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'I-D.ietf-lisp-introduction') == Outdated reference: A later version (-31) exists of draft-ietf-lisp-rfc6833bis-06 == Outdated reference: A later version (-29) exists of draft-ietf-lisp-sec-14 ** Downref: Normative reference to an Informational RFC: RFC 3232 ** Obsolete normative reference: RFC 5226 (Obsoleted by RFC 8126) ** Downref: Normative reference to an Informational RFC: RFC 6115 ** Obsolete normative reference: RFC 6834 (Obsoleted by RFC 9302) ** Downref: Normative reference to an Experimental RFC: RFC 6836 ** Downref: Normative reference to an Experimental RFC: RFC 7052 ** Downref: Normative reference to an Experimental RFC: RFC 7215 ** Downref: Normative reference to an Informational RFC: RFC 7835 ** Downref: Normative reference to an Experimental RFC: RFC 8061 == Outdated reference: A later version (-13) exists of draft-ietf-lisp-eid-mobility-00 == Outdated reference: A later version (-15) exists of draft-ietf-lisp-mn-01 == Outdated reference: A later version (-14) exists of draft-ietf-lisp-predictive-rlocs-00 == Outdated reference: A later version (-09) exists of draft-ietf-lisp-signal-free-multicast-06 == Outdated reference: A later version (-12) exists of draft-ietf-lisp-vpn-00 Summary: 12 errors (**), 0 flaws (~~), 19 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group D. Farinacci 3 Internet-Draft V. Fuller 4 Intended status: Standards Track D. Meyer 5 Expires: May 15, 2018 D. Lewis 6 Cisco Systems 7 A. Cabellos (Ed.) 8 UPC/BarcelonaTech 9 November 11, 2017 11 The Locator/ID Separation Protocol (LISP) 12 draft-ietf-lisp-rfc6830bis-07 14 Abstract 16 This document describes the data-plane protocol for the Locator/ID 17 Separation Protocol (LISP). LISP defines two namespaces, End-point 18 Identifiers (EIDs) that identify end-hosts and Routing Locators 19 (RLOCs) that identify network attachment points. With this, LISP 20 effectively separates control from data, and allows routers to create 21 overlay networks. LISP-capable routers exchange encapsulated packets 22 according to EID-to-RLOC mappings stored in a local map-cache. The 23 map-cache is populated by the LISP Control-Plane protocol 24 [I-D.ietf-lisp-rfc6833bis]. 26 LISP requires no change to either host protocol stacks or to underlay 27 routers and offers Traffic Engineering, multihoming and mobility, 28 among other features. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at https://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on May 15, 2018. 47 Copyright Notice 49 Copyright (c) 2017 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (https://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 65 2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 4 66 3. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 4 67 4. Basic Overview . . . . . . . . . . . . . . . . . . . . . . . 9 68 4.1. Packet Flow Sequence . . . . . . . . . . . . . . . . . . 11 69 5. LISP Encapsulation Details . . . . . . . . . . . . . . . . . 13 70 5.1. LISP IPv4-in-IPv4 Header Format . . . . . . . . . . . . . 14 71 5.2. LISP IPv6-in-IPv6 Header Format . . . . . . . . . . . . . 15 72 5.3. Tunnel Header Field Descriptions . . . . . . . . . . . . 16 73 6. LISP EID-to-RLOC Map-Cache . . . . . . . . . . . . . . . . . 20 74 7. Dealing with Large Encapsulated Packets . . . . . . . . . . . 20 75 7.1. A Stateless Solution to MTU Handling . . . . . . . . . . 21 76 7.2. A Stateful Solution to MTU Handling . . . . . . . . . . . 22 77 8. Using Virtualization and Segmentation with LISP . . . . . . . 22 78 9. Routing Locator Selection . . . . . . . . . . . . . . . . . . 23 79 10. Routing Locator Reachability . . . . . . . . . . . . . . . . 24 80 10.1. Echo Nonce Algorithm . . . . . . . . . . . . . . . . . . 27 81 10.2. RLOC-Probing Algorithm . . . . . . . . . . . . . . . . . 28 82 11. EID Reachability within a LISP Site . . . . . . . . . . . . . 29 83 12. Routing Locator Hashing . . . . . . . . . . . . . . . . . . . 30 84 13. Changing the Contents of EID-to-RLOC Mappings . . . . . . . . 31 85 13.1. Clock Sweep . . . . . . . . . . . . . . . . . . . . . . 32 86 13.2. Solicit-Map-Request (SMR) . . . . . . . . . . . . . . . 32 87 13.3. Database Map-Versioning . . . . . . . . . . . . . . . . 34 88 14. Multicast Considerations . . . . . . . . . . . . . . . . . . 35 89 15. Router Performance Considerations . . . . . . . . . . . . . . 35 90 16. Mobility Considerations . . . . . . . . . . . . . . . . . . . 36 91 16.1. Slow Mobility . . . . . . . . . . . . . . . . . . . . . 36 92 16.2. Fast Mobility . . . . . . . . . . . . . . . . . . . . . 36 93 16.3. LISP Mobile Node Mobility . . . . . . . . . . . . . . . 37 94 17. LISP xTR Placement and Encapsulation Methods . . . . . . . . 38 95 17.1. First-Hop/Last-Hop xTRs . . . . . . . . . . . . . . . . 39 96 17.2. Border/Edge xTRs . . . . . . . . . . . . . . . . . . . . 39 97 17.3. ISP Provider Edge (PE) xTRs . . . . . . . . . . . . . . 40 98 17.4. LISP Functionality with Conventional NATs . . . . . . . 40 99 17.5. Packets Egressing a LISP Site . . . . . . . . . . . . . 41 100 18. Traceroute Considerations . . . . . . . . . . . . . . . . . . 41 101 18.1. IPv6 Traceroute . . . . . . . . . . . . . . . . . . . . 42 102 18.2. IPv4 Traceroute . . . . . . . . . . . . . . . . . . . . 42 103 18.3. Traceroute Using Mixed Locators . . . . . . . . . . . . 43 104 19. Security Considerations . . . . . . . . . . . . . . . . . . . 43 105 20. Network Management Considerations . . . . . . . . . . . . . . 44 106 21. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 44 107 21.1. LISP UDP Port Numbers . . . . . . . . . . . . . . . . . 44 108 22. References . . . . . . . . . . . . . . . . . . . . . . . . . 44 109 22.1. Normative References . . . . . . . . . . . . . . . . . . 44 110 22.2. Informative References . . . . . . . . . . . . . . . . . 47 111 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 51 112 Appendix B. Document Change Log . . . . . . . . . . . . . . . . 51 113 B.1. Changes to draft-ietf-lisp-rfc6830bis-06 . . . . . . . . 52 114 B.2. Changes to draft-ietf-lisp-rfc6830bis-06 . . . . . . . . 52 115 B.3. Changes to draft-ietf-lisp-rfc6830bis-05 . . . . . . . . 52 116 B.4. Changes to draft-ietf-lisp-rfc6830bis-04 . . . . . . . . 52 117 B.5. Changes to draft-ietf-lisp-rfc6830bis-03 . . . . . . . . 53 118 B.6. Changes to draft-ietf-lisp-rfc6830bis-02 . . . . . . . . 53 119 B.7. Changes to draft-ietf-lisp-rfc6830bis-01 . . . . . . . . 53 120 B.8. Changes to draft-ietf-lisp-rfc6830bis-00 . . . . . . . . 53 121 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 53 123 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. 137 LISP is an overlay protocol that separates control from data-plane, 138 this document specifies the data-plane, how LISP-capable routers 139 (Tunnel Routers) exchange packets by encapsulating them to the 140 appropriate location. Tunnel routers are equipped with a cache, 141 called map-cache, that contains EID-to-RLOC mappings. The map-cache 142 is populated using the LISP Control-Plane protocol 143 [I-D.ietf-lisp-rfc6833bis]. 145 LISP does not require changes to either host protocol stack or to 146 underlay routers. By separating the EID from the RLOC space, LISP 147 offers native Traffic Engineering, multihoming and mobility, among 148 other features. 150 Creation of LISP was initially motivated by discussions during the 151 IAB-sponsored Routing and Addressing Workshop held in Amsterdam in 152 October 2006 (see [RFC4984]) 154 This document specifies the LISP data-plane encapsulation and other 155 LISP forwarding node functionality while [I-D.ietf-lisp-rfc6833bis] 156 specifies the LISP control plane. LISP deployment guidelines can be 157 found in [RFC7215] and [RFC6835] describes considerations for network 158 operational management. Finally, [I-D.ietf-lisp-introduction] 159 describes the LISP architecture. 161 2. Requirements Notation 163 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 164 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 165 document are to be interpreted as described in [RFC2119]. 167 3. Definition of Terms 169 Provider-Independent (PI) Addresses: PI addresses are an address 170 block assigned from a pool where blocks are not associated with 171 any particular location in the network (e.g., from a particular 172 service provider) and are therefore not topologically aggregatable 173 in the routing system. 175 Provider-Assigned (PA) Addresses: PA addresses are an address block 176 assigned to a site by each service provider to which a site 177 connects. Typically, each block is a sub-block of a service 178 provider Classless Inter-Domain Routing (CIDR) [RFC4632] block and 179 is aggregated into the larger block before being advertised into 180 the global Internet. Traditionally, IP multihoming has been 181 implemented by each multihomed site acquiring its own globally 182 visible prefix. LISP uses only topologically assigned and 183 aggregatable address blocks for RLOCs, eliminating this 184 demonstrably non-scalable practice. 186 Routing Locator (RLOC): An RLOC is an IPv4 [RFC0791] or IPv6 187 [RFC8200] address of an Egress Tunnel Router (ETR). An RLOC is 188 the output of an EID-to-RLOC mapping lookup. An EID maps to one 189 or more RLOCs. Typically, RLOCs are numbered from topologically 190 aggregatable blocks that are assigned to a site at each point to 191 which it attaches to the global Internet; where the topology is 192 defined by the connectivity of provider networks, RLOCs can be 193 thought of as PA addresses. Multiple RLOCs can be assigned to the 194 same ETR device or to multiple ETR devices at a site. 196 Endpoint ID (EID): An EID is a 32-bit (for IPv4) or 128-bit (for 197 IPv6) value used in the source and destination address fields of 198 the first (most inner) LISP header of a packet. The host obtains 199 a destination EID the same way it obtains a destination address 200 today, for example, through a Domain Name System (DNS) [RFC1034] 201 lookup or Session Initiation Protocol (SIP) [RFC3261] exchange. 202 The source EID is obtained via existing mechanisms used to set a 203 host's "local" IP address. An EID used on the public Internet 204 must have the same properties as any other IP address used in that 205 manner; this means, among other things, that it must be globally 206 unique. An EID is allocated to a host from an EID-Prefix block 207 associated with the site where the host is located. An EID can be 208 used by a host to refer to other hosts. Note that EID blocks MAY 209 be assigned in a hierarchical manner, independent of the network 210 topology, to facilitate scaling of the mapping database. In 211 addition, an EID block assigned to a site may have site-local 212 structure (subnetting) for routing within the site; this structure 213 is not visible to the global routing system. In theory, the bit 214 string that represents an EID for one device can represent an RLOC 215 for a different device. As the architecture is realized, if a 216 given bit string is both an RLOC and an EID, it must refer to the 217 same entity in both cases. When used in discussions with other 218 Locator/ID separation proposals, a LISP EID will be called an 219 "LEID". Throughout this document, any references to "EID" refer 220 to an LEID. 222 EID-Prefix: An EID-Prefix is a power-of-two block of EIDs that are 223 allocated to a site by an address allocation authority. EID- 224 Prefixes are associated with a set of RLOC addresses that make up 225 a "database mapping". EID-Prefix allocations can be broken up 226 into smaller blocks when an RLOC set is to be associated with the 227 larger EID-Prefix block. A globally routed address block (whether 228 PI or PA) is not inherently an EID-Prefix. A globally routed 229 address block MAY be used by its assignee as an EID block. The 230 converse is not supported. That is, a site that receives an 231 explicitly allocated EID-Prefix may not use that EID-Prefix as a 232 globally routed prefix. This would require coordination and 233 cooperation with the entities managing the mapping infrastructure. 234 Once this has been done, that block could be removed from the 235 globally routed IP system, if other suitable transition and access 236 mechanisms are in place. Discussion of such transition and access 237 mechanisms can be found in [RFC6832] and [RFC7215]. 239 End-system: An end-system is an IPv4 or IPv6 device that originates 240 packets with a single IPv4 or IPv6 header. The end-system 241 supplies an EID value for the destination address field of the IP 242 header when communicating globally (i.e., outside of its routing 243 domain). An end-system can be a host computer, a switch or router 244 device, or any network appliance. 246 Ingress Tunnel Router (ITR): An ITR is a router that resides in a 247 LISP site. Packets sent by sources inside of the LISP site to 248 destinations outside of the site are candidates for encapsulation 249 by the ITR. The ITR treats the IP destination address as an EID 250 and performs an EID-to-RLOC mapping lookup. The router then 251 prepends an "outer" IP header with one of its routable RLOCs (in 252 the RLOC space) in the source address field and the result of the 253 mapping lookup in the destination address field. Note that this 254 destination RLOC MAY be an intermediate, proxy device that has 255 better knowledge of the EID-to-RLOC mapping closer to the 256 destination EID. In general, an ITR receives IP packets from site 257 end-systems on one side and sends LISP-encapsulated IP packets 258 toward the Internet on the other side. 260 Specifically, when a service provider prepends a LISP header for 261 Traffic Engineering purposes, the router that does this is also 262 regarded as an ITR. The outer RLOC the ISP ITR uses can be based 263 on the outer destination address (the originating ITR's supplied 264 RLOC) or the inner destination address (the originating host's 265 supplied EID). 267 TE-ITR: A TE-ITR is an ITR that is deployed in a service provider 268 network that prepends an additional LISP header for Traffic 269 Engineering purposes. 271 Egress Tunnel Router (ETR): An ETR is a router that accepts an IP 272 packet where the destination address in the "outer" IP header is 273 one of its own RLOCs. The router strips the "outer" header and 274 forwards the packet based on the next IP header found. In 275 general, an ETR receives LISP-encapsulated IP packets from the 276 Internet on one side and sends decapsulated IP packets to site 277 end-systems on the other side. ETR functionality does not have to 278 be limited to a router device. A server host can be the endpoint 279 of a LISP tunnel as well. 281 TE-ETR: A TE-ETR is an ETR that is deployed in a service provider 282 network that strips an outer LISP header for Traffic Engineering 283 purposes. 285 xTR: An xTR is a reference to an ITR or ETR when direction of data 286 flow is not part of the context description. "xTR" refers to the 287 router that is the tunnel endpoint and is used synonymously with 288 the term "Tunnel Router". For example, "An xTR can be located at 289 the Customer Edge (CE) router" indicates both ITR and ETR 290 functionality at the CE router. 292 Re-encapsulating Tunneling in RTRs: Re-encapsulating Tunneling 293 occurs when an RTR (Re-encapsulating Tunnel Router) acts like an 294 ETR to remove a LISP header, then acts as an ITR to prepend a new 295 LISP header. Doing this allows a packet to be re-routed by the 296 RTR without adding the overhead of additional tunnel headers. Any 297 references to tunnels in this specification refer to dynamic 298 encapsulating tunnels; they are never statically configured. When 299 using multiple mapping database systems, care must be taken to not 300 create re-encapsulation loops through misconfiguration. 302 LISP Router: A LISP router is a router that performs the functions 303 of any or all of the following: ITR, ETR, RTR, Proxy-ITR (PITR), 304 or Proxy-ETR (PETR). 306 EID-to-RLOC Map-Cache: The EID-to-RLOC map-cache is generally 307 short-lived, on-demand table in an ITR that stores, tracks, and is 308 responsible for timing out and otherwise validating EID-to-RLOC 309 mappings. This cache is distinct from the full "database" of EID- 310 to-RLOC mappings; it is dynamic, local to the ITR(s), and 311 relatively small, while the database is distributed, relatively 312 static, and much more global in scope. 314 EID-to-RLOC Database: The EID-to-RLOC Database is a global 315 distributed database that contains all known EID-Prefix-to-RLOC 316 mappings. Each potential ETR typically contains a small piece of 317 the database: the EID-to-RLOC mappings for the EID-Prefixes 318 "behind" the router. These map to one of the router's own 319 globally visible IP addresses. Note that there MAY be transient 320 conditions when the EID-Prefix for the site and Locator-Set for 321 each EID-Prefix may not be the same on all ETRs. This has no 322 negative implications, since a partial set of Locators can be 323 used. 325 Recursive Tunneling: Recursive Tunneling occurs when a packet has 326 more than one LISP IP header. Additional layers of tunneling MAY 327 be employed to implement Traffic Engineering or other re-routing 328 as needed. When this is done, an additional "outer" LISP header 329 is added, and the original RLOCs are preserved in the "inner" 330 header. Any references to tunnels in this specification refer to 331 dynamic encapsulating tunnels; they are never statically 332 configured. 334 LISP Header: LISP header is a term used in this document to refer 335 to the outer IPv4 or IPv6 header, a UDP header, and a LISP- 336 specific 8-octet header that follow the UDP header and that an ITR 337 prepends or an ETR strips. 339 Address Family Identifier (AFI): AFI is a term used to describe an 340 address encoding in a packet. An address family that pertains to 341 the data-plane. See [AFN] and [RFC3232] for details. An AFI 342 value of 0 used in this specification indicates an unspecified 343 encoded address where the length of the address is 0 octets 344 following the 16-bit AFI value of 0. 346 Negative Mapping Entry: A negative mapping entry, also known as a 347 negative cache entry, is an EID-to-RLOC entry where an EID-Prefix 348 is advertised or stored with no RLOCs. That is, the Locator-Set 349 for the EID-to-RLOC entry is empty or has an encoded Locator count 350 of 0. This type of entry could be used to describe a prefix from 351 a non-LISP site, which is explicitly not in the mapping database. 352 There are a set of well-defined actions that are encoded in a 353 Negative Map-Reply. 355 Data-Probe: A Data-Probe is a LISP-encapsulated data packet where 356 the inner-header destination address equals the outer-header 357 destination address used to trigger a Map-Reply by a decapsulating 358 ETR. In addition, the original packet is decapsulated and 359 delivered to the destination host if the destination EID is in the 360 EID-Prefix range configured on the ETR. Otherwise, the packet is 361 discarded. A Data-Probe is used in some of the mapping database 362 designs to "probe" or request a Map-Reply from an ETR; in other 363 cases, Map-Requests are used. See each mapping database design 364 for details. When using Data-Probes, by sending Map-Requests on 365 the underlying routing system, EID-Prefixes must be advertised. 366 However, this is discouraged if the core is to scale by having 367 less EID-Prefixes stored in the core router's routing tables. 369 Proxy-ITR (PITR): A PITR is defined and described in [RFC6832]. A 370 PITR acts like an ITR but does so on behalf of non-LISP sites that 371 send packets to destinations at LISP sites. 373 Proxy-ETR (PETR): A PETR is defined and described in [RFC6832]. A 374 PETR acts like an ETR but does so on behalf of LISP sites that 375 send packets to destinations at non-LISP sites. 377 Route-returnability: Route-returnability is an assumption that the 378 underlying routing system will deliver packets to the destination. 379 When combined with a nonce that is provided by a sender and 380 returned by a receiver, this limits off-path data insertion. A 381 route-returnability check is verified when a message is sent with 382 a nonce, another message is returned with the same nonce, and the 383 destination of the original message appears as the source of the 384 returned message. 386 LISP site: LISP site is a set of routers in an edge network that are 387 under a single technical administration. LISP routers that reside 388 in the edge network are the demarcation points to separate the 389 edge network from the core network. 391 Client-side: Client-side is a term used in this document to indicate 392 a connection initiation attempt by an EID. The ITR(s) at the LISP 393 site are the first to get involved in obtaining database Map-Cache 394 entries by sending Map-Request messages. 396 Server-side: Server-side is a term used in this document to indicate 397 that a connection initiation attempt is being accepted for a 398 destination EID. The ETR(s) at the destination LISP site may be 399 the first to send Map-Replies to the source site initiating the 400 connection. The ETR(s) at this destination site can obtain 401 mappings by gleaning information from Map-Requests, Data-Probes, 402 or encapsulated packets. 404 Locator-Status-Bits (LSBs): Locator-Status-Bits are present in the 405 LISP header. They are used by ITRs to inform ETRs about the up/ 406 down status of all ETRs at the local site. These bits are used as 407 a hint to convey up/down router status and not path reachability 408 status. The LSBs can be verified by use of one of the Locator 409 reachability algorithms described in Section 10. 411 Anycast Address: Anycast Address is a term used in this document to 412 refer to the same IPv4 or IPv6 address configured and used on 413 multiple systems at the same time. An EID or RLOC can be an 414 anycast address in each of their own address spaces. 416 4. Basic Overview 418 One key concept of LISP is that end-systems operate the same way they 419 do today. The IP addresses that hosts use for tracking sockets and 420 connections, and for sending and receiving packets, do not change. 421 In LISP terminology, these IP addresses are called Endpoint 422 Identifiers (EIDs). 424 Routers continue to forward packets based on IP destination 425 addresses. When a packet is LISP encapsulated, these addresses are 426 referred to as Routing Locators (RLOCs). Most routers along a path 427 between two hosts will not change; they continue to perform routing/ 428 forwarding lookups on the destination addresses. For routers between 429 the source host and the ITR as well as routers from the ETR to the 430 destination host, the destination address is an EID. For the routers 431 between the ITR and the ETR, the destination address is an RLOC. 433 Another key LISP concept is the "Tunnel Router". A Tunnel Router 434 prepends LISP headers on host-originated packets and strips them 435 prior to final delivery to their destination. The IP addresses in 436 this "outer header" are RLOCs. During end-to-end packet exchange 437 between two Internet hosts, an ITR prepends a new LISP header to each 438 packet, and an ETR strips the new header. The ITR performs EID-to- 439 RLOC lookups to determine the routing path to the ETR, which has the 440 RLOC as one of its IP addresses. 442 Some basic rules governing LISP are: 444 o End-systems only send to addresses that are EIDs. They don't know 445 that addresses are EIDs versus RLOCs but assume that packets get 446 to their intended destinations. In a system where LISP is 447 deployed, LISP routers intercept EID-addressed packets and assist 448 in delivering them across the network core where EIDs cannot be 449 routed. The procedure a host uses to send IP packets does not 450 change. 452 o EIDs are typically IP addresses assigned to hosts. 454 o Other types of EID are supported by LISP, see [RFC8060] for 455 further information. 457 o LISP routers mostly deal with Routing Locator addresses. See 458 details in Section 4.1 to clarify what is meant by "mostly". 460 o RLOCs are always IP addresses assigned to routers, preferably 461 topologically oriented addresses from provider CIDR (Classless 462 Inter-Domain Routing) blocks. 464 o When a router originates packets, it may use as a source address 465 either an EID or RLOC. When acting as a host (e.g., when 466 terminating a transport session such as Secure SHell (SSH), 467 TELNET, or the Simple Network Management Protocol (SNMP)), it may 468 use an EID that is explicitly assigned for that purpose. An EID 469 that identifies the router as a host MUST NOT be used as an RLOC; 470 an EID is only routable within the scope of a site. A typical BGP 471 configuration might demonstrate this "hybrid" EID/RLOC usage where 472 a router could use its "host-like" EID to terminate iBGP sessions 473 to other routers in a site while at the same time using RLOCs to 474 terminate eBGP sessions to routers outside the site. 476 o Packets with EIDs in them are not expected to be delivered end-to- 477 end in the absence of an EID-to-RLOC mapping operation. They are 478 expected to be used locally for intra-site communication or to be 479 encapsulated for inter-site communication. 481 o EID-Prefixes are likely to be hierarchically assigned in a manner 482 that is optimized for administrative convenience and to facilitate 483 scaling of the EID-to-RLOC mapping database. The hierarchy is 484 based on an address allocation hierarchy that is independent of 485 the network topology. 487 o EIDs may also be structured (subnetted) in a manner suitable for 488 local routing within an Autonomous System (AS). 490 An additional LISP header MAY be prepended to packets by a TE-ITR 491 when re-routing of the path for a packet is desired. A potential 492 use-case for this would be an ISP router that needs to perform 493 Traffic Engineering for packets flowing through its network. In such 494 a situation, termed "Recursive Tunneling", an ISP transit acts as an 495 additional ITR, and the RLOC it uses for the new prepended header 496 would be either a TE-ETR within the ISP (along an intra-ISP traffic 497 engineered path) or a TE-ETR within another ISP (an inter-ISP traffic 498 engineered path, where an agreement to build such a path exists). 500 In order to avoid excessive packet overhead as well as possible 501 encapsulation loops, this document recommends that a maximum of two 502 LISP headers can be prepended to a packet. For initial LISP 503 deployments, it is assumed that two headers is sufficient, where the 504 first prepended header is used at a site for Location/Identity 505 separation and the second prepended header is used inside a service 506 provider for Traffic Engineering purposes. 508 Tunnel Routers can be placed fairly flexibly in a multi-AS topology. 509 For example, the ITR for a particular end-to-end packet exchange 510 might be the first-hop or default router within a site for the source 511 host. Similarly, the ETR might be the last-hop router directly 512 connected to the destination host. Another example, perhaps for a 513 VPN service outsourced to an ISP by a site, the ITR could be the 514 site's border router at the service provider attachment point. 515 Mixing and matching of site-operated, ISP-operated, and other Tunnel 516 Routers is allowed for maximum flexibility. 518 4.1. Packet Flow Sequence 520 This section provides an example of the unicast packet flow, 521 including also control-plane information as specified in 522 [I-D.ietf-lisp-rfc6833bis]. The example also assumes the following 523 conditions: 525 o Source host "host1.abc.example.com" is sending a packet to 526 "host2.xyz.example.com", exactly what host1 would do if the site 527 was not using LISP. 529 o Each site is multihomed, so each Tunnel Router has an address 530 (RLOC) assigned from the service provider address block for each 531 provider to which that particular Tunnel Router is attached. 533 o The ITR(s) and ETR(s) are directly connected to the source and 534 destination, respectively, but the source and destination can be 535 located anywhere in the LISP site. 537 o Map-Requests are sent to the mapping database system by using the 538 LISP control-plane protocol documented in 539 [I-D.ietf-lisp-rfc6833bis]. A Map-Request is sent for an external 540 destination when the destination is not found in the forwarding 541 table or matches a default route. 543 o Map-Replies are sent on the underlying routing system topology 544 using the [I-D.ietf-lisp-rfc6833bis] control-plane protocol. 546 Client host1.abc.example.com wants to communicate with server 547 host2.xyz.example.com: 549 1. host1.abc.example.com wants to open a TCP connection to 550 host2.xyz.example.com. It does a DNS lookup on 551 host2.xyz.example.com. An A/AAAA record is returned. This 552 address is the destination EID. The locally assigned address of 553 host1.abc.example.com is used as the source EID. An IPv4 or IPv6 554 packet is built and forwarded through the LISP site as a normal 555 IP packet until it reaches a LISP ITR. 557 2. The LISP ITR must be able to map the destination EID to an RLOC 558 of one of the ETRs at the destination site. The specific method 559 used to do this is not described in this example. See 560 [I-D.ietf-lisp-rfc6833bis] for further information. 562 3. The ITR sends a LISP Map-Request as specified in 563 [I-D.ietf-lisp-rfc6833bis]. Map-Requests SHOULD be rate-limited. 565 4. The mapping system helps forwarding the Map-Request to the 566 corresponding ETR. When the Map-Request arrives at one of the 567 ETRs at the destination site, it will process the packet as a 568 control message. 570 5. The ETR looks at the destination EID of the Map-Request and 571 matches it against the prefixes in the ETR's configured EID-to- 572 RLOC mapping database. This is the list of EID-Prefixes the ETR 573 is supporting for the site it resides in. If there is no match, 574 the Map-Request is dropped. Otherwise, a LISP Map-Reply is 575 returned to the ITR. 577 6. The ITR receives the Map-Reply message, parses the message (to 578 check for format validity), and stores the mapping information 579 from the packet. This information is stored in the ITR's EID-to- 580 RLOC map-cache. Note that the map-cache is an on-demand cache. 581 An ITR will manage its map-cache in such a way that optimizes for 582 its resource constraints. 584 7. Subsequent packets from host1.abc.example.com to 585 host2.xyz.example.com will have a LISP header prepended by the 586 ITR using the appropriate RLOC as the LISP header destination 587 address learned from the ETR. Note that the packet MAY be sent 588 to a different ETR than the one that returned the Map-Reply due 589 to the source site's hashing policy or the destination site's 590 Locator-Set policy. 592 8. The ETR receives these packets directly (since the destination 593 address is one of its assigned IP addresses), checks the validity 594 of the addresses, strips the LISP header, and forwards packets to 595 the attached destination host. 597 9. In order to defer the need for a mapping lookup in the reverse 598 direction, an ETR can OPTIONALLY create a cache entry that maps 599 the source EID (inner-header source IP address) to the source 600 RLOC (outer-header source IP address) in a received LISP packet. 601 Such a cache entry is termed a "gleaned" mapping and only 602 contains a single RLOC for the EID in question. More complete 603 information about additional RLOCs SHOULD be verified by sending 604 a LISP Map-Request for that EID. Both the ITR and the ETR may 605 also influence the decision the other makes in selecting an RLOC. 607 5. LISP Encapsulation Details 609 Since additional tunnel headers are prepended, the packet becomes 610 larger and can exceed the MTU of any link traversed from the ITR to 611 the ETR. It is RECOMMENDED in IPv4 that packets do not get 612 fragmented as they are encapsulated by the ITR. Instead, the packet 613 is dropped and an ICMP Unreachable/Fragmentation-Needed message is 614 returned to the source. 616 This specification RECOMMENDS that implementations provide support 617 for one of the proposed fragmentation and reassembly schemes. Two 618 existing schemes are detailed in Section 7. 620 Since IPv4 or IPv6 addresses can be either EIDs or RLOCs, the LISP 621 architecture supports IPv4 EIDs with IPv6 RLOCs (where the inner 622 header is in IPv4 packet format and the outer header is in IPv6 623 packet format) or IPv6 EIDs with IPv4 RLOCs (where the inner header 624 is in IPv6 packet format and the outer header is in IPv4 packet 625 format). The next sub-sections illustrate packet formats for the 626 homogeneous case (IPv4-in-IPv4 and IPv6-in-IPv6), but all 4 627 combinations MUST be supported. Additional types of EIDs are defined 628 in [RFC8060]. 630 5.1. LISP IPv4-in-IPv4 Header Format 632 0 1 2 3 633 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 1 634 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 635 / |Version| IHL |Type of Service| Total Length | 636 / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 637 | | Identification |Flags| Fragment Offset | 638 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 639 OH | Time to Live | Protocol = 17 | Header Checksum | 640 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 641 | | Source Routing Locator | 642 \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 643 \ | Destination Routing Locator | 644 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 645 / | Source Port = xxxx | Dest Port = 4341 | 646 UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 647 \ | UDP Length | UDP Checksum | 648 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 649 L |N|L|E|V|I|R|K|K| Nonce/Map-Version | 650 I \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 651 S / | Instance ID/Locator-Status-Bits | 652 P +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 653 / |Version| IHL |Type of Service| Total Length | 654 / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 655 | | Identification |Flags| Fragment Offset | 656 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 657 IH | Time to Live | Protocol | Header Checksum | 658 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 659 | | Source EID | 660 \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 661 \ | Destination EID | 662 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 664 IHL = IP-Header-Length 666 5.2. LISP IPv6-in-IPv6 Header Format 668 0 1 2 3 669 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 1 670 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 671 / |Version| Traffic Class | Flow Label | 672 / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 673 | | Payload Length | Next Header=17| Hop Limit | 674 v +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 675 | | 676 O + + 677 u | | 678 t + Source Routing Locator + 679 e | | 680 r + + 681 | | 682 H +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 683 d | | 684 r + + 685 | | 686 ^ + Destination Routing Locator + 687 | | | 688 \ + + 689 \ | | 690 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 691 / | Source Port = xxxx | Dest Port = 4341 | 692 UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 693 \ | UDP Length | UDP Checksum | 694 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 695 L |N|L|E|V|I|R|K|K| Nonce/Map-Version | 696 I \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 697 S / | Instance ID/Locator-Status-Bits | 698 P +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 699 / |Version| Traffic Class | Flow Label | 700 / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 701 / | Payload Length | Next Header | Hop Limit | 702 v +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 703 | | 704 I + + 705 n | | 706 n + Source EID + 707 e | | 708 r + + 709 | | 710 H +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 711 d | | 712 r + + 713 | | 715 ^ + Destination EID + 716 \ | | 717 \ + + 718 \ | | 719 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 721 5.3. Tunnel Header Field Descriptions 723 Inner Header (IH): The inner header is the header on the datagram 724 received from the originating host. The source and destination IP 725 addresses are EIDs [RFC0791] [RFC8200]. 727 Outer Header: (OH) The outer header is a new header prepended by an 728 ITR. The address fields contain RLOCs obtained from the ingress 729 router's EID-to-RLOC Cache. The IP protocol number is "UDP (17)" 730 from [RFC0768]. The setting of the Don't Fragment (DF) bit 731 'Flags' field is according to rules listed in Sections 7.1 and 732 7.2. 734 UDP Header: The UDP header contains an ITR selected source port when 735 encapsulating a packet. See Section 12 for details on the hash 736 algorithm used to select a source port based on the 5-tuple of the 737 inner header. The destination port MUST be set to the well-known 738 IANA-assigned port value 4341. 740 UDP Checksum: The 'UDP Checksum' field SHOULD be transmitted as zero 741 by an ITR for either IPv4 [RFC0768] or IPv6 encapsulation 742 [RFC6935] [RFC6936]. When a packet with a zero UDP checksum is 743 received by an ETR, the ETR MUST accept the packet for 744 decapsulation. When an ITR transmits a non-zero value for the UDP 745 checksum, it MUST send a correctly computed value in this field. 746 When an ETR receives a packet with a non-zero UDP checksum, it MAY 747 choose to verify the checksum value. If it chooses to perform 748 such verification, and the verification fails, the packet MUST be 749 silently dropped. If the ETR chooses not to perform the 750 verification, or performs the verification successfully, the 751 packet MUST be accepted for decapsulation. The handling of UDP 752 zero checksums over IPv6 for all tunneling protocols, including 753 LISP, is subject to the applicability statement in [RFC6936]. 755 UDP Length: The 'UDP Length' field is set for an IPv4-encapsulated 756 packet to be the sum of the inner-header IPv4 Total Length plus 757 the UDP and LISP header lengths. For an IPv6-encapsulated packet, 758 the 'UDP Length' field is the sum of the inner-header IPv6 Payload 759 Length, the size of the IPv6 header (40 octets), and the size of 760 the UDP and LISP headers. 762 N: The N-bit is the nonce-present bit. When this bit is set to 1, 763 the low-order 24 bits of the first 32 bits of the LISP header 764 contain a Nonce. See Section 10.1 for details. Both N- and 765 V-bits MUST NOT be set in the same packet. If they are, a 766 decapsulating ETR MUST treat the 'Nonce/Map-Version' field as 767 having a Nonce value present. 769 L: The L-bit is the 'Locator-Status-Bits' field enabled bit. When 770 this bit is set to 1, the Locator-Status-Bits in the second 771 32 bits of the LISP header are in use. 773 x 1 x x 0 x x x 774 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 775 |N|L|E|V|I|R|K|K| Nonce/Map-Version | 776 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 777 | Locator-Status-Bits | 778 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 780 E: The E-bit is the echo-nonce-request bit. This bit MUST be ignored 781 and has no meaning when the N-bit is set to 0. When the N-bit is 782 set to 1 and this bit is set to 1, an ITR is requesting that the 783 nonce value in the 'Nonce' field be echoed back in LISP- 784 encapsulated packets when the ITR is also an ETR. See 785 Section 10.1 for details. 787 V: The V-bit is the Map-Version present bit. When this bit is set to 788 1, the N-bit MUST be 0. Refer to Section 13.3 for more details. 789 This bit indicates that the LISP header is encoded in this 790 case as: 792 0 x 0 1 x x x x 793 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 794 |N|L|E|V|I|R|K|K| Source Map-Version | Dest Map-Version | 795 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 796 | Instance ID/Locator-Status-Bits | 797 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 799 I: The I-bit is the Instance ID bit. See Section 8 for more details. 800 When this bit is set to 1, the 'Locator-Status-Bits' field is 801 reduced to 8 bits and the high-order 24 bits are used as an 802 Instance ID. If the L-bit is set to 0, then the low-order 8 bits 803 are transmitted as zero and ignored on receipt. The format of the 804 LISP header would look like this: 806 x x x x 1 x x x 807 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 808 |N|L|E|V|I|R|K|K| Nonce/Map-Version | 809 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 810 | Instance ID | LSBs | 811 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 813 R: The R-bit is a Reserved bit for future use. It MUST be set to 0 814 on transmit and MUST be ignored on receipt. 816 KK: The KK-bits are a 2-bit field used when encapsualted packets are 817 encrypted. The field is set to 00 when the packet is not 818 encrypted. See [RFC8061] for further information. 820 LISP Nonce: The LISP 'Nonce' field is a 24-bit value that is 821 randomly generated by an ITR when the N-bit is set to 1. Nonce 822 generation algorithms are an implementation matter but are 823 required to generate different nonces when sending to different 824 destinations. However, the same nonce can be used for a period of 825 time to the same destination. The nonce is also used when the 826 E-bit is set to request the nonce value to be echoed by the other 827 side when packets are returned. When the E-bit is clear but the 828 N-bit is set, a remote ITR is either echoing a previously 829 requested echo-nonce or providing a random nonce. See 830 Section 10.1 for more details. 832 LISP Locator-Status-Bits (LSBs): When the L-bit is also set, the 833 'Locator-Status-Bits' field in the LISP header is set by an ITR to 834 indicate to an ETR the up/down status of the Locators in the 835 source site. Each RLOC in a Map-Reply is assigned an ordinal 836 value from 0 to n-1 (when there are n RLOCs in a mapping entry). 837 The Locator-Status-Bits are numbered from 0 to n-1 from the least 838 significant bit of the field. The field is 32 bits when the I-bit 839 is set to 0 and is 8 bits when the I-bit is set to 1. When a 840 Locator-Status-Bit is set to 1, the ITR is indicating to the ETR 841 that the RLOC associated with the bit ordinal has up status. See 842 Section 10 for details on how an ITR can determine the status of 843 the ETRs at the same site. When a site has multiple EID-Prefixes 844 that result in multiple mappings (where each could have a 845 different Locator-Set), the Locator-Status-Bits setting in an 846 encapsulated packet MUST reflect the mapping for the EID-Prefix 847 that the inner-header source EID address matches. If the LSB for 848 an anycast Locator is set to 1, then there is at least one RLOC 849 with that address, and the ETR is considered 'up'. 851 When doing ITR/PITR encapsulation: 853 o The outer-header 'Time to Live' field (or 'Hop Limit' field, in 854 the case of IPv6) SHOULD be copied from the inner-header 'Time to 855 Live' field. 857 o The outer-header 'Type of Service' field (or the 'Traffic Class' 858 field, in the case of IPv6) SHOULD be copied from the inner-header 859 'Type of Service' field (with one exception; see below). 861 When doing ETR/PETR decapsulation: 863 o The inner-header 'Time to Live' field (or 'Hop Limit' field, in 864 the case of IPv6) SHOULD be copied from the outer-header 'Time to 865 Live' field, when the Time to Live value of the outer header is 866 less than the Time to Live value of the inner header. Failing to 867 perform this check can cause the Time to Live of the inner header 868 to increment across encapsulation/decapsulation cycles. This 869 check is also performed when doing initial encapsulation, when a 870 packet comes to an ITR or PITR destined for a LISP site. 872 o The inner-header 'Type of Service' field (or the 'Traffic Class' 873 field, in the case of IPv6) SHOULD be copied from the outer-header 874 'Type of Service' field (with one exception; see below). 876 Note that if an ETR/PETR is also an ITR/PITR and chooses to re- 877 encapsulate after decapsulating, the net effect of this is that the 878 new outer header will carry the same Time to Live as the old outer 879 header minus 1. 881 Copying the Time to Live (TTL) serves two purposes: first, it 882 preserves the distance the host intended the packet to travel; 883 second, and more importantly, it provides for suppression of looping 884 packets in the event there is a loop of concatenated tunnels due to 885 misconfiguration. See Section 18.3 for TTL exception handling for 886 traceroute packets. 888 The Explicit Congestion Notification ('ECN') field occupies bits 6 889 and 7 of both the IPv4 'Type of Service' field and the IPv6 'Traffic 890 Class' field [RFC3168]. The 'ECN' field requires special treatment 891 in order to avoid discarding indications of congestion [RFC3168]. 892 ITR encapsulation MUST copy the 2-bit 'ECN' field from the inner 893 header to the outer header. Re-encapsulation MUST copy the 2-bit 894 'ECN' field from the stripped outer header to the new outer header. 895 If the 'ECN' field contains a congestion indication codepoint (the 896 value is '11', the Congestion Experienced (CE) codepoint), then ETR 897 decapsulation MUST copy the 2-bit 'ECN' field from the stripped outer 898 header to the surviving inner header that is used to forward the 899 packet beyond the ETR. These requirements preserve CE indications 900 when a packet that uses ECN traverses a LISP tunnel and becomes 901 marked with a CE indication due to congestion between the tunnel 902 endpoints. 904 6. LISP EID-to-RLOC Map-Cache 906 ITRs and PITRs maintain an on-demand cache, referred as LISP EID-to- 907 RLOC Map-Cache, that contains mappings from EID-prefixes to locator 908 sets. The cache is used to encapsulate packets from the EID space to 909 the corresponding RLOC network attachment point. 911 When an ITR/PITR receives a packet from inside of the LISP site to 912 destinations outside of the site a longest-prefix match lookup of the 913 EID is done to the map-cache. 915 When the lookup succeeds, the locator-set retrieved from the map- 916 cache is used to send the packet to the EID's topological location. 918 If the lookup fails, the ITR/PITR needs to retrieve the mapping using 919 the LISP control-plane protocol [I-D.ietf-lisp-rfc6833bis]. The 920 mapping is then stored in the local map-cache to forward subsequent 921 packets addressed to the same EID-prefix. 923 The map-cache is a local cache of mappings, entries are expired based 924 on the associated Time to live. In addition, entries can be updated 925 with more current information, see Section 13 for further information 926 on this. Finally, the map-cache also contains reachability 927 information about EIDs and RLOCs, and uses LISP reachability 928 information mechanisms to determine the reachability of RLOCs, see 929 Section 10 for the specific mechanisms. 931 7. Dealing with Large Encapsulated Packets 933 This section proposes two mechanisms to deal with packets that exceed 934 the path MTU between the ITR and ETR. 936 It is left to the implementor to decide if the stateless or stateful 937 mechanism should be implemented. Both or neither can be used, since 938 it is a local decision in the ITR regarding how to deal with MTU 939 issues, and sites can interoperate with differing mechanisms. 941 Both stateless and stateful mechanisms also apply to Re-encapsulating 942 and Recursive Tunneling, so any actions below referring to an ITR 943 also apply to a TE-ITR. 945 7.1. A Stateless Solution to MTU Handling 947 An ITR stateless solution to handle MTU issues is described as 948 follows: 950 1. Define H to be the size, in octets, of the outer header an ITR 951 prepends to a packet. This includes the UDP and LISP header 952 lengths. 954 2. Define L to be the size, in octets, of the maximum-sized packet 955 an ITR can send to an ETR without the need for the ITR or any 956 intermediate routers to fragment the packet. 958 3. Define an architectural constant S for the maximum size of a 959 packet, in octets, an ITR must receive from the source so the 960 effective MTU can be met. That is, L = S + H. 962 When an ITR receives a packet from a site-facing interface and adds H 963 octets worth of encapsulation to yield a packet size greater than L 964 octets (meaning the received packet size was greater than S octets 965 from the source), it resolves the MTU issue by first splitting the 966 original packet into 2 equal-sized fragments. A LISP header is then 967 prepended to each fragment. The size of the encapsulated fragments 968 is then (S/2 + H), which is less than the ITR's estimate of the path 969 MTU between the ITR and its correspondent ETR. 971 When an ETR receives encapsulated fragments, it treats them as two 972 individually encapsulated packets. It strips the LISP headers and 973 then forwards each fragment to the destination host of the 974 destination site. The two fragments are reassembled at the 975 destination host into the single IP datagram that was originated by 976 the source host. Note that reassembly can happen at the ETR if the 977 encapsulated packet was fragmented at or after the ITR. 979 This behavior is performed by the ITR when the source host originates 980 a packet with the 'DF' field of the IP header set to 0. When the 981 'DF' field of the IP header is set to 1, or the packet is an IPv6 982 packet originated by the source host, the ITR will drop the packet 983 when the size is greater than L and send an ICMP Unreachable/ 984 Fragmentation-Needed message to the source with a value of S, where S 985 is (L - H). 987 When the outer-header encapsulation uses an IPv4 header, an 988 implementation SHOULD set the DF bit to 1 so ETR fragment reassembly 989 can be avoided. An implementation MAY set the DF bit in such headers 990 to 0 if it has good reason to believe there are unresolvable path MTU 991 issues between the sending ITR and the receiving ETR. 993 This specification RECOMMENDS that L be defined as 1500. 995 7.2. A Stateful Solution to MTU Handling 997 An ITR stateful solution to handle MTU issues is described as follows 998 and was first introduced in [OPENLISP]: 1000 1. The ITR will keep state of the effective MTU for each Locator per 1001 Map-Cache entry. The effective MTU is what the core network can 1002 deliver along the path between the ITR and ETR. 1004 2. When an IPv6-encapsulated packet, or an IPv4-encapsulated packet 1005 with the DF bit set to 1, exceeds what the core network can 1006 deliver, one of the intermediate routers on the path will send an 1007 ICMP Unreachable/Fragmentation-Needed message to the ITR. The 1008 ITR will parse the ICMP message to determine which Locator is 1009 affected by the effective MTU change and then record the new 1010 effective MTU value in the Map-Cache entry. 1012 3. When a packet is received by the ITR from a source inside of the 1013 site and the size of the packet is greater than the effective MTU 1014 stored with the Map-Cache entry associated with the destination 1015 EID the packet is for, the ITR will send an ICMP Unreachable/ 1016 Fragmentation-Needed message back to the source. The packet size 1017 advertised by the ITR in the ICMP Unreachable/Fragmentation- 1018 Needed message is the effective MTU minus the LISP encapsulation 1019 length. 1021 Even though this mechanism is stateful, it has advantages over the 1022 stateless IP fragmentation mechanism, by not involving the 1023 destination host with reassembly of ITR fragmented packets. 1025 8. Using Virtualization and Segmentation with LISP 1027 There are several cases where segregation is needed at the EID level. 1028 For instance, this is the case for deployments containing overlapping 1029 addresses, traffic isolation policies or multi-tenant virtualization. 1030 For these and other scenarios where segregation is needed, Instance 1031 IDs are used. 1033 An Instance ID can be carried in a LISP-encapsulated packet. An ITR 1034 that prepends a LISP header will copy a 24-bit value used by the LISP 1035 router to uniquely identify the address space. The value is copied 1036 to the 'Instance ID' field of the LISP header, and the I-bit is set 1037 to 1. 1039 When an ETR decapsulates a packet, the Instance ID from the LISP 1040 header is used as a table identifier to locate the forwarding table 1041 to use for the inner destination EID lookup. 1043 For example, an 802.1Q VLAN tag or VPN identifier could be used as a 1044 24-bit Instance ID. See [I-D.ietf-lisp-vpn] for LISP VPN use-case 1045 details. 1047 The Instance ID that is stored in the mapping database when LISP-DDT 1048 [I-D.ietf-lisp-ddt] is used is 32 bits in length. That means the 1049 control-plane can store more instances than a given data-plane can 1050 use. Multiple data-planes can use the same 32-bit space as long as 1051 the low-order 24 bits don't overlap among xTRs. 1053 9. Routing Locator Selection 1055 Both the client-side and server-side may need control over the 1056 selection of RLOCs for conversations between them. This control is 1057 achieved by manipulating the 'Priority' and 'Weight' fields in EID- 1058 to-RLOC Map-Reply messages. Alternatively, RLOC information MAY be 1059 gleaned from received tunneled packets or EID-to-RLOC Map-Request 1060 messages. 1062 The following are different scenarios for choosing RLOCs and the 1063 controls that are available: 1065 o The server-side returns one RLOC. The client-side can only use 1066 one RLOC. The server-side has complete control of the selection. 1068 o The server-side returns a list of RLOCs where a subset of the list 1069 has the same best Priority. The client can only use the subset 1070 list according to the weighting assigned by the server-side. In 1071 this case, the server-side controls both the subset list and load- 1072 splitting across its members. The client-side can use RLOCs 1073 outside of the subset list if it determines that the subset list 1074 is unreachable (unless RLOCs are set to a Priority of 255). Some 1075 sharing of control exists: the server-side determines the 1076 destination RLOC list and load distribution while the client-side 1077 has the option of using alternatives to this list if RLOCs in the 1078 list are unreachable. 1080 o The server-side sets a Weight of 0 for the RLOC subset list. In 1081 this case, the client-side can choose how the traffic load is 1082 spread across the subset list. Control is shared by the server- 1083 side determining the list and the client determining load 1084 distribution. Again, the client can use alternative RLOCs if the 1085 server-provided list of RLOCs is unreachable. 1087 o Either side (more likely the server-side ETR) decides not to send 1088 a Map-Request. For example, if the server-side ETR does not send 1089 Map-Requests, it gleans RLOCs from the client-side ITR, giving the 1090 client-side ITR responsibility for bidirectional RLOC reachability 1091 and preferability. Server-side ETR gleaning of the client-side 1092 ITR RLOC is done by caching the inner-header source EID and the 1093 outer-header source RLOC of received packets. The client-side ITR 1094 controls how traffic is returned and can alternate using an outer- 1095 header source RLOC, which then can be added to the list the 1096 server-side ETR uses to return traffic. Since no Priority or 1097 Weights are provided using this method, the server-side ETR MUST 1098 assume that each client-side ITR RLOC uses the same best Priority 1099 with a Weight of zero. In addition, since EID-Prefix encoding 1100 cannot be conveyed in data packets, the EID-to-RLOC Cache on 1101 Tunnel Routers can grow to be very large. 1103 o A "gleaned" Map-Cache entry, one learned from the source RLOC of a 1104 received encapsulated packet, is only stored and used for a few 1105 seconds, pending verification. Verification is performed by 1106 sending a Map-Request to the source EID (the inner-header IP 1107 source address) of the received encapsulated packet. A reply to 1108 this "verifying Map-Request" is used to fully populate the Map- 1109 Cache entry for the "gleaned" EID and is stored and used for the 1110 time indicated from the 'TTL' field of a received Map-Reply. When 1111 a verified Map-Cache entry is stored, data gleaning no longer 1112 occurs for subsequent packets that have a source EID that matches 1113 the EID-Prefix of the verified entry. This "gleaning" mechanism 1114 is OPTIONAL. 1116 RLOCs that appear in EID-to-RLOC Map-Reply messages are assumed to be 1117 reachable when the R-bit for the Locator record is set to 1. When 1118 the R-bit is set to 0, an ITR or PITR MUST NOT encapsulate to the 1119 RLOC. Neither the information contained in a Map-Reply nor that 1120 stored in the mapping database system provides reachability 1121 information for RLOCs. Note that reachability is not part of the 1122 mapping system and is determined using one or more of the Routing 1123 Locator reachability algorithms described in the next section. 1125 10. Routing Locator Reachability 1127 Several mechanisms for determining RLOC reachability are currently 1128 defined: 1130 1. An ETR may examine the Locator-Status-Bits in the LISP header of 1131 an encapsulated data packet received from an ITR. If the ETR is 1132 also acting as an ITR and has traffic to return to the original 1133 ITR site, it can use this status information to help select an 1134 RLOC. 1136 2. An ITR may receive an ICMP Network Unreachable or Host 1137 Unreachable message for an RLOC it is using. This indicates that 1138 the RLOC is likely down. Note that trusting ICMP messages may 1139 not be desirable, but neither is ignoring them completely. 1140 Implementations are encouraged to follow current best practices 1141 in treating these conditions. 1143 3. An ITR that participates in the global routing system can 1144 determine that an RLOC is down if no BGP Routing Information Base 1145 (RIB) route exists that matches the RLOC IP address. 1147 4. An ITR may receive an ICMP Port Unreachable message from a 1148 destination host. This occurs if an ITR attempts to use 1149 interworking [RFC6832] and LISP-encapsulated data is sent to a 1150 non-LISP-capable site. 1152 5. An ITR may receive a Map-Reply from an ETR in response to a 1153 previously sent Map-Request. The RLOC source of the Map-Reply is 1154 likely up, since the ETR was able to send the Map-Reply to the 1155 ITR. 1157 6. When an ETR receives an encapsulated packet from an ITR, the 1158 source RLOC from the outer header of the packet is likely up. 1160 7. An ITR/ETR pair can use the Locator reachability algorithms 1161 described in this section, namely Echo-Noncing or RLOC-Probing. 1163 When determining Locator up/down reachability by examining the 1164 Locator-Status-Bits from the LISP-encapsulated data packet, an ETR 1165 will receive up-to-date status from an encapsulating ITR about 1166 reachability for all ETRs at the site. CE-based ITRs at the source 1167 site can determine reachability relative to each other using the site 1168 IGP as follows: 1170 o Under normal circumstances, each ITR will advertise a default 1171 route into the site IGP. 1173 o If an ITR fails or if the upstream link to its PE fails, its 1174 default route will either time out or be withdrawn. 1176 Each ITR can thus observe the presence or lack of a default route 1177 originated by the others to determine the Locator-Status-Bits it sets 1178 for them. 1180 RLOCs listed in a Map-Reply are numbered with ordinals 0 to n-1. The 1181 Locator-Status-Bits in a LISP-encapsulated packet are numbered from 0 1182 to n-1 starting with the least significant bit. For example, if an 1183 RLOC listed in the 3rd position of the Map-Reply goes down (ordinal 1184 value 2), then all ITRs at the site will clear the 3rd least 1185 significant bit (xxxx x0xx) of the 'Locator-Status-Bits' field for 1186 the packets they encapsulate. 1188 When an ETR decapsulates a packet, it will check for any change in 1189 the 'Locator-Status-Bits' field. When a bit goes from 1 to 0, the 1190 ETR, if acting also as an ITR, will refrain from encapsulating 1191 packets to an RLOC that is indicated as down. It will only resume 1192 using that RLOC if the corresponding Locator-Status-Bit returns to a 1193 value of 1. Locator-Status-Bits are associated with a Locator-Set 1194 per EID-Prefix. Therefore, when a Locator becomes unreachable, the 1195 Locator-Status-Bit that corresponds to that Locator's position in the 1196 list returned by the last Map-Reply will be set to zero for that 1197 particular EID-Prefix. 1199 When ITRs at the site are not deployed in CE routers, the IGP can 1200 still be used to determine the reachability of Locators, provided 1201 they are injected into the IGP. This is typically done when a /32 1202 address is configured on a loopback interface. 1204 When ITRs receive ICMP Network Unreachable or Host Unreachable 1205 messages as a method to determine unreachability, they will refrain 1206 from using Locators that are described in Locator lists of Map- 1207 Replies. However, using this approach is unreliable because many 1208 network operators turn off generation of ICMP Destination Unreachable 1209 messages. 1211 If an ITR does receive an ICMP Network Unreachable or Host 1212 Unreachable message, it MAY originate its own ICMP Destination 1213 Unreachable message destined for the host that originated the data 1214 packet the ITR encapsulated. 1216 Also, BGP-enabled ITRs can unilaterally examine the RIB to see if a 1217 locator address from a Locator-Set in a mapping entry matches a 1218 prefix. If it does not find one and BGP is running in the Default- 1219 Free Zone (DFZ), it can decide to not use the Locator even though the 1220 Locator-Status-Bits indicate that the Locator is up. In this case, 1221 the path from the ITR to the ETR that is assigned the Locator is not 1222 available. More details are in [I-D.meyer-loc-id-implications]. 1224 Optionally, an ITR can send a Map-Request to a Locator, and if a Map- 1225 Reply is returned, reachability of the Locator has been determined. 1226 Obviously, sending such probes increases the number of control 1227 messages originated by Tunnel Routers for active flows, so Locators 1228 are assumed to be reachable when they are advertised. 1230 This assumption does create a dependency: Locator unreachability is 1231 detected by the receipt of ICMP Host Unreachable messages. When a 1232 Locator has been determined to be unreachable, it is not used for 1233 active traffic; this is the same as if it were listed in a Map-Reply 1234 with Priority 255. 1236 The ITR can test the reachability of the unreachable Locator by 1237 sending periodic Requests. Both Requests and Replies MUST be rate- 1238 limited. Locator reachability testing is never done with data 1239 packets, since that increases the risk of packet loss for end-to-end 1240 sessions. 1242 When an ETR decapsulates a packet, it knows that it is reachable from 1243 the encapsulating ITR because that is how the packet arrived. In 1244 most cases, the ETR can also reach the ITR but cannot assume this to 1245 be true, due to the possibility of path asymmetry. In the presence 1246 of unidirectional traffic flow from an ITR to an ETR, the ITR SHOULD 1247 NOT use the lack of return traffic as an indication that the ETR is 1248 unreachable. Instead, it MUST use an alternate mechanism to 1249 determine reachability. 1251 10.1. Echo Nonce Algorithm 1253 When data flows bidirectionally between Locators from different 1254 sites, a data-plane mechanism called "nonce echoing" can be used to 1255 determine reachability between an ITR and ETR. When an ITR wants to 1256 solicit a nonce echo, it sets the N- and E-bits and places a 24-bit 1257 nonce [RFC4086] in the LISP header of the next encapsulated data 1258 packet. 1260 When this packet is received by the ETR, the encapsulated packet is 1261 forwarded as normal. When the ETR next sends a data packet to the 1262 ITR, it includes the nonce received earlier with the N-bit set and 1263 E-bit cleared. The ITR sees this "echoed nonce" and knows that the 1264 path to and from the ETR is up. 1266 The ITR will set the E-bit and N-bit for every packet it sends while 1267 in the echo-nonce-request state. The time the ITR waits to process 1268 the echoed nonce before it determines the path is unreachable is 1269 variable and is a choice left for the implementation. 1271 If the ITR is receiving packets from the ETR but does not see the 1272 nonce echoed while being in the echo-nonce-request state, then the 1273 path to the ETR is unreachable. This decision may be overridden by 1274 other Locator reachability algorithms. Once the ITR determines that 1275 the path to the ETR is down, it can switch to another Locator for 1276 that EID-Prefix. 1278 Note that "ITR" and "ETR" are relative terms here. Both devices MUST 1279 be implementing both ITR and ETR functionality for the echo nonce 1280 mechanism to operate. 1282 The ITR and ETR may both go into the echo-nonce-request state at the 1283 same time. The number of packets sent or the time during which echo 1284 nonce requests are sent is an implementation-specific setting. 1285 However, when an ITR is in the echo-nonce-request state, it can echo 1286 the ETR's nonce in the next set of packets that it encapsulates and 1287 subsequently continue sending echo-nonce-request packets. 1289 This mechanism does not completely solve the forward path 1290 reachability problem, as traffic may be unidirectional. That is, the 1291 ETR receiving traffic at a site may not be the same device as an ITR 1292 that transmits traffic from that site, or the site-to-site traffic is 1293 unidirectional so there is no ITR returning traffic. 1295 The echo-nonce algorithm is bilateral. That is, if one side sets the 1296 E-bit and the other side is not enabled for echo-noncing, then the 1297 echoing of the nonce does not occur and the requesting side may 1298 erroneously consider the Locator unreachable. An ITR SHOULD only set 1299 the E-bit in an encapsulated data packet when it knows the ETR is 1300 enabled for echo-noncing. This is conveyed by the E-bit in the RLOC- 1301 probe Map-Reply message. 1303 Note that other Locator reachability mechanisms are being researched 1304 and can be used to compliment or even override the echo nonce 1305 algorithm. See the next section for an example of control-plane 1306 probing. 1308 10.2. RLOC-Probing Algorithm 1310 RLOC-Probing is a method that an ITR or PITR can use to determine the 1311 reachability status of one or more Locators that it has cached in a 1312 Map-Cache entry. The probe-bit of the Map-Request and Map-Reply 1313 messages is used for RLOC-Probing. 1315 RLOC-Probing is done in the control plane on a timer basis, where an 1316 ITR or PITR will originate a Map-Request destined to a locator 1317 address from one of its own locator addresses. A Map-Request used as 1318 an RLOC-probe is NOT encapsulated and NOT sent to a Map-Server or to 1319 the mapping database system as one would when soliciting mapping 1320 data. The EID record encoded in the Map-Request is the EID-Prefix of 1321 the Map-Cache entry cached by the ITR or PITR. The ITR may include a 1322 mapping data record for its own database mapping information that 1323 contains the local EID-Prefixes and RLOCs for its site. RLOC-probes 1324 are sent periodically using a jittered timer interval. 1326 When an ETR receives a Map-Request message with the probe-bit set, it 1327 returns a Map-Reply with the probe-bit set. The source address of 1328 the Map-Reply is set according to the procedure described in 1329 [I-D.ietf-lisp-rfc6833bis]. The Map-Reply SHOULD contain mapping 1330 data for the EID-Prefix contained in the Map-Request. This provides 1331 the opportunity for the ITR or PITR that sent the RLOC-probe to get 1332 mapping updates if there were changes to the ETR's database mapping 1333 entries. 1335 There are advantages and disadvantages of RLOC-Probing. The greatest 1336 benefit of RLOC-Probing is that it can handle many failure scenarios 1337 allowing the ITR to determine when the path to a specific Locator is 1338 reachable or has become unreachable, thus providing a robust 1339 mechanism for switching to using another Locator from the cached 1340 Locator. RLOC-Probing can also provide rough Round-Trip Time (RTT) 1341 estimates between a pair of Locators, which can be useful for network 1342 management purposes as well as for selecting low delay paths. The 1343 major disadvantage of RLOC-Probing is in the number of control 1344 messages required and the amount of bandwidth used to obtain those 1345 benefits, especially if the requirement for failure detection times 1346 is very small. 1348 Continued research and testing will attempt to characterize the 1349 tradeoffs of failure detection times versus message overhead. 1351 11. EID Reachability within a LISP Site 1353 A site may be multihomed using two or more ETRs. The hosts and 1354 infrastructure within a site will be addressed using one or more EID- 1355 Prefixes that are mapped to the RLOCs of the relevant ETRs in the 1356 mapping system. One possible failure mode is for an ETR to lose 1357 reachability to one or more of the EID-Prefixes within its own site. 1358 When this occurs when the ETR sends Map-Replies, it can clear the 1359 R-bit associated with its own Locator. And when the ETR is also an 1360 ITR, it can clear its Locator-Status-Bit in the encapsulation data 1361 header. 1363 It is recognized that there are no simple solutions to the site 1364 partitioning problem because it is hard to know which part of the 1365 EID-Prefix range is partitioned and which Locators can reach any sub- 1366 ranges of the EID-Prefixes. This problem is under investigation with 1367 the expectation that experiments will tell us more. Note that this 1368 is not a new problem introduced by the LISP architecture. The 1369 problem exists today when a multihomed site uses BGP to advertise its 1370 reachability upstream. 1372 12. Routing Locator Hashing 1374 When an ETR provides an EID-to-RLOC mapping in a Map-Reply message to 1375 a requesting ITR, the Locator-Set for the EID-Prefix may contain 1376 different Priority values for each locator address. When more than 1377 one best Priority Locator exists, the ITR can decide how to load- 1378 share traffic against the corresponding Locators. 1380 The following hash algorithm may be used by an ITR to select a 1381 Locator for a packet destined to an EID for the EID-to-RLOC mapping: 1383 1. Either a source and destination address hash or the traditional 1384 5-tuple hash can be used. The traditional 5-tuple hash includes 1385 the source and destination addresses; source and destination TCP, 1386 UDP, or Stream Control Transmission Protocol (SCTP) port numbers; 1387 and the IP protocol number field or IPv6 next-protocol fields of 1388 a packet that a host originates from within a LISP site. When a 1389 packet is not a TCP, UDP, or SCTP packet, the source and 1390 destination addresses only from the header are used to compute 1391 the hash. 1393 2. Take the hash value and divide it by the number of Locators 1394 stored in the Locator-Set for the EID-to-RLOC mapping. 1396 3. The remainder will yield a value of 0 to "number of Locators 1397 minus 1". Use the remainder to select the Locator in the 1398 Locator-Set. 1400 Note that when a packet is LISP encapsulated, the source port number 1401 in the outer UDP header needs to be set. Selecting a hashed value 1402 allows core routers that are attached to Link Aggregation Groups 1403 (LAGs) to load-split the encapsulated packets across member links of 1404 such LAGs. Otherwise, core routers would see a single flow, since 1405 packets have a source address of the ITR, for packets that are 1406 originated by different EIDs at the source site. A suggested setting 1407 for the source port number computed by an ITR is a 5-tuple hash 1408 function on the inner header, as described above. 1410 Many core router implementations use a 5-tuple hash to decide how to 1411 balance packet load across members of a LAG. The 5-tuple hash 1412 includes the source and destination addresses of the packet and the 1413 source and destination ports when the protocol number in the packet 1414 is TCP or UDP. For this reason, UDP encoding is used for LISP 1415 encapsulation. 1417 13. Changing the Contents of EID-to-RLOC Mappings 1419 Since the LISP architecture uses a caching scheme to retrieve and 1420 store EID-to-RLOC mappings, the only way an ITR can get a more up-to- 1421 date mapping is to re-request the mapping. However, the ITRs do not 1422 know when the mappings change, and the ETRs do not keep track of 1423 which ITRs requested its mappings. For scalability reasons, it is 1424 desirable to maintain this approach but need to provide a way for 1425 ETRs to change their mappings and inform the sites that are currently 1426 communicating with the ETR site using such mappings. 1428 When adding a new Locator record in lexicographic order to the end of 1429 a Locator-Set, it is easy to update mappings. We assume that new 1430 mappings will maintain the same Locator ordering as the old mapping 1431 but will just have new Locators appended to the end of the list. So, 1432 some ITRs can have a new mapping while other ITRs have only an old 1433 mapping that is used until they time out. When an ITR has only an 1434 old mapping but detects bits set in the Locator-Status-Bits that 1435 correspond to Locators beyond the list it has cached, it simply 1436 ignores them. However, this can only happen for locator addresses 1437 that are lexicographically greater than the locator addresses in the 1438 existing Locator-Set. 1440 When a Locator record is inserted in the middle of a Locator-Set, to 1441 maintain lexicographic order, the SMR procedure in Section 13.2 is 1442 used to inform ITRs and PITRs of the new Locator-Status-Bit mappings. 1444 When a Locator record is removed from a Locator-Set, ITRs that have 1445 the mapping cached will not use the removed Locator because the xTRs 1446 will set the Locator-Status-Bit to 0. So, even if the Locator is in 1447 the list, it will not be used. For new mapping requests, the xTRs 1448 can set the Locator AFI to 0 (indicating an unspecified address), as 1449 well as setting the corresponding Locator-Status-Bit to 0. This 1450 forces ITRs with old or new mappings to avoid using the removed 1451 Locator. 1453 If many changes occur to a mapping over a long period of time, one 1454 will find empty record slots in the middle of the Locator-Set and new 1455 records appended to the Locator-Set. At some point, it would be 1456 useful to compact the Locator-Set so the Locator-Status-Bit settings 1457 can be efficiently packed. 1459 We propose here three approaches for Locator-Set compaction: one 1460 operational mechanism and two protocol mechanisms. The operational 1461 approach uses a clock sweep method. The protocol approaches use the 1462 concept of Solicit-Map-Requests and Map-Versioning. 1464 13.1. Clock Sweep 1466 The clock sweep approach uses planning in advance and the use of 1467 count-down TTLs to time out mappings that have already been cached. 1468 The default setting for an EID-to-RLOC mapping TTL is 24 hours. So, 1469 there is a 24-hour window to time out old mappings. The following 1470 clock sweep procedure is used: 1472 1. 24 hours before a mapping change is to take effect, a network 1473 administrator configures the ETRs at a site to start the clock 1474 sweep window. 1476 2. During the clock sweep window, ETRs continue to send Map-Reply 1477 messages with the current (unchanged) mapping records. The TTL 1478 for these mappings is set to 1 hour. 1480 3. 24 hours later, all previous cache entries will have timed out, 1481 and any active cache entries will time out within 1 hour. During 1482 this 1-hour window, the ETRs continue to send Map-Reply messages 1483 with the current (unchanged) mapping records with the TTL set to 1484 1 minute. 1486 4. At the end of the 1-hour window, the ETRs will send Map-Reply 1487 messages with the new (changed) mapping records. So, any active 1488 caches can get the new mapping contents right away if not cached, 1489 or in 1 minute if they had the mapping cached. The new mappings 1490 are cached with a TTL equal to the TTL in the Map-Reply. 1492 13.2. Solicit-Map-Request (SMR) 1494 Soliciting a Map-Request is a selective way for ETRs, at the site 1495 where mappings change, to control the rate they receive requests for 1496 Map-Reply messages. SMRs are also used to tell remote ITRs to update 1497 the mappings they have cached. 1499 Since the ETRs don't keep track of remote ITRs that have cached their 1500 mappings, they do not know which ITRs need to have their mappings 1501 updated. As a result, an ETR will solicit Map-Requests (called an 1502 SMR message) from those sites to which it has been sending 1503 encapsulated data for the last minute. In particular, an ETR will 1504 send an SMR to an ITR to which it has recently sent encapsulated 1505 data. This can only occur when both ITR and ETR functionality reside 1506 in the same router. 1508 An SMR message is simply a bit set in a Map-Request message. An ITR 1509 or PITR will send a Map-Request when they receive an SMR message. 1510 Both the SMR sender and the Map-Request responder MUST rate-limit 1511 these messages. Rate-limiting can be implemented as a global rate- 1512 limiter or one rate-limiter per SMR destination. 1514 The following procedure shows how an SMR exchange occurs when a site 1515 is doing Locator-Set compaction for an EID-to-RLOC mapping: 1517 1. When the database mappings in an ETR change, the ETRs at the site 1518 begin to send Map-Requests with the SMR bit set for each Locator 1519 in each Map-Cache entry the ETR caches. 1521 2. A remote ITR that receives the SMR message will schedule sending 1522 a Map-Request message to the source locator address of the SMR 1523 message or to the mapping database system. A newly allocated 1524 random nonce is selected, and the EID-Prefix used is the one 1525 copied from the SMR message. If the source Locator is the only 1526 Locator in the cached Locator-Set, the remote ITR SHOULD send a 1527 Map-Request to the database mapping system just in case the 1528 single Locator has changed and may no longer be reachable to 1529 accept the Map-Request. 1531 3. The remote ITR MUST rate-limit the Map-Request until it gets a 1532 Map-Reply while continuing to use the cached mapping. When 1533 Map-Versioning as described in Section 13.3 is used, an SMR 1534 sender can detect if an ITR is using the most up-to-date database 1535 mapping. 1537 4. The ETRs at the site with the changed mapping will reply to the 1538 Map-Request with a Map-Reply message that has a nonce from the 1539 SMR-invoked Map-Request. The Map-Reply messages SHOULD be rate- 1540 limited. This is important to avoid Map-Reply implosion. 1542 5. The ETRs at the site with the changed mapping record the fact 1543 that the site that sent the Map-Request has received the new 1544 mapping data in the Map-Cache entry for the remote site so the 1545 Locator-Status-Bits are reflective of the new mapping for packets 1546 going to the remote site. The ETR then stops sending SMR 1547 messages. 1549 For security reasons, an ITR MUST NOT process unsolicited Map- 1550 Replies. To avoid Map-Cache entry corruption by a third party, a 1551 sender of an SMR-based Map-Request MUST be verified. If an ITR 1552 receives an SMR-based Map-Request and the source is not in the 1553 Locator-Set for the stored Map-Cache entry, then the responding Map- 1554 Request MUST be sent with an EID destination to the mapping database 1555 system. Since the mapping database system is a more secure way to 1556 reach an authoritative ETR, it will deliver the Map-Request to the 1557 authoritative source of the mapping data. 1559 When an ITR receives an SMR-based Map-Request for which it does not 1560 have a cached mapping for the EID in the SMR message, it MAY not send 1561 an SMR-invoked Map-Request. This scenario can occur when an ETR 1562 sends SMR messages to all Locators in the Locator-Set it has stored 1563 in its map-cache but the remote ITRs that receive the SMR may not be 1564 sending packets to the site. There is no point in updating the ITRs 1565 until they need to send, in which case they will send Map-Requests to 1566 obtain a Map-Cache entry. 1568 13.3. Database Map-Versioning 1570 When there is unidirectional packet flow between an ITR and ETR, and 1571 the EID-to-RLOC mappings change on the ETR, it needs to inform the 1572 ITR so encapsulation to a removed Locator can stop and can instead be 1573 started to a new Locator in the Locator-Set. 1575 An ETR, when it sends Map-Reply messages, conveys its own Map-Version 1576 Number. This is known as the Destination Map-Version Number. ITRs 1577 include the Destination Map-Version Number in packets they 1578 encapsulate to the site. When an ETR decapsulates a packet and 1579 detects that the Destination Map-Version Number is less than the 1580 current version for its mapping, the SMR procedure described in 1581 Section 13.2 occurs. 1583 An ITR, when it encapsulates packets to ETRs, can convey its own Map- 1584 Version Number. This is known as the Source Map-Version Number. 1585 When an ETR decapsulates a packet and detects that the Source Map- 1586 Version Number is greater than the last Map-Version Number sent in a 1587 Map-Reply from the ITR's site, the ETR will send a Map-Request to one 1588 of the ETRs for the source site. 1590 A Map-Version Number is used as a sequence number per EID-Prefix, so 1591 values that are greater are considered to be more recent. A value of 1592 0 for the Source Map-Version Number or the Destination Map-Version 1593 Number conveys no versioning information, and an ITR does no 1594 comparison with previously received Map-Version Numbers. 1596 A Map-Version Number can be included in Map-Register messages as 1597 well. This is a good way for the Map-Server to assure that all ETRs 1598 for a site registering to it will be synchronized according to Map- 1599 Version Number. 1601 See [RFC6834] for a more detailed analysis and description of 1602 Database Map-Versioning. 1604 14. Multicast Considerations 1606 A multicast group address, as defined in the original Internet 1607 architecture, is an identifier of a grouping of topologically 1608 independent receiver host locations. The address encoding itself 1609 does not determine the location of the receiver(s). The multicast 1610 routing protocol, and the network-based state the protocol creates, 1611 determine where the receivers are located. 1613 In the context of LISP, a multicast group address is both an EID and 1614 a Routing Locator. Therefore, no specific semantic or action needs 1615 to be taken for a destination address, as it would appear in an IP 1616 header. Therefore, a group address that appears in an inner IP 1617 header built by a source host will be used as the destination EID. 1618 The outer IP header (the destination Routing Locator address), 1619 prepended by a LISP router, can use the same group address as the 1620 destination Routing Locator, use a multicast or unicast Routing 1621 Locator obtained from a Mapping System lookup, or use other means to 1622 determine the group address mapping. 1624 With respect to the source Routing Locator address, the ITR prepends 1625 its own IP address as the source address of the outer IP header. 1626 Just like it would if the destination EID was a unicast address. 1627 This source Routing Locator address, like any other Routing Locator 1628 address, MUST be globally routable. 1630 There are two approaches for LISP-Multicast, one that uses native 1631 multicast routing in the underlay with no support from the Mapping 1632 System and the other that uses only unicast routing in the underlay 1633 with support from the Mapping System. See [RFC6831] and 1634 [I-D.ietf-lisp-signal-free-multicast], respectively, for details. 1635 Details for LISP-Multicast and interworking with non-LISP sites are 1636 described in [RFC6831] and [RFC6832]. 1638 15. Router Performance Considerations 1640 LISP is designed to be very "hardware-based forwarding friendly". A 1641 few implementation techniques can be used to incrementally implement 1642 LISP: 1644 o When a tunnel-encapsulated packet is received by an ETR, the outer 1645 destination address may not be the address of the router. This 1646 makes it challenging for the control plane to get packets from the 1647 hardware. This may be mitigated by creating special Forwarding 1648 Information Base (FIB) entries for the EID-Prefixes of EIDs served 1649 by the ETR (those for which the router provides an RLOC 1650 translation). These FIB entries are marked with a flag indicating 1651 that control-plane processing should be performed. The forwarding 1652 logic of testing for particular IP protocol number values is not 1653 necessary. There are a few proven cases where no changes to 1654 existing deployed hardware were needed to support the LISP data- 1655 plane. 1657 o On an ITR, prepending a new IP header consists of adding more 1658 octets to a MAC rewrite string and prepending the string as part 1659 of the outgoing encapsulation procedure. Routers that support 1660 Generic Routing Encapsulation (GRE) tunneling [RFC2784] or 6to4 1661 tunneling [RFC3056] may already support this action. 1663 o A packet's source address or interface the packet was received on 1664 can be used to select VRF (Virtual Routing/Forwarding). The VRF's 1665 routing table can be used to find EID-to-RLOC mappings. 1667 For performance issues related to map-cache management, see 1668 Section 19. 1670 16. Mobility Considerations 1672 There are several kinds of mobility, of which only some might be of 1673 concern to LISP. Essentially, they are as follows. 1675 16.1. Slow Mobility 1677 A site wishes to change its attachment points to the Internet, and 1678 its LISP Tunnel Routers will have new RLOCs when it changes upstream 1679 providers. Changes in EID-to-RLOC mappings for sites are expected to 1680 be handled by configuration, outside of LISP. 1682 An individual endpoint wishes to move but is not concerned about 1683 maintaining session continuity. Renumbering is involved. LISP can 1684 help with the issues surrounding renumbering [RFC4192] [LISA96] by 1685 decoupling the address space used by a site from the address spaces 1686 used by its ISPs [RFC4984]. 1688 16.2. Fast Mobility 1690 Fast endpoint mobility occurs when an endpoint moves relatively 1691 rapidly, changing its IP-layer network attachment point. Maintenance 1692 of session continuity is a goal. This is where the Mobile IPv4 1693 [RFC5944] and Mobile IPv6 [RFC6275] [RFC4866] mechanisms are used and 1694 primarily where interactions with LISP need to be explored, such as 1695 the mechanisms in [I-D.ietf-lisp-eid-mobility] when the EID moves but 1696 the RLOC is in the network infrastructure. 1698 In LISP, one possibility is to "glean" information. When a packet 1699 arrives, the ETR could examine the EID-to-RLOC mapping and use that 1700 mapping for all outgoing traffic to that EID. It can do this after 1701 performing a route-returnability check, to ensure that the new 1702 network location does have an internal route to that endpoint. 1703 However, this does not cover the case where an ITR (the node assigned 1704 the RLOC) at the mobile-node location has been compromised. 1706 Mobile IP packet exchange is designed for an environment in which all 1707 routing information is disseminated before packets can be forwarded. 1708 In order to allow the Internet to grow to support expected future 1709 use, we are moving to an environment where some information may have 1710 to be obtained after packets are in flight. Modifications to IP 1711 mobility should be considered in order to optimize the behavior of 1712 the overall system. Anything that decreases the number of new EID- 1713 to-RLOC mappings needed when a node moves, or maintains the validity 1714 of an EID-to-RLOC mapping for a longer time, is useful. 1716 In addition to endpoints, a network can be mobile, possibly changing 1717 xTRs. A "network" can be as small as a single router and as large as 1718 a whole site. This is different from site mobility in that it is 1719 fast and possibly short-lived, but different from endpoint mobility 1720 in that a whole prefix is changing RLOCs. However, the mechanisms 1721 are the same, and there is no new overhead in LISP. A map request 1722 for any endpoint will return a binding for the entire mobile prefix. 1724 If mobile networks become a more common occurrence, it may be useful 1725 to revisit the design of the mapping service and allow for dynamic 1726 updates of the database. 1728 The issue of interactions between mobility and LISP needs to be 1729 explored further. Specific improvements to the entire system will 1730 depend on the details of mapping mechanisms. Mapping mechanisms 1731 should be evaluated on how well they support session continuity for 1732 mobile nodes. See [I-D.ietf-lisp-predictive-rlocs] for more recent 1733 mechanisms which can provide near-zero packet loss during handoffs. 1735 16.3. LISP Mobile Node Mobility 1737 A mobile device can use the LISP infrastructure to achieve mobility 1738 by implementing the LISP encapsulation and decapsulation functions 1739 and acting as a simple ITR/ETR. By doing this, such a "LISP mobile 1740 node" can use topologically independent EID IP addresses that are not 1741 advertised into and do not impose a cost on the global routing 1742 system. These EIDs are maintained at the edges of the mapping system 1743 in LISP Map-Servers and Map-Resolvers) and are provided on demand to 1744 only the correspondents of the LISP mobile node. 1746 Refer to [I-D.ietf-lisp-mn] for more details for when the EID and 1747 RLOC are co-located in the roaming node. 1749 17. LISP xTR Placement and Encapsulation Methods 1751 This section will explore how and where ITRs and ETRs can be placed 1752 in the network and will discuss the pros and cons of each scenario. 1753 For a more detailed networkd design deployment recommendation, refer 1754 to [RFC7215]. 1756 There are two basic deployment tradeoffs to consider: centralized 1757 versus distributed caches; and flat, Recursive, or Re-encapsulating 1758 Tunneling. When deciding on centralized versus distributed caching, 1759 the following issues should be considered: 1761 o Are the xTRs spread out so that the caches are spread across all 1762 the memories of each router? A centralized cache is when an ITR 1763 keeps a cache for all the EIDs it is encapsulating to. The packet 1764 takes a direct path to the destination Locator. A distributed 1765 cache is when an ITR needs help from other Re-Encapsulating Tunnel 1766 Routers (RTRs) because it does not store all the cache entries for 1767 the EIDs it is encapsulating to. So, the packet takes a path 1768 through RTRs that have a different set of cache entries. 1770 o Should management "touch points" be minimized by only choosing a 1771 few xTRs, just enough for redundancy? 1773 o In general, using more ITRs doesn't increase management load, 1774 since caches are built and stored dynamically. On the other hand, 1775 using more ETRs does require more management, since EID-Prefix-to- 1776 RLOC mappings need to be explicitly configured. 1778 When deciding on flat, Recursive, or Re-Encapsulating Tunneling, the 1779 following issues should be considered: 1781 o Flat tunneling implements a single encapsulation path between the 1782 source site and destination site. This generally offers better 1783 paths between sources and destinations with a single encapsulation 1784 path. 1786 o Recursive Tunneling is when encapsulated traffic is again further 1787 encapsulated in another tunnel, either to implement VPNs or to 1788 perform Traffic Engineering. When doing VPN-based tunneling, the 1789 site has some control, since the site is prepending a new 1790 encapsulation header. In the case of TE-based tunneling, the site 1791 may have control if it is prepending a new tunnel header, but if 1792 the site's ISP is doing the TE, then the site has no control. 1793 Recursive Tunneling generally will result in suboptimal paths but 1794 with the benefit of steering traffic to parts of the network that 1795 have more resources available. 1797 o The technique of Re-Encapsulation ensures that packets only 1798 require one encapsulation header. So, if a packet needs to be re- 1799 routed, it is first decapsulated by the RTR and then Re- 1800 Encapsulated with a new encapsulation header using a new RLOC. 1802 The next sub-sections will examine where xTRs and RTRs can reside in 1803 the network. 1805 17.1. First-Hop/Last-Hop xTRs 1807 By locating xTRs close to hosts, the EID-Prefix set is at the 1808 granularity of an IP subnet. So, at the expense of more EID-Prefix- 1809 to-RLOC sets for the site, the caches in each xTR can remain 1810 relatively small. But caches always depend on the number of non- 1811 aggregated EID destination flows active through these xTRs. 1813 With more xTRs doing encapsulation, the increase in control traffic 1814 grows as well: since the EID granularity is greater, more Map- 1815 Requests and Map-Replies are traveling between more routers. 1817 The advantage of placing the caches and databases at these stub 1818 routers is that the products deployed in this part of the network 1819 have better price-memory ratios than their core router counterparts. 1820 Memory is typically less expensive in these devices, and fewer routes 1821 are stored (only IGP routes). These devices tend to have excess 1822 capacity, both for forwarding and routing states. 1824 LISP functionality can also be deployed in edge switches. These 1825 devices generally have layer-2 ports facing hosts and layer-3 ports 1826 facing the Internet. Spare capacity is also often available in these 1827 devices. 1829 17.2. Border/Edge xTRs 1831 Using Customer Edge (CE) routers for xTR placement allows the EID 1832 space associated with a site to be reachable via a small set of RLOCs 1833 assigned to the CE-based xTRs for that site. 1835 This offers the opposite benefit of the first-hop/last-hop xTR 1836 scenario: the number of mapping entries and network management touch 1837 points is reduced, allowing better scaling. 1839 One disadvantage is that fewer network resources are used to reach 1840 host endpoints, thereby centralizing the point-of-failure domain and 1841 creating network choke points at the CE xTR. 1843 Note that more than one CE xTR at a site can be configured with the 1844 same IP address. In this case, an RLOC is an anycast address. This 1845 allows resilience between the CE xTRs. That is, if a CE xTR fails, 1846 traffic is automatically routed to the other xTRs using the same 1847 anycast address. However, this comes with the disadvantage where the 1848 site cannot control the entrance point when the anycast route is 1849 advertised out from all border routers. Another disadvantage of 1850 using anycast Locators is the limited advertisement scope of /32 (or 1851 /128 for IPv6) routes. 1853 17.3. ISP Provider Edge (PE) xTRs 1855 The use of ISP PE routers as xTRs is not the typical deployment 1856 scenario envisioned in this specification. This section attempts to 1857 capture some of the reasoning behind this preference for implementing 1858 LISP on CE routers. 1860 The use of ISP PE routers for xTR placement gives an ISP, rather than 1861 a site, control over the location of the ETRs. That is, the ISP can 1862 decide whether the xTRs are in the destination site (in either CE 1863 xTRs or last-hop xTRs within a site) or at other PE edges. The 1864 advantage of this case is that two encapsulation headers can be 1865 avoided. By having the PE be the first router on the path to 1866 encapsulate, it can choose a TE path first, and the ETR can 1867 decapsulate and Re-Encapsulate for a new encapsuluation path to the 1868 destination end site. 1870 An obvious disadvantage is that the end site has no control over 1871 where its packets flow or over the RLOCs used. Other disadvantages 1872 include difficulty in synchronizing path liveness updates between CE 1873 and PE routers. 1875 As mentioned in earlier sections, a combination of these scenarios is 1876 possible at the expense of extra packet header overhead; if both site 1877 and provider want control, then Recursive or Re-Encapsulating Tunnels 1878 are used. 1880 17.4. LISP Functionality with Conventional NATs 1882 LISP routers can be deployed behind Network Address Translator (NAT) 1883 devices to provide the same set of packet services hosts have today 1884 when they are addressed out of private address space. 1886 It is important to note that a locator address in any LISP control 1887 message MUST be a routable address and therefore [RFC1918] addresses 1888 SHOULD only be presence when running in a local environment. When a 1889 LISP xTR is configured with private RLOC addresses and resides behind 1890 a NAT device and desires to communicate on the Internet, the private 1891 addresses MUST be used only in the outer IP header so the NAT device 1892 can translate properly. Otherwise, EID addresses MUST be translated 1893 before encapsulation is performed when LISP VPNs are not in use. 1894 Both NAT translation and LISP encapsulation functions could be co- 1895 located in the same device. 1897 17.5. Packets Egressing a LISP Site 1899 When a LISP site is using two ITRs for redundancy, the failure of one 1900 ITR will likely shift outbound traffic to the second. This second 1901 ITR's cache may not be populated with the same EID-to-RLOC mapping 1902 entries as the first. If this second ITR does not have these 1903 mappings, traffic will be dropped while the mappings are retrieved 1904 from the mapping system. The retrieval of these messages may 1905 increase the load of requests being sent into the mapping system. 1907 18. Traceroute Considerations 1909 When a source host in a LISP site initiates a traceroute to a 1910 destination host in another LISP site, it is highly desirable for it 1911 to see the entire path. Since packets are encapsulated from the ITR 1912 to the ETR, the hop across the tunnel could be viewed as a single 1913 hop. However, LISP traceroute will provide the entire path so the 1914 user can see 3 distinct segments of the path from a source LISP host 1915 to a destination LISP host: 1917 Segment 1 (in source LISP site based on EIDs): 1919 source host ---> first hop ... next hop ---> ITR 1921 Segment 2 (in the core network based on RLOCs): 1923 ITR ---> next hop ... next hop ---> ETR 1925 Segment 3 (in the destination LISP site based on EIDs): 1927 ETR ---> next hop ... last hop ---> destination host 1929 For segment 1 of the path, ICMP Time Exceeded messages are returned 1930 in the normal manner as they are today. The ITR performs a TTL 1931 decrement and tests for 0 before encapsulating. Therefore, the ITR's 1932 hop is seen by the traceroute source as having an EID address (the 1933 address of the site-facing interface). 1935 For segment 2 of the path, ICMP Time Exceeded messages are returned 1936 to the ITR because the TTL decrement to 0 is done on the outer 1937 header, so the destinations of the ICMP messages are the ITR RLOC 1938 address and the source RLOC address of the encapsulated traceroute 1939 packet. The ITR looks inside of the ICMP payload to inspect the 1940 traceroute source so it can return the ICMP message to the address of 1941 the traceroute client and also retain the core router IP address in 1942 the ICMP message. This is so the traceroute client can display the 1943 core router address (the RLOC address) in the traceroute output. The 1944 ETR returns its RLOC address and responds to the TTL decrement to 0, 1945 as the previous core routers did. 1947 For segment 3, the next-hop router downstream from the ETR will be 1948 decrementing the TTL for the packet that was encapsulated, sent into 1949 the core, decapsulated by the ETR, and forwarded because it isn't the 1950 final destination. If the TTL is decremented to 0, any router on the 1951 path to the destination of the traceroute, including the next-hop 1952 router or destination, will send an ICMP Time Exceeded message to the 1953 source EID of the traceroute client. The ICMP message will be 1954 encapsulated by the local ITR and sent back to the ETR in the 1955 originated traceroute source site, where the packet will be delivered 1956 to the host. 1958 18.1. IPv6 Traceroute 1960 IPv6 traceroute follows the procedure described above, since the 1961 entire traceroute data packet is included in the ICMP Time Exceeded 1962 message payload. Therefore, only the ITR needs to pay special 1963 attention to forwarding ICMP messages back to the traceroute source. 1965 18.2. IPv4 Traceroute 1967 For IPv4 traceroute, we cannot follow the above procedure, since IPv4 1968 ICMP Time Exceeded messages only include the invoking IP header and 1969 8 octets that follow the IP header. Therefore, when a core router 1970 sends an IPv4 Time Exceeded message to an ITR, all the ITR has in the 1971 ICMP payload is the encapsulated header it prepended, followed by a 1972 UDP header. The original invoking IP header, and therefore the 1973 identity of the traceroute source, is lost. 1975 The solution we propose to solve this problem is to cache traceroute 1976 IPv4 headers in the ITR and to match them up with corresponding IPv4 1977 Time Exceeded messages received from core routers and the ETR. The 1978 ITR will use a circular buffer for caching the IPv4 and UDP headers 1979 of traceroute packets. It will select a 16-bit number as a key to 1980 find them later when the IPv4 Time Exceeded messages are received. 1981 When an ITR encapsulates an IPv4 traceroute packet, it will use the 1982 16-bit number as the UDP source port in the encapsulating header. 1983 When the ICMP Time Exceeded message is returned to the ITR, the UDP 1984 header of the encapsulating header is present in the ICMP payload, 1985 thereby allowing the ITR to find the cached headers for the 1986 traceroute source. The ITR puts the cached headers in the payload 1987 and sends the ICMP Time Exceeded message to the traceroute source 1988 retaining the source address of the original ICMP Time Exceeded 1989 message (a core router or the ETR of the site of the traceroute 1990 destination). 1992 The signature of a traceroute packet comes in two forms. The first 1993 form is encoded as a UDP message where the destination port is 1994 inspected for a range of values. The second form is encoded as an 1995 ICMP message where the IP identification field is inspected for a 1996 well-known value. 1998 18.3. Traceroute Using Mixed Locators 2000 When either an IPv4 traceroute or IPv6 traceroute is originated and 2001 the ITR encapsulates it in the other address family header, one 2002 cannot get all 3 segments of the traceroute. Segment 2 of the 2003 traceroute cannot be conveyed to the traceroute source, since it is 2004 expecting addresses from intermediate hops in the same address format 2005 for the type of traceroute it originated. Therefore, in this case, 2006 segment 2 will make the tunnel look like one hop. All the ITR has to 2007 do to make this work is to not copy the inner TTL to the outer, 2008 encapsulating header's TTL when a traceroute packet is encapsulated 2009 using an RLOC from a different address family. This will cause no 2010 TTL decrement to 0 to occur in core routers between the ITR and ETR. 2012 19. Security Considerations 2014 Security considerations for LISP are discussed in [RFC7833], in 2015 addition [I-D.ietf-lisp-sec] provides authentication and integrity to 2016 LISP mappings. 2018 A complete LISP threat analysis can be found in [RFC7835], in what 2019 follows we provide a summary. 2021 The optional mechanisms of gleaning is offered to directly obtain a 2022 mapping from the LISP encapsulated packets. Specifically, an xTR can 2023 learn the EID-to-RLOC mapping by inspecting the source RLOC and 2024 source EID of an encapsulated packet, and insert this new mapping 2025 into its map-cache. An off-path attacker can spoof the source EID 2026 address to divert the traffic sent to the victim's spoofed EID. If 2027 the attacker spoofs the source RLOC, it can mount a DoS attack by 2028 redirecting traffic to the spoofed victim;s RLOC, potentially 2029 overloading it. 2031 The LISP Data-Plane defines several mechanisms to monitor RLOC data- 2032 plane reachability, in this context Locator-Status Bits, Nonce- 2033 Present and Echo-Nonce bits of the LISP encapsulation header can be 2034 manipulated by an attacker to mount a DoS attack. An off-path 2035 attacker able to spoof the RLOC of a victim's xTR can manipulate such 2036 mechanisms to declare a set of RLOCs unreachable. This can be used 2037 also, for instance, to declare only one RLOC reachable with the aim 2038 of overload it. 2040 Map-Versioning is a data-plane mechanism used to signal a peering xTR 2041 that a local EID-to-RLOC mapping has been updated, so that the 2042 peering xTR uses LISP Control-Plane signaling message to retrieve a 2043 fresh mapping. This can be used by an attacker to forge the map- 2044 versioning field of a LISP encapsulated header and force an excessive 2045 amount of signaling between xTRs that may overload them. 2047 Most of the attack vectors can be mitigated with careful deployment 2048 and configuration, information learned opportunistically (such as LSB 2049 or gleaning) should be verified with other reachability mechanisms. 2050 In addition, systematic rate-limitation and filtering is an effective 2051 technique to mitigate attacks that aim to overload the control-plane. 2053 20. Network Management Considerations 2055 Considerations for network management tools exist so the LISP 2056 protocol suite can be operationally managed. These mechanisms can be 2057 found in [RFC7052] and [RFC6835]. 2059 21. IANA Considerations 2061 This section provides guidance to the Internet Assigned Numbers 2062 Authority (IANA) regarding registration of values related to this 2063 data-plane LISP specification, in accordance with BCP 26 [RFC5226]. 2065 21.1. LISP UDP Port Numbers 2067 The IANA registry has allocated UDP port numbers 4341 and 4342 for 2068 lisp-data and lisp-control operation, respectively. IANA has updated 2069 the description for UDP ports 4341 and 4342 as follows: 2071 lisp-data 4341 udp LISP Data Packets 2072 lisp-control 4342 udp LISP Control Packets 2074 22. References 2076 22.1. Normative References 2078 [I-D.ietf-lisp-ddt] 2079 Fuller, V., Lewis, D., Ermagan, V., Jain, A., and A. 2080 Smirnov, "LISP Delegated Database Tree", draft-ietf-lisp- 2081 ddt-09 (work in progress), January 2017. 2083 [I-D.ietf-lisp-introduction] 2084 Cabellos-Aparicio, A. and D. Saucez, "An Architectural 2085 Introduction to the Locator/ID Separation Protocol 2086 (LISP)", draft-ietf-lisp-introduction-13 (work in 2087 progress), April 2015. 2089 [I-D.ietf-lisp-rfc6833bis] 2090 Fuller, V., Farinacci, D., and A. Cabellos-Aparicio, 2091 "Locator/ID Separation Protocol (LISP) Control-Plane", 2092 draft-ietf-lisp-rfc6833bis-06 (work in progress), October 2093 2017. 2095 [I-D.ietf-lisp-sec] 2096 Maino, F., Ermagan, V., Cabellos-Aparicio, A., and D. 2097 Saucez, "LISP-Security (LISP-SEC)", draft-ietf-lisp-sec-14 2098 (work in progress), October 2017. 2100 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 2101 DOI 10.17487/RFC0768, August 1980, 2102 . 2104 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 2105 DOI 10.17487/RFC0791, September 1981, 2106 . 2108 [RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G., 2109 and E. Lear, "Address Allocation for Private Internets", 2110 BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996, 2111 . 2113 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2114 Requirement Levels", BCP 14, RFC 2119, 2115 DOI 10.17487/RFC2119, March 1997, 2116 . 2118 [RFC2404] Madson, C. and R. Glenn, "The Use of HMAC-SHA-1-96 within 2119 ESP and AH", RFC 2404, DOI 10.17487/RFC2404, November 2120 1998, . 2122 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 2123 of Explicit Congestion Notification (ECN) to IP", 2124 RFC 3168, DOI 10.17487/RFC3168, September 2001, 2125 . 2127 [RFC3232] Reynolds, J., Ed., "Assigned Numbers: RFC 1700 is Replaced 2128 by an On-line Database", RFC 3232, DOI 10.17487/RFC3232, 2129 January 2002, . 2131 [RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker, 2132 "Randomness Requirements for Security", BCP 106, RFC 4086, 2133 DOI 10.17487/RFC4086, June 2005, 2134 . 2136 [RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing 2137 (CIDR): The Internet Address Assignment and Aggregation 2138 Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August 2139 2006, . 2141 [RFC4868] Kelly, S. and S. Frankel, "Using HMAC-SHA-256, HMAC-SHA- 2142 384, and HMAC-SHA-512 with IPsec", RFC 4868, 2143 DOI 10.17487/RFC4868, May 2007, 2144 . 2146 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 2147 IANA Considerations Section in RFCs", RFC 5226, 2148 DOI 10.17487/RFC5226, May 2008, 2149 . 2151 [RFC5496] Wijnands, IJ., Boers, A., and E. Rosen, "The Reverse Path 2152 Forwarding (RPF) Vector TLV", RFC 5496, 2153 DOI 10.17487/RFC5496, March 2009, 2154 . 2156 [RFC5944] Perkins, C., Ed., "IP Mobility Support for IPv4, Revised", 2157 RFC 5944, DOI 10.17487/RFC5944, November 2010, 2158 . 2160 [RFC6115] Li, T., Ed., "Recommendation for a Routing Architecture", 2161 RFC 6115, DOI 10.17487/RFC6115, February 2011, 2162 . 2164 [RFC6275] Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility 2165 Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July 2166 2011, . 2168 [RFC6834] Iannone, L., Saucez, D., and O. Bonaventure, "Locator/ID 2169 Separation Protocol (LISP) Map-Versioning", RFC 6834, 2170 DOI 10.17487/RFC6834, January 2013, 2171 . 2173 [RFC6836] Fuller, V., Farinacci, D., Meyer, D., and D. Lewis, 2174 "Locator/ID Separation Protocol Alternative Logical 2175 Topology (LISP+ALT)", RFC 6836, DOI 10.17487/RFC6836, 2176 January 2013, . 2178 [RFC7052] Schudel, G., Jain, A., and V. Moreno, "Locator/ID 2179 Separation Protocol (LISP) MIB", RFC 7052, 2180 DOI 10.17487/RFC7052, October 2013, 2181 . 2183 [RFC7214] Andersson, L. and C. Pignataro, "Moving Generic Associated 2184 Channel (G-ACh) IANA Registries to a New Registry", 2185 RFC 7214, DOI 10.17487/RFC7214, May 2014, 2186 . 2188 [RFC7215] Jakab, L., Cabellos-Aparicio, A., Coras, F., Domingo- 2189 Pascual, J., and D. Lewis, "Locator/Identifier Separation 2190 Protocol (LISP) Network Element Deployment 2191 Considerations", RFC 7215, DOI 10.17487/RFC7215, April 2192 2014, . 2194 [RFC7833] Howlett, J., Hartman, S., and A. Perez-Mendez, Ed., "A 2195 RADIUS Attribute, Binding, Profiles, Name Identifier 2196 Format, and Confirmation Methods for the Security 2197 Assertion Markup Language (SAML)", RFC 7833, 2198 DOI 10.17487/RFC7833, May 2016, 2199 . 2201 [RFC7835] Saucez, D., Iannone, L., and O. Bonaventure, "Locator/ID 2202 Separation Protocol (LISP) Threat Analysis", RFC 7835, 2203 DOI 10.17487/RFC7835, April 2016, 2204 . 2206 [RFC8061] Farinacci, D. and B. Weis, "Locator/ID Separation Protocol 2207 (LISP) Data-Plane Confidentiality", RFC 8061, 2208 DOI 10.17487/RFC8061, February 2017, 2209 . 2211 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2212 (IPv6) Specification", STD 86, RFC 8200, 2213 DOI 10.17487/RFC8200, July 2017, 2214 . 2216 22.2. Informative References 2218 [AFN] IANA, "Address Family Numbers", August 2016, 2219 . 2221 [CHIAPPA] Chiappa, J., "Endpoints and Endpoint names: A Proposed", 2222 1999, 2223 . 2225 [I-D.ietf-lisp-eid-mobility] 2226 Portoles-Comeras, M., Ashtaputre, V., Moreno, V., Maino, 2227 F., and D. Farinacci, "LISP L2/L3 EID Mobility Using a 2228 Unified Control Plane", draft-ietf-lisp-eid-mobility-00 2229 (work in progress), May 2017. 2231 [I-D.ietf-lisp-mn] 2232 Farinacci, D., Lewis, D., Meyer, D., and C. White, "LISP 2233 Mobile Node", draft-ietf-lisp-mn-01 (work in progress), 2234 October 2017. 2236 [I-D.ietf-lisp-predictive-rlocs] 2237 Farinacci, D. and P. Pillay-Esnault, "LISP Predictive 2238 RLOCs", draft-ietf-lisp-predictive-rlocs-00 (work in 2239 progress), June 2017. 2241 [I-D.ietf-lisp-signal-free-multicast] 2242 Moreno, V. and D. Farinacci, "Signal-Free LISP Multicast", 2243 draft-ietf-lisp-signal-free-multicast-06 (work in 2244 progress), August 2017. 2246 [I-D.ietf-lisp-vpn] 2247 Moreno, V. and D. Farinacci, "LISP Virtual Private 2248 Networks (VPNs)", draft-ietf-lisp-vpn-00 (work in 2249 progress), May 2017. 2251 [I-D.meyer-loc-id-implications] 2252 Meyer, D. and D. Lewis, "Architectural Implications of 2253 Locator/ID Separation", draft-meyer-loc-id-implications-01 2254 (work in progress), January 2009. 2256 [LISA96] Lear, E., Tharp, D., Katinsky, J., and J. Coffin, 2257 "Renumbering: Threat or Menace?", Usenix Tenth System 2258 Administration Conference (LISA 96), October 1996. 2260 [OPENLISP] 2261 Iannone, L., Saucez, D., and O. Bonaventure, "OpenLISP 2262 Implementation Report", Work in Progress, July 2008. 2264 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 2265 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 2266 . 2268 [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. 2269 Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, 2270 DOI 10.17487/RFC2784, March 2000, 2271 . 2273 [RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains 2274 via IPv4 Clouds", RFC 3056, DOI 10.17487/RFC3056, February 2275 2001, . 2277 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 2278 A., Peterson, J., Sparks, R., Handley, M., and E. 2279 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 2280 DOI 10.17487/RFC3261, June 2002, 2281 . 2283 [RFC4107] Bellovin, S. and R. Housley, "Guidelines for Cryptographic 2284 Key Management", BCP 107, RFC 4107, DOI 10.17487/RFC4107, 2285 June 2005, . 2287 [RFC4192] Baker, F., Lear, E., and R. Droms, "Procedures for 2288 Renumbering an IPv6 Network without a Flag Day", RFC 4192, 2289 DOI 10.17487/RFC4192, September 2005, 2290 . 2292 [RFC4866] Arkko, J., Vogt, C., and W. Haddad, "Enhanced Route 2293 Optimization for Mobile IPv6", RFC 4866, 2294 DOI 10.17487/RFC4866, May 2007, 2295 . 2297 [RFC4984] Meyer, D., Ed., Zhang, L., Ed., and K. Fall, Ed., "Report 2298 from the IAB Workshop on Routing and Addressing", 2299 RFC 4984, DOI 10.17487/RFC4984, September 2007, 2300 . 2302 [RFC6480] Lepinski, M. and S. Kent, "An Infrastructure to Support 2303 Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480, 2304 February 2012, . 2306 [RFC6518] Lebovitz, G. and M. Bhatia, "Keying and Authentication for 2307 Routing Protocols (KARP) Design Guidelines", RFC 6518, 2308 DOI 10.17487/RFC6518, February 2012, 2309 . 2311 [RFC6831] Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas, "The 2312 Locator/ID Separation Protocol (LISP) for Multicast 2313 Environments", RFC 6831, DOI 10.17487/RFC6831, January 2314 2013, . 2316 [RFC6832] Lewis, D., Meyer, D., Farinacci, D., and V. Fuller, 2317 "Interworking between Locator/ID Separation Protocol 2318 (LISP) and Non-LISP Sites", RFC 6832, 2319 DOI 10.17487/RFC6832, January 2013, 2320 . 2322 [RFC6835] Farinacci, D. and D. Meyer, "The Locator/ID Separation 2323 Protocol Internet Groper (LIG)", RFC 6835, 2324 DOI 10.17487/RFC6835, January 2013, 2325 . 2327 [RFC6837] Lear, E., "NERD: A Not-so-novel Endpoint ID (EID) to 2328 Routing Locator (RLOC) Database", RFC 6837, 2329 DOI 10.17487/RFC6837, January 2013, 2330 . 2332 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 2333 UDP Checksums for Tunneled Packets", RFC 6935, 2334 DOI 10.17487/RFC6935, April 2013, 2335 . 2337 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 2338 for the Use of IPv6 UDP Datagrams with Zero Checksums", 2339 RFC 6936, DOI 10.17487/RFC6936, April 2013, 2340 . 2342 [RFC8060] Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical 2343 Address Format (LCAF)", RFC 8060, DOI 10.17487/RFC8060, 2344 February 2017, . 2346 Appendix A. Acknowledgments 2348 An initial thank you goes to Dave Oran for planting the seeds for the 2349 initial ideas for LISP. His consultation continues to provide value 2350 to the LISP authors. 2352 A special and appreciative thank you goes to Noel Chiappa for 2353 providing architectural impetus over the past decades on separation 2354 of location and identity, as well as detailed reviews of the LISP 2355 architecture and documents, coupled with enthusiasm for making LISP a 2356 practical and incremental transition for the Internet. 2358 The authors would like to gratefully acknowledge many people who have 2359 contributed discussions and ideas to the making of this proposal. 2360 They include Scott Brim, Andrew Partan, John Zwiebel, Jason Schiller, 2361 Lixia Zhang, Dorian Kim, Peter Schoenmaker, Vijay Gill, Geoff Huston, 2362 David Conrad, Mark Handley, Ron Bonica, Ted Seely, Mark Townsley, 2363 Chris Morrow, Brian Weis, Dave McGrew, Peter Lothberg, Dave Thaler, 2364 Eliot Lear, Shane Amante, Ved Kafle, Olivier Bonaventure, Luigi 2365 Iannone, Robin Whittle, Brian Carpenter, Joel Halpern, Terry 2366 Manderson, Roger Jorgensen, Ran Atkinson, Stig Venaas, Iljitsch van 2367 Beijnum, Roland Bless, Dana Blair, Bill Lynch, Marc Woolward, Damien 2368 Saucez, Damian Lezama, Attilla De Groot, Parantap Lahiri, David 2369 Black, Roque Gagliano, Isidor Kouvelas, Jesper Skriver, Fred Templin, 2370 Margaret Wasserman, Sam Hartman, Michael Hofling, Pedro Marques, Jari 2371 Arkko, Gregg Schudel, Srinivas Subramanian, Amit Jain, Xu Xiaohu, 2372 Dhirendra Trivedi, Yakov Rekhter, John Scudder, John Drake, Dimitri 2373 Papadimitriou, Ross Callon, Selina Heimlich, Job Snijders, Vina 2374 Ermagan, Fabio Maino, Victor Moreno, Chris White, Clarence Filsfils, 2375 Alia Atlas, Florin Coras and Alberto Rodriguez. 2377 This work originated in the Routing Research Group (RRG) of the IRTF. 2378 An individual submission was converted into the IETF LISP working 2379 group document that became this RFC. 2381 The LISP working group would like to give a special thanks to Jari 2382 Arkko, the Internet Area AD at the time that the set of LISP 2383 documents were being prepared for IESG last call, and for his 2384 meticulous reviews and detailed commentaries on the 7 working group 2385 last call documents progressing toward standards-track RFCs. 2387 Appendix B. Document Change Log 2389 [RFC Editor: Please delete this section on publication as RFC.] 2391 B.1. Changes to draft-ietf-lisp-rfc6830bis-06 2393 o Posted November 2017. 2395 o Rephrase how Instance-IDs are used and don't refer to [RFC1918] 2396 addresses. 2398 B.2. Changes to draft-ietf-lisp-rfc6830bis-06 2400 o Posted October 2017. 2402 o Put RTR definition before it is used. 2404 o Rename references that are now working group drafts. 2406 o Remove "EIDs MUST NOT be used as used by a host to refer to other 2407 hosts. Note that EID blocks MAY LISP RLOCs". 2409 o Indicate what address-family can appear in data packets. 2411 o ETRs may, rather than will, be the ones to send Map-Replies. 2413 o Recommend, rather than mandate, max encapsulation headers to 2. 2415 o Reference VPN draft when introducing Instance-ID. 2417 o Indicate that SMRs can be sent when ITR/ETR are in the same node. 2419 o Clarify when private addreses can be used. 2421 B.3. Changes to draft-ietf-lisp-rfc6830bis-05 2423 o Posted August 2017. 2425 o Make it clear that a Reencapsulating Tunnel Router is an RTR. 2427 B.4. Changes to draft-ietf-lisp-rfc6830bis-04 2429 o Posted July 2017. 2431 o Changed reference of IPv6 RFC2460 to RFC8200. 2433 o Indicate that the applicability statement for UDP zero checksums 2434 over IPv6 adheres to RFC6936. 2436 B.5. Changes to draft-ietf-lisp-rfc6830bis-03 2438 o Posted May 2017. 2440 o Move the control-plane related codepoints in the IANA 2441 Considerations section to RFC6833bis. 2443 B.6. Changes to draft-ietf-lisp-rfc6830bis-02 2445 o Posted April 2017. 2447 o Reflect some editorial comments from Damien Sausez. 2449 B.7. Changes to draft-ietf-lisp-rfc6830bis-01 2451 o Posted March 2017. 2453 o Include references to new RFCs published. 2455 o Change references from RFC6833 to RFC6833bis. 2457 o Clarified LCAF text in the IANA section. 2459 o Remove references to "experimental". 2461 B.8. Changes to draft-ietf-lisp-rfc6830bis-00 2463 o Posted December 2016. 2465 o Created working group document from draft-farinacci-lisp 2466 -rfc6830-00 individual submission. No other changes made. 2468 Authors' Addresses 2470 Dino Farinacci 2471 Cisco Systems 2472 Tasman Drive 2473 San Jose, CA 95134 2474 USA 2476 EMail: farinacci@gmail.com 2477 Vince Fuller 2478 Cisco Systems 2479 Tasman Drive 2480 San Jose, CA 95134 2481 USA 2483 EMail: vince.fuller@gmail.com 2485 Dave Meyer 2486 Cisco Systems 2487 170 Tasman Drive 2488 San Jose, CA 2489 USA 2491 EMail: dmm@1-4-5.net 2493 Darrel Lewis 2494 Cisco Systems 2495 170 Tasman Drive 2496 San Jose, CA 2497 USA 2499 EMail: darlewis@cisco.com 2501 Albert Cabellos 2502 UPC/BarcelonaTech 2503 Campus Nord, C. Jordi Girona 1-3 2504 Barcelona, Catalunya 2505 Spain 2507 EMail: acabello@ac.upc.edu