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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Unused Reference: 'RFC0791' is defined on line 466, but no explicit reference was found in the text ** Obsolete normative reference: RFC 3315 (Obsoleted by RFC 8415) ** Obsolete normative reference: RFC 3633 (Obsoleted by RFC 8415) == Outdated reference: A later version (-09) exists of draft-ietf-6man-rfc6434-bis-05 == Outdated reference: A later version (-08) exists of draft-templin-6man-rio-redirect-05 Summary: 2 errors (**), 0 flaws (~~), 4 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group F. Templin, Ed. 3 Internet-Draft Boeing Research & Technology 4 Intended status: Informational March 2, 2018 5 Expires: September 3, 2018 7 IPv6 Prefix Delegation Models 8 draft-templin-v6ops-pdhost-19.txt 10 Abstract 12 IPv6 prefixes are typically delegated to requesting routers which 13 assign them to their downstream-attached links and networks. This 14 document considers prefix delegation models according to whether the 15 requesting router acts as a router on behalf of any downstream 16 networks, as a host on behalf of its local applications or as both. 18 Status of This Memo 20 This Internet-Draft is submitted in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at https://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on September 3, 2018. 35 Copyright Notice 37 Copyright (c) 2018 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents 42 (https://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents 44 carefully, as they describe your rights and restrictions with respect 45 to this document. Code Components extracted from this document must 46 include Simplified BSD License text as described in Section 4.e of 47 the Trust Legal Provisions and are provided without warranty as 48 described in the Simplified BSD License. 50 Table of Contents 52 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 53 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 54 3. Multi-Addressing Considerations . . . . . . . . . . . . . . . 6 55 4. Multi-Addressing Alternatives for Delegated Prefixes . . . . 6 56 5. Address Autoconfiguration Considerations . . . . . . . . . . 7 57 6. MLD/DAD Implications . . . . . . . . . . . . . . . . . . . . 7 58 7. Dynamic Routing Protocol Implications . . . . . . . . . . . . 8 59 8. IPv6 Neighbor Discovery Implications . . . . . . . . . . . . 8 60 9. ICMPv6 Implications . . . . . . . . . . . . . . . . . . . . . 9 61 10. Prefix Delegation Services . . . . . . . . . . . . . . . . . 9 62 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 63 12. Security Considerations . . . . . . . . . . . . . . . . . . . 9 64 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 65 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 66 14.1. Normative References . . . . . . . . . . . . . . . . . . 11 67 14.2. Informative References . . . . . . . . . . . . . . . . . 12 68 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 13 69 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 13 71 1. Introduction 73 IPv6 Prefix Delegation (PD) entails 1) the communication of a prefix 74 from a server to a requesting router, 2) a representation of the 75 prefix in the network's Routing Information Base (RIB) and the first- 76 hop router's forwarding information base (FIB), and 3) a control 77 messaging service to maintain prefix lifetimes. Following 78 delegation, the prefix is available for the requesting router's 79 exclusive use and is not shared with any other nodes. This document 80 considers prefix delegation models where the requesting router acts 81 as a router on behalf of any downstream networks, as a host on behalf 82 of its local applications or as both. 84 For nodes that connect downstream-attached networks (e.g., a 85 cellphone that connects a "tethered" Internet of Things, a host with 86 a complex internal network of virtual machines, etc.), the prefix 87 delegation model is shown in Figure 1: 89 .--. 90 ,-( )-. 91 ( ) 92 ( network 'N' ) +----------+ 93 `-(_______)-' |Server 'S'| 94 +----------+ 95 +---------------------+ 96 | first-hop router 'F'| 97 +----------+----------+ 98 | 99 upstream link | 100 | 101 +----------+----------+ 102 | upstream interface | 103 +---------------------+ 104 | | 105 |requesting router 'R'| 106 | (Prefix 'P') | 107 | | 108 +--+-+--+-+--+-----+--+ 109 |A1| |A2| |A3| ... |Aj| 110 +--+-+--+-+--+-----+--+ 111 | downstream interface| 112 +----------+----------+ 113 | 114 downstream link | 115 | 116 X----+-------------+--------+----+---------------+---X 117 | | | | 118 +---++-+--+ +---++-+--+ +---++-+--+ +---++-+--+ 119 | |Ak| | | |Al| | | |Am| | | |A*| | 120 | +--+ | | +--+ | | +--+ | | +--+ | 121 | host H1 | | host H2 | | host H3 | ... | host Hn | 122 +---------+ +---------+ +---------+ +---------+ 124 <-------------- Downstream Network -------------> 126 Figure 1: Classic Routing Model 128 In this model, when server 'S' delegates prefix 'P', first-hop router 129 'F' configures a FIB entry with requesting router ''R' as the next 130 hop, and the prefix is injected into network 'N's RIB. Meanwhile, 131 'R' distributes 'P' to its downstream external (physical) and/or 132 internal (virtual) networks. 'R' assigns addresses 'A(*)' taken from 133 'P' to downstream interfaces, and hosts 'H(i)' on downstream networks 134 assign addresses 'A(*)' taken from 'P' to their interface attachments 135 to the downstream link. 'R' then acts as a router for hosts 'H(i)' 136 on downstream networks and as a host on behalf of its local 137 applications, i.e., the same as for any router. 139 This document also considers the case when 'R' does not have any 140 downstream interfaces, and can use 'P' solely for its own internal 141 addressing purposes. In that case, requesting node 'R' assigns 'P' 142 to a virtual interface (e.g., a loopback) that serves as a downstream 143 interface. 145 'R' can then function under the weak end system (aka "weak host") 146 model [RFC1122][RFC8028] by assigning addresses taken from 'P' to a 147 virtual interface as shown in Figure 2: 149 x 150 | 151 upstream link | 152 | 153 +----------+----------+ 154 | upstream Interface | 155 +---------------------+ 156 | | 157 | requesting node 'R' | 158 | | 159 +--+-+--+-+--+-----+--+ 160 |A1| |A2| |A3| ... |An| 161 +--+-+--+-+--+-----+--+ 162 | virtual Interface | 163 +---------------------+ 165 Figure 2: Weak End System Model 167 'R' could instead function under the strong end system (aka "strong 168 host") model [RFC1122][RFC8028] by assigning IPv6 addresses taken 169 from 'P' to an upstream interface as shown in Figure 3: 171 x 172 | 173 upstream link | 174 | 175 +----------+----------+ 176 | upstream interface | 177 +--+-+--+-+--+-----+--+ 178 |A1| |A2| |A3| ... |An| 179 +--+-+--+-+--+-----+--+ 180 | | 181 | requesting node 'R' | 182 | | 183 +---------------------+ 184 | virtual interface | 185 +---------------------+ 187 Figure 3: Strong End System Model 189 The major benefit for a node managing a delegated prefix in either 190 the weak or strong end system models is multi-addressing. With IPv6 191 PD-based multi-addressing, the node can configure an unlimited supply 192 of addresses to make them available for local applications without 193 requiring coordination with other nodes on upstream interfaces. 195 The following sections present considerations for nodes that employ 196 IPv6 PD mechanisms. 198 2. Terminology 200 The terminology of the normative references apply, and the terms 201 "node", "host" and "router" are the same as defined in [RFC8200]. 203 The following terms are defined for the purposes of this document: 205 shared prefix 206 an IPv6 prefix that may be advertised to more than one node on the 207 link, e.g., in a Router Advertisement (RA) message Prefix 208 Information Option (PIO) [RFC4861]. The router that advertises 209 the prefix must consider the prefix as on-link so that the IPv6 210 Neighbor Discovery (ND) address resolution function will identify 211 the correct neighbor for each packet. 213 individual prefix 214 an IPv6 prefix that is advertised to exactly one node on the link, 215 where the node may be unaware that the prefix is individual and 216 may not participate in prefix maintenance procedures. The router 217 that advertises the prefix can consider the prefix as on-link or 218 not on-link. In the former case, the router performs address 219 resolution and only forwards those packets that match one of the 220 node's configured addresses so that the node will not receive 221 unwanted packets. In the latter case, the router can simply 222 forward all packets matching the prefix to the node which must 223 then drop any packets that do not match one of its configured 224 addresses. An example individual prefix service is documented in 225 [RFC8273]. 227 delegated prefix 228 an IPv6 prefix that is explicitly conveyed to a node for its own 229 exclusive use, where the node is an active participant in prefix 230 delegation and maintenance procedures. The first-hop router 231 simply forwards all packets matching the prefix to the requesting 232 node. The requesting node associates the prefix with downstream 233 and/or internal virtual interfaces (i.e., and not the upstream 234 interface). 236 3. Multi-Addressing Considerations 238 IPv6 allows nodes to assign multiple addresses to a single interface. 239 [RFC7934] discusses options for multi-addressing as well as use cases 240 where multi-addressing may be desirable. Address configuration 241 options for multi-addressing include StateLess Address 242 AutoConfiguration (SLAAC) [RFC4862], Dynamic Host Configuration 243 Protocol for IPv6 (DHCPv6) address configuration [RFC3315], manual 244 configuration, etc. 246 Nodes configure addresses from a shared or individual prefix and 247 assign them to the upstream interface over which the prefix was 248 received. When the node assigns the addresses, it is required to use 249 Multicast Listener Discovery (MLD) [RFC3810] to join the appropriate 250 solicited-node multicast group(s) and to use the Duplicate Address 251 Detection (DAD) algorithm [RFC4862] to ensure that no other node 252 configures a duplicate address. 254 In contrast, a node that configures addresses from a delegated prefix 255 can assign them without invoking MLD/DAD on an upstream interface, 256 since the prefix has been delegated to the node for its own exclusive 257 use and is not shared with any other nodes. 259 4. Multi-Addressing Alternatives for Delegated Prefixes 261 When a node receives a delegated prefix, it has many alternatives for 262 provisioning the prefix to its local interfaces and/or downstream 263 networks. [RFC7278] discusses alternatives for provisioning a prefix 264 obtained by a User Equipment (UE) device under the 3rd Generation 265 Partnership Program (3GPP) service model. This document considers 266 the more general case when the node receives a delegated prefix 267 explicitly provided for its own exclusive use. 269 When the node receives the prefix, it can distribute the prefix to 270 downstream networks and configure zero or more addresses for itself 271 on downstream interfaces. The node then acts as a router on behalf 272 of its downstream networks and configures a default route via a 273 neighbor on an upstream interface. 275 The node could instead (or in addition) use portions of the delegated 276 prefix for its own multi-addressing purposes. In a first 277 alternative, the node can assign as many addresses as it wants from 278 the prefix to virtual interfaces. In that case, applications running 279 on the node can use the addresses according to the weak end system 280 model. 282 In a second alternative, the node can assign as many addresses as it 283 wants from the prefix to the upstream interface over which the prefix 284 was received. In that case, applications running on the node can use 285 the addresses according to the strong end system model. 287 In both of these latter two cases, the node assigns the prefix itself 288 to a virtual interface so that unused portions of the prefix are 289 correctly identified as unreachable. The node then acts as a host on 290 behalf of its local applications even though neighbors on the 291 upstream link see it as a router. 293 5. Address Autoconfiguration Considerations 295 Nodes that act according to the weak/strong host models as discussed 296 in the previous section autoconfigure addresses from delegated 297 prefixes according to Section 6 of IPv6 Node Requirements 298 [I-D.ietf-6man-rfc6434-bis]. 300 As a recipient of a delegated prefix, the node is also required to 301 recognize the Subnet Router Anycast address [RFC4291]. Therefore, 302 the node's use of the Subnet Router Anycast address must be 303 indistinguishable from the behavior of an ordinary router when viewed 304 from the outside world. 306 6. MLD/DAD Implications 308 When a node configures addresses for itself from a shared or 309 individual prefix, it performs MLD/DAD by sending multicast messages 310 over upstream interfaces to test whether there is another node on the 311 link that configures a duplicate address. When there are many such 312 addresses and/or many such nodes, this could result in substantial 313 multicast traffic that affects all nodes on the link. 315 When a node configures addresses for itself from a delegated prefix, 316 it can configure as many addresses as it wants but does not perform 317 MLD/DAD for any of the addresses over upstream interfaces. This 318 means that the node can configure arbitrarily many addresses without 319 causing any multicast messaging over the upstream interface that 320 could disturb other nodes. 322 7. Dynamic Routing Protocol Implications 324 Nodes that receive delegated prefixes can be configured to either 325 participate or not participate in a dynamic routing protocol over the 326 upstream interface, according to the deployment model. When there 327 are many nodes on the upstream link, dynamic routing protocol 328 participation might be impractical due to scaling limitations, and 329 may also be exacerbated by factors such as node mobility. 331 Unless it participates in a dynamic routing protocol, the node 332 initially has only a default route pointing to a neighbor via an 333 upstream interface. This means that packets sent by the node over an 334 upstream interface will initially go through a default router even if 335 there is a better first-hop node on the link. 337 8. IPv6 Neighbor Discovery Implications 339 When a node receives a shared or individual prefix with "L=1" and has 340 a packet to send to an IPv6 destination within the prefix, it is 341 required to use the IPv6 ND address resolution function over the 342 upstream interface to resolve the link-layer address of a neighbor 343 that configures the address. When a node receives a shared or 344 individual prefix with "L=0" and has a packet to send to an IPv6 345 destination within the prefix, if the address is not one of the 346 node's own addresses it sends the packet to a default router since 347 "L=0" makes no statement about on-link or off-link properties of the 348 prefix [RFC4861]. 350 When a node receives a delegated prefix, it acts as a simple host to 351 send Router Solicitation (RS) messages over upstream interfaces 352 (i.e., the same as described in Section 4.2 of [RFC7084]) but also 353 sets the "Router" flag to TRUE in its Neighbor Advertisement 354 messages. The node considers the upstream interfaces as non- 355 advertising interfaces [RFC4861], i.e., it does not send RA messages 356 over the upstream interfaces. The node further does not perform the 357 IPv6 ND address resolution function over upstream interfaces, since 358 the delegated prefix is by definition not to be associated with an 359 upstream interface. 361 In all cases, the current first-hop router may send a Redirect 362 message that updates the node's neighbor cache so that future packets 363 can use a better first-hop node on the link. The Redirect can apply 364 either to a singleton destination address, or to an entire 365 destination prefix as described in [I-D.templin-6man-rio-redirect]. 367 9. ICMPv6 Implications 369 The Internet Control Message Protocol for IPv6 (ICMPv6) includes a 370 set of control message types [RFC4443] including Destination 371 Unreachable (DU). 373 According to [RFC4443], routers should return DU messages (subject to 374 rate limiting) with code 0 ("No route to destination") when a packet 375 arrives for which there is no matching entry in the routing table, 376 and with code 3 ("Address unreachable") when the IPv6 destination 377 address cannot be resolved. 379 According to [RFC4443], hosts should return DU messages (subject to 380 rate limiting) with code 3 to internal applications when the IPv6 381 destination address cannot be resolved, and with code 4 ("Port 382 unreachable") if the IPv6 destination address is one of its own 383 addresses but the transport protocol has no listener. 385 Nodes that obtain and manage delegated prefixes per this document 386 observe the same procedures as described for both routers and hosts 387 above. 389 10. Prefix Delegation Services 391 Selection of prefix delegation services must be considered according 392 to specific use cases. An example service is that offered by DHCPv6 393 [RFC3633]. An alternative service based on IPv6 ND messaging has 394 also been proposed [I-D.pioxfolks-6man-pio-exclusive-bit]. 396 Other, non-router, mechanisms may exist, such as proprietary IPAMs, 397 [I-D.ietf-anima-prefix-management] and 398 [I-D.sun-casm-address-pool-management-yang]. 400 11. IANA Considerations 402 This document introduces no IANA considerations. 404 12. Security Considerations 406 Security considerations for IPv6 Neighbor Discovery [RFC4861] and any 407 applicable PD mechanisms apply to this document. Nodes that receive 408 delegated prefixes do not perform MLD/DAD procedures on their 409 upstream interfaces, meaning that they cannot contribute to multicast 410 messaging congestion on the upstream link. Also, routers that 411 delegate prefixes keep only a single neighbor cache entry for each 412 prefix delegation recipient, meaning that the router's neighbor cache 413 cannot be subject to resource exhaustion attacks. 415 For shared and individual prefixes, if the router that advertises the 416 prefix considers the prefix as on-link the IPv6 ND address resolution 417 function will prevent unwanted IPv6 packets from reaching the node. 418 For delegated prefixes and individual prefixes that are not 419 considered on-link, the router delivers all packets that match the 420 prefix to the unicast link-layer address of the node (i.e., as 421 determined by resolution of the node's link-local address) even if 422 they do not match one of the node's configured addresses. In the 423 latter case, the node may receive unwanted IPv6 packets via an 424 upstream interface that do not match either a configured IPv6 address 425 or a transport listener. The node then drops the packets and 426 observes the "Destination Unreachable - Address/Port unreachable" 427 procedures discussed in Section 9. 429 The node may also receive IPv6 packets via an upstream interface that 430 do not match any of the node's delegated prefixes. In that case, the 431 node drops the packets and observes the "Destination Unreachable - No 432 route to destination" procedures discussed in Section 9. Dropping 433 the packets is necessary to avoid a reflection attack that would 434 cause the node to forward packets received from an upstream interface 435 via the same or a different upstream interface. 437 In all cases, the node must decide whether or not to send DUs 438 according to the specific operational scenario. In trusted networks, 439 the node should send DU messages to provide useful information to 440 potential correspondents. In untrusted networks, the node can 441 refrain from sending DU messages to avoid providing sensitive 442 information to potential attackers. 444 13. Acknowledgements 446 This work was motivated by discussions on the v6ops list. Mark 447 Smith, Ricardo Pelaez-Negro, Edwin Cordeiro, Fred Baker, Naveen 448 Lakshman, Ole Troan, Bob Hinden, Brian Carpenter, Joel Halpern, 449 Albert Manfredi, Dusan Mudric and Paul Marks provided useful comments 450 that have greatly improved the document. 452 This work is aligned with the NASA Safe Autonomous Systems Operation 453 (SASO) program under NASA contract number NNA16BD84C. 455 This work is aligned with the FAA as per the SE2025 contract number 456 DTFAWA-15-D-00030. 458 This work is aligned with the Boeing Information Technology (BIT) 459 MobileNet program and the Boeing Research & Technology (BR&T) 460 enterprise autonomy program. 462 14. References 464 14.1. Normative References 466 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 467 DOI 10.17487/RFC0791, September 1981, 468 . 470 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 471 C., and M. Carney, "Dynamic Host Configuration Protocol 472 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 473 2003, . 475 [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic 476 Host Configuration Protocol (DHCP) version 6", RFC 3633, 477 DOI 10.17487/RFC3633, December 2003, 478 . 480 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 481 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 482 DOI 10.17487/RFC3810, June 2004, 483 . 485 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 486 Control Message Protocol (ICMPv6) for the Internet 487 Protocol Version 6 (IPv6) Specification", STD 89, 488 RFC 4443, DOI 10.17487/RFC4443, March 2006, 489 . 491 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 492 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 493 DOI 10.17487/RFC4861, September 2007, 494 . 496 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 497 Address Autoconfiguration", RFC 4862, 498 DOI 10.17487/RFC4862, September 2007, 499 . 501 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 502 (IPv6) Specification", STD 86, RFC 8200, 503 DOI 10.17487/RFC8200, July 2017, 504 . 506 14.2. Informative References 508 [I-D.ietf-6man-rfc6434-bis] 509 Chown, T., Loughney, J., and T. Winters, "IPv6 Node 510 Requirements", draft-ietf-6man-rfc6434-bis-05 (work in 511 progress), February 2018. 513 [I-D.ietf-anima-prefix-management] 514 Jiang, S., Du, Z., Carpenter, B., and Q. Sun, "Autonomic 515 IPv6 Edge Prefix Management in Large-scale Networks", 516 draft-ietf-anima-prefix-management-07 (work in progress), 517 December 2017. 519 [I-D.pioxfolks-6man-pio-exclusive-bit] 520 Kline, E. and M. Abrahamsson, "IPv6 Router Advertisement 521 Prefix Information Option eXclusive Flag", draft- 522 pioxfolks-6man-pio-exclusive-bit-02 (work in progress), 523 March 2017. 525 [I-D.sun-casm-address-pool-management-yang] 526 Sun, Q., Xie, C., Boucadair, M., Peng, T., and Y. Lee, "A 527 YANG Data Model for Address Pool Management", draft-sun- 528 casm-address-pool-management-yang-00 (work in progress), 529 March 2017. 531 [I-D.templin-6man-rio-redirect] 532 Templin, F. and j. woodyatt, "Route Information Options in 533 IPv6 Neighbor Discovery", draft-templin-6man-rio- 534 redirect-05 (work in progress), October 2017. 536 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 537 Communication Layers", STD 3, RFC 1122, 538 DOI 10.17487/RFC1122, October 1989, 539 . 541 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 542 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 543 2006, . 545 [RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic 546 Requirements for IPv6 Customer Edge Routers", RFC 7084, 547 DOI 10.17487/RFC7084, November 2013, 548 . 550 [RFC7278] Byrne, C., Drown, D., and A. Vizdal, "Extending an IPv6 551 /64 Prefix from a Third Generation Partnership Project 552 (3GPP) Mobile Interface to a LAN Link", RFC 7278, 553 DOI 10.17487/RFC7278, June 2014, 554 . 556 [RFC7934] Colitti, L., Cerf, V., Cheshire, S., and D. Schinazi, 557 "Host Address Availability Recommendations", BCP 204, 558 RFC 7934, DOI 10.17487/RFC7934, July 2016, 559 . 561 [RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by 562 Hosts in a Multi-Prefix Network", RFC 8028, 563 DOI 10.17487/RFC8028, November 2016, 564 . 566 [RFC8273] Brzozowski, J. and G. Van de Velde, "Unique IPv6 Prefix 567 per Host", RFC 8273, DOI 10.17487/RFC8273, December 2017, 568 . 570 Appendix A. Change Log 572 Changes from -18 to -19: 574 o added new section on Prefix Delegation Services 576 Changes from -17 to -18: 578 o re-worked discussion on the prefix delegation service in Section 1 580 o updated figures in Section 1 582 Changes from -16 to -17: 584 o added supporting text in the introduction to discuss the 585 Delegating Router's relationship with the Requesting Router and 586 with supporting intrastructure in the operator's network 588 o updated figures in introduction to include representation of 589 operator's network 591 o added new section on Address Autoconfiguration Considerations 593 Author's Address 594 Fred L. Templin (editor) 595 Boeing Research & Technology 596 P.O. Box 3707 597 Seattle, WA 98124 598 USA 600 Email: fltemplin@acm.org