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'3GPP-SCEN') -- Obsolete informational reference (is this intentional?): RFC 2283 (Obsoleted by RFC 2858) == Outdated reference: A later version (-07) exists of draft-ooms-v6ops-bgp-tunnel-00 == Outdated reference: A later version (-12) exists of draft-ietf-dnsop-ipv6-dns-issues-00 -- Unexpected draft version: The latest known version of draft-many-ngtrans-connect-ipv6-igp is -01, but you're referring to -02. == Outdated reference: A later version (-24) exists of draft-ietf-ngtrans-isatap-11 Summary: 10 errors (**), 0 flaws (~~), 8 warnings (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Draft J. Wiljakka, 3 Document: draft-ietf-v6ops-3gpp-analysis-01.txt Editor 4 Expires: July 2003 Nokia 6 January 2003 8 Analysis on IPv6 Transition in 3GPP Networks 10 Status of this Memo 12 This document is an Internet-Draft and is in full conformance with 13 all provisions of Section 10 of RFC2026. 15 Internet-Drafts are working documents of the Internet Engineering 16 Task Force (IETF), its areas, and its working groups. Note that 17 other groups may also distribute working documents as Internet- 18 Drafts. 20 Internet-Drafts are draft documents valid for a maximum of six 21 months and may be updated, replaced, or obsoleted by other 22 documents at any time. It is inappropriate to use Internet-Drafts 23 as reference material or to cite them other than as "work in 24 progress." 26 The list of current Internet-Drafts can be accessed at 27 http://www.ietf.org/ietf/1id-abstracts.txt 28 The list of Internet-Draft Shadow Directories can be accessed at 29 http://www.ietf.org/shadow.html. 31 Abstract 33 This document analyzes making the transition to IPv6 in Third 34 Generation Partnership Project (3GPP) General Packet Radio Service 35 (GPRS) packet networks. The focus is on analyzing different 36 transition scenarios, applicable transition mechanisms and finding 37 solutions for those transition scenarios. In these scenarios, the 38 User Equipment (UE) connects to other nodes, e.g. in the Internet, 39 and IPv6/IPv4 transition mechanisms are needed. 41 Table of Contents 43 1. Introduction..................................................2 44 1.1 Scope of this Document....................................3 45 1.2 Abbreviations.............................................3 46 1.3 Terminology...............................................4 47 2. Transition mechanisms.........................................4 48 2.1 Dual Stack................................................5 49 2.2 Tunneling.................................................5 50 2.3 Protocol translators......................................5 51 3. GPRS Transition scenarios.....................................6 52 3.1 Dual Stack UE connecting to IPv4 and IPv6 nodes...........6 53 3.2 IPv6 UE connecting to an IPv6 node through an IPv4 network 7 54 3.3 IPv4 UE connecting to an IPv4 node through an IPv6 network10 55 3.4 IPv6 UE connecting to an IPv4 node.......................10 56 3.5 IPv4 UE connecting to an IPv6 node.......................12 57 4. Transition Scenarios with IMS................................13 58 4.1 DNS interworking in IMS..................................13 59 4.2 UE connecting to a node in an IPv4 network through IMS...13 60 4.3 Two IMS islands connected over IPv4 network..............15 61 5. Security Considerations......................................15 62 6. Changes from draft-ietf-v6ops-3gpp-analysis-00.txt...........15 63 7. Copyright....................................................15 64 8. References...................................................16 65 8.1 Normative................................................16 66 8.2 Informative..............................................17 67 9. Authors and Acknowledgements.................................19 68 10. Editor's Contact Information................................19 70 1. Introduction 72 This document describes and analyzes the process of transition to 73 IPv6 in Third Generation Partnership Project (3GPP) General Packet 74 Radio Service (GPRS) packet networks. The authors can be found in 75 Authors and Acknowledgements section. Comments, input and feedback 76 from the people in the IETF v6ops Working Group are appreciated. 78 This document analyzes the transition scenarios in 3GPP packet 79 data networks that might come up in the deployment phase of IPv6. 80 The transition scenarios are documented in [3GPP-SCEN] and this 81 document will further analyze them. The scenarios are divided into 82 two categories: GPRS scenarios and IMS scenarios. 84 GPRS scenarios are the following: 85 - Dual Stack UE connecting to IPv4 and IPv6 nodes 86 - IPv6 UE connecting to an IPv6 node through an IPv4 network 87 - IPv4 UE connecting to an IPv4 node through an IPv6 network 88 - IPv6 UE connecting to an IPv4 node 89 - IPv4 UE connecting to an IPv6 node 91 Two IMS scenarios are: 92 - UE connecting to a node in an IPv4 network through IMS 93 - Two IMS islands connected via IPv4 network 95 The focus is on analyzing different transition scenarios, 96 applicable transition mechanisms and finding solutions for those 97 transition scenarios. In the scenarios, the User Equipment (UE) 98 connects to nodes in other networks, e.g. in the Internet and 99 IPv6/IPv4 transition mechanisms are needed. 101 1.1 Scope of this Document 103 The scope of this informational document is to analyze and solve 104 the possible transition scenarios in the 3GPP defined GPRS network 105 where a UE connects to, or is contacted from the Internet, or 106 another UE. The document covers scenarios with and without the use 107 of the SIP based IP Multimedia Core Network Subsystem (IMS). This 108 document is not focused on radio interface issues; both 3GPP Second 109 (GSM) and Third Generation (UMTS) radio network architectures will 110 be covered by these scenarios. 112 The transition mechanisms specified by the IETF Ngtrans / v6ops 113 Working Group shall be used. This document shall not specify any 114 new transition mechanisms, but if a need for a new mechanism is 115 found, this will be reported to the v6ops Working Group. 117 1.2 Abbreviations 119 2G Second Generation Mobile Telecommunications, for 120 example GSM and GPRS technologies. 121 3G Third Generation Mobile Telecommunications, for example 122 UMTS technology. 123 3GPP Third Generation Partnership Project 124 ALG Application Level Gateway 125 APN Access Point Name. The APN is a logical name referring 126 to a GGSN and an external network. 127 CSCF Call Session Control Function (in 3GPP Release 5 IMS) 128 GGSN Gateway GPRS Support Node (a default router for 3GPP 129 User Equipment) 130 GPRS General Packet Radio Service 131 GSM Global System for Mobile Communications 132 IMS IP Multimedia (Core Network) Subsystem, 3GPP Release 5 133 IPv6-only part of the network 134 ISP Internet Service Provider 135 NAT Network Address Translator 136 NAPT-PT Network Address Port Translation - Protocol Translation 137 NAT-PT Network Address Translation - Protocol Translation 138 PDP Packet Data Protocol 139 PPP Point-to-Point Protocol 140 SIIT Stateless IP/ICMP Translation Algorithm 141 SIP Session Initiation Protocol 142 UE User Equipment, for example a UMTS mobile handset 143 UMTS Universal Mobile Telecommunications System 145 1.3 Terminology 147 Some terms used in 3GPP transition scenarios and analysis documents 148 are briefly defined here. 150 Dual Stack UE Dual Stack UE is a 3GPP mobile handset having dual 151 stack implemented. It is capable of activating 152 both IPv4 and IPv6 PDP contexts. Dual stack UE may 153 be capable of tunneling. 155 IPv6 UE IPv6 UE is an IPv6-only 3GPP mobile handset. It is 156 only capable of activating IPv6 PDP contexts. 158 IPv4 UE IPv4 UE is an IPv4-only 3GPP mobile handset. It is 159 only capable of activating IPv4 PDP contexts. 161 IPv4 node IPv4 node is here defined to be IPv4 capable node 162 the UE is communicating with. The IPv4 node can 163 be, for example, an application server or another 164 UE. 166 IPv6 node IPv6 node is here defined to be IPv6 capable node 167 the UE is communicating with. The IPv6 node can 168 be, for example, an application server or another 169 UE. 171 2. Transition mechanisms 173 This chapter briefly introduces some transition mechanisms 174 specified by the IETF. Applicability of different transition 175 mechanisms to 3GPP networks is discussed in chapters 3 and 4. 177 The IPv4/IPv6 transition methods can be divided to: 179 - dual IPv4/IPv6 stack 180 - tunneling 181 - protocol translators 183 2.1 Dual Stack 185 The dual IPv4/IPv6 stack is specified in [RFC2893]. If we consider 186 the 3GPP GPRS core network, dual stack implementation in the GGSN 187 enables support for both IPv4 and IPv6 and it is also needed to 188 perform IPv6 in IPv4 tunneling. UEs with dual stack and public / 189 global IP addresses can often access both IPv4 and IPv6 services 190 without additional translators in the network. 192 2.2 Tunneling 194 Tunneling is a transition mechanism that requires dual IPv4/IPv6 195 stack functionality in the encapsulating and decapsulating nodes. 196 Basic tunneling alternatives are IPv6-in-IPv4 and IPv4-in-IPv6. 197 IPv6-in-IPv4 tunneling mechanisms are implemented by virtual 198 interfaces that are configured over one or more physical IPv4 199 interfaces. Sending nodes encapsulate IPv6 packets in IPv4 packets 200 when the IPv6 routing table determines that the next hop toward the 201 IPv6 destination address is via a tunnel interface. Receiving nodes 202 decapsulate IPv6 packets from IPv4 packets that arrive on tunnel 203 interfaces. Tunneling can be static or dynamic. 205 Static (configured) tunnel interfaces are virtual IPv6 point-to- 206 point links over IPv4. They require static configuration of the 207 IPv6 source, IPv6 next-hop and IPv4 destination addresses for IPv6- 208 in-IPv4 encapsulation. The IPv6 destination address is specified by 209 the application and is used to determine the IPv6 next-hop address 210 via longest-prefix-match in the IPv6 routing table. Configured 211 tunnels are specified in [RFC2893]. 213 Dynamic (automatic) tunnel interfaces are virtual IPv6 point-to- 214 multipoint links over IPv4. They require static configuration of 215 the IPv6 source address only. Like in static tunneling, the IPv6 216 destination address is specified by the application and is used to 217 determine the IPv6 next-hop address via a longest-prefix-match 218 lookup in the IPv6 routing table. But unlike static tunnels, the 219 IPv4 destination address is derived from the IPv6 next-hop address 220 in some way, for example, via direct encoding in the IPv6 next-hop 221 address. This enables stateless encapsulation of IPv6-in-IPv4. 222 This means that the IPv4 source address is taken from an IPv4 223 interface over which the automatic tunnel is configured. Examples 224 of dynamic tunneling mechanisms are "6to4" [RFC3056], [ISATAP], 225 [DSTM] and [TEREDO]. 227 2.3 Protocol translators 229 A translator can be defined as an intermediate component between a 230 native IPv4 node and a native IPv6 node to enable direct 231 communication between them without requiring any modifications to 232 the end nodes. 234 Header conversion is a translation mechanism. In header conversion, 235 IPv6 packet headers are converted to IPv4 packet headers, and vice 236 versa, and checksums are adjusted or recalculated if necessary. 237 NAT-PT (Network Address Translator / Protocol Translator) [RFC2766] 238 using SIIT [RFC2765] is an example of such a mechanism. 240 Translators are typically needed when the two communicating nodes 241 do not share the same IP version. Translation can actually happen 242 at Layer 3 (using NAT-like techniques), Layer 4 (using a TCP/UDP 243 proxy) or Layer 7 (using application relays) 245 3. GPRS Transition scenarios 247 This section discusses the scenarios that might occur when a GPRS 248 UE contacts services or other nodes, e.g. a web server in the 249 Internet. 251 The following scenarios described by [3GPP-SCEN] are analyzed here. 252 In all of the scenarios, the UE is part of a network where there is 253 at least one router of the same IP version, i.e. GGSN, and it is 254 connecting to a node in a different network. 256 1) Dual Stack UE connecting to IPv4 and IPv6 nodes 257 2) IPv6 UE connecting to an IPv6 node through an IPv4 network 258 3) IPv4 UE connecting to an IPv4 node through an IPv6 network 259 4) IPv6 UE connecting to an IPv4 node 260 5) IPv4 UE connecting to an IPv6 node 262 3.1 Dual Stack UE connecting to IPv4 and IPv6 nodes 264 In this scenario, the UE is capable of communicating with both IPv4 265 and IPv6 nodes by activating IPv4 or IPv6 PDP context. This also 266 requires that the GGSN is supporting both IPv4 and IPv6. The dual 267 stack UE may have both stacks or only one of them active 268 simultaneously. If "IPv6 in IPv4" tunneling is needed, it is often 269 beneficial to activate IPv6 PDP context and make encapsulation / 270 decapsulation in the network (like described in section 3.2). 272 However, if the GGSN does not support IPv6, and an application on 273 the UE needs to communicate with an IPv6 node, the UE may activate 274 an IPv4 PDP context and tunnel IPv6 packets in IPv4 packets using a 275 tunneling mechanism. Tunneling in the UE requires dual stack 276 capability in the UE. The use of private IPv4 addresses in the UE 277 depends on the support of these addresses by the tunneling 278 mechanism and the deployment scenario. In some cases public IPv4 279 addresses are required, but if the tunnel endpoints are in the same 280 private domain or the tunneling mechanism works through IPv4 NAT, 281 private IPv4 addresses can be used. One deployment scenario example 282 is using laptop computer and a UMTS UE as a modem. IPv6 packets are 283 encapsulated in IPv4 packets in the laptop computer and IPv4 PDP 284 context is activated. Although "IPv6 in IPv4" tunneling in the UE 285 can be either automatic or configured (by the user), the first 286 alternative is more probable, because it is expected that most UE 287 users just want to use an application in their UE; they might not 288 even care, whether the network connection is IPv4 or IPv6. 290 When analyzing a dual stack UE behavior, an application running on 291 a UE can identify whether the endpoint required is an IPv4 or IPv6 292 capable node by examining the address to discover what address 293 family category it falls into. Alternatively if a user supplies a 294 name to be resolved, the DNS may contain records sufficient to 295 identify which protocol should be used to initiate connection with 296 the endpoint. Since the UE is capable of native communication with 297 both protocols, one of the main concerns of an operator is correct 298 address space and routing management. The operator must maintain 299 address spaces for both protocols. Public IPv4 addresses often are 300 a scarce resource for the operator and typically it is not possible 301 for a UE to have a globally unique IPv4 address continually 302 allocated for its use. Use of private IPv4 addresses means use of 303 NATs (Network Address Translators) when communicating with a peer 304 node outside the operator's network. In large networks, NAT systems 305 can become very complex, expensive and difficult to maintain. 307 As a general guideline, IPv6 communication (native or tunneled from 308 the UE) is preferred to IPv4 communication going through IPv4 NATs 309 to the same dual stack peer node. In this scenario, the UE talks to 310 the DNS resolver using the IP version that is available via the 311 activated PDP context. The DNS resolver in the network should be 312 dual stack. Also keeping the Internet name space unfragmented is an 313 important thing for the operation of the Internet [DNStrans]. 315 3.2 IPv6 UE connecting to an IPv6 node through an IPv4 network 317 The best solution for this scenario is obtained with tunneling, 318 i.e. "IPv6 in IPv4" tunneling is a requirement. An IPv6 PDP context 319 is activated between the UE and the GGSN. Tunneling is handled in 320 the network, because IPv6 UE is not capable of tunneling (it does 321 not have the dual stack functionality needed for tunneling). 322 Encapsulating node can be the GGSN, the edge router between the 323 border of the operator's IPv6 network and the public Internet, or 324 any other dual stack node within the operator's IP network. The 325 encapsulation (uplink) and decapsulation (downlink) can be handled 326 by the same network element. Typically the tunneling handled by the 327 network elements is transparent to the UEs and the IP traffic looks 328 like native IPv6 traffic to them. For the applications, tunneling 329 enables end-to-end IPv6 connectivity. Note that this scenario is 330 comparable to 6bone [6BONE] network operation. 332 "IPv6 in IPv4" tunnels between the IPv6 islands can be static or 333 dynamic. The selection of the type of tunneling mechanism is up to 334 the operator / ISP deployment scenario and only generic 335 recommendations can be given in this document. 337 The following subsections are focused on the usage of different 338 tunneling mechanisms when the peer node is in the operator's 339 network or outside the operator's network. The authors note that 340 where the actual 3GPP network ends and which parts of the network 341 belong to the ISP(s) also depends on the deployment scenario. The 342 authors are also not commenting how many ISP functions the 3GPP 343 operator should perform. However, many 3GPP operators are ISPs of 344 some sort themselves. 346 3.2.1 Tunneling inside the 3GPP operator's network 348 Many GPRS operators already have IPv4 backbone networks deployed 349 and they are gradually migrating them while introducing IPv6 350 islands. IPv6 backbones can be considered quite rare in the first 351 phases of the transition. If the 3GPP operator already has IPv6 352 widely deployed in its network, this subsection is not so relevant. 354 In initial, smaller scale IPv6 deployment, where a small number of 355 IPv6 in IPv4 tunnels are required to connect the IPv6 islands over 356 the 3GPP operator's IPv4 network, manually configured tunnels can 357 be used. In a 3GPP network, one IPv6 island could contain the GGSN 358 while another island contains the operator's IPv6 application 359 servers. However, manually configured tunnels can be an 360 administrative burden when the number of islands and therefore 361 tunnels rises. 363 It is also possible to use dynamic tunneling mechanisms such as 364 "6to4" [RFC3056] and IGP/EGP routing protocol based tunneling 365 mechanisms [BGP][IGP]. Routing protocol based mechanisms such as 366 [BGP] consist of running BGP between the neighboring router tunnel 367 endpoints and using multi-protocol BGP extensions to exchange 368 reachability information of IPv6 prefixes. The routers use this 369 information to create IPv6 in IPv4 tunnel interfaces and route IPv6 370 packets over the IPv4 network. It is possible to combine this with 371 different types of tunnels. 373 "6to4" nodes use special IPv6 addresses with a "6to4" prefix 374 containing the IPv4 address of the corresponding "IPv6 in IPv4" 375 tunnel endpoint ("6to4" router) which performs encapsulation / 376 decapsulation. When connecting two nodes with "6to4" addresses, the 377 corresponding "6to4" routers use the IPv4 addresses specified in 378 the "6to4" prefixes to tunnel IPv6 packets through the IPv4 379 network. But if only one of them has a "6to4" address, a "6to4" 380 relay must be present to perform the missing "6to4" router 381 functionality for the native-IPv6 node. In this case there are two 382 deployment options for "IPv6 in IPv4" tunneling between the "6to4" 383 router and the relay. The first option assumes that "6to4" routers 384 using a given relay each have a default IPv6 route (configured 385 tunnel) pointing to that relay. The other one consists of using an 386 IPv6 exterior routing protocol; this way the set of "6to4" routers 387 using a given relay obtain native IPv6 routes from it using a 388 routing protocol such as BGP4+ [RFC2283]. Although this solution is 389 more complex, it provides effective policy control, i.e. BGP4+ 390 policy determines which "6to4" routers are able to use which relay. 392 The conclusion is that in most "internal" 3GPP scenarios it is 393 preferred to use manually configured tunnels or EGP/IGP based 394 tunneling mechanisms, if it is not feasible to enable IPv6 in the 395 network infrastructure yet. 397 3.2.2 Tunneling outside the 3GPP operator's network 399 This subsection includes the case when the peer node is outside the 400 operator's network. In that case the "IPv6 in IPv4" tunnel starting 401 point can be in the operator's network - encapsulating node can be 402 e.g. the GGSN or the edge router. 404 The case is pretty straightforward if the upstream ISP provides 405 native IPv6 connectivity to the Internet. If there is no native 406 IPv6 connectivity available in the 3GPP network, an "IPv6 in IPv4" 407 tunnel should be configured from e.g. the GGSN to the dual stack 408 border gateway in order to access the upstream ISP. 410 If the ISP only provides IPv4 connectivity, then the IPv6 traffic 411 initiated from the 3GPP network should be transported tunneled in 412 IPv4 to the ISP. Defining the tunnel endpoint depends on the 413 deployment scenario. 415 Usage of manually configured "IPv6 in IPv4" tunneling is sensible 416 if the number of the tunnels can be kept limited. It is assumed 417 that a maximum of 10-15 configured "IPv6 in IPv4" tunnels from the 418 3GPP network towards the ISP / Internet should be sufficient. 420 Usage of dynamic tunneling, such as "6to4", can also be considered, 421 but the scalability problems arise when thinking about the great 422 number of UEs in the 3GPP networks. If we consider the "6to4" 423 tunneling mechanism and the 3GPP addressing model (a unique /64 424 prefix allocated for each primary PDP context), a /48 "6to4" prefix 425 would only be enough for approximately 65000 UEs. Thus, a few 426 public IPv4 addresses would be needed depending on the size of the 427 operator. Other issues to keep in mind with respect to the "6to4" 428 mechanism are that reverse DNS is not yet completely solved and 429 there are some security considerations associated with the use of 430 "6to4" relay routers (see [6to4SEC]). Moreover, in a later phase of 431 the transition period, there will be a need for assigning new 432 (native IPv6) addresses to all "6to4" nodes in order to enable 433 native IPv6 connectivity. 435 The conclusion is that in most "external" 3GPP scenarios it is 436 preferred to use a few manually configured tunnels. 438 3.3 IPv4 UE connecting to an IPv4 node through an IPv6 network 440 3GPP networks are expected to support both IPv4 and IPv6 for a long 441 time, on the UE-GGSN link and between the GGSN and external 442 networks. For this scenario it is useful to split the end-to-end 443 IPv4 UE to IPv4 node communication into UE-to-GGSN and GGSN-to- 444 v4NODE. An IPv6-capable GGSN is expected to support both IPv6 and 445 IPv4 UEs. Therefore an IPv4-only UE will be able to use an IPv4 446 link (PDP context) to connect to the GGSN without the need to 447 communicate over an IPv6 network. Regarding the GGSN-to-v4NODE 448 communication, typically the transport network between the GGSN and 449 external networks will support only IPv4 in the early stages and 450 migrate to dual stack, since these networks are already deployed. 451 Therefore it is not envisaged that tunneling of IPv4 in IPv6 will 452 be required from the GGSN to external IPv4 networks either. In the 453 longer run, 3GPP operators may need to phase out IPv4 UEs and the 454 IPv4 transport network. This would leave only IPv6 UEs. Therefore, 455 overall, the transition scenario involving an IPv4 UE communicating 456 with an IPv4 peer through an IPv6 network is not considered very 457 likely in 3GPP networks. 459 3.4 IPv6 UE connecting to an IPv4 node 461 IPv6 nodes can communicate with IPv4 hosts by making use of a 462 translator (SIIT [RFC2765], NAT-PT [RFC2766]) within the local 463 network. For some applications, application proxies can be 464 appropriate (e.g. HTTP, email relays, etc.). Such applications will 465 not be transparent to the UE. Hence, a flexible mechanism with 466 minimal manual intervention should be used to configure these 467 proxies on IPv6 UEs. Within the 3GPP architecture, application 468 proxies can be placed on the GGSN external interface (Gi), or 469 inside the service network. 471 However, since it is difficult to anticipate all possible 472 applications, there is a need for translators that can translate 473 headers independent of the type of application being used. 475 Due to the significant lack of IPv4 addresses in some domains, port 476 multiplexing is likely to be a necessary feature for translators 477 (i.e. NAPT-PT). 479 When NA(P)T-PT is used, it needs to be placed on the GGSN external 480 (Gi) interface, typically separate from the GGSN. NA(P)T-PT can be 481 installed, for example, on the edge of the operator's network and 482 the public Internet. NA(P)T-PT will intercept DNS requests and 483 other applications that include IP addresses in their payloads, 484 translate the IP header (and payload for some applications if 485 necessary) and forward packets through its IPv4 interface. 487 NA(P)T-PT introduces limitations that are expected to be magnified 488 within the 3GPP architecture. Some of these limitations are listed 489 below (notice that some of them are also relevant for IPv4 NAT). We 490 note here that [Unmaneval] section 3.2 analyzes the problem with 491 address translation. However, the NAT-PT issues should be clearly 492 documented in an RFC in the v6ops Working Group and a decision 493 should be made, whether revisiting the NAT-PT RFC is necessary / 494 what kind of update is needed. 496 1. NA(P)T-PT is a single point of failure for all ongoing 497 connections. 499 2. Additional forwarding delays due to further processing, when 500 compared to normal IP forwarding. 502 3. Problems with source address selection due to the inclusion of 503 a DNS ALG on the same node [NATPT-DNS]. 505 4. NA(P)T-PT does not work (without application level gateways) 506 for applications that embed IP addresses in their payload. 508 5. NA(P)T-PT breaks DNSSEC. 510 6. NA(P)T-PT does not scale very well in large networks. 512 3GPP networks are expected to handle a very large number of 513 subscribers on a single GGSN (default router). Each GGSN is 514 expected to handle hundreds of thousands of connections. 515 Furthermore, high reliability is expected for 3GPP networks. 516 Consequently, a single point of failure on the GGSN external 517 interface, would raise concerns on the overall network reliability. 518 In addition, IPv6 users are expected to use delay-sensitive 519 applications provided by IMS. Hence, there is a need to minimize 520 forwarding delays within the IP backbone. Furthermore, due to the 521 unprecedented number of connections handled by the default routers 522 (GGSN) in 3GPP networks, a network design that forces traffic to go 523 through a single node at the edge of the network (typical NA(P)T-PT 524 configuration) is not likely to scale. Translation mechanisms 525 should allow for multiple translators, for load sharing and 526 redundancy purposes. 528 To minimize the problems associated with NA(P)T-PT, the following 529 actions can be recommended: 531 1. Separate the DNS ALG from the NA(P)T-PT node (in the "IPv6 532 to IPv4" case). 534 2. Ensure (if possible) that NA(P)T-PT does not become a 535 single point of failure. 537 3. Allow for load sharing between different translators. That 538 is, it should be possible for different connections to go 539 through different translators. Note that load sharing alone 540 does not prevent NA(P)T-PT from becoming a single point of 541 failure. 543 There are some ways to fix the problems with NA(P)T-PT, one 544 suggestion is [NAT64]. 546 When thinking the DNS issues, the IPv6 UE needs to find the IPv4 547 address in the DNS, thus the DNS resolver in the network must be 548 dual stack [DNStrans]. Note that DNSSEC is broken if NA(P)T-PT is 549 used. 551 3.5 IPv4 UE connecting to an IPv6 node 553 The legacy IPv4 nodes are mostly nodes that support the 554 applications that are popular today in the IPv4 Internet: mostly e- 555 mail, and web-browsing. These applications will, of course, be 556 supported in the IPv6 Internet of the future. However, the legacy 557 IPv4 UEs are not going to be updated to support the future 558 applications. As these application are designed for IPv6, and to 559 use the advantages of newer platforms, the legacy IPv4 nodes will 560 not be able to profit from them. Thus, they will continue to 561 support the legacy services. 563 Taking the above into account, the traffic to and from the legacy 564 IPv4 UE is restricted to a few applications. These applications 565 already today mostly rely on proxies or local servers to 566 communicate between private address space networks and the 567 Internet. The same methods and technology can be used for IPv4 to 568 IPv6 transition. 570 An alternative solution could be a general network address 571 translation mechanisms such as NAT46 [NAT64]. 573 When thinking the DNS issues, the DNS zones containing AAAA records 574 for the IPv6 nodes need to be served by at least one IPv4 575 accessible DNS server [DNStrans]. 577 4. Transition Scenarios with IMS 579 As the IMS is exclusively IPv6, the number of possible transition 580 scenarios is reduced dramatically. In the following, the possible 581 transition scenarios are listed. Those scenarios are analyzed in 582 sections 4.2 and 4.3. 584 1) UE connecting to a node in an IPv4 network through IMS 585 2) Two IMS islands connected over IPv4 network 587 4.1 DNS interworking in IMS 589 Currently, there is a consensus in the IETF that even in the IPv6 590 Internet the DNS resolvers have to be dual stack. 592 To perform DNS resolution in the IMS, the UE can be configured as a 593 stub resolver pointing to a recursive DNS resolver. This 594 communication can happen over IPv6. However, in the process to find 595 the IPv6 address of a SIP server, the recursive DNS resolver may 596 need to access data that is available only on some IPv4 DNS 597 servers, see [DNStrans], [v6namespace] and [DNSreq]. One way to 598 achieve this is to make the DNS resolver be dual stack. As DNS 599 traffic is not directly related to the IMS functionality, this is 600 not in contradiction with the IPv6-only nature of the IMS. 602 4.2 UE connecting to a node in an IPv4 network through IMS 604 This scenario occurs when an IMS UE (IPv6) connects to a node in 605 the IPv4 Internet through the IMS, or vice versa. This happens when 606 the other node is a part of a different system than 3GPP, e.g. a 607 fixed PC, with only IPv4 capabilities. 609 Apparently there will be a number of legacy IPv4 nodes in the 610 Internet that will communicate with the IMS UEs. As the IMS is 611 exclusively IPv6 [3GPP 23.221], translators have to be used in the 612 communication between the IPv6 IMS and legacy IPv4 hosts, i.e. 613 making a dual stack based solution is not feasible. This section 614 aims to give an overview on how that interworking can be handled. 616 As control (or signaling) and user (or data) traffic are separated 617 in SIP, and thus, the IMS, the translation of the IMS traffic has 618 to be done on two levels - Session Initiation Protocol (SIP) 619 [RFC3261], and Session Description Protocol (SDP) [RFC2327] 621 [RFC3266] on the one hand (Mm-interface), and on the actual user 622 data traffic level on the other (Mb-interface). 624 SIP and SDP transition has to be made in an SIP/SDP Application 625 Level Gateway. The ALG has to change the IP addresses transported 626 in the SIP messages and the SDP payload of those messages to the 627 appropriate version. In addition, there has to be interoperability 628 for DNS queries; see section 4.1 for details. 630 On the user data transport level, the translation is IPv4-IPv6 631 protocol translation, where the user data traffic transported is 632 translated from IPv6 to IPv4, and vice versa. 634 The legacy IPv4 host's address can be mapped to an IPv6 address for 635 the IMS, and this address is then used within the IMS to route the 636 traffic to the appropriate user traffic translator. This mapping 637 can be done by the SIP/SDP ALG for the SIP traffic. The user 638 traffic translator would do the similar mapping for the user 639 traffic. However, in order to have an IPv4 address for the IMS UE, 640 and to be able to route the user traffic within the legacy IPv4 641 network to the correct translator, there has to be an IPv4 address 642 allocated for the duration of the session from the user traffic 643 translator. The allocation of this address from the user traffic 644 translator has to be done by the SIP/SDP ALG in order for the 645 SIP/SDP ALG to know the correct IPv4 address. This can be achieved 646 by using a protocol for the ALG to do the allocation such as MEGACO 647 [RFC3015]. 649 +-------------------------------+ +----------+ 650 | +------+ | |+--------+| 651 | |S-CSCF|---||SIP ALG ||\ 652 | | +------+ | |+--------+| \ -------- 653 +-|+ | / | | | | | | 654 | | | +------+ +------+ | | + | -| |- 655 | |-|-|P-CSCF|--------|I-CSCF| | | | | | () | 656 | | +------+ +------+ | |+--------+| / ------ 657 | |-----------------------------------|| NAT-PT ||/ 658 +--+ | IPv6 | |+--------+| IPv4 659 UE | | | | 660 | IP Multimedia CN Subsystem | |Translator| 661 +-------------------------------+ +----------+ 662 Figure 1: UE using IMS to contact a legacy phone 664 Figure 1 shows a possible configuration scenario where the SIP ALG 665 is separate to the CSCFs. The translator can either be set up in a 666 single device with both SIP translation and media translation, or 667 those functionalities can be divided to two different entities with 668 an interface in between. 670 4.3 Two IMS islands connected over IPv4 network 672 At the early stages of IMS deployment, there may be cases where two 673 IMS islands are separated by an IPv4 network such as the legacy 674 Internet. Here both the UEs and the IMS islands are IPv6-only. 675 However, the IPv6 islands are not native IPv6 connected. 677 In this scenario, the end-to-end SIP connections would be based on 678 IPv6. The only issue is to make connection between two IPv6-only 679 IMS islands over IPv4 network. So, in practice, this scenario is 680 very closely related to GPRS scenario represented in section 4.2. 682 IPv4 / IPv6 interworking can be taken care of in the network; the 683 basic options are static and dynamic tunneling. The tunnel starting 684 point or endpoint should be located on the edge of the IMS domain. 685 Static "IPv6 in IPv4" tunnels configured between different IMS 686 domains would be a good solution. Note that this scenario is 687 comparable to 6bone [6BONE] network operation. 689 5. Security Considerations 691 1. Problems have been identified in the case of the 692 reachability of IPv4 and IPv6 nodes (use of DNS through 693 NAT-PT). NAT-PT DNS ALG problems are described in [NATPT- 694 DNS] and [Unmaneval]. 696 2. The 3GPP specifications do not currently define the usage 697 of DNS Security. They neither disallow the usage of DNSSEC, 698 nor do they mandate it. 700 3. NAT-PT breaks DNSSEC. 702 6. Changes from draft-ietf-v6ops-3gpp-analysis-00.txt 704 - Editorial changes in some sections 705 - Copyright statement added 706 - References categorized to Normative and Informative 707 - Added and removed some references 708 - Splitting the analysis in two parts in 3.2 710 7. Copyright 712 The following copyright notice is copied from [RFC2026], Section 713 10.4. It describes the applicable copyright for this document. 715 Copyright (C) The Internet Society January 22, 2003. All Rights 716 Reserved. 718 This document and translations of it may be copied and furnished to 719 others, and derivative works that comment on or otherwise explain 720 it or assist in its implementation may be prepared, copied, 721 published and distributed, in whole or in part, without restriction 722 of any kind, provided that the above copyright notice and this 723 paragraph are included on all such copies and derivative works. 724 However, this document itself may not be modified in any way, such 725 as by removing the copyright notice or references to the Internet 726 Society or other Internet organizations, except as needed for the 727 purpose of developing Internet standards in which case the 728 procedures for copyrights defined in the Internet Standards process 729 must be followed, or as required to translate it into languages 730 other than English. 732 The limited permissions granted above are perpetual and will not be 733 revoked by the Internet Society or its successors or assignees. 735 This document and the information contained herein is provided on 736 an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET 737 ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR 738 IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 739 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 740 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 742 8. References 744 8.1 Normative 746 [RFC2026] Bradner, S.: The Internet Standards Process -- Revision 747 3, RFC 2026, October 1996. 749 [RFC2327] Handley, M., Jacobson, V.: SDP: Session Description 750 Protocol, RFC 2327, April 1998. 752 [RFC2663] Srisuresh, P., Holdrege, M.: IP Network Address 753 Translator (NAT) Terminology and Considerations, RFC 2663, August 754 1999. 756 [RFC2765] Nordmark, E.: Stateless IP/ICMP Translation Algorithm 757 (SIIT), RFC 2765, February 2000. 759 [RFC2766] Tsirtsis, G., Srisuresh, P.: Network Address Translation 760 - Protocol Translation (NAT-PT), RFC 2766, February 2000. 762 [RFC2893] Gilligan, R., Nordmark, E.: Transition Mechanisms for 763 IPv6 Hosts and Routers, RFC 2893, August 2000. 765 [RFC3015] Cuervo, F., et al: Megaco Protocol Version 1.0, RFC 3015, 766 November 2000. 768 [RFC3056] Carpenter, B., Moore, K.: Connection of IPv6 Domains via 769 IPv4 Clouds, RFC 3056, February 2001. 771 [RFC3261] J. Rosenberg, et al: SIP: Session Initiation Protocol, 772 June 2002. 774 [RFC3266] S. Olson, G. Camarillo, A. B. Roach: Support for IPv6 in 775 Session Description Protocol (SDP), June 2002. 777 [3GPP-SCEN] Soininen, J. (editor): "Transition Scenarios for 3GPP 778 Networks", October 2002, draft-ietf-v6ops-3gpp-cases-02.txt, work 779 in progress. 781 [3GPP-23.060] 3GPP TS 23.060 V5.4.0, "General Packet Radio Service 782 (GPRS); Service description; Stage 2 (Release 5)", December 2002. 784 [3GPP 23.221] 3GPP TS 23.221 V5.7.0, "Architectural requirements 785 (Release 5)", December 2002. 787 [3GPP-23.228] 3GPP TS 23.228 V5.7.0, "IP Multimedia Subsystem 788 (IMS); Stage 2 (Release 5)", December 2002. 790 [3GPP 24.228] 3GPP TS 24.228 V5.3.0, "Signalling flows for the IP 791 multimedia call control based on SIP and SDP; Stage 3 (Release 5)", 792 December 2002. 794 [3GPP 24.229] 3GPP TS 24.229 V5.3.0, "IP Multimedia Call Control 795 Protocol based on SIP and SDP; Stage 3 (Release 5)", December 2002. 797 8.2 Informative 799 [RFC2283] Bates, T., Chandra, R., Katz, D., Rekhter, Y.: 800 Multiprotocol Extensions for BGP-4, RFC 2283, February 1998. 802 [RFC3314] Wasserman, M. (editor): "Recommendations for IPv6 in 3GPP 803 Standards", September 2002. 805 [6to4SEC] Savola, P.: "Security Considerations for 6to4", January 806 2003, draft-savola-v6ops-6to4-security-02.txt, work in progress. 808 [BGP] De Clercq, J., Gastaud, G., Ooms, D., Prevost, S., Le 809 Faucheur, F.: "Connecting IPv6 Islands across IPv4 Clouds with 810 BGP", October 2002, draft-ooms-v6ops-bgp-tunnel-00.txt, work in 811 progress. 813 [DNSreq] Durand, A., Ihren, J.: "NGtrans IPv6 DNS operational 814 requirements and roadmap", March 2002, draft-ietf-ngtrans-dns-ops- 815 req-04.txt, work in progress, the draft has expired. 817 [DNStrans] Durand, A.: "IPv6 DNS transition issues", October 2002, 818 draft-ietf-dnsop-ipv6-dns-issues-00.txt, work in progress. 820 [DSTM] Bound, J., et al: "Dual Stack Transition Mechanism (DSTM)", 821 July 2002, draft-ietf-ngtrans-dstm-08.txt, work in progress, the 822 draft has expired. 824 [IGP] Cristallo, G., Gastaud, G., Ooms, D., Galand, D., Preguica, 825 C., Baudot, A., Diribarne, G.: "Connecting IPv6 islands within an 826 IPv4 AS", February 2002, draft-many-ngtrans-connect-ipv6-igp- 827 02.txt, work in progress, the draft has expired. 829 [ISATAP] Templin, F., et al: "Intra-Site Automatic Tunnel 830 Addressing Protocol (ISATAP)", January 2003, draft-ietf-ngtrans- 831 isatap-11.txt, work in progress. 833 [NAT64] Durand, A.: "NAT64 - NAT46", June 2002, draft-durand- 834 ngtrans-nat64-nat46-00.txt, work in progress, the draft has 835 expired. 837 [NATPT-DNS] Durand, A.: "Issues with NAT-PT DNS ALG in RFC2766", 838 January 2002, draft-durand-natpt-dns-alg-issues-00.txt, work in 839 progress, the draft has expired. 841 [TEREDO] Huitema, C.: "Teredo: Tunneling IPv6 over UDP Through 842 NATs", September 2002, draft-ietf-ngtrans-shipworm-08.txt, work in 843 progress. 845 [Unmaneval] Huitema, C., Austein, R., Dilettante, B., Satapati, S., 846 van der Pol, R.: "Evaluation of Transition Mechanisms for Unmanaged 847 Networks", November 2002, draft-huitema-ngtrans-unmaneval-01.txt, 848 work in progress. 850 [v6namespace] Ihren, J.: "IPv4-to-IPv6 migration and DNS namespace 851 fragmentation", March 2002, draft-ietf-dnsop-v6-name-space- 852 fragmentation-01.txt, work in progress, the draft has expired. 854 [6BONE] http://www.6bone.net 856 9. Authors and Acknowledgements 858 This document is written by: 860 Alain Durand, Sun Microsystems 861 863 Karim El-Malki, Ericsson Radio Systems 864 866 Paul Francis, Tahoe Networks 867 869 Niall Richard Murphy, Enigma Consulting Limited 870 872 Hugh Shieh, AT&T Wireless 873 875 Jonne Soininen, Nokia 876 878 Hesham Soliman, Ericsson Radio Systems 879 881 Margaret Wasserman, Wind River 882 884 Juha Wiljakka, Nokia 885 887 The authors would like to thank Gabor Bajko, Ajay Jain, Ivan 888 Laloux, Pekka Savola, Pedro Serna, Fred Templin, Anand Thakur and 889 Rod Van Meter for their valuable input. 891 10. Editor's Contact Information 893 Comments or questions regarding this document should be sent to the 894 v6ops mailing list or directly to the document editor: 896 Juha Wiljakka 897 Nokia 898 Sinitaival 5 Phone: +358 7180 47562 899 FIN-33720 TAMPERE, Finland Email: juha.wiljakka@nokia.com