1745 providing architectural impetus over the past decades on separation 1746 of location and identity, as well as detailed reviews of the LISP 1747 architecture and documents, coupled with enthusiasm for making LISP a 1748 practical and incremental transition for the Internet. 1750 The authors would like to gratefully acknowledge many people who have 1751 contributed discussions and ideas to the making of this proposal. 1752 They include Scott Brim, Andrew Partan, John Zwiebel, Jason Schiller, 1753 Lixia Zhang, Dorian Kim, Peter Schoenmaker, Vijay Gill, Geoff Huston, 1754 David Conrad, Mark Handley, Ron Bonica, Ted Seely, Mark Townsley, 1755 Chris Morrow, Brian Weis, Dave McGrew, Peter Lothberg, Dave Thaler, 1756 Eliot Lear, Shane Amante, Ved Kafle, Olivier Bonaventure, Luigi 1757 Iannone, Robin Whittle, Brian Carpenter, Joel Halpern, Terry 1758 Manderson, Roger Jorgensen, Ran Atkinson, Stig Venaas, Iljitsch van 1759 Beijnum, Roland Bless, Dana Blair, Bill Lynch, Marc Woolward, Damien 1760 Saucez, Damian Lezama, Attilla De Groot, Parantap Lahiri, David 1761 Black, Roque Gagliano, Isidor Kouvelas, Jesper Skriver, Fred Templin, 1762 Margaret Wasserman, Sam Hartman, Michael Hofling, Pedro Marques, Jari 1763 Arkko, Gregg Schudel, Srinivas Subramanian, Amit Jain, Xu Xiaohu, 1764 Dhirendra Trivedi, Yakov Rekhter, John Scudder, John Drake, Dimitri 1765 Papadimitriou, Ross Callon, Selina Heimlich, Job Snijders, Vina 1766 Ermagan, Fabio Maino, Victor Moreno, Chris White, Clarence Filsfils, 1767 Alia Atlas, Florin Coras and Alberto Rodriguez. 1769 This work originated in the Routing Research Group (RRG) of the IRTF. 1770 An individual submission was converted into the IETF LISP working 1771 group document that became this RFC. 1773 The LISP working group would like to give a special thanks to Jari 1774 Arkko, the Internet Area AD at the time that the set of LISP 1775 documents were being prepared for IESG last call, and for his 1776 meticulous reviews and detailed commentaries on the 7 working group 1777 last call documents progressing toward standards-track RFCs. 1779 Appendix B. Document Change Log 1781 [RFC Editor: Please delete this section on publication as RFC.] 1783 B.1. Changes to draft-ietf-lisp-rfc6830bis-18 1785 o Posted mid-September 2018. 1787 o Changes to reflect comments from Secdir review (Mirja). 1789 B.2. Changes to draft-ietf-lisp-rfc6830bis-17 1791 o Posted September 2018. 1793 o Indicate in the "Changes since RFC 6830" section why the document 1794 has been shortened in length. 1796 o Make reference to RFC 8085 about UDP congestion control. 1798 o More editorial changes from multiple IESG reviews. 1800 B.3. Changes to draft-ietf-lisp-rfc6830bis-16 1802 o Posted late August 2018. 1804 o Distinguish the message type names between ICMP for IPv4 and ICMP 1805 for IPv6 for handling MTU issues. 1807 B.4. Changes to draft-ietf-lisp-rfc6830bis-15 1809 o Posted August 2018. 1811 o Final editorial changes before RFC submission for Proposed 1812 Standard. 1814 o Added section "Changes since RFC 6830" so implementers are 1815 informed of any changes since the last RFC publication. 1817 B.5. Changes to draft-ietf-lisp-rfc6830bis-14 1819 o Posted July 2018 IETF week. 1821 o Put obsolete of RFC 6830 in Intro section in addition to abstract. 1823 B.6. Changes to draft-ietf-lisp-rfc6830bis-13 1825 o Posted March IETF Week 2018. 1827 o Clarified that a new nonce is required per RLOC. 1829 o Removed 'Clock Sweep' section. This text must be placed in a new 1830 OAM document. 1832 o Some references changed from normative to informative 1834 B.7. Changes to draft-ietf-lisp-rfc6830bis-12 1836 o Posted July 2018. 1838 o Fixed Luigi editorial comments to ready draft for RFC status. 1840 B.8. Changes to draft-ietf-lisp-rfc6830bis-11 1842 o Posted March 2018. 1844 o Removed sections 16, 17 and 18 (Mobility, Deployment and 1845 Traceroute considerations). This text must be placed in a new OAM 1846 document. 1848 B.9. Changes to draft-ietf-lisp-rfc6830bis-10 1850 o Posted March 2018. 1852 o Updated section 'Router Locator Selection' stating that the Data- 1853 Plane MUST follow what's stored in the Map-Cache (priorities and 1854 weights). 1856 o Section 'Routing Locator Reachability': Removed bullet point 2 1857 (ICMP Network/Host Unreachable),3 (hints from BGP),4 (ICMP Port 1858 Unreachable),5 (receive a Map-Reply as a response) and RLOC 1859 probing 1861 o Removed 'Solicit-Map Request'. 1863 B.10. Changes to draft-ietf-lisp-rfc6830bis-09 1865 o Posted January 2018. 1867 o Add more details in section 5.3 about DSCP processing during 1868 encapsulation and decapsulation. 1870 o Added clarity to definitions in the Definition of Terms section 1871 from various commenters. 1873 o Removed PA and PI definitions from Definition of Terms section. 1875 o More editorial changes. 1877 o Removed 4342 from IANA section and move to RFC6833 IANA section. 1879 B.11. Changes to draft-ietf-lisp-rfc6830bis-08 1881 o Posted January 2018. 1883 o Remove references to research work for any protocol mechanisms. 1885 o Document scanned to make sure it is RFC 2119 compliant. 1887 o Made changes to reflect comments from document WG shepherd Luigi 1888 Iannone. 1890 o Ran IDNITs on the document. 1892 B.12. Changes to draft-ietf-lisp-rfc6830bis-07 1894 o Posted November 2017. 1896 o Rephrase how Instance-IDs are used and don't refer to [RFC1918] 1897 addresses. 1899 B.13. Changes to draft-ietf-lisp-rfc6830bis-06 1901 o Posted October 2017. 1903 o Put RTR definition before it is used. 1905 o Rename references that are now working group drafts. 1907 o Remove "EIDs MUST NOT be used as used by a host to refer to other 1908 hosts. Note that EID blocks MAY LISP RLOCs". 1910 o Indicate what address-family can appear in data packets. 1912 o ETRs may, rather than will, be the ones to send Map-Replies. 1914 o Recommend, rather than mandate, max encapsulation headers to 2. 1916 o Reference VPN draft when introducing Instance-ID. 1918 o Indicate that SMRs can be sent when ITR/ETR are in the same node. 1920 o Clarify when private addresses can be used. 1922 B.14. Changes to draft-ietf-lisp-rfc6830bis-05 1924 o Posted August 2017. 1926 o Make it clear that a Re-encapsulating Tunnel Router is an RTR. 1928 B.15. Changes to draft-ietf-lisp-rfc6830bis-04 1930 o Posted July 2017. 1932 o Changed reference of IPv6 RFC2460 to RFC8200. 1934 o Indicate that the applicability statement for UDP zero checksums 1935 over IPv6 adheres to RFC6936. 1937 B.16. Changes to draft-ietf-lisp-rfc6830bis-03 1939 o Posted May 2017. 1941 o Move the control-plane related codepoints in the IANA 1942 Considerations section to RFC6833bis. 1944 B.17. Changes to draft-ietf-lisp-rfc6830bis-02 1946 o Posted April 2017. 1948 o Reflect some editorial comments from Damien Sausez. 1950 B.18. Changes to draft-ietf-lisp-rfc6830bis-01 1952 o Posted March 2017. 1954 o Include references to new RFCs published. 1956 o Change references from RFC6833 to RFC6833bis. 1958 o Clarified LCAF text in the IANA section. 1960 o Remove references to "experimental". 1962 B.19. Changes to draft-ietf-lisp-rfc6830bis-00 1964 o Posted December 2016. 1966 o Created working group document from draft-farinacci-lisp 1967 -rfc6830-00 individual submission. No other changes made. 1969 Authors' Addresses 1970 Dino Farinacci 1971 Cisco Systems 1972 Tasman Drive 1973 San Jose, CA 95134 1974 USA 1976 EMail: farinacci@gmail.com 1978 Vince Fuller 1979 Cisco Systems 1980 Tasman Drive 1981 San Jose, CA 95134 1982 USA 1984 EMail: vince.fuller@gmail.com 1986 Dave Meyer 1987 Cisco Systems 1988 170 Tasman Drive 1989 San Jose, CA 1990 USA 1992 EMail: dmm@1-4-5.net 1994 Darrel Lewis 1995 Cisco Systems 1996 170 Tasman Drive 1997 San Jose, CA 1998 USA 2000 EMail: darlewis@cisco.com 2002 Albert Cabellos 2003 UPC/BarcelonaTech 2004 Campus Nord, C. Jordi Girona 1-3 2005 Barcelona, Catalunya 2006 Spain 2008 EMail: acabello@ac.upc.edu