Internet Draft J. Wiljakka (ed.) Document: draft-ietf-v6ops-3gpp-analysis-05.txt Nokia Expires: March 2004 September 2003 Analysis on IPv6 Transition in 3GPP Networks Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract This document analyzes the transition to IPv6 in Third Generation Partnership Project (3GPP) General Packet Radio Service (GPRS) packet networks. The focus is on analyzing different transition scenarios, applicable transition mechanisms and finding solutions for those transition scenarios. In these scenarios, the User Equipment (UE) connects to other nodes, e.g. in the Internet, and IPv6/IPv4 transition mechanisms are needed. Wiljakka, Editor Expires: March 2004 [Page 1]
Analysis on IPv6 Transition in 3GPP Networks Sept 2003 Table of Contents 1. Introduction..................................................2 1.1 Scope of this Document....................................3 1.2 Abbreviations.............................................3 1.3 Terminology...............................................4 2. Transition Mechanisms and DNS Guidelines......................4 2.1 Dual Stack................................................5 2.2 Tunneling.................................................5 2.3 Protocol Translators......................................5 2.4 DNS Guidelines for IPv4/IPv6 Transition...................6 3. GPRS Transition Scenarios.....................................6 3.1 Dual Stack UE Connecting to IPv4 and IPv6 Nodes...........6 3.2 IPv6 UE Connecting to an IPv6 Node through an IPv4 Network ..............................................................7 3.3 IPv4 UE Connecting to an IPv4 Node through an IPv6 Network ..............................................................9 3.4 IPv6 UE Connecting to an IPv4 Node.......................10 3.5 IPv4 UE Connecting to an IPv6 Node.......................11 4. IMS Transition Scenarios.....................................12 4.1 UE Connecting to a Node in an IPv4 Network through IMS...12 4.2 Two IMS Islands Connected over IPv4 Network..............14 5. About 3GPP UE IPv4/IPv6 Configuration........................14 6. Security Considerations......................................15 7. Changes from draft-ietf-v6ops-3gpp-analysis-04.txt...........15 8. Intellectual Property Statement..............................15 9. Copyright....................................................16 10. References..................................................17 10.1 Normative...............................................17 10.2 Informative.............................................17 11. Authors and Acknowledgements................................19 12. Editor's Contact Information................................19 1. Introduction This document describes and analyzes the process of transition to IPv6 in Third Generation Partnership Project (3GPP) General Packet Radio Service (GPRS) packet networks. The authors can be found in Authors and Acknowledgements section. This document analyzes the transition scenarios in 3GPP packet data networks that might come up in the deployment phase of IPv6. The transition scenarios are documented in [RFC3574] and this document will further analyze them. The scenarios are divided into two categories: GPRS scenarios and IP Multimedia Subsystem (IMS) scenarios. GPRS scenarios are the following: - Dual Stack UE connecting to IPv4 and IPv6 nodes Wiljakka, Editor Expires: March 2004 [Page 2]
Analysis on IPv6 Transition in 3GPP Networks Sept 2003 - IPv6 UE connecting to an IPv6 node through an IPv4 network - IPv4 UE connecting to an IPv4 node through an IPv6 network - IPv6 UE connecting to an IPv4 node - IPv4 UE connecting to an IPv6 node IMS scenarios are the following: - UE connecting to a node in an IPv4 network through IMS - Two IMS islands connected via IPv4 network The focus is on analyzing different transition scenarios, applicable transition mechanisms and finding solutions for those transition scenarios. In the scenarios, the User Equipment (UE) connects to nodes in other networks, e.g. in the Internet and IPv6/IPv4 transition mechanisms are needed. 1.1 Scope of this Document The scope of this Best Current Practices document is to analyze and solve the possible transition scenarios in the 3GPP defined GPRS network where a UE connects to, or is contacted from, the Internet or another UE. The document covers scenarios with and without the use of the SIP based IP Multimedia Core Network Subsystem (IMS). This document does not focus on radio interface issues; both 3GPP Second (GSM) and Third Generation (UMTS) radio network architectures will be covered by these scenarios. The transition mechanisms specified by the IETF Ngtrans and v6ops Working Groups shall be used. This document shall not specify any new transition mechanisms, but if a need for a new mechanism is found, that will be reported to the IETF v6ops Working Group. 1.2 Abbreviations 2G Second Generation Mobile Telecommunications, for example GSM and GPRS technologies. 3G Third Generation Mobile Telecommunications, for example UMTS technology. 3GPP Third Generation Partnership Project ALG Application Level Gateway APN Access Point Name. The APN is a logical name referring to a GGSN and an external network. CSCF Call Session Control Function (in 3GPP Release 5 IMS) DNS Domain Name System EGP Exterior Gateway Protocol GGSN Gateway GPRS Support Node (a default router for 3GPP User Equipment) GPRS General Packet Radio Service GSM Global System for Mobile Communications HLR Home Location Register Wiljakka, Editor Expires: March 2004 [Page 3]
Analysis on IPv6 Transition in 3GPP Networks Sept 2003 IGP Interior Gateway Protocol IMS IP Multimedia (Core Network) Subsystem, 3GPP Release 5 IPv6-only part of the network ISP Internet Service Provider NAT Network Address Translator NAPT-PT Network Address Port Translation - Protocol Translation NAT-PT Network Address Translation - Protocol Translation OTA Over The Air PCO-IE Protocol Configuration Options Information Element PDP Packet Data Protocol PPP Point-to-Point Protocol SGSN Serving GPRS Support Node SIIT Stateless IP/ICMP Translation Algorithm SIP Session Initiation Protocol UE User Equipment, for example a UMTS mobile handset UMTS Universal Mobile Telecommunications System 1.3 Terminology Some terms used in 3GPP transition scenarios and analysis documents are briefly defined here. Dual Stack UE Dual Stack UE is a 3GPP mobile handset having both IPv4 and IPv6 stacks. It is capable of activating both IPv4 and IPv6 Packet Data Protocol (PDP) contexts. Dual stack UE may be capable of tunneling. IPv6 UE IPv6 UE is an IPv6-only 3GPP mobile handset. It is only capable of activating IPv6 PDP contexts. IPv4 UE IPv4 UE is an IPv4-only 3GPP mobile handset. It is only capable of activating IPv4 PDP contexts. IPv4 node IPv4 node is here defined to be IPv4 capable node the UE is communicating with. The IPv4 node can be, for example, an application server or another UE. IPv6 node IPv6 node is here defined to be IPv6 capable node the UE is communicating with. The IPv6 node can be, for example, an application server or another UE. 2. Transition Mechanisms and DNS Guidelines This chapter briefly introduces some transition mechanisms specified by the IETF. The applicability of different transition mechanisms to 3GPP networks is discussed in chapters 3 and 4. DNS Wiljakka, Editor Expires: March 2004 [Page 4]
Analysis on IPv6 Transition in 3GPP Networks Sept 2003 recommendations related to IPv4/IPv6 transition are briefly summarized in section 2.4. The IPv4/IPv6 transition methods can be divided to: - dual IPv4/IPv6 stack - tunneling - protocol translators 2.1 Dual Stack The dual IPv4/IPv6 stack is specified in [RFC2893]. If we consider the 3GPP GPRS core network, dual stack implementation in the GGSN enables support for IPv4 and IPv6 PDP contexts. UEs with dual stack and public (global) IP addresses can often access both IPv4 and IPv6 services without additional translators in the network. 2.2 Tunneling Tunneling is a transition mechanism that requires dual IPv4/IPv6 stack functionality in the encapsulating and decapsulating nodes. Basic tunneling alternatives are IPv6-in-IPv4 and IPv4-in-IPv6. Tunneling can be static or dynamic. Static (configured) tunnels are fixed IPv6 links over IPv4, and they are specified in [RFC2893]. Dynamic (automatic) tunnels are virtual IPv6 links over IPv4 where the tunnel endpoints are not configured, i.e. the links are created dynamically. 2.3 Protocol Translators A translator can be defined as an intermediate component between a native IPv4 node and a native IPv6 node to enable direct communication between them without requiring any modifications to the end nodes. Header conversion is a translation mechanism. In header conversion, IPv6 packet headers are converted to IPv4 packet headers, or vice versa, and checksums are adjusted or recalculated if necessary. NAT-PT (Network Address Translator / Protocol Translator) [RFC2766] using SIIT [RFC2765] is an example of such a mechanism. Translators may be needed in some cases when the communicating nodes do not share the same IP version; in others, it may be possible to avoid such communication altogether. Translation can actually happen at Layer 3 (using NAT-like techniques), Layer 4 (using a TCP/UDP proxy) or Layer 7 (using application relays). Wiljakka, Editor Expires: March 2004 [Page 5]
Analysis on IPv6 Transition in 3GPP Networks Sept 2003 2.4 DNS Guidelines for IPv4/IPv6 Transition [DNStrans] provides guidelines to operate DNS in a mixed world of IPv4 and IPv6 transport. The recommended administrative policies are the following: - every recursive DNS server SHOULD be either IPv4-only or dual stack, - every single DNS zone SHOULD be served by at least one IPv4 reachable DNS server. This rules out IPv6-only DNS servers performing full recursion and DNS zones served only by IPv6-only DNS servers. This approach could be revisited if/when translation techniques between IPv4 and IPv6 were to be widely deployed. 3. GPRS Transition Scenarios This section discusses the scenarios that might occur when a GPRS UE contacts services or other nodes, e.g. a web server in the Internet. The following scenarios described by [RFC3574] are analyzed here. In all of the scenarios, the UE is part of a network where there is at least one router of the same IP version, i.e. the GGSN, and the UE is connecting to a node in a different network. 1) Dual Stack UE connecting to IPv4 and IPv6 nodes 2) IPv6 UE connecting to an IPv6 node through an IPv4 network 3) IPv4 UE connecting to an IPv4 node through an IPv6 network 4) IPv6 UE connecting to an IPv4 node 5) IPv4 UE connecting to an IPv6 node 3.1 Dual Stack UE Connecting to IPv4 and IPv6 Nodes In this scenario, the dual stack UE is capable of communicating with both IPv4 and IPv6 nodes. It is recommended to activate an IPv6 PDP context when communicating with an IPv6 peer node and an IPv4 PDP context when communicating with an IPv4 peer node. If the 3GPP network supports both IPv4 and IPv6 PDP contexts, the UE activates the appropriate PDP context depending on the type of application it has started or depending on the address of the peer host it needs to communicate with. If IPv6 PDP contexts are available and "IPv6 in IPv4" tunneling is needed, it is recommended to activate an IPv6 PDP context and perform tunneling in the network. This case is described in more detail in section 3.2. However, the UE may attach to a 3GPP network, in which the Serving GPRS Support Node (SGSN), the GGSN and the Home Location Register (HLR) support IPv4 PDP contexts, but may not support IPv6 PDP Wiljakka, Editor Expires: March 2004 [Page 6]
Analysis on IPv6 Transition in 3GPP Networks Sept 2003 contexts. If the 3GPP network does not support IPv6 PDP contexts, and an application on the UE needs to communicate with an IPv6(- only) node, the UE may activate an IPv4 PDP context and encapsulate IPv6 packets in IPv4 packets using a tunneling mechanism. This might happen in very early phases of IPv6 deployment. To generally solve this problem (IPv6 not available in the 3GPP network), this document strongly recommends the 3GPP operators to deploy basic IPv6 support in their GPRS networks, which can in most cases be handled by making software upgrades in the network elements. As a general guideline, IPv6 communication (native or tunneled from the UE) is preferred to IPv4 communication going through IPv4 NATs to the same dual stack peer node. When analyzing a dual stack UE behavior, an application running on a UE can identify whether the endpoint required is an IPv4 or IPv6 capable node by examining the address to discover what address family it falls into. Alternatively, if a user supplies a name to be resolved, the DNS may contain records sufficient to identify which protocol should be used to initiate the connection with the endpoint. Since the UE is capable of native communication with both protocols, one of the main concerns of an operator is the correct address space and routing management. The operator must maintain address spaces for both protocols. Public IPv4 addresses are often a scarce resource for the operator and typically it is not possible for a UE to have a globally unique IPv4 address continuously allocated for its use. Use of private IPv4 addresses means use of NATs when communicating with a peer node outside the operator's network. In large networks, NAT systems can become very complex, expensive and difficult to maintain. For DNS recommendations, we refer to section 2.4. 3.2 IPv6 UE Connecting to an IPv6 Node through an IPv4 Network The best solution for this scenario is obtained with tunneling, i.e. "IPv6 in IPv4" tunneling is a requirement. An IPv6 PDP context is activated between the UE and the GGSN. Tunneling is handled in the network, because IPv6 UE is not capable of tunneling (it does not have the dual stack functionality needed for tunneling). The encapsulating node can be the GGSN, the edge router between the border of the operator's IPv6 network and the public Internet, or any other dual stack node within the operator's IP network. The encapsulation (uplink) and decapsulation (downlink) can be handled by the same network element. Typically the tunneling handled by the network elements is transparent to the UEs and IP traffic looks like native IPv6 traffic to them. For the applications, tunneling enables end-to-end IPv6 connectivity. Note that this scenario is comparable to 6bone [6BONE] network operation. Wiljakka, Editor Expires: March 2004 [Page 7]
Analysis on IPv6 Transition in 3GPP Networks Sept 2003 "IPv6 in IPv4" tunnels between IPv6 islands can be either static or dynamic. The selection of the type of tunneling mechanism is up to the operator / ISP deployment scenario and only generic recommendations can be given in this document. The following subsections are focused on the usage of different tunneling mechanisms when the peer node is in the operator's network or outside the operator's network. The authors note that where the actual 3GPP network ends and which parts of the network belong to the ISP(s) also depends on the deployment scenario. The authors are not commenting how many ISP functions the 3GPP operator should perform. However, many 3GPP operators are ISPs of some sort themselves. ISP transition scenarios are documented in [ISP-scen]. 3.2.1 Tunneling inside the 3GPP Operator's Network Many GPRS operators already have IPv4 backbone networks deployed and they are gradually migrating them while introducing IPv6 islands. IPv6 backbones can be considered quite rare in the first phases of the transition. If the 3GPP operator already has IPv6 widely deployed in its network, this subsection is not so relevant. In initial IPv6 deployment, where a small number of IPv6 in IPv4 tunnels are required to connect the IPv6 islands over the 3GPP operator's IPv4 network, manually configured tunnels can be used. In a 3GPP network, one IPv6 island can contain the GGSN while another island can contain the operator's IPv6 application servers. However, manually configured tunnels can be an administrative burden when the number of islands and therefore tunnels rises. In that case, upgrading parts of the backbone to dual stack may be the simplest choice. The administrative burden could also be mitigated by using automated management tools which are typically necessary to manage large networks anyway. Even a dynamic tunneling mechanism or an IGP/EGP routing protocol based tunneling mechanism can be considered if other methods are not suitable. Connection redundancy should also be noted as an important requirement in 3GPP networks. Static tunnels on their own don't provide a routing recovery solution for all scenarios where an IPv6 route goes down. However, they may provide an adequate solution depending on the design of the network and in presence of other router redundancy mechanisms. On the other hand, IGP/EGP based mechanisms can provide redundancy. Wiljakka, Editor Expires: March 2004 [Page 8]
Analysis on IPv6 Transition in 3GPP Networks Sept 2003 3.2.2 Tunneling outside the 3GPP Operator's Network This subsection includes the case when the peer node is outside the operator's network. In that case the "IPv6 in IPv4" tunnel starting point can be in the operator's network - encapsulating node can be e.g. the GGSN or the edge router. The case is pretty straightforward if the upstream ISP provides native IPv6 connectivity to the Internet. If there is no native IPv6 connectivity available in the 3GPP network, an "IPv6 in IPv4" tunnel should be configured from e.g. the GGSN to the dual stack border gateway in order to access the upstream ISP. If the ISP only provides IPv4 connectivity, then the IPv6 traffic initiated from the 3GPP network should be transported tunneled in IPv4 to the ISP. Usage of configured "IPv6 in IPv4" tunneling is recommended. As the number of the tunnels outside of the 3GPP network is limited, no more than a couple of tunnels should be needed. ISP transition scenarios are described in [ISP-scen]. 3.3 IPv4 UE Connecting to an IPv4 Node through an IPv6 Network 3GPP networks are expected to support both IPv4 and IPv6 for a long time, on the UE-GGSN link and between the GGSN and external networks. For this scenario, it is useful to split the end-to-end IPv4 UE to IPv4 node communication into UE-to-GGSN and GGSN-to- v4NODE. An IPv6-capable GGSN is expected to support both IPv6 and IPv4 UEs. Therefore an IPv4-only UE will be able to use an IPv4 link (PDP context) to connect to the GGSN without the need to communicate over an IPv6 network. Regarding the GGSN-to-v4NODE communication, typically the transport network between the GGSN and external networks will support only IPv4 in the early stages and migrate to dual stack, since these networks are already deployed. Therefore it is not envisaged that tunneling of IPv4 in IPv6 will be required from the GGSN to external IPv4 networks either. In the longer run, 3GPP operators may need to phase out IPv4 UEs and the IPv4 transport network. This would leave only IPv6 UEs. Therefore, overall, the transition scenario involving an IPv4 UE communicating with an IPv4 peer through an IPv6 network is not considered very likely in 3GPP networks. Wiljakka, Editor Expires: March 2004 [Page 9]
Analysis on IPv6 Transition in 3GPP Networks Sept 2003 3.4 IPv6 UE Connecting to an IPv4 Node IPv6(-only) nodes can communicate with IPv4(-only) nodes by making use of a translator (e.g. SIIT [RFC2765], NAT-PT [RFC2766]) within the local network. For many applications, application proxies can be appropriate (e.g. HTTP, email relays, etc.). Such applications will not be transparent to the UE. Hence, a flexible mechanism with minimal manual intervention should be used to configure these proxies on IPv6 UEs. Within the 3GPP architecture, application proxies can be placed on the GGSN external interface (Gi), or inside the service network. However, since it is difficult to anticipate all the possible applications, there can be a need for translators that can translate headers independent of the type of application being used. This section describes a solution based on the use of translators, but does not strongly recommend using translators as a general solution. The authors note that NAT-PT applicability statement work is being done in the v6ops wg and that document will be used as a reference in this document. Due to the significant lack of IPv4 addresses in some domains, port multiplexing is likely to be a necessary feature for translators (i.e. NAPT-PT). If NA(P)T-PT is used, it needs to be placed on the GGSN external (Gi) interface, typically separate from the GGSN. NA(P)T-PT can be installed, for example, on the edge of the operator's network and the public Internet. NA(P)T-PT will intercept DNS requests and other applications that include IP addresses in their payloads, translate the IP header (and payload for some applications if necessary) and forward packets through its IPv4 interface. NA(P)T-PT introduces limitations that are expected to be magnified within the 3GPP architecture. Some of these limitations are listed below (notice that some of them are also relevant for IPv4 NAT). We note here that [v4v6trans] analyzes the issues when translating between IPv4 and IPv6. NAT-PT applicability statement document (currently being written in v6ops wg) will also be used as a reference in this document. 1. NA(P)T-PT is a single point of failure for all ongoing connections. 2. There are additional forwarding delays due to further processing, when compared to normal IP forwarding. 3. There are problems with source address selection due to the inclusion of a DNS ALG on the same node [NATPT-DNS]. Wiljakka, Editor Expires: March 2004 [Page 10]
Analysis on IPv6 Transition in 3GPP Networks Sept 2003 4. NA(P)T-PT does not work (without application level gateways) for applications that embed IP addresses in their payload. 5. NA(P)T-PT breaks DNSSEC. 6. NA(P)T-PT does not scale very well in large networks. 3GPP networks are expected to handle a very large number of subscribers on a single GGSN (default router). Each GGSN is expected to handle hundreds of thousands of connections. Furthermore, high reliability is expected for 3GPP networks. Consequently, a single point of failure on the GGSN external interface would raise concerns on the overall network reliability. In addition, IPv6 users are expected to use delay-sensitive applications provided by IMS. Hence, there is a need to minimize forwarding delays within the IP backbone. Furthermore, due to the unprecedented number of connections handled by the default routers (GGSN) in 3GPP networks, a network design that forces traffic to go through a single node at the edge of the network (typical NA(P)T-PT configuration) is not likely to scale. Translation mechanisms should allow for multiple translators, for load sharing and redundancy purposes. To minimize the problems associated with NA(P)T-PT, the following actions can be recommended: 1. Separate the DNS ALG from the NA(P)T-PT node (in the "IPv6 to IPv4" case). 2. Ensure (if possible) that NA(P)T-PT does not become a single point of failure. 3. Allow for load sharing between different translators. That is, it should be possible for different connections to go through different translators. Note that load sharing alone does not prevent NA(P)T-PT from becoming a single point of failure. 3.5 IPv4 UE Connecting to an IPv6 Node The legacy IPv4 nodes are mostly nodes that support the applications that are popular today in the IPv4 Internet: mostly e- mail and web-browsing. These applications will, of course, be supported in the IPv6 Internet of the future. However, the legacy IPv4 UEs are not going to be updated to support the future applications. As these applications are designed for IPv6, and to use the advantages of newer platforms, the legacy IPv4 nodes will not be able to profit from them. Thus, they will continue to support the legacy services. Wiljakka, Editor Expires: March 2004 [Page 11]
Analysis on IPv6 Transition in 3GPP Networks Sept 2003 Taking the above into account, the traffic to and from the legacy IPv4 UE is restricted to a few applications. These applications already mostly rely on proxies or local servers to communicate between private address space networks and the Internet. The same methods and technology can be used for IPv4 to IPv6 transition. For DNS recommendations, we refer to section 2.4. 4. IMS Transition Scenarios As the IMS is exclusively IPv6, the number of possible transition scenarios is reduced dramatically. The possible IMS scenarios are listed below and analyzed in sections 4.1 and 4.2. 1) UE connecting to a node in an IPv4 network through IMS 2) Two IMS islands connected over IPv4 network For DNS recommendations, we refer to section 2.4. As DNS traffic is not directly related to the IMS functionality, the recommendations are not in contradiction with the IPv6-only nature of the IMS. 4.1 UE Connecting to a Node in an IPv4 Network through IMS This scenario occurs when an IMS UE (IPv6) connects to a node in the IPv4 Internet through the IMS, or vice versa. This happens when the other node is a part of a different system than 3GPP, e.g. a fixed PC, with only IPv4 capabilities. There will probably be few legacy IPv4 nodes in the Internet that will communicate with the IMS UEs. It is assumed that the solution described here is used for limited cases, in which communications with a small number of legacy IPv4 SIP equipment are needed. As the IMS is exclusively IPv6 [3GPP 23.221], translators have to be used in the communication between the IPv6 IMS and legacy IPv4 hosts, i.e. making a dual stack based solution is not feasible. This section aims to give a brief overview on how that interworking can be handled. This section presents higher level details of a solution based on the use of a translator and SIP ALG. [3GPPtr] provides additional information and presents a bit different solution proposal based on SIP Edge Proxy and IP Address/Port Mapper. The authors recommend to solve the general SIP/SDP IPv4/IPv6 transition problem in the IETF SIP wg(s). As control (or signaling) and user (or data) traffic are separated in SIP, and thus, the IMS, the translation of the IMS traffic has to be done on two levels - Session Initiation Protocol (SIP) Wiljakka, Editor Expires: March 2004 [Page 12]
Analysis on IPv6 Transition in 3GPP Networks Sept 2003 [RFC3261], and Session Description Protocol (SDP) [RFC2327] [RFC3266] on the one hand (Mm-interface), and on the actual user data traffic level on the other (Mb-interface). SIP and SDP transition has to be made in an SIP/SDP Application Level Gateway. The ALG has to change the IP addresses transported in the SIP messages and the SDP payload of those messages to the appropriate version. In addition, there has to be interoperability for DNS queries; see section 2.4 for details. On the user data transport level, the translation is IPv4-IPv6 protocol translation, where the user data traffic transported is translated from IPv6 to IPv4, and vice versa. The legacy IPv4 host's address can be mapped to an IPv6 address for the IMS, and this address is then used within the IMS to route the traffic to the appropriate user traffic translator. This mapping can be done by the SIP/SDP ALG for the SIP traffic. The user traffic translator would do the similar mapping for the user traffic. However, in order to have an IPv4 address for the IMS UE, and to be able to route the user traffic within the legacy IPv4 network to the correct translator, there has to be an IPv4 address allocated for the duration of the session from the user traffic translator. The allocation of this address from the user traffic translator has to be done by the SIP/SDP ALG in order for the SIP/SDP ALG to know the correct IPv4 address. This can be achieved by using a protocol for the ALG to do the allocation. +-------------------------------+ +------------+ | +------+ | | +--------+ | | |S-CSCF|---| |SIP ALG | |\ | | +------+ | | +--------+ | \ -------- +-|+ | / | | | | | | | | | +------+ +------+ | | + | -| |- | |-|-|P-CSCF|--------|I-CSCF| | | | | | () | | | +------+ +------+ | |+----------+| / ------ | |-----------------------------------||Translator||/ +--+ | IPv6 | |+----------+| IPv4 UE | | |Interworking| | IP Multimedia CN Subsystem | |Unit | +-------------------------------+ +------------+ Figure 1: UE using IMS to contact a legacy phone Figure 1 shows a possible configuration scenario where the SIP ALG is separated from the CSCFs. The translator can either be set up in a single device with both SIP translation and media translation, or those functionalities can be divided to two different entities with an interface in between. We call the combined network element on Wiljakka, Editor Expires: March 2004 [Page 13]
Analysis on IPv6 Transition in 3GPP Networks Sept 2003 the edge of the IPv6-only IMS an "Interworking Unit" in this document. One alternative is to use a suitable subset of NAT-PT [RFC2766] in this network element to take care of the media (user data) IPv4/IPv6 translation. The problems related to NAT-PT are documented in section 3.4. 4.2 Two IMS Islands Connected over IPv4 Network At the early stages of IMS deployment, there may be cases where two IMS islands are separated by an IPv4 network such as the legacy Internet. Here both the UEs and the IMS islands are IPv6-only. However, the IPv6 islands are not native IPv6 connected. In this scenario, the end-to-end SIP connections are based on IPv6. The only issue is to make connection between two IPv6-only IMS islands over IPv4 network. This scenario is closely related to GPRS scenario represented in section 3.2. and similar tunneling solutions are applicable also in this scenario. 5. About 3GPP UE IPv4/IPv6 Configuration This informative section aims to give a brief overview on the configuration needed in the UE in order to access IP based services. There can also be other application specific settings in the UE that are not described here. To be able to access IPv6 or IPv4 based services, settings need to be done in the UE. The GGSN Access Point has to be defined when using, for example, the web browsing application. One possibility is to use Over The Air (OTA) configuration to configure the GPRS settings. The user can visit the operator WWW page and subscribe the GPRS Access Point settings to his/her UE and receive the settings via Short Message Service (SMS). After the user has accepted the settings and a PDP context has been activated, the user can start browsing. The Access Point settings can also be typed in manually or be pre-configured by the operator or the UE manufacturer. DNS server addresses typically also need to be configured in the UE. In the case of IPv4 type PDP context, the (IPv4) DNS server addresses can be received in the PDP context activation (a control plane mechanism). Same kind of mechanism is also available for IPv6: so-called Protocol Configuration Options Information Element (PCO-IE) specified by the 3GPP [3GPP-24.008]. It is also possible to use [DHCPv6-SL] or [RFC3315] and [DHCP-DNS] for receiving DNS server addresses. The authors note that the general IPv6 DNS discovery problem is being solved by the IETF dnsop Working Group. The DNS server addresses can also be received using OTA configuration, or typed in manually in the UE. Wiljakka, Editor Expires: March 2004 [Page 14]
Analysis on IPv6 Transition in 3GPP Networks Sept 2003 When accessing IMS services, the UE needs to know the P-CSCF IPv6 address. 3GPP-specific PCO-IE mechanism, or DHCPv6-based mechanism ([DHCPv6-SL] or [RFC3315] and [RFC3319]) can be used. OTA or manual configuration can also be possible. IMS subscriber authentication and registration to the IMS and SIP integrity protection are not discussed here. 6. Security Considerations Editor's note: This section may need updating. 1. NAT-PT DNS ALG problems are described in [NATPT-DNS] and [v4v6trans]. 2. The 3GPP specifications do not currently define the usage of DNS Security. They neither disallow the usage of DNSSEC, nor do they mandate it. 3. NAT-PT breaks DNSSEC. 7. Changes from draft-ietf-v6ops-3gpp-analysis-04.txt - (Major part of) The issues handled: http://danforsberg.info:8080/draft-ietf-v6ops-3gpp- analysis/index - The only DNS reference now is draft-ietf-dnsop-ipv6-transport- guidelines-00.txt, all DNS discussion is now in section 2.4 - Section 5 "About 3GPP UE IPv4/IPv6 Configuration" added - draft-elmalki-v6ops-3gpp-translator put as an informational reference in section 4.1; a recommendation has been added to solve the general SIP/SDP transition problem in SIP wg(s) - NAT64 reference removed - 6to4 references removed - IGP and BGP references removed (expired drafts) - Some abbreviations added - Intellectual Property Statement added - Editorial changes in many sections 8. Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of Wiljakka, Editor Expires: March 2004 [Page 15]
Analysis on IPv6 Transition in 3GPP Networks Sept 2003 claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. 9. Copyright The following copyright notice is copied from [RFC2026], Section 10.4. It describes the applicable copyright for this document. Copyright (C) The Internet Society September 10, 2003. All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assignees. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Wiljakka, Editor Expires: March 2004 [Page 16]
Analysis on IPv6 Transition in 3GPP Networks Sept 2003 10. References 10.1 Normative [RFC2026] Bradner, S.: The Internet Standards Process -- Revision 3, RFC 2026, October 1996. [RFC2663] Srisuresh, P., Holdrege, M.: IP Network Address Translator (NAT) Terminology and Considerations, RFC 2663, August 1999. [RFC2765] Nordmark, E.: Stateless IP/ICMP Translation Algorithm (SIIT), RFC 2765, February 2000. [RFC2766] Tsirtsis, G., Srisuresh, P.: Network Address Translation - Protocol Translation (NAT-PT), RFC 2766, February 2000. [RFC2893] Gilligan, R., Nordmark, E.: Transition Mechanisms for IPv6 Hosts and Routers, RFC 2893, August 2000. [RFC3261] Rosenberg, J., et al.: SIP: Session Initiation Protocol, RFC 3261, June 2002. [RFC3574] Soininen, J. (editor): Transition Scenarios for 3GPP Networks, RFC 3574, August 2003. [3GPP-23.060] 3GPP TS 23.060 V5.4.0, "General Packet Radio Service (GPRS); Service description; Stage 2 (Release 5)", December 2002. [3GPP 23.221] 3GPP TS 23.221 V5.7.0, "Architectural requirements (Release 5)", December 2002. [3GPP-23.228] 3GPP TS 23.228 V5.7.0, "IP Multimedia Subsystem (IMS); Stage 2 (Release 5)", December 2002. [3GPP 24.228] 3GPP TS 24.228 V5.3.0, "Signalling flows for the IP multimedia call control based on SIP and SDP; Stage 3 (Release 5)", December 2002. [3GPP 24.229] 3GPP TS 24.229 V5.3.0, "IP Multimedia Call Control Protocol based on SIP and SDP; Stage 3 (Release 5)", December 2002. 10.2 Informative [RFC2283] Bates, T., Chandra, R., Katz, D., Rekhter, Y.: Multiprotocol Extensions for BGP-4, RFC 2283, February 1998. [RFC2327] Handley, M., Jacobson, V.: SDP: Session Description Protocol, RFC 2327, April 1998. Wiljakka, Editor Expires: March 2004 [Page 17]
Analysis on IPv6 Transition in 3GPP Networks Sept 2003 [RFC3266] Olson, S., Camarillo, G., Roach, A. B.: Support for IPv6 in Session Description Protocol (SDP), June 2002. [RFC3314] Wasserman, M. (editor): Recommendations for IPv6 in 3GPP Standards, September 2002. [RFC3315] Droms, R. et al.: Dynamic Host Configuration Protocol for IPv6 (DHCPv6), July 2003. [RFC3319] Schulzrinne, H., Volz, B.: Dynamic Host Configuration Protocol (DHCPv6) Options for Session Initiation Protocol (SIP) Servers, July 2003. [3GPPtr] El Malki K., et al.: "IPv6-IPv4 Translators in 3GPP Networks", June 2003, draft-elmalki-v6ops-3gpp-translator-00.txt, work in progress. [DHCP-DNS] Droms, R. (ed.): "DNS Configuration options for DHCPv6", August 2003, draft-ietf-dhc-dhcpv6-opt-dnsconfig-04.txt, work in progress. [DHCP-SL] Droms, R.: "A Guide to Implementing Stateless DHCPv6 Service", April 2003, draft-ietf-dhc-dhcpv6-stateless-00.txt, work in progress. [DNStrans] Durand, A. and Ihren, J.: "DNS IPv6 transport operational guidelines", June 2003, draft-ietf-dnsop-ipv6- transport-guidelines-00.txt, work in progress. [ISP-scen] Lind, M. (Editor): "Scenarios for Introducing IPv6 into ISP Networks", June 2003, draft-lind-v6ops-isp-scenarios-00.txt, work in progress. [NATPT-DNS] Durand, A.: "Issues with NAT-PT DNS ALG in RFC2766", January 2003, draft-durand-v6ops-natpt-dns-alg-issues-00.txt, work in progress, the draft has expired. [v4v6trans] van der Pol, R., Satapati, S., Sivakumar, S.: "Issues when translating between IPv4 and IPv6", January 2003, draft-vanderpol-v6ops-translation-issues-00.txt, work in progress, the draft has expired. [3GPP-24.008] 3GPP TS 24.008 V5.8.0, "Mobile radio interface Layer 3 specification; Core network protocols; Stage 3 (Release 5)", June 2003. [6BONE] http://www.6bone.net Wiljakka, Editor Expires: March 2004 [Page 18]
Analysis on IPv6 Transition in 3GPP Networks Sept 2003 11. Authors and Acknowledgements This document is written by: Alain Durand, Sun Microsystems <Alain.Durand@sun.com> Karim El-Malki, Ericsson Radio Systems <Karim.El-Malki@era.ericsson.se> Niall Richard Murphy, Enigma Consulting Limited <niallm@enigma.ie> Hugh Shieh, AT&T Wireless <hugh.shieh@attws.com> Jonne Soininen, Nokia <jonne.soininen@nokia.com> Hesham Soliman, Flarion <h.soliman@flarion.com> Margaret Wasserman, Wind River <mrw@windriver.com> Juha Wiljakka, Nokia <juha.wiljakka@nokia.com> The authors would like to thank Heikki Almay, Gabor Bajko, Ajay Jain, Jarkko Jouppi, Ivan Laloux, Janne Rinne, Pekka Savola, Pedro Serna, Fred Templin, Anand Thakur and Rod Van Meter for their valuable input. 12. Editor's Contact Information Comments or questions regarding this document should be sent to the v6ops mailing list or directly to the document editor: Juha Wiljakka Nokia Visiokatu 3 Phone: +358 7180 48372 FIN-33720 TAMPERE, Finland Email: juha.wiljakka@nokia.com Wiljakka, Editor Expires: March 2004 [Page 19]
