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The Mobile Router, after connecting to the access link, SHOULD not send any routing protocol updates on the egress interface because the routing information from the Mobile Router might adversely affect IPv6 route aggregation on the Home Network. However, the Mobile Router must register its binding as if it was accessing a foreign link. -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (April 1, 2004) is 7331 days in the past. Is this intentional? 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'3') (Obsoleted by RFC 4862) ** Obsolete normative reference: RFC 3513 (ref. '4') (Obsoleted by RFC 4291) == Outdated reference: A later version (-03) exists of draft-ietf-nemo-basic-support-02 == Outdated reference: A later version (-06) exists of draft-ietf-nemo-requirements-02 ** Downref: Normative reference to an Informational draft: draft-ietf-nemo-requirements (ref. '8') == Outdated reference: A later version (-06) exists of draft-ietf-nemo-terminology-01 ** Downref: Normative reference to an Informational draft: draft-ietf-nemo-terminology (ref. '9') -- Possible downref: Normative reference to a draft: ref. '10' Summary: 12 errors (**), 0 flaws (~~), 13 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Mobility P. Thubert 3 Internet-Draft Cisco Systems 4 Expires: September 30, 2004 R. Wakikawa 5 Keio University 6 V. Devarapalli 7 Nokia 8 April 1, 2004 10 NEMO Home Network models 11 draft-ietf-nemo-home-network-models-00 13 Status of this Memo 15 This document is an Internet-Draft and is in full conformance with 16 all provisions of Section 10 of RFC2026. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that other 20 groups may also distribute working documents as Internet-Drafts. 22 Internet-Drafts are draft documents valid for a maximum of six months 23 and may be updated, replaced, or obsoleted by other documents at any 24 time. It is inappropriate to use Internet-Drafts as reference 25 material or to cite them other than as "work in progress." 27 The list of current Internet-Drafts can be accessed at http:// 28 www.ietf.org/ietf/1id-abstracts.txt. 30 The list of Internet-Draft Shadow Directories can be accessed at 31 http://www.ietf.org/shadow.html. 33 This Internet-Draft will expire on September 30, 2004. 35 Copyright Notice 37 Copyright (C) The Internet Society (2004). All Rights Reserved. 39 Abstract 41 This paper documents some usage patterns and the associated issues 42 when deploying a Home Network for Nemo enabled Mobile Routers, 43 conforming the NEMO Basic Support draft [7]. 45 The aim here is specifically to provide some examples of organization 46 of the Home Network, as they were discussed in the NEMO and NEMO 47 Design mailing lists. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 52 2. Terminology and concepts . . . . . . . . . . . . . . . . . . . 4 53 3. General Expectations . . . . . . . . . . . . . . . . . . . . . 6 54 4. Extended Home Network . . . . . . . . . . . . . . . . . . . . 7 55 4.1 Returning Home . . . . . . . . . . . . . . . . . . . . . . . . 8 56 5. Aggregated Home . . . . . . . . . . . . . . . . . . . . . . . 9 57 5.1 Returning Home . . . . . . . . . . . . . . . . . . . . . . . . 10 58 6. Virtual Home Network . . . . . . . . . . . . . . . . . . . . . 11 59 7. Mobile Home . . . . . . . . . . . . . . . . . . . . . . . . . 13 60 8. Changes from version 00 to 01 . . . . . . . . . . . . . . . . 15 61 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16 62 References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 63 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 17 64 A. Returning Home emulation in the virtual case . . . . . . . . . 18 65 Intellectual Property and Copyright Statements . . . . . . . . 19 67 1. Introduction 69 This document assumes that the reader is familiar with Mobile IPv6 as 70 defined in [6], and with the concept of Mobile Router defined in the 71 NEMO terminology document [9]. 73 Four different organizations of the Home Network including a 74 hierachical construction are documented: 76 Extended Home Network: In this disposition, the Home Network is but 77 one subnet of a larger aggregation that encompasses the Mobile 78 Networks, called extended Home Network. When at Home, a Mobile 79 Router performs normal routing between the Home Link and the 80 Mobile Networks. 82 Aggregated Home Network: In this disposition, the Home Network 83 actually overlaps with the Mobile Networks. When at Home, a Mobile 84 Router acts as a bridge between the Home Link and the Mobile 85 Networks. 87 Virtual Home Network: In this disposition, there is no physical Home 88 Link at all for the Mobile Routers to come back Home to. 90 Mobile Home Network: In this disposition, there is a bitwise 91 hierarchy of Home Networks. A global Home Network is advertised to 92 the infrastructure by a head Home Agent and further subnetted into 93 Mobile Networks. Each subnet is owned by a Mobile Router that 94 registers it in a NEMO fashion while acting as a Home Agent for 95 that network. 97 In all cases, the Home Agents collectively advertise only the 98 aggregation of the Mobile Networks. The dichotomy is kept within the 99 Home Agents and the Mobile Routers, as opposed to advertised by means 100 of routing protocols to other parties. 102 Also, it is valid for a Mobile Router to register using an address 103 from one of its own NEMO-Prefixes in all three cases. 105 The examples provided here aim at illustrating the NEMO Basic Support 106 draft [7] but are by no mean at limiting its scope of application. 108 2. Terminology and concepts 110 The key words MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, 111 SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL in this document are to be 112 interpreted as described in RFC2119 [5]. 114 The following terms used in this document are defined in the IPv6 115 Addressing Architecture document [4]: 117 link-local unicast address 119 link-local scope multicast address 121 The following terms used in this document are defined in the mobile 122 IPv6 specification [6]: 124 home agent (HA) 126 The following terms used in this document are defined in the mobile 127 network terminology document [9]: 129 mobile router (MR) 131 mobile network 133 mobile host (MH) 135 This draft uses the following additional or modified terminology: 137 Home Link: The link attached to the interface at the Home Agent on 138 which the Home Prefix is configured. The interface can be a 139 virtual interface, in which case the Home Link is a virtual Home 140 Link. 142 Home Network: The Network formed by the application of the Home 143 Prefix on the Home Link. With NEMO, the concept of Home Network is 144 extended as explained below. 146 Home Address: With Mobile IPv6, a Home Address is derived from the 147 Home Network prefix. This is generalized in NEMO, with some 148 limitations: A Home Address can be either derived from the Home 149 Network or from one of the Mobile Router's NEMO-prefixes. 151 MRHA Tunnel: The bi-directional tunnel between a Mobile Router and 152 its Home Agent 154 Mobile Aggregated Prefix: An aggregation of NEMO-Prefixes. 156 Aggregated Home Network: The Home Network associated with a Mobile 157 Aggregated Prefix. This Aggregation is advertised as a subnet on 158 the Home Link, and thus used as Home Network for NEMO purposes. 160 Extended Home Network: The network associated with the aggregation of 161 one or more Home Network(s) and Mobile Network(s). As opposed to 162 the Mobile IPv6 Home Network that is a subnet, the extended Home 163 Network is an aggregation and is further subnetted. 165 Virtual Home Network: The Home Network associated with a Virtual 166 Network. The Extended Home Network and the Aggregated Home Network 167 can be configured as Virtual Home Network. 169 Mobile Home Network: A Mobile Network that is also a Home Network. 170 The MR that own the NEMO-Prefix acts as a Home Agent for it. 172 3. General Expectations 174 With Mobile IPv6, the Home Network is generally a physical network 175 interconnecting the Home Agents, and the Mobile Nodes that are at 176 Home. NEMO extends the concept of Home so that it is not only a flat 177 subnet composed of Home Addresses but an aggregation that is itself 178 subnetted in mobile and Home Networks. This aggregation is still 179 referred to as Home. 181 As an example, say that the aggregation has a global routing prefix 182 of m = 48 bits (A:B:C::/48), with subnet ID size of n = 16 bits ( n + 183 m = 64). 185 Say that a Mobile Router, MR1, owns the NEMO-Prefix A:B:C:1::/64: 186 With basic NEMO, and depending on the deployment, MR1 may register 187 using a Home Address from the Home network, A:B:C:0::1, say, or a 188 Home Address, A:B:C:1::1, say, from one of its NEMO-Prefixes. 190 In a given deployment, one subnet may be reserved for the Home Link 191 (say A:B:C:0::/64) while the others are attributed to Mobile Routers 192 as Mobile Networks (as A:B:C:1::/64 for MR1). Another approach could 193 be to configure the Aggregation of Mobile Networks as the subnet on 194 the Home Link, and let the Mobile Routers manage the overlapping 195 networks. Finally, the aggregation could be configured on a virtual 196 network, with no physical Home Link at all, in which case Home means 197 topologically and administratively close to the Home Agent that owns 198 the virtual network. 200 The following sections provide additional information on these forms 201 of Home Network: 203 4. Extended Home Network 205 One simple approach can be to reserve one or several subnets from an 206 aggregation for the Home Link, and to use the other subnets as 207 NEMO-Prefixes. In that case, the Home Network and the Mobile Networks 208 do not overlap. The aggregation is called an extended Home Network. 210 | 211 route v /48 A:B:C::/48 213 HA 214 | /64 A:B:C:0::/64 215 --+-----+--+- . -+- . -+-- 216 | | | | 217 MR1 MR2 MRi MRN 218 /64 /64 /64 /64 A:B:C:i::/64 0 < i <= N 220 extended Home Network 221 <-----------------------------------------------------------> 223 Home Net Mobile Net Mobile Net ... Mobile Net 224 <------------><------------><------------> ... <------------> 226 In that configuration: 228 o There is one physical Home Network and multiple Mobile Networks 230 o The Home and the NEMO-prefixes are tailored to allow for IPv6 231 Stateless Address Autoconfiguration with typical interface 232 identifier length for the type of interface (can be for example / 233 64). 235 o The prefix length of the extended Home Network is shorter than 236 that of the Home Network and the NEMO-prefixes, since it is an 237 aggregation (can be for example /48). 239 o The Mobile Routers are assigned individually a Home Address from 240 the Home Network and use is to register their NEMO-Prefix(es). In 241 that case, the Home Agent performs DAD in the Home Network as 242 prescribed by Mobile IPv6 for the Home Addresses. 244 o Alternatively, a Mobile Router could also form a Home Address from 245 one of its prefixes and use it to register, performing its own DAD 246 on its ingress network. 248 4.1 Returning Home 250 In the extended Home Network model, the Home Network is configured on 251 a physical interface of the Home Agent, the Home Link. 253 A Mobile Router returns Home by connecting directly to the Home Link, 254 and dropping the MRHA tunnel. 256 If the Home Address of the Mobile Router is derived from one of its 257 Mobile Networks, then the MR may connect to the Home Link using an 258 egress interface and autoconfigure an address on the Home Link. The 259 MR recognizes the prefix of its Home Agent in order to decide that it 260 is Home. Note that in that case the Home Address does not match the 261 Home Prefix. 263 When at Home, the Mobile Router ensures the connectivity of the 264 Mobile Network using standard router operations. 266 In particular, if the HA has the necessary information to continue 267 routing to the NEMO-Prefixes in the absence of registration, for 268 instance if the Home Address of the Mobile Router is derived from the 269 Home Network, and if the HA uses a static route to the 270 NEMO-Prefix(es) via that address, then the participation of the MR to 271 the Home IGP is not required. 273 But in the general case, when the MR is at Home, it resumes IGP 274 operations on the Home Link in order to advertise its Mobile 275 Networks. 277 Alternate procedures for ensuring the connectivity of the Mobile 278 Networks when at Home are described in Section 6. In Particular, it 279 is 281 5. Aggregated Home 283 One other approach is to consider that the Aggregation of all the 284 NEMO-prefixes is used plainly as the Home Network, refered to as the 285 Aggregated Home Network. This means that the Mobile Aggregated Prefix 286 is configured on the Home Link and advertised by the Home Agent as a 287 subnet. 289 HA 290 | /56 Aggreg /56 291 --+-----+--+- . -+- . -+-- 292 | | | | 293 MR1 MR2 MRi MRN 294 ------ ------ ------ ------ 295 /64 /64 /64 /64 Aggreg|i /64 0 < i <= N 297 Aggregated Home 298 <-----------------------------------------------------------> 300 Mobile Net Mobile Net Mobile Net ... Mobile Net 301 <------------><------------><------------> ... <------------> 303 Note: a Mobile Router coming Home sees overlapping prefixes between 304 the ingress and the egress interface and some specific support may be 305 needed. 307 A node on the Home Link will compute that the Aggregated Home Network 308 is actually a subnet on the Home Link and may use it for 309 autoconfiguration purposes. Such a node may also install a connected 310 route to the Aggregated Home Network over the Home Link. 312 As a result, unless the node has a better (longest match) route to a 313 given NEMO-Prefix, it will lookup all MNNs using Neighbor Discovery 314 over the Home Link. 316 Thus, the Home Agent MUST intercept all the packets to the MNNs on 317 the registered prefixes. In order to do so, the Home Agent MAY 318 perform ND proxying for all addresses in all registered Mobile 319 Network Prefixes, and protect the NEMO-Prefix space from 320 autoconfiguration by uncontrolled visitors on the Home Link. 322 Alternatives based on a routing protocol or ICMP redirect may apply 323 in some cases. 325 5.1 Returning Home 327 The Aggregated Home Prefix is configured on a physical interface of 328 the Home Agent, the Home Link. As a consequence, the Home Agent has a 329 connected route to the Aggregated Home Network over the Home Link. 331 A Mobile Router returns Home by connecting directly to the Home Link, 332 and dropping the MRHA tunnel. The Mobile Router recognizes its Home 333 Link by a prefix match with its Home Agent. Note that it must expect 334 a shorter prefix than that of its Mobile Networks, even if its Home 335 Address is formed out of one of its NEMO-Prefixes, but that the Home 336 Address matches the Home Network Prefix. 338 When a Mobile Router connects to the Home Link using its egress 339 interface, it MAY set up a bridge between its ingress interface(s) 340 and the Home Link. Alternatively, the Mobile Router MAY perform ND 341 proxying for all addresses in its NEMO-Prefixes, between the egress 342 and the related ingress interface. Since the prefixes on the egress 343 and ingress interfaces are overlapping, routing is disallowed. 345 HA 346 | /56 Aggreg /56 347 --+-----+--+- . -+- . -+-- 348 | | | | 349 MR1 MR2 MRi MRN 350 ------ ------ ------ ------ 351 /64 /64 /64 /64 Aggreg|i /64 0 < i <= N 353 Bridging between egress and ingress 355 Alternatively, if the MR has a single ingress Interface, the Mobile 356 Router may use the Mobile Link to connect to the Home Link, merging 357 the two links in a single consistent network. 359 HA 360 | /56 Aggreg /56 361 --+-----+--+- . -+- . -+-- 362 /64 /64 /64 /64 Aggreg|i /64 0 < i <= N 363 ------ ------ ------ ------ 364 MR1 MR2 MRi MRN 365 | | | | 367 Merging the Home and the Mobile Networks 369 This fits the connected route model, since the Aggregated Home is 370 truly located on that network. 372 6. Virtual Home Network 374 The Home Link can be configured on the Home Agent on a virtual link, 375 in which case there's no physical Home Link for Mobile Routers to 376 return Home or for Home Agents to discover each others and perform 377 the ND level interactions as described in Mobile IPv6. [6] 379 /48 eg: A:B:C::/48 380 HA 381 | /64 A:C:C:E::/64 382 --+-----+--+- . -+- . -+-- 383 | | | | 384 MR1 MR2 MRi MRN 385 /64 /64 /64 /64 A:B:C:i::/64 0 < i <= N 387 Virtual Home Network 389 The Extended Home network and the Aggregated Home network models can 390 be adapted for virtual links. There is no change in the way Home 391 Addresses are allocated. As in the case of a physical link, the Home 392 Address of a Mobile router is constructed based on the Home Prefix or 393 one of the prefixes of its Mobile Network(s). 395 There are certain advantages to making the Home Link a virtual link: 397 A virtual link may not experience any disruption related to 398 physical maintenance or to hardware problems, so it is more 399 available than a physical link. The high availability of the Home 400 Link is critical for the mobility service. 402 The Home Agent does not have to defend the Mobile Router's Home 403 Address through Proxy Neighbor Discovery. The Home Agent does not 404 also have to perform Duplicate Address Detection (DAD) for the 405 Mobile Router's Home Address when it receives a Binding Update 406 from the Mobile Router. 408 The Mobile Router does not have to implement the Returning Home 409 procedure (section 11.5.4 of Mobile IPv6. [6]). 411 In order for a Mobile Router to emulate returning Home, it can 412 connect to one or more access link(s) configured for that purpose on 413 the Home Agent. The Mobile Router, after connecting to the access 414 link, SHOULD not send any routing protocol updates on the egress 415 interface because the routing information from the Mobile Router 416 might adversely affect IPv6 route aggregation on the Home Network. 417 However, the Mobile Router must register its binding as if it was 418 accessing a foreign link. 420 There are also some drawbacks to the virtual Home Link approach: 422 There can be only one Home Agent since Mobile IPv6 relies on 423 Neighbor Discovery on the Home Link for other HA discovery and for 424 Duplicate Address Detection. 426 The Home Agent must maintain a Binding Cache entry for a Mobile 427 Router and forwarding state for its Mobile Network even when the 428 Mobile Router is directly connected to it. All traffic to and from 429 the Mobile Network is sent through the bi-directional tunnel 430 regardless of the Mobile Router location. This results in a 431 tunneling overhead even though the Mobile Router is connected to 432 the Home Network. 434 Some solutions can be proposed in order to perform an equivalent of 435 returning Home on a virtual Home Network. One such approach is 436 sketched in appendix as an illustration. 438 7. Mobile Home 440 In this disposition, there is a bitwise hierarchy of Home Networks. A 441 global Home Network is advertised to the infrastructure by a head 442 Home Agent(s) and further subnetted into Mobile Networks. As a 443 result, only the Home Agent(s) responsible for the most global 444 (shortest prefix) aggregation receive all the packets for all the 445 NEMO-prefixes, which are leaves in the hierarchy tree. 447 Each subnet is owned by a Mobile Router that registers it in a NEMO 448 fashion while acting as a Home Agent for that network. This Mobile 449 Router is at Home at the upper level of hierarchy. This configuration 450 is referred to as Mobile Home. 452 An example of that is the Cab Co configuration. Say a Taxi Company 453 owns a /32 prefix. This prefix is advertised at a fixed point, the 454 Headquarters say. Regional offices are deployed around the world. 455 Even though these regional offices are relatively stable in terms of 456 location and prefix requirement -say this changes every few years- 457 making them mobile allows a simpler management when a move has to 458 take place, or should the ISP service change. Finally, each regional 459 office owns a number of taxis, each one equipped with a mobile router 460 and an associated /64 prefix. 462 To illustrate this, here is a possible addressing scheme: 464 global Home Network CAB:C0::/32 owned by HQ 465 <-------------------------------------------------------------------> 467 HQ extended Home Net Mobile Home for SFO office 468 (casa) 469 CAB:C0:CA5A::/48 CAB:C0:5F0::/48 470 <----------------------------> ... <--------------------------------> 471 | 472 Home for offices HQ | 473 CAB:C0:CA5A:CA5A::/64 MN | 474 <----------------------><----> | 475 CAB:C0:CA5A:CA5A::CA5A | 476 CAB:C0:CA5A:CA5A::CA5B | 477 are HAs on link with for each office a route like | 478 | 479 CAB:C0:CA5A:CA5A::5F0 <---------------------- via 480 is the Home addr 481 of SFO office 483 and recursively for each Office, say San Francisco (SFO) as example: 485 Mobile Home Network CAB:C0:5f0::/48 owned by SFO office 486 <------------------------------------------------------------------> 488 HQ Home Network Mobile Networks for taxis 489 for offices 490 CAB:C0:5F0:5F0::/64 CAB:C0:5F0:CAB1::/64 CAB:C0:5F0:....::/6 491 <-------------------><-------------------> ... <-------------------> 492 CAB:C0:5F0:5F0::5F0 | 493 is HA on link with for | 494 each taxi a route like | 495 | 496 CAB:C0:5F0:5F0::CAB1 <------ via 497 is the Home addrSsync 498 of CAB 1 500 Note that the hierarchy occurs at a configuration level and may not 501 be reflected in the actual connection between nodes. For instance in 502 the Cab Co case, cabs are roaming within the city, each one attaching 503 to a different hot spot, while the regional office is connected to 504 the infrastructure using some ISP connection. 506 But it is also possible to reflect the organizational hierarchy in a 507 moving cloud of Mobile Router. If a Mobile Home Agent acts as root-MR 508 for a nested configuration of its own MRs, then the communication 509 between MRs is confined within the nested structure. 511 This can be illustrated in the case of a fleet at sea. Say that now 512 SFO is a communication ship of a fleet, using a satellite link to 513 join the infrastructure, and that the cabs are Mobile Routers 514 installed on smaller ships, equipped with low range radios. 516 If SFO is also the root-MR of a nested structure of cabs, the 517 communication between cabs is relayed by SFO and does not require the 518 satellite link. SFO recursively terminates the nested tunnels to the 519 cabs and reencapsulates all the packets between the nested cloud and 520 correspondents in the infrastructure in a single tunnel to CA5A, this 521 providing for nested NEMO Route Optimization. 523 8. Changes from version 00 to 01 525 Added Mobile Home Section 527 9. Acknowledgements 529 The authors wish to thank: 531 Erik Nordmark, Kent Leung, Thierry Ernst, TJ Kniveton, Patrick 532 Wetterwald and Alexandru Petrescu for their contributions. 534 References 536 [1] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) 537 Specification", RFC 2460, December 1998. 539 [2] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery 540 for IP Version 6 (IPv6)", RFC 2461, December 1998. 542 [3] Thomson, S. and T. Narten, "IPv6 Stateless Address 543 Autoconfiguration", RFC 2462, December 1998. 545 [4] Hinden, R. and S. Deering, "Internet Protocol Version 6 (IPv6) 546 Addressing Architecture", RFC 3513, April 2003. 548 [5] Bradner, S., "Key words for use in RFCs to Indicate Requirement 549 Levels", BCP 14, RFC 2119, March 1997. 551 [6] Johnson, D., Perkins, C. and J. Arkko, "Mobility Support in 552 IPv6", draft-ietf-mobileip-ipv6-24 (work in progress), July 553 2003. 555 [7] Devarapalli, V., "Nemo Basic Support Protocol", 556 draft-ietf-nemo-basic-support-02 (work in progress), December 557 2003. 559 [8] Ernst, T., "Network Mobility Support Goals and Requirements", 560 draft-ietf-nemo-requirements-02 (work in progress), February 561 2004. 563 [9] Ernst, T. and H. Lach, "Network Mobility Support Terminology", 564 draft-ietf-nemo-terminology-01 (work in progress), February 565 2004. 567 [10] Wakikawa, R., Devarapalli, V. and P. Thubert, "Inter Home 568 Agents Protocol (HAHA)", draft-wakikawa-mip6-nemo-haha-01 (work 569 in progress), February 2004. 571 Authors' Addresses 573 Pascal Thubert 574 Cisco Systems Technology Center 575 Village d'Entreprises Green Side 576 400, Avenue Roumanille 577 Biot - Sophia Antipolis 06410 578 FRANCE 580 EMail: pthubert@cisco.com 582 Ryuji Wakikawa 583 Keio University and WIDE 584 5322 Endo Fujisawa Kanagawa 585 252-8520 586 JAPAN 588 EMail: ryuji@sfc.wide.ad.jp 590 Vijay Devarapalli 591 Nokia Research Center 592 313 Fairchild Drive 593 Mountain View, CA 94043 594 USA 596 EMail: vijay.devarapalli@nokia.com 598 Appendix A. Returning Home emulation in the virtual case 600 When a Home Link is virtual, all traffic to and from the Mobile 601 Network is sent through the bi-directional tunnel even at the Home 602 Link. This section describes one possible mechanism that extends 603 basic NEMO to eliminate this tunneling overhead. 605 Although the Home Link is virtual, the Home Agent has at least one 606 physical link to communicate with the external world. One or several 607 of such links, called the virtual Home Access Links, are conceptually 608 associated with the virtual Home Link and considered as part of Home. 610 When accessing one of its virtual Home Access Links, a Mobile Router 611 autoconfigures a Care-of Address from a Router Advertisement as it 612 would do on any visited link, in order to perform the next binding 613 flow. 615 If the Mobile Router is configured to recognize the virtual Home 616 Access Links as part of Home, it deregisters by sending a Binding 617 update with null lifetime sourced at the CareOf. Alternatively, the 618 Home Agent may indicate that the MR has moved to the virtual Home 619 Access Links as a status code in the binding acknowledgement. The 620 status code implies that Home Agent successsful de-register the 621 binding at the virtual Home Access Link. Detection of the virtual 622 Home Access Links is achieved by a prefix comparison(s) between the 623 care-of address and the prefix(es) on the virtual Home Access 624 Link(s). 626 With both approaches, the result of the binding flow is a 627 deregistration. Consequently, both the Mobile Router and the Home 628 Agent disable the bi-directional tunnel. At that point, the Home 629 Agent configures its forwarding in order to reach the Mobile Router 630 and its mobile networks at Home. For instance, this may take the form 631 of a route to the Mobile Network prefixes via the MR Home Address, 632 and a connected host route to the MR Home Address via the virtual 633 Home Access link. 635 After successful binding de-registration, the Mobile Router MUST 636 receive packets meant to the Mobile Router's Home Address at the 637 Virtual Home Link. How to intercept packets addressed to the Home 638 Address depends on implementations of the Mobile Router. If the Home 639 Address is not configured at the egress interface, the Mobile Router 640 MUST use proxy Neighbor Discovery to intercept all packets addressed 641 to the Home Address on the virtual Home Link. Otherwise, the Mobile 642 Router does not have to perform any special operation at the virtual 643 Home Link. 645 Intellectual Property Statement 647 The IETF takes no position regarding the validity or scope of any 648 intellectual property or other rights that might be claimed to 649 pertain to the implementation or use of the technology described in 650 this document or the extent to which any license under such rights 651 might or might not be available; neither does it represent that it 652 has made any effort to identify any such rights. 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