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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-06.txt Nokia 4 Expires: March 2004 6 September 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 the transition to IPv6 in Third Generation 34 Partnership Project (3GPP) General Packet Radio Service (GPRS) 35 packet networks. The focus is on analyzing different transition 36 scenarios, applicable transition mechanisms and finding solutions 37 for those transition scenarios. In these scenarios, the User 38 Equipment (UE) connects to other nodes, e.g. in the Internet, and 39 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 and DNS Guidelines......................4 48 2.1 Dual Stack................................................5 49 2.2 Tunneling.................................................5 50 2.3 Protocol Translators......................................5 51 2.4 DNS Guidelines for IPv4/IPv6 Transition...................6 52 3. GPRS Transition Scenarios.....................................6 53 3.1 Dual Stack UE Connecting to IPv4 and IPv6 Nodes...........6 54 3.2 IPv6 UE Connecting to an IPv6 Node through an IPv4 Network 7 55 3.3 IPv4 UE Connecting to an IPv4 Node through an IPv6 Network 9 56 3.4 IPv6 UE Connecting to an IPv4 Node.......................10 57 3.5 IPv4 UE Connecting to an IPv6 Node.......................11 58 4. IMS Transition Scenarios.....................................11 59 4.1 UE Connecting to a Node in an IPv4 Network through IMS...11 60 4.2 Two IMS Islands Connected over IPv4 Network..............13 61 5. About 3GPP UE IPv4/IPv6 Configuration........................13 62 6. Security Considerations......................................14 63 7. References...................................................15 64 7.1 Normative................................................15 65 7.2 Informative..............................................16 66 8. Contributors.................................................17 67 9. Authors and Acknowledgements.................................17 68 10. Editor's Contact Information................................18 69 11. Changes from draft-ietf-v6ops-3gpp-analysis-05.txt..........18 70 12. Intellectual Property Statement.............................18 71 13. Copyright...................................................19 72 Appendix A - On the Use of Generic Translators in the 3GPP Networks 73 .................................................................20 75 1. Introduction 77 This document describes and analyzes the process of transition to 78 IPv6 in Third Generation Partnership Project (3GPP) General Packet 79 Radio Service (GPRS) packet networks. The authors can be found in 80 Authors and Acknowledgements section. 82 This document analyzes the transition scenarios in 3GPP packet 83 data networks that might come up in the deployment phase of IPv6. 85 The transition scenarios are documented in [RFC3574] and this 86 document will further analyze them. The scenarios are divided into 87 two categories: GPRS scenarios and IP Multimedia Subsystem (IMS) 88 scenarios. 90 GPRS scenarios are the following: 91 - Dual Stack UE connecting to IPv4 and IPv6 nodes 92 - IPv6 UE connecting to an IPv6 node through an IPv4 network 93 - IPv4 UE connecting to an IPv4 node through an IPv6 network 94 - IPv6 UE connecting to an IPv4 node 95 - IPv4 UE connecting to an IPv6 node 97 IMS scenarios are the following: 98 - UE connecting to a node in an IPv4 network through IMS 99 - Two IMS islands connected via IPv4 network 101 The focus is on analyzing different transition scenarios, 102 applicable transition mechanisms and finding solutions for those 103 transition scenarios. In the scenarios, the User Equipment (UE) 104 connects to nodes in other networks, e.g. in the Internet and 105 IPv6/IPv4 transition mechanisms are needed. 107 1.1 Scope of this Document 109 The scope of this Best Current Practices document is to analyze and 110 solve the possible transition scenarios in the 3GPP defined GPRS 111 network where a UE connects to, or is contacted from, the Internet 112 or another UE. The document covers scenarios with and without the 113 use of the SIP based IP Multimedia Core Network Subsystem (IMS). 114 This document does not focus on radio interface issues; both 3GPP 115 Second (GSM) and Third Generation (UMTS) radio network 116 architectures will be covered by these scenarios. 118 The transition mechanisms specified by the IETF Ngtrans and v6ops 119 Working Groups shall be used. This document shall not specify any 120 new transition mechanisms, but if a need for a new mechanism is 121 found, that will be reported to the IETF v6ops Working Group. 123 1.2 Abbreviations 125 2G Second Generation Mobile Telecommunications, for 126 example GSM and GPRS technologies. 127 3G Third Generation Mobile Telecommunications, for example 128 UMTS technology. 129 3GPP Third Generation Partnership Project 130 ALG Application Level Gateway 131 APN Access Point Name. The APN is a logical name referring 132 to a GGSN and an external network. 133 CSCF Call Session Control Function (in 3GPP Release 5 IMS) 134 DNS Domain Name System 135 GGSN Gateway GPRS Support Node (a default router for 3GPP 136 User Equipment) 137 GPRS General Packet Radio Service 138 GSM Global System for Mobile Communications 139 HLR Home Location Register 140 IMS IP Multimedia (Core Network) Subsystem, 3GPP Release 5 141 IPv6-only part of the network 142 ISP Internet Service Provider 143 NAT Network Address Translator 144 NAPT-PT Network Address Port Translation - Protocol Translation 145 NAT-PT Network Address Translation - Protocol Translation 146 PCO-IE Protocol Configuration Options Information Element 147 PDP Packet Data Protocol 148 PPP Point-to-Point Protocol 149 SGSN Serving GPRS Support Node 150 SIIT Stateless IP/ICMP Translation Algorithm 151 SIP Session Initiation Protocol 152 UE User Equipment, for example a UMTS mobile handset 153 UMTS Universal Mobile Telecommunications System 155 1.3 Terminology 157 Some terms used in 3GPP transition scenarios and analysis documents 158 are briefly defined here. 160 Dual Stack UE Dual Stack UE is a 3GPP mobile handset having both 161 IPv4 and IPv6 stacks. It is capable of activating 162 both IPv4 and IPv6 Packet Data Protocol (PDP) 163 contexts. Dual stack UE may be capable of tunneling. 165 IPv6 UE IPv6 UE is an IPv6-only 3GPP mobile handset. It is 166 only capable of activating IPv6 PDP contexts. 168 IPv4 UE IPv4 UE is an IPv4-only 3GPP mobile handset. It is 169 only capable of activating IPv4 PDP contexts. 171 IPv4 node IPv4 node is here defined to be IPv4 capable node 172 the UE is communicating with. The IPv4 node can 173 be, for example, an application server or another 174 UE. 176 IPv6 node IPv6 node is here defined to be IPv6 capable node 177 the UE is communicating with. The IPv6 node can 178 be, for example, an application server or another 179 UE. 181 2. Transition Mechanisms and DNS Guidelines 183 This chapter briefly introduces some transition mechanisms 184 specified by the IETF. In addition to that, DNS recommendations are 185 given. The applicability of different transition mechanisms to 3GPP 186 networks is discussed in chapters 3 and 4. 188 The IPv4/IPv6 transition methods can be divided to: 190 - dual IPv4/IPv6 stack 191 - tunneling 192 - protocol translators 194 2.1 Dual Stack 196 The dual IPv4/IPv6 stack is specified in [RFC2893]. If we consider 197 the 3GPP GPRS core network, dual stack implementation in the 198 Gateway GPRS Support Node (GGSN) enables support for IPv4 and IPv6 199 PDP contexts. UEs with dual stack and public (global) IP addresses 200 can typically access both IPv4 and IPv6 services without additional 201 translators in the network. However, it is good to remember that 202 public IPv4 addresses are a scarce resource and in many cases IPv4 203 NATs are deployed. Public/global IP addresses are also needed for 204 peer-to-peer services: the node needs a public/global IP address 205 that is visible to other nodes. 207 2.2 Tunneling 209 Tunneling is a transition mechanism that requires dual IPv4/IPv6 210 stack functionality in the encapsulating and decapsulating nodes. 211 Basic tunneling alternatives are IPv6-in-IPv4 and IPv4-in-IPv6. 213 Tunneling can be static or dynamic. Static (configured) tunnels are 214 fixed IPv6 links over IPv4, and they are specified in [RFC2893]. 215 Dynamic (automatic) tunnels are virtual IPv6 links over IPv4 where 216 the tunnel endpoints are not configured, i.e. the links are created 217 dynamically. 219 2.3 Protocol Translators 221 A translator can be defined as an intermediate component between a 222 native IPv4 node and a native IPv6 node to enable direct 223 communication between them without requiring any modifications to 224 the end nodes. 226 Header conversion is a translation mechanism. In header conversion, 227 IPv6 packet headers are converted to IPv4 packet headers, or vice 228 versa, and checksums are adjusted or recalculated if necessary. 229 NAT-PT (Network Address Translator / Protocol Translator) [RFC2766] 230 using SIIT [RFC2765] is an example of such a mechanism. 232 Translators may be needed in some cases when the communicating 233 nodes do not share the same IP version; in others, it may be 234 possible to avoid such communication altogether. Translation can 235 actually happen at Layer 3 (using NAT-like techniques), Layer 4 236 (using a TCP/UDP proxy) or Layer 7 (using application relays). 238 2.4 DNS Guidelines for IPv4/IPv6 Transition 240 [DNStrans] provides guidelines to operate DNS in a mixed world of 241 IPv4 and IPv6 transport. The recommendations (including the 242 keywords) are copied verbatim from [DNStrans]: 244 "In order to preserve name space continuity, the following 245 administrative policies are RECOMMENDED: 246 - every recursive DNS server SHOULD be either IPv4-only or 247 dual stack, 248 - every single DNS zone SHOULD be served by at least one IPv4 249 reachable DNS server. 251 This rules out IPv6-only DNS server performing full recursion and 252 DNS zones served only by IPv6-only DNS servers. This approach 253 could be revisited if/when translation techniques between IPv4 and 254 IPv6 were to be widely deployed. 256 In order to enforce the second point, the zone validation process 257 SHOULD ensure that there is at least one IPv4 address record 258 available for the name servers of any child delegations within the 259 zone." 261 3. GPRS Transition Scenarios 263 This section discusses the scenarios that might occur when a GPRS 264 UE contacts services or other nodes, e.g. a web server in the 265 Internet. 267 The following scenarios described by [RFC3574] are analyzed here. 268 In all of the scenarios, the UE is part of a network where there is 269 at least one router of the same IP version, i.e. the GGSN, and the 270 UE is connecting to a node in a different network. 272 1) Dual Stack UE connecting to IPv4 and IPv6 nodes 273 2) IPv6 UE connecting to an IPv6 node through an IPv4 network 274 3) IPv4 UE connecting to an IPv4 node through an IPv6 network 275 4) IPv6 UE connecting to an IPv4 node 276 5) IPv4 UE connecting to an IPv6 node 278 3.1 Dual Stack UE Connecting to IPv4 and IPv6 Nodes 280 In this scenario, the dual stack UE is capable of communicating 281 with both IPv4 and IPv6 nodes. It is recommended to activate an 282 IPv6 PDP context when communicating with an IPv6 peer node and an 283 IPv4 PDP context when communicating with an IPv4 peer node. If the 284 3GPP network supports both IPv4 and IPv6 PDP contexts, the UE 285 activates the appropriate PDP context depending on the type of 286 application it has started or depending on the address of the peer 287 host it needs to communicate with. If IPv6 PDP contexts are 288 available and IPv6-in-IPv4 tunneling is needed, it is recommended 289 to activate an IPv6 PDP context and perform tunneling in the 290 network. This case is described in more detail in section 3.2. 292 However, the UE may attach to a 3GPP network, in which the Serving 293 GPRS Support Node (SGSN), the GGSN, and the Home Location Register 294 (HLR) support IPv4 PDP contexts, but do not support IPv6 PDP 295 contexts. If the 3GPP network does not support IPv6 PDP contexts, 296 and an application on the UE needs to communicate with an IPv6(- 297 only) node, the UE may activate an IPv4 PDP context and encapsulate 298 IPv6 packets in IPv4 packets using a tunneling mechanism. This 299 might happen in very early phases of IPv6 deployment. To generally 300 solve this problem (IPv6 not available in the 3GPP network), this 301 document strongly recommends the 3GPP operators to deploy basic 302 IPv6 support in their GPRS networks, which can in most cases be 303 handled by making software upgrades in the network elements. 305 As a general guideline, IPv6 communication is preferred to IPv4 306 communication going through IPv4 NATs to the same dual stack peer 307 node. 309 When analyzing a dual stack UE behavior, an application running on 310 a UE can identify whether the endpoint required is an IPv4 or IPv6 311 capable node by examining the address to discover what address 312 family it falls into. Alternatively, if a user supplies a name to 313 be resolved, the DNS may contain records sufficient to identify 314 which protocol should be used to initiate the connection with the 315 endpoint. Since the UE is capable of native communication with both 316 protocols, one of the main concerns of an operator is the correct 317 address space and routing management. The operator must maintain 318 address spaces for both protocols. Public IPv4 addresses are often 319 a scarce resource for the operator and typically it is not possible 320 for a UE to have a globally unique IPv4 address continuously 321 allocated for its use. Use of private IPv4 addresses means use of 322 NATs when communicating with a peer node outside the operator's 323 network. In large networks, NAT systems can become very complex, 324 expensive and difficult to maintain. 326 For DNS recommendations, we refer to section 2.4. 328 3.2 IPv6 UE Connecting to an IPv6 Node through an IPv4 Network 330 The best solution for this scenario is obtained with tunneling, 331 i.e. IPv6-in-IPv4 tunneling is a requirement. An IPv6 PDP context 332 is activated between the UE and the GGSN. Tunneling is handled in 333 the network, because IPv6 UE is not capable of tunneling (it does 334 not have the dual stack functionality needed for tunneling). The 335 encapsulating node can be the GGSN, the edge router between the 336 border of the operator's IPv6 network and the public Internet, or 337 any other dual stack node within the operator's IP network. The 338 encapsulation (uplink) and decapsulation (downlink) can be handled 339 by the same network element. Typically the tunneling handled by the 340 network elements is transparent to the UEs and IP traffic looks 341 like native IPv6 traffic to them. For the applications, tunneling 342 enables end-to-end IPv6 connectivity. Note that this scenario is 343 comparable to 6bone [6BONE] network operation. 345 IPv6-in-IPv4 tunnels between IPv6 islands can be either static or 346 dynamic. The selection of the type of tunneling mechanism is up to 347 the operator / ISP deployment scenario and only generic 348 recommendations can be given in this document. 350 The following subsections are focused on the usage of different 351 tunneling mechanisms when the peer node is in the operator's 352 network or outside the operator's network. The authors note that 353 where the actual 3GPP network ends and which parts of the network 354 belong to the ISP(s) also depends on the deployment scenario. The 355 authors are not commenting how many ISP functions the 3GPP operator 356 should perform. However, many 3GPP operators are ISPs of some sort 357 themselves. ISP transition scenarios are documented in [ISP-scen]. 359 3.2.1 Tunneling inside the 3GPP Operator's Network 361 Many GPRS operators already have IPv4 backbone networks deployed 362 and they are gradually migrating them while introducing IPv6 363 islands. IPv6 backbones can be considered quite rare in the first 364 phases of the transition. If the 3GPP operator already has IPv6 365 widely deployed in its network, this subsection is not so relevant. 367 In initial IPv6 deployment, where a small number of IPv6-in-IPv4 368 tunnels are required to connect the IPv6 islands over the 3GPP 369 operator's IPv4 network, manually configured tunnels can be used. 370 In a 3GPP network, one IPv6 island can contain the GGSN while 371 another island can contain the operator's IPv6 application servers. 372 However, manually configured tunnels can be an administrative 373 burden when the number of islands and therefore tunnels rises. In 374 that case, upgrading parts of the backbone to dual stack may be the 375 simplest choice. The administrative burden could also be mitigated 376 by using automated management tools which are typically necessary 377 to manage large networks anyway. 379 Connection redundancy should also be noted as an important 380 requirement in 3GPP networks. Static tunnels on their own don't 381 provide a routing recovery solution for all scenarios where an IPv6 382 route goes down. However, they may provide an adequate solution 383 depending on the design of the network and in presence of other 384 router redundancy mechanisms. On the other hand, routing protocol 385 based mechanisms can provide redundancy. 387 3.2.2 Tunneling outside the 3GPP Operator's Network 389 This subsection includes the case when the peer node is outside the 390 operator's network. In that case the IPv6-in-IPv4 tunnel starting 391 point can be in the operator's network - encapsulating node can be 392 e.g. the GGSN or the edge router. 394 The case is pretty straightforward if the upstream ISP provides 395 native IPv6 connectivity to the Internet. If there is no native 396 IPv6 connectivity available in the 3GPP network, an IPv6-in-IPv4 397 tunnel should be configured from e.g. the GGSN to the dual stack 398 border gateway in order to access the upstream ISP. 400 If the ISP only provides IPv4 connectivity, then the IPv6 traffic 401 initiated from the 3GPP network should be transported tunneled in 402 IPv4 to the ISP. 404 Usage of configured IPv6-in-IPv4 tunneling is recommended. As the 405 number of the tunnels outside of the 3GPP network is limited, no 406 more than a couple of tunnels should be needed. 408 ISP transition scenarios are described in [ISP-scen]. 410 3.3 IPv4 UE Connecting to an IPv4 Node through an IPv6 Network 412 3GPP networks are expected to support both IPv4 and IPv6 for a long 413 time, on the UE-GGSN link and between the GGSN and external 414 networks. For this scenario, it is useful to split the end-to-end 415 IPv4 UE to IPv4 node communication into UE-to-GGSN and GGSN-to- 416 v4NODE. An IPv6-capable GGSN is expected to support both IPv6 and 417 IPv4 UEs. Therefore an IPv4-only UE will be able to use an IPv4 418 link (PDP context) to connect to the GGSN without the need to 419 communicate over an IPv6 network. 421 Regarding the GGSN-to-v4NODE communication, typically the transport 422 network between the GGSN and external networks will support only 423 IPv4 in the early stages and migrate to dual stack, since these 424 networks are already deployed. Therefore it is not envisaged that 425 tunneling of IPv4-in-IPv6 will be required from the GGSN to 426 external IPv4 networks either. In the longer run, 3GPP operators 427 may need to phase out IPv4 UEs and the IPv4 transport network. This 428 would leave only IPv6 UEs. 430 Therefore, overall, the transition scenario involving an IPv4 UE 431 communicating with an IPv4 peer through an IPv6 network is not 432 considered very likely in 3GPP networks. 434 3.4 IPv6 UE Connecting to an IPv4 Node 436 As a general guideline, IPv6-only UEs are not recommended in the 437 early phases of transition until the IPv6 deployment has become so 438 prevalent that direct communication with IPv4(-only) nodes will no 439 longer be necessary. It is assumed that IPv4 will remain useful for 440 quite a long time, so in general, dual-stack implementation in the 441 UE can be recommended. This recommendation naturally includes 442 manufacturing dual-stack UEs instead of IPv4-only UEs. 444 However, if there is a need to connect to an IPv4(-only) node from 445 an IPv6-only UE, it is possible to use specific translation and 446 proxying techniques; generic IP protocol translation is not 447 recommended. There are three main ways for IPv6(-only) nodes to 448 communicate with IPv4(-only) nodes (excluding avoiding such 449 communication in the first place): 451 1. the use of generic-purpose translator (e.g. NAT-PT [RFC2766]) 452 in the local network (not recommended as a general solution), 454 2. the use of specific-purpose protocol relays (e.g., IPv6<->IPv4 455 TCP relay configured for a couple of ports only [RFC3142]) or 456 application proxies (e.g., HTTP proxy, SMTP relay) in the 457 local network, or 459 3. the use of specific-purpose mechanisms (as described above in 460 2) in the foreign network; these are indistinguishable from 461 the IPv6-enabled services from the IPv6 UE's perspective, and 462 not discussed further here. 464 For many applications, application proxies can be appropriate (e.g. 465 HTTP proxies, SMTP relays, etc.). Such application proxies will not 466 be transparent to the UE. Hence, a flexible mechanism with minimal 467 manual intervention should be used to configure these proxies on 468 IPv6 UEs. Within the 3GPP architecture, application proxies can be 469 placed on the GGSN external interface (Gi), or inside the service 470 network. 472 The authors note that NAT-PT applicability statement work is being 473 done in the v6ops wg. The problems related to NAT-PT usage in 3GPP 474 networks are documented in appendix A. 476 3.5 IPv4 UE Connecting to an IPv6 Node 478 The legacy IPv4 nodes are mostly nodes that support the 479 applications that are popular today in the IPv4 Internet: mostly e- 480 mail and web-browsing. These applications will, of course, be 481 supported in the future IPv6 Internet. However, the legacy IPv4 UEs 482 are not going to be updated to support the future applications. As 483 these applications are designed for IPv6, and to use the advantages 484 of newer platforms, the legacy IPv4 nodes will not be able to 485 profit from them. Thus, they will continue to support the legacy 486 services. 488 Taking the above into account, the traffic to and from the legacy 489 IPv4 UE is restricted to a few applications. These applications 490 already mostly rely on proxies or local servers to communicate 491 between private address space networks and the Internet. The same 492 methods and technology can be used for IPv4 to IPv6 transition. 494 For DNS recommendations, we refer to section 2.4. 496 4. IMS Transition Scenarios 498 As the IMS is exclusively IPv6, the number of possible transition 499 scenarios is reduced dramatically. The possible IMS scenarios are 500 listed below and analyzed in sections 4.1 and 4.2. 502 1) UE connecting to a node in an IPv4 network through IMS 503 2) Two IMS islands connected over IPv4 network 505 For DNS recommendations, we refer to section 2.4. As DNS traffic is 506 not directly related to the IMS functionality, the recommendations 507 are not in contradiction with the IPv6-only nature of the IMS. 509 4.1 UE Connecting to a Node in an IPv4 Network through IMS 511 This scenario occurs when an IMS UE (IPv6) connects to a node in 512 the IPv4 Internet through the IMS, or vice versa. This happens when 513 the other node is a part of a different system than 3GPP, e.g. a 514 fixed PC, with only IPv4 capabilities. 516 The first priority is to upgrade the legacy IPv4 nodes to dual- 517 stack, eliminating this particular problem in that specific 518 deployment. 520 Still, it is difficult to estimate how many non-upgradeable legacy 521 IPv4 nodes need to communicate with the IMS UEs. It is assumed that 522 the solution described here is used for limited cases, in which 523 communications with a small number of legacy IPv4 SIP equipment are 524 needed. 526 As the IMS is exclusively IPv6 [3GPP 23.221], translators have to 527 be used in the communication between the IPv6 IMS and legacy IPv4 528 hosts, i.e. making a dual stack based solution is not feasible. 529 This section aims to give a brief overview on how that interworking 530 can be handled. 532 This section presents higher level details of a solution based on 533 the use of a translator and SIP ALG. [3GPPtr] provides additional 534 information and presents a bit different solution proposal based on 535 SIP Edge Proxy and IP Address/Port Mapper. The authors recommend to 536 solve the general SIP/SDP IPv4/IPv6 transition problem in the IETF 537 SIP wg(s). 539 As control (or signaling) and user (or data) traffic are separated 540 in SIP, and thus, the IMS, the translation of the IMS traffic has 541 to be done at two levels: 542 1)Session Initiation Protocol (SIP) [RFC3261], and 543 Session Description Protocol (SDP) [RFC2327] [RFC3266] 544 (Mm-interface) 545 2)the user data traffic (Mb-interface) 547 SIP and SDP transition has to be made in an SIP/SDP Application 548 Level Gateway. The ALG has to change the IP addresses transported 549 in the SIP messages and the SDP payload of those messages to the 550 appropriate version. In addition, there has to be interoperability 551 for DNS queries; see section 2.4 for details. 553 On the user data transport level, the translation is IPv4-IPv6 554 protocol translation, where the user data traffic transported is 555 translated from IPv6 to IPv4, and vice versa. 557 The legacy IPv4 host's address can be mapped to an IPv6 address for 558 the IMS, and this address is then used within the IMS to route the 559 traffic to the appropriate user traffic translator. This mapping 560 can be done by the SIP/SDP ALG for the SIP traffic. The user 561 traffic translator would do the similar mapping for the user 562 traffic. However, in order to have an IPv4 address for the IMS UE, 563 and to be able to route the user traffic within the legacy IPv4 564 network to the correct translator, there has to be an IPv4 address 565 allocated for the duration of the session from the user traffic 566 translator. The allocation of this address from the user traffic 567 translator has to be done by the SIP/SDP ALG in order for the 568 SIP/SDP ALG to know the correct IPv4 address. This can be achieved 569 by using a protocol for the ALG to do the allocation. 571 +-------------------------------+ +------------+ 572 | +------+ | | +--------+ | 573 | |S-CSCF|---| |SIP ALG | |\ 574 | | +------+ | | +--------+ | \ -------- 575 +-|+ | / | | | | | | 576 | | | +------+ +------+ | | + | -| |- 577 | |-|-|P-CSCF|--------|I-CSCF| | | | | | () | 578 | | +------+ +------+ | |+----------+| / ------ 579 | |-----------------------------------||Translator||/ 580 +--+ | IPv6 | |+----------+| IPv4 581 UE | | |Interworking| 582 | IP Multimedia CN Subsystem | |Unit | 583 +-------------------------------+ +------------+ 585 Figure 1: UE using IMS to contact a legacy phone 587 Figure 1 shows a possible configuration scenario where the SIP ALG 588 is separated from the CSCFs. The translator can either be set up in 589 a single device with both SIP translation and media translation, or 590 those functionalities can be divided to two different entities with 591 an interface in between. We call the combined network element on 592 the edge of the IPv6-only IMS an "Interworking Unit" in this 593 document. A SIP-specific translation mechanism, which could e.g. 594 re-use limited subsets of NAT-PT [RFC2766], needs to be specified. 595 The problems related to NAT-PT are discussed in appendix A. 597 4.2 Two IMS Islands Connected over IPv4 Network 599 At the early stages of IMS deployment, there may be cases where two 600 IMS islands are separated by an IPv4 network such as the legacy 601 Internet. Here both the UEs and the IMS islands are IPv6-only. 602 However, the IPv6 islands are not connected natively with IPv6. 604 In this scenario, the end-to-end SIP connections are based on IPv6. 605 The only issue is to make connection between two IPv6-only IMS 606 islands over IPv4 network. This scenario is closely related to GPRS 607 scenario represented in section 3.2. and similar tunneling 608 solutions are applicable also in this scenario. 610 5. About 3GPP UE IPv4/IPv6 Configuration 612 This informative section aims to give a brief overview on the 613 configuration needed in the UE in order to access IP based 614 services. There can also be other application specific settings in 615 the UE that are not described here. 617 To be able to access IPv6 or IPv4 based services, settings need to 618 be done in the UE. The GGSN Access Point has to be defined when 619 using, for example, the web browsing application. One possibility 620 is to use over the air configuration to configure the GPRS 621 settings. The user can visit the operator WWW page and subscribe 622 the GPRS Access Point settings to his/her UE and receive the 623 settings via Short Message Service (SMS). After the user has 624 accepted the settings and a PDP context has been activated, the 625 user can start browsing. The Access Point settings can also be 626 typed in manually or be pre-configured by the operator or the UE 627 manufacturer. 629 DNS server addresses typically also need to be configured in the 630 UE. In the case of IPv4 type PDP context, the (IPv4) DNS server 631 addresses can be received in the PDP context activation (a control 632 plane mechanism). Same kind of mechanism is also available for 633 IPv6: so-called Protocol Configuration Options Information Element 634 (PCO-IE) specified by the 3GPP [3GPP-24.008]. It is also possible 635 to use [DHCPv6-SL] or [RFC3315] and [DHCP-DNS] for receiving DNS 636 server addresses. The authors note that the general IPv6 DNS 637 discovery problem is being solved by the IETF dnsop Working Group. 638 The DNS server addresses can also be received over the air (using 639 SMS), or typed in manually in the UE. 641 When accessing IMS services, the UE needs to know the P-CSCF IPv6 642 address. 3GPP-specific PCO-IE mechanism, or DHCPv6-based mechanism 643 ([DHCPv6-SL] or [RFC3315] and [RFC3319]) can be used. Manual 644 configuration or configuration over the air is also possible. IMS 645 subscriber authentication and registration to the IMS and SIP 646 integrity protection are not discussed here. 648 6. Security Considerations 650 There are some generic security considerations when moving to dual- 651 stack IPv4/IPv6 deployment which are not analyzed at length here. 652 Two examples of these are ensuring that the access controls and 653 firewalls have similar (or known) security properties with both 654 IPv4 and IPv6, and that enabling IPv6 does not jeopardize the 655 access to the IPv4 services (e.g., in the form of misbehavior 656 towards DNS AAAA record lookups or operationally worse quality IP 657 transit services). 659 This memo recommends the use of a relatively small number of 660 techniques, which all of them have their own security 661 considerations, including: 663 - native upstream access or tunneling by the 3GPP network 664 operator, 665 - use of routing protocols to ensure redundancy, 666 - use of locally-deployed specific-purpose protocol relays and 667 application proxies to reach IPv4(-only) nodes from IPv6-only 668 UEs, or 669 - a specific mechanism for SIP signalling and media translation 671 These (except for the last one, naturally) have relatively well- 672 known security considerations, which are also discussed in the 673 specific documents. However, in particular one should note that a 674 proper configuration of locally-deployed relays and proxies is very 675 important, so that the outsiders will not have access to them, to 676 be used for abuse, laundering attacks, or circumventing access 677 controls. 679 In particular, this memo does not recommend the following 680 techniques which each have a number of security issues, not further 681 analyzed here: 683 - NAT-PT or other translator as a generic-purpose transition 684 mechanism, 685 - the use of IPv6 transition mechanisms (except dual stack) at 686 the UEs. 688 7. References 690 7.1 Normative 692 [RFC2026] Bradner, S.: The Internet Standards Process -- Revision 693 3, RFC 2026, October 1996. 695 [RFC2663] Srisuresh, P., Holdrege, M.: IP Network Address 696 Translator (NAT) Terminology and Considerations, RFC 2663, August 697 1999. 699 [RFC2765] Nordmark, E.: Stateless IP/ICMP Translation Algorithm 700 (SIIT), RFC 2765, February 2000. 702 [RFC2766] Tsirtsis, G., Srisuresh, P.: Network Address Translation 703 - Protocol Translation (NAT-PT), RFC 2766, February 2000. 705 [RFC2893] Gilligan, R., Nordmark, E.: Transition Mechanisms for 706 IPv6 Hosts and Routers, RFC 2893, August 2000. 708 [RFC3261] Rosenberg, J., et al.: SIP: Session Initiation Protocol, 709 RFC 3261, June 2002. 711 [RFC3574] Soininen, J. (editor): Transition Scenarios for 3GPP 712 Networks, RFC 3574, August 2003. 714 [3GPP-23.060] 3GPP TS 23.060 V5.4.0, "General Packet Radio Service 715 (GPRS); Service description; Stage 2 (Release 5)", December 2002. 717 [3GPP 23.221] 3GPP TS 23.221 V5.7.0, "Architectural requirements 718 (Release 5)", December 2002. 720 [3GPP-23.228] 3GPP TS 23.228 V5.7.0, "IP Multimedia Subsystem 721 (IMS); Stage 2 (Release 5)", December 2002. 723 [3GPP 24.228] 3GPP TS 24.228 V5.3.0, "Signalling flows for the IP 724 multimedia call control based on SIP and SDP; Stage 3 (Release 5)", 725 December 2002. 727 [3GPP 24.229] 3GPP TS 24.229 V5.3.0, "IP Multimedia Call Control 728 Protocol based on SIP and SDP; Stage 3 (Release 5)", December 2002. 730 7.2 Informative 732 [RFC2327] Handley, M., Jacobson, V.: SDP: Session Description 733 Protocol, RFC 2327, April 1998. 735 [RFC3142] Hagino, J., Yamamoto, K.: An IPv6-to-IPv4 Transport Relay 736 Translator, RFC 3142, June 2001. 738 [RFC3266] Olson, S., Camarillo, G., Roach, A. B.: Support for IPv6 739 in Session Description Protocol (SDP), June 2002. 741 [RFC3314] Wasserman, M. (editor): Recommendations for IPv6 in 3GPP 742 Standards, September 2002. 744 [RFC3315] Droms, R. et al.: Dynamic Host Configuration Protocol for 745 IPv6 (DHCPv6), July 2003. 747 [RFC3319] Schulzrinne, H., Volz, B.: Dynamic Host Configuration 748 Protocol (DHCPv6) Options for Session Initiation Protocol (SIP) 749 Servers, July 2003. 751 [3GPPtr] El Malki K., et al.: "IPv6-IPv4 Translators in 3GPP 752 Networks", June 2003, draft-elmalki-v6ops-3gpp-translator-00.txt, 753 work in progress. 755 [DHCP-DNS] Droms, R. (ed.): "DNS Configuration options for DHCPv6", 756 August 2003, draft-ietf-dhc-dhcpv6-opt-dnsconfig-04.txt, work in 757 progress. 759 [DHCP-SL] Droms, R.: "A Guide to Implementing Stateless DHCPv6 760 Service", April 2003, draft-ietf-dhc-dhcpv6-stateless-00.txt, work 761 in progress. 763 [DNStrans] Durand, A. and Ihren, J.: "DNS IPv6 transport 764 operational guidelines", June 2003, draft-ietf-dnsop-ipv6- 765 transport-guidelines-00.txt, work in progress. 767 [ISP-scen] Lind, M. (Editor): "Scenarios for Introducing IPv6 into 768 ISP Networks", June 2003, draft-lind-v6ops-isp-scenarios-00.txt, 769 work in progress. 771 [NATPT-DNS] Durand, A.: "Issues with NAT-PT DNS ALG in RFC2766", 772 January 2003, draft-durand-v6ops-natpt-dns-alg-issues-00.txt, work 773 in progress, the draft has expired. 775 [v4v6trans] van der Pol, R., Satapati, S., Sivakumar, S.: 776 "Issues when translating between IPv4 and IPv6", January 2003, 777 draft-vanderpol-v6ops-translation-issues-00.txt, work in progress, 778 the draft has expired. 780 [3GPP-24.008] 3GPP TS 24.008 V5.8.0, "Mobile radio interface Layer 781 3 specification; Core network protocols; Stage 3 (Release 5)", June 782 2003. 784 [6BONE] http://www.6bone.net 786 8. Contributors 788 Pekka Savola has contributed both text and his IPv6 experience to 789 this document. He has provided a large number of helpful comments 790 on the v6ops mailing list. 792 9. Authors and Acknowledgements 794 This document is written by: 796 Alain Durand, Sun Microsystems 797 799 Karim El-Malki, Ericsson Radio Systems 800 802 Niall Richard Murphy, Enigma Consulting Limited 803 805 Hugh Shieh, AT&T Wireless 806 808 Jonne Soininen, Nokia 809 810 Hesham Soliman, Flarion 811 813 Margaret Wasserman, Wind River 814 816 Juha Wiljakka, Nokia 817 819 The authors would like to thank Heikki Almay, Gabor Bajko, Ajay 820 Jain, Jarkko Jouppi, Ivan Laloux, Janne Rinne, Pedro Serna, Fred 821 Templin, Anand Thakur and Rod Van Meter for their valuable input. 823 10. Editor's Contact Information 825 Comments or questions regarding this document should be sent to the 826 v6ops mailing list or directly to the document editor: 828 Juha Wiljakka 829 Nokia 830 Visiokatu 3 Phone: +358 7180 48372 831 FIN-33720 TAMPERE, Finland Email: juha.wiljakka@nokia.com 833 11. Changes from draft-ietf-v6ops-3gpp-analysis-05.txt 835 - Handled issues from: 836 http://danforsberg.info:8080/draft-ietf-v6ops-3gpp- 837 analysis/index 838 - Security considerations section updated 839 - Editorial / textual changes in many sections 840 - Appendix A created 842 12. Intellectual Property Statement 844 The IETF takes no position regarding the validity or scope of any 845 intellectual property or other rights that might be claimed to 846 pertain to the implementation or use of the technology described in 847 this document or the extent to which any license under such rights 848 might or might not be available; neither does it represent that it 849 has made any effort to identify any such rights. Information on the 850 IETF's procedures with respect to rights in standards-track and 851 standards-related documentation can be found in BCP-11. Copies of 852 claims of rights made available for publication and any assurances 853 of licenses to be made available, or the result of an attempt made 854 to obtain a general license or permission for the use of such 855 proprietary rights by implementers or users of this specification 856 can be obtained from the IETF Secretariat. 858 The IETF invites any interested party to bring to its attention any 859 copyrights, patents or patent applications, or other proprietary 860 rights which may cover technology that may be required to practice 861 this standard. Please address the information to the IETF Executive 862 Director. 864 13. Copyright 866 The following copyright notice is copied from [RFC2026], Section 867 10.4. It describes the applicable copyright for this document. 869 Copyright (C) The Internet Society September 26, 2003. All Rights 870 Reserved. 872 This document and translations of it may be copied and furnished to 873 others, and derivative works that comment on or otherwise explain 874 it or assist in its implementation may be prepared, copied, 875 published and distributed, in whole or in part, without restriction 876 of any kind, provided that the above copyright notice and this 877 paragraph are included on all such copies and derivative works. 878 However, this document itself may not be modified in any way, such 879 as by removing the copyright notice or references to the Internet 880 Society or other Internet organizations, except as needed for the 881 purpose of developing Internet standards in which case the 882 procedures for copyrights defined in the Internet Standards process 883 must be followed, or as required to translate it into languages 884 other than English. 886 The limited permissions granted above are perpetual and will not be 887 revoked by the Internet Society or its successors or assignees. 889 This document and the information contained herein is provided on 890 an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET 891 ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR 892 IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 893 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 894 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 896 Appendix A - On the Use of Generic Translators in the 3GPP Networks 898 This appendix lists mainly 3GPP-specific arguments about generic 899 translators, even though the use of generic translators is 900 discouraged. The section may be removed in future versions of the 901 memo. 903 Due to the significant lack of IPv4 addresses in some domains, port 904 multiplexing is likely to be a necessary feature for translators 905 (i.e. NAPT-PT). If NA(P)T-PT is used, it needs to be placed on the 906 GGSN external (Gi) interface, typically separate from the GGSN. 907 NA(P)T-PT can be installed, for example, on the edge of the 908 operator's network and the public Internet. NA(P)T-PT will 909 intercept DNS requests and other applications that include IP 910 addresses in their payloads, translate the IP header (and payload 911 for some applications if necessary) and forward packets through its 912 IPv4 interface. 914 NA(P)T-PT introduces limitations that are expected to be magnified 915 within the 3GPP architecture. Some of these limitations are listed 916 below (notice that some of them are also relevant for IPv4 NAT). We 917 note here that [v4v6trans] analyzes the issues when translating 918 between IPv4 and IPv6. NAT-PT applicability statement document 919 (currently being written in v6ops wg) will also be used as a 920 reference in this document. 922 1. NA(P)T-PT is a single point of failure for all ongoing 923 connections. 925 2. There are additional forwarding delays due to further 926 processing, when compared to normal IP forwarding. 928 3. There are problems with source address selection due to the 929 inclusion of a DNS ALG on the same node [NATPT-DNS]. 931 4. NA(P)T-PT does not work (without application level gateways) 932 for applications that embed IP addresses in their payload. 934 5. NA(P)T-PT breaks DNSSEC. 936 6. NA(P)T-PT does not scale very well in large networks. 938 3GPP networks are expected to handle a very large number of 939 subscribers on a single GGSN (default router). Each GGSN is 940 expected to handle hundreds of thousands of connections. 941 Furthermore, high reliability is expected for 3GPP networks. 942 Consequently, a single point of failure on the GGSN external 943 interface would raise concerns on the overall network reliability. 944 In addition, IPv6 users are expected to use delay-sensitive 945 applications provided by IMS. Hence, there is a need to minimize 946 forwarding delays within the IP backbone. Furthermore, due to the 947 unprecedented number of connections handled by the default routers 948 (GGSN) in 3GPP networks, a network design that forces traffic to go 949 through a single node at the edge of the network (typical NA(P)T-PT 950 configuration) is not likely to scale. Translation mechanisms 951 should allow for multiple translators, for load sharing and 952 redundancy purposes. 954 To minimize the problems associated with NA(P)T-PT, the following 955 actions can be recommended: 957 1. Separate the DNS ALG from the NA(P)T-PT node (in the "IPv6 to 958 IPv4" case). 960 2. Ensure (if possible) that NA(P)T-PT does not become a single 961 point of failure. 963 3. Allow for load sharing between different translators. That is, 964 it should be possible for different connections to go through 965 different translators. Note that load sharing alone does not 966 prevent NA(P)T-PT from becoming a single point of failure.