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'7') (Obsoleted by RFC 4301) ** Obsolete normative reference: RFC 2402 (ref. '8') (Obsoleted by RFC 4302, RFC 4305) ** Obsolete normative reference: RFC 2406 (ref. '9') (Obsoleted by RFC 4303, RFC 4305) ** Obsolete normative reference: RFC 2460 (ref. '10') (Obsoleted by RFC 8200) ** Obsolete normative reference: RFC 2461 (ref. '11') (Obsoleted by RFC 4861) ** Obsolete normative reference: RFC 2463 (ref. '12') (Obsoleted by RFC 4443) ** Downref: Normative reference to an Informational RFC: RFC 3232 (ref. '13') Summary: 13 errors (**), 0 flaws (~~), 7 warnings (==), 6 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group P. Thubert 3 Internet-Draft M. Molteni 4 Expires: December 24, 2003 Cisco Systems 5 June 25, 2003 7 IPv6 Reverse Routing Header and its application to Mobile Networks 8 draft-thubert-nemo-reverse-routing-header-02 10 Status of this Memo 12 This document is an Internet-Draft and is in full conformance with 13 all provisions of Section 10 of RFC2026. 15 Internet-Drafts are working documents of the Internet Engineering 16 Task Force (IETF), its areas, and its working groups. Note that other 17 groups may also distribute working documents as Internet-Drafts. 19 Internet-Drafts are draft documents valid for a maximum of six months 20 and may be updated, replaced, or obsoleted by other documents at any 21 time. It is inappropriate to use Internet-Drafts as reference 22 material or to cite them other than as "work in progress." 24 The list of current Internet-Drafts can be accessed at http:// 25 www.ietf.org/ietf/1id-abstracts.txt. 27 The list of Internet-Draft Shadow Directories can be accessed at 28 http://www.ietf.org/shadow.html. 30 This Internet-Draft will expire on December 24, 2003. 32 Copyright Notice 34 Copyright (C) The Internet Society (2003). All Rights Reserved. 36 Abstract 38 Already existing proposals enable Mobile Networks by extending Mobile 39 IP to support Mobile Routers. In order to enable nested Mobile 40 Networks, some involve the overhead of nested tunnels between the 41 Mobile Routers and their Home Agents. 43 This proposal allows the building of a nested Mobile Network avoiding 44 the nested tunnel overhead. This is accomplished by using a new 45 routing header, called the reverse routing header, and by overlaying 46 a layer 3 tree topology on the evolving Mobile Network. 48 Table of Contents 50 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 3 51 1.1 Recursive complexity . . . . . . . . . . . . . . . . . . . 3 52 2. Terminology and Assumptions . . . . . . . . . . . . . . . 5 53 2.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 54 2.2 Assumptions . . . . . . . . . . . . . . . . . . . . . . . 6 55 3. An Example . . . . . . . . . . . . . . . . . . . . . . . . 7 56 4. New Routing Headers . . . . . . . . . . . . . . . . . . . 11 57 4.1 Routing Header Type 2 (MIPv6 RH with extended semantics) . 11 58 4.2 Routing Header Type 4 (The Reverse Routing Header) . . . . 13 59 4.3 Extension Header order . . . . . . . . . . . . . . . . . . 15 60 5. ICMP . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 61 6. Modifications to IPv6 Neighbor Discovery . . . . . . . . . 19 62 6.1 Modified Router Advertisement Message Format . . . . . . . 19 63 6.2 New Tree Information Option Format . . . . . . . . . . . . 20 64 7. Binding Cache Management . . . . . . . . . . . . . . . . . 23 65 7.1 Binding Updates . . . . . . . . . . . . . . . . . . . . . 23 66 7.2 RRH Heartbeat . . . . . . . . . . . . . . . . . . . . . . 23 67 8. Home Agent Operation . . . . . . . . . . . . . . . . . . . 24 68 9. Mobile Router Operation . . . . . . . . . . . . . . . . . 26 69 9.1 Processing of ICMP "RRH too small" . . . . . . . . . . . . 26 70 9.2 Processing of ICMP error . . . . . . . . . . . . . . . . . 27 71 9.3 Processing of RHH for Outbound Packets . . . . . . . . . . 27 72 9.4 Processing of Tree Information Option . . . . . . . . . . 28 73 9.5 Processing of the extended Routing Header Type 2 . . . . . 28 74 9.6 Decapsulation . . . . . . . . . . . . . . . . . . . . . . 30 75 10. Mobile Host Operation . . . . . . . . . . . . . . . . . . 30 76 11. Security Considerations . . . . . . . . . . . . . . . . . 30 77 11.1 IPsec Processing . . . . . . . . . . . . . . . . . . . . . 31 78 11.1.1 Routing Header type 2 . . . . . . . . . . . . . . . . . . 31 79 11.1.2 Routing Header type 4 . . . . . . . . . . . . . . . . . . 31 80 11.2 New Threats . . . . . . . . . . . . . . . . . . . . . . . 32 81 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 32 82 References . . . . . . . . . . . . . . . . . . . . . . . . 33 83 Authors' Addresses . . . . . . . . . . . . . . . . . . . . 34 84 A. Optimizations . . . . . . . . . . . . . . . . . . . . . . 35 85 A.1 Path Optimization with RRH . . . . . . . . . . . . . . . . 35 86 A.2 Packet Size Optimization . . . . . . . . . . . . . . . . . 36 87 A.2.1 Routing Header Type 3 (Home Address option replacement) . 37 88 B. Multi Homing . . . . . . . . . . . . . . . . . . . . . . . 39 89 B.1 Multi-Homed Mobile Network . . . . . . . . . . . . . . . . 39 90 B.2 Multihomed Mobile Router . . . . . . . . . . . . . . . . . 40 91 C. Changes from Previous Version of the Draft . . . . . . . . 41 92 Intellectual Property and Copyright Statements . . . . . . 42 94 1. Introduction 96 This document assumes the reader is familiar with the Mobile Networks 97 terminology defined in [2] and with Mobile IPv6 defined in [1]. 99 Generally a Mobile Network may be either simple (a network with one 100 mobile router) or nested, single or multi-homed. This proposal starts 101 from the assumption that nested Mobile Networks will be the norm, and 102 so presents a solution that avoids the tunnel within tunnel overhead 103 of already existing proposals. 105 The solution is based on a single bi-directional tunnel between the 106 first Mobile Router (MR) to forward a packet and its Home Agent (HA). 107 By using IPsec ESP on that tunnel, home equivalent privacy is 108 obtained without further encapsulation. 110 The solution uses a new Routing Header (RH), called the Reverse 111 Routing Header (RRH), to provide an optimized path for the single 112 tunnel. RRH is a variant of IPv4 Loose Source and Record Route (LSRR) 113 [6] adapted for IPv6. RRH records the route out of the nested Mobile 114 Network and can be trivially converted into a routing header for 115 packets destined to the Mobile Network. 117 This version focuses on single-homed Mobile Networks. Hints for 118 further optimizations and multi-homing are given in the appendixes. 120 Local Fixed Node (LFN) and Correspondent Node (CN) operations are 121 left unchanged as in Mobile IPv6 [1]. Specifically the CN can also be 122 a LFN. 124 Section 3 proposes an example to illustrate the operation of the 125 proposed solution, leaving detailed specifications to the remaining 126 chapters. The reader may refer to Section 2.1 for the specific 127 terminology. 129 1.1 Recursive complexity 131 A number of drafts and publications suggest -or can be extended to- a 132 model where the Home Agent and any arbitrary Correspondent would 133 actually get individual binding from the chain of nested Mobile 134 Routers, and form a routing header appropriately. 136 An intermediate MR would keep track of all the pending communications 137 between hosts in its subtree of Mobile Networks and their CNs, and a 138 binding message to each CN each time it changes its point of 139 attachment. 141 If this was done, then each CN, by receiving all the binding messages 142 and processing them recursively, could infer a partial topology of 143 the nested Mobile Network, sufficient to build a multi-hop routing 144 header for packets sent to nodes inside the nested Mobile Network. 146 However, this extension has a cost: 148 1. Binding Update storm 150 when one MR changes its point of attachment, it needs to send a 151 BU to all the CNs of each node behind him. When the Mobile 152 Network is nested, the number of nodes and relative CNs can be 153 huge, leading to congestions and drops. 155 2. Protocol Hacks 157 Also, in order to send the BUs, the MR has to keep track of all 158 the traffic it forwards to maintain his list of CNs. In case of 159 IPSec tunneled traffic, that CN information may not be available. 161 3. CN operation 163 The computation burden of the CN becomes heavy, because it has to 164 analyze each BU in a recursive fashion in order to infer nested 165 Mobile Network topology required to build a multi hop routing 166 header. 168 4. Missing BU 170 If a CN doesn't receive the full set of PSBU sent by the MR, it 171 will not be able to infer the full path to a node inside the 172 nested Mobile Network. The RH will be incomplete and the packet 173 may or may not be delivered. 175 5. Obsolete BU 177 If the Binding messages are sent asynchronously by each MR, then, 178 when the relative position of MRs and/or the TLMR point of 179 attachment change rapidly, the image of Mobile Network that the 180 CN maintains is highly unstable. If only one BU in the chain is 181 obsolete due to the movement of an intermediate MR, the 182 connectivity may be lost. 184 A conclusion is that the path information must be somehow aggregated 185 to provide the CN with consistent snapshots of the full path across 186 the Mobile Network. This can be achieved by an IPv6 form of loose 187 source / record route header, that we introduce here as a Reverse 188 Routing Header 190 2. Terminology and Assumptions 192 2.1 Terminology 194 Simple Mobile Network 196 One or more IP subnets attached to a MR and mobile as a unit, with 197 respect to the rest of the Internet. A simple Mobile Network can 198 be either single or multi-homed. 200 The IP subnets may have any kind of topology and may contain fixed 201 routers. All the access points of the Mobile Network (to which 202 further MRs may attach) are on the same layer 2 link of the MR. 204 We like to represent a simple single-homed Mobile Network as an 205 hanger, because it has only one uplink hook and a bar to which 206 multiple hooks can be attached. Graphically we use the question 207 mark "?" to show the uplink hook (interface) connected to the MR, 208 and the "=" sign to represent the bar: 210 ? 211 MR1 212 | 213 =============== 215 Nested Mobile Network 217 A group of simple Mobile Networks recursively attached together 218 and implementing nested Mobility as defined in [2]. 220 ? 221 MR1 222 | 223 ====?===============?==== 224 MR2 MR3 225 | | 226 =========== ===?==========?=== 227 MR4 MR5 228 | | 229 ========== ============ 231 IPv6 Mobile Host 233 A IPv6 Host, with support for MIPv6 MN, and the additional Nemo 234 capability described in this draft. 236 Home prefix 238 Network prefix, which identifies the home link within the Internet 239 topology. 241 Mobile Network prefix 243 Network prefix, common to all IP addresses in the Mobile Network 244 when the MR is attached to the home link. It may or may not be a 245 subset of the Home subnet prefix. 247 Inbound direction: 249 direction from outside the Mobile Network to inside 251 Outbound direction: 253 direction from inside the Mobile Network to outside 255 2.2 Assumptions 257 We make the following assumptions: 259 1. A MR has one Home Agent and one Home Address -> one primary CoA. 261 2. A MR attaches to a single Attachment Router as default router. 263 3. A MR may have more than one uplink interface. 265 4. An interface can be either wired or wireless. The text assumes 266 that interfaces are wireless for generality. 268 5. Each simple Mobile Network may have more that one L2 Access 269 Point, all of them controlled by the same Attachment Router, 270 which we assume to be the Mobile Router. 272 Since an MR has only one primary CoA, only one uplink interface can 273 be used at a given point of time. Since the MR attaches to a single 274 attachment router, if due care is applied to avoid loops, then the 275 resulting topology is a tree. 277 3. An Example 279 The nested Mobile Network in the following figure has a tree 280 topology, according to the assumptions in Section 2.2. In the tree 281 each node is a simple Mobile Network, represented by its MR. 283 +---------------------+ 284 | Internet |---CN 285 +---------------|-----+ 286 / Access Router 287 MR3_HA | 288 ======?====== 289 MR1 290 | 291 ====?=============?==============?=== 292 MR5 MR2 MR6 293 | | | 294 =========== ===?========= ============= 295 MR3 296 | 297 ==|=========?== <-- Mobile Network3 298 LFN1 MR4 299 | 300 ========= 302 An example nested Mobile Network 304 This example focuses on a Mobile Network node at depth 3 (Mobile 305 Network3) inside the tree, represented by its mobile router MR3. The 306 path to the Top Level Mobile Router (TLMR) MR1 and then the Internet 307 is 309 MR3 -> MR2 -> MR1 -> Internet 311 Consider the case where a LFN belonging to Mobile Network3 sends a 312 packet to a CN in the Internet, and the CN replies back. With the 313 tunnel within tunnel approach described by [3], we would have three 314 bi-directional nested tunnels: 316 -----------. 317 --------/ /-----------. 318 -------/ | | /----------- 319 CN ------( - - | - - - | - - - | - - - | - - - (-------- LFN 320 MR3_HA -------\ | | \----------- MR3 321 MR2_HA --------\ \----------- MR2 322 MR1_HA ----------- MR1 324 Depending on the relative location of MR1_HA, MR2_HA and MR3_HA, this 325 may lead to a very inefficient "pinball" routing in the 326 Infrastructure. 328 On the other hand, with the RRH approach we would have only one 329 bi-directional tunnel: 331 --------------------------------- MR1 ---- MR2 ---- MR3 332 CN ------( - - - - - - - - - - - - - - - - (-------- LFN 333 MR3_HA --------------------------------- MR1 ---- MR2 ---- MR3 335 The first mobile router on the path, MR3, in addition to tunneling 336 the packet to its HA, adds a reverse routing header with N = 3 337 pre-allocated slots. Choosing the right value for N is discussed in 338 Section 6.2. The bottom slot is equivalent to the MIPv6 Home Address 339 option. MR3 inserts its home address MR3_HoA into slot 0. 341 The outer packet has source MR3's Care of Address, MR3_CoA, and 342 destination MR3's Home Agent, MR3_HA: 344 <-------------- outer IPv6 header --------------------> 345 +-------+-------++ -- ++----+-------+-------+---------+ +------- 346 |oSRC |oDST |: :|oRRH| slot2 | slot1 | slot0 | | 347 |MR3_CoA|MR3_HA |:oEXT:|type| | |MR3_HoA | |iPACKET 348 | | |: :| 4 | | | | | 349 +-------+-------++ -- ++----+-------+-------+---------+ +------- 351 The second router on the path, MR2, notices that the packet already 352 contains an RRH, and so it overwrites the source address of the 353 packet with its own address, MR2_CoA, putting the old source address, 354 MR3_CoA, in the first free slot of the RRH. 356 The outer packet now has source MR2_CoA and destination MR3_HA; the 357 RRH from top to bottom is MR3_CoA | MR3_HoA: 359 <-------------- outer IPv6 header --------------------> 360 +-------+-------++ -- ++----+-------+-------+---------+ +------- 361 |oSRC |oDST |: :|oRRH| slot2 | slot1 | slot0 | | 362 |MR2_CoA|MR3_HA |:oEXT:|type| |MR3_CoA|MR3_HoA | |iPACKET 363 | | |: :| 4 | | | | | 364 +-------+-------++ -- ++----+-------+-------+---------+ +------- 365 In general the process followed by the second router is repeated by 366 all the routers on the path, including the TLMR (in this example 367 MR1). When the packet leaves MR1 the source address is MR1_CoA and 368 the RRH is MR2_CoA | MR3_CoA | MR3_HoA: 370 <-------------- outer IPv6 header --------------------> 371 +-------+-------++ -- ++----+-------+-------+---------+ +------- 372 |oSRC |oDST |: :|oRRH| slot2 | slot1 | slot0 | | 373 |MR1_CoA|MR3_HA |:oEXT:|type|MR2_CoA|MR3_CoA|MR3_HoA | |iPACKET 374 | | |: :| 4 | | | | | 375 +-------+-------++ -- ++----+-------+-------+---------+ +------- 377 In a colloquial way we may say that while the packet travels from MR3 378 to MR3_HA, the Mobile Network tunnel end point "telescopes" from MR3 379 to MR2 to MR1. 381 When the home agent MR3_HA receives the packet it notices that it 382 contains a RRH and it looks at the bottom entry, MR3_HoA. This entry 383 is used as if it were a MIPv6 Home Address destination option, i.e. 384 as an index into the Binding Cache. When decapsulating the inner 385 packet the home agent performs the checks described in Section 8, and 386 if successful it forwards the inner packet to CN. 388 MR3_HA stores two items in the Bind Cache Entry associated with MR3: 389 the address entries from RRH, to be used to build the RH, and the 390 packet source address MR1_CoA, to be used as the first hop. 392 Further packets from the CN to the LFN are plain IPv6 packets. 393 Destination is LFN, and so the packet reaches MR3's home network. 395 MR3_HA intercepts it, does a Bind Cache prefix lookup and obtains as 396 match the MR3 entry, containing the first hop and the information 397 required to build the RH. It then puts the packet in the tunnel 398 MR3_HA -- MR3 as follows: source address MR3_HA and destination 399 address the first hop, MR1_CoA. The RH is trivially built out of the 400 previous RRH: MR2_CoA | MR3_CoA | MR3_HoA: 402 <-------------- outer IPv6 header --------------------> 403 +-------+-------++ -- ++----+-------+-------+---------+ +------- 404 |oSRC |oDST |: :|oRH | | | | | 405 |MR3_HA |MR1_CoA|:oEXT:|type|MR2_CoA|MR3_CoA|MR3_HoA | |iPACKET 406 | | |: :| 2 | | | | | 407 +-------+-------++ -- ++----+-------+-------+---------+ +------- 408 The packet is routed with plain IP routing up to the first 409 destination MR1_CoA. 411 The RH of the outer packet is type 2 as in MIPv6 [1], but has 412 additional semantics inherited from type 0: it contains the path 413 information to traverse the nested Mobile Network from the TLMR to 414 the tunnel endpoint MR3. Each intermediate destination forwards the 415 packet to the following destination in the routing header. The 416 security aspects of this are treated in Section 11.2. 418 MR1, which is the initial destination in the IP header, looks at the 419 RH and processes it according to Section 9, updating the RH and the 420 destination and sending it to MR2_CoA. MR2 does the same and so on 421 until the packet reaches the tunnel endpoint, MR3. 423 When the packet reaches MR3, the source address in the IP header is 424 MR3_HA, the destination is MR3_CoA and in the RH there is one segment 425 left, MR3_HoA. As a consequence the packet belongs to the MR3_HA -- 426 MR3 tunnel. MR3 decapsulates the inner packet, applying the rules 427 described in Section 9 and sends it to LFN. The packet that reaches 428 LFN is the plain IPv6 packet that was sent by CN. 430 4. New Routing Headers 432 This draft modifies the MIPv6 Routing Header type 2 and introduces 433 two new Routing Headers, type 3 and 4. Type 3, which is an 434 optimization of type 4 will be discussed in Appendix A.2.1. The draft 435 presents their operation in the context of Mobile Routers although 436 the formats are not tied to Mobile IP and could be used in other 437 situations. 439 4.1 Routing Header Type 2 (MIPv6 RH with extended semantics) 441 Mobile IPv6 uses a Routing header to carry the Home Address for 442 packets sent from a Correspondent Node to a Mobile Node. In [1], this 443 Routing header (Type 2) is restricted to carry only one IPv6 address. 444 The format proposed here extends the Routing Header type 2 to be 445 multi-hop. 447 The processing of the multi-hop RH type 2 inherits from the RH type 0 448 described in IPv6 [10]. Specifically: the restriction on multicast 449 addresses is the same; a RH type 2 is not examined or processed until 450 it reaches the node identified in the Destination Address field of 451 the IPv6 header; in that node, the RH type 0 algorithm applies, with 452 added security checks. 454 The construction of the multi-hop RH type 2 by the HA is described in 455 Section 8; the processing by the MRs is described in Section 9.5; and 456 the security aspects are treated in Section 11.2. 458 The destination node of a packet containing a RH type 2 can be a MR 459 or some other kind of node. If it is a MR it will perform the 460 algorithm described in Section 9.5, otherwise it will operate as 461 prescribed by IPv6 [10] when the routing type is unrecognized. 463 The multi-hop Routing Header type 2, as extended by this draft, has 464 the following format: 466 0 1 2 3 467 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 468 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 469 | Next Header | Hdr Ext Len | Routing Type=2| Segments Left | 470 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 471 | Reserved | 472 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 473 | | 474 + + 475 | | 476 + Address[1] + 477 | | 478 + + 479 | | 480 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 481 | | 482 + + 483 | | 484 + Address[2] + 485 | | 486 + + 487 | | 488 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 489 . . . 490 . . . 491 . . . 492 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 493 | | 494 + + 495 | | 496 + Address[n] + 497 | | 498 + + 499 | | 500 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 502 Next Header 504 8-bit selector. Identifies the type of header immediately 505 following the Routing header. Uses the same values as the IPv4 506 Protocol field [13]. 508 Hdr Ext Len 510 8-bit unsigned integer. Length of the Routing header in 8-octet 511 units, not including the first 8 octets. For the Type 2 Routing 512 header, Hdr Ext Len is equal to two times the number of addresses 513 in the header. 515 Routing Type 517 8-bit unsigned integer. Set to 2. 519 Segments Left 521 8-bit unsigned integer. Number of route segments remaining, i.e., 522 number of explicitly listed intermediate nodes still to be visited 523 before reaching the final destination. 525 Reserved 527 32-bit reserved field. Initialized to zero for transmission; 528 ignored on reception. 530 Address[1..n] 532 Vector of 128-bit addresses, numbered 1 to n. 534 4.2 Routing Header Type 4 (The Reverse Routing Header) 536 The Routing Header type 4, or Reverse Routing Header (RRH), is a 537 variant of IPv4 loose source and record route (LSRR) [6] adapted for 538 IPv6. 540 Addresses are added from bottom to top (0 to n-1 in the picture). The 541 RRH is designed to help the destination build an RH for the return 542 path. 544 When a RRH is present in a packet, the rule for upper-layer checksum 545 computing is that the source address used in the pseudo-header is 546 that of the original source, located in the slot 0 of the RRH, unless 547 the RRH slot 0 is empty, in which case the source in the IP header of 548 the packet is used. 550 As the 'segment left' field of the generic RH is reassigned to the 551 number of segments used, an IPv6 node that does not support RRH will 552 discard the packet, unless the RRH is empty. 554 The RRH contains n pre-allocated address slots, to be filled by each 555 MR in the path. It is possible to optimize the number of slots using 556 the Tree Information Option described in Section 6.2. 558 The Type 4 Routing Header has the following format: 560 0 1 2 3 561 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 562 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 563 | Next Header | Hdr Ext Len | Routing Type=4| Segments Used | 564 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 565 | Sequence Number | 566 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 567 | | 568 + + 569 | | 570 + Slot[n-1] + 571 | | 572 + + 573 | | 574 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 575 . . . 576 . . . 577 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 578 | | 579 + + 580 | | 581 + Slot[1] (1st MR CoA) + 582 | | 583 + + 584 | | 585 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 586 | | 587 + + 588 | | 589 + Slot[0] (Home address) + 590 | | 591 + + 592 | | 593 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 595 Next Header 597 8-bit selector. Identifies the type of header immediately 598 following the Routing header. Uses the same values as the IPv4 599 Protocol field [13]. 601 Hdr Ext Len 603 8-bit unsigned integer. Length of the Routing header in 8-octet 604 units, not including the first 8 octets. For the Type 4 Routing 605 header, Hdr Ext Len is equal to two times the number of addresses 606 in the header. 608 Routing Type 610 8-bit unsigned integer. Set to 4. 612 Segments Used 614 8-bit unsigned integer. Number of slots used. Initially set to 1 615 by the MR when only the Home Address is there. Incremented by the 616 MRs on the way as they add the packets source addresses to the 617 RRH. 619 Sequence Number 621 32-bit unsigned integer. The Sequence Number starts at 0, and is 622 incremented by the source upon each individual packet. Using the 623 Radia Perlman's lollipop algorithm, values between 0 and 255 are 624 'negative', left to indicate a reboot or the loss of HA 625 connectivity, and are skipped when wrapping and upon positive 626 Binding Ack. The sequence number is used to check the freshness of 627 the RRH; anti-replay protection is left to IPsec AH. 629 Slot[n-1..0] 631 Vector of 128-bit addresses, numbered n-1 to 0. 633 When applied to the Nemo problem, the RRH can be used to update the 634 HA on the actual location of the MR. Only MRs forwarding packets on 635 an egress interface while not at home update it on the fly. 637 A RRH is inserted by the first MR on the Mobile Network outbound 638 path, as part of the reverse tunnel encapsulation; it is removed by 639 the associated HA when the tunneled packet is decapsulated. 641 4.3 Extension Header order 643 The RH type 2 is to be placed as any RH as described in [10] section 644 4.1. If a RH type 0 is present in the packet, then the RH type 2 is 645 placed immediately after the RH type 0, and the RH type 0 MUST be 646 consumed before the RH type 2. 648 RH type 3 and 4 are mutually exclusive. They are to be placed right 649 after the Hop-by-Hop Options header if any, or else right after the 650 IPv6 header. 652 As a result, the order prescribed in section 4.1 of RFC 2460 becomes: 654 IPv6 header 656 Hop-by-Hop Options header 658 Routing header type 3 or 4 660 Destination Options header (note 1) 662 Routing header type 0 664 Routing header type 2 666 Fragment header 668 Authentication header (note 2) 670 Encapsulating Security Payload header (note 2) 672 Destination Options header (note 3) 674 upper-layer header 676 5. ICMP 678 The RRH could have fewer slots than the number of MRs in the path 679 because either the nested Mobile Network topology is changing too 680 quickly or the MR that inserted the RRH could have a wrong 681 representation of the topology. 683 To solve this problem a new ICMP message is introduced, "RRH 684 Warning", type 64. Note that this ICMP message creates a new class of 685 warning messages besides the error messages and the control messages 686 of ICMP. 688 This message allows a MR on the path to propose a larger number of 689 slots to the MR that creates the RRH. The Proposed Size MUST be 690 larger than the current size and MUST NOT be larger than 8. 692 The originating MR must rate-limit the ICMP messages to avoid 693 excessive ICMP traffic in the case of the source failing to operate 694 as requested. 696 The originating MR must insert an RH type 2 based on the RRH in the 697 associated IP header, in order to route the ICMP message back to the 698 source of the reverse tunnel. A MR that receives this ICMP message is 699 the actual destination and it MUST NOT forward it to the (LFN) source 700 of the tunneled packet. 702 A MR on the path that finds no more space in the RRH SHOULD send an 703 ICMP "RRH warning" back to the MR that inserted the RRH. On the other 704 hand, a MR should always be able, by receiving TI option with up to 705 date tree depth (see Section Section 6.2). to correctly size the RRH 706 to insert in an outgoing packet. 708 The type 64 ICMP has the following format: 710 0 1 2 3 711 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 712 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 713 | Type = 64 | Code = 0 | Checksum | 714 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 715 | Current Size | Proposed Size | Reserved | 716 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 717 | As much of invoking packet | 718 + as will fit without the ICMPv6 packet + 719 | exceeding the minimum IPv6 MTU | 720 . . 721 . . 722 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 724 Type 726 64 [To Be Assigned] 728 Code 0: RRH too small 730 The originating MR requires the source to set the RRH size to a 731 larger value. The packet that triggered the ICMP will still be 732 forwarded by the MR, but the path cannot be totally optimized (see 733 Section 9.3). 735 Checksum 737 The ICMP checksum [12]. 739 Current Size 741 RRH size of the invoking packet, as a reference. 743 Proposed Size 745 The new value, expressed as a number of IPv6 addresses that can 746 fit in the RRH. 748 Reserved 750 16-bit reserved field. Initialized to zero for transmission; 751 ignored on reception. 753 6. Modifications to IPv6 Neighbor Discovery 755 6.1 Modified Router Advertisement Message Format 757 Mobile IPv6 [1] modifies the format of the Router Advertisement 758 message [11] by the addition of a single flag bit (H) to indicate 759 that the router sending the Advertisement message is serving as a 760 home agent on this link. 762 This draft adds another single flag bit (N) to indicate that the 763 router sending the advertisement message is a MR. This means that the 764 link on which the message is sent is a Mobile Network, which may or 765 may not be at home. 767 The Router Advertisement message has the following format: 769 0 1 2 3 770 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 771 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 772 | Type | Code | Checksum | 773 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 774 | Cur Hop Limit |M|O|H|N|Reservd| Router Lifetime | 775 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 776 | Reachable Time | 777 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 778 | Retrans Timer | 779 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 780 | Options ... 781 +-+-+-+-+-+-+-+-+-+-+-+- 783 This format represents the following changes over that originally 784 specified for Neighbor Discovery [11]: 786 Home Agent (H) 788 The Home Agent (H) bit is set in a Router Advertisement to 789 indicate that the router sending this Router Advertisement is also 790 functioning as a Mobile IP home agent on this link. 792 NEMO Capable (N) 794 The NEMO Capable (N) bit is set in a Router Advertisement to 795 indicate that the router sending this Router Advertisement is also 796 functioning as a Mobile Router on this link, so that the link is a 797 Mobile Network, possibly away from home. 799 6.2 New Tree Information Option Format 801 This draft defines a new Tree Information option, used in Router 802 Advertisement messages. Fields set by the TLMR are propagated 803 transparently by the MRs. Mobile Routers SHOULD add that option to 804 the Router Advertisement messages sent over the ingress interfaces. 806 The Tree Information option has the following format: 808 0 1 2 3 809 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 810 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 811 | Type | Length = 6 | TreePreference| TreeDepth | 812 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 813 |F|H| Reserved | Bandwidth | DelayTime | 814 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 815 | MRPreference | BootTimeRandom | 816 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 817 | PathCRC | 818 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 819 | | 820 + + 821 | | 822 + Tree TLMR Identifier + 823 | | 824 + + 825 | | 826 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 827 | | 828 + + 829 | | 830 + Tree Group + 831 | | 832 + + 833 | | 834 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 836 Type 838 8-bit unsigned integer set to 10 by the TLMR. 840 Length 842 8-bit unsigned integer set to 6 by the TLMR. The length of the 843 option (including the type and length fields) in units of 8 844 octets. 846 TreePreference 848 8-bit unsigned integer set by the TLMR to its configured 849 preference. Range from 0 = lowest to 255 = highest. 851 TreeDepth 853 8-bit unsigned integer set to 0 by the TLMR and incremented by 1 854 by each MR down the tree. 856 Fixed (F) 858 1-bit flag. Set by the TLMR to indicate that it is either attached 859 to a fixed network or at home. 861 Home (H) 863 1-bit flag. Set by the TLMR to indicate that it is also 864 functioning as a HA, for re-homing purposes. 866 Reserved 868 6-bit unsigned integer, set to 0 by the TLMR. 870 Bandwidth 872 8-bit unsigned integer set by the TLMR and decremented by MRs with 873 lower egress bandwidth. This is a power of 2 so that the available 874 egress bandwidth in bps is between 2^Bandwidth and 875 2^(Bandwidth+1). 0 means 'unspecified' and can not be modified 876 down the tree. 878 DelayTime 880 16-bit unsigned integer set by the TLMR. Tree time constant in 881 milliseconds. 883 MRPreference 885 8-bit signed integer. Set by each MR to its configured preference. 886 Range from 0 = lowest to 255 = highest. 888 BootTimeRandom 890 24-bit unsigned integer set by each MR to a random value that the 891 MR generates at boot time. 893 PathCRC 895 32-bit unsigned integer CRC, updated by each MR. This is the 896 result of a CRC-32c computation on a bit string obtained by 897 appending the received value and the MR CareOf Address. TLMRs use 898 a 'previous value' of zeroes to initially set the pathCRC. 900 Tree TLMR Identifier 902 IPv6 global address, set by the TLMR. Identifier of the tree. 904 Tree Group 906 IPv6 global address, set by the TLMR. Identifier of the tree 907 group. A MR may use the Tree Group in its tree selection 908 algorithm. 910 The TLMR MUST include this option in its Router Advertisements. 912 A MR receiving this option from its Attachment Router MUST update the 913 TreeDepth, MRPreference, BootTimeRandom and PathCRC fields, and MUST 914 propagate it on its ingress interface(s), as described in Section 915 9.4. 917 The alignment requirement of the Tree Information option is 8n. 919 7. Binding Cache Management 921 7.1 Binding Updates 923 Binding Updates are still used as described in MIPv6 [1] for Home 924 Registration and de-registration, but only when the MR registers for 925 the first time with its HA. 927 Since the BU doesn't contain the full NEMO path to the MR, it cannot 928 be used in this design of nested Mobile Networks. 930 7.2 RRH Heartbeat 932 Subsequent updates (or just refreshes) to the CoA binding are 933 obtained as one of the results of processing the RRH by the HA. 935 When the MR becomes aware of a topology change in the tree (for 936 examples it changes point of attachment, it obtains a new CoA, it 937 receives a Tree Information Option in an RA message that indicates a 938 change in the attachment tree) or in the absence of traffic (detected 939 by a timeout) to the HA, it must send an RRH Heartbeat (IP packet 940 with the RRH and empty payload). 942 8. Home Agent Operation 944 This section inherits from chapter 10 of MIPv6 [1], which is kept 945 unmodified except for parts 10.5 and 10.6 which are extended. This 946 draft mostly adds the opportunity for a MN to update the Binding 947 Cache of its Home Agent using RRH, though it does not change the fact 948 that MNs still need to select a home agent, register and deregister 949 to it, using the MIP Bind Update. 951 This draft extends [1] section 10.6 as follows: 953 o The entry point of the tunnel is now checked against the TLMR as 954 opposed to the primary CoA. 956 o The Binding Cache can be updated based on RRH with proper AH 957 authentication. 959 As further explained in Section 7.1, this specification modifies MIP 960 so that the HA can rely on the RH type 4 (RRH) to update its Bind 961 Cache Entry (BCE), when the Mobile Node moves. The conceptual content 962 of the BCE is extended to contain a sequence counter, and the 963 sequence of hops within the --potentially nested-- Mobile Network to 964 a given Mobile Node. The sequence counter is initially set to 0. 966 When the HA receives a packet destined to itself, it checks for the 967 presence of a Routing Header of type 3 or 4. Both contain as least 968 the entry for the home address of the MN in slot 0; this replaces the 969 MIP Home Address Option and allows the HA to determine the actual 970 source of the packet, to access the corresponding security 971 association. 973 As explained in Section 11.2, the HA MUST verify the authenticity of 974 the packet using IPSEC AH and drop packets that were not issued by 975 the proper Mobile Node. An RRH is considered only if the packet is 976 authenticated and if its sequence number is higher than the one saved 977 in the BCE. 979 Also, an RRH is considered only if an initial Bind Update exchange 980 has been successfully completed between the Mobile Node and its Home 981 Agent for Home Registration. If the RRH is valid, then the Bind Cache 982 Entry is revalidated for a lifetime as configured from the initial 983 Bind Update. 985 The BCE abstract data is updated as follows: 987 The first hop for the return path is the last hop on the path of 988 the incoming packet, that is between the HA and the Top Level 989 Mobile Router (TLMR) of the Mobile Network. The HA saves the IP 990 address of the TLMR from the source field in the IP header. 992 The rest of the path to the MN is found in the RRH. 994 The sequence counter semantics is changed as described in Section 995 4.2 997 This draft extends [1] section 10.5 as follows: 999 A Home Agent advertises the prefixes of its registered Mobile 1000 Routers, during the registration period, on the local Interior 1001 Gateway Protocol (IGP). 1003 The Routing Header type 2 is extended to be multi-hop. 1005 The Home Agent is extended to support routes to prefixes that are 1006 owned by Mobile Routers. This can be configured statically, or can be 1007 exchanged using a routing protocol as in [3], which is out of the 1008 scope of this document. As a consequence of this process, the Home 1009 Agent which is selected by a Mobile Router advertises reachability of 1010 the MR prefixes for the duration of the registration over the local 1011 IGP. 1013 When a HA gets a packet for which the destination is a node behind a 1014 Mobile Router, it places the packet in the tunnel to the associated 1015 MR. This ends up with a packet which destination address in the IP 1016 Header is the TLMR, and with a Routing Header of type 2 for the rest 1017 of the way to the Mobile Router, which may be multi-hop. 1019 To build the RH type 2 from the RRH, the HA sets the type to 2, and 1020 clears the bits 32-63 (byte 4 to 7). 1022 9. Mobile Router Operation 1024 This section inherits from chapter 11 of [1], which is extended to 1025 support Mobile Networks and Mobile Routers as a specific case of 1026 Mobile Node. 1028 This draft extends section 11.2.1 of MIPv6 [1] as follows: 1030 o When not at home, an MR uses a reverse tunnel with its HA for all 1031 the traffic that is sourced in its mobile network(s); traffic 1032 originated further down a nested network is not tunneled twice but 1033 for exception cases. 1035 o The full path to and within the Mobile Network is piggy-backed 1036 with the traffic on a per-packet basis to cope with rapid 1037 movement. This makes the packet construction different from MIPv6. 1039 The MR when not at home sets up a bi-directional tunnel with its HA. 1040 The reverse direction MR -> HA is needed to assure transparent 1041 topological correctness to LFNs, as in [3]. But, as opposed to that 1042 solution, nested tunnels are generally avoided. 1044 9.1 Processing of ICMP "RRH too small" 1046 The New ICMP message "RRH too Small" is presented in Section 5. This 1047 message is addressed to the MR which performs the tunnel 1048 encapsulation and generates the RRH. 1050 Hence, a MR that receives the ICMP "RRH too small" MUST NOT propagate 1051 it to the originating LFN or inner tunnel source, but MUST process it 1052 for itself. 1054 If the Current Size in the ICMP messages matches the actual current 1055 number of slots in RRH, and if the ICMP passes some safety checks as 1056 described in Section 5, then the MR MAY adapt the number of slots to 1057 the Proposed Size. 1059 9.2 Processing of ICMP error 1061 ICMP back { 1063 if RRH is present { 1064 compute RH type 2 based on RRH 1065 get packet source from IP header 1066 send ICMP error to source including RH type 2. 1067 } 1068 else { 1069 get packet source from IP header 1070 send ICMP error to source with no RH. 1071 } 1072 } 1074 When the MR receives an ICMP error message, it checks whether it is 1075 the final destination of the packet by looking at the included 1076 packet. If the included packet has an RRH, then the MR will use the 1077 RRH to forward the ICMP to the original source of the packet. 1079 9.3 Processing of RHH for Outbound Packets 1081 if no RRH in outer header /* First Mobile Router specific */ 1082 or RRH present but saturated { /* Need a nested encapsulation */ 1084 if RRH is saturated { 1085 do ICMP back (RRH too small) 1086 } 1088 /* put packet in sliding reverse tunnel */ 1089 insert new IP header plus RRH 1090 set source address to the MR Home Address 1091 set destination address to the MR Home Agent Address 1092 add an RRH with all slots zeroed out 1093 compute IPsec AH on the resulting packet 1094 } 1096 /* All MRs including first */ 1097 if packet size <= MTU { 1098 select first free slot in RRH bottom up 1099 set it to source address from IP header 1100 overwrite source address in IP header with MR CareOf 1101 transmit packet 1102 } else { 1103 do ICMP back (Packet too Big) 1104 } 1105 If the packet already contains an RRH in the outer header, and has a 1106 spare slot, the MR adds the source address from the packet IP header 1107 to the RRH and overwrites the source address in the IP header with 1108 its CoA. As a result, the packets are always topologically correct. 1110 Else, if the RRH is present but is saturated, and therefore the 1111 source IP can not be added, the MR sends a ICMP 'RRH too small' to 1112 the tunnel endpoint which originated the outer packet, using the RRH 1113 info to route it back. The ICMP message is a warning, and the packet 1114 is not discarded. Rather, the MR does a nested encapsulation of the 1115 packet in its own reverse tunnel home with an additional RRH. 1117 Else, if the packet does not have an RRH, the MR puts it in its 1118 reverse tunnel, sourced at the CoA, with an RRH indicating in slot 0 1119 the Home Address of the MR, and with proper IPsec AH as described 1120 further in Section 11.1. 1122 9.4 Processing of Tree Information Option 1124 The Tree Information option in Router Advertisement messages allows 1125 the Mobile Router to select a tree and learn about its capabilities. 1126 The treeDepth can be used to compute the optimum number of slots in 1127 the RRH. 1129 The RRH contains an entry for the home address in slot 0, and one for 1130 every CareOf on the way but that of the last Mobile Router (TLMR). As 1131 the TLMR sets the treeDepth to 0 and each MR increments it on the way 1132 down the tree, the optimum number of slots is normally (treeDepth+1), 1133 where treeDepth is the depth advertised by the MR over its Mobile 1134 Networks. 1136 9.5 Processing of the extended Routing Header Type 2 1138 if Segments Left = 0 { 1140 /* new check: packet must be looped back internally */ 1141 if packet doesn't come from a loopback interface { 1142 discard the packet 1143 return 1144 } 1146 proceed to process the next header in the packet, whose type is 1147 identified by the Next Header field in the Routing header 1148 } 1149 else if Hdr Ext Len is odd { 1150 send an ICMP Parameter Problem, Code 0, message to the Source 1151 Address, pointing to the Hdr Ext Len field, and discard the 1152 packet 1154 } 1155 else { 1156 compute n, the number of addresses in the Routing header, by 1157 dividing Hdr Ext Len by 2 1159 if Segments Left is greater than n { 1160 send an ICMP Parameter Problem, Code 0, message to the Source 1161 Address, pointing to the Segments Left field, and discard the 1162 packet 1163 } 1164 else { 1165 decrement Segments Left by 1; 1167 compute i, the index of the next address to be visited in 1168 the address vector, by subtracting Segments Left from n 1170 if Address [i] or the IPv6 Destination Address is multicast { 1171 discard the packet 1172 } 1173 else { 1174 /* new security check */ 1175 if Address [i] doesn't belong to one of the Mobile Network prefixes { 1176 discard the packet 1177 return 1178 } 1180 /* new check: keep MIPv6 behavior: prevent packets from being 1181 * forwarded outside the node. 1182 */ 1183 if Segments Left equals 0 and Address[i] isn't the node's own 1184 home address { 1185 discard the packet 1186 return 1187 } 1188 swap the IPv6 Destination Address and Address[i] 1189 if the IPv6 Hop Limit is less than or equal to 1 { 1190 send an ICMP Time Exceeded -- Hop Limit Exceeded in 1191 Transit message to the Source Address and discard the 1192 packet 1193 } 1194 else { 1195 decrement the Hop Limit by 1 1196 resubmit the packet to the IPv6 module for transmission 1197 to the new destination; 1198 } 1199 } 1200 } 1201 } 1203 9.6 Decapsulation 1205 A MR when decapsulating a packet from its HA must perform the 1206 following checks 1208 1. Destination address 1210 The destination address of the inner packet must belong to one of 1211 the Mobile Network prefixes. 1213 10. Mobile Host Operation 1215 When it is at Home, a Mobile Host issues packets with source set to 1216 its home address and with destination set to its CN, in a plain IPv6 1217 format. 1219 When a MH is not at home but is attached to a foreign link in the 1220 Fixed Infrastructure, it SHOULD use MIPv6 as opposed to this draft to 1221 manage its mobility. 1223 When a MH is visiting a foreign Mobile Network, it forwards its 1224 outbound packets over the reverse tunnel (including RRH) to its HA. 1225 One can view that operation as a first MR process applied on a plain 1226 IPv6 packet issued by a LFN. 1228 As a result, the encapsulating header include: 1230 with source set to the MH COA and destination set to the MH HA 1232 with slot 0 set to the MH Home Address 1234 The inner packet is the plain IPv6 packet from the MH Home Address to 1235 the CN. 1237 11. Security Considerations 1239 This section is not complete; further work is needed to analyse and 1240 solve the security problems of record and source route. 1242 Compared to MIPv6, the main security problem seems to be the fact 1243 that the RRH can be modified in transit by an in-axis attacker. It 1244 has to be noted that an in-axis attacker (for example any MR in the 1245 Mobile Network) can perform more effective attacks than modifying the 1246 RRH. 1248 Selecting the tree to attach to is a security critical operation 1249 outside of the scope of this draft. 1251 11.1 IPsec Processing 1253 The IPsec [7] AH [8] and ESP [9] can be used in tunnel mode to 1254 provide different security services to the tunnel between a MR and 1255 its HA. ESP tunnel mode SHOULD be used to provide confidentiality and 1256 authentication to the inner packet. AH tunnel mode MUST be used to 1257 provide authentication of the outer IP header fields, especially the 1258 Routing Headers. 1260 11.1.1 Routing Header type 2 1262 Due to the possible usage of Doors [5] to enable IPv4 traversal, the 1263 Routing Header type 2 cannot be treated as type 0 for the purpose of 1264 IPsec processing (i.e. it cannot be included in its intierity in the 1265 Integrity Check Value (ICV) computation, because NAT/PAT may mangle 1266 one of the MR care-of-addresses along the HA-MR path. 1268 The sender (the HA) will put the slot 0 entry (the MR Home Address) 1269 of the RH as destination of the outer packet, will zero out 1270 completely the Routing Header and will perform the ICV computation. 1272 The receiver (the MR) will put the slot 0 entry as destination of the 1273 outer packet, will zero out the Routing Header and will perform the 1274 ICV verification. 1276 11.1.2 Routing Header type 4 1278 The Routing Header type 4 is "partially mutable", and as such can be 1279 included in the Authentication Data calculation. Given the way type 4 1280 is processed, the sender cannot order the field so that it appears as 1281 it will at the receiver; this means the receiver will have to shuffle 1282 the fields. 1284 The sender (the MR) will zero out all the slots and the Segment Used 1285 field of the RRH, and will put as source address of the outer packet 1286 its Home Address, and then will perform the ICV computation. 1288 The receiver (the HA) will put the entry in slot 0 (the MR Home 1289 Address) in the source address and will zero out all the slots and 1290 the Segment Used field of the RRH, and then will perform the ICV 1291 verification. 1293 11.2 New Threats 1295 The RH type 4 is used to construct a MIPv6 RH type 2 with additional 1296 semantics, as described in Section 4.1. Since RH type 2 becomes a 1297 multi hop option like RH type 0, care must be applied to avoid the 1298 spoofing attack that can be performed with the IPv4 source route 1299 option. This is why IPv6 [10] takes special care in responding to 1300 packets carrying Routing Headers. 1302 AH authenticates the MR Home Address identity and the RRH sequence 1303 number. The RRH sequence number is to be used to check the freshness 1304 of the RRH; anti-replay protection can be obtained if the receiver 1305 enables the anti-replay service of AH [8]. 1307 As a consequence, the only kind of successful attack seems to require 1308 to be able to modify the packet in flight. 1310 If one of the RRH entry is faked either to an address outside the 1311 tree or to an address that doesn't match the tree topology (not 1312 belonging to one of the Mobile Network prefixes at that level) then 1313 the reply packet containing a RH type 2 built out of the previous RRH 1314 will be dropped by the first MR that processes that entry, as 1315 described in Section 9. 1317 It is still an issue how to validate that the source of the outer 1318 packet is the actual TLMR as opposed to a forged IP address put by an 1319 on-axis attacker outside the Mobile Network. 1321 12. Acknowledgements 1323 The authors wish to thank David Auerbach, Fred Baker, Dana Blair, 1324 Steve Deering, Dave Forster, Thomas Fossati, Francois Le Faucheur, 1325 Kent Leung, Massimo Lucchina, Vincent Ribiere, Dan Shell and Patrick 1326 Wetterwald -last but not least :)-. 1328 References 1330 [1] Perkins, C., Johnson, D. and J. Arkko, "Mobility Support in 1331 IPv6", draft-ietf-mobileip-ipv6-21 (work in progress), March 1332 2003. 1334 [2] Lach, H. and T. Ernst, "Network Mobility Support Terminology", 1335 draft-ietf-nemo-terminology-00 (work in progress), May 2003. 1337 [3] Kniveton, T., "Mobile Router Tunneling Protocol", 1338 draft-kniveton-mobrtr-03 (work in progress), November 2002. 1340 [4] Deering, S. and B. Zill, "Redundant Address Deletion when 1341 Encapsulating IPv6 in IPv6", 1342 draft-deering-ipv6-encap-addr-deletion-00 (work in progress), 1343 November 2001. 1345 [5] Thubert, P., Molteni, M. and P. Wetterwald, "IPv4 traversal for 1346 MIPv6 based Mobile Routers", 1347 draft-thubert-nemo-ipv4-traversal-00 (work in progress), March 1348 2003. 1350 [6] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1351 1981. 1353 [7] Kent, S. and R. Atkinson, "Security Architecture for the 1354 Internet Protocol", RFC 2401, November 1998. 1356 [8] Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402, 1357 November 1998. 1359 [9] Kent, S. and R. Atkinson, "IP Encapsulating Security Payload 1360 (ESP)", RFC 2406, November 1998. 1362 [10] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) 1363 Specification", RFC 2460, December 1998. 1365 [11] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery 1366 for IP Version 6 (IPv6)", RFC 2461, December 1998. 1368 [12] Conta, A. and S. Deering, "Internet Control Message Protocol 1369 (ICMPv6) for the Internet Protocol Version 6 (IPv6) 1370 Specification", RFC 2463, December 1998. 1372 [13] Reynolds, J., "Assigned Numbers: RFC 1700 is Replaced by an 1373 On-line Database", RFC 3232, January 2002. 1375 Authors' Addresses 1377 Pascal Thubert 1378 Cisco Systems Technology Center 1379 Village d'Entreprises Green Side 1380 400, Avenue Roumanille 1381 Biot - Sophia Antipolis 06410 1382 FRANCE 1384 EMail: pthubert@cisco.com 1386 Marco Molteni 1387 Cisco Systems Technology Center 1388 Village d'Entreprises Green Side 1389 400, Avenue Roumanille 1390 Biot - Sophia Antipolis 06410 1391 FRANCE 1393 EMail: mmolteni@cisco.com 1395 Appendix A. Optimizations 1397 A.1 Path Optimization with RRH 1399 The body of the draft presents RRH as a header that circulates in the 1400 reverse tunnel exclusively. The RRH format by itself has no such 1401 limitation. This section illustrates a potential optimization for 1402 end-to-end traffic between a Mobile Network Node and its 1403 Correspondent Node. 1405 The MNN determines that it is part of a Mobile Network by screening 1406 the Tree Information option in the RA messages from its Attachment 1407 Router. In particular, the MNN knows the TreeDepth as advertised by 1408 the AR. An initial test phase could be derived from MIPv6 to decide 1409 whether optimization with a given CN is possible. 1411 When an MNN performs end-to-end optimization with a CN, the MNN 1412 inserts an empty RRH inside its packets, as opposed to tunneling them 1413 home, which is the default behavior of a Mobile Host as described in 1414 Section 10. 1416 The number of slots in the RRH is initially the AR treeDepth plus 1, 1417 but all slots are clear as opposed to the MR process as described in 1418 Section 9. The source address in the header is the MNN address, and 1419 the destination is the CN. 1421 The AR of the MNN is by definition an MR. Since an RRH is already 1422 present in the packet, the MR does not put the packets from the MNN 1423 on its reverse tunnel, but acts as an intermediate MR; it adds the 1424 source address of the packet (the MNN's address) in the RRH (in slot 1425 0) and stamps its careOf instead in the IP header source address 1426 field. Recursively, all the MRs on a nested network trace in path in 1427 the RRH and take over the source IP. 1429 The support required on the CN side extends MIPv6 in a way similar to 1430 the extension that this draft proposes for the HA side. The CN is 1431 required to parse the RRH when it is valid, refresh its BCE 1432 accordingly, and include an RH type 2 with the full path to its 1433 packets to the MNN. 1435 Note that there is no Bind Update between the MNN and the CN. The RRH 1436 must be secured based on tokens exchanged in the test phase. For the 1437 sake of security, it may be necessary to add fields to the RRH or to 1438 add a separate option in the Mobility Header. 1440 A.2 Packet Size Optimization 1442 RRH allows to update the Correspondent BCE on a per packet basis, 1443 which is the highest resolution that we can achieve. While this may 1444 cope with highly mobile and nested configurations, it can also be an 1445 overkill in some situations. 1447 The RRH comes at a cost: it requires processing in all intermediate 1448 Mobile Routers and in the Correspondent Node. Also, a RRH increases 1449 the packet size by more than the size of an IP address per hop in the 1450 Mobile Network. 1452 This is why an additional Routing Header is proposed (type 3). The 1453 semantics of type 3 are very close to type 4 but: 1455 o Type 3 has only one slot, for the Home Address of the source. 1457 o When it can not add the source to the RH type 3 of an outbound 1458 packet, an intermediate MR: 1460 * MR MUST NOT send ICMP (RRH too small) 1462 * MUST NOT put the packet in a reverse tunnel 1464 Rather, it simply overwrites the source and forwards the packet up 1465 the tree as if the RRH had been properly updated. 1467 o Since the path information is not available, the correspondent 1468 MUST NOT update its BCE based on the RH type 3. The CN (or HA) 1469 identifies the source from the entry in slot 0 and may reconstruct 1470 the initial packet using the CareOf in slot 1 as source for AH 1471 purposes. 1473 /* MR processing on outbound packet with RH type 3 support */ 1474 { 1476 if no RH type 3 or 4 in outer header /* First Mobile Router specific */ 1477 or RH type 4 present but saturated { /* Need a nested encapsulation */ 1479 if RRH is saturated { 1480 do ICMP back (RRH too small) 1481 } 1483 /* put packet in sliding reverse tunnel */ 1484 insert new IP header plus RRH 1485 set source address to the MR Home Address 1486 set destination address to the MR Home Agent Address 1487 add an RRH with all slots zeroed out 1488 compute IPsec AH on the resulting packet 1489 } 1491 /* All MRs including first */ 1492 if packet size > MTU { 1493 do ICMP back (Packet too Big) 1494 } else if RRH { 1495 select first free slot in RRH bottom up 1496 set it to source address from IP header 1497 overwrite source address in IP header with MR CareOf 1498 transmit packet 1499 } else if RH type 3 { 1500 if slot 0 is still free { 1501 /* this is end-to-end optimization */ 1502 set it to source address from IP header 1503 } 1504 overwrite source address in IP header with MR CareOf 1505 transmit packet 1506 } 1507 } 1509 A.2.1 Routing Header Type 3 (Home Address option replacement) 1511 This is an RH-based alternative to the Home Address destination 1512 option. Its usage is described in Appendix A.2. 1514 The decision to send RH type 3 or type 4 is up to the source of the 1515 RRH. Several algorithms may apply, one out of N being the simplest. 1517 IPsec HA processing is done as described in Section 11.1 for Type 4. 1519 The Type 3 Routing Header has the following format: 1521 0 1 2 3 1522 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1523 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1524 | Next Header | Hdr Ext Len | Routing Type=3| Segments Used | 1525 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1526 | Reserved | 1527 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1528 | | 1529 + + 1530 | | 1531 + Home Address + 1532 | | 1533 + + 1534 | | 1535 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1537 Next Header 1539 8-bit selector. Identifies the type of header immediately 1540 following the Routing header. Uses the same values as the IPv4 1541 Protocol field [13]. 1543 Hdr Ext Len 1545 8-bit unsigned integer. Length of the Routing header in 8-octet 1546 units, not including the first 8 octets. For the Type 3 Routing 1547 header, Hdr Ext Len is always 2. 1549 Routing Type 1551 8-bit unsigned integer. Set to 3. 1553 Segment Used 1555 8-bit unsigned integer. Number of slots used. Either 0 or 1. When 1556 the field is zero, then there is no MR on the path and it is valid 1557 for a CN that does not support RRH to ignore this header. 1559 Reserved 1561 32-bit reserved field. Initialized to zero for transmission; 1562 ignored on reception. 1564 Home Address 1566 128-bit home address of the source of the packet. 1568 Appendix B. Multi Homing 1570 B.1 Multi-Homed Mobile Network 1572 Consider difference between situation A and B in this diagram: 1574 ===?== ==?=== 1575 MR1 MR2 1576 | | 1577 ==?=====?== ==?====== situation A 1578 MR3 MR4 MR5 1579 | | | 1580 === === === 1582 ===?== ==?=== 1583 MR1 MR2 1584 | | 1585 ==?=====?=======?====== situation B 1586 MR3 MR4 MR5 1587 | | | 1588 === === === 1590 Going from A to B, MR5 may now choose between MR1 and MR2 for its 1591 Attachment (default) Router. In terms of Tree Information, MR5, as 1592 well as MR3 and MR4, now sees the MR1's tree and MR2's tree. Once MR5 1593 selects its AR, MR2, say, MR5 belongs to the associated tree and 1594 whether MR1 can be reached or not makes no difference. 1596 As long as each MR has a single default router for all its outbound 1597 traffic, 2 different logical trees can be mapped over the physical 1598 configurations in both situations, and once the trees are 1599 established, both cases are equivalent for the processing of RRH. 1601 Note that MR5 MUST use a CareOf based on a prefix owned by its AR as 1602 source of the reverse tunnel, even if other prefixes are present on 1603 the Mobile Network, to ensure that a RH type 2 can be securely routed 1604 back. 1606 B.2 Multihomed Mobile Router 1608 Consider the difference between situation B and C in this diagram: 1610 ===?== ==?=== 1611 MR1 MR2 1612 | | 1613 ==?=====?=======?====== situation B 1614 MR3 MR4 MR5 1615 | | | 1616 === === === 1618 ==? ?== 1619 MR1 1620 | 1621 ==?=====?=======?====== situation C 1622 MR3 MR4 MR5 1623 | | | 1624 === === === 1626 In situation C, MR2's egress interface and its properties are 1627 migrated to MR1. MR1 has now 2 different Home Addresses, 2 Home 1628 Agents, and 2 active interfaces. 1630 If MR1 uses both CareOf addresses at a given point of time, and if 1631 they belong to different prefixes to be used via different attachment 1632 routers, then MR1 actually belongs to 2 trees. It must perform some 1633 routing logic to decide whether to forward packets on either egress 1634 interface. Also, it MUST advertise both tree information sets in its 1635 RA messages. 1637 The difference between situations C and B is that when an attached 1638 router (MR5, say) selects a tree and forwards egress packets via MR1, 1639 it can not be sure that MR1 will actually forward the packets over 1640 that tree. If MR5 has selected a given tree for a specific reason, 1641 then a new source route header is needed to enforce that path on MR1. 1643 The other way around, MR5 may leave the decision up to MR1. If MR1 1644 uses the same attachment router for a given flow or at least a given 1645 destination, then the destination receives consistent RRHs. 1646 Otherwise, the BCE cache will flap, but as both paths are valid, the 1647 traffic still makes it through. 1649 Appendix C. Changes from Previous Version of the Draft 1651 From -01 to -02 1653 Made optional the usage of ICMP warning "RRH too small" (Section 1654 5). 1656 Changed the IPsec processing for Routing Header type 2 (Section 1657 11.1). 1659 From -00 to -01 1661 Added new Tree Information Option fields: 1663 A 8 bits Bandwidth indication that provides an idea of the 1664 egress bandwidth. 1666 A CRC-32 that changes with the egress path out of the tree. 1668 a 32 bits unsigned integer, built by each MR out of a high 1669 order configured preference and 24 bits random constant. This 1670 can help as a tie break in Attachment Router selection. 1672 Reduced the 'negative' part of the lollipop space to 0..255 1674 Fixed acknowledgements (sorry Patrick :) 1676 Changed the type of Tree Information Option from 7 to 10. 1678 Intellectual Property Statement 1680 The IETF takes no position regarding the validity or scope of any 1681 intellectual property or other rights that might be claimed to 1682 pertain to the implementation or use of the technology described in 1683 this document or the extent to which any license under such rights 1684 might or might not be available; neither does it represent that it 1685 has made any effort to identify any such rights. Information on the 1686 IETF's procedures with respect to rights in standards-track and 1687 standards-related documentation can be found in BCP-11. 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