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Checking references for intended status: Informational ---------------------------------------------------------------------------- ** 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reference: RFC 3315 (Obsoleted by RFC 8415) ** Obsolete normative reference: RFC 3633 (Obsoleted by RFC 8415) == Outdated reference: A later version (-09) exists of draft-ietf-6man-rfc6434-bis-08 == Outdated reference: A later version (-08) exists of draft-templin-6man-rio-redirect-06 Summary: 2 errors (**), 0 flaws (~~), 3 warnings (==), 1 comment (--).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 June 14, 2018 5 Expires: December 16, 2018 7 Multi-Addressing Considerations for IPv6 Prefix Delegation 8 draft-templin-v6ops-pdhost-21.txt 10 Abstract 12 IPv6 prefixes are typically delegated to requesting routers which 13 assign them to their downstream-attached links and networks. The 14 requesting node can provision the prefix according to whether it acts 15 as a router on behalf of any downstream networks and/or as a host on 16 behalf of its local applications. In the latter case, the requesting 17 node can use portions of the delegated prefix for its own multi- 18 addressing purposes. This document therefore considers prefix 19 delegation consideations for both the classic routing and various 20 multi-addressing use cases. 22 Status of This Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at https://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on December 16, 2018. 39 Copyright Notice 41 Copyright (c) 2018 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (https://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 57 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 58 3. Multi-Addressing Considerations . . . . . . . . . . . . . . . 6 59 4. Multi-Addressing Alternatives for Delegated Prefixes . . . . 7 60 5. Address Autoconfiguration Considerations . . . . . . . . . . 8 61 6. MLD/DAD Implications . . . . . . . . . . . . . . . . . . . . 8 62 7. Dynamic Routing Protocol Implications . . . . . . . . . . . . 8 63 8. IPv6 Neighbor Discovery Implications . . . . . . . . . . . . 9 64 9. ICMPv6 Implications . . . . . . . . . . . . . . . . . . . . . 9 65 10. Prefix Delegation Services . . . . . . . . . . . . . . . . . 10 66 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 67 12. Security Considerations . . . . . . . . . . . . . . . . . . . 10 68 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 69 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 70 14.1. Normative References . . . . . . . . . . . . . . . . . . 11 71 14.2. Informative References . . . . . . . . . . . . . . . . . 12 72 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 13 73 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 14 75 1. Introduction 77 IPv6 Prefix Delegation (PD) entails 1) the communication of a prefix 78 from a server to a requesting router, 2) a representation of the 79 prefix in the network's Routing Information Base (RIB) and the first- 80 hop router's forwarding information base (FIB), and 3) a control 81 messaging service to maintain prefix lifetimes. Following 82 delegation, the prefix is available for the requesting router's 83 exclusive use and is not shared with any other nodes. This document 84 considers multi-addressing considerations for requesting nodes that 85 acts as a router on behalf of any downstream networks and/or as a 86 host on behalf of its local applications. 88 For nodes that connect downstream-attached networks (e.g., a 89 cellphone that connects a "tethered" Internet of Things (IoT), a 90 laptop computer with a complex internal network of virtual machines, 91 etc.), the classic routing model applies as shown in Figure 1: 93 .---------. 94 ,-( )-. 95 ( +----------+ ) 96 ( |Server 'S'| ) 97 ( +----------+ ) 98 ( Network 'N' ) 99 `-(__________)-' 100 | 101 +----------+----------+ 102 | first-hop router 'F'| 103 +----------+----------+ 104 | 105 upstream link | 106 | 107 +----------+----------+ 108 | upstream interface | 109 +---------------------+ 110 | | 111 |requesting router 'R'| 112 | (Prefix 'P') | 113 | | 114 +--+-+--+-+--+-----+--+ 115 |A1| |A2| |A3| ... |Aj| 116 +--+-+--+-+--+-----+--+ 117 |downstream interfaces| 118 +----------+----------+ 119 | 120 internal and/or external | 121 downstream links | 122 X----+-------------+--------+----+---------------+---X 123 | | | | 124 +---++-+--+ +---++-+--+ +---++-+--+ +---++-+--+ 125 | |Ak| | | |Al| | | |Am| | | |A*| | 126 | +--+ | | +--+ | | +--+ | | +--+ | 127 | host H1 | | host H2 | | host H3 | ... | host Hn | 128 +---------+ +---------+ +---------+ +---------+ 130 <-------------- Downstream Network -------------> 132 Figure 1: Classic Routing Model 134 In the classic routing model, requesting router 'R' has one or more 135 upstream interfaces and connects zero or more internal and/or 136 external downstream networks. When 'R' requests a prefix delegation, 137 the following sequence of events transpires: 139 o Server 'S' located in network 'N' delegates prefix 'P' via first- 140 hop router 'F' to requesting router 'R'. 142 o 'P' is injected into the RIB for 'N', and 'F' configures a FIB 143 entry with 'R' as the next hop. 145 o R' receives 'P' and assigns zero or more addresses 'A(*)' taken 146 from 'P' to its downstream interfaces 148 o 'R' advertises zero or more sub-prefixes taken from 'P' in RA 149 messages to hosts 'H(i)' on downstream networks. 151 o 'R' delegates zero or more sub-prefixes taken from 'P' to 152 requesting routers in downstream networks. 154 o 'R' acts as a router for hosts 'H(i)' on downstream networks and 155 as a host on behalf of its local applications. 157 This document also considers the case when 'R' uses portions of 'P' 158 for its own internal multi-addressing purposes. [RFC7934] provides 159 Best Current Practice (BCP) motivations for the benefits of multi- 160 addressing, while an operational means for providing nodes with 161 multiple addresses is given in [RFC8273]. The following multi- 162 addressing alternatives for delegated prefixes compliment this 163 framework while providing greater efficiency since no duplicate 164 address queries over the upstream link are needed (see:Section 3). 166 In a first alternative, when requesting node 'R' receives prefix 'P', 167 it can assign addresses taken from 'P' to downstream virtual 168 interfaces (e.g., a loopback) as shown in Figure 2: 170 x 171 | 172 upstream link | 173 | 174 +----------+----------+ 175 | upstream Interface | 176 +---------------------+ 177 | | 178 | requesting node 'R' | 179 | | 180 +--+-+--+-+--+-----+--+ 181 |A1| |A2| |A3| ... |An| 182 +--+-+--+-+--+-----+--+ 183 | virtual interfaces | 184 +---------------------+ 186 Figure 2: Address Assignment to Downstream Virtual Interfaces 188 In a second alternative, 'R' could assign Pv6 addresses taken from 189 'P' to the upstream interface over which the prefix was received as 190 shown in Figure 3: 192 x 193 | 194 upstream link | 195 | 196 +----------+----------+ 197 | upstream interface | 198 +--+-+--+-+--+-----+--+ 199 |A1| |A2| |A3| ... |An| 200 +--+-+--+-+--+-----+--+ 201 | | 202 | requesting node 'R' | 203 | | 204 +---------------------+ 206 Figure 3: Upstream Interface Address Assignment 208 In a third alternative, 'R' could assign IPv6 addresses taken from 209 'P' to its local applications which appear as "psuedo" virtual 210 interfaces as shown in Figure 4: 212 x 213 | 214 upstream link | 215 | 216 +----------+----------+ 217 | upstream Interface | 218 +---------------------+ 219 | | 220 | requesting node 'R' | 221 | | 222 +--+-+--+-+--+-----+--+ 223 |A1| |A2| |A3| ... |An| 224 +--+-+--+-+--+-----+--+ 225 | Applications | 226 +---------------------+ 228 Figure 4: Application Addresssing Model 230 With these IPv6 PD-based multi-addressing considerations, the node 231 can configure an unlimited supply of addresses to make them available 232 for local applications without requiring coordination with other 233 nodes on upstream interfaces. The following sections present 234 considerations for nodes that employ IPv6 PD mechanisms. 236 2. Terminology 238 The terminology of the normative references apply, and the terms 239 "node", "host" and "router" are the same as defined in [RFC8200]. 241 The following terms are defined for the purposes of this document: 243 shared prefix 244 an IPv6 prefix that may be advertised to more than one node on the 245 link, e.g., in a Router Advertisement (RA) message Prefix 246 Information Option (PIO) [RFC4861]. The router that advertises 247 the prefix must consider the prefix as on-link so that the IPv6 248 Neighbor Discovery (ND) address resolution function will identify 249 the correct neighbor for each packet. 251 individual prefix 252 an IPv6 prefix that is advertised to exactly one node on the link, 253 where the node may be unaware that the prefix is individual and 254 may not participate in prefix maintenance procedures. The router 255 that advertises the prefix can consider the prefix as on-link or 256 not on-link. In the former case, the router performs address 257 resolution and only forwards those packets that match one of the 258 node's configured addresses so that the node will not receive 259 unwanted packets. In the latter case, the router can simply 260 forward all packets matching the prefix to the node which must 261 then drop any packets that do not match one of its configured 262 addresses. An example individual prefix service is documented in 263 [RFC8273]. 265 delegated prefix 266 an IPv6 prefix that is explicitly conveyed to a node for its own 267 exclusive use, where the node is an active participant in prefix 268 delegation and maintenance procedures. The first-hop router 269 simply forwards all packets matching the prefix to the requesting 270 node. The requesting node associates the prefix with downstream 271 and/or internal virtual interfaces (i.e., and not the upstream 272 interface). 274 3. Multi-Addressing Considerations 276 IPv6 allows nodes to assign multiple addresses to a single interface. 277 [RFC7934] discusses options for multi-addressing as well as use cases 278 where multi-addressing may be desirable. Address configuration 279 options for multi-addressing include StateLess Address 280 AutoConfiguration (SLAAC) [RFC4862], Dynamic Host Configuration 281 Protocol for IPv6 (DHCPv6) address configuration [RFC3315], manual 282 configuration, etc. 284 Nodes configure addresses from a shared or individual prefix and 285 assign them to the upstream interface over which the prefix was 286 received. When the node assigns the addresses, it is required to use 287 Multicast Listener Discovery (MLD) [RFC3810] to join the appropriate 288 solicited-node multicast group(s) and to use the Duplicate Address 289 Detection (DAD) algorithm [RFC4862] to ensure that no other node 290 configures a duplicate address. 292 In contrast, a node that configures addresses from a delegated prefix 293 can assign them without invoking MLD/DAD on an upstream interface, 294 since the prefix has been delegated to the node for its own exclusive 295 use and is not shared with any other nodes. 297 4. Multi-Addressing Alternatives for Delegated Prefixes 299 When a node receives a delegated prefix, it has many alternatives for 300 provisioning the prefix to its local interfaces and/or downstream 301 networks. [RFC7278] discusses alternatives for provisioning a prefix 302 obtained by a User Equipment (UE) device under the 3rd Generation 303 Partnership Program (3GPP) service model. This document considers 304 the more general case when the node receives a delegated prefix 305 explicitly provided for its own exclusive use. 307 When the node receives the prefix, it can distribute the prefix to 308 internal (virtual) or external (physical) downstream networks and 309 configure zero or more addresses for itself on downstream interfaces. 310 The node then acts as a router on behalf of its downstream networks. 312 The node could instead (or in addition) use portions of the delegated 313 prefix for its own multi-addressing purposes. In a first 314 alternative, the node can assign as many addresses as it wants from 315 the prefix to downstream virtual interfaces. 317 In a second alternative, the node can assign as many addresses as it 318 wants from the prefix to the upstream interface over which the prefix 319 was received. 321 In a third alternative, the node can assign addresses taken from the 322 delegated prefix to its local applications. The applications 323 themselves then serve as virtual interfaces, i.e., instead of using a 324 traditional virtual interface such as a loopback. (Note that, in the 325 future, the practice of assigning unique non-link-local IPv6 326 addresses to applications could obviate the need for transport 327 protocol port numbers.) 329 In these multi-addressing cases, the node assigns the prefix itself 330 to a virtual interface so that unused portions of the prefix are 331 correctly identified as unreachable. The node then acts as a host on 332 behalf of its local applications even though neighbors on the 333 upstream link consider it as a router. 335 5. Address Autoconfiguration Considerations 337 Nodes autoconfigure addresses according to Section 6 of IPv6 Node 338 Requirements [I-D.ietf-6man-rfc6434-bis]. 340 Nodes configure at least one non-link-local adddress, i.e., for 341 network management and error reporting purposes. 343 Nodes recognize the Subnet Router Anycast address [RFC4291] for each 344 delegated prefix. Therefore, the node's use of the Subnet Router 345 Anycast address must be indistinguishable from the behavior of an 346 ordinary router when viewed from the outside world. 348 6. MLD/DAD Implications 350 When a node configures addresses for itself from a shared or 351 individual prefix, it performs MLD/DAD by sending multicast messages 352 over the upstream interface to test whether there is another node on 353 the link that configures a duplicate address. When there are many 354 such addresses and/or many such nodes, this could result in 355 substantial multicast traffic that affects all nodes on the link. 357 When a node configures addresses for itself from a delegated prefix, 358 it can configure as many addresses as it wants but need not perform 359 MLD/DAD for any of the addresses over the upstream interface. This 360 means that the node can configure arbitrarily many addresses without 361 causing any multicast messaging over the upstream interface that 362 could disturb other nodes. 364 7. Dynamic Routing Protocol Implications 366 Nodes that receive delegated prefixes can be configured to either 367 participate or not participate in a dynamic routing protocol over the 368 upstream interface. When there are many nodes on the upstream link, 369 dynamic routing protocol participation might be impractical due to 370 scaling limitations, and may also be exacerbated by factors such as 371 node mobility. 373 Unless it participates in a dynamic routing protocol, the node 374 initially has only a default route pointing to a neighbor via an 375 upstream interface. This means that packets sent by the node over an 376 upstream interface will initially go through a default router even if 377 there is a better first-hop node on the link. 379 8. IPv6 Neighbor Discovery Implications 381 When a node receives a shared or individual prefix with "L=1" and has 382 a packet to send to an IPv6 destination within the prefix, it is 383 required to use the IPv6 ND address resolution function over the 384 upstream interface to resolve the link-layer address of a neighbor 385 that configures the address. When a node receives a shared or 386 individual prefix with "L=0" and has a packet to send to an IPv6 387 destination within the prefix, if the address is not one of the 388 node's own addresses it sends the packet to a default router since 389 "L=0" makes no statement about on-link or off-link properties of the 390 prefix [RFC4861]. 392 When a node receives a delegated prefix, it acts as a simple host to 393 send Router Solicitation (RS) messages over the upstream interface 394 (i.e., the same as described in Section 4.2 of [RFC7084]) but also 395 sets the "Router" flag to TRUE in its Neighbor Advertisement 396 messages. The node considers the upstream interface as a non- 397 advertising interface [RFC4861], i.e., it does not send RA messages 398 over the upstream interface. The node further does not perform the 399 IPv6 ND address resolution function over the upstream interface, 400 since the delegated prefix is by definition not to be associated with 401 the interface. 403 In all cases, the current first-hop router may send a Redirect 404 message that updates the node's neighbor cache so that future packets 405 can use a better first-hop node on the link. The Redirect can apply 406 either to a singleton destination address, or to an entire 407 destination prefix as described in [I-D.templin-6man-rio-redirect]. 409 9. ICMPv6 Implications 411 The Internet Control Message Protocol for IPv6 (ICMPv6) includes a 412 set of control message types [RFC4443] including Destination 413 Unreachable (DU). 415 According to [RFC4443], routers should return DU messages (subject to 416 rate limiting) with code 0 ("No route to destination") when a packet 417 arrives for which there is no matching entry in the routing table, 418 and with code 3 ("Address unreachable") when the IPv6 destination 419 address cannot be resolved. 421 According to [RFC4443], hosts should return DU messages (subject to 422 rate limiting) with code 3 to internal applications when the IPv6 423 destination address cannot be resolved, and with code 4 ("Port 424 unreachable") if the IPv6 destination address is one of its own 425 addresses but the transport protocol has no listener. 427 Nodes that obtain and manage delegated prefixes per this document 428 observe the same procedures as described for both routers and hosts 429 above. 431 10. Prefix Delegation Services 433 Selection of prefix delegation services must be considered according 434 to specific use cases. An example service is that offered by DHCPv6 435 [RFC3633]. An alternative service based on IPv6 ND messaging has 436 also been proposed [I-D.pioxfolks-6man-pio-exclusive-bit]. 438 Other, non-router, mechanisms may exist, such as proprietary IPAMs, 439 [I-D.ietf-anima-prefix-management] and 440 [I-D.sun-casm-address-pool-management-yang]. 442 11. IANA Considerations 444 This document introduces no IANA considerations. 446 12. Security Considerations 448 Security considerations for IPv6 Neighbor Discovery [RFC4861] and any 449 applicable PD mechanisms apply to this document. Nodes that receive 450 delegated prefixes need not perform MLD/DAD procedures on their 451 upstream interfaces, meaning that they can avoid introducing 452 multicast messaging congestion on the upstream link. Also, routers 453 that delegate prefixes keep only a single neighbor cache entry for 454 each prefix delegation recipient, meaning that the router's neighbor 455 cache cannot be subject to resource exhaustion attacks. 457 For shared and individual prefixes, if the router that advertises the 458 prefix considers the prefix as on-link the IPv6 ND address resolution 459 function will prevent unwanted IPv6 packets from reaching the node. 460 For delegated prefixes and individual prefixes that are not 461 considered on-link, the router delivers all packets that match the 462 prefix to the unicast link-layer address of the node (i.e., as 463 determined by resolution of the node's link-local address) even if 464 they do not match one of the node's configured addresses. In that 465 case, the node may receive unwanted IPv6 packets via an upstream 466 interface that do not match either a configured IPv6 address or a 467 transport listener. The node then drops the packets and observes the 468 "Destination Unreachable - Address/Port unreachable" procedures 469 discussed in Section 9. 471 The node may also receive IPv6 packets via an upstream interface that 472 do not match any of the node's delegated prefixes. In that case, the 473 node drops the packets and observes the "Destination Unreachable - No 474 route to destination" procedures discussed in Section 9. Dropping 475 the packets is necessary to avoid a reflection attack that would 476 cause the node to forward packets received from an upstream interface 477 via the same or a different upstream interface. 479 In all cases, the node must decide whether or not to send DUs 480 according to the specific operational scenario. In trusted networks, 481 the node should send DU messages to provide useful information to 482 potential correspondents. In untrusted networks, the node can 483 refrain from sending DU messages to avoid providing sensitive 484 information to potential attackers. 486 13. Acknowledgements 488 This work was motivated by discussions on the v6ops list. Mark 489 Smith, Ricardo Pelaez-Negro, Edwin Cordeiro, Fred Baker, Ron Bonica, 490 Naveen Lakshman, Ole Troan, Bob Hinden, Brian Carpenter, Joel 491 Halpern, Albert Manfredi, Dusan Mudric, Paul Marks, Joe Touch and 492 Alex Petrescu provided useful comments that have greatly improved the 493 document. 495 This work is aligned with the NASA Safe Autonomous Systems Operation 496 (SASO) program under NASA contract number NNA16BD84C. 498 This work is aligned with the FAA as per the SE2025 contract number 499 DTFAWA-15-D-00030. 501 This work is aligned with the Boeing Information Technology (BIT) 502 MobileNet program and the Boeing Research & Technology (BR&T) 503 enterprise autonomy program. 505 14. References 507 14.1. Normative References 509 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 510 C., and M. Carney, "Dynamic Host Configuration Protocol 511 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 512 2003, . 514 [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic 515 Host Configuration Protocol (DHCP) version 6", RFC 3633, 516 DOI 10.17487/RFC3633, December 2003, 517 . 519 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 520 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 521 DOI 10.17487/RFC3810, June 2004, 522 . 524 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 525 Control Message Protocol (ICMPv6) for the Internet 526 Protocol Version 6 (IPv6) Specification", STD 89, 527 RFC 4443, DOI 10.17487/RFC4443, March 2006, 528 . 530 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 531 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 532 DOI 10.17487/RFC4861, September 2007, 533 . 535 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 536 Address Autoconfiguration", RFC 4862, 537 DOI 10.17487/RFC4862, September 2007, 538 . 540 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 541 (IPv6) Specification", STD 86, RFC 8200, 542 DOI 10.17487/RFC8200, July 2017, 543 . 545 14.2. Informative References 547 [I-D.ietf-6man-rfc6434-bis] 548 Chown, T., Loughney, J., and T. Winters, "IPv6 Node 549 Requirements", draft-ietf-6man-rfc6434-bis-08 (work in 550 progress), March 2018. 552 [I-D.ietf-anima-prefix-management] 553 Jiang, S., Du, Z., Carpenter, B., and Q. Sun, "Autonomic 554 IPv6 Edge Prefix Management in Large-scale Networks", 555 draft-ietf-anima-prefix-management-07 (work in progress), 556 December 2017. 558 [I-D.pioxfolks-6man-pio-exclusive-bit] 559 Kline, E. and M. Abrahamsson, "IPv6 Router Advertisement 560 Prefix Information Option eXclusive Flag", draft- 561 pioxfolks-6man-pio-exclusive-bit-02 (work in progress), 562 March 2017. 564 [I-D.sun-casm-address-pool-management-yang] 565 Sun, Q., Xie, C., Boucadair, M., Peng, T., and Y. Lee, "A 566 YANG Data Model for Address Pool Management", draft-sun- 567 casm-address-pool-management-yang-00 (work in progress), 568 March 2017. 570 [I-D.templin-6man-rio-redirect] 571 Templin, F. and j. woodyatt, "Route Information Options in 572 IPv6 Neighbor Discovery", draft-templin-6man-rio- 573 redirect-06 (work in progress), May 2018. 575 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 576 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 577 2006, . 579 [RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic 580 Requirements for IPv6 Customer Edge Routers", RFC 7084, 581 DOI 10.17487/RFC7084, November 2013, 582 . 584 [RFC7278] Byrne, C., Drown, D., and A. Vizdal, "Extending an IPv6 585 /64 Prefix from a Third Generation Partnership Project 586 (3GPP) Mobile Interface to a LAN Link", RFC 7278, 587 DOI 10.17487/RFC7278, June 2014, 588 . 590 [RFC7934] Colitti, L., Cerf, V., Cheshire, S., and D. Schinazi, 591 "Host Address Availability Recommendations", BCP 204, 592 RFC 7934, DOI 10.17487/RFC7934, July 2016, 593 . 595 [RFC8273] Brzozowski, J. and G. Van de Velde, "Unique IPv6 Prefix 596 per Host", RFC 8273, DOI 10.17487/RFC8273, December 2017, 597 . 599 Appendix A. Change Log 601 << RFC Editor - remove prior to publication >> 603 Changes from -20to -21: 605 o Re-worked classic routing model section 607 o Included multi-addressing case where addresses may be assigned to 608 applications 610 o Removed strong/weak end system discussions 612 Changes from -19 to -20: 614 o figure 1 updates to show Server as being somewhere in the network 616 o Introductory material to show relation to other RFCs on multi- 617 addressing 619 Changes from -18 to -19: 621 o added new section on Prefix Delegation Services 623 Changes from -17 to -18: 625 o re-worked discussion on the prefix delegation service in Section 1 627 o updated figures in Section 1 629 Changes from -16 to -17: 631 o added supporting text in the introduction to discuss the 632 Delegating Router's relationship with the Requesting Router and 633 with supporting intrastructure in the operator's network 635 o updated figures in introduction to include representation of 636 operator's network 638 o added new section on Address Autoconfiguration Considerations 640 Author's Address 642 Fred L. Templin (editor) 643 Boeing Research & Technology 644 P.O. Box 3707 645 Seattle, WA 98124 646 USA 648 Email: fltemplin@acm.org