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'22' Summary: 9 errors (**), 0 flaws (~~), 12 warnings (==), 9 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Internet Draft A. Petrescu, ed. 2 Document: draft-petrescu-nemo-mrha-02.txt M. Catalina-Gallego 3 Expires: September 2003 C. Janneteau 4 H.-Y. Lach 5 A. Olivereau 6 Motorola 8 March 2003 10 Issues in Designing Mobile IPv6 Network Mobility 11 with the MR-HA Bidirectional Tunnel (MRHA) 12 14 Status of this Nemo 16 This document is an Internet-Draft and is in full conformance 17 with all provisions of Section 10 of RFC2026. 19 Internet-Drafts are working documents of the Internet Engineering 20 Task Force (IETF), its areas, and its working groups. Note that 21 other groups may also distribute working documents as Internet- 22 Drafts. 24 Internet-Drafts are draft documents valid for a maximum of six 25 months and may be updated, replaced, or obsoleted by other documents 26 at any time. It is inappropriate to use Internet-Drafts as 27 reference material or to cite them other than as "work in progress." 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/ietf/1id-abstracts.txt 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 Abstract 36 This document describes several issues relevant to the design of a 37 network mobility support solution that relies on the bi-directional 38 tunnel between Mobile Router and Home Agent, with Mobile IP. 39 Examples of issues are: conflicting Mobile IP and RIPng/OSPF 40 requirements on link-local addresses, HA/BR co-location, and 41 "cross-over" tunnels. 43 Table of Contents 45 Status of this Nemo................................................i 46 Abstract...........................................................i 47 Conventions Used in this Document.................................ii 48 1. Introduction....................................................1 49 2. Definitions.....................................................1 50 3. NEMO "Basic" preliminary descriptions...........................1 51 4. Issues..........................................................2 52 4.1 Implementation-independent specification terms...............2 53 4.2 Allow for deployment flexibility.............................3 54 4.3 Dynamic routing protocol and the HA..........................3 55 4.4 Link-local addresses.........................................3 56 4.5 Mobile Router as a Mobile Host...............................4 57 4.6 Neighbour Discovery for MR's egress interface................4 58 4.7 Separation of routing and mobility for MR....................5 59 4.8 Prefix-based routing and host-based routing exceptions.......5 60 4.9 IPv4 Issues..................................................5 61 4.10 "Cross-over" tunnels........................................6 62 5. Security Considerations.........................................6 63 5.1 A tool: HA ingress filtering.................................6 64 Acknowledgements...................................................6 65 References.........................................................7 66 Changes............................................................9 67 A. Motivation for Full Addresses in Binding Updates................9 68 A.1 Description of a Home Network................................9 69 A.2 Scenarios...................................................10 70 A.2.1 Manual Mobile Networks..................................11 71 A.2.2 Scenarios with Co-located HA and BR.....................11 72 A.2.3 Scenarios with HA and BR Separated......................16 73 A.3 MR Redirects to BR..........................................20 74 A.4 Informing the HA about the Route to MR......................20 75 A.4.1 ICMP Redirect from BR to HA.............................21 76 A.4.2 Static Route Method.....................................21 77 A.4.3 Dynamic Route Method....................................23 78 B. Examples and Other Issues......................................23 79 B.1 Example of issue for Mobile Router as Mobile Host...........23 80 B.2 Multicast Subscriptions of the MR...........................23 81 B.3 Examples of issues for Neighbour Discovery for MR...........24 82 B.4 Router Renumbering..........................................24 83 B.5 Example of disconnected operation issue.....................25 84 B.6 Example for the "cross-over" tunnels issue..................25 85 B.7 Example of use of HA ingress filtering......................26 86 C. A Digression...................................................27 87 Intellectual Property Rights Considerations.......................27 88 Chairs' Addresses.................................................28 89 Authors' Addresses................................................28 90 Copyright Notice..................................................29 92 Conventions used in this document 94 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 95 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in 96 this document are to be interpreted as described in RFC-2119 [1]. 98 1. Introduction 100 This document describes several issues relevant to the design of a 101 network mobility support solution that relies on the bi-directional 102 tunnel between Mobile Router and Home Agent, with Mobile IP. 103 Examples of issues are: conflicting Mobile IP and RIPng/OSPF 104 requirements on link-local addresses, HA/BR co-location and 105 "cross-over" tunnels. 107 The Mobile Router is using Binding Updates, Binding 108 Acknowledgments, Binding Requests and Binding Errors with the Home 109 Agent to maintain the MRHA bidirectional tunnel. 111 The document is organized as follows: the next section presents a 112 short perspective on three preliminary proposals for a NEMO "Basic" 113 type of solution; the following section lists the issues that 114 appear in this type of protocols. Two additional sections, or 115 appendices, give more detail of issues by way of motivations, 116 examples and other related issues. 118 2. Definitions 120 Complete NEMO terminology can be found in [9]. 122 MH: a mobile host, which is a mobile node (MN) as defined by Mobile 123 IPv6, except all router parts. In Mobile IPv6 terminology, MN 124 can be either a host or a router. An MH can only be a host. 126 MR_HoA: mobile router's Home Address, or the home address of the 127 mobile (egress) interface of the mobile router. 129 MNP: mobile network prefix, or the prefix of the link of the mobile 130 network that will move away. Note that in the most general 131 case a single MR may route multiple prefixes, in which case 132 there would be multiples MNPs per one mobile network. 134 FN: fixed node on the home link. It doesn't stand for fixed 135 network. 137 3. NEMO "Basic" preliminary descriptions 139 An exhaustive description of the proposals to support mobile 140 networks or mobile routers with Mobile IP bi-directional tunnel can 141 hardly fit in the usual space reserved for an Internet Draft, which 142 is traditionally a short document. We retain three main 143 descriptions: Cisco Mobile IPv4 for Mobile Routers [4], MRTP [13] 144 and the "Basic" approach [22]. 146 MRTP is a method of enabling mobile routers by using dynamic tunnel 147 registrations between the AR's point of attachment and its HA. 148 This tunnel allows the HA to tunnel all traffic for the mobile 149 network prefix to the MR, and also lets the MR forward all mobile 150 network traffic back to the home network, where it is topologically 151 correct, and can avoid ingress routing in the visited network. 153 MRTP does not suffer from the authorization problem of how to show 154 that the MR owns the routing authority for the Mobile Network. 156 The approach relies on the bidirectional tunnel between MR and HA. 157 The solution proposed is valid for Mobile IPv6 as for Mobile IPv4. 158 The MR and HA behaviours still represent a sensitive departure from 159 the Mobile IPv6 protocol in that MR informs its HA directly about 160 the tunnel interface and dynamically triggers additions of routing 161 table entries in the HA's routing table for the MR's tunnel. In 162 addition, the most recent version of the draft proposes usage of 163 the PSBUs in order to inform the HA about the prefix of the mobile 164 network (thus a combination with the PSBU approach). Moreover, the 165 considerations about dynamic routing in this draft refer only to 166 how dynamic routing would work with a MR, but not about the 167 necessity of running a routing protocol between HA and MR. 169 In the Mobile IPv4 case, the network mobility support with the MRHA 170 tunnel has been reported at least by various teams at Cisco [4] and 171 NASA [14]. 173 The Basic protocol proposed in [22] takes a different tack at 174 assigning the home addresses: it assigns it to the MR's ingress 175 interface, instead of the egress interface. In addition, it 176 proposes a two step approach for the search algorithm in the HA's 177 binding cache: the first step is a search based on a key that is a 178 full /128 address, while the second step is a search based on 179 longest-prefix match. A new aspect is that this proposals relies 180 also on a (yet to be developped) prefix delegation scheme where the 181 HA assigns the mobile network prefix to MR, in a dynamic manner. 183 For a more detailed analysis on the first two approaches (MRTP and 184 Cisco Mobile Routers) see sections A.4.2 and A.4.3. 186 4. Issues 188 The following is a list of issues that we believe might be relevant 189 when designing a Basic type of solution by the NEMO WG. Some of 190 the issues are exemplified in the Appendices. 192 4.1 Implementation-independent specification terms 194 The specification of the basic network mobility support should be 195 expressed with implementation-independent terms. In other words, 196 clear distinction should be made between the specification of the 197 protocol and a description of a possible implementation of this 198 protocol. Especially, since it is to be based on Mobile IP(v6), the 199 basic NEMO support specification should not make any assumption on 200 how Mobile IP(v6) is implemented but instead re-use (and possibly 201 extend) data structures from the Mobile IP(v6) specification 202 (e.g. Binding Cache), and eventually introduce new ones if 203 needed. Below are two examples of how attention should be payed in 204 the specification of the protocol. 206 The bi-directional approach requires MR's HA to configure a 207 "forwarding information" for the mobile network prefix towards the 208 mobile router. Since the Mobile IP(v6) specification introduces a 209 dedicated structure, so-called Binding Cache, to store 210 mobility-related "forwading information" on the HA, the 211 specification of basic NEMO support should re-use/extend the 212 Binding Cache to include the new mobility-related "forwarding 213 information" for a mobile network. Even though a Binding Cache may 214 be implemented as an extension of a routing table, the 215 specification should relate to the Binding Cache and not the 216 routing table. For instance, the specification should relate to 217 the "forwading information" to be configured on MR's HA for the 218 mobile network prefix in terms of a prefix entry in the Binding 219 Cache instead of an entry in the routing table of MR's HA. 220 Especially, Mobile IP(v6) specification does not specify any 221 routing table for a HA. 223 Similarly, the specification should not assume that a tunnel, 224 e.g. the MRHA bi-directionnal tunnel, is visible as a virtual 225 network interface on the MR or HA. This is an 226 implementation-related consideration that may not be true for all 227 IP(v6)/MobileIP(v6) stacks. 229 Such considerations will allow to clearly draw the line between the 230 specification and a description of a possible implementation, and 231 as a result ease any future implementation of the basic NEMO 232 support as an extention of an existing Mobile IPv6 implementation. 234 4.2 Allow for deployment flexibility 236 The basic NEMO support specification should not assume MR's HA to 237 be co-located with the Border Router (BR) of MR's home network. The 238 HA should be allowed to be a one-interface machine, separated from 239 BR, that does only NEMO HA functionalities (as a Mobile IP(v6) HA 240 can be). This way, HA can be deployed in a home domain without the 241 need to upgrade deployed BRs offering an easy deployment path. 243 4.3 Dynamic routing protocol and the HA 245 Considering the case of a HA deployed as a one-interface machine 246 not co-located with BR, the basic NEMO support specification should 247 not mandate the HA to run a routing protocol, even in situation 248 when MR runs a routing protocol. On the other hand, such HA should 249 allow MR and BR to continue running the dynamic routing protocol as 250 if MR was at home. Suffices it for the HA to: (1) join the 251 corresponding multicast address, intercept all packets addressed to 252 the link-local address of MR and encapsulate towards current MR CoA 253 and (2) relay, or forward, towards BR all dynamic routing message 254 exchanges coming from MR. 256 4.4 Link-local addresses 258 According to section 10.4.2 of Mobile IPv6 spec [12] the HA will 259 not allow re-direction of traffic of a Home Address towards a CoA, 260 when that Home Address is link-local. Two relevant paragraphs: 262 "However, packets addressed to the mobile node's link-local 263 address MUST NOT be tunneled to the mobile node." 265 "Multicast packets addressed to a multicast address with 266 link-local scope [], to which the mobile node is subscribed, 267 MUST NOT be tunneled to the mobile node;" 269 which exposes, of course, the very nature of link-local addresses: 270 they are local, not going anywhere. 272 On another hand, OSPF for IPv6 [5] requires that: 274 "On all OSPF interfaces except virtual links, OSPF packets are 275 sent using the interface's associated link-local unicast address 276 as source." 278 Moreover, RIPng [16] requires that: (1) next hop addresses in 279 routing tables managed by RIPng be link-local and (2) a large part 280 of RIPng messages be originated and adressed to link-local 281 addresses: 283 "An address specified as a next hop must be a link-local 284 address." 286 or 288 "Response Messages: [...] the source of the datagram must be a 289 link-local address." 291 or 293 "Generating Response messages: [...] The IPv6 source address 294 must be a link-local address of the possible addresses of the 295 sending router's interface, except when replying to a unicast 296 Request Message from a port other than the RIPng port." 298 Overall, keeping in mind that Mobile IPv6 is not dealing with 299 link-local home addresses and that routing protocols and forwarding 300 process make substantial use of link-local addresses, the issue is 301 clearly how to make the routing protocols work together with Mobile 302 IPv6. Basic NEMO support specification should enable redirection of 303 traffic destined to MR's link-local addresses. 305 4.5 Mobile Router as a Mobile Host 307 There are several scenarios that involve an MR that needs to act as 308 a MH too, that is, send normal BUs and use existing Mobile IPv6. 309 Applications running on the MR should take advantage of MR's 310 session continuity and universal reachability at its home address. 311 For more example issues see section B. 313 4.6 Neighbour Discovery for MR's egress interface 315 Neighbour Discover on the MR's egress interface is particularly 316 delicate in that Neighbour Discovery should act differently when MR 317 is at home and when MR is in a foreign network. A simple example 318 is that when MR is at home, it has little reason to listen to RAs. 319 However, when MR is in a foreign network, receiving RAs is very 320 important in order to have a good working of Mobile IPv6. For more 321 example issues see section B. 323 4.7 Separation of routing and mobility for MR 325 The necessity of the distinction between mobility vs. routing 326 exchanges holds true irrespective to whether dynamic or static 327 routing is used. If static routing is used, then BR has routes 328 towards the mobile network through the MR, and MR has routes 329 towards the Internet through the BR. If dynamic routing is used, 330 then the MR and BR dynamically exchange routing information that is 331 manually configured in the routing configuration files of MR and of 332 BR, as well as routing information that is delivered by other 333 routers external to the home network (be it beyond the BR or beyond 334 the MR). The entities concerned with routing in the home network 335 are only BR and MR. This behaviour should continue when network 336 mobility is introduced, presumably by deploying an HA (but not 337 touching the BR). MR and HA should exchange only the information 338 related to mobility but not the information related to routing. 340 4.8 Prefix-based routing and host-based routing exceptions 342 Prefix-based hierarchical routing (where the mobile network link 343 has a prefix that is a subset of the home-network link) is the 344 preferred type of routing for IPv6. Practically though, it is 345 possible for the BR to have a routing table entry containing the 346 prefix of the mobile network, as well as a host-based entry that 347 points to a certain LFN also in the mobile network. Those two 348 entries might or might not have the same common sub-prefix. With a 349 MR at home, being a normal router, BR will know how to forward to 350 all hosts behind the MR as well as only to the specific LFN of the 351 host-based route. This behaviour should be maintained when the MR 352 is no longer at home and when it has a bidirectional tunnel MRHA. 354 4.9 IPv4 Issues 356 The mechanisms and issues described in this draft for IPv6 mobile 357 networks can be applied for IPv4 network mobility as well. RFC 358 3344 [21] provides important intuititve support for IPv4 network 359 mobility through the 'R' bit in Registration Requests/Replies. 360 Some solutions have already been successfully tested in [4] and 361 [14]. The support provided in RFC 3344 [21] as well as those 362 solutions keep the HA co-located with the BR. In a general case in 363 which the BR and HA are kept on separate machines (scenarios 9 to 364 16 in section A.2.3) the same issues as in IPv6 apply to the IPv4 365 case. 367 Additionally, in Mobile IPv4 there is a distinction between the MN 368 and FA functionality, and it is possible to have the FA separated 369 from the MN, whereas in IPv6 MN and FA are always co-located. This 370 gets us to the following additional cases: 372 -When the MR is in a visited network it can send BU's using a 373 co-located care-of address or a Foreing Agent care-of address 374 if an FA is available. In the latter case, two reverse 375 tunneling modes are possible: direct delivery style and 376 encapsulated delivery style [17]. 378 -The MR may be itself a FA for Leaf Mobile Nodes (LMNs), or the 379 mobile network may contain a FA for LMNs. 381 4.10 "Cross-over" tunnels 383 A rough definition: two MR-HA tunnels are "crossing over" each 384 other when the path between one tunnel's endpoints includes only 385 one of the other tunnel's endpoints. 387 Support of nested mobile networks is possible only when the path 388 from MR2 to MR1's HA does not go through MR1 (path considered when 389 both mobile routers are at home and no tunnels are in place). 391 An example of the dynamics of two MR-HA crossing tunnels is given 392 in section B.6. 394 5. Security Considerations 396 A detailed threat analysis is to be performed for a NEMO "Basic" 397 type of solution. But that's what the Charter says anyways. 399 One issue is related to when the MR runs a dynamic routing 400 protocol. In that case, MR is able to inform the routers in the 401 home domain about new routes (or "inject" routes in the home 402 domain). Considering that MR might be a small device, not locked 403 in a highly secured room, not a tamper-proof device, potentially 404 being stolen, then it is clear that the ability to introduce routes 405 in the home domain, and worse, propagating upper to backbones, is 406 inducing serious risks. 408 5.1 A tool: HA ingress filtering 410 Home Agents supporting mobile networks are normally able to perform 411 ingress filtering, so that only topologically correct packets leave 412 the HA. See section B.7 on how HA could do ingress filtering. 414 Acknowledgements 416 Authors of this document acknowledge the following WG members and 417 non-members for their remarks, improvements to this draft and 418 fruitful discussions: 420 Tim Leinumeller for many insightful remarks and implementation 421 aspects. 423 Mattias Petterson. 425 Vijay Devarapalli. 427 TJ Kniveton. 429 Pekka P„„kk÷nen. 431 Mooi Choo Chuah. 433 Erik Nordmark. 435 References 437 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 438 Levels", BCP 14, RFC 2119, March 1997 440 [2] Arkko, Jari, Devarapalli, Vijay, and Dupont, Francis, "Using 441 IPsec to Protect Mobile IPv6 Signaling between Mobile Nodes 442 and Home Agents", draft-ietf-mobileip-mipv6-ha-ipsec-03.txt, 443 IETF Internet Draft, February 2003. (Work in Progress). 445 [3] Baker, F. and Atkinson, R., "RIP-2 MD5 Authentication", RFC 446 2082, January 1997. 448 [4] Cisco authors, "Cisco Mobile Networks", whitepaper browsed 449 March 3rd, 2003 at 450 http://www.cisco.com/univercd/cc/td/doc/product/software/ 451 ios122/122newft/122t/122t4/ftmbrout.pdf 453 [5] Coltun, R., Ferguson, D. and Moy, J., "OSPF for IPv6", RFC 454 2740, December 1999. 456 [6] Conta, A. and Deering, S.,"Generic Packet Tunneling in IPv6 457 Specification", RFC 2473, December 1998. 459 [7] Crawford, M., "Router Renumbering for IPv6", RFC 2894, August 460 2000. 462 [8] Ernst, Thierry, Olivereau, Alexis, Bellier, Ludovic, 463 Castelluccia, Claude and Lach, Hong-Yon, "Mobile Networks 464 Support in Mobile IPv6", 465 draft-ernst-mobileip-v6-network-03.txt, IETF Internet Draft, 466 March 2002. (Work in Progress). 468 [9] Ernst, Thierry and Lach, Hong-Yon, "Network Mobility Support 469 Terminology", draft-ernst-nemo-terminology-01.txt, IETF 470 Internet Draft, November 2002. (Work in Progress). 472 [10] Harkins, D., Mankin, A., Narten, T., Nikander, P., Nordmark, 473 E., Patil, B. and Roberts, P., "Threat Models introduced by 474 Mobile IPv6 and Requirements for Security", 475 draft-ietf-mobileip-mipv6-scrty-reqts-02.txt, IETF Internet 476 Draft, November 2001. (Work in Progress). 478 [11] Hedrick, C., "Routing Information Protocol", RFC 1058, June 479 1998. 481 [12] Johnson, David B., Perkins, Charles E. and Arkko, Jari, 482 "Mobility Support in IPv6", draft-ietf-mobileip-ipv6-20.txt, 483 IETF Internet Draft, January 2003. (Work in Progress). 485 [13] Kniveton, Timothy J., Malinen, Jari T. and Devarapalli, Vijay, 486 "Mobile Router Tunneling Protocol", 487 draft-kniveton-mobrtr-03.txt, IETF Internet Draft, November 488 2003. (Work in Progress). 490 [14] Leung, K. and Shell, D. and Ivancic, W. D. and Stewart, 491 D. H. and Bell, T. L. and Kachmar, B. A., "Application of 492 Mobile-IP to Space and Aeronautical Networks", IEEE Proceedngs 493 of the Aerospace Conference, 2001. 495 [15] Malkin, G., "RIP Version 2, Carrying Additional Information", 496 RFC 1723, November 1994. 498 [16] Malkin, G., "RIPng for IPv6", RFC 2080, January 1997. 500 [17] Montenegro, G., ed., "Reverse Tunneling for Mobile IP, 501 revised", RFC 3024, January 2001. 503 [18] Moy, J., "OSPF Version 2", RFC 2328, April 1998. 505 [19] Narten, T., Nordmark, E. and Simpson, W., "Neighbour Discovery 506 for IP Version 6 (IPv6)", RFC 2461, December 1998. 508 [20] Perkins, C., "IP Encapsulation within IP", RFC 2003, October 509 1996. 511 [21] Perkins, C., ed., "IP Mobility Support for IPv4", RFC 3344, 512 August 2002. 514 [22] Wakikawa, R., Uehara, K., Mitsuya, K. and Ernst, T., "Basic 515 Network Mobility Support", draft-wakikawa-nemo-basic-00.txt, 516 IETF Internet Draft, February 2003. (Work in Progress). 518 Changes 519 October 2002: revision 00 submitted. 520 November 2002: revision 01: 521 -added discussion on multicast addresses with link-local scope. 522 -added Chairs' addresses. 523 -modified the abstract to better express the fact that /128s are 524 probably sufficient. 525 -added section on v4 issues, and Mobile IPv4 issues. 526 -added an empty IPR section. 527 March 2003: revision 02: 528 -major overhaul from revision 01: shorter, focused on main 529 issues, integrated some ml discussions, moved large "Motivation" 530 parts to appendices. 531 -added MH definition and used MH instead of MN when MR acts as an 532 MH. 533 -added more detailed acknowledgements. 534 -added "cross-over" tunnels discussion. 535 -added HA ingress filtering. 537 Appendix A: Motivation for Full Addresses in Binding Updates 539 An initial remark is that traffic coming from outside the home 540 link, or from other hosts on the home link, and directed to hosts 541 in the mobile network (or behind the mobile router) only need to go 542 through the L2 address of the mobile router (corresponding to its 543 L3 address). With Proxy ND [19], it is the HA that pretends to own 544 MR's L3 address by advertising new associations of the MR's L3 545 address to the its own L2 address, thus intercepting MR's home 546 traffic and forwarding it to the current CoA of the MR. 548 With this in mind, it can be stated that when the MR is in a 549 foreign network, traffic coming from hosts in the mobile network 550 and towards anywhere to the Internet, is first forwarded by the MR 551 through the reverse tunnel MRHA to the HA. Then HA decapsulates 552 and forwards to the address specified in the inner packet. 554 A.1 Description of a Home Network 556 When designing a NEMO solution with the MRHA tunnel, the first 557 steps are to carefully consider the actual behaviour of the home 558 network when the mobile network is at home, employing normal 559 routing. Then this behaviour should be maintained as much as 560 possible when the MR is not at home (e.g. MR should be able to send 561 redirects through the MRHA tunnel); reciprocically, the normal 562 behaviour of an FR at home should change when that FR is an MR and 563 is at home (e.g. when MR at home, the MRHA tunnel should be torn 564 down). When the MR is in a foreign network, its presence at home 565 is simulated by the HA (as in Mobile IPv6 for hosts). 567 Let us consider a simple case of a home network that supports 568 movement of one of its links. The home network is made up of a 569 home link and a mobile network link, separated by the Mobile 570 Router. The home network is connected to the Internet via the 571 Border Router, as presented in the figure: 572 ---- 573 | FN | 574 ---- 575 | ------- 576 home link -------------------| HA/BR |---> Internet 577 | ------- 578 ---- ----- 579 | MR | | LFN | 580 ---- ----- 581 | | 582 mobile link --------- 584 Current specification for Mobile IPv6 implies that the HA can be 585 either co-located with the BR, or it can act as a separate 586 one-interface machine (this is advantageous for deploying Mobile 587 IPv6 without changing BRs). For mobile networks, the latter mode 588 can be pictured like this: 590 ---- ---- 591 | FN | | HA | 592 ---- ---- 593 | | ---- 594 home link -------------------| BR |------> Internet 595 | ---- 596 ---- ----- 597 | MR | | LFN | 598 ---- ----- 599 | | 600 mobile network link --------- 602 It is assumed that routes outside the home link are managed by BR 603 and MR, either in a static manner (operator fills in routing 604 tables) or dynamic manner (application software partially manages 605 routing tables). Remark that even when the dynamic style is used, 606 it is still true that operator fills initial routing configuration 607 files, where she/he puts the image of the network as being what the 608 operator believes it to be. The dynamic behaviour of routing 609 protocols intervenes when certain links come down or up due to 610 failures, the operator view is no longer true, and the routers 611 manage to find alternative paths. Also, the dynamic behaviour 612 helps obtaining shortest paths over large networks, relying on 613 several local operator's views of smaller sized networks. Addition 614 of mobility should not change this. 616 If static routing is used instead of dynamic routing, then static 617 routes are added manually both on MR and on the BR. When 618 considering adding *static* routes in a *dynamic* manner for 619 prefixes shorter than /128 by Mobile IP, authors of this document 620 realize (in truth, hopefully) that Mobile IP starts using semantics 621 that are traditionally belonging to routing protocols. 623 A.2 Scenarios 625 For the sake of completetess, we first describe a simple "manual" 626 scenario for mobile networks based on the MRHA tunnel, that exposes 627 relative simplicity, that uses static routing and doesn't use 628 Mobile IP. 630 Then, adding the Mobile IP behaviour, we present detailed scenarios 631 of communication between an FN on the home link and an LFN on the 632 mobile network link and a CN on the Internet, when the mobile 633 network is at home and away from home in a visited network, and 634 when the HA is co-located with the BR and separated from the BR. 635 All in all, 16 simple scenarios are presented. 637 The scenarios where HA is co-located with BR (1 up to 8) expose 638 that there is no need for MR to communicate prefixes to its HA via 639 BUs. In a normal routing function, when the MR is at home, it 640 exchanges routing information with the BR (co-located with the HA) 641 and thus those prefixes are communicated by e.g. RIP or OSPF. When 642 the MR is not at home, this behaviour continues, but through the 643 MRHA tunnel. 645 The scenarios where HA and BR are separated (9 up to 16) expose 646 that HA needs an entry in its routing table in order to be capable 647 of forwarding packets to the MR (when it is not at home). 649 An additional scenario is then presented where MR at home is using 650 ICMP Redirect, a functionality that might be needed even when the 651 MR is not at home. 653 A.2.1 Manual Mobile Networks 655 Authors of this draft have experimented with "manual" mobile 656 networks in IPv4, where the addition of routes and tunnels on the 657 MR and on the BR are done manually, by operators talking on the 658 phone. 660 A home network was used that contains about 10 routers and about 12 661 subnets. That home network is connected to the Internet with a BR. 662 All routers have static routes among them. 664 Then, one slice of that home network (the mobile network) 665 containing one "MR", one normal router and 6 subnets, was 666 disconnected from home, and moved across the Atlantic. Once the 667 "MR" was connected on the other side, it was manually configured 668 with a new IPv4 address, mask and default route. Then a tunnel 669 interface and a route were manually set up on the MR, a tunnel 670 interface and a route were manually set up on the BR. All other 671 routes on all other routers where not touched. Mobile IP software 672 was not used. 674 The entire network (the home and the mobile network) looked, and 675 acted, as if the mobile slice were at home. During this, several 676 applications were tested between hosts in the mobile network, hosts 677 in the home network and hosts on the Internet (incidentally, one of 678 the applications was relying on Mobile IPv4 for hosts, but in no 679 relation with the mobile network moving). 681 Again, this "manual" mobile networks scenario was not using any 682 dynamic routing protocol, and the tunnel was not supporting any 683 form of broadcast of multicast. 685 A.2.2 Scenarios with Co-located HA and BR 687 1. FN sends packet to LFN, mobile network home, HA/BR colocated 688 ---- 689 | FN | 690 ---- 691 | ------- 692 home link -------------------| HA/BR |---> Internet 693 | ------- 694 ---- ----- 695 | MR | | LFN | 696 ---- ----- 697 | | 698 mobile link --------- 700 -FN scans its routing table for LFN's address, and finds default 701 route towards BR. 702 -FN sends NS for L2 address of BR. 703 -BR replies NA. 704 -FN sends packet to BR. 705 -HA scans its BC to find out whether MR is at home; BR scans its 706 routing table for LFN's address, and finds route through MR; 707 -BR sends NS for MR. 708 -MR replies NA with its L2 address. 709 -BR forwards packet to MR and sends ICMP Redirect to FN such that 710 subsequent packets from FN to LFN go straight through MR and not 711 through BR. 712 -MR forwards packet to FN. 714 The sensitive issue exposed here is the way in which initially the 715 packet travels from FN to BR to MR, the dynamic addition of an 716 entry in the routing table of the FN (even if FN doesn't run a 717 routing protocol) and that subsequent packets will not go through 718 BR, but from FN to MR to LFN. 720 2. FN sends packet to LFN, mobile network visits, HA/BR colocated 721 ---- / 722 | FN | / 723 ---- ----------/ 724 | ------- | | 725 ----------------| HA/BR |---| Internet | 726 home link ------- | | 727 ----------\ 728 \ 729 \ ---- Visited link 730 --| AR |------ 731 ---- | 732 | 733 ---- ----- 734 | MR | | LFN | 735 ---- ----- 736 | | 737 --------- 738 mobile net 740 -FN scans its routing table for LFN's address, and finds default 741 route towards BR. 742 -FN sends NS for L2 address of BR. 743 -BR replies NA. 744 -FN sends packet to BR. 745 -BR scans its routing table for LFN's address, and finds route 746 through MR; 747 -BR (being an HA) scans its BC and its routing table and finds it 748 needs to encapsulate this packet towards MR's CoA. 749 -BR encapsulates through the MRHA tunnel to MR's CoA. 750 -MR decapsulates and forwards to LFN. 752 3. LFN sends packet to FN, mobile network home, HA/BR colocated 753 ---- 754 | FN | 755 ---- 756 | ------- 757 home link -------------------| HA/BR |---> Internet 758 | ------- 759 ---- ----- 760 | MR | | LFN | 761 ---- ----- 762 | | 763 mobile link --------- 765 -LFN scans its routing table for FN's address, and finds default 766 route towards MR. 767 -LFN sends NS for L2 address of MR. 768 -MR replies NA. 769 -LFN sends packet to MR. 770 -MR scans its routing table for LFN's address, and finds route 771 'on-link'; 772 -MR sends NS for FN. 773 -FN replies NA with its L2 address. 774 -MR forwards packet to FN. 776 4. LFN sends packet to FN, mobile network visits, HA/BR colocated 777 ---- / 778 | FN | / 779 ---- ----------/ 780 | ------- | | 781 ----------------| HA/BR |---| Internet | 782 home link ------- | | 783 ----------\ 784 \ 785 \ ---- Visited link 786 --| AR |------ 787 ---- | 788 | 789 ---- ----- 790 | MR | | LFN | 791 ---- ----- 792 | | 793 --------- 794 mobile net 796 -LFN scans its routing table for FN's address, and finds default 797 route towards MR. 798 -LFN sends NS for L2 address of MR. 799 -MR replies NA. 800 -LFN sends packet to MR. 801 -MR encapsulates this packet through the MRHA tunnel and sends to 802 HA. 803 -HA receives this packet and decapsulates. 804 -HA scans its routing table for FN's address, and finds route 805 'on-link'; 806 -HA sends NS for FN. 807 -FN replies NA with its L2 address. 809 -HA forwards packet to FN (on behalf of the MR). 811 5. CN sends packet to LFN, mobile network home, HA/BR co-located 812 ---- CN link 813 --| BR1|------ 814 / ---- | 815 / | 816 ----------/ ---- 817 ------- | | | CN | 818 ----------------| HA/BR |---| Internet | ---- 819 | home link ------- | | 820 ---- ----- ----------\ 821 | MR | | LFN | \ 822 ---- ----- \ 823 | | 824 --------- 825 mobile net link 827 -BR receives packet from CN towards LFN. 828 -HA scans its BC to see whether MR is at home; BR scans its routing 829 table and finds dest through MR. 830 -BR sends NS for L2 address of MR and MR replies NA. 831 -BR forwards packet to MR. 832 -MR forwards packet to LFN. 834 6. CN sends packet to LFN, mobile network visits, HA/BR colocated 836 ---- CN link 837 --| BR1|------ 838 / ---- | 839 / | 840 ----------/ ---- 841 ------- | | | CN | 842 ---| HA/BR |---| Internet | ---- 843 ------- | | 844 ----------\ 845 \ 846 \ ---- Visited link 847 --| AR |------ 848 ---- | 849 | 850 ---- ----- 851 | MR | | LFN | 852 ---- ----- 853 | | 854 --------- 855 mobile net 856 -BR receives packet from CN towards LFN. 857 -BR scans its routing table and finds dest through MR. 858 -BR scans its routing table and its BC and realizes it needs to 859 send this through the MRHA tunnel. 860 -BR sends the packet through the MRHA tunnel to MR. 861 -MR decapsulates and forwards to LFN. 863 (this is sometimes referred to as triangular routing, since the 864 packet from CN to LFN travels artificially through BR) 866 7. LFN sends packet to CN, mobile network home, HA/BR colocated 868 ---- CN link 869 --| BR1|------ 870 / ---- | 871 / | 872 ----------/ ---- 873 ------- | | | CN | 874 ----------------| HA/BR |---| Internet | ---- 875 | home link ------- | | 876 ---- ----- ----------\ 877 | MR | | LFN | \ 878 ---- ----- \ 879 | | 880 --------- 881 mobile net link 883 -MR receives packet from LFN towards CN. 884 -MR scans its routing table to and finds dest through BR. 885 -BR forwards packet to Internet towards CN. 886 -BR1 forwards packet to CN. 888 8. LFN sends packet to CN, mobile network visits, HA/BR colocated 889 ---- CN link 890 --| BR1|------ 891 / ---- | 892 / | 893 ----------/ ---- 894 ------- | | | CN | 895 ---| HA/BR |---| Internet | ---- 896 ------- | | 897 ----------\ 898 \ 899 \ ---- Visited link 900 --| AR |------ 901 ---- | 902 | 903 ---- ----- 904 | MR | | LFN | 905 ---- ----- 906 | | 907 --------- 908 mobile net 909 -MR receives packet from LFN towards CN. 910 -MR scans its tables and finds it needs to send it through the MRHA 911 tunnel. 912 -BR receives this packet, decapsulates and forwards to Internet. 913 -BR1 forwards this packet to CN. 915 (this is sometimes referred to as triangular routing, since the 916 packet from LFN to CN travels artificially through BR) 918 A.2.3 Scenarios with HA and BR Separated 920 9. FN sends packet to LFN, mobile network home, HA separated BR 921 ---- ---- 922 | FN | | HA | 923 ---- ---- 924 | | ---- 925 home link -------------------| BR |------> Internet 926 | ---- 927 ---- ----- 928 | MR | | LFN | 929 ---- ----- 930 | | 931 mobile network link --------- 933 -FN scans its routing table for LFN's address, and finds default 934 route towards BR. 935 -FN sends NS for L2 address of BR. 936 -BR replies NA. 937 -FN sends packet to BR. 938 -BR scans its routing table for LFN's address, and finds route 939 through MR; 940 -BR sends NS for MR. 941 -MR replies NA with its L2 address. 942 -BR forwards packet to MR and sends ICMP Redirect to FN such that 943 subsequent packets from FN to LFN go straight through MR and not 944 through BR. 945 -MR forwards packet to FN. 947 10. FN sends packet to LFN, mobile network visits, HA separated BR 949 ---- ---- / 950 | FN | | HA | / 951 ---- ---- ----------/ 952 | | ---- | | 953 -------------------| BR |---| Internet | 954 home link ---- | | 955 ----------\ 956 \ 957 \ ---- Visited link 958 --| AR |------ 959 ---- | 960 | 961 ---- ----- 962 | MR | | LFN | 963 ---- ----- 964 | | 965 --------- 966 mobile net 968 -FN scans its routing table for LFN's address, and finds default 969 route towards BR. 970 -FN sends NS for L2 address of BR. 971 -BR replies NA. 972 -FN sends packet to BR. 973 -BR scans its routing table for LFN's address, and finds route 974 through MR; 975 -BR sends NS for MR. 976 -HA replies NA with its L2 address (on behalf of MR). 977 -BR forwards packet to HA and sends ICMP Redirect to FN such that 978 subsequent packets from FN to LFN go straight through MR and not 979 through BR. BR also sends ICMP Redirect to HA, such that HA knows 980 a route through MR. The logic of this last ICMP Redirect is 981 described in section 6.1. 982 -HA scans its routing table for LFN's address, and finds through MR; 983 -HA scans binding cache and finds 'through MRHA tunnel'; 984 -HA encapsulates and sends packet to MR. 985 -MR decapsulates and forwards to LFN. 987 The problem in the above case is how to inform the HA about the 988 route towards MR. When MR at home, and HA being a host, normally 989 HA doesn't have a route towards MR. 991 11. LFN sends packet to FN, mobile network home, HA separated BR 992 ---- ---- 993 | FN | | HA | 994 ---- ---- 995 | | ---- 996 home link -------------------| BR |------> Internet 997 | ---- 998 ---- ----- 999 | MR | | LFN | 1000 ---- ----- 1001 | | 1002 mobile network link --------- 1004 -LFN scans its routing table for FN's address, and finds default 1005 route towards MR. 1006 -LFN sends NS for L2 address of MR. 1007 -MR replies NA. 1008 -LFN sends packet to MR. 1009 -MR scans its routing table for LFN's address, and finds route 1010 'on-link'; 1011 -MR sends NS for FN. 1012 -FN replies NA with its L2 address. 1013 -MR forwards packet to FN. 1015 12. LFN sends packet to FN, mobile network visits, HA separated BR 1016 ---- ---- / 1017 | FN | | HA | / 1018 ---- ---- ----------/ 1019 | | ---- | | 1020 -------------------| BR |---| Internet | 1021 home link ---- | | 1022 ----------\ 1023 \ 1024 \ ---- Visited link 1025 --| AR |------ 1026 ---- | 1027 | 1028 ---- ----- 1029 | MR | | LFN | 1030 ---- ----- 1031 | | 1032 --------- 1033 mobile net 1035 -LFN scans its routing table for FN's address, and finds default 1036 route towards MR. 1037 -LFN sends NS for L2 address of MR. MR replies NA. 1038 -LFN sends packet to MR. 1039 -MR encapsulates this packet through the MRHA tunnel and sends to 1040 HA. 1041 -HA receives this packet and decapsulates. 1042 -HA scans its routing table for FN's address, and finds route 1043 'on-link'; 1044 -HA sends NS for FN. FN replies NA with its L2 address. 1045 -HA forwards packet to FN (on behalf of the MR). 1047 13. CN sends packet to LFN, mobile network home, HA separated BR 1049 ---- CN link 1050 --| BR1|------ 1051 ---- / ---- | 1052 | HA | / | 1053 ---- ----------/ ---- 1054 | ---- | | | CN | 1055 -----------------| BR |---| Internet | ---- 1056 | home link ---- | | 1057 ---- ----- ----------\ 1058 | MR | | LFN | \ 1059 ---- ----- \ 1060 | | 1061 --------- 1062 mobile net link 1064 -BR receives packet from CN towards LFN. 1065 -BR scans its routing table to and finds dest through MR. 1066 -BR sends NS for L2 address of MR. 1067 -MR replies NA. 1068 -BR forwards packet to MR. 1069 -MR forwards packet to LFN. 1071 14. CN sends packet to LFN, mobile network visits, HA separated BR 1073 ---- CN link 1074 --| BR1|------ 1075 ---- / ---- | 1076 | HA | / | 1077 ---- ----------/ ---- 1078 | ---- | | | CN | 1079 ---------| BR |---| Internet | ---- 1080 ---- | | 1081 ----------\ 1082 \ 1083 \ ---- Visited link 1084 --| AR |------ 1085 ---- | 1086 | 1087 ---- ----- 1088 | MR | | LFN | 1089 ---- ----- 1090 | | 1091 --------- 1092 mobile net 1093 -BR receives packet from CN towards LFN. 1094 -BR scans its routing table to and finds dest through MR. 1095 -BR sends NS for L2 address of MR. HA replies NA on behalf of MR. 1096 -BR sends Redirect to HA informing it about a route towards MR. 1097 -Simultaneously with previous packet, BR forwards packet to HA. 1098 -HA scans its routing table and finds an entry to MR (added as a 1099 result to ICMP redirect), it also has a BC entry for MR, so it 1100 sends the packet through the MRHA tunnel. 1102 The problem in the above case is how to inform the HA about the 1103 route towards MR. When MR at home, and HA being a host, normally 1104 HA doesn't have a route towards MR. 1106 15. LFN sends packet to CN, mobile network home, HA separated BR 1108 ---- CN link 1109 --| BR1|------ 1110 ---- / ---- | 1111 | HA | / | 1112 ---- ----------/ ---- 1113 | ---- | | | CN | 1114 -------------------| BR |---| Internet | ---- 1115 | home link ---- | | 1116 ---- ----- ----------\ 1117 | MR | | LFN | \ 1118 ---- ----- \ 1119 | | 1120 --------- 1121 mobile net link 1123 -MR receives packet from LFN towards CN. 1124 -MR scans its routing table and finds dest through BR. 1125 -BR sends packet to CN 1126 16. LFN sends packet to CN, mobile network visits, HA separated BR 1127 ---- CN link 1128 --| BR1|------ 1129 ---- / ---- | 1130 | HA | / | 1131 ---- ----------/ ---- 1132 | ---- | | | CN | 1133 ----------| BR |---| Internet | ---- 1134 ---- | | 1135 ----------\ 1136 \ 1137 \ ---- Visited link 1138 --| AR |------ 1139 ---- | 1140 | 1141 ---- ----- 1142 | MR | | LFN | 1143 ---- ----- 1144 | | 1145 --------- 1146 mobile net 1147 -MR receives packet from LFN towards CN. 1148 -MR encapsulates this packet through the MRHA tunnel. 1149 -HA receives this packet, decapsulates and sends to CN. 1151 A.3 MR Redirects to BR 1153 Also, consider the scenario where the FN has a default route 1154 towards the MR instead of the BR, and sending packets to a CN on 1155 the Internet. This might very well happen when the MR is at home 1156 and sending RAs, in addition to the RAs sent by the BR. FN might 1157 configure a default route through the MR instead of the BR. If MR 1158 is at home, MR will redirect the FN towards the BR. So, even if 1159 this looks like a wrong configuration on the FN (its default route 1160 should point to BR and not MR), packets will still travel correctly 1161 when MR is at home. This should be maintained when the MR is not 1162 at home. There are two possibilities: either the HA (replacing the 1163 MR) redirects the FN towards the BR, or it is the MR itself that 1164 sends the respective ICMP redirect message to the FN (through the 1165 MRHA tunnel). The first case supposes that HA maintains a routing 1166 table, which contains routes towards the mobile network. This is 1167 less desirable if the HA is not co-located with BR, and where we 1168 prefer not to have routing interactions with the HA. The latter 1169 case is more plausible, keeping the default routing behaviour to 1170 the MR. 1172 A.4 Informing the HA about the Route to MR 1174 In certain scenarios presented previously, with the HA dissociated 1175 from the BR and the MR in the visited network, there is a need for 1176 the HA to maintain in its routing table an entry towards the MR. A 1177 scenario where packets from CN towards LFN are looping between BR 1178 and HA has been described in detail in section 3.2.4 of [8]. 1179 Several solutions exist to avoid this looping, described below. 1181 A.4.1 ICMP Redirect from BR to HA 1183 One alternative for avoiding the loop problem is by using ICMP 1184 Redirects [19] sent by BR to HA in order to communicate to HA the 1185 route it misses towards the MR. ICMP Redirects are deployed and 1186 used in existing networks. The classic behaviour of ICMP Redirects 1187 is presented in scenario 1. Scenarios 10 and 14 with 1188 MR-not-at-home and BR dissociated from HA, present the fact that 1189 classic ICMP Redirects are not triggered normally and thus 1190 modifications are needed. 1192 In addition to the normal behaviour with ICMP Redirects, described 1193 in [19], it could be modified according to the following. The 1194 decision by BR to send ICMP Redirect towards HA can be taken in at 1195 least three ways: 1197 -allow a number of iterations of a packet looping between HA and 1198 BR and after this fixed number decide to send the Redirect to HA 1199 such as the looping stops. This modifies the normal behaviour 1200 of BR. 1202 -another possibility is for BR to react at the moment it receives 1203 the proxy NA from HA (on behalf of the MR), compare to the 1204 current entry it has in the Neighbour Cache for MR, and then 1205 decide that, because MR has moved away, send Redirect to HA to 1206 inform HA about the route to MR. This is the route (or set of 1207 routes) normally maintained by the BR with the MR, doesn't 1208 contain any form of the new position (CoA) of the MR. This 1209 route, or set of routes (in which case a set of Redirects are 1210 sent), is copied from BR's routing table. All routes that have 1211 destination the MR's home address need to be communicated to HA 1212 with ICMP Redirects. This modifies the normal behaviour of BR. 1214 -yet another possibility is to consider modifications on HA (from 1215 vanilla Mobile IPv6), but don't touch BR, such that HA generates 1216 a new packet, thus obtaining a classic ICMP Redirect from BR. 1218 When the HA receives a packet that is not for itself, it 1219 encapsulates it with an IP-in-IP tunnel, having the src address 1220 its own address and the destination address copied from the dst 1221 address of the original packet. Then try to route this packet 1222 and find the default route towards BR. Then BR sends a normal 1223 ICMP Redirect informing HA there is a better route for this 1224 packet towards MR. Thus HA acquires the MR route dynamically. 1225 The packet will be passed on by BR to HA again, and further 1226 details are needed here. Remark that this is equivalent to one 1227 iteration of the loop (a particular case of the fixed iterations 1228 loop mentioned previously). 1230 A.4.2 Static Route Method 1232 This is proposed by [4] and [13], where a route is statically 1233 introduced in the HA upon receiption of a Binding Update from 1234 MR. This route for MR's prefix may point towards MR's home address 1235 (next hop), towards a specific tunnel to MR's home address(output 1236 interface), or towards a specific tunnel to MR's care-of address 1237 (output interface). 1239 The first approach proposed in [4] suggests to configure a new 1240 static tunnel on the MR's HA towards MR_HoA. This static tunnel, 1241 that we call here MR_HoA_tunnel, is to be used as output interface 1242 of a new static entry added in the routing table of HA for MR's 1243 prefix: MR prefix -> MR_HoA_tunnel. Upon reception of a data 1244 packet from CN addressed to a LFN, MR's HA will consult its routing 1245 table and find a match for that packet for this static route since 1246 LFN address matches MR's prefix. As a results it will encapsulate 1247 the packet with an additional header that will have MR's HA as 1248 source address and MR_HoA as destination address. In order to 1249 forward this packet, now addressed to MR's Home Address, the MR 1250 will first consult its binding cache and discover MR's Care-of 1251 address. It will thus send the packet through the MRHA tunnel 1252 towards MR's current location. It is worth mentionning that this 1253 approach introduces a double encapsulation of an incoming packet to 1254 be forwarded to the MR: the first is due to the MR_HoA_tunnel, the 1255 second to the MRHA tunnel. 1257 The second approach proposed in [13] suggests a similar method but 1258 avoids the overhead introduced by the two tunnels. It consists in 1259 configuring a static route in MR's HA routing table for MR's prefix 1260 towards MR's Home Address: MR prefix -> MR_HoA. Upon reception of 1261 a data packet from CN addressed to a LFN, MR's HA will consult its 1262 routing table and, again, find a match for that packet for this 1263 static route since LFN address matches MR's prefix. This indicates 1264 the MR's HA that the packet should be routed towards MR_HoA. From 1265 its binding cache it discovers MR's CoA and as a consequence 1266 forwards the incoming packet from the CN directly through the MRHA 1267 tunnel. This approach reduces the overhead of the MR_HoA_tunnel but 1268 requires a suitable coordination of the routing table and binding 1269 cache on the HA. 1271 A third possible approach is similar to the previous one but 1272 directly uses the MR's care-of address as the tunnel termination 1273 point instead of MR's home address. As such the new static entry 1274 added in the routing table of HA for MR's prefix is then MR prefix 1275 -> MRHA_tunnel. 1277 Analyzed from the perspective where HA is separated from BR, and 1278 where MR doesn't normally maintain routes with HA, then this 1279 addition might seem superfluous. Consider a situation where MR and 1280 BR maintain routing information and where that manual route is 1281 added on HA. When the MR is not at home, consider that 1282 administrator decides to add a new fixed subnet at home, with its 1283 own router neighbouring with BR on the home link. Consider the new 1284 subnet's prefix being a longer prefix derived from the prefix 1285 assigned to the MR's subnet. This is perfectly feasible by 1286 changing configurations on the MR and BR. That can work perfectly 1287 even if MR is not at home. But if HA doesn't participate in this 1288 exchange (which is the case if HA separated from BR) then the 1289 manual route added previously in the HA is no longer valid. Thus, 1290 a potential issue. 1292 Using PSBUs as proposed in [8] and [13] has many side-effects not 1293 clearly considered. When the mobile network is assigned several 1294 prefixes instead of one, then it is not clear whether several BUs 1295 are being sent or only one with several prefixes inside. Remark 1296 that in the vanilla Mobile IPv6 case, only one CoA can be sent with 1297 a BU (the alternative CoA is only an alternative not a substitute). 1299 A.4.3 Dynamic Route Method 1301 It is possible for the HA, being either separated or co-located 1302 with the BR, to run a specific routing protocol, participating in 1303 the routing interactions between BR and all other neighbouring 1304 routers on the home link. Thus, the HA always has the necessary 1305 route it needs to join the MR's network. 1307 If the HA is a one-interface machine, and separated from the BR, it 1308 seems that it maintains information that is not always necessary to 1309 its well working as a HA. For example, it will maintain routes to 1310 all neighbouring routers, be it fixed or mobile. The routes to the 1311 fixed neighbouring routers are not necessary for its working as a 1312 host, since it suffices to only have a default route towards a BR, 1313 that will normally dynamically Redirect it towards the other fixed 1314 routers. Moreover, if HA runs a dynamic routing protocol, its 1315 route updates will never be taken into account by other routers, 1316 since they will always be one hop further than the routes already 1317 known by them. Thus it might be possible to have the HA as a 1318 silent routing, only receiving route updates from the neighbouring 1319 routers, but never sending route updates, since it does not have a 1320 network behind it (it is a "host") whose reachability it needs to 1321 advertise. 1323 RIP [11] supports having a silent host that only listens to update 1324 messages, but does not advertise new routes. With OSPF [18] the 1325 "listening only" requirement is complicated by the fact that the HA 1326 would needs to participate in OSPF's HELLO protocol. 1328 The advantage of using this solution is that it does not require 1329 additional changes to Mobile IPv6, and PSBUs are not needed. The 1330 disadvantage is that if the MR does not run a routing protocol then 1331 we still need some way of telling the HA the routes to the MNPs. 1333 Appendix B: Examples and Other Issues 1335 B.1 Example of issue for Mobile Router as Mobile Host 1337 If the MR is at home and it has an address configured on the moving 1338 interface other than a link-local address, then the MR can act as 1339 an MH too, and send normal Mobile IPv6 BUs, binding that Home 1340 Address to a newly configured CoA; thus allowing the MR to be an MH 1341 for itself only, ignoring the LFNs. If the MR at home doesn't have 1342 other addresses than link-local on the mobile interface then the MR 1343 can not send normal Mobile IPv6 BUs and can not be an MH. It can 1344 however be an MR for the hosts on the mobile network. 1346 B.2 Multicast Subscriptions of the MR 1347 When the MR is at home, it normally joins certain multicast groups 1348 related to routing (e.g. all-routers multicast group with site 1349 scope). This is assumed by dynamic routing protocols, or by 1350 renumbering mechanisms. When the MR is no longer at home, its 1351 multicast subscription should continue as if it were at home. This 1352 can be achieved by "home subscription" techniques considered in 1353 relation with Mobile IPv6. 1355 B.3 Examples of issues for Neighbour Discovery for MR 1357 When MR is at home and sends RA towards the home link, it should 1358 not advertise itself as being capable of being a default router 1359 (Router Lifetime should be 0). 1361 When the MR is visiting, it should not respond to RSs sent on the 1362 visited link and it should not send RAs on the visited link. 1364 When the MR is at home, it doesn't normally use any information 1365 received from RAs sent by a neighbouring router, i.e. the BR. It 1366 has a link-local address and if it has a larger scope address 1367 configured on an interface, then that is normally done manually. 1368 Actually, routers are usually prohibited from using information 1369 received in RAs more than for logging and synchronization purposes. 1370 When the MR is in a foreign network, it needs a way to configure a 1371 Care-of Address. In the hosts case this is done by stateless or 1372 stateful autoconf. In the MR case, the stateful is possible, while 1373 the stateless is normally prohibited. A good way for address 1374 autococnfiguration for the MR should be identified, be it DHCP, or 1375 modified RAs, or modified router's behaviour to accept RAs. 1377 Assume the MR is at home and a non-link-local (site- or global) 1378 home address is configured on the interface connecting to the home 1379 link (supposedly the same interface that will change CoAs when 1380 visiting). The MR-at-home will do periodic NAs for this home 1381 address; this behaviour should stop when MR is visiting. This 1382 modified behaviour is already taken into consideration by Mobile 1383 IPv6 MN. In the particular MR case, most ND operations of MR are 1384 delegated to the HA, and such most entries of Neighbour Cache, 1385 Destination Cache that are related to the home link will disappear. 1386 New entries that are relevant in the foreign network will populate 1387 those tables. When coming back home, all ND entries should be 1388 replaced back with the entries related to the home network. 1390 Another specific case in point is the default route. As already 1391 presented with the router behaviour with respect to RAs, a default 1392 route is not normally configured by MR from a received RA. When 1393 the MR is in a foreign network, it should have a default route that 1394 points to its BR (but through the MRHA tunnel) and another 1395 non-tunnelled default route towards the current AR. Moreover, all 1396 MR's routing table entries that pointed to BR when the MR was at 1397 home, should still continue to point to BR (through the MRHA 1398 tunnel). The same is true for all routing table entries of the BR. 1400 B.4 Router Renumbering 1401 Router Renumbering for IPv6 [7] is a technique where routers of a 1402 home network are instructed to change the prefixes they advertise. 1403 In the context here, it should be possible for the MR to be 1404 re-numbered when it is at home as well as when it is visiting. 1406 The renumbering mechanisms provided by Mobile IPv6 (mobile prefix 1407 solicitations and advertisements) are not relevant for changing the 1408 prefixes advertised by the MR towards the mobile network; but these 1409 mechanisms should still be used for MR when MR is acting as an MH. 1410 In order for router renumbering to work for MR when acting as MR, 1411 the MR should at least be able to maintain its multicast 1412 subscription to all-routers group valid at home. 1414 B.5 Example of disconnected operation issue 1416 An example of an important inconvenient of using exclusively 1417 vanilla Mobile IPv6 with MRHA is when nesting: consider two mobile 1418 networks, each MR having its own HA in different domains. The 1419 first MR attaches to an AR and the second MR attaches under the 1420 first mobile network. In this case, two LFNs situated one on the 1421 first net and the second on the second net are capable to 1422 communicate with each other, but communication goes through both 1423 first MR's HA and through second's. In practice this exposes a 1424 paradox where if first MR loses connection to AR, then even if the 1425 two nets stay attached, the two LFNs can not communicate. 1427 B.6 Example for the "cross-over" tunnels issue 1429 Consider the following example, where both MRs are at home and where 1430 MR1's mobile network contains HA2. MR1 belongs to HA1 and MR2 1431 belongs to HA2. 1432 ----------/ 1433 ------- | | 1434 -----------------------| HA1/BR|---| Internet | 1435 | ------- | | 1436 | ---------- 1437 ----- ----- 1438 | MR1 | | HA2 | 1439 ----- ----- 1440 | | 1441 ------------ 1442 | 1443 ----- ----- 1444 | MR2 | | LFN | 1445 ----- ----- 1446 | | 1447 ------------ 1449 In the next step, consider that the MR2's mobile network goes visit 1450 AR, like in the figure below: 1452 ----------/ 1453 ------- | | 1454 ---------------| HA1/BR|---| Internet | 1455 | ------- | | 1456 ----- ----- ----------\ 1457 | MR1 | | HA2 | \ 1458 ----- ----- ----- 1459 | | | AR | 1460 ------------ ----- 1461 | 1462 ----- ----- 1463 | MR2 | | LFN | 1464 ----- ----- 1465 | | 1466 ------------ 1468 The tunnel setup procedure of this movement is between MR2 and HA2. 1469 This tunnel can be easily setup; consider now the next movement: 1471 ----------/ 1472 ------- | | 1473 | HA1/BR|---| Internet | 1474 ------- | | 1475 ----------\ 1476 \ 1477 ----- 1478 | AR | 1479 ----- 1480 | 1481 ----- ----- 1482 | MR2 | | LFN | 1483 ----- ----- 1484 | | 1485 ------------ 1486 | 1487 ----- ----- 1488 | MR1 | | HA2 | 1489 ----- ----- 1490 | | 1491 ------------ 1493 After this movement, MR1 tries to setup its bidirectional tunnel 1494 with HA1, by sending a BU to HA1. This BU is encapsulated by MR2 1495 towards HA2. However, HA2 is no longer at home (having moved 1496 together with MR1); thus the tunnel between MR1 and HA1 can not be 1497 set up, because if it were set up, it would have "crossed over" the 1498 tunnel between MR2 and HA2. If one were to draw the two tunnels in 1499 the above picture, a tunnel would be between MR2 and HA2 and the 1500 other between MR1 and HA1. The path MR1-HA1 includes only the MR2 1501 endpoint of the tunnel MR2-HA2. 1503 B.7 Example of use of HA ingress filtering 1505 HA should verify that packets it receives from the MRHA tunnel have 1506 a source address that matches what's in HA's routing table. HA 1507 should have a route for the mobile prefix pointing into the MRHA 1508 tunnel, and the LFN should have use a source address derived from 1509 that prefix when sending its packets. Other packets will be 1510 dropped. 1512 Appendix C: A Digression 1514 Two types of approaches have been distinguished in designing a 1515 network mobility support with Mobile IPv6 and the bidirectional 1516 tunnel. 1518 Clean-slate Mobile IP-centric approach 1520 In this approach, it is assumed that a home network is in fact a 1521 new 1-link network. This home network connects to the Internet 1522 with one or more BRs. The BRs have HA functionality with Mobile IP 1523 for hosts. There are no other routers or hosts in the home network 1524 than the BRs and the MRs. MRs are seldom at home. MRs and BRs 1525 would presumably have little need to run a dynamic routing 1526 protocol. Most, if not all, routing information exhanges happen 1527 with Mobile IP BUs. 1529 Nodes in the mobile networks communicate with CNs. Those CNs are 1530 anywhere in the Internet, but not in the home network (there's no 1531 node in the home network than BRs and/or other MRs). 1533 Evolutionary approach 1535 In this type of approach, it is assumed that a home network is 1536 already deployed. The home network has several routers that run 1537 dynamic routing protocols (non-Mobile IP) to maintain connectivity 1538 between various endpoints. The home network is connected to the 1539 Internet with one or more BRs. 1541 From this, it is possible to "mobilize" some slices (or chunks of 1542 this network), maintaining session continuity and reachability at a 1543 permanent home address for fixed nodes of that slice. Consider 1544 that the slice that needs to be physically disconnected from the 1545 home network uses a router (called "MR") that connects the slice to 1546 the home network. A minimal deployment effort could be the 1547 following: (1) modify software on MR and (2) place a new box with 1548 new software on the link where MR was connecting the slice to the 1549 home network (this entity called "HA"). MR and the slice move away 1550 and HA stays in place. 1552 Intellectual Property Rights Considerations 1554 Consult Motorola on IPR (authors believe no IPR here, but depends 1555 who asks; the complete and authoritative answers can be found from 1556 IPD or Public Relations of Motorola, corelated with IPD of ECRL). 1558 Chairs' Addresses 1560 Thierry Ernst, Timothy J. Kniveton 1561 French National Institute for Communication Systems Lab 1562 Research in Computer Science and Nokia Research Center 1563 Control 313 Fairchild Drive 1564 Visiting Researcher at WIDE Mountain View, California 94043 1565 Project USA 1566 Jun Murai lab. Faculty of Phone: +1 650 625-2025 1567 Environmental Information, EMail: timothy.kniveton@nokia.com 1568 Keio University. Fax: +1 650 625-2502 1569 5322 Endo, Fujisawa-shi, Kanagawa 1570 252-8520, Japan. 1571 Phone : +81-466-49-1100 1572 Fax : +81-466-49-1395 1573 E-mail: ernst@sfc.wide.ad.jp 1574 Web: 1575 http://www.sfc.wide.ad.jp/~ernst/ 1577 Authors' Addresses 1579 Alexandru Petrescu Miguel Catalina-Gallego 1580 Motorola Labs Motorola Labs 1581 Espace Technologique de St Aubin Espace Technologique de St Aubin 1582 Gif-sur-Yvette 91193 Gif-sur-Yvette 91193 1583 France France 1584 Phone: +33 1 69354827 Phone: +33 1 69352541 1585 Alexandru.Petrescu@motorola.com Miguel.Catalina@motorola.com 1587 Christophe Janneteau Hong-Yon Lach 1588 Motorola Labs Motorola Labs 1589 Espace Technologique de St Aubin Espace Technologique de St Aubin 1590 Gif-sur-Yvette 91193 Gif-sur-Yvette 91193 1591 France France 1592 Phone: +33 1 69352548 Phone: +33 1 69352536 1593 Christophe.Janneteau@motorola.com Hong-Yon.Lach@motorola.com 1595 Alexis Olivereau 1596 Motorola Labs 1597 Espace Technologique de St Aubin 1598 Gif-sur-Yvette 91193 1599 France 1600 Phone: +33 1 69352516 1601 Alexis@motorola.com 1603 Copyright (C) The Internet Society (2002). 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