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RFC 2119 keyword, line 491: '... MUST be ignored by the receiver....' (12 more instances...) Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the RFC 3978 Section 5.4 Copyright Line does not match the current year == Line 311 has weird spacing: '... option regro...' == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'MUST not' in this paragraph: The following values MUST not change during the propagation of the TIO down the tree: Type, Length, G, H, TreePreference, TreeDelay and TreeID. All other fields of the TIO are updated at each hop of the propagation. -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. 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'2') (Obsoleted by RFC 4862) ** Obsolete normative reference: RFC 3775 (ref. '3') (Obsoleted by RFC 6275) ** Downref: Normative reference to an Informational draft: draft-ietf-nemo-requirements (ref. '5') ** Downref: Normative reference to an Informational draft: draft-ietf-nemo-terminology (ref. '6') == Outdated reference: A later version (-07) exists of draft-ietf-nemo-multihoming-issues-06 Summary: 10 errors (**), 0 flaws (~~), 7 warnings (==), 7 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 NEMO Working Group P. Thubert 3 Internet-Draft Cisco 4 Expires: May 21, 2007 C. Bontoux 5 Fortinet 6 N. Montavont 7 LSIIT - ULP 8 November 17, 2006 10 Nested Nemo Tree Discovery 11 draft-thubert-tree-discovery-04.txt 13 Status of this Memo 15 By submitting this Internet-Draft, each author represents that any 16 applicable patent or other IPR claims of which he or she is aware 17 have been or will be disclosed, and any of which he or she becomes 18 aware will be disclosed, in accordance with Section 6 of BCP 79. 20 Internet-Drafts are working documents of the Internet Engineering 21 Task Force (IETF), its areas, and its working groups. Note that 22 other groups may also distribute working documents as Internet- 23 Drafts. 25 Internet-Drafts are draft documents valid for a maximum of six months 26 and may be updated, replaced, or obsoleted by other documents at any 27 time. It is inappropriate to use Internet-Drafts as reference 28 material or to cite them other than as "work in progress." 30 The list of current Internet-Drafts can be accessed at 31 http://www.ietf.org/ietf/1id-abstracts.txt. 33 The list of Internet-Draft Shadow Directories can be accessed at 34 http://www.ietf.org/shadow.html. 36 This Internet-Draft will expire on May 21, 2007. 38 Copyright Notice 40 Copyright (C) The Internet Society (2006). 42 Abstract 44 The purpose of this paper is to describe a minimum set of features 45 that extends the Nemo basic support [4] in order to avoid loops in 46 the nested Nemo case. As a result, Mobile Routers assemble into a 47 tree that can be optimized based on various metrics. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 53 2. Terms and Abbreviations . . . . . . . . . . . . . . . . . . . 4 55 3. Motivations . . . . . . . . . . . . . . . . . . . . . . . . . 5 56 3.1 Multi-Homed nested mobile network . . . . . . . . . . . . 5 57 3.2 Loops in nested Nemo . . . . . . . . . . . . . . . . . . . 6 59 4. Router Advertisement extensions . . . . . . . . . . . . . . . 8 60 4.1 Router Advertisement message . . . . . . . . . . . . . . . 8 61 4.2 Tree Information Option . . . . . . . . . . . . . . . . . 8 62 4.3 TIO suboption . . . . . . . . . . . . . . . . . . . . . . 11 63 4.3.1 Format . . . . . . . . . . . . . . . . . . . . . . . . 11 64 4.3.2 Pad1 . . . . . . . . . . . . . . . . . . . . . . . . . 11 65 4.3.3 PadN . . . . . . . . . . . . . . . . . . . . . . . . . 12 66 4.3.4 Bandwidth Suboption . . . . . . . . . . . . . . . . . 12 67 4.3.5 Stable time Suboption . . . . . . . . . . . . . . . . 13 68 4.3.6 Tree Group ID Suboption . . . . . . . . . . . . . . . 14 69 4.3.7 Path Free Medium Time Suboption . . . . . . . . . . . 14 71 5. Tree Discovery . . . . . . . . . . . . . . . . . . . . . . . . 16 72 5.1 tree selection . . . . . . . . . . . . . . . . . . . . . . 17 73 5.2 Sub-tree mobility . . . . . . . . . . . . . . . . . . . . 17 74 5.3 Administrative depth . . . . . . . . . . . . . . . . . . . 18 75 5.4 DRL entries states and stability . . . . . . . . . . . . . 18 76 5.4.1 Held-Up . . . . . . . . . . . . . . . . . . . . . . . 19 77 5.4.2 Held-Down . . . . . . . . . . . . . . . . . . . . . . 20 78 5.4.3 Collision . . . . . . . . . . . . . . . . . . . . . . 20 79 5.4.4 Instability . . . . . . . . . . . . . . . . . . . . . 21 80 5.5 Legacy Routers . . . . . . . . . . . . . . . . . . . . . . 21 82 6. Directed Acyclic Graph Discovery . . . . . . . . . . . . . . . 21 84 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 86 8. Security Considerations . . . . . . . . . . . . . . . . . . . 22 88 9. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 89 9.1 Changes from version 00 to 01 . . . . . . . . . . . . . . 22 90 9.2 Changes from version 01 to 02 . . . . . . . . . . . . . . 22 91 9.3 Changes from version 02 to 03 . . . . . . . . . . . . . . 22 92 9.4 Changes from version 03 to 04 . . . . . . . . . . . . . . 22 94 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 23 96 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 24 97 11.1 Normative Reference . . . . . . . . . . . . . . . . . . . 24 98 11.2 Informative Reference . . . . . . . . . . . . . . . . . . 24 100 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 25 102 Intellectual Property and Copyright Statements . . . . . . . . 26 104 1. Introduction 106 As per Nemo Basic support [4], a Mobile Router autoconfigures a 107 single Care of Address (CoA) to register to its Home Agent and 108 terminate its Mobile Router-Home Agent tunnel. That Care of Address 109 is the Mobile Router point of attachment to the nested Nemo. 111 Consequently, if loops are avoided, the nested Nemo assumes the shape 112 of a tree. The nodes of the tree are Mobile Routers, the root is 113 either a fixed or a Mobile Router, called in the latter case the root 114 Mobile Router in NEMO terminology [6]. The leaves are mobile or 115 fixed hosts, called Local Fixed Nodes, Local Mobile Nodes and 116 Visiting Mobile Nodes in the NEMO terminology. 118 This paper provides (1) a minimum extension to IPv6 Neighbor 119 Discovery Router Advertisements in order to ensure that Mobile 120 Routers attaching to one another actually avoid loops and end up 121 forming a tree, and (2) the minimum common part of all Mobile Router 122 algorithms that is required to ensure that whatever their specific 123 decisions, loops between Mobile Routers will be avoided. 125 The method is based on an autonomous decision by each Mobile Router 126 with no global state convergence such as a MANET proactive routing 127 protocol. In fact, Mobile Routers may make different decisions from 128 a same input, based on their own configuration and their own 129 algorithms. 131 In order to build trees of Mobile Routers, we propose an extension to 132 the ICMP Router Advertisement (RA) message, the Tree Information 133 Option (TIO). The TIO allows Mobile Routers to advertise the tree 134 they belong to, and to select and move to the best location within 135 the available trees. Mobile Routers propagate the TIO in RA down the 136 tree, updating some metrics such as the tree depth, leaving alone 137 root information such as the tree identifier, and sending the result 138 in RAs over the ingress interfaces. 140 2. Terms and Abbreviations 142 This document assumes that the reader is familiar with Mobile IPv6 as 143 defined in [3] and with the concept of Mobile Router defined in the 144 Nemo terminology document [6]. 146 For the needs of this paper, the following new definitions are 147 introduced: 149 Nemo clusterhead: The root of a tree of mobile routers. When the 150 tree of Mobile Routers is attached to the infrastructure, the 151 fixed Access Router may act as cluster head if it supports the 152 Tree Information Option described in this document. If it does 153 not, then the clusterhead coincides with the root Mobile Router in 154 NEMO terminology. A clusterhead is elected even when the tree is 155 not attached to the infrastructure. A stand-alone Mobile Router 156 is a clusterhead. 158 Floating Tree: A Nested Nemo which clusterhead is a Mobile Router 159 that is not attached to an Access Router. 161 Grounded Tree: A Nested Nemo whose clusterhead is attached to the 162 infrastructure. In other words, the clusterhead is either a fixed 163 router that supports Router Advertisement - Tree Information 164 Option or is a Mobile Router which attachment router is a fixed 165 router that does not support Router Advertisement - Tree 166 Information Option. 168 Mobile Access Router: A Mobile Router that provides Access Router 169 services to other Mobile Routers. 171 Attachment Router: The Router that is selected as Access Router by a 172 Mobile Router, making it its parent in the nested NEMO tree. 174 Propagation: The action by a Mobile Router that consists in receiving 175 a Router Advertisement Tree Information Option from its Attachment 176 Router, recomputing a few specific fields, removing unknown 177 suboptions, and appending the resulting TIO to RAs sent over the 178 ingress interfaces. 180 3. Motivations 182 3.1 Multi-Homed nested mobile network 184 A nested mobile network that is made of multiple Mobile Routers 185 having a direct connection to the Internet is said to be multi-homed. 186 Multihoming in Nemo offers useful properties to Mobile Network Nodes. 187 The NEMO multihoming issues [9] draft lists potential multi-homed 188 configurations for Nemo and explains the different problems and 189 advantages that some configurations may introduce. Multihoming 190 offers three main abilities to the Nemo: it allows route recovery on 191 failure, redundancy and load-sharing between Mobile Routers (or 192 between interfaces of a given Mobile Router). However, for the 193 moment, there is no requirements nor protocol that would define in 194 interaction between several egress interfaces inside a Nemo. 196 In a nested Nemo, the hierarchy of Mobile Routers increases the 197 complexity of the route and/or router selection for Mobile Network 198 Nodes. Each level of a Nemo implies the usage of a new tunnel 199 between the Mobile Router and its home agent. Thus if a Mobile 200 Network Node connects to a sub-Nemo which is also a sub-Nemo, packets 201 from the Mobile Network Node will be encapsulated three times. 203 When the Nemo where the MN is connected to is multi-homed, the MN may 204 have the choice between several Attachment Router to be its default 205 router. Reference [7] introduces new options in Router Advertisement 206 to allow any node on a link to choose between several routers. This 207 option mainly consists of a 2-bits flag that indicates the preference 208 of the router (low, medium or high). Furthermore, the same flag can 209 be set in the Route Information option indicating the preference of a 210 specific prefix. Therefore, any node can determine its best default 211 router(s) according to a given destination and its best router for 212 default, which will be used by default. 214 However this preference is only useful in a flat topology; It gives a 215 way to the node to choose between different attachment routers 216 advertising prefixes on the node link. But if the node is inside a 217 hierarchical topology the node can not learn the depth of each 218 attachment router, and might not select the most efficient path. 220 One of the usage of the new option introduced in this document is to 221 distribute information on the hierarchy of Mobile Routers. This 222 information can be distributed to Attachment Routers, Mobile Routers 223 and Mobile Network Nodes as well in order to allow better route 224 selection and to increase the knowledge of the Nemo topology on each 225 node. 227 3.2 Loops in nested Nemo 229 When several Mobile Routers attach to each other to form a nested 230 Nemo, loops can be created if they are not explicitly avoided. In 231 the simplest case, when egress and ingress interfaces of A Mobile 232 Router are all wireless, a mobile router may be listening to Router 233 Advertisement from its own ingress interface, creating a confliction 234 problem. In the general case, arbitrary attachment of Mobile Routers 235 will form graphs that are not exempt of loops. For instance: Assume 236 a nested Nemo where Mobile Router1 is connected to the 237 infrastructure, and Mobile Router3 is attached to Mobile Router2. 238 Say that Mobile Router2 can hear both Mobile Router3 and Mobile 239 Router1 over its wireless egress interface. If Mobile Router2 select 240 Mobile Router1, the connectivity to the infrastructure is provided 241 for all. But if Mobile Router2 selects Mobile Router3, Mobile 242 Router2 and Mobile Router3 end up forming a loop and are disconnected 243 from their Home Agents. 245 With Nemo basic support, a Mobile Router uses a single primary Care 246 Of Address to attach to the nested structure. As a result, if loops 247 are avoided, the nested NEMO end up forming a tree. It is beneficial 248 to be able to form that tree in an optimum fashion for a given set of 249 metrics such as tree depth. 251 The shape of a nested Nemo may change rapidly due to Mobile Routers 252 movement. It is thus impractical to expect each Mobile Router to be 253 able to maintain states about the whole tree structure in a link 254 state fashion. On the contrary, it is also beneficial to allow each 255 Mobile Router to make its own independent selection based on a 256 minimum information about its immediate neighbors, in order to 257 reestablish the tree quickly upon erratic movements. 259 Each Mobile Router should be able to make its own attachment router 260 selection based on its own condition (eg battery level), its own set 261 of constraints that may not apply to other Mobile Routers in the 262 tree, and in general its own algorithm. As a result, the 263 standardization effort should concentrate on a common minimum set of 264 rules that must be common to all Mobile Routers in order to prevent 265 routing loops in the nested NEMO while leaving Mobile Routers 266 independent in their Attachment Router selection algorithms. 268 4. Router Advertisement extensions 270 New extensions of Router Advertisement are proposed to distribute the 271 knowledge of the Mobile Router hierarchy inside a nested Nemo. These 272 extensions are defined in different options/sub-options: a flag bit 273 from the reserved flag field of Router Advertisement message is used 274 to indicate whether the sending router is a Mobile Router or not; a 275 new option is defined to transport minimum information on the tree to 276 avoid loops generation; 278 4.1 Router Advertisement message 280 We propose to use a reserved flag of the Router Advertisement message 281 to inform whether the sending router is a Mobile Router or not. 283 0 1 2 3 284 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 1 285 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 286 | Type | Code | Checksum | 287 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 288 | Cur Hop Limit |M|O|H|N|Reservd| Router Lifetime | 289 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 290 | Reachable Time | 291 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 292 | Retrans Timer | 293 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 294 | Options ... 295 +-+-+-+-+-+-+-+-+-+-+-+- 297 Figure 1: Router Advertisement 299 Nemo enabled router (N) 301 The Nemo enabled router (N) bit is set when the sending router is a 302 Mobile Router. 304 4.2 Tree Information Option 306 The Tree Information Option carries a number of metrics and other 307 information that allows a Mobile Router to discover a tree and select 308 its point of attachment while avoiding loop generation. 310 The option is a container option, which might contain a number of 311 suboptions. The base option regroups the minimum information set 312 that is mandatory in all cases. 314 A TIO can also be used by Mobile Network Nodes to select their best 315 default router. If the default router of a non-Mobile Router sends 316 Router Advertisements with a Tree Information Option, the non-Mobile 317 Router MUST set the N flag of its own Router Advertisement to 0 and 318 copy the Tree Discovery Option in its own Router Advertisement. 320 0 1 2 3 321 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 1 322 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 323 | Type | Length |G|H|B| Reserved | 324 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 325 | TreePref. | BootTimeRandom | 326 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 327 | MR Preference | TreeDepth | TreeDelay | 328 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 329 | PathDigest | 330 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 331 | | 332 + + 333 | TreeID | 334 + + 335 | | 336 + + 337 | | 338 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 339 | sub-option(s)... 340 +-+-+-+-+-+-+-+-+-+-+-+-+-+ 342 Figure 2: RA Tree Information Option 344 Type: 8-bit unsigned integer set to 10 by the clusterhead. Value is 345 "TBD". 347 Length: 8-bit unsigned integer set to 4 when there is no suboption. 348 The length of the option (including the type and length fields and 349 the suboptions) in units of 8 octets. 351 Grounded (G): The Grounded (G) flag is set when the clusterhead is 352 attached to a fixed network infrastructure (such as the Internet). 354 Home (H): The Home (H) flag is set when the clusterhead is attached 355 to its home network. 357 Battery (B): The Battery (B) flag is indicates that a parent in the 358 tree operates on batteries, an indication of a costly operation. 359 It is set by a mobile router which operates on battery and when 360 set, it is left set as it is propagated down the tree. 362 Reserved: 13-bit unsigned integer set to 0 by the clusterhead. 364 TreePreference: 8-bit unsigned integer set by the clusterhead to its 365 preference and unchanged at propagation. Default is 0 (lowest 366 preference). The tree preference provides a mechanism to engineer 367 the mesh of mobile routers, for instance indicating the most 368 preferred home gateway or the communication ship in a fleet at 369 sea. 371 BootTimeRandom: A random value computed at boot time and recomputed 372 in case of a duplication with another Attachment Router. The 373 concatenation of the Preference and the BootTimeRandom is a 32-bit 374 extended preference that is used to resolve collisions. It is set 375 by each Mobile Router at propagation time. 377 Preference: The administrative preference of that (mobile) Access 378 Router. Default is 0. 255 is the highest possible preference. 379 Set by each Mobile Router at propagation time. 381 TreeDepth: 8-bit unsigned integer. The tree depth of the clusterhead 382 is 0 if it is a fixed router and 1 if it is a Mobile Router. The 383 tree Depth of a tree Node is the depth of its attachment router as 384 received in a TIO, incremented by at least one. All nodes in the 385 tree advertise their tree depth in the Tree Information Options 386 that they append to the RA messages over their ingress interfaces 387 as part of the propagation process. 389 TreeDelay: 16-bit unsigned integer set by the clusterhead indicating 390 the delay before changing the tree configuration, in milliseconds. 391 A default value is 128ms. It is expected to be an order of 392 magnitude smaller than the RA-interval so if the clusterhead has a 393 sub-second RA-interval, the Tree delay may be shorter than 100ms. 394 It is also expected to be an order of magnitude longer than the 395 typical propagation delay inside the nested Nemo. 397 PathDigest: 32-bit unsigned integer CRC, updated by each Mobile 398 Router. This is the result of a CRC-32c computation on a bit 399 string obtained by appending the received value and the Mobile 400 Router Care of Address. clusterheads use a 'previous value' of 401 zeroes to initially set the PathDigest. 403 TreeID: 128-bit unsigned integer which uniquely identify a tree. 404 This value is set by the clusterhead. The global IPv6 home 405 address of the clusterhead can be used. 407 The following values MUST not change during the propagation of the 408 TIO down the tree: Type, Length, G, H, TreePreference, TreeDelay and 409 TreeID. All other fields of the TIO are updated at each hop of the 410 propagation. 412 4.3 TIO suboption 414 In addition to the minimum options presented in the base option, a 415 number of suboptions are defined for the TIO: 417 4.3.1 Format 419 0 1 2 3 420 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 1 421 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 422 | Subopt. Type | Subopt Length | Suboption Data... 423 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 425 Figure 3: TIO suboption generic format 427 Suboption Type: 8-bit identifier of the type of mobility option. 428 When processing a TIO containing a suboption for which the 429 suboption Type value is not recognized by the receiver, the 430 receiver MUST silently ignore and skip over the suboption, 431 correctly handling any remaining options in the message. 433 Suboption Length: 8-bit unsigned integer, representing the length in 434 octets of the suboption, not including the suboption Type and 435 Length fields. 437 Suboption Data: A variable length field that contains data specific 438 to the option. 440 The following subsections specify the TIO suboptions which are 441 currently defined for use in the Mobility Header. 443 Implementations MUST silently ignore any TIO suboptions options that 444 they do not understand. 446 TIO suboptions may have alignment requirements. Following the 447 convention in IPv6, these options are aligned in a packet so that 448 multi-octet values within the Option Data field of each option fall 449 on natural boundaries (i.e., fields of width n octets are placed at 450 an integer multiple of n octets from the start of the header, for n = 451 1, 2, 4, or 8). 453 4.3.2 Pad1 455 The Pad1 suboption does not have any alignment requirements. Its 456 format is as follows: 458 0 459 0 1 2 3 4 5 6 7 460 +-+-+-+-+-+-+-+-+ 461 | Type = 0 | 462 +-+-+-+-+-+-+-+-+ 464 Figure 4: Pad 1 466 NOTE! the format of the Pad1 option is a special case - it has 467 neither Option Length nor Option Data fields. 469 The Pad1 option is used to insert one octet of padding in the TIO to 470 enable suboptions alignment. If more than one octet of padding is 471 required, the PadN option, described next, should be used rather than 472 multiple Pad1 options. 474 4.3.3 PadN 476 The PadN option does not have any alignment requirements. Its format 477 is as follows: 479 0 1 480 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 481 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - - 482 | Type = 1 | Subopt Length | Subopt Data 483 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - - 485 Figure 5: Pad N 487 The PadN option is used to insert two or more octets of padding in 488 the TIO to enable suboptions alignment. For N (N > 1) octets of 489 padding, the Option Length field contains the value N-2, and the 490 Option Data consists of N-2 zero-valued octets. PadN Option data 491 MUST be ignored by the receiver. 493 4.3.4 Bandwidth Suboption 495 This suboption carries the maximum bandwidth available up the tree 496 via a specific parent. It is the lowest speed of the links on the 497 way and does not reflect the actual use of those links in run time. 498 The value is expressed in the log base 2 of the speed, expressed in 499 bps. The Bandwidth suboption does not have any alignment 500 requirements. Its format is as follows: 502 0 1 2 503 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 504 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---------------+ 505 | Type = 2 | Length = 1 | Bandwidth | 506 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---------------+ 508 Figure 6: Bandwidth Suboption 510 Type: Set to 2 for the Bandwidth suboption. 512 Length: Set to 1 for the Bandwidth suboption. 514 Bandwidth: 8-bit unsigned integer. The Log2 of the speed of the path 515 expressed in bps. The clusterhead initializes that field using 516 the speed of the link to the Access Router to which it is attached 517 or 0xFF if it is floating. An attached MR propagates it as the 518 minimum of the Bandwidth as received in the TIO from the parent 519 and the access speed between the MR and the parent. As a result, 520 the value received from a candidate AR is that of the bottleneck 521 between that AR and the wire access. 523 4.3.5 Stable time Suboption 525 This suboption carries an indicator of the stability of a network. 526 This indicator is the time since the branch to which the MR is 527 attached has remained unchanged. The value is expressed in the log 528 base 2 of that duration, expressed in milliseconds. The Stable time 529 suboption does not have any alignment requirements. Its format is as 530 follows: 532 0 1 2 533 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 534 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---------------+ 535 | Type = 3 | Length = 1 | Stable time | 536 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---------------+ 538 Figure 7: Stable time 540 Type: Set to 3 for the Stable time suboption. 542 Length: Set to 1 for the Stable time suboption. 544 Stable time: 8-bit unsigned integer. The Log2 of the time since the 545 last change in the attachment branch, expressed in milliseconds. 546 This is set by the MR as it propagates the TIO down the tree, 547 indicating for how long the PathDigest in the TIO from its parent 548 has remained unchanged. 550 4.3.6 Tree Group ID Suboption 552 This suboption carries the Group ID for the tree. It is set by the 553 clusterhead and is left unchanged by the MR that propagates the TIO 554 down the tree. The Tree Group ID Suboption has an alignment 555 requirement of 8n+6. Its format is as follows: 557 0 1 2 3 558 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 1 559 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 560 | Type = 4 | Length = 16 | 561 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 562 | | 563 + + 564 | Tree | 565 + Group ID + 566 | | 567 + + 568 | | 569 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 571 Figure 8: Tree Group ID Suboption 573 Type: 8-bit unsigned integer. Its value is 4 for the Tree Group ID 574 suboption. 576 Length: 8-bit unsigned integer. Its value is 16 for the Tree Group 577 ID suboption. 579 Tree Group ID: 128-bit unsigned integer which identify a group for a 580 tree. This value is set by the clusterhead. It can be set 581 administratively, for instance to an IPv6 multicast group. 583 4.3.7 Path Free Medium Time Suboption 585 This suboption carries the Free Medium Time available up the tree via 586 a specific parent at a given point of time. It is an indication of 587 whether bandwidth is available to place VoIP calls for instance. As 588 defined by the Quality of Service (QoS) Task Group of the Wi-Fi 589 Alliance, the Medium Time describes the amount of time admitted to 590 access the medium, in units of 32 microsecond periods per second. 592 The Free Medium Time is the amount of time left the medium, in other 593 words ((1000000/32) - SIGMA(MT)). The Path Free Medium Time is the 594 lowest available Free Medium Time along the way and it reflects the 595 actual use of those links in run time. 597 The Path Free Medium Time suboption does not have any alignment 598 requirements. Its format is as follows: 600 0 1 2 3 601 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 1 602 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 603 | Type = 5 | Length = 2 | Path Free Medium Time | 604 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 606 Figure 9: Path Free Medium Time Suboption 608 Type: Set to 5 for the Path Free Medium Time Suboption. 610 Length: Set to 2 for the Path Free Medium Time Suboption. 612 Path Free MT: 16-bit unsigned integer. The amount of Medium Time 613 that is available along the path to the clusterhead in units of 32 614 microsecond periods per second. The clusterhead initializes that 615 field to the Free MT on the link where the TIO is issued. An 616 attached MR propagates it as the minimum of the Path Free MT as 617 received in the TIO from the parent and the Path Free MT on the 618 link on which the TIO is propagated. As a result, the value 619 received from a candidate AR is that of the bottleneck between 620 that AR and the clusterhead. 622 5. Tree Discovery 624 Here follows a set of rules and definitions that MUST be followed by 625 all Mobile Routers: 627 1. A Mobile Router that is not attached to an Attachment Router is 628 the Nemo clusterhead of its own floating tree. It's depth is 1. 630 2. A Mobile Router that is attached to an Attachment Router that 631 does not support TIO, is the clusterhead of its own grounded 632 tree. It's depth is 1. 634 3. A router sending a RA without TIO is considered a grounded 635 Attachment Router at depth 0. 637 4. The Nemo clusterhead of a tree exposes the tree in the Router 638 Advertisement Tree Information Option and Mobile Routers 639 propagate the TIO down the tree with the RAs that they forward 640 over their ingress links. 642 5. A Mobile Router that is already part of a tree MAY move at any 643 time and with no delay in order to get closer to the clusterhead 644 of its current tree - i.e. in order to reduce its own tree depth. 645 But A Mobile Router MUST NOT move down the tree that it is 646 attached to. Mobile Routers MUST ignore RAs that are received 647 from other routers located deeper within the same tree. 649 6. A Mobile Router may move from its current tree into any different 650 tree at any time and whatever the depth it reaches in the new 651 tree, but it may have to wait for a Tree Hop timer to elapse in 652 order to do so. The Mobile Router will join that other tree if 653 it is more preferable for reasons of connectivity, configured 654 preference, free Medium Time, size, security, bandwidth, tree 655 depth, or whatever metrics the Mobile Router cares to use. 657 7. If a Mobile Router has selected a new attachment router but has 658 not moved yet (because it is waiting for Tree Hop timer to 659 elapse), the Mobile Router is unstable and refrains from sending 660 Router Advertisement - Tree Information Options. 662 8. When A Mobile Router joins a tree, moves within its tree, or when 663 it receives a modified TIO from its current attachment router, 664 the Mobile Router sends an unsolicited Router Advertisement 665 message on all its mobile networks (i.e. all its ingress 666 interfaces). The RA contains a TIO that propagates the new tree 667 information. At the same time, the Mobile Router MAY send a 668 Binding Update to its home agent or a local proxy of some sort, 669 because the tree it is attached to has changed. If the Mobile 670 Router fails to reach its Home Agent, it MAY attempt to roll back 671 the movement or to retry the Home Agent discovery procedure. 673 9. This allows the new higher parts of the tree to take place first 674 eventually dragging their sub-tree with them, and allowing 675 stepped sub-tree reconfigurations, limiting relative movements. 677 5.1 tree selection 679 The tree selection is implementation and algorithm dependent. In 680 order to limit erratic movements, and all metrics being equal, Mobile 681 Routers SHOULD stick to their previous selection. Also, Mobile 682 Routers SHOULD provide a mean to filter out candidate Attachment 683 Routers whose availability is detected as fluctuating, at least when 684 more stable choices are available. For instance, the Mobile Router 685 MAY place the failed Attachment Router in a Hold Down mode that 686 ensures that the Attachment Router will not be reused for a given 687 period of time. 689 The known trees are associated with the Attachment Router that 690 advertises them and kept in a list by extending the Default Router 691 List. DRL entries are extended to store the information received 692 from the last TIO. These entries are managed by states and timers 693 described in the next section. 695 When connection to a fixed network is not possible or preferable for 696 security or other reasons, scattered trees should aggregate as much 697 as possible into larger trees in order to allow inner connectivity. 698 How to balance these trees is implementation dependent, and MAY use a 699 specific visitor-counter suboption in the TIO. 701 A Mobile Router SHOULD verify that bidirectional connectivity is 702 available with a candidate Attachment Router before it attaches to 703 that candidate. Some layer 2 such as 802.11 infrastructure mode will 704 provide for this, while others such as 802.11 adhoc mode will not. 705 If the layer 2 does not guarantee the bidirectional connectivity, 706 then the MR needs to make sure that it can reach the AR. This can be 707 achieved using Neighbor Sollicitation and refraining from attaching 708 to an AR for which no neighbor cache exists, or the state is still 709 INCOMPLETE. 711 5.2 Sub-tree mobility 713 It might be perceived as beneficial for a sub-tree to move as a 714 whole. The way it would work is for a Mobile Router to stay 715 clusterhead even if itself is attached into a parent tree. But the 716 loop avoidance is based on the knowledge of the tree that the Mobile 717 Router visit, preventing a Mobile Router to move down a same tree. 718 So without additional support, tree-level loops could form. 720 To avoid this, it is possible to add a path vector suboption to the 721 TIO that reflects the nesting of trees. If a root-Mobile Router 722 joins a parent tree, then it needs to add its treeID to the path 723 vector, but it can not join if the treeID is already listed. 725 A specific case is the root-Mobile Router of a tree that attaches to 726 a fixed Access Router. That root-Mobile Router might omit to 727 consider a TIO that comes from the new Attachment Router and decide 728 to stay root, in order to keep the tree consistency from the nested 729 Mobile Routers standpoint. This does not create loops, even if the 730 path vector is not present 732 5.3 Administrative depth 734 When the tree is formed under a common administration, or when a 735 Mobile Router performs a certain role within a community, it might be 736 beneficial to associate a range of acceptable depth with that MR. 737 For instance, a MR that has limited battery should be a leaf unless 738 there is no other choice, and thus expose an exagerated depth. On 739 the other hane, a MR that is designed for backhaul should operate in 740 a low range of depth. 742 With Tree Discovery, a MR has to expose a depth that is incremented 743 from its parent's depth as receive in the TIO. In particular, a MR 744 might expose a depth which is incremented by more than one from its 745 parent's depth, in order to fit in its own administrative range. So 746 a depth of N does not mean that there is precisely N Mobile Routers 747 on the way, but at most N. 749 5.4 DRL entries states and stability 751 Attachment routers in the DRL may or may not be usable for roaming 752 depending on runtime conditions. The following states are defined: 754 Current This Attachment Router is used for roaming 756 Candidate This Attachment Router can be used for roaming. 758 Held-Up This Attachment Router can not be used till tree hop timer 759 elapses. This does not occur for a fixed Attachment Router that 760 does not send a TIO since the tree delay is null in that case. 762 Held-Down This Attachment Router can not be used till hold down timer 763 elapses. At the end of the hold-down period, the router is 764 removed from the DRL, and will be reinserted if it appears again 765 with a RA. 767 Collision This Attachment Router can not be used till its next RA. 769 5.4.1 Held-Up 771 This state is managed by the tree Hop timer, it serves 2 purposes: 773 Delay the reattachment of a sub-tree that has been forced to 774 detach. This allows to make sure that when a sub-tree has 775 detached, the Router Advertisement - Tree Information Option that 776 is initiated by the new clusterhead has spread down the sub-tree 777 so that two different trees have formed. 779 Limit Router Advertisement - Tree Information Option storms when 780 two trees collide. The idea is that between the nodes from tree A 781 that wish to move to tree B, those that see the highest place in 782 tree B will move first and advertise their new locations before 783 other nodes from tree A actually move. 785 A new tree is discovered upon a router advertisement message with or 786 without a Router Advertisement - Tree Information Option. The Mobile 787 Router joins the tree by selecting the source of the RA message as 788 its attachment router (default gateway) and propagating the TIO 789 accordingly. 791 When a new tree is discovered, the candidate Attachment Router that 792 advertises the new tree is placed in a held up state for the duration 793 of a Tree Hop timer. If the new Attachment Router is more preferable 794 than the current one, the Mobile Router expects to jump and becomes 795 unstable. 797 A Mobile Router that is unstable may discover other Attachment 798 Routers from the same new tree during the instability phase. It 799 needs to start a new Tree Hop timer for all these. The first timer 800 that elapses for a given new tree clears them all for that tree, 801 allowing the Mobile Router to jump to the highest position available 802 in the new tree. 804 The duration of the Tree Hop timer depends on the tree delay of the 805 new tree and on the depth of Attachment Router that triggers it: 807 (AR's depth + random) * AR's tree_delay (where 0 <= random < 1). It 808 is randomized in order to limit collisions and synchronizations. 810 5.4.2 Held-Down 812 When a router is 'removed' from the Default Router List, it is 813 actually held down for a hold down timer period, in order to prevent 814 flapping. This happens when an Attachment Router disappears (upon 815 expiration timer), and when an Attachment Router is tried but can not 816 reach the Home Agent (upon expiration of another Attachment Router, 817 or upon tree hop for that Attachment Router). 819 An Attachment Router that is held down is not considered for the 820 purpose of roaming. When the hold down timer elapses, the Attachment 821 Router is removed from the DRL. 823 5.4.3 Collision 825 A race condition occurs if 2 Mobile Routers send Router Advertisement 826 - Tree Information Option at the same time and wish to join each 827 other. In order to detect the situation, Mobile Routers time stamp 828 the sending of Router Advertisement - Tree Information Option. Any 829 Router Advertisement - Tree Information Option received within a 830 short media-dependant period introduces a risk. To divide the risk, 831 A 32bits extended preference is added in the TIO. The first byte is 832 the clusterhead preference, the remaining 24 bits is a boot time 833 computed random. 835 A Mobile Router that decides to join an Attachment Router will do so 836 between (Attachment Router depth) and (Attachment Router depth + 1) 837 times the Attachment Router tree delay. But since a Mobile Router is 838 unstable as soon as it receives the Router Advertisement - Tree 839 Information Option from the preferred Attachment Router, it will 840 restrain from sending a Router Advertisement - Tree Information 841 Option between the time it receives the RA and the time it actually 842 jumps. So the crossing of RA may only happen during the propagation 843 time between the Attachment Router and the Mobile Router, plus some 844 internal queuing and processing time within each machine. It is 845 expected that one tree delay normally covers that interval, but 846 ultimately it is up to the implementation and the configuration of 847 the Attachment Router to define the duration of risk window. 849 There is risk of a collision when a Mobile Router receives an RA, for 850 an other mobile router that is more preferable than the current 851 Attachment Router, within the risk window. In the face of a 852 potential collision, the Mobile Router with the lowest extended 853 preference processes the Router Advertisement - Tree Information 854 Option normally, while the router with the highest preference places 855 the other in collision state, does not start the tree hop timer, and 856 does not become instable. It is expected that next RAs between the 857 two will not cross anyway. 859 5.4.4 Instability 861 A Mobile Router is instable when it is prepared to move shortly to 862 another Attachment Router. This happens typically when the Mobile 863 Router has selected a more preferred candidate Attachment Router and 864 has to wait for the tree hop timer to elapse before roaming. 865 Instability may also occur when the current Attachment Router is lost 866 and the next best is still held up. Instability is resolved when the 867 tree hop timer of all the Attachment Router (s) causing instability 868 elapse. Such Attachment Router is changes state to Current or Held- 869 Down. 871 Instability is transient (in the order of tree hop timers). When a 872 Mobile Router is unstable, it MUST NOT send RAs with TIO. This 873 avoids loops when Mobile Router A wishes to attach to Mobile Router B 874 and Mobile Router B wishes to attach to Mobile Router A. Unless RA 875 cross (see Collision section), a Mobile Router receives TIO from 876 stable Attachment Routers, which do not plan to attach to itself, so 877 the Mobile Router can safely attach to them. 879 5.5 Legacy Routers 881 A legacy router sends its Router Advertisements without a TIO. 882 Consequently, a legacy router can be mistaken for a fixed Access 883 Router when it is placed within a nested NEMO structure, and defeat 884 the loop avoidance mechanism. Consequently, it is important for the 885 administrator to prevent address autoconfiguration by visiting Mobile 886 Routers from such a legacy router. 888 6. Directed Acyclic Graph Discovery 890 Tree Discovery builds trees, which are a specific form of a Directed 891 Acyclic Graph (DAG). In a more general Fashion, TD can be adapted to 892 form DAGs, oriented towards the clusterhead. This is DAG Discovery. 894 In Section 5.3, TD enables a given MR to expose a depth that is 895 incremented by more than one with regards to its parent. When it 896 does so, a MR can elect a number of alternate parents as feasible 897 successors. A feasible successor belongs to the same tree as the MR 898 parent, and has a depth that is less than that of the MR. 900 The links MR to feasible successors complete the tree as built by TD 901 into a DAG towards the clusterhead. The DAG enables alternate exit 902 paths for a multihomed Mobile Router. 904 7. IANA Considerations 906 Section 4.2. requires the definition of a new option to Neighbor 907 discovery [1] messages, the Router Advertisement - Tree Information 908 Option (RA-TIO). The Router Advertisement - Tree Information Option 909 has been assigned the value TBD within the numbering space for IPv6 910 Neighbor Discovery Option Formats. 912 8. Security Considerations 914 At the current level of this draft, the TIO bears the security level 915 of the RA and the link. Nothing is added to it. A deeper threat 916 analysis would be required to eventually propose additional security. 918 9. Changes 920 9.1 Changes from version 00 to 01 922 Added text on sub-tree mobility from the discussion with Marcelo. 924 Added text on nested legacy routers from the discussion with 925 Marcelo. 927 9.2 Changes from version 01 to 02 929 Improved text on instability 931 Changed the formula for the 4 bytes number used in collision 932 avoidance 934 9.3 Changes from version 02 to 03 936 Added suboptions for tree group, stable time and bandwidth. 938 Added administrative depth and increment by more than 1. 940 Added words on bidirectional check using ND. 942 Added DAG discovery. 944 9.4 Changes from version 03 to 04 946 Added suboptions for Path Free Medium Time. 948 10. Acknowledgments 950 The authors wish to thank Marco Molteni and Patrick Wetterwald 951 (cisco) for their participation to this design and the review of the 952 document, and Massimo Villari (university of Messina), for his early 953 work on simulation and research on the subject. This work is also 954 based on prior publications, in particular HMRA [8] by Hosik Cho and 955 Eun-Kyoung Paik from Seoul National University and other non IETF 956 publications coauthored with Thierry Ernst and Thomas Noel. Finally, 957 thanks to Marcelo Bagnulo Braun for his constructive review. 959 11. References 961 11.1 Normative Reference 963 [1] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery 964 for IP Version 6 (IPv6)", RFC 2461, December 1998. 966 [2] Thomson, S. and T. Narten, "IPv6 Stateless Address 967 Autoconfiguration", RFC 2462, December 1998. 969 [3] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in 970 IPv6", RFC 3775, June 2004. 972 [4] Devarapalli, V., Wakikawa, R., Petrescu, A., and P. Thubert, 973 "Network Mobility (NEMO) Basic Support Protocol", RFC 3963, 974 January 2005. 976 [5] Ernst, T., "Network Mobility Support Goals and Requirements", 977 draft-ietf-nemo-requirements-06 (work in progress), 978 November 2006. 980 [6] Ernst, T. and H. Lach, "Network Mobility Support Terminology", 981 draft-ietf-nemo-terminology-06 (work in progress), 982 November 2006. 984 [7] Draves, R. and D. Thaler, "Default Router Preferences and More- 985 Specific Routes", RFC 4191, November 2005. 987 11.2 Informative Reference 989 [8] Cho, H., "Hierarchical Mobile Router Advertisement for nested 990 mobile networks", draft-cho-nemo-hmra-00 (work in progress), 991 January 2004. 993 [9] Ng, C., "Analysis of Multihoming in Network Mobility Support", 994 draft-ietf-nemo-multihoming-issues-06 (work in progress), 995 June 2006. 997 Authors' Addresses 999 Pascal Thubert 1000 Cisco Systems 1001 Village d'Entreprises Green Side 1002 400, Avenue de Roumanille 1003 Batiment T3 1004 Biot - Sophia Antipolis 06410 1005 FRANCE 1007 Phone: +33 4 97 23 26 34 1008 Email: pthubert@cisco.com 1010 Caroline Bontoux 1011 Fortinet 1012 Sophia Antipolis 1013 Biot 06410 1014 FRANCE 1016 Email: cbontoux@fortinet.com 1018 Nicolas Montavont 1019 LSIIT - Univerity Louis Pasteur 1020 Pole API, bureau C444 1021 Boulevard Sebastien Brant 1022 Illkirch 67400 1023 FRANCE 1025 Phone: (33) 3 90 24 45 87 1026 Email: montavont@dpt-info.u-strasbg.fr 1027 URI: http://www-r2.u-strasbg.fr/~montavont/ 1029 Intellectual Property Statement 1031 The IETF takes no position regarding the validity or scope of any 1032 Intellectual Property Rights or other rights that might be claimed to 1033 pertain to the implementation or use of the technology described in 1034 this document or the extent to which any license under such rights 1035 might or might not be available; nor does it represent that it has 1036 made any independent effort to identify any such rights. 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