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'3GPP-SCEN') -- Obsolete informational reference (is this intentional?): RFC 2283 (Obsoleted by RFC 2858) == Outdated reference: A later version (-07) exists of draft-ooms-v6ops-bgp-tunnel-00 == Outdated reference: A later version (-12) exists of draft-ietf-dnsop-ipv6-dns-issues-00 -- Unexpected draft version: The latest known version of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 == Outdated reference: A later version (-24) exists of draft-ietf-ngtrans-isatap-12 Summary: 10 errors (**), 0 flaws (~~), 8 warnings (==), 4 comments (--).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 (ed.) 3 Document: draft-ietf-v6ops-3gpp-analysis-02.txt Nokia 4 Expires: September 2003 6 March 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 8 54 3.3 IPv4 UE Connecting to an IPv4 Node through an IPv6 Network10 55 3.4 IPv6 UE Connecting to an IPv4 Node.......................11 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...14 60 4.3 Two IMS Islands Connected over IPv4 Network..............16 61 5. Security Considerations......................................16 62 6. Changes from draft-ietf-v6ops-3gpp-analysis-01.txt...........16 63 7. Copyright....................................................16 64 8. References...................................................17 65 8.1 Normative................................................17 66 8.2 Informative..............................................18 67 9. Authors and Acknowledgements.................................20 68 10. Editor's Contact Information................................20 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. 313 Keeping the Internet name space unfragmented is an important thing. 314 This covers IPv4 and IPv6. It means that any record in the public 315 Internet should be available unmodified to any nodes, IPv4 or IPv6, 316 regardless of the transport being used. The recommended approach 317 is: every recursive DNS server should be either IPv4-only or dual 318 stack and every single DNS zone should be served by at least an 319 IPv4 reachable DNS server. This recommendation rules out IPv6-only 320 recursive DNS servers and DNS zones served by IPv6-only DNS servers 321 and this approach could be revisited if translation techniques 322 between IPv4 and IPv6 were to be widely deployed [DNStrans]. 324 3.2 IPv6 UE Connecting to an IPv6 Node through an IPv4 Network 326 The best solution for this scenario is obtained with tunneling, 327 i.e. "IPv6 in IPv4" tunneling is a requirement. An IPv6 PDP context 328 is activated between the UE and the GGSN. Tunneling is handled in 329 the network, because IPv6 UE is not capable of tunneling (it does 330 not have the dual stack functionality needed for tunneling). 331 Encapsulating node can be the GGSN, the edge router between the 332 border of the operator's IPv6 network and the public Internet, or 333 any other dual stack node within the operator's IP network. The 334 encapsulation (uplink) and decapsulation (downlink) can be handled 335 by the same network element. Typically the tunneling handled by the 336 network elements is transparent to the UEs and the IP traffic looks 337 like native IPv6 traffic to them. For the applications, tunneling 338 enables end-to-end IPv6 connectivity. Note that this scenario is 339 comparable to 6bone [6BONE] network operation. 341 "IPv6 in IPv4" tunnels between the IPv6 islands can be static or 342 dynamic. The selection of the type of tunneling mechanism is up to 343 the operator / ISP deployment scenario and only generic 344 recommendations can be given in this document. 346 The following subsections are focused on the usage of different 347 tunneling mechanisms when the peer node is in the operator's 348 network or outside the operator's network. The authors note that 349 where the actual 3GPP network ends and which parts of the network 350 belong to the ISP(s) also depends on the deployment scenario. The 351 authors are also not commenting how many ISP functions the 3GPP 352 operator should perform. However, many 3GPP operators are ISPs of 353 some sort themselves. 355 3.2.1 Tunneling inside the 3GPP Operator's Network 357 Many GPRS operators already have IPv4 backbone networks deployed 358 and they are gradually migrating them while introducing IPv6 359 islands. IPv6 backbones can be considered quite rare in the first 360 phases of the transition. If the 3GPP operator already has IPv6 361 widely deployed in its network, this subsection is not so relevant. 363 In initial, smaller scale IPv6 deployment, where a small number of 364 IPv6 in IPv4 tunnels are required to connect the IPv6 islands over 365 the 3GPP operator's IPv4 network, manually configured tunnels can 366 be used. In a 3GPP network, one IPv6 island could contain the GGSN 367 while another island contains the operator's IPv6 application 368 servers. However, manually configured tunnels can be an 369 administrative burden when the number of islands and therefore 370 tunnels rises. 372 It is also possible to use dynamic tunneling mechanisms such as 373 "6to4" [RFC3056] and IGP/EGP routing protocol based tunneling 374 mechanisms [BGP][IGP]. Routing protocol based mechanisms such as 375 [BGP] consist of running BGP between the neighboring router tunnel 376 endpoints and using multi-protocol BGP extensions to exchange 377 reachability information of IPv6 prefixes. The routers use this 378 information to create IPv6 in IPv4 tunnel interfaces and route IPv6 379 packets over the IPv4 network. It is possible to combine this with 380 different types of tunnels. 382 "6to4" nodes use special IPv6 addresses with a "6to4" prefix 383 containing the IPv4 address of the corresponding "IPv6 in IPv4" 384 tunnel endpoint ("6to4" router) which performs encapsulation / 385 decapsulation. When connecting two nodes with "6to4" addresses, the 386 corresponding "6to4" routers use the IPv4 addresses specified in 387 the "6to4" prefixes to tunnel IPv6 packets through the IPv4 388 network. But if only one of them has a "6to4" address, a "6to4" 389 relay must be present to perform the missing "6to4" router 390 functionality for the native-IPv6 node. In this case there are two 391 deployment options for "IPv6 in IPv4" tunneling between the "6to4" 392 router and the relay. The first option assumes that "6to4" routers 393 using a given relay each have a default IPv6 route (configured 394 tunnel) pointing to that relay. The other one consists of using an 395 IPv6 exterior routing protocol; this way the set of "6to4" routers 396 using a given relay obtain native IPv6 routes from it using a 397 routing protocol such as BGP4+ [RFC2283]. Although this solution is 398 more complex, it provides effective policy control, i.e. BGP4+ 399 policy determines which "6to4" routers are able to use which relay. 401 The conclusion is that in most "internal" 3GPP scenarios it is 402 preferred to use manually configured tunnels or EGP/IGP based 403 tunneling mechanisms, if it is not feasible to enable IPv6 in the 404 network infrastructure yet. 406 3.2.2 Tunneling outside the 3GPP Operator's Network 408 This subsection includes the case when the peer node is outside the 409 operator's network. In that case the "IPv6 in IPv4" tunnel starting 410 point can be in the operator's network - encapsulating node can be 411 e.g. the GGSN or the edge router. 413 The case is pretty straightforward if the upstream ISP provides 414 native IPv6 connectivity to the Internet. If there is no native 415 IPv6 connectivity available in the 3GPP network, an "IPv6 in IPv4" 416 tunnel should be configured from e.g. the GGSN to the dual stack 417 border gateway in order to access the upstream ISP. 419 If the ISP only provides IPv4 connectivity, then the IPv6 traffic 420 initiated from the 3GPP network should be transported tunneled in 421 IPv4 to the ISP. Defining the tunnel endpoint depends on the 422 deployment scenario. 424 Usage of manually configured "IPv6 in IPv4" tunneling is sensible 425 if the number of the tunnels can be kept limited. It is assumed 426 that a maximum of 10-15 configured "IPv6 in IPv4" tunnels from the 427 3GPP network towards the ISP / Internet should be sufficient. 429 Usage of dynamic tunneling, such as "6to4", can also be considered, 430 but the scalability problems arise when thinking about the great 431 number of UEs in the 3GPP networks. If we consider the "6to4" 432 tunneling mechanism and the 3GPP addressing model (a unique /64 433 prefix allocated for each primary PDP context), a /48 "6to4" prefix 434 would only be enough for approximately 65000 UEs. Thus, a few 435 public IPv4 addresses would be needed depending on the size of the 436 operator. Other issues to keep in mind with respect to the "6to4" 437 mechanism are that reverse DNS is not yet completely solved and 438 there are some security considerations associated with the use of 439 "6to4" relay routers (see [6to4SEC]). Moreover, in a later phase of 440 the transition period, there will be a need for assigning new 441 (native IPv6) addresses to all "6to4" nodes in order to enable 442 native IPv6 connectivity. 444 The conclusion is that in most "external" 3GPP scenarios it is 445 preferred to use a few manually configured tunnels. 447 3.3 IPv4 UE Connecting to an IPv4 Node through an IPv6 Network 449 3GPP networks are expected to support both IPv4 and IPv6 for a long 450 time, on the UE-GGSN link and between the GGSN and external 451 networks. For this scenario it is useful to split the end-to-end 452 IPv4 UE to IPv4 node communication into UE-to-GGSN and GGSN-to- 453 v4NODE. An IPv6-capable GGSN is expected to support both IPv6 and 454 IPv4 UEs. Therefore an IPv4-only UE will be able to use an IPv4 455 link (PDP context) to connect to the GGSN without the need to 456 communicate over an IPv6 network. Regarding the GGSN-to-v4NODE 457 communication, typically the transport network between the GGSN and 458 external networks will support only IPv4 in the early stages and 459 migrate to dual stack, since these networks are already deployed. 460 Therefore it is not envisaged that tunneling of IPv4 in IPv6 will 461 be required from the GGSN to external IPv4 networks either. In the 462 longer run, 3GPP operators may need to phase out IPv4 UEs and the 463 IPv4 transport network. This would leave only IPv6 UEs. Therefore, 464 overall, the transition scenario involving an IPv4 UE communicating 465 with an IPv4 peer through an IPv6 network is not considered very 466 likely in 3GPP networks. 468 3.4 IPv6 UE Connecting to an IPv4 Node 470 IPv6 nodes can communicate with IPv4 hosts by making use of a 471 translator (SIIT [RFC2765], NAT-PT [RFC2766]) within the local 472 network. For some applications, application proxies can be 473 appropriate (e.g. HTTP, email relays, etc.). Such applications will 474 not be transparent to the UE. Hence, a flexible mechanism with 475 minimal manual intervention should be used to configure these 476 proxies on IPv6 UEs. Within the 3GPP architecture, application 477 proxies can be placed on the GGSN external interface (Gi), or 478 inside the service network. 480 However, since it is difficult to anticipate all possible 481 applications, there is a need for translators that can translate 482 headers independent of the type of application being used. 484 Due to the significant lack of IPv4 addresses in some domains, port 485 multiplexing is likely to be a necessary feature for translators 486 (i.e. NAPT-PT). 488 When NA(P)T-PT is used, it needs to be placed on the GGSN external 489 (Gi) interface, typically separate from the GGSN. NA(P)T-PT can be 490 installed, for example, on the edge of the operator's network and 491 the public Internet. NA(P)T-PT will intercept DNS requests and 492 other applications that include IP addresses in their payloads, 493 translate the IP header (and payload for some applications if 494 necessary) and forward packets through its IPv4 interface. 496 NA(P)T-PT introduces limitations that are expected to be magnified 497 within the 3GPP architecture. Some of these limitations are listed 498 below (notice that some of them are also relevant for IPv4 NAT). We 499 note here that [Unmaneval] section 3.2 analyzes the problem with 500 address translation. However, the NAT-PT issues should be clearly 501 documented in an RFC in the v6ops Working Group and a decision 502 should be made, whether revisiting the NAT-PT RFC is necessary / 503 what kind of update is needed. 505 1. NA(P)T-PT is a single point of failure for all ongoing 506 connections. 508 2. Additional forwarding delays due to further processing, when 509 compared to normal IP forwarding. 511 3. Problems with source address selection due to the inclusion of 512 a DNS ALG on the same node [NATPT-DNS]. 514 4. NA(P)T-PT does not work (without application level gateways) 515 for applications that embed IP addresses in their payload. 517 5. NA(P)T-PT breaks DNSSEC. 519 6. NA(P)T-PT does not scale very well in large networks. 521 3GPP networks are expected to handle a very large number of 522 subscribers on a single GGSN (default router). Each GGSN is 523 expected to handle hundreds of thousands of connections. 524 Furthermore, high reliability is expected for 3GPP networks. 525 Consequently, a single point of failure on the GGSN external 526 interface, would raise concerns on the overall network reliability. 527 In addition, IPv6 users are expected to use delay-sensitive 528 applications provided by IMS. Hence, there is a need to minimize 529 forwarding delays within the IP backbone. Furthermore, due to the 530 unprecedented number of connections handled by the default routers 531 (GGSN) in 3GPP networks, a network design that forces traffic to go 532 through a single node at the edge of the network (typical NA(P)T-PT 533 configuration) is not likely to scale. Translation mechanisms 534 should allow for multiple translators, for load sharing and 535 redundancy purposes. 537 To minimize the problems associated with NA(P)T-PT, the following 538 actions can be recommended: 540 1. Separate the DNS ALG from the NA(P)T-PT node (in the "IPv6 541 to IPv4" case). 543 2. Ensure (if possible) that NA(P)T-PT does not become a 544 single point of failure. 546 3. Allow for load sharing between different translators. That 547 is, it should be possible for different connections to go 548 through different translators. Note that load sharing alone 549 does not prevent NA(P)T-PT from becoming a single point of 550 failure. 552 There are some ways to fix the problems with NA(P)T-PT, one 553 suggestion is [NAT64]. 555 When thinking the DNS issues, the IPv6 UE needs to find the IPv4 556 address in the DNS [DNStrans]. Note that DNSSEC is broken if 557 NA(P)T-PT is used. 559 3.5 IPv4 UE Connecting to an IPv6 Node 561 The legacy IPv4 nodes are mostly nodes that support the 562 applications that are popular today in the IPv4 Internet: mostly e- 563 mail, and web-browsing. These applications will, of course, be 564 supported in the IPv6 Internet of the future. However, the legacy 565 IPv4 UEs are not going to be updated to support the future 566 applications. As these application are designed for IPv6, and to 567 use the advantages of newer platforms, the legacy IPv4 nodes will 568 not be able to profit from them. Thus, they will continue to 569 support the legacy services. 571 Taking the above into account, the traffic to and from the legacy 572 IPv4 UE is restricted to a few applications. These applications 573 already today mostly rely on proxies or local servers to 574 communicate between private address space networks and the 575 Internet. The same methods and technology can be used for IPv4 to 576 IPv6 transition. 578 An alternative solution could be a general network address 579 translation mechanisms such as NAT46 [NAT64]. 581 When thinking the DNS issues, the DNS zones containing AAAA records 582 for the IPv6 nodes need to be served by at least one IPv4 583 accessible DNS server [DNStrans]. 585 4. Transition Scenarios with IMS 587 As the IMS is exclusively IPv6, the number of possible transition 588 scenarios is reduced dramatically. In the following, the possible 589 transition scenarios are listed. Those scenarios are analyzed in 590 sections 4.2 and 4.3. 592 1) UE connecting to a node in an IPv4 network through IMS 593 2) Two IMS islands connected over IPv4 network 595 4.1 DNS Interworking in IMS 597 The recommended approach (as documented in [DNStrans]) currently is 598 that every recursive DNS server should be either IPv4-only or dual 599 stack and every single DNS zone should be served by at least an 600 IPv4 reachable DNS server. The recommendation rules out IPv6-only 601 recursive DNS servers and DNS zones served by IPv6-only DNS 602 servers. 604 To perform DNS resolution in the IMS, the UE can be configured as a 605 stub resolver pointing to a recursive DNS resolver. This 606 communication can happen over IPv6. However, in the process to find 607 the IPv6 address of a SIP server, the recursive DNS resolver may 608 need to access data that is available only on some IPv4 DNS 609 servers, see [DNStrans]. One way to achieve this is to make the DNS 610 resolver be dual stack. As DNS traffic is not directly related to 611 the IMS functionality, this is not in contradiction with the IPv6- 612 only nature of the IMS. 614 4.2 UE Connecting to a Node in an IPv4 Network through IMS 616 This scenario occurs when an IMS UE (IPv6) connects to a node in 617 the IPv4 Internet through the IMS, or vice versa. This happens when 618 the other node is a part of a different system than 3GPP, e.g. a 619 fixed PC, with only IPv4 capabilities. 621 There will probably be few legacy IPv4 nodes in the Internet that 622 will communicate with the IMS UEs. It is assumed that the solution 623 described here is used for limited cases, in which communications 624 with a small number of legacy IPv4 SIP equipment are needed. As the 625 IMS is exclusively IPv6 [3GPP 23.221], translators have to be used 626 in the communication between the IPv6 IMS and legacy IPv4 hosts, 627 i.e. making a dual stack based solution is not feasible. This 628 section aims to give an overview on how that interworking can be 629 handled. 631 As control (or signaling) and user (or data) traffic are separated 632 in SIP, and thus, the IMS, the translation of the IMS traffic has 633 to be done on two levels - Session Initiation Protocol (SIP) 634 [RFC3261], and Session Description Protocol (SDP) [RFC2327] 635 [RFC3266] on the one hand (Mm-interface), and on the actual user 636 data traffic level on the other (Mb-interface). 638 SIP and SDP transition has to be made in an SIP/SDP Application 639 Level Gateway. The ALG has to change the IP addresses transported 640 in the SIP messages and the SDP payload of those messages to the 641 appropriate version. In addition, there has to be interoperability 642 for DNS queries; see section 4.1 for details. 644 On the user data transport level, the translation is IPv4-IPv6 645 protocol translation, where the user data traffic transported is 646 translated from IPv6 to IPv4, and vice versa. 648 The legacy IPv4 host's address can be mapped to an IPv6 address for 649 the IMS, and this address is then used within the IMS to route the 650 traffic to the appropriate user traffic translator. This mapping 651 can be done by the SIP/SDP ALG for the SIP traffic. The user 652 traffic translator would do the similar mapping for the user 653 traffic. However, in order to have an IPv4 address for the IMS UE, 654 and to be able to route the user traffic within the legacy IPv4 655 network to the correct translator, there has to be an IPv4 address 656 allocated for the duration of the session from the user traffic 657 translator. The allocation of this address from the user traffic 658 translator has to be done by the SIP/SDP ALG in order for the 659 SIP/SDP ALG to know the correct IPv4 address. This can be achieved 660 by using a protocol for the ALG to do the allocation such as MEGACO 661 [RFC3015]. 663 +-------------------------------+ +----------+ 664 | +------+ | |+--------+| 665 | |S-CSCF|---||SIP ALG ||\ 666 | | +------+ | |+--------+| \ -------- 667 +-|+ | / | | | | | | 668 | | | +------+ +------+ | | + | -| |- 669 | |-|-|P-CSCF|--------|I-CSCF| | | | | | () | 670 | | +------+ +------+ | |+--------+| / ------ 671 | |-----------------------------------|| NAT-PT ||/ 672 +--+ | IPv6 | |+--------+| IPv4 673 UE | | | | 674 | IP Multimedia CN Subsystem | |Translator| 675 +-------------------------------+ +----------+ 677 Figure 1: UE using IMS to contact a legacy phone 679 Figure 1 shows a possible configuration scenario where the SIP ALG 680 is separate to the CSCFs. The translator can either be set up in a 681 single device with both SIP translation and media translation, or 682 those functionalities can be divided to two different entities with 683 an interface in between. 685 A special situation is when the IPv4-only destination node is 686 registered to a SIP proxy that happens to be dual stack. In such a 687 case, the connection from the edge of the IMS to the destination 688 network could be either IPv4 or IPv6, as the SIP INVITE message 689 sent by the IMS UE involves DNS address resolution only for the 690 destination SIP proxy (and not for the destination node). If IPv4 691 is used (from the edge of the IMS to the destination SIP proxy), 692 then no further IPv4-IPv6 interworking is needed outside the IMS 693 domain, as IPv4-IPv6 translation will be performed on the edge of 694 the IMS. 696 On the other hand, when IPv6 is used to connect both SIP proxies 697 (that is more likely), translation is not taken care of in the IMS 698 because there is no way of detecting that the destination node is 699 IPv4-only (i.e., only the IP version of the destination SIP proxy 700 can be detected from the DNS reply). Thus, IPv6 to IPv4 translation 701 should be performed in the destination SIP domain (for example, 702 implemented in the dual stack SIP proxy). In addition, it could 703 also happen (especially in the initial stages of IPv6 deployment) 704 that end-to-end IPv6 connectivity between the IMS and the 705 destination domain is not yet available. Thus, this would be 706 equivalent to the scenario described in 4.3 (two IPv6 islands 707 connecting through an IPv4 network) and an IPv6 in IPv4 tunneling 708 mechanism should be used (in addition to IPv4-IPv6 translation in 709 the destination domain). 711 4.3 Two IMS Islands Connected over IPv4 Network 713 At the early stages of IMS deployment, there may be cases where two 714 IMS islands are separated by an IPv4 network such as the legacy 715 Internet. Here both the UEs and the IMS islands are IPv6-only. 716 However, the IPv6 islands are not native IPv6 connected. 718 In this scenario, the end-to-end SIP connections would be based on 719 IPv6. The only issue is to make connection between two IPv6-only 720 IMS islands over IPv4 network. So, in practice, this scenario is 721 very closely related to GPRS scenario represented in section 4.2. 723 IPv4 / IPv6 interworking can be taken care of in the network; the 724 basic options are static and dynamic tunneling. The tunnel starting 725 point or endpoint should be located on the edge of the IMS domain. 726 Static "IPv6 in IPv4" tunnels configured between different IMS 727 domains would be a good solution. Note that this scenario is 728 comparable to 6bone [6BONE] network operation. 730 5. Security Considerations 732 1. Problems have been identified in the case of the 733 reachability of IPv4 and IPv6 nodes (use of DNS through 734 NAT-PT). NAT-PT DNS ALG problems are described in [NATPT- 735 DNS] and [Unmaneval]. 737 2. The 3GPP specifications do not currently define the usage 738 of DNS Security. They neither disallow the usage of DNSSEC, 739 nor do they mandate it. 741 3. NAT-PT breaks DNSSEC. 743 6. Changes from draft-ietf-v6ops-3gpp-analysis-01.txt 745 - Editorial changes in some sections 746 - Subsection 4.2: adding short description on destination 747 network dual stack SIP proxy case 749 7. Copyright 751 The following copyright notice is copied from [RFC2026], Section 752 10.4. It describes the applicable copyright for this document. 754 Copyright (C) The Internet Society March 01, 2003. All Rights 755 Reserved. 757 This document and translations of it may be copied and furnished to 758 others, and derivative works that comment on or otherwise explain 759 it or assist in its implementation may be prepared, copied, 760 published and distributed, in whole or in part, without restriction 761 of any kind, provided that the above copyright notice and this 762 paragraph are included on all such copies and derivative works. 763 However, this document itself may not be modified in any way, such 764 as by removing the copyright notice or references to the Internet 765 Society or other Internet organizations, except as needed for the 766 purpose of developing Internet standards in which case the 767 procedures for copyrights defined in the Internet Standards process 768 must be followed, or as required to translate it into languages 769 other than English. 771 The limited permissions granted above are perpetual and will not be 772 revoked by the Internet Society or its successors or assignees. 774 This document and the information contained herein is provided on 775 an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET 776 ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR 777 IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 778 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 779 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 781 8. References 783 8.1 Normative 785 [RFC2026] Bradner, S.: The Internet Standards Process -- Revision 786 3, RFC 2026, October 1996. 788 [RFC2327] Handley, M., Jacobson, V.: SDP: Session Description 789 Protocol, RFC 2327, April 1998. 791 [RFC2663] Srisuresh, P., Holdrege, M.: IP Network Address 792 Translator (NAT) Terminology and Considerations, RFC 2663, August 793 1999. 795 [RFC2765] Nordmark, E.: Stateless IP/ICMP Translation Algorithm 796 (SIIT), RFC 2765, February 2000. 798 [RFC2766] Tsirtsis, G., Srisuresh, P.: Network Address Translation 799 - Protocol Translation (NAT-PT), RFC 2766, February 2000. 801 [RFC2893] Gilligan, R., Nordmark, E.: Transition Mechanisms for 802 IPv6 Hosts and Routers, RFC 2893, August 2000. 804 [RFC3015] Cuervo, F., et al: Megaco Protocol Version 1.0, RFC 3015, 805 November 2000. 807 [RFC3056] Carpenter, B., Moore, K.: Connection of IPv6 Domains via 808 IPv4 Clouds, RFC 3056, February 2001. 810 [RFC3261] J. Rosenberg, et al: SIP: Session Initiation Protocol, 811 June 2002. 813 [RFC3266] S. Olson, G. Camarillo, A. B. Roach: Support for IPv6 in 814 Session Description Protocol (SDP), June 2002. 816 [3GPP-SCEN] Soininen, J. (editor): "Transition Scenarios for 3GPP 817 Networks", January 2003, draft-ietf-v6ops-3gpp-cases-02.txt, work 818 in progress. 820 [3GPP-23.060] 3GPP TS 23.060 V5.4.0, "General Packet Radio Service 821 (GPRS); Service description; Stage 2 (Release 5)", December 2002. 823 [3GPP 23.221] 3GPP TS 23.221 V5.7.0, "Architectural requirements 824 (Release 5)", December 2002. 826 [3GPP-23.228] 3GPP TS 23.228 V5.7.0, "IP Multimedia Subsystem 827 (IMS); Stage 2 (Release 5)", December 2002. 829 [3GPP 24.228] 3GPP TS 24.228 V5.3.0, "Signalling flows for the IP 830 multimedia call control based on SIP and SDP; Stage 3 (Release 5)", 831 December 2002. 833 [3GPP 24.229] 3GPP TS 24.229 V5.3.0, "IP Multimedia Call Control 834 Protocol based on SIP and SDP; Stage 3 (Release 5)", December 2002. 836 8.2 Informative 838 [RFC2283] Bates, T., Chandra, R., Katz, D., Rekhter, Y.: 839 Multiprotocol Extensions for BGP-4, RFC 2283, February 1998. 841 [RFC3314] Wasserman, M. (editor): "Recommendations for IPv6 in 3GPP 842 Standards", September 2002. 844 [6to4SEC] Savola, P.: "Security Considerations for 6to4", January 845 2003, draft-savola-v6ops-6to4-security-02.txt, work in progress. 847 [BGP] De Clercq, J., Gastaud, G., Ooms, D., Prevost, S., Le 848 Faucheur, F.: "Connecting IPv6 Islands across IPv4 Clouds with 849 BGP", October 2002, draft-ooms-v6ops-bgp-tunnel-00.txt, work in 850 progress. 852 [DNStrans] Durand, A.: "IPv6 DNS transition issues", October 2002, 853 draft-ietf-dnsop-ipv6-dns-issues-00.txt, work in progress. 855 [DSTM] Bound, J., et al: "Dual Stack Transition Mechanism (DSTM)", 856 July 2002, draft-ietf-ngtrans-dstm-08.txt, work in progress, the 857 draft has expired. 859 [IGP] Cristallo, G., Gastaud, G., Ooms, D., Galand, D., Preguica, 860 C., Baudot, A., Diribarne, G.: "Connecting IPv6 islands within an 861 IPv4 AS", February 2002, draft-many-ngtrans-connect-ipv6-igp- 862 02.txt, work in progress, the draft has expired. 864 [ISATAP] Templin, F., et al: "Intra-Site Automatic Tunnel 865 Addressing Protocol (ISATAP)", January 2003, draft-ietf-ngtrans- 866 isatap-12.txt, work in progress. 868 [NAT64] Durand, A.: "NAT64 - NAT46", June 2002, draft-durand- 869 ngtrans-nat64-nat46-00.txt, work in progress, the draft has 870 expired. 872 [NATPT-DNS] Durand, A.: "Issues with NAT-PT DNS ALG in RFC2766", 873 January 2002, draft-durand-natpt-dns-alg-issues-00.txt, work in 874 progress, the draft has expired. 876 [TEREDO] Huitema, C.: "Teredo: Tunneling IPv6 over UDP Through 877 NATs", September 2002, draft-ietf-ngtrans-shipworm-08.txt, work in 878 progress. 880 [Unmaneval] Huitema, C., Austein, R., Dilettante, B., Satapati, S., 881 van der Pol, R.: "Evaluation of Transition Mechanisms for Unmanaged 882 Networks", November 2002, draft-huitema-ngtrans-unmaneval-01.txt, 883 work in progress. 885 [6BONE] http://www.6bone.net 887 9. Authors and Acknowledgements 889 This document is written by: 891 Alain Durand, Sun Microsystems 892 894 Karim El-Malki, Ericsson Radio Systems 895 897 Paul Francis, Tahoe Networks 898 900 Niall Richard Murphy, Enigma Consulting Limited 901 903 Hugh Shieh, AT&T Wireless 904 906 Jonne Soininen, Nokia 907 909 Hesham Soliman, Ericsson Radio Systems 910 912 Margaret Wasserman, Wind River 913 915 Juha Wiljakka, Nokia 916 918 The authors would like to thank Gabor Bajko, Ajay Jain, Ivan 919 Laloux, Pekka Savola, Pedro Serna, Fred Templin, Anand Thakur and 920 Rod Van Meter for their valuable input. 922 10. Editor's Contact Information 924 Comments or questions regarding this document should be sent to the 925 v6ops mailing list or directly to the document editor: 927 Juha Wiljakka 928 Nokia 929 Visiokatu 3 Phone: +358 7180 48372 930 FIN-33720 TAMPERE, Finland Email: juha.wiljakka@nokia.com