idnits 2.17.1 draft-ietf-lisp-rfc6830bis-09.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 (February 13, 2018) is 2262 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) == Unused Reference: 'RFC4632' is defined on line 2088, but no explicit reference was found in the text == Unused Reference: 'I-D.ietf-lisp-sec' is defined on line 2149, but no explicit reference was found in the text == Outdated reference: A later version (-31) exists of draft-ietf-lisp-rfc6833bis-07 == Outdated reference: A later version (-13) exists of draft-ietf-lisp-eid-mobility-01 == Outdated reference: A later version (-15) exists of draft-ietf-lisp-introduction-13 == Outdated reference: A later version (-15) exists of draft-ietf-lisp-mn-01 == Outdated reference: A later version (-14) exists of draft-ietf-lisp-predictive-rlocs-01 == Outdated reference: A later version (-29) exists of draft-ietf-lisp-sec-14 == Outdated reference: A later version (-09) exists of draft-ietf-lisp-signal-free-multicast-07 == Outdated reference: A later version (-12) exists of draft-ietf-lisp-vpn-01 -- Obsolete informational reference (is this intentional?): RFC 6834 (Obsoleted by RFC 9302) Summary: 0 errors (**), 0 flaws (~~), 11 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group D. Farinacci 3 Internet-Draft V. Fuller 4 Intended status: Standards Track D. Meyer 5 Expires: August 17, 2018 D. Lewis 6 Cisco Systems 7 A. Cabellos (Ed.) 8 UPC/BarcelonaTech 9 February 13, 2018 11 The Locator/ID Separation Protocol (LISP) 12 draft-ietf-lisp-rfc6830bis-09 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 Status of This Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at https://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on August 17, 2018. 45 Copyright Notice 47 Copyright (c) 2018 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (https://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 63 2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 4 64 3. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 4 65 4. Basic Overview . . . . . . . . . . . . . . . . . . . . . . . 8 66 4.1. Packet Flow Sequence . . . . . . . . . . . . . . . . . . 10 67 5. LISP Encapsulation Details . . . . . . . . . . . . . . . . . 12 68 5.1. LISP IPv4-in-IPv4 Header Format . . . . . . . . . . . . . 13 69 5.2. LISP IPv6-in-IPv6 Header Format . . . . . . . . . . . . . 14 70 5.3. Tunnel Header Field Descriptions . . . . . . . . . . . . 15 71 6. LISP EID-to-RLOC Map-Cache . . . . . . . . . . . . . . . . . 19 72 7. Dealing with Large Encapsulated Packets . . . . . . . . . . . 20 73 7.1. A Stateless Solution to MTU Handling . . . . . . . . . . 20 74 7.2. A Stateful Solution to MTU Handling . . . . . . . . . . . 21 75 8. Using Virtualization and Segmentation with LISP . . . . . . . 22 76 9. Routing Locator Selection . . . . . . . . . . . . . . . . . . 22 77 10. Routing Locator Reachability . . . . . . . . . . . . . . . . 24 78 10.1. Echo Nonce Algorithm . . . . . . . . . . . . . . . . . . 26 79 10.2. RLOC-Probing Algorithm . . . . . . . . . . . . . . . . . 28 80 11. EID Reachability within a LISP Site . . . . . . . . . . . . . 28 81 12. Routing Locator Hashing . . . . . . . . . . . . . . . . . . . 29 82 13. Changing the Contents of EID-to-RLOC Mappings . . . . . . . . 30 83 13.1. Clock Sweep . . . . . . . . . . . . . . . . . . . . . . 31 84 13.2. Solicit-Map-Request (SMR) . . . . . . . . . . . . . . . 31 85 13.3. Database Map-Versioning . . . . . . . . . . . . . . . . 33 86 14. Multicast Considerations . . . . . . . . . . . . . . . . . . 34 87 15. Router Performance Considerations . . . . . . . . . . . . . . 34 88 16. Mobility Considerations . . . . . . . . . . . . . . . . . . . 35 89 16.1. Slow Mobility . . . . . . . . . . . . . . . . . . . . . 35 90 16.2. Fast Mobility . . . . . . . . . . . . . . . . . . . . . 35 91 16.3. LISP Mobile Node Mobility . . . . . . . . . . . . . . . 36 92 17. LISP xTR Placement and Encapsulation Methods . . . . . . . . 37 93 17.1. First-Hop/Last-Hop xTRs . . . . . . . . . . . . . . . . 38 94 17.2. Border/Edge xTRs . . . . . . . . . . . . . . . . . . . . 38 95 17.3. ISP Provider Edge (PE) xTRs . . . . . . . . . . . . . . 39 96 17.4. LISP Functionality with Conventional NATs . . . . . . . 39 97 17.5. Packets Egressing a LISP Site . . . . . . . . . . . . . 40 98 18. Traceroute Considerations . . . . . . . . . . . . . . . . . . 40 99 18.1. IPv6 Traceroute . . . . . . . . . . . . . . . . . . . . 41 100 18.2. IPv4 Traceroute . . . . . . . . . . . . . . . . . . . . 41 101 18.3. Traceroute Using Mixed Locators . . . . . . . . . . . . 42 102 19. Security Considerations . . . . . . . . . . . . . . . . . . . 42 103 20. Network Management Considerations . . . . . . . . . . . . . . 43 104 21. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 43 105 21.1. LISP UDP Port Numbers . . . . . . . . . . . . . . . . . 43 106 22. References . . . . . . . . . . . . . . . . . . . . . . . . . 43 107 22.1. Normative References . . . . . . . . . . . . . . . . . . 43 108 22.2. Informative References . . . . . . . . . . . . . . . . . 45 109 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 49 110 Appendix B. Document Change Log . . . . . . . . . . . . . . . . 49 111 B.1. Changes to draft-ietf-lisp-rfc6830bis-09 . . . . . . . . 50 112 B.2. Changes to draft-ietf-lisp-rfc6830bis-08 . . . . . . . . 50 113 B.3. Changes to draft-ietf-lisp-rfc6830bis-07 . . . . . . . . 50 114 B.4. Changes to draft-ietf-lisp-rfc6830bis-06 . . . . . . . . 50 115 B.5. Changes to draft-ietf-lisp-rfc6830bis-05 . . . . . . . . 51 116 B.6. Changes to draft-ietf-lisp-rfc6830bis-04 . . . . . . . . 51 117 B.7. Changes to draft-ietf-lisp-rfc6830bis-03 . . . . . . . . 51 118 B.8. Changes to draft-ietf-lisp-rfc6830bis-02 . . . . . . . . 51 119 B.9. Changes to draft-ietf-lisp-rfc6830bis-01 . . . . . . . . 51 120 B.10. Changes to draft-ietf-lisp-rfc6830bis-00 . . . . . . . . 52 121 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 52 123 1. Introduction 125 This document describes the Locator/Identifier Separation Protocol 126 (LISP). LISP is an encapsulation protocol built around the 127 fundamental idea of separating the topological location of a network 128 attachment point from the node's identity [CHIAPPA]. As a result 129 LISP creates two namespaces: Endpoint Identifiers (EIDs), that are 130 used to identify end-hosts (e.g., nodes or Virtual Machines) and 131 routable Routing Locators (RLOCs), used to identify network 132 attachment points. LISP then defines functions for mapping between 133 the two namespaces and for encapsulating traffic originated by 134 devices using non-routable EIDs for transport across a network 135 infrastructure that routes and forwards using RLOCs. LISP 136 encapsulation uses a dynamic form of tunneling where no static 137 provisioning is required or necessary. 139 LISP is an overlay protocol that separates control from data-plane, 140 this document specifies the data-plane, how LISP-capable routers 141 (Tunnel Routers) exchange packets by encapsulating them to the 142 appropriate location. Tunnel routers are equipped with a cache, 143 called map-cache, that contains EID-to-RLOC mappings. The map-cache 144 is populated using the LISP Control-Plane protocol 145 [I-D.ietf-lisp-rfc6833bis]. 147 LISP does not require changes to either host protocol stack or to 148 underlay routers. By separating the EID from the RLOC space, LISP 149 offers native Traffic Engineering, multihoming and mobility, among 150 other features. 152 Creation of LISP was initially motivated by discussions during the 153 IAB-sponsored Routing and Addressing Workshop held in Amsterdam in 154 October 2006 (see [RFC4984]). 156 This document specifies the LISP data-plane encapsulation and other 157 LISP forwarding node functionality while [I-D.ietf-lisp-rfc6833bis] 158 specifies the LISP control plane. LISP deployment guidelines can be 159 found in [RFC7215] and [RFC6835] describes considerations for network 160 operational management. Finally, [I-D.ietf-lisp-introduction] 161 describes the LISP architecture. 163 2. Requirements Notation 165 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 166 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 167 document are to be interpreted as described in [RFC2119]. 169 3. Definition of Terms 171 Address Family Identifier (AFI): AFI is a term used to describe an 172 address encoding in a packet. An address family that pertains to 173 the data-plane. See [AFN] and [RFC3232] for details. An AFI 174 value of 0 used in this specification indicates an unspecified 175 encoded address where the length of the address is 0 octets 176 following the 16-bit AFI value of 0. 178 Anycast Address: Anycast Address is a term used in this document to 179 refer to the same IPv4 or IPv6 address configured and used on 180 multiple systems at the same time. An EID or RLOC can be an 181 anycast address in each of their own address spaces. 183 Client-side: Client-side is a term used in this document to indicate 184 a connection initiation attempt by an end-system represented by an 185 EID. 187 Data-Probe: A Data-Probe is a LISP-encapsulated data packet where 188 the inner-header destination address equals the outer-header 189 destination address used to trigger a Map-Reply by a decapsulating 190 ETR. In addition, the original packet is decapsulated and 191 delivered to the destination host if the destination EID is in the 192 EID-Prefix range configured on the ETR. Otherwise, the packet is 193 discarded. A Data-Probe is used in some of the mapping database 194 designs to "probe" or request a Map-Reply from an ETR; in other 195 cases, Map-Requests are used. See each mapping database design 196 for details. When using Data-Probes, by sending Map-Requests on 197 the underlying routing system, EID-Prefixes must be advertised. 199 Egress Tunnel Router (ETR): An ETR is a router that accepts an IP 200 packet where the destination address in the "outer" IP header is 201 one of its own RLOCs. The router strips the "outer" header and 202 forwards the packet based on the next IP header found. In 203 general, an ETR receives LISP-encapsulated IP packets from the 204 Internet on one side and sends decapsulated IP packets to site 205 end-systems on the other side. ETR functionality does not have to 206 be limited to a router device. A server host can be the endpoint 207 of a LISP tunnel as well. 209 EID-to-RLOC Database: The EID-to-RLOC Database is a global 210 distributed database that contains all known EID-Prefix-to-RLOC 211 mappings. Each potential ETR typically contains a small piece of 212 the database: the EID-to-RLOC mappings for the EID-Prefixes 213 "behind" the router. These map to one of the router's own 214 globally visible IP addresses. Note that there MAY be transient 215 conditions when the EID-Prefix for the site and Locator-Set for 216 each EID-Prefix may not be the same on all ETRs. This has no 217 negative implications, since a partial set of Locators can be 218 used. 220 EID-to-RLOC Map-Cache: The EID-to-RLOC map-cache is generally 221 short-lived, on-demand table in an ITR that stores, tracks, and is 222 responsible for timing out and otherwise validating EID-to-RLOC 223 mappings. This cache is distinct from the full "database" of EID- 224 to-RLOC mappings; it is dynamic, local to the ITR(s), and 225 relatively small, while the database is distributed, relatively 226 static, and much more global in scope. 228 EID-Prefix: An EID-Prefix is a power-of-two block of EIDs that are 229 allocated to a site by an address allocation authority. EID- 230 Prefixes are associated with a set of RLOC addresses. EID-Prefix 231 allocations can be broken up into smaller blocks when an RLOC set 232 is to be associated with the larger EID-Prefix block. 234 End-System: An end-system is an IPv4 or IPv6 device that originates 235 packets with a single IPv4 or IPv6 header. The end-system 236 supplies an EID value for the destination address field of the IP 237 header when communicating globally (i.e., outside of its routing 238 domain). An end-system can be a host computer, a switch or router 239 device, or any network appliance. 241 Endpoint ID (EID): An EID is a 32-bit (for IPv4) or 128-bit (for 242 IPv6) value used in the source and destination address fields of 243 the first (most inner) LISP header of a packet. The host obtains 244 a destination EID the same way it obtains a destination address 245 today, for example, through a Domain Name System (DNS) [RFC1034] 246 lookup or Session Initiation Protocol (SIP) [RFC3261] exchange. 247 The source EID is obtained via existing mechanisms used to set a 248 host's "local" IP address. An EID used on the public Internet 249 MUST have the same properties as any other IP address used in that 250 manner; this means, among other things, that it MUST be globally 251 unique. An EID is allocated to a host from an EID-Prefix block 252 associated with the site where the host is located. An EID can be 253 used by a host to refer to other hosts. Note that EID blocks MAY 254 be assigned in a hierarchical manner, independent of the network 255 topology, to facilitate scaling of the mapping database. In 256 addition, an EID block assigned to a site MAY have site-local 257 structure (subnetting) for routing within the site; this structure 258 is not visible to the global routing system. In theory, the bit 259 string that represents an EID for one device can represent an RLOC 260 for a different device. When used in discussions with other 261 Locator/ID separation proposals, a LISP EID will be called an 262 "LEID". Throughout this document, any references to "EID" refer 263 to an LEID. 265 Ingress Tunnel Router (ITR): An ITR is a router that resides in a 266 LISP site. Packets sent by sources inside of the LISP site to 267 destinations outside of the site are candidates for encapsulation 268 by the ITR. The ITR treats the IP destination address as an EID 269 and performs an EID-to-RLOC mapping lookup. The router then 270 prepends an "outer" IP header with one of its routable RLOCs (in 271 the RLOC space) in the source address field and the result of the 272 mapping lookup in the destination address field. Note that this 273 destination RLOC MAY be an intermediate, proxy device that has 274 better knowledge of the EID-to-RLOC mapping closer to the 275 destination EID. In general, an ITR receives IP packets from site 276 end-systems on one side and sends LISP-encapsulated IP packets 277 toward the Internet on the other side. 279 Specifically, when a service provider prepends a LISP header for 280 Traffic Engineering purposes, the router that does this is also 281 regarded as an ITR. The outer RLOC the ISP ITR uses can be based 282 on the outer destination address (the originating ITR's supplied 283 RLOC) or the inner destination address (the originating host's 284 supplied EID). 286 LISP Header: LISP header is a term used in this document to refer 287 to the outer IPv4 or IPv6 header, a UDP header, and a LISP- 288 specific 8-octet header that follow the UDP header and that an ITR 289 prepends or an ETR strips. 291 LISP Router: A LISP router is a router that performs the functions 292 of any or all of the following: ITR, ETR, RTR, Proxy-ITR (PITR), 293 or Proxy-ETR (PETR). 295 LISP Site: LISP site is a set of routers in an edge network that are 296 under a single technical administration. LISP routers that reside 297 in the edge network are the demarcation points to separate the 298 edge network from the core network. 300 Locator-Status-Bits (LSBs): Locator-Status-Bits are present in the 301 LISP header. They are used by ITRs to inform ETRs about the up/ 302 down status of all ETRs at the local site. These bits are used as 303 a hint to convey up/down router status and not path reachability 304 status. The LSBs can be verified by use of one of the Locator 305 reachability algorithms described in Section 10. 307 Negative Mapping Entry: A negative mapping entry, also known as a 308 negative cache entry, is an EID-to-RLOC entry where an EID-Prefix 309 is advertised or stored with no RLOCs. That is, the Locator-Set 310 for the EID-to-RLOC entry is empty or has an encoded Locator count 311 of 0. This type of entry could be used to describe a prefix from 312 a non-LISP site, which is explicitly not in the mapping database. 313 There are a set of well-defined actions that are encoded in a 314 Negative Map-Reply. 316 Proxy-ETR (PETR): A PETR is defined and described in [RFC6832]. A 317 PETR acts like an ETR but does so on behalf of LISP sites that 318 send packets to destinations at non-LISP sites. 320 Proxy-ITR (PITR): A PITR is defined and described in [RFC6832]. A 321 PITR acts like an ITR but does so on behalf of non-LISP sites that 322 send packets to destinations at LISP sites. 324 Recursive Tunneling: Recursive Tunneling occurs when a packet has 325 more than one LISP IP header. Additional layers of tunneling MAY 326 be employed to implement Traffic Engineering or other re-routing 327 as needed. When this is done, an additional "outer" LISP header 328 is added, and the original RLOCs are preserved in the "inner" 329 header. 331 Re-Encapsulating Tunneling Router (RTR): An RTR acts like an ETR to 332 remove a LISP header, then acts as an ITR to prepend a new LISP 333 header. This is known as Re-encapsulating Tunneling. Doing this 334 allows a packet to be re-routed by the RTR without adding the 335 overhead of additional tunnel headers. When using multiple 336 mapping database systems, care must be taken to not create re- 337 encapsulation loops through misconfiguration. 339 Route-Returnability: Route-returnability is an assumption that the 340 underlying routing system will deliver packets to the destination. 341 When combined with a nonce that is provided by a sender and 342 returned by a receiver, this limits off-path data insertion. A 343 route-returnability check is verified when a message is sent with 344 a nonce, another message is returned with the same nonce, and the 345 destination of the original message appears as the source of the 346 returned message. 348 Routing Locator (RLOC): An RLOC is an IPv4 [RFC0791] or IPv6 349 [RFC8200] address of an Egress Tunnel Router (ETR). An RLOC is 350 the output of an EID-to-RLOC mapping lookup. An EID maps to zero 351 or more RLOCs. Typically, RLOCs are numbered from blocks that are 352 assigned to a site at each point to which it attaches to the 353 underlay network; where the topology is defined by the 354 connectivity of provider networks. Multiple RLOCs can be assigned 355 to the same ETR device or to multiple ETR devices at a site. 357 Server-side: Server-side is a term used in this document to indicate 358 that a connection initiation attempt is being accepted for a 359 destination EID. 361 TE-ETR: A TE-ETR is an ETR that is deployed in a service provider 362 network that strips an outer LISP header for Traffic Engineering 363 purposes. 365 TE-ITR: A TE-ITR is an ITR that is deployed in a service provider 366 network that prepends an additional LISP header for Traffic 367 Engineering purposes. 369 xTR: An xTR is a reference to an ITR or ETR when direction of data 370 flow is not part of the context description. "xTR" refers to the 371 router that is the tunnel endpoint and is used synonymously with 372 the term "Tunnel Router". For example, "An xTR can be located at 373 the Customer Edge (CE) router" indicates both ITR and ETR 374 functionality at the CE router. 376 4. Basic Overview 378 One key concept of LISP is that end-systems operate the same way they 379 do today. The IP addresses that hosts use for tracking sockets and 380 connections, and for sending and receiving packets, do not change. 382 In LISP terminology, these IP addresses are called Endpoint 383 Identifiers (EIDs). 385 Routers continue to forward packets based on IP destination 386 addresses. When a packet is LISP encapsulated, these addresses are 387 referred to as Routing Locators (RLOCs). Most routers along a path 388 between two hosts will not change; they continue to perform routing/ 389 forwarding lookups on the destination addresses. For routers between 390 the source host and the ITR as well as routers from the ETR to the 391 destination host, the destination address is an EID. For the routers 392 between the ITR and the ETR, the destination address is an RLOC. 394 Another key LISP concept is the "Tunnel Router". A Tunnel Router 395 prepends LISP headers on host-originated packets and strips them 396 prior to final delivery to their destination. The IP addresses in 397 this "outer header" are RLOCs. During end-to-end packet exchange 398 between two Internet hosts, an ITR prepends a new LISP header to each 399 packet, and an ETR strips the new header. The ITR performs EID-to- 400 RLOC lookups to determine the routing path to the ETR, which has the 401 RLOC as one of its IP addresses. 403 Some basic rules governing LISP are: 405 o End-systems only send to addresses that are EIDs. EIDs are 406 typically IP addresses assigned to hosts (other types of EID are 407 supported by LISP, see [RFC8060] for further information). End- 408 systems don't know that addresses are EIDs versus RLOCs but assume 409 that packets get to their intended destinations. In a system 410 where LISP is deployed, LISP routers intercept EID-addressed 411 packets and assist in delivering them across the network core 412 where EIDs cannot be routed. The procedure a host uses to send IP 413 packets does not change. 415 o LISP routers mostly deal with Routing Locator addresses. See 416 details in Section 4.1 to clarify what is meant by "mostly". 418 o RLOCs are always IP addresses assigned to routers, preferably 419 topologically oriented addresses from provider CIDR (Classless 420 Inter-Domain Routing) blocks. 422 o When a router originates packets, it MAY use as a source address 423 either an EID or RLOC. When acting as a host (e.g., when 424 terminating a transport session such as Secure SHell (SSH), 425 TELNET, or the Simple Network Management Protocol (SNMP)), it MAY 426 use an EID that is explicitly assigned for that purpose. An EID 427 that identifies the router as a host MUST NOT be used as an RLOC; 428 an EID is only routable within the scope of a site. A typical BGP 429 configuration might demonstrate this "hybrid" EID/RLOC usage where 430 a router could use its "host-like" EID to terminate iBGP sessions 431 to other routers in a site while at the same time using RLOCs to 432 terminate eBGP sessions to routers outside the site. 434 o Packets with EIDs in them are not expected to be delivered end-to- 435 end in the absence of an EID-to-RLOC mapping operation. They are 436 expected to be used locally for intra-site communication or to be 437 encapsulated for inter-site communication. 439 o EIDs MAY also be structured (subnetted) in a manner suitable for 440 local routing within an Autonomous System (AS). 442 An additional LISP header MAY be prepended to packets by a TE-ITR 443 when re-routing of the path for a packet is desired. A potential 444 use-case for this would be an ISP router that needs to perform 445 Traffic Engineering for packets flowing through its network. In such 446 a situation, termed "Recursive Tunneling", an ISP transit acts as an 447 additional ITR, and the RLOC it uses for the new prepended header 448 would be either a TE-ETR within the ISP (along an intra-ISP traffic 449 engineered path) or a TE-ETR within another ISP (an inter-ISP traffic 450 engineered path, where an agreement to build such a path exists). 452 In order to avoid excessive packet overhead as well as possible 453 encapsulation loops, this document recommends that a maximum of two 454 LISP headers can be prepended to a packet. For initial LISP 455 deployments, it is assumed that two headers is sufficient, where the 456 first prepended header is used at a site for Location/Identity 457 separation and the second prepended header is used inside a service 458 provider for Traffic Engineering purposes. 460 Tunnel Routers can be placed fairly flexibly in a multi-AS topology. 461 For example, the ITR for a particular end-to-end packet exchange 462 might be the first-hop or default router within a site for the source 463 host. Similarly, the ETR might be the last-hop router directly 464 connected to the destination host. Another example, perhaps for a 465 VPN service outsourced to an ISP by a site, the ITR could be the 466 site's border router at the service provider attachment point. 467 Mixing and matching of site-operated, ISP-operated, and other Tunnel 468 Routers is allowed for maximum flexibility. 470 4.1. Packet Flow Sequence 472 This section provides an example of the unicast packet flow, 473 including also control-plane information as specified in 474 [I-D.ietf-lisp-rfc6833bis]. The example also assumes the following 475 conditions: 477 o Source host "host1.abc.example.com" is sending a packet to 478 "host2.xyz.example.com", exactly what host1 would do if the site 479 was not using LISP. 481 o Each site is multihomed, so each Tunnel Router has an address 482 (RLOC) assigned from the service provider address block for each 483 provider to which that particular Tunnel Router is attached. 485 o The ITR(s) and ETR(s) are directly connected to the source and 486 destination, respectively, but the source and destination can be 487 located anywhere in the LISP site. 489 o A Map-Request is sent for an external destination when the 490 destination is not found in the forwarding table or matches a 491 default route. Map-Requests are sent to the mapping database 492 system by using the LISP control-plane protocol documented in 493 [I-D.ietf-lisp-rfc6833bis]. 495 o Map-Replies are sent on the underlying routing system topology 496 using the [I-D.ietf-lisp-rfc6833bis] control-plane protocol. 498 Client host1.abc.example.com wants to communicate with server 499 host2.xyz.example.com: 501 1. host1.abc.example.com wants to open a TCP connection to 502 host2.xyz.example.com. It does a DNS lookup on 503 host2.xyz.example.com. An A/AAAA record is returned. This 504 address is the destination EID. The locally assigned address of 505 host1.abc.example.com is used as the source EID. An IPv4 or IPv6 506 packet is built and forwarded through the LISP site as a normal 507 IP packet until it reaches a LISP ITR. 509 2. The LISP ITR must be able to map the destination EID to an RLOC 510 of one of the ETRs at the destination site. The specific method 511 used to do this is not described in this example. See 512 [I-D.ietf-lisp-rfc6833bis] for further information. 514 3. The ITR sends a LISP Map-Request as specified in 515 [I-D.ietf-lisp-rfc6833bis]. Map-Requests SHOULD be rate-limited. 517 4. The mapping system helps forwarding the Map-Request to the 518 corresponding ETR. When the Map-Request arrives at one of the 519 ETRs at the destination site, it will process the packet as a 520 control message. 522 5. The ETR looks at the destination EID of the Map-Request and 523 matches it against the prefixes in the ETR's configured EID-to- 524 RLOC mapping database. This is the list of EID-Prefixes the ETR 525 is supporting for the site it resides in. If there is no match, 526 the Map-Request is dropped. Otherwise, a LISP Map-Reply is 527 returned to the ITR. 529 6. The ITR receives the Map-Reply message, parses the message (to 530 check for format validity), and stores the mapping information 531 from the packet. This information is stored in the ITR's EID-to- 532 RLOC map-cache. Note that the map-cache is an on-demand cache. 533 An ITR will manage its map-cache in such a way that optimizes for 534 its resource constraints. 536 7. Subsequent packets from host1.abc.example.com to 537 host2.xyz.example.com will have a LISP header prepended by the 538 ITR using the appropriate RLOC as the LISP header destination 539 address learned from the ETR. Note that the packet MAY be sent 540 to a different ETR than the one that returned the Map-Reply due 541 to the source site's hashing policy or the destination site's 542 Locator-Set policy. 544 8. The ETR receives these packets directly (since the destination 545 address is one of its assigned IP addresses), checks the validity 546 of the addresses, strips the LISP header, and forwards packets to 547 the attached destination host. 549 9. In order to defer the need for a mapping lookup in the reverse 550 direction, an ETR can OPTIONALLY create a cache entry that maps 551 the source EID (inner-header source IP address) to the source 552 RLOC (outer-header source IP address) in a received LISP packet. 553 Such a cache entry is termed a "glean mapping" and only contains 554 a single RLOC for the EID in question. More complete information 555 about additional RLOCs SHOULD be verified by sending a LISP Map- 556 Request for that EID. Both the ITR and the ETR MAY also 557 influence the decision the other makes in selecting an RLOC. 559 5. LISP Encapsulation Details 561 Since additional tunnel headers are prepended, the packet becomes 562 larger and can exceed the MTU of any link traversed from the ITR to 563 the ETR. It is RECOMMENDED in IPv4 that packets do not get 564 fragmented as they are encapsulated by the ITR. Instead, the packet 565 is dropped and an ICMP Unreachable/Fragmentation-Needed message is 566 returned to the source. 568 In the case when fragmentation is needed, this specification 569 RECOMMENDS that implementations provide support for one of the 570 proposed fragmentation and reassembly schemes. Two existing schemes 571 are detailed in Section 7. 573 Since IPv4 or IPv6 addresses can be either EIDs or RLOCs, the LISP 574 architecture supports IPv4 EIDs with IPv6 RLOCs (where the inner 575 header is in IPv4 packet format and the outer header is in IPv6 576 packet format) or IPv6 EIDs with IPv4 RLOCs (where the inner header 577 is in IPv6 packet format and the outer header is in IPv4 packet 578 format). The next sub-sections illustrate packet formats for the 579 homogeneous case (IPv4-in-IPv4 and IPv6-in-IPv6), but all 4 580 combinations MUST be supported. Additional types of EIDs are defined 581 in [RFC8060]. 583 5.1. LISP IPv4-in-IPv4 Header Format 585 0 1 2 3 586 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 1 587 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 588 / |Version| IHL | DSCP |ECN| Total Length | 589 / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 590 | | Identification |Flags| Fragment Offset | 591 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 592 OH | Time to Live | Protocol = 17 | Header Checksum | 593 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 594 | | Source Routing Locator | 595 \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 596 \ | Destination Routing Locator | 597 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 598 / | Source Port = xxxx | Dest Port = 4341 | 599 UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 600 \ | UDP Length | UDP Checksum | 601 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 602 L |N|L|E|V|I|R|K|K| Nonce/Map-Version | 603 I \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 604 S / | Instance ID/Locator-Status-Bits | 605 P +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 606 / |Version| IHL | DSCP |ECN| Total Length | 607 / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 608 | | Identification |Flags| Fragment Offset | 609 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 610 IH | Time to Live | Protocol | Header Checksum | 611 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 612 | | Source EID | 613 \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 614 \ | Destination EID | 615 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 617 IHL = IP-Header-Length 619 5.2. LISP IPv6-in-IPv6 Header Format 621 0 1 2 3 622 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 1 623 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 624 / |Version| DSCP |ECN| Flow Label | 625 / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 626 | | Payload Length | Next Header=17| Hop Limit | 627 v +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 628 | | 629 O + + 630 u | | 631 t + Source Routing Locator + 632 e | | 633 r + + 634 | | 635 H +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 636 d | | 637 r + + 638 | | 639 ^ + Destination Routing Locator + 640 | | | 641 \ + + 642 \ | | 643 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 644 / | Source Port = xxxx | Dest Port = 4341 | 645 UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 646 \ | UDP Length | UDP Checksum | 647 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 648 L |N|L|E|V|I|R|K|K| Nonce/Map-Version | 649 I \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 650 S / | Instance ID/Locator-Status-Bits | 651 P +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 652 / |Version| DSCP |ECN| Flow Label | 653 / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 654 / | Payload Length | Next Header | Hop Limit | 655 v +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 656 | | 657 I + + 658 n | | 659 n + Source EID + 660 e | | 661 r + + 662 | | 663 H +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 664 d | | 665 r + + 666 | | 668 ^ + Destination EID + 669 \ | | 670 \ + + 671 \ | | 672 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 674 5.3. Tunnel Header Field Descriptions 676 Inner Header (IH): The inner header is the header on the 677 datagram received from the originating host [RFC0791] [RFC8200] 678 [RFC2474]. The source and destination IP addresses are EIDs. 680 Outer Header: (OH) The outer header is a new header prepended by an 681 ITR. The address fields contain RLOCs obtained from the ingress 682 router's EID-to-RLOC Cache. The IP protocol number is "UDP (17)" 683 from [RFC0768]. The setting of the Don't Fragment (DF) bit 684 'Flags' field is according to rules listed in Sections 7.1 and 685 7.2. 687 UDP Header: The UDP header contains an ITR selected source port when 688 encapsulating a packet. See Section 12 for details on the hash 689 algorithm used to select a source port based on the 5-tuple of the 690 inner header. The destination port MUST be set to the well-known 691 IANA-assigned port value 4341. 693 UDP Checksum: The 'UDP Checksum' field SHOULD be transmitted as zero 694 by an ITR for either IPv4 [RFC0768] and IPv6 encapsulation 695 [RFC6935] [RFC6936]. When a packet with a zero UDP checksum is 696 received by an ETR, the ETR MUST accept the packet for 697 decapsulation. When an ITR transmits a non-zero value for the UDP 698 checksum, it MUST send a correctly computed value in this field. 699 When an ETR receives a packet with a non-zero UDP checksum, it MAY 700 choose to verify the checksum value. If it chooses to perform 701 such verification, and the verification fails, the packet MUST be 702 silently dropped. If the ETR chooses not to perform the 703 verification, or performs the verification successfully, the 704 packet MUST be accepted for decapsulation. The handling of UDP 705 zero checksums over IPv6 for all tunneling protocols, including 706 LISP, is subject to the applicability statement in [RFC6936]. 708 UDP Length: The 'UDP Length' field is set for an IPv4-encapsulated 709 packet to be the sum of the inner-header IPv4 Total Length plus 710 the UDP and LISP header lengths. For an IPv6-encapsulated packet, 711 the 'UDP Length' field is the sum of the inner-header IPv6 Payload 712 Length, the size of the IPv6 header (40 octets), and the size of 713 the UDP and LISP headers. 715 N: The N-bit is the nonce-present bit. When this bit is set to 1, 716 the low-order 24 bits of the first 32 bits of the LISP header 717 contain a Nonce. See Section 10.1 for details. Both N- and 718 V-bits MUST NOT be set in the same packet. If they are, a 719 decapsulating ETR MUST treat the 'Nonce/Map-Version' field as 720 having a Nonce value present. 722 L: The L-bit is the 'Locator-Status-Bits' field enabled bit. When 723 this bit is set to 1, the Locator-Status-Bits in the second 724 32 bits of the LISP header are in use. 726 x 1 x x 0 x x x 727 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 728 |N|L|E|V|I|R|K|K| Nonce/Map-Version | 729 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 730 | Locator-Status-Bits | 731 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 733 E: The E-bit is the echo-nonce-request bit. This bit MUST be ignored 734 and has no meaning when the N-bit is set to 0. When the N-bit is 735 set to 1 and this bit is set to 1, an ITR is requesting that the 736 nonce value in the 'Nonce' field be echoed back in LISP- 737 encapsulated packets when the ITR is also an ETR. See 738 Section 10.1 for details. 740 V: The V-bit is the Map-Version present bit. When this bit is set to 741 1, the N-bit MUST be 0. Refer to Section 13.3 for more details. 742 This bit indicates that the LISP header is encoded in this 743 case as: 745 0 x 0 1 x x x x 746 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 747 |N|L|E|V|I|R|K|K| Source Map-Version | Dest Map-Version | 748 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 749 | Instance ID/Locator-Status-Bits | 750 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 752 I: The I-bit is the Instance ID bit. See Section 8 for more details. 753 When this bit is set to 1, the 'Locator-Status-Bits' field is 754 reduced to 8 bits and the high-order 24 bits are used as an 755 Instance ID. If the L-bit is set to 0, then the low-order 8 bits 756 are transmitted as zero and ignored on receipt. The format of the 757 LISP header would look like this: 759 x x x x 1 x x x 760 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 761 |N|L|E|V|I|R|K|K| Nonce/Map-Version | 762 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 763 | Instance ID | LSBs | 764 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 766 R: The R-bit is a Reserved bit for future use. It MUST be set to 0 767 on transmit and MUST be ignored on receipt. 769 KK: The KK-bits are a 2-bit field used when encapsulated packets are 770 encrypted. The field is set to 00 when the packet is not 771 encrypted. See [RFC8061] for further information. 773 LISP Nonce: The LISP 'Nonce' field is a 24-bit value that is 774 randomly generated by an ITR when the N-bit is set to 1. Nonce 775 generation algorithms are an implementation matter but are 776 required to generate different nonces when sending to different 777 destinations. However, the same nonce can be used for a period of 778 time when encapsulating to the same ETR. The nonce is also used 779 when the E-bit is set to request the nonce value to be echoed by 780 the other side when packets are returned. When the E-bit is clear 781 but the N-bit is set, a remote ITR is either echoing a previously 782 requested echo-nonce or providing a random nonce. See 783 Section 10.1 for more details. 785 LISP Locator-Status-Bits (LSBs): When the L-bit is also set, the 786 'Locator-Status-Bits' field in the LISP header is set by an ITR to 787 indicate to an ETR the up/down status of the Locators in the 788 source site. Each RLOC in a Map-Reply is assigned an ordinal 789 value from 0 to n-1 (when there are n RLOCs in a mapping entry). 790 The Locator-Status-Bits are numbered from 0 to n-1 from the least 791 significant bit of the field. The field is 32 bits when the I-bit 792 is set to 0 and is 8 bits when the I-bit is set to 1. When a 793 Locator-Status-Bit is set to 1, the ITR is indicating to the ETR 794 that the RLOC associated with the bit ordinal has up status. See 795 Section 10 for details on how an ITR can determine the status of 796 the ETRs at the same site. When a site has multiple EID-Prefixes 797 that result in multiple mappings (where each could have a 798 different Locator-Set), the Locator-Status-Bits setting in an 799 encapsulated packet MUST reflect the mapping for the EID-Prefix 800 that the inner-header source EID address matches. If the LSB for 801 an anycast Locator is set to 1, then there is at least one RLOC 802 with that address, and the ETR is considered 'up'. 804 When doing ITR/PITR encapsulation: 806 o The outer-header 'Time to Live' field (or 'Hop Limit' field, in 807 the case of IPv6) SHOULD be copied from the inner-header 'Time to 808 Live' field. 810 o The outer-header 'Differentiated Services Code Point' (DSCP) field 811 (or the 'Traffic Class' field, in the case of IPv6) SHOULD be 812 copied from the inner-header DSCP field ('Traffic Class' field, in 813 the case of IPv6) considering the exception listed below. 815 o The 'Explicit Congestion Notification' (ECN) field (bits 6 and 7 816 of the IPv6 'Traffic Class' field) requires special treatment in 817 order to avoid discarding indications of congestion [RFC3168]. 818 ITR encapsulation MUST copy the 2-bit 'ECN' field from the inner 819 header to the outer header. Re-encapsulation MUST copy the 2-bit 820 'ECN' field from the stripped outer header to the new outer 821 header. 823 When doing ETR/PETR decapsulation: 825 o The inner-header 'Time to Live' field (or 'Hop Limit' field, in 826 the case of IPv6) SHOULD be copied from the outer-header 'Time to 827 Live' field, when the Time to Live value of the outer header is 828 less than the Time to Live value of the inner header. Failing to 829 perform this check can cause the Time to Live of the inner header 830 to increment across encapsulation/decapsulation cycles. This 831 check is also performed when doing initial encapsulation, when a 832 packet comes to an ITR or PITR destined for a LISP site. 834 o The inner-header 'Differentiated Services Code Point' (DSCP) field 835 (or the 'Traffic Class' field, in the case of IPv6) SHOULD be 836 copied from the outer-header DSCP field ('Traffic Class' field, in 837 the case of IPv6) considering the exception listed below. 839 o The 'Explicit Congestion Notification' (ECN) field (bits 6 and 7 840 of the IPv6 'Traffic Class' field) requires special treatment in 841 order to avoid discarding indications of congestion [RFC3168]. If 842 the 'ECN' field contains a congestion indication codepoint (the 843 value is '11', the Congestion Experienced (CE) codepoint), then 844 ETR decapsulation MUST copy the 2-bit 'ECN' field from the 845 stripped outer header to the surviving inner header that is used 846 to forward the packet beyond the ETR. These requirements preserve 847 CE indications when a packet that uses ECN traverses a LISP tunnel 848 and becomes marked with a CE indication due to congestion between 849 the tunnel endpoints. 851 Note that if an ETR/PETR is also an ITR/PITR and chooses to re- 852 encapsulate after decapsulating, the net effect of this is that the 853 new outer header will carry the same Time to Live as the old outer 854 header minus 1. 856 Copying the Time to Live (TTL) serves two purposes: first, it 857 preserves the distance the host intended the packet to travel; 858 second, and more importantly, it provides for suppression of looping 859 packets in the event there is a loop of concatenated tunnels due to 860 misconfiguration. See Section 18.3 for TTL exception handling for 861 traceroute packets. 863 The Explicit Congestion Notification ('ECN') field occupies bits 6 864 and 7 of both the IPv4 'Type of Service' field and the IPv6 'Traffic 865 Class' field [RFC3168]. The 'ECN' field requires special treatment 866 in order to avoid discarding indications of congestion [RFC3168]. An 867 ITR/PITR encapsulation MUST copy the 2-bit 'ECN' field from the inner 868 header to the outer header. Re-encapsulation MUST copy the 2-bit 869 'ECN' field from the stripped outer header to the new outer header. 870 If the 'ECN' field contains a congestion indication codepoint (the 871 value is '11', the Congestion Experienced (CE) codepoint), then ETR/ 872 PETR decapsulation MUST copy the 2-bit 'ECN' field from the stripped 873 outer header to the surviving inner header that is used to forward 874 the packet beyond the ETR. These requirements preserve CE 875 indications when a packet that uses ECN traverses a LISP tunnel and 876 becomes marked with a CE indication due to congestion between the 877 tunnel endpoints. 879 6. LISP EID-to-RLOC Map-Cache 881 ITRs and PITRs maintain an on-demand cache, referred as LISP EID-to- 882 RLOC Map-Cache, that contains mappings from EID-prefixes to locator 883 sets. The cache is used to encapsulate packets from the EID space to 884 the corresponding RLOC network attachment point. 886 When an ITR/PITR receives a packet from inside of the LISP site to 887 destinations outside of the site a longest-prefix match lookup of the 888 EID is done to the map-cache. 890 When the lookup succeeds, the Locator-Set retrieved from the map- 891 cache is used to send the packet to the EID's topological location. 893 If the lookup fails, the ITR/PITR needs to retrieve the mapping using 894 the LISP control-plane protocol [I-D.ietf-lisp-rfc6833bis]. The 895 mapping is then stored in the local map-cache to forward subsequent 896 packets addressed to the same EID-prefix. 898 The map-cache is a local cache of mappings, entries are expired based 899 on the associated Time to live. In addition, entries can be updated 900 with more current information, see Section 13 for further information 901 on this. Finally, the map-cache also contains reachability 902 information about EIDs and RLOCs, and uses LISP reachability 903 information mechanisms to determine the reachability of RLOCs, see 904 Section 10 for the specific mechanisms. 906 7. Dealing with Large Encapsulated Packets 908 This section proposes two mechanisms to deal with packets that exceed 909 the path MTU between the ITR and ETR. 911 It is left to the implementor to decide if the stateless or stateful 912 mechanism SHOULD be implemented. Both or neither can be used, since 913 it is a local decision in the ITR regarding how to deal with MTU 914 issues, and sites can interoperate with differing mechanisms. 916 Both stateless and stateful mechanisms also apply to Re-encapsulating 917 and Recursive Tunneling, so any actions below referring to an ITR 918 also apply to a TE-ITR. 920 7.1. A Stateless Solution to MTU Handling 922 An ITR stateless solution to handle MTU issues is described as 923 follows: 925 1. Define H to be the size, in octets, of the outer header an ITR 926 prepends to a packet. This includes the UDP and LISP header 927 lengths. 929 2. Define L to be the size, in octets, of the maximum-sized packet 930 an ITR can send to an ETR without the need for the ITR or any 931 intermediate routers to fragment the packet. 933 3. Define an architectural constant S for the maximum size of a 934 packet, in octets, an ITR MUST receive from the source so the 935 effective MTU can be met. That is, L = S + H. 937 When an ITR receives a packet from a site-facing interface and adds H 938 octets worth of encapsulation to yield a packet size greater than L 939 octets (meaning the received packet size was greater than S octets 940 from the source), it resolves the MTU issue by first splitting the 941 original packet into 2 equal-sized fragments. A LISP header is then 942 prepended to each fragment. The size of the encapsulated fragments 943 is then (S/2 + H), which is less than the ITR's estimate of the path 944 MTU between the ITR and its correspondent ETR. 946 When an ETR receives encapsulated fragments, it treats them as two 947 individually encapsulated packets. It strips the LISP headers and 948 then forwards each fragment to the destination host of the 949 destination site. The two fragments are reassembled at the 950 destination host into the single IP datagram that was originated by 951 the source host. Note that reassembly can happen at the ETR if the 952 encapsulated packet was fragmented at or after the ITR. 954 This behavior is performed by the ITR when the source host originates 955 a packet with the 'DF' field of the IP header set to 0. When the 956 'DF' field of the IP header is set to 1, or the packet is an IPv6 957 packet originated by the source host, the ITR will drop the packet 958 when the size is greater than L and send an ICMP Unreachable/ 959 Fragmentation-Needed message to the source with a value of S, where S 960 is (L - H). 962 When the outer-header encapsulation uses an IPv4 header, an 963 implementation SHOULD set the DF bit to 1 so ETR fragment reassembly 964 can be avoided. An implementation MAY set the DF bit in such headers 965 to 0 if it has good reason to believe there are unresolvable path MTU 966 issues between the sending ITR and the receiving ETR. 968 This specification RECOMMENDS that L be defined as 1500. 970 7.2. A Stateful Solution to MTU Handling 972 An ITR stateful solution to handle MTU issues is described as follows 973 and was first introduced in [OPENLISP]: 975 1. The ITR will keep state of the effective MTU for each Locator per 976 Map-Cache entry. The effective MTU is what the core network can 977 deliver along the path between the ITR and ETR. 979 2. When an IPv6-encapsulated packet, or an IPv4-encapsulated packet 980 with the DF bit set to 1, exceeds what the core network can 981 deliver, one of the intermediate routers on the path will send an 982 ICMP Unreachable/Fragmentation-Needed message to the ITR. The 983 ITR will parse the ICMP message to determine which Locator is 984 affected by the effective MTU change and then record the new 985 effective MTU value in the Map-Cache entry. 987 3. When a packet is received by the ITR from a source inside of the 988 site and the size of the packet is greater than the effective MTU 989 stored with the Map-Cache entry associated with the destination 990 EID the packet is for, the ITR will send an ICMP Unreachable/ 991 Fragmentation-Needed message back to the source. The packet size 992 advertised by the ITR in the ICMP Unreachable/Fragmentation- 993 Needed message is the effective MTU minus the LISP encapsulation 994 length. 996 Even though this mechanism is stateful, it has advantages over the 997 stateless IP fragmentation mechanism, by not involving the 998 destination host with reassembly of ITR fragmented packets. 1000 8. Using Virtualization and Segmentation with LISP 1002 There are several cases where segregation is needed at the EID level. 1003 For instance, this is the case for deployments containing overlapping 1004 addresses, traffic isolation policies or multi-tenant virtualization. 1005 For these and other scenarios where segregation is needed, Instance 1006 IDs are used. 1008 An Instance ID can be carried in a LISP-encapsulated packet. An ITR 1009 that prepends a LISP header will copy a 24-bit value used by the LISP 1010 router to uniquely identify the address space. The value is copied 1011 to the 'Instance ID' field of the LISP header, and the I-bit is set 1012 to 1. 1014 When an ETR decapsulates a packet, the Instance ID from the LISP 1015 header is used as a table identifier to locate the forwarding table 1016 to use for the inner destination EID lookup. 1018 For example, an 802.1Q VLAN tag or VPN identifier could be used as a 1019 24-bit Instance ID. See [I-D.ietf-lisp-vpn] for LISP VPN use-case 1020 details. 1022 The Instance ID that is stored in the mapping database when LISP-DDT 1023 [RFC8111] is used is 32 bits in length. That means the control-plane 1024 can store more instances than a given data-plane can use. Multiple 1025 data-planes can use the same 32-bit space as long as the low-order 24 1026 bits don't overlap among xTRs. 1028 9. Routing Locator Selection 1030 Both the client-side and server-side MAY need control over the 1031 selection of RLOCs for conversations between them. This control is 1032 achieved by manipulating the 'Priority' and 'Weight' fields in EID- 1033 to-RLOC Map-Reply messages. Alternatively, RLOC information MAY be 1034 gleaned from received tunneled packets or EID-to-RLOC Map-Request 1035 messages. 1037 The following are different scenarios for choosing RLOCs and the 1038 controls that are available: 1040 o The server-side returns one RLOC. The client-side can only use 1041 one RLOC. The server-side has complete control of the selection. 1043 o The server-side returns a list of RLOCs where a subset of the list 1044 has the same best Priority. The client can only use the subset 1045 list according to the weighting assigned by the server-side. In 1046 this case, the server-side controls both the subset list and load- 1047 splitting across its members. The client-side can use RLOCs 1048 outside of the subset list if it determines that the subset list 1049 is unreachable (unless RLOCs are set to a Priority of 255). Some 1050 sharing of control exists: the server-side determines the 1051 destination RLOC list and load distribution while the client-side 1052 has the option of using alternatives to this list if RLOCs in the 1053 list are unreachable. 1055 o The server-side sets a Weight of zero for the RLOC subset list. 1056 In this case, the client-side can choose how the traffic load is 1057 spread across the subset list. Control is shared by the server- 1058 side determining the list and the client-side determining load 1059 distribution. Again, the client can use alternative RLOCs if the 1060 server-provided list of RLOCs is unreachable. 1062 o Either side (more likely the server-side ETR) decides not to send 1063 a Map-Request. For example, if the server-side ETR does not send 1064 Map-Requests, it gleans RLOCs from the client-side ITR, giving the 1065 client-side ITR responsibility for bidirectional RLOC reachability 1066 and preferability. Server-side ETR gleaning of the client-side 1067 ITR RLOC is done by caching the inner-header source EID and the 1068 outer-header source RLOC of received packets. The client-side ITR 1069 controls how traffic is returned and can alternate using an outer- 1070 header source RLOC, which then can be added to the list the 1071 server-side ETR uses to return traffic. Since no Priority or 1072 Weights are provided using this method, the server-side ETR MUST 1073 assume that each client-side ITR RLOC uses the same best Priority 1074 with a Weight of zero. In addition, since EID-Prefix encoding 1075 cannot be conveyed in data packets, the EID-to-RLOC Cache on 1076 Tunnel Routers can grow to be very large. 1078 o A "gleaned" Map-Cache entry, one learned from the source RLOC of a 1079 received encapsulated packet, is only stored and used for a few 1080 seconds, pending verification. Verification is performed by 1081 sending a Map-Request to the source EID (the inner-header IP 1082 source address) of the received encapsulated packet. A reply to 1083 this "verifying Map-Request" is used to fully populate the Map- 1084 Cache entry for the "gleaned" EID and is stored and used for the 1085 time indicated from the 'TTL' field of a received Map-Reply. When 1086 a verified Map-Cache entry is stored, data gleaning no longer 1087 occurs for subsequent packets that have a source EID that matches 1088 the EID-Prefix of the verified entry. This "gleaning" mechanism 1089 is OPTIONAL. 1091 RLOCs that appear in EID-to-RLOC Map-Reply messages are assumed to be 1092 reachable when the R-bit for the Locator record is set to 1. When 1093 the R-bit is set to 0, an ITR or PITR MUST NOT encapsulate to the 1094 RLOC. Neither the information contained in a Map-Reply nor that 1095 stored in the mapping database system provides reachability 1096 information for RLOCs. Note that reachability is not part of the 1097 mapping system and is determined using one or more of the Routing 1098 Locator reachability algorithms described in the next section. 1100 10. Routing Locator Reachability 1102 Several mechanisms for determining RLOC reachability are currently 1103 defined: 1105 1. An ETR MAY examine the Locator-Status-Bits in the LISP header of 1106 an encapsulated data packet received from an ITR. If the ETR is 1107 also acting as an ITR and has traffic to return to the original 1108 ITR site, it can use this status information to help select an 1109 RLOC. 1111 2. An ITR MAY receive an ICMP Network Unreachable or Host 1112 Unreachable message for an RLOC it is using. This indicates that 1113 the RLOC is likely down. Note that trusting ICMP messages may 1114 not be desirable, but neither is ignoring them completely. 1115 Implementations are encouraged to follow current best practices 1116 in treating these conditions [I-D.ietf-opsec-icmp-filtering]. 1118 3. When an ITR participates in the routing protocol that operates in 1119 the underlay routing system, it can determine that an RLOC is 1120 down when no Routing Information Base (RIB) entry exists that 1121 matches the RLOC IP address. 1123 4. An ITR MAY receive an ICMP Port Unreachable message from a 1124 destination host. This occurs if an ITR attempts to use 1125 interworking [RFC6832] and LISP-encapsulated data is sent to a 1126 non-LISP-capable site. 1128 5. An ITR MAY receive a Map-Reply from an ETR in response to a 1129 previously sent Map-Request. The RLOC source of the Map-Reply is 1130 likely up, since the ETR was able to send the Map-Reply to the 1131 ITR. 1133 6. When an ETR receives an encapsulated packet from an ITR, the 1134 source RLOC from the outer header of the packet is likely up. 1136 7. An ITR/ETR pair can use the Locator reachability algorithms 1137 described in this section, namely Echo-Noncing or RLOC-Probing. 1139 When determining Locator up/down reachability by examining the 1140 Locator-Status-Bits from the LISP-encapsulated data packet, an ETR 1141 will receive up-to-date status from an encapsulating ITR about 1142 reachability for all ETRs at the site. CE-based ITRs at the source 1143 site can determine reachability relative to each other using the site 1144 IGP as follows: 1146 o Under normal circumstances, each ITR will advertise a default 1147 route into the site IGP. 1149 o If an ITR fails or if the upstream link to its PE fails, its 1150 default route will either time out or be withdrawn. 1152 Each ITR can thus observe the presence or lack of a default route 1153 originated by the others to determine the Locator-Status-Bits it sets 1154 for them. 1156 RLOCs listed in a Map-Reply are numbered with ordinals 0 to n-1. The 1157 Locator-Status-Bits in a LISP-encapsulated packet are numbered from 0 1158 to n-1 starting with the least significant bit. For example, if an 1159 RLOC listed in the 3rd position of the Map-Reply goes down (ordinal 1160 value 2), then all ITRs at the site will clear the 3rd least 1161 significant bit (xxxx x0xx) of the 'Locator-Status-Bits' field for 1162 the packets they encapsulate. 1164 When an ETR decapsulates a packet, it will check for any change in 1165 the 'Locator-Status-Bits' field. When a bit goes from 1 to 0, the 1166 ETR, if acting also as an ITR, will refrain from encapsulating 1167 packets to an RLOC that is indicated as down. It will only resume 1168 using that RLOC if the corresponding Locator-Status-Bit returns to a 1169 value of 1. Locator-Status-Bits are associated with a Locator-Set 1170 per EID-Prefix. Therefore, when a Locator becomes unreachable, the 1171 Locator-Status-Bit that corresponds to that Locator's position in the 1172 list returned by the last Map-Reply will be set to zero for that 1173 particular EID-Prefix. Refer to Section 19 for security related 1174 issues regarding Locator-Status-Bits. 1176 When ITRs at the site are not deployed in CE routers, the IGP can 1177 still be used to determine the reachability of Locators, provided 1178 they are injected into the IGP. This is typically done when a /32 1179 address is configured on a loopback interface. 1181 When ITRs receive ICMP Network Unreachable or Host Unreachable 1182 messages as a method to determine unreachability, they will refrain 1183 from using Locators that are described in Locator lists of Map- 1184 Replies. However, using this approach is unreliable because many 1185 network operators turn off generation of ICMP Destination Unreachable 1186 messages. 1188 If an ITR does receive an ICMP Network Unreachable or Host 1189 Unreachable message, it MAY originate its own ICMP Destination 1190 Unreachable message destined for the host that originated the data 1191 packet the ITR encapsulated. 1193 Also, BGP-enabled ITRs can unilaterally examine the RIB to see if a 1194 locator address from a Locator-Set in a mapping entry matches a 1195 prefix. If it does not find one and BGP is running in the Default- 1196 Free Zone (DFZ), it can decide to not use the Locator even though the 1197 Locator-Status-Bits indicate that the Locator is up. In this case, 1198 the path from the ITR to the ETR that is assigned the Locator is not 1199 available. More details are in [I-D.meyer-loc-id-implications]. 1201 Optionally, an ITR can send a Map-Request to a Locator, and if a Map- 1202 Reply is returned, reachability of the Locator has been determined. 1203 Obviously, sending such probes increases the number of control 1204 messages originated by Tunnel Routers for active flows, so Locators 1205 are assumed to be reachable when they are advertised. 1207 This assumption does create a dependency: Locator unreachability is 1208 detected by the receipt of ICMP Host Unreachable messages. When a 1209 Locator has been determined to be unreachable, it is not used for 1210 active traffic; this is the same as if it were listed in a Map-Reply 1211 with Priority 255. 1213 The ITR can test the reachability of the unreachable Locator by 1214 sending periodic Requests. Both Requests and Replies MUST be rate- 1215 limited. Locator reachability testing is never done with data 1216 packets, since that increases the risk of packet loss for end-to-end 1217 sessions. 1219 When an ETR decapsulates a packet, it knows that it is reachable from 1220 the encapsulating ITR because that is how the packet arrived. In 1221 most cases, the ETR can also reach the ITR but cannot assume this to 1222 be true, due to the possibility of path asymmetry. In the presence 1223 of unidirectional traffic flow from an ITR to an ETR, the ITR SHOULD 1224 NOT use the lack of return traffic as an indication that the ETR is 1225 unreachable. Instead, it MUST use an alternate mechanism to 1226 determine reachability. 1228 10.1. Echo Nonce Algorithm 1230 When data flows bidirectionally between Locators from different 1231 sites, a data-plane mechanism called "nonce echoing" can be used to 1232 determine reachability between an ITR and ETR. When an ITR wants to 1233 solicit a nonce echo, it sets the N- and E-bits and places a 24-bit 1234 nonce [RFC4086] in the LISP header of the next encapsulated data 1235 packet. 1237 When this packet is received by the ETR, the encapsulated packet is 1238 forwarded as normal. When the ETR next sends a data packet to the 1239 ITR, it includes the nonce received earlier with the N-bit set and 1240 E-bit cleared. The ITR sees this "echoed nonce" and knows that the 1241 path to and from the ETR is up. 1243 The ITR will set the E-bit and N-bit for every packet it sends while 1244 in the echo-nonce-request state. The time the ITR waits to process 1245 the echoed nonce before it determines the path is unreachable is 1246 variable and is a choice left for the implementation. 1248 If the ITR is receiving packets from the ETR but does not see the 1249 nonce echoed while being in the echo-nonce-request state, then the 1250 path to the ETR is unreachable. This decision MAY be overridden by 1251 other Locator reachability algorithms. Once the ITR determines that 1252 the path to the ETR is down, it can switch to another Locator for 1253 that EID-Prefix. 1255 Note that "ITR" and "ETR" are relative terms here. Both devices MUST 1256 be implementing both ITR and ETR functionality for the echo nonce 1257 mechanism to operate. 1259 The ITR and ETR MAY both go into the echo-nonce-request state at the 1260 same time. The number of packets sent or the time during which echo 1261 nonce requests are sent is an implementation-specific setting. 1262 However, when an ITR is in the echo-nonce-request state, it can echo 1263 the ETR's nonce in the next set of packets that it encapsulates and 1264 subsequently continue sending echo-nonce-request packets. 1266 This mechanism does not completely solve the forward path 1267 reachability problem, as traffic may be unidirectional. That is, the 1268 ETR receiving traffic at a site MAY not be the same device as an ITR 1269 that transmits traffic from that site, or the site-to-site traffic is 1270 unidirectional so there is no ITR returning traffic. 1272 The echo-nonce algorithm is bilateral. That is, if one side sets the 1273 E-bit and the other side is not enabled for echo-noncing, then the 1274 echoing of the nonce does not occur and the requesting side may 1275 erroneously consider the Locator unreachable. An ITR SHOULD only set 1276 the E-bit in an encapsulated data packet when it knows the ETR is 1277 enabled for echo-noncing. This is conveyed by the E-bit in the RLOC- 1278 probe Map-Reply message. 1280 Note other Locator Reachability mechanisms can be used to compliment 1281 or even override the echo nonce algorithm. See the next section for 1282 an example of control-plane probing. 1284 10.2. RLOC-Probing Algorithm 1286 RLOC-Probing is a method that an ITR or PITR can use to determine the 1287 reachability status of one or more Locators that it has cached in a 1288 Map-Cache entry. The probe-bit of the Map-Request and Map-Reply 1289 messages is used for RLOC-Probing. 1291 RLOC-Probing is done in the control plane on a timer basis, where an 1292 ITR or PITR will originate a Map-Request destined to a locator 1293 address from one of its own locator addresses. A Map-Request used as 1294 an RLOC-probe is NOT encapsulated and NOT sent to a Map-Server or to 1295 the mapping database system as one would when soliciting mapping 1296 data. The EID record encoded in the Map-Request is the EID-Prefix of 1297 the Map-Cache entry cached by the ITR or PITR. The ITR MAY include a 1298 mapping data record for its own database mapping information that 1299 contains the local EID-Prefixes and RLOCs for its site. RLOC-probes 1300 are sent periodically using a jittered timer interval. 1302 When an ETR receives a Map-Request message with the probe-bit set, it 1303 returns a Map-Reply with the probe-bit set. The source address of 1304 the Map-Reply is set according to the procedure described in 1305 [I-D.ietf-lisp-rfc6833bis]. The Map-Reply SHOULD contain mapping 1306 data for the EID-Prefix contained in the Map-Request. This provides 1307 the opportunity for the ITR or PITR that sent the RLOC-probe to get 1308 mapping updates if there were changes to the ETR's database mapping 1309 entries. 1311 There are advantages and disadvantages of RLOC-Probing. The greatest 1312 benefit of RLOC-Probing is that it can handle many failure scenarios 1313 allowing the ITR to determine when the path to a specific Locator is 1314 reachable or has become unreachable, thus providing a robust 1315 mechanism for switching to using another Locator from the cached 1316 Locator. RLOC-Probing can also provide rough Round-Trip Time (RTT) 1317 estimates between a pair of Locators, which can be useful for network 1318 management purposes as well as for selecting low delay paths. The 1319 major disadvantage of RLOC-Probing is in the number of control 1320 messages required and the amount of bandwidth used to obtain those 1321 benefits, especially if the requirement for failure detection times 1322 is very small. 1324 11. EID Reachability within a LISP Site 1326 A site MAY be multihomed using two or more ETRs. The hosts and 1327 infrastructure within a site will be addressed using one or more EID- 1328 Prefixes that are mapped to the RLOCs of the relevant ETRs in the 1329 mapping system. One possible failure mode is for an ETR to lose 1330 reachability to one or more of the EID-Prefixes within its own site. 1331 When this occurs when the ETR sends Map-Replies, it can clear the 1332 R-bit associated with its own Locator. And when the ETR is also an 1333 ITR, it can clear its Locator-Status-Bit in the encapsulation data 1334 header. 1336 It is recognized that there are no simple solutions to the site 1337 partitioning problem because it is hard to know which part of the 1338 EID-Prefix range is partitioned and which Locators can reach any sub- 1339 ranges of the EID-Prefixes. Note that this is not a new problem 1340 introduced by the LISP architecture. The problem exists today when a 1341 multihomed site uses BGP to advertise its reachability upstream. 1343 12. Routing Locator Hashing 1345 When an ETR provides an EID-to-RLOC mapping in a Map-Reply message 1346 that is stored in the map-cache of a requesting ITR, the Locator-Set 1347 for the EID-Prefix MAY contain different Priority and Weight values 1348 for each locator address. When more than one best Priority Locator 1349 exists, the ITR can decide how to load-share traffic against the 1350 corresponding Locators. 1352 The following hash algorithm MAY be used by an ITR to select a 1353 Locator for a packet destined to an EID for the EID-to-RLOC mapping: 1355 1. Either a source and destination address hash or the traditional 1356 5-tuple hash can be used. The traditional 5-tuple hash includes 1357 the source and destination addresses; source and destination TCP, 1358 UDP, or Stream Control Transmission Protocol (SCTP) port numbers; 1359 and the IP protocol number field or IPv6 next-protocol fields of 1360 a packet that a host originates from within a LISP site. When a 1361 packet is not a TCP, UDP, or SCTP packet, the source and 1362 destination addresses only from the header are used to compute 1363 the hash. 1365 2. Take the hash value and divide it by the number of Locators 1366 stored in the Locator-Set for the EID-to-RLOC mapping. 1368 3. The remainder will yield a value of 0 to "number of Locators 1369 minus 1". Use the remainder to select the Locator in the 1370 Locator-Set. 1372 Note that when a packet is LISP encapsulated, the source port number 1373 in the outer UDP header needs to be set. Selecting a hashed value 1374 allows core routers that are attached to Link Aggregation Groups 1375 (LAGs) to load-split the encapsulated packets across member links of 1376 such LAGs. Otherwise, core routers would see a single flow, since 1377 packets have a source address of the ITR, for packets that are 1378 originated by different EIDs at the source site. A suggested setting 1379 for the source port number computed by an ITR is a 5-tuple hash 1380 function on the inner header, as described above. 1382 Many core router implementations use a 5-tuple hash to decide how to 1383 balance packet load across members of a LAG. The 5-tuple hash 1384 includes the source and destination addresses of the packet and the 1385 source and destination ports when the protocol number in the packet 1386 is TCP or UDP. For this reason, UDP encoding is used for LISP 1387 encapsulation. 1389 13. Changing the Contents of EID-to-RLOC Mappings 1391 Since the LISP architecture uses a caching scheme to retrieve and 1392 store EID-to-RLOC mappings, the only way an ITR can get a more up-to- 1393 date mapping is to re-request the mapping. However, the ITRs do not 1394 know when the mappings change, and the ETRs do not keep track of 1395 which ITRs requested its mappings. For scalability reasons, it is 1396 desirable to maintain this approach but need to provide a way for 1397 ETRs to change their mappings and inform the sites that are currently 1398 communicating with the ETR site using such mappings. 1400 When adding a new Locator record in lexicographic order to the end of 1401 a Locator-Set, it is easy to update mappings. We assume that new 1402 mappings will maintain the same Locator ordering as the old mapping 1403 but will just have new Locators appended to the end of the list. So, 1404 some ITRs can have a new mapping while other ITRs have only an old 1405 mapping that is used until they time out. When an ITR has only an 1406 old mapping but detects bits set in the Locator-Status-Bits that 1407 correspond to Locators beyond the list it has cached, it simply 1408 ignores them. However, this can only happen for locator addresses 1409 that are lexicographically greater than the locator addresses in the 1410 existing Locator-Set. 1412 When a Locator record is inserted in the middle of a Locator-Set, to 1413 maintain lexicographic order, the SMR procedure in Section 13.2 is 1414 used to inform ITRs and PITRs of the new Locator-Status-Bit mappings. 1416 When a Locator record is removed from a Locator-Set, ITRs that have 1417 the mapping cached will not use the removed Locator because the xTRs 1418 will set the Locator-Status-Bit to 0. So, even if the Locator is in 1419 the list, it will not be used. For new mapping requests, the xTRs 1420 can set the Locator AFI to 0 (indicating an unspecified address), as 1421 well as setting the corresponding Locator-Status-Bit to 0. This 1422 forces ITRs with old or new mappings to avoid using the removed 1423 Locator. 1425 If many changes occur to a mapping over a long period of time, one 1426 will find empty record slots in the middle of the Locator-Set and new 1427 records appended to the Locator-Set. At some point, it would be 1428 useful to compact the Locator-Set so the Locator-Status-Bit settings 1429 can be efficiently packed. 1431 We propose here three approaches for Locator-Set compaction: one 1432 operational mechanism and two protocol mechanisms. The operational 1433 approach uses a clock sweep method. The protocol approaches use the 1434 concept of Solicit-Map-Requests and Map-Versioning. 1436 13.1. Clock Sweep 1438 The clock sweep approach uses planning in advance and the use of 1439 count-down TTLs to time out mappings that have already been cached. 1440 The default setting for an EID-to-RLOC mapping TTL is 24 hours. So, 1441 there is a 24-hour window to time out old mappings. The following 1442 clock sweep procedure is used: 1444 1. 24 hours before a mapping change is to take effect, a network 1445 administrator configures the ETRs at a site to start the clock 1446 sweep window. 1448 2. During the clock sweep window, ETRs continue to send Map-Reply 1449 messages with the current (unchanged) mapping records. The TTL 1450 for these mappings is set to 1 hour. 1452 3. 24 hours later, all previous cache entries will have timed out, 1453 and any active cache entries will time out within 1 hour. During 1454 this 1-hour window, the ETRs continue to send Map-Reply messages 1455 with the current (unchanged) mapping records with the TTL set to 1456 1 minute. 1458 4. At the end of the 1-hour window, the ETRs will send Map-Reply 1459 messages with the new (changed) mapping records. So, any active 1460 caches can get the new mapping contents right away if not cached, 1461 or in 1 minute if they had the mapping cached. The new mappings 1462 are cached with a TTL equal to the TTL in the Map-Reply. 1464 13.2. Solicit-Map-Request (SMR) 1466 Soliciting a Map-Request is a selective way for ETRs, at the site 1467 where mappings change, to control the rate they receive requests for 1468 Map-Reply messages. SMRs are also used to tell remote ITRs to update 1469 the mappings they have cached. 1471 Since the ETRs don't keep track of remote ITRs that have cached their 1472 mappings, they do not know which ITRs need to have their mappings 1473 updated. As a result, an ETR will solicit Map-Requests (called an 1474 SMR message) from those sites to which it has been sending 1475 encapsulated data for the last minute. In particular, an ETR will 1476 send an SMR to an ITR to which it has recently sent encapsulated 1477 data. This can only occur when both ITR and ETR functionality reside 1478 in the same router. 1480 An SMR message is simply a bit set in a Map-Request message. An ITR 1481 or PITR will send a Map-Request when they receive an SMR message. 1482 Both the SMR sender and the Map-Request responder MUST rate-limit 1483 these messages. Rate-limiting can be implemented as a global rate- 1484 limiter or one rate-limiter per SMR destination. 1486 The following procedure shows how an SMR exchange occurs when a site 1487 is doing Locator-Set compaction for an EID-to-RLOC mapping: 1489 1. When the database mappings in an ETR change, the ETRs at the site 1490 begin to send Map-Requests with the SMR bit set for each Locator 1491 in each Map-Cache entry the ETR caches. 1493 2. A remote ITR that receives the SMR message will schedule sending 1494 a Map-Request message to the source locator address of the SMR 1495 message or to the mapping database system. A newly allocated 1496 random nonce is selected, and the EID-Prefix used is the one 1497 copied from the SMR message. If the source Locator is the only 1498 Locator in the cached Locator-Set, the remote ITR SHOULD send a 1499 Map-Request to the database mapping system just in case the 1500 single Locator has changed and may no longer be reachable to 1501 accept the Map-Request. 1503 3. The remote ITR MUST rate-limit the Map-Request until it gets a 1504 Map-Reply while continuing to use the cached mapping. When 1505 Map-Versioning as described in Section 13.3 is used, an SMR 1506 sender can detect if an ITR is using the most up-to-date database 1507 mapping. 1509 4. The ETRs at the site with the changed mapping will reply to the 1510 Map-Request with a Map-Reply message that has a nonce from the 1511 SMR-invoked Map-Request. The Map-Reply messages SHOULD be rate- 1512 limited. This is important to avoid Map-Reply implosion. 1514 5. The ETRs at the site with the changed mapping record the fact 1515 that the site that sent the Map-Request has received the new 1516 mapping data in the Map-Cache entry for the remote site so the 1517 Locator-Status-Bits are reflective of the new mapping for packets 1518 going to the remote site. The ETR then stops sending SMR 1519 messages. 1521 For security reasons, an ITR MUST NOT process unsolicited Map- 1522 Replies. To avoid Map-Cache entry corruption by a third party, a 1523 sender of an SMR-based Map-Request MUST be verified. If an ITR 1524 receives an SMR-based Map-Request and the source is not in the 1525 Locator-Set for the stored Map-Cache entry, then the responding Map- 1526 Request MUST be sent with an EID destination to the mapping database 1527 system. Since the mapping database system is a more secure way to 1528 reach an authoritative ETR, it will deliver the Map-Request to the 1529 authoritative source of the mapping data. 1531 When an ITR receives an SMR-based Map-Request for which it does not 1532 have a cached mapping for the EID in the SMR message, it may not send 1533 an SMR-invoked Map-Request. This scenario can occur when an ETR 1534 sends SMR messages to all Locators in the Locator-Set it has stored 1535 in its map-cache but the remote ITRs that receive the SMR may not be 1536 sending packets to the site. There is no point in updating the ITRs 1537 until they need to send, in which case they will send Map-Requests to 1538 obtain a Map-Cache entry. 1540 13.3. Database Map-Versioning 1542 When there is unidirectional packet flow between an ITR and ETR, and 1543 the EID-to-RLOC mappings change on the ETR, it needs to inform the 1544 ITR so encapsulation to a removed Locator can stop and can instead be 1545 started to a new Locator in the Locator-Set. 1547 An ETR, when it sends Map-Reply messages, conveys its own Map-Version 1548 Number. This is known as the Destination Map-Version Number. ITRs 1549 include the Destination Map-Version Number in packets they 1550 encapsulate to the site. When an ETR decapsulates a packet and 1551 detects that the Destination Map-Version Number is less than the 1552 current version for its mapping, the SMR procedure described in 1553 Section 13.2 occurs. 1555 An ITR, when it encapsulates packets to ETRs, can convey its own Map- 1556 Version Number. This is known as the Source Map-Version Number. 1557 When an ETR decapsulates a packet and detects that the Source Map- 1558 Version Number is greater than the last Map-Version Number sent in a 1559 Map-Reply from the ITR's site, the ETR will send a Map-Request to one 1560 of the ETRs for the source site. 1562 A Map-Version Number is used as a sequence number per EID-Prefix, so 1563 values that are greater are considered to be more recent. A value of 1564 0 for the Source Map-Version Number or the Destination Map-Version 1565 Number conveys no versioning information, and an ITR does no 1566 comparison with previously received Map-Version Numbers. 1568 A Map-Version Number can be included in Map-Register messages as 1569 well. This is a good way for the Map-Server to assure that all ETRs 1570 for a site registering to it will be synchronized according to Map- 1571 Version Number. 1573 See [RFC6834] for a more detailed analysis and description of 1574 Database Map-Versioning. 1576 14. Multicast Considerations 1578 A multicast group address, as defined in the original Internet 1579 architecture, is an identifier of a grouping of topologically 1580 independent receiver host locations. The address encoding itself 1581 does not determine the location of the receiver(s). The multicast 1582 routing protocol, and the network-based state the protocol creates, 1583 determine where the receivers are located. 1585 In the context of LISP, a multicast group address is both an EID and 1586 a Routing Locator. Therefore, no specific semantic or action needs 1587 to be taken for a destination address, as it would appear in an IP 1588 header. Therefore, a group address that appears in an inner IP 1589 header built by a source host will be used as the destination EID. 1590 The outer IP header (the destination Routing Locator address), 1591 prepended by a LISP router, can use the same group address as the 1592 destination Routing Locator, use a multicast or unicast Routing 1593 Locator obtained from a Mapping System lookup, or use other means to 1594 determine the group address mapping. 1596 With respect to the source Routing Locator address, the ITR prepends 1597 its own IP address as the source address of the outer IP header. 1598 Just like it would if the destination EID was a unicast address. 1599 This source Routing Locator address, like any other Routing Locator 1600 address, MUST be globally routable. 1602 There are two approaches for LISP-Multicast, one that uses native 1603 multicast routing in the underlay with no support from the Mapping 1604 System and the other that uses only unicast routing in the underlay 1605 with support from the Mapping System. See [RFC6831] and 1606 [I-D.ietf-lisp-signal-free-multicast], respectively, for details. 1607 Details for LISP-Multicast and interworking with non-LISP sites are 1608 described in [RFC6831] and [RFC6832]. 1610 15. Router Performance Considerations 1612 LISP is designed to be very "hardware-based forwarding friendly". A 1613 few implementation techniques can be used to incrementally implement 1614 LISP: 1616 o When a tunnel-encapsulated packet is received by an ETR, the outer 1617 destination address may not be the address of the router. This 1618 makes it challenging for the control plane to get packets from the 1619 hardware. This may be mitigated by creating special Forwarding 1620 Information Base (FIB) entries for the EID-Prefixes of EIDs served 1621 by the ETR (those for which the router provides an RLOC 1622 translation). These FIB entries are marked with a flag indicating 1623 that control-plane processing SHOULD be performed. The forwarding 1624 logic of testing for particular IP protocol number values is not 1625 necessary. There are a few proven cases where no changes to 1626 existing deployed hardware were needed to support the LISP data- 1627 plane. 1629 o On an ITR, prepending a new IP header consists of adding more 1630 octets to a MAC rewrite string and prepending the string as part 1631 of the outgoing encapsulation procedure. Routers that support 1632 Generic Routing Encapsulation (GRE) tunneling [RFC2784] or 6to4 1633 tunneling [RFC3056] may already support this action. 1635 o A packet's source address or interface the packet was received on 1636 can be used to select VRF (Virtual Routing/Forwarding). The VRF's 1637 routing table can be used to find EID-to-RLOC mappings. 1639 For performance issues related to map-cache management, see 1640 Section 19. 1642 16. Mobility Considerations 1644 There are several kinds of mobility, of which only some might be of 1645 concern to LISP. Essentially, they are as follows. 1647 16.1. Slow Mobility 1649 A site wishes to change its attachment points to the Internet, and 1650 its LISP Tunnel Routers will have new RLOCs when it changes upstream 1651 providers. Changes in EID-to-RLOC mappings for sites are expected to 1652 be handled by configuration, outside of LISP. 1654 An individual endpoint wishes to move but is not concerned about 1655 maintaining session continuity. Renumbering is involved. LISP can 1656 help with the issues surrounding renumbering [RFC4192] [LISA96] by 1657 decoupling the address space used by a site from the address spaces 1658 used by its ISPs [RFC4984]. 1660 16.2. Fast Mobility 1662 Fast endpoint mobility occurs when an endpoint moves relatively 1663 rapidly, changing its IP-layer network attachment point. Maintenance 1664 of session continuity is a goal. This is where the Mobile IPv4 1665 [RFC5944] and Mobile IPv6 [RFC6275] [RFC4866] mechanisms are used and 1666 primarily where interactions with LISP need to be explored, such as 1667 the mechanisms in [I-D.ietf-lisp-eid-mobility] when the EID moves but 1668 the RLOC is in the network infrastructure. 1670 In LISP, one possibility is to "glean" information. When a packet 1671 arrives, the ETR could examine the EID-to-RLOC mapping and use that 1672 mapping for all outgoing traffic to that EID. It can do this after 1673 performing a route-returnability check, to ensure that the new 1674 network location does have an internal route to that endpoint. 1675 However, this does not cover the case where an ITR (the node assigned 1676 the RLOC) at the mobile-node location has been compromised. 1678 Mobile IP packet exchange is designed for an environment in which all 1679 routing information is disseminated before packets can be forwarded. 1680 In order to allow the Internet to grow to support expected future 1681 use, we are moving to an environment where some information may have 1682 to be obtained after packets are in flight. Modifications to IP 1683 mobility should be considered in order to optimize the behavior of 1684 the overall system. Anything that decreases the number of new EID- 1685 to-RLOC mappings needed when a node moves, or maintains the validity 1686 of an EID-to-RLOC mapping for a longer time, is useful. 1688 In addition to endpoints, a network can be mobile, possibly changing 1689 xTRs. A "network" can be as small as a single router and as large as 1690 a whole site. This is different from site mobility in that it is 1691 fast and possibly short-lived, but different from endpoint mobility 1692 in that a whole prefix is changing RLOCs. However, the mechanisms 1693 are the same, and there is no new overhead in LISP. A map request 1694 for any endpoint will return a binding for the entire mobile prefix. 1696 If mobile networks become a more common occurrence, it may be useful 1697 to revisit the design of the mapping service and allow for dynamic 1698 updates of the database. 1700 The issue of interactions between mobility and LISP needs to be 1701 explored further. Specific improvements to the entire system will 1702 depend on the details of mapping mechanisms. Mapping mechanisms 1703 should be evaluated on how well they support session continuity for 1704 mobile nodes. See [I-D.ietf-lisp-predictive-rlocs] for more recent 1705 mechanisms which can provide near-zero packet loss during handoffs. 1707 16.3. LISP Mobile Node Mobility 1709 A mobile device can use the LISP infrastructure to achieve mobility 1710 by implementing the LISP encapsulation and decapsulation functions 1711 and acting as a simple ITR/ETR. By doing this, such a "LISP mobile 1712 node" can use topologically independent EID IP addresses that are not 1713 advertised into and do not impose a cost on the global routing 1714 system. These EIDs are maintained at the edges of the mapping system 1715 in LISP Map-Servers and Map-Resolvers) and are provided on demand to 1716 only the correspondents of the LISP mobile node. 1718 Refer to [I-D.ietf-lisp-mn] for more details for when the EID and 1719 RLOC are co-located in the roaming node. 1721 17. LISP xTR Placement and Encapsulation Methods 1723 This section will explore how and where ITRs and ETRs can be placed 1724 in the network and will discuss the pros and cons of each scenario. 1725 For a more detailed network design deployment recommendation, refer 1726 to [RFC7215]. 1728 There are two basic deployment tradeoffs to consider: centralized 1729 versus distributed caches; and flat, Recursive, or Re-encapsulating 1730 Tunneling. When deciding on centralized versus distributed caching, 1731 the following issues SHOULD be considered: 1733 o Are the xTRs spread out so that the caches are spread across all 1734 the memories of each router? A centralized cache is when an ITR 1735 keeps a cache for all the EIDs it is encapsulating to. The packet 1736 takes a direct path to the destination Locator. A distributed 1737 cache is when an ITR needs help from other Re-Encapsulating Tunnel 1738 Routers (RTRs) because it does not store all the cache entries for 1739 the EIDs it is encapsulating to. So, the packet takes a path 1740 through RTRs that have a different set of cache entries. 1742 o Should management "touch points" be minimized by only choosing a 1743 few xTRs, just enough for redundancy? 1745 o In general, using more ITRs doesn't increase management load, 1746 since caches are built and stored dynamically. On the other hand, 1747 using more ETRs does require more management, since EID-Prefix-to- 1748 RLOC mappings need to be explicitly configured. 1750 When deciding on flat, Recursive, or Re-Encapsulating Tunneling, the 1751 following issues SHOULD be considered: 1753 o Flat tunneling implements a single encapsulation path between the 1754 source site and destination site. This generally offers better 1755 paths between sources and destinations with a single encapsulation 1756 path. 1758 o Recursive Tunneling is when encapsulated traffic is again further 1759 encapsulated in another tunnel, either to implement VPNs or to 1760 perform Traffic Engineering. When doing VPN-based tunneling, the 1761 site has some control, since the site is prepending a new 1762 encapsulation header. In the case of TE-based tunneling, the site 1763 MAY have control if it is prepending a new tunnel header, but if 1764 the site's ISP is doing the TE, then the site has no control. 1765 Recursive Tunneling generally will result in suboptimal paths but 1766 with the benefit of steering traffic to parts of the network that 1767 have more resources available. 1769 o The technique of Re-Encapsulation ensures that packets only 1770 require one encapsulation header. So, if a packet needs to be re- 1771 routed, it is first decapsulated by the RTR and then Re- 1772 Encapsulated with a new encapsulation header using a new RLOC. 1774 The next sub-sections will examine where xTRs and RTRs can reside in 1775 the network. 1777 17.1. First-Hop/Last-Hop xTRs 1779 By locating xTRs close to hosts, the EID-Prefix set is at the 1780 granularity of an IP subnet. So, at the expense of more EID-Prefix- 1781 to-RLOC sets for the site, the caches in each xTR can remain 1782 relatively small. But caches always depend on the number of non- 1783 aggregated EID destination flows active through these xTRs. 1785 With more xTRs doing encapsulation, the increase in control traffic 1786 grows as well: since the EID granularity is greater, more Map- 1787 Requests and Map-Replies are traveling between more routers. 1789 The advantage of placing the caches and databases at these stub 1790 routers is that the products deployed in this part of the network 1791 have better price-memory ratios than their core router counterparts. 1792 Memory is typically less expensive in these devices, and fewer routes 1793 are stored (only IGP routes). These devices tend to have excess 1794 capacity, both for forwarding and routing states. 1796 LISP functionality can also be deployed in edge switches. These 1797 devices generally have layer-2 ports facing hosts and layer-3 ports 1798 facing the Internet. Spare capacity is also often available in these 1799 devices. 1801 17.2. Border/Edge xTRs 1803 Using Customer Edge (CE) routers for xTR placement allows the EID 1804 space associated with a site to be reachable via a small set of RLOCs 1805 assigned to the CE-based xTRs for that site. 1807 This offers the opposite benefit of the first-hop/last-hop xTR 1808 scenario: the number of mapping entries and network management touch 1809 points is reduced, allowing better scaling. 1811 One disadvantage is that fewer network resources are used to reach 1812 host endpoints, thereby centralizing the point-of-failure domain and 1813 creating network choke points at the CE xTR. 1815 Note that more than one CE xTR at a site can be configured with the 1816 same IP address. In this case, an RLOC is an anycast address. This 1817 allows resilience between the CE xTRs. That is, if a CE xTR fails, 1818 traffic is automatically routed to the other xTRs using the same 1819 anycast address. However, this comes with the disadvantage where the 1820 site cannot control the entrance point when the anycast route is 1821 advertised out from all border routers. Another disadvantage of 1822 using anycast Locators is the limited advertisement scope of /32 (or 1823 /128 for IPv6) routes. 1825 17.3. ISP Provider Edge (PE) xTRs 1827 The use of ISP PE routers as xTRs is not the typical deployment 1828 scenario envisioned in this specification. This section attempts to 1829 capture some of the reasoning behind this preference for implementing 1830 LISP on CE routers. 1832 The use of ISP PE routers for xTR placement gives an ISP, rather than 1833 a site, control over the location of the ETRs. That is, the ISP can 1834 decide whether the xTRs are in the destination site (in either CE 1835 xTRs or last-hop xTRs within a site) or at other PE edges. The 1836 advantage of this case is that two encapsulation headers can be 1837 avoided. By having the PE be the first router on the path to 1838 encapsulate, it can choose a TE path first, and the ETR can 1839 decapsulate and Re-Encapsulate for a new encapsulation path to the 1840 destination end site. 1842 An obvious disadvantage is that the end site has no control over 1843 where its packets flow or over the RLOCs used. Other disadvantages 1844 include difficulty in synchronizing path liveness updates between CE 1845 and PE routers. 1847 As mentioned in earlier sections, a combination of these scenarios is 1848 possible at the expense of extra packet header overhead; if both site 1849 and provider want control, then Recursive or Re-Encapsulating Tunnels 1850 are used. 1852 17.4. LISP Functionality with Conventional NATs 1854 LISP routers can be deployed behind Network Address Translator (NAT) 1855 devices to provide the same set of packet services hosts have today 1856 when they are addressed out of private address space. 1858 It is important to note that a locator address in any LISP control 1859 message MUST be a routable address and therefore [RFC1918] addresses 1860 SHOULD only be presence when running in a local environment. When a 1861 LISP xTR is configured with private RLOC addresses and resides behind 1862 a NAT device and desires to communicate on the Internet, the private 1863 addresses MUST be used only in the outer IP header so the NAT device 1864 can translate properly. Otherwise, EID addresses MUST be translated 1865 before encapsulation is performed when LISP VPNs are not in use. 1866 Both NAT translation and LISP encapsulation functions could be co- 1867 located in the same device. 1869 17.5. Packets Egressing a LISP Site 1871 When a LISP site is using two ITRs for redundancy, the failure of one 1872 ITR will likely shift outbound traffic to the second. This second 1873 ITR's cache MAY not be populated with the same EID-to-RLOC mapping 1874 entries as the first. If this second ITR does not have these 1875 mappings, traffic will be dropped while the mappings are retrieved 1876 from the mapping system. The retrieval of these messages may 1877 increase the load of requests being sent into the mapping system. 1879 18. Traceroute Considerations 1881 When a source host in a LISP site initiates a traceroute to a 1882 destination host in another LISP site, it is highly desirable for it 1883 to see the entire path. Since packets are encapsulated from the ITR 1884 to the ETR, the hop across the tunnel could be viewed as a single 1885 hop. However, LISP traceroute will provide the entire path so the 1886 user can see 3 distinct segments of the path from a source LISP host 1887 to a destination LISP host: 1889 Segment 1 (in source LISP site based on EIDs): 1891 source host ---> first hop ... next hop ---> ITR 1893 Segment 2 (in the core network based on RLOCs): 1895 ITR ---> next hop ... next hop ---> ETR 1897 Segment 3 (in the destination LISP site based on EIDs): 1899 ETR ---> next hop ... last hop ---> destination host 1901 For segment 1 of the path, ICMP Time Exceeded messages are returned 1902 in the normal manner as they are today. The ITR performs a TTL 1903 decrement and tests for 0 before encapsulating. Therefore, the ITR's 1904 hop is seen by the traceroute source as having an EID address (the 1905 address of the site-facing interface). 1907 For segment 2 of the path, ICMP Time Exceeded messages are returned 1908 to the ITR because the TTL decrement to 0 is done on the outer 1909 header, so the destinations of the ICMP messages are the ITR RLOC 1910 address and the source RLOC address of the encapsulated traceroute 1911 packet. The ITR looks inside of the ICMP payload to inspect the 1912 traceroute source so it can return the ICMP message to the address of 1913 the traceroute client and also retain the core router IP address in 1914 the ICMP message. This is so the traceroute client can display the 1915 core router address (the RLOC address) in the traceroute output. The 1916 ETR returns its RLOC address and responds to the TTL decrement to 0, 1917 as the previous core routers did. 1919 For segment 3, the next-hop router downstream from the ETR will be 1920 decrementing the TTL for the packet that was encapsulated, sent into 1921 the core, decapsulated by the ETR, and forwarded because it isn't the 1922 final destination. If the TTL is decremented to 0, any router on the 1923 path to the destination of the traceroute, including the next-hop 1924 router or destination, will send an ICMP Time Exceeded message to the 1925 source EID of the traceroute client. The ICMP message will be 1926 encapsulated by the local ITR and sent back to the ETR in the 1927 originated traceroute source site, where the packet will be delivered 1928 to the host. 1930 18.1. IPv6 Traceroute 1932 IPv6 traceroute follows the procedure described above, since the 1933 entire traceroute data packet is included in the ICMP Time Exceeded 1934 message payload. Therefore, only the ITR needs to pay special 1935 attention to forwarding ICMP messages back to the traceroute source. 1937 18.2. IPv4 Traceroute 1939 For IPv4 traceroute, we cannot follow the above procedure, since IPv4 1940 ICMP Time Exceeded messages only include the invoking IP header and 1941 8 octets that follow the IP header. Therefore, when a core router 1942 sends an IPv4 Time Exceeded message to an ITR, all the ITR has in the 1943 ICMP payload is the encapsulated header it prepended, followed by a 1944 UDP header. The original invoking IP header, and therefore the 1945 identity of the traceroute source, is lost. 1947 The solution we propose to solve this problem is to cache traceroute 1948 IPv4 headers in the ITR and to match them up with corresponding IPv4 1949 Time Exceeded messages received from core routers and the ETR. The 1950 ITR will use a circular buffer for caching the IPv4 and UDP headers 1951 of traceroute packets. It will select a 16-bit number as a key to 1952 find them later when the IPv4 Time Exceeded messages are received. 1953 When an ITR encapsulates an IPv4 traceroute packet, it will use the 1954 16-bit number as the UDP source port in the encapsulating header. 1956 When the ICMP Time Exceeded message is returned to the ITR, the UDP 1957 header of the encapsulating header is present in the ICMP payload, 1958 thereby allowing the ITR to find the cached headers for the 1959 traceroute source. The ITR puts the cached headers in the payload 1960 and sends the ICMP Time Exceeded message to the traceroute source 1961 retaining the source address of the original ICMP Time Exceeded 1962 message (a core router or the ETR of the site of the traceroute 1963 destination). 1965 The signature of a traceroute packet comes in two forms. The first 1966 form is encoded as a UDP message where the destination port is 1967 inspected for a range of values. The second form is encoded as an 1968 ICMP message where the IP identification field is inspected for a 1969 well-known value. 1971 18.3. Traceroute Using Mixed Locators 1973 When either an IPv4 traceroute or IPv6 traceroute is originated and 1974 the ITR encapsulates it in the other address family header, one 1975 cannot get all 3 segments of the traceroute. Segment 2 of the 1976 traceroute cannot be conveyed to the traceroute source, since it is 1977 expecting addresses from intermediate hops in the same address format 1978 for the type of traceroute it originated. Therefore, in this case, 1979 segment 2 will make the tunnel look like one hop. All the ITR has to 1980 do to make this work is to not copy the inner TTL to the outer, 1981 encapsulating header's TTL when a traceroute packet is encapsulated 1982 using an RLOC from a different address family. This will cause no 1983 TTL decrement to 0 to occur in core routers between the ITR and ETR. 1985 19. Security Considerations 1987 Security considerations for LISP are discussed in [RFC7833]. 1989 A complete LISP threat analysis can be found in [RFC7835], in what 1990 follows we provide a summary. 1992 The optional mechanisms of gleaning is offered to directly obtain a 1993 mapping from the LISP encapsulated packets. Specifically, an xTR can 1994 learn the EID-to-RLOC mapping by inspecting the source RLOC and 1995 source EID of an encapsulated packet, and insert this new mapping 1996 into its map-cache. An off-path attacker can spoof the source EID 1997 address to divert the traffic sent to the victim's spoofed EID. If 1998 the attacker spoofs the source RLOC, it can mount a DoS attack by 1999 redirecting traffic to the spoofed victim's RLOC, potentially 2000 overloading it. 2002 The LISP Data-Plane defines several mechanisms to monitor RLOC data- 2003 plane reachability, in this context Locator-Status Bits, Nonce- 2004 Present and Echo-Nonce bits of the LISP encapsulation header can be 2005 manipulated by an attacker to mount a DoS attack. An off-path 2006 attacker able to spoof the RLOC of a victim's xTR can manipulate such 2007 mechanisms to declare a set of RLOCs unreachable. This can be used 2008 also, for instance, to declare only one RLOC reachable with the aim 2009 of overload it. 2011 Map-Versioning is a data-plane mechanism used to signal a peering xTR 2012 that a local EID-to-RLOC mapping has been updated, so that the 2013 peering xTR uses LISP Control-Plane signaling message to retrieve a 2014 fresh mapping. This can be used by an attacker to forge the map- 2015 versioning field of a LISP encapsulated header and force an excessive 2016 amount of signaling between xTRs that may overload them. 2018 Most of the attack vectors can be mitigated with careful deployment 2019 and configuration, information learned opportunistically (such as LSB 2020 or gleaning) SHOULD be verified with other reachability mechanisms. 2021 In addition, systematic rate-limitation and filtering is an effective 2022 technique to mitigate attacks that aim to overload the control-plane. 2024 20. Network Management Considerations 2026 Considerations for network management tools exist so the LISP 2027 protocol suite can be operationally managed. These mechanisms can be 2028 found in [RFC7052] and [RFC6835]. 2030 21. IANA Considerations 2032 This section provides guidance to the Internet Assigned Numbers 2033 Authority (IANA) regarding registration of values related to this 2034 data-plane LISP specification, in accordance with BCP 26 [RFC8126]. 2036 21.1. LISP UDP Port Numbers 2038 The IANA registry has allocated UDP port number 4341 for the LISP 2039 data-plane. IANA has updated the description for UDP port 4341 as 2040 follows: 2042 lisp-data 4341 udp LISP Data Packets 2044 22. References 2046 22.1. Normative References 2048 [I-D.ietf-lisp-rfc6833bis] 2049 Fuller, V., Farinacci, D., and A. Cabellos-Aparicio, 2050 "Locator/ID Separation Protocol (LISP) Control-Plane", 2051 draft-ietf-lisp-rfc6833bis-07 (work in progress), December 2052 2017. 2054 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 2055 DOI 10.17487/RFC0768, August 1980, 2056 . 2058 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 2059 DOI 10.17487/RFC0791, September 1981, 2060 . 2062 [RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G., 2063 and E. Lear, "Address Allocation for Private Internets", 2064 BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996, 2065 . 2067 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2068 Requirement Levels", BCP 14, RFC 2119, 2069 DOI 10.17487/RFC2119, March 1997, 2070 . 2072 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 2073 "Definition of the Differentiated Services Field (DS 2074 Field) in the IPv4 and IPv6 Headers", RFC 2474, 2075 DOI 10.17487/RFC2474, December 1998, 2076 . 2078 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 2079 of Explicit Congestion Notification (ECN) to IP", 2080 RFC 3168, DOI 10.17487/RFC3168, September 2001, 2081 . 2083 [RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker, 2084 "Randomness Requirements for Security", BCP 106, RFC 4086, 2085 DOI 10.17487/RFC4086, June 2005, 2086 . 2088 [RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing 2089 (CIDR): The Internet Address Assignment and Aggregation 2090 Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August 2091 2006, . 2093 [RFC5944] Perkins, C., Ed., "IP Mobility Support for IPv4, Revised", 2094 RFC 5944, DOI 10.17487/RFC5944, November 2010, 2095 . 2097 [RFC6275] Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility 2098 Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July 2099 2011, . 2101 [RFC7833] Howlett, J., Hartman, S., and A. Perez-Mendez, Ed., "A 2102 RADIUS Attribute, Binding, Profiles, Name Identifier 2103 Format, and Confirmation Methods for the Security 2104 Assertion Markup Language (SAML)", RFC 7833, 2105 DOI 10.17487/RFC7833, May 2016, 2106 . 2108 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 2109 Writing an IANA Considerations Section in RFCs", BCP 26, 2110 RFC 8126, DOI 10.17487/RFC8126, June 2017, 2111 . 2113 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2114 (IPv6) Specification", STD 86, RFC 8200, 2115 DOI 10.17487/RFC8200, July 2017, 2116 . 2118 22.2. Informative References 2120 [AFN] IANA, "Address Family Numbers", August 2016, 2121 . 2123 [CHIAPPA] Chiappa, J., "Endpoints and Endpoint names: A Proposed", 2124 1999, 2125 . 2127 [I-D.ietf-lisp-eid-mobility] 2128 Portoles-Comeras, M., Ashtaputre, V., Moreno, V., Maino, 2129 F., and D. Farinacci, "LISP L2/L3 EID Mobility Using a 2130 Unified Control Plane", draft-ietf-lisp-eid-mobility-01 2131 (work in progress), November 2017. 2133 [I-D.ietf-lisp-introduction] 2134 Cabellos-Aparicio, A. and D. Saucez, "An Architectural 2135 Introduction to the Locator/ID Separation Protocol 2136 (LISP)", draft-ietf-lisp-introduction-13 (work in 2137 progress), April 2015. 2139 [I-D.ietf-lisp-mn] 2140 Farinacci, D., Lewis, D., Meyer, D., and C. White, "LISP 2141 Mobile Node", draft-ietf-lisp-mn-01 (work in progress), 2142 October 2017. 2144 [I-D.ietf-lisp-predictive-rlocs] 2145 Farinacci, D. and P. Pillay-Esnault, "LISP Predictive 2146 RLOCs", draft-ietf-lisp-predictive-rlocs-01 (work in 2147 progress), November 2017. 2149 [I-D.ietf-lisp-sec] 2150 Maino, F., Ermagan, V., Cabellos-Aparicio, A., and D. 2151 Saucez, "LISP-Security (LISP-SEC)", draft-ietf-lisp-sec-14 2152 (work in progress), October 2017. 2154 [I-D.ietf-lisp-signal-free-multicast] 2155 Moreno, V. and D. Farinacci, "Signal-Free LISP Multicast", 2156 draft-ietf-lisp-signal-free-multicast-07 (work in 2157 progress), November 2017. 2159 [I-D.ietf-lisp-vpn] 2160 Moreno, V. and D. Farinacci, "LISP Virtual Private 2161 Networks (VPNs)", draft-ietf-lisp-vpn-01 (work in 2162 progress), November 2017. 2164 [I-D.ietf-opsec-icmp-filtering] 2165 Gont, F., Gont, G., and C. Pignataro, "Recommendations for 2166 filtering ICMP messages", draft-ietf-opsec-icmp- 2167 filtering-04 (work in progress), July 2013. 2169 [I-D.meyer-loc-id-implications] 2170 Meyer, D. and D. Lewis, "Architectural Implications of 2171 Locator/ID Separation", draft-meyer-loc-id-implications-01 2172 (work in progress), January 2009. 2174 [LISA96] Lear, E., Tharp, D., Katinsky, J., and J. Coffin, 2175 "Renumbering: Threat or Menace?", Usenix Tenth System 2176 Administration Conference (LISA 96), October 1996. 2178 [OPENLISP] 2179 Iannone, L., Saucez, D., and O. Bonaventure, "OpenLISP 2180 Implementation Report", Work in Progress, July 2008. 2182 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 2183 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 2184 . 2186 [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. 2187 Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, 2188 DOI 10.17487/RFC2784, March 2000, 2189 . 2191 [RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains 2192 via IPv4 Clouds", RFC 3056, DOI 10.17487/RFC3056, February 2193 2001, . 2195 [RFC3232] Reynolds, J., Ed., "Assigned Numbers: RFC 1700 is Replaced 2196 by an On-line Database", RFC 3232, DOI 10.17487/RFC3232, 2197 January 2002, . 2199 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 2200 A., Peterson, J., Sparks, R., Handley, M., and E. 2201 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 2202 DOI 10.17487/RFC3261, June 2002, 2203 . 2205 [RFC4192] Baker, F., Lear, E., and R. Droms, "Procedures for 2206 Renumbering an IPv6 Network without a Flag Day", RFC 4192, 2207 DOI 10.17487/RFC4192, September 2005, 2208 . 2210 [RFC4866] Arkko, J., Vogt, C., and W. Haddad, "Enhanced Route 2211 Optimization for Mobile IPv6", RFC 4866, 2212 DOI 10.17487/RFC4866, May 2007, 2213 . 2215 [RFC4984] Meyer, D., Ed., Zhang, L., Ed., and K. Fall, Ed., "Report 2216 from the IAB Workshop on Routing and Addressing", 2217 RFC 4984, DOI 10.17487/RFC4984, September 2007, 2218 . 2220 [RFC6831] Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas, "The 2221 Locator/ID Separation Protocol (LISP) for Multicast 2222 Environments", RFC 6831, DOI 10.17487/RFC6831, January 2223 2013, . 2225 [RFC6832] Lewis, D., Meyer, D., Farinacci, D., and V. Fuller, 2226 "Interworking between Locator/ID Separation Protocol 2227 (LISP) and Non-LISP Sites", RFC 6832, 2228 DOI 10.17487/RFC6832, January 2013, 2229 . 2231 [RFC6834] Iannone, L., Saucez, D., and O. Bonaventure, "Locator/ID 2232 Separation Protocol (LISP) Map-Versioning", RFC 6834, 2233 DOI 10.17487/RFC6834, January 2013, 2234 . 2236 [RFC6835] Farinacci, D. and D. Meyer, "The Locator/ID Separation 2237 Protocol Internet Groper (LIG)", RFC 6835, 2238 DOI 10.17487/RFC6835, January 2013, 2239 . 2241 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 2242 UDP Checksums for Tunneled Packets", RFC 6935, 2243 DOI 10.17487/RFC6935, April 2013, 2244 . 2246 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 2247 for the Use of IPv6 UDP Datagrams with Zero Checksums", 2248 RFC 6936, DOI 10.17487/RFC6936, April 2013, 2249 . 2251 [RFC7052] Schudel, G., Jain, A., and V. Moreno, "Locator/ID 2252 Separation Protocol (LISP) MIB", RFC 7052, 2253 DOI 10.17487/RFC7052, October 2013, 2254 . 2256 [RFC7215] Jakab, L., Cabellos-Aparicio, A., Coras, F., Domingo- 2257 Pascual, J., and D. Lewis, "Locator/Identifier Separation 2258 Protocol (LISP) Network Element Deployment 2259 Considerations", RFC 7215, DOI 10.17487/RFC7215, April 2260 2014, . 2262 [RFC7835] Saucez, D., Iannone, L., and O. Bonaventure, "Locator/ID 2263 Separation Protocol (LISP) Threat Analysis", RFC 7835, 2264 DOI 10.17487/RFC7835, April 2016, 2265 . 2267 [RFC8060] Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical 2268 Address Format (LCAF)", RFC 8060, DOI 10.17487/RFC8060, 2269 February 2017, . 2271 [RFC8061] Farinacci, D. and B. Weis, "Locator/ID Separation Protocol 2272 (LISP) Data-Plane Confidentiality", RFC 8061, 2273 DOI 10.17487/RFC8061, February 2017, 2274 . 2276 [RFC8111] Fuller, V., Lewis, D., Ermagan, V., Jain, A., and A. 2277 Smirnov, "Locator/ID Separation Protocol Delegated 2278 Database Tree (LISP-DDT)", RFC 8111, DOI 10.17487/RFC8111, 2279 May 2017, . 2281 Appendix A. Acknowledgments 2283 An initial thank you goes to Dave Oran for planting the seeds for the 2284 initial ideas for LISP. His consultation continues to provide value 2285 to the LISP authors. 2287 A special and appreciative thank you goes to Noel Chiappa for 2288 providing architectural impetus over the past decades on separation 2289 of location and identity, as well as detailed reviews of the LISP 2290 architecture and documents, coupled with enthusiasm for making LISP a 2291 practical and incremental transition for the Internet. 2293 The authors would like to gratefully acknowledge many people who have 2294 contributed discussions and ideas to the making of this proposal. 2295 They include Scott Brim, Andrew Partan, John Zwiebel, Jason Schiller, 2296 Lixia Zhang, Dorian Kim, Peter Schoenmaker, Vijay Gill, Geoff Huston, 2297 David Conrad, Mark Handley, Ron Bonica, Ted Seely, Mark Townsley, 2298 Chris Morrow, Brian Weis, Dave McGrew, Peter Lothberg, Dave Thaler, 2299 Eliot Lear, Shane Amante, Ved Kafle, Olivier Bonaventure, Luigi 2300 Iannone, Robin Whittle, Brian Carpenter, Joel Halpern, Terry 2301 Manderson, Roger Jorgensen, Ran Atkinson, Stig Venaas, Iljitsch van 2302 Beijnum, Roland Bless, Dana Blair, Bill Lynch, Marc Woolward, Damien 2303 Saucez, Damian Lezama, Attilla De Groot, Parantap Lahiri, David 2304 Black, Roque Gagliano, Isidor Kouvelas, Jesper Skriver, Fred Templin, 2305 Margaret Wasserman, Sam Hartman, Michael Hofling, Pedro Marques, Jari 2306 Arkko, Gregg Schudel, Srinivas Subramanian, Amit Jain, Xu Xiaohu, 2307 Dhirendra Trivedi, Yakov Rekhter, John Scudder, John Drake, Dimitri 2308 Papadimitriou, Ross Callon, Selina Heimlich, Job Snijders, Vina 2309 Ermagan, Fabio Maino, Victor Moreno, Chris White, Clarence Filsfils, 2310 Alia Atlas, Florin Coras and Alberto Rodriguez. 2312 This work originated in the Routing Research Group (RRG) of the IRTF. 2313 An individual submission was converted into the IETF LISP working 2314 group document that became this RFC. 2316 The LISP working group would like to give a special thanks to Jari 2317 Arkko, the Internet Area AD at the time that the set of LISP 2318 documents were being prepared for IESG last call, and for his 2319 meticulous reviews and detailed commentaries on the 7 working group 2320 last call documents progressing toward standards-track RFCs. 2322 Appendix B. Document Change Log 2324 [RFC Editor: Please delete this section on publication as RFC.] 2326 B.1. Changes to draft-ietf-lisp-rfc6830bis-09 2328 o Posted January 2018. 2330 o Add more details in section 5.3 about DSCP processing during 2331 encapsulation and decapsulation. 2333 o Added clarity to definitions in the Definition of Terms section 2334 from various commenters. 2336 o Removed PA and PI definitions from Definition of Terms section. 2338 o More editorial changes. 2340 o Removed 4342 from IANA section and move to RFC6833 IANA section. 2342 B.2. Changes to draft-ietf-lisp-rfc6830bis-08 2344 o Posted January 2018. 2346 o Remove references to research work for any protocol mechanisms. 2348 o Document scanned to make sure it is RFC 2119 compliant. 2350 o Made changes to reflect comments from document WG shepherd Luigi 2351 Iannone. 2353 o Ran IDNITs on the document. 2355 B.3. Changes to draft-ietf-lisp-rfc6830bis-07 2357 o Posted November 2017. 2359 o Rephrase how Instance-IDs are used and don't refer to [RFC1918] 2360 addresses. 2362 B.4. Changes to draft-ietf-lisp-rfc6830bis-06 2364 o Posted October 2017. 2366 o Put RTR definition before it is used. 2368 o Rename references that are now working group drafts. 2370 o Remove "EIDs MUST NOT be used as used by a host to refer to other 2371 hosts. Note that EID blocks MAY LISP RLOCs". 2373 o Indicate what address-family can appear in data packets. 2375 o ETRs may, rather than will, be the ones to send Map-Replies. 2377 o Recommend, rather than mandate, max encapsulation headers to 2. 2379 o Reference VPN draft when introducing Instance-ID. 2381 o Indicate that SMRs can be sent when ITR/ETR are in the same node. 2383 o Clarify when private addreses can be used. 2385 B.5. Changes to draft-ietf-lisp-rfc6830bis-05 2387 o Posted August 2017. 2389 o Make it clear that a Reencapsulating Tunnel Router is an RTR. 2391 B.6. Changes to draft-ietf-lisp-rfc6830bis-04 2393 o Posted July 2017. 2395 o Changed reference of IPv6 RFC2460 to RFC8200. 2397 o Indicate that the applicability statement for UDP zero checksums 2398 over IPv6 adheres to RFC6936. 2400 B.7. Changes to draft-ietf-lisp-rfc6830bis-03 2402 o Posted May 2017. 2404 o Move the control-plane related codepoints in the IANA 2405 Considerations section to RFC6833bis. 2407 B.8. Changes to draft-ietf-lisp-rfc6830bis-02 2409 o Posted April 2017. 2411 o Reflect some editorial comments from Damien Sausez. 2413 B.9. Changes to draft-ietf-lisp-rfc6830bis-01 2415 o Posted March 2017. 2417 o Include references to new RFCs published. 2419 o Change references from RFC6833 to RFC6833bis. 2421 o Clarified LCAF text in the IANA section. 2423 o Remove references to "experimental". 2425 B.10. Changes to draft-ietf-lisp-rfc6830bis-00 2427 o Posted December 2016. 2429 o Created working group document from draft-farinacci-lisp 2430 -rfc6830-00 individual submission. No other changes made. 2432 Authors' Addresses 2434 Dino Farinacci 2435 Cisco Systems 2436 Tasman Drive 2437 San Jose, CA 95134 2438 USA 2440 EMail: farinacci@gmail.com 2442 Vince Fuller 2443 Cisco Systems 2444 Tasman Drive 2445 San Jose, CA 95134 2446 USA 2448 EMail: vince.fuller@gmail.com 2450 Dave Meyer 2451 Cisco Systems 2452 170 Tasman Drive 2453 San Jose, CA 2454 USA 2456 EMail: dmm@1-4-5.net 2458 Darrel Lewis 2459 Cisco Systems 2460 170 Tasman Drive 2461 San Jose, CA 2462 USA 2464 EMail: darlewis@cisco.com 2465 Albert Cabellos 2466 UPC/BarcelonaTech 2467 Campus Nord, C. Jordi Girona 1-3 2468 Barcelona, Catalunya 2469 Spain 2471 EMail: acabello@ac.upc.edu