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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IPv6 Group R. Droms 3 Internet-Draft P. Thubert 4 Intended status: Informational Cisco 5 Expires: June 8, 2008 December 6, 2007 7 DHCPv6 Prefix Delegation for NEMO 8 draft-ietf-nemo-dhcpv6-pd-03 10 Status of this Memo 12 By submitting this Internet-Draft, each author represents that any 13 applicable patent or other IPR claims of which he or she is aware 14 have been or will be disclosed, and any of which he or she becomes 15 aware will be disclosed, in accordance with Section 6 of BCP 79. 17 Internet-Drafts are working documents of the Internet Engineering 18 Task Force (IETF), its areas, and its working groups. Note that 19 other groups may also distribute working documents as Internet- 20 Drafts. 22 Internet-Drafts are draft documents valid for a maximum of six months 23 and may be updated, replaced, or obsoleted by other documents at any 24 time. It is inappropriate to use Internet-Drafts as reference 25 material or to cite them other than as "work in progress." 27 The list of current Internet-Drafts can be accessed at 28 http://www.ietf.org/ietf/1id-abstracts.txt. 30 The list of Internet-Draft Shadow Directories can be accessed at 31 http://www.ietf.org/shadow.html. 33 This Internet-Draft will expire on June 8, 2008. 35 Copyright Notice 37 Copyright (C) The IETF Trust (2007). 39 Abstract 41 One aspect of network mobility support is the assignment of a prefix 42 or prefixes to a Mobile Router (MR) for use on the links in the 43 Mobile Network. DHCPv6 prefix delegation can be used for this 44 configuration task. 46 1. Introduction 48 One aspect of network mobility support is the assignment of a prefix 49 or prefixes to a Mobile Router for use on the links in the Mobile 50 Network. DHCPv6 prefix delegation [RFC3633] (DHCPv6PD) can be used 51 for this configuration task. 53 2. Terminology 55 The key words MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, 56 SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL in this document are to be 57 interpreted as described in RFC2119 [RFC2119]. 59 The following terms used in this document are defined in the IPv6 60 Addressing Architecture document [RFC3513]: 61 link-local unicast address 62 link-local scope multicast address 64 The following terms used in this document are defined in the mobile 65 IPv6 specification [RFC3775]: 66 home agent (HA) 67 home link 69 The following terms used in this document are defined in the Mobile 70 Network terminology document [I-D.ietf-nemo-terminology]: 71 Mobile Router (MR) 72 Mobile Network 73 mobile host (MH) 75 The following terms used in this document are defined in the DHCPv6 76 [RFC3315] and DHCPv6 prefix delegation [RFC3633] specifications: 77 delegating router (DR) 78 requesting router (RR) 79 DHCPv6 relay agent 81 3. Application of DHCPv6 prefix delegation to mobile networks for 82 delegation of home prefixes 84 The NEMO Basic protocol [RFC3963] extends the mobile IPv6 protocol 85 [RFC3775] to enable network mobility. In this extension, a MR uses 86 the mobile IPv6 protocol to establish a maintain a session with its 87 HA, and uses bidirectional tunneling between the MR and HA to provide 88 a path through which hosts attached to links in the Mobile Network 89 can maintain connectivity with nodes not in the Mobile Network. 91 The requirements for NEMO [I-D.ietf-nemo-requirements] include the 92 ability of the MR to receive delegated prefixes that can then be 93 assigned to links in the Mobile Network. DHCPv6PD can be used to 94 meet this requirement for prefix delegation. 96 To use DHCPv6PD for Mobile Networks, the HA assumes the role of 97 either the DR or a DHCPv6 relay agent and the MR assumes the role of 98 the RR. Throughout the remainder of this document, the HA will be 99 assumed to be acting as a DHCPv6PD DR or relay agent and the MR will 100 be assumed to be acting as a RR. 102 If the HA is acts as relay agent, some other device acts as the DR. 103 For example, the server providing DHCPv6 service in the home network 104 might also provide NEMO DHCPv6PD service. Or, a home network with 105 several HAs might configure one of those HAs as a DHCPv6PD server 106 while the other HAs act as relay agents. 108 The HA and MR exchange DHCPv6PD protocol messages through the tunnel 109 connecting them. The tunnel acts as the link labeled "DSL to 110 subscriber premises" in figure 1 of the DHCPv6PD specification. 112 The DHCPv6PD server is provisioned with prefixes to be assigned using 113 any of the prefix assignment mechanisms described in the DHCPv6PD 114 specifications. Other updates to the HA data structures required as 115 a side effect of prefix delegation are specified by the particular 116 network mobility protocol. For example, in the case of Basic Network 117 Mobility Support [RFC3963], the HA would add an entry in its binding 118 cache registering the delegated prefix to the MR to which the prefix 119 was delegated. 121 3.1. When the MR uses DHCPv6 123 The MR initiates a DHCPv6 message exchange for prefix delegation 124 whenever it establishes an MRHA tunnel to its HA. If the MR does not 125 have any active delegated prefixes (with unexpired leases), the MR 126 initiates a DHCPv6 message exchange with a DHCPv6 Solicit message as 127 described in section 17 of RFC 3315 and section 12 of RFC 3633. If 128 the MR has one or more active delegated prefixes, the MR initiates a 129 DHCPv6 message exchange with a DHCPv6 Confirm message as described in 130 section 18.1.2 of RFC 3315 and section 12 of RFC 3633. 132 3.2. Use of MRHA tunnel for DHCPv6 messages 134 The DHCPv6 specification requires the use of link-local unicast and 135 link-local scope multicast addresses in DHCPv6 messages (except in 136 certain cases as defined in section 22.12 of the DHCPv6 137 specification). Section 10.4.2 of the mobile IPv6 specification 138 describes forwarding of intercepted packets, and the third paragraph 139 of that section begins: 141 However, packets addressed to the mobile node's link-local address 142 MUST NOT be tunneled to the mobile node. 144 The DHCPv6 messages exchanged between the HA and the MR originate 145 only with the HA and the MR, and therefore are not "intercepted 146 packets" and may be sent between the HA and the MR through the 147 tunnel. 149 Even though the MRHA tunnel is a point to point connection, the MR 150 SHOULD use multicast DHCPv6 messages as described in RFC 3315 over 151 that tunnel. 153 3.3. Exchanging DHCPv6 messages when MR is at home 155 When the MR is on its home link, the HA uses the home link to 156 exchange DHCPv6PD messages with the MR. It is the responsibility of 157 the implementation to determine when the MR is on its home link and 158 to avoid use of any existing tunnel. 160 3.4. Minimizing DHCPv6PD messages 162 DHCPv6PD in a Mobile Network can be combined with the Rapid Commit 163 option [RFC3315] to provide DHCPv6 prefix delegation with a two 164 message exchange between the mobile node and the DHCPv6 PD server. 166 3.5. DHCPv6PD and DHAAD 168 The MR acting as RR needs a direct link to the DR (or relay) 169 function. When the MR is away from Home, that link is the MRHA 170 tunnel. If a MR needs to obtain a prefix by means of DHCPv6PD, it 171 has to locate a HA that is capable of serving either as a DHCPv6PD 172 relay agent or server. Since the use of DHCPv6PD is optional and 173 comes as an addition to existing protocols [RFC 3775] and [RFC 3963], 174 it can not be expected that all HAs are DHCPv6PD capable. 176 This specification extends Dynamic Home Agent Address Discovery and 177 the Home Agent Information Option in order to enable the detection by 178 a MR of all HAs that are DHCPv6PD capable. A new 'D' bit is 179 introduced to let Home Agents advertise that they are willing to 180 participate to DHCP. Note that there is no need for the MR acting as 181 RR to know whether a HA is actually a DR or simply acting as a relay. 183 3.5.1. Modified Dynamic Home Agent Address Discovery Request 185 A new flag (D) (Support for DHCPv6PD) is introduced in the DHAAD 186 Request message, defined in [RFC3775] and [RFC 3963]. The Mobile 187 Router sets this flag to indicate that it wants to discover Home 188 Agents participating to DHCPv6 Prefix Delegation. 190 A the MR which sets the 'D' flag MUST also set the 'R' flag, to 191 declare that it is a Mobile Router and asks for a HA that supports 192 Mobile Routers, as defined in [RFC 3963]. 194 0 1 2 3 195 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 1 196 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 197 | Type | Code | Checksum | 198 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 199 | Identifier |R|D| Reserved | 200 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 202 DHCPv6PD Support Flag (D) 204 A one-bit flag that when set indicates that the Mobile Router 205 wants to discover Home Agents participating to DHCPv6 Prefix 206 Delegation. 208 For a description of the other fields in the message, see [RFC3775] 209 and [RFC 3963]. 211 3.5.2. Modified Dynamic Home Agent Address Discovery Reply 213 A new flag (D) (Support for DHCPv6PD) is introduced in the DHAAD 214 Reply message, defined in [RFC3775] and [RFC 3963]. If a Home Agent 215 receives a Dynamic Home Agent Discovery request message with the 216 DHCPv6PD Support Flag set, it MUST reply with a list of Home Agents 217 participating to DHCPv6PD. 219 The DHCPv6PD Support Flag MUST be set if there is at least one Home 220 Agent participating to DHCPv6PD. In that case, the reply will list 221 only those HAs that participate to DHCPv6PD, whether they act as 222 servers (DRs) or relays. 224 A HA that supports DHCPv6PD MUST support Mobile Routers as well, so 225 if the 'D' bit is set, then the 'R' bit should be set as well. So 226 there is no need in an implementation to support the case where some 227 HAs would support Mobile Routers while others would be participating 228 to DHCPv6 Prefix Delegation but none could do both. 230 If none of the Home Agents support DHCPv6PD, the Home Agent MAY reply 231 with a list of Home Agents that only support NEMO basic Mobile 232 Routers or Mobile IPv6 Mobile Nodes. In this case, the DHCPv6PD 233 Support Flag MUST be set to 0. 235 The modified message format is as follows. 237 0 1 2 3 238 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 1 239 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 240 | Type | Code | Checksum | 241 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 242 | Identifier |R|D| Reserved | 243 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 244 | | 245 + + 246 + + 247 | | 248 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 250 DHCPv6PD Support Flag (D) 252 A one-bit flag that when set indicates that the Home Agents 253 listed in this message participate to DHCPv6 Prefix Delegation. 255 For a description of the other fields in the message, see [RFC3775] 256 and [RFC 3963]. 258 3.5.3. Modified Home Agent Information Option 260 A new flag (D) (Support for DHCPv6PD) is introduced in the Home Agent 261 Information Option defined in [RFC3775] and [RFC 3963]. 263 If a Home Agent participates to DHCPv6PD, it SHOULD set the flag. If 264 the HA sets the 'D' flag, then it MUST also set the 'R' flag, 265 Indicating that it supports Mobile Routers, as defined in [RFC 3963]. 267 0 1 2 3 268 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 1 269 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 270 | Type | Length |R|D| Reserved | 271 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 272 | Home Agent Preference | Home Agent Lifetime | 273 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 275 DHCPv6PD Support Flag (D) 277 A one-bit flag that when set indicates that the Home Agents 278 participates to DHCPv6 Prefix Delegation. 280 For a description of the other fields in the message, see [RFC3775] 281 and [RFC 3963]. 283 3.6. Location of DHCPv6PD Delegating Router function 285 Support of DHCPv6PD for a Mobile Network is optional. 287 The use of a DHCPv6 relay agent is not defined for DHCPv6PD in the 288 DHCPv6PD specification [RFC3633]. If the DHCPv6PD DR function is 289 implemented in the HA for the MR, no relay agent function is 290 required. 292 It may be desirable to use a single DR to manage RRs in a network 293 with multiple HAs. In this scenario, the HAs will act as DHCP relay 294 agents, forwarding messages between the RRs and the DR. 296 Use of the DHCPv6 relay agent function with DHCPv6PD requires that 297 there be some mechanism through which routing information for the 298 delegated prefixes can be added to the appropriate routing 299 infrastructure. If the HA is acting as a DHCPv6 relay agent, the HA 300 SHOULD add a route to the delegated prefix and advertise that route 301 after receiving a binding update for the prefix from the RR 302 [RFC3963]. 304 In particular, if the MR uses NEMO explicit mode, then it must add 305 the delegated prefix to prefix list in the Binding Update messages. 306 If the binding cache is cleared before the prefix valid lifetime, the 307 MR might bind that prefix again using explicit mode, till the 308 lifetime expires. 310 In implicit mode, the HA must save the delegated prefix with the 311 binding cache entry of the Mobile Router. When the BCE is cleared, 312 the HA loses the information about the delegated prefix. Because the 313 MR will use DHCPv6 when it reestablishes its tunnel to the HA (see 314 Section 3.1), the HA will be able to add the delegated prefix back to 315 the BCE. 317 At the time this draft was written, one way in which a DR can 318 explicitly notify a relay agent about delegated prefixes, is to use 319 the "DHCP Relay Agent Assignment Notification Option" 320 [I-D.ietf-dhc-dhcpv6-agentopt-delegate]. 322 Another alternative, if the RR is part of the same administrative 323 domain as the home network to which it is attached through the HA, 324 and the RR can be trusted, the RR can use a routing protocol like 325 OSPF to advertise any delegated prefixes. 327 NEMO explicit mode is recommended to take advantage of the function 328 already defined for NEMO. 330 3.7. Other DHCPv6 functions 332 The DHCPv6 messages exchanged between the MR and the HA may also be 333 used for other DHCPv6 functions in addition to DHCPv6PD. For 334 example, the HA may assign global addresses to the MR and may pass 335 other configuration information such as a list of available DNS 336 recursive resolvers to the MR using the same DHCPv6 messages as used 337 for DHCPV6PD. 339 The HA may act as a DHCPv6 relay agent for MHs while it acts as a DR 340 for MRs. 342 4. Changes in this draft 344 4.1. Revision -01 346 Removed section 3.2, "Delegating Access Prefixes". 348 Modified sections 3 and 3.6 (was section 3.1.3), "Location of 349 DHCPv6PD Delegating Router function," to allow for DHCPv6PD through a 350 relay agent and to allow for a single DR on a home network to perform 351 PD for RRs through more than one HA. 353 Added section 3.1 describing when the MR should use DHCPv6 PD. 355 Added section 3.4 describing use of Rapid Commit to minimize DHCPv6PD 356 messages and 358 Added section 3.5 recommending that DHCPv6PD and DHAAD be kept 359 independent and describing flags indicating availability of PD 360 service from HA. 362 Added section 3.7 describing the use of DHCPv6 for other 363 configuration in parallel with PD. 365 5. Security Considerations 367 This document describes the use of DHCPv6 for prefix delegation in 368 Mobile Networks. It does not introduce any additional security 369 considerations beyond those described in the "Security 370 Considerations" section of the DHCPv6 base specification [RFC3315] 371 and the "Security Considerations" of the DHCPv6 Prefix Delegation 372 specification [RFC3633]. 374 Following the DHCPv6 Prefix Delegation specification, HAs and MRs 375 SHOULD use DHCPv6 authentication as described in section 376 "Authentication of DHCP messages" of the DHCPv6 specification 377 [RFC3315], to guard against attacks mounted through prefix 378 delegation. 380 6. IANA Considerations 382 This document describes the use of DHCPv6 for prefix delegation in 383 Mobile Networks. It does not introduce any additional IANA 384 considerations. 386 7. Normative References 388 [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic 389 Host Configuration Protocol (DHCP) version 6", RFC 3633, 390 December 2003. 392 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 393 Requirement Levels", BCP 14, RFC 2119, March 1997. 395 [RFC3513] Hinden, R. and S. Deering, "Internet Protocol Version 6 396 (IPv6) Addressing Architecture", RFC 3513, April 2003. 398 [RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support 399 in IPv6", RFC 3775, June 2004. 401 [I-D.ietf-nemo-terminology] 402 Ernst, T. and H. Lach, "Network Mobility Support 403 Terminology", draft-ietf-nemo-terminology-06 (work in 404 progress), November 2006. 406 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 407 and M. Carney, "Dynamic Host Configuration Protocol for 408 IPv6 (DHCPv6)", RFC 3315, July 2003. 410 [I-D.ietf-nemo-requirements] 411 Ernst, T., "Network Mobility Support Goals and 412 Requirements", draft-ietf-nemo-requirements-06 (work in 413 progress), November 2006. 415 [RFC3963] Devarapalli, V., Wakikawa, R., Petrescu, A., and P. 416 Thubert, "Network Mobility (NEMO) Basic Support Protocol", 417 RFC 3963, January 2005. 419 [I-D.ietf-dhc-dhcpv6-agentopt-delegate] 420 Droms, R., "DHCPv6 Relay Agent Assignment Notification 421 (RAAN) Option", draft-ietf-dhc-dhcpv6-agentopt-delegate-02 422 (work in progress), November 2006. 424 Authors' Addresses 426 Ralph Droms 427 Cisco 428 1414 Massachusetts Avenue 429 Boxborough, MA 01719 430 USA 432 Phone: +1 978.936.1674 433 Email: rdroms@cisco.com 435 Pascal Thubert 436 Cisco 437 Village d'Entreprises Green Side 438 400, Avenue Roumanille 439 Biot - Sophia Antipolis 06410 440 FRANCE 442 Email: pthubert@cisco.com 444 Full Copyright Statement 446 Copyright (C) The IETF Trust (2007). 448 This document is subject to the rights, licenses and restrictions 449 contained in BCP 78, and except as set forth therein, the authors 450 retain all their rights. 452 This document and the information contained herein are provided on an 453 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 454 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 455 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 456 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 457 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 458 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 460 Intellectual Property 462 The IETF takes no position regarding the validity or scope of any 463 Intellectual Property Rights or other rights that might be claimed to 464 pertain to the implementation or use of the technology described in 465 this document or the extent to which any license under such rights 466 might or might not be available; nor does it represent that it has 467 made any independent effort to identify any such rights. 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