INTERNET-DRAFT Jari Arkko Internet Engineering Task Force Peter Hedman Gerben Kuijpers Hesham Soliman Ericsson John Loughney Pertti Suomela Juha Wiljakka Nokia Issued: May 17, 2002 Expires: November 17, 2002 IPv6 for Some Second and Third Generation Cellular Hosts Status of This Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC 2026. 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 As the deployment of second and third generation cellular networks progresses, a large number of cellular hosts are being connected to the Internet. Standardization organizations are making IPv6 mandatory in their specifications. However, the concept of IPv6 covers many aspects and numerous specifications. In addition, the characteristics of cellular links in terms of bandwidth, cost and delay put special requirements on how IPv6 is used. This document considers IPv6 for cellular hosts that attach to the General Packet Radio Service (GPRS), or Universal Mobile Telecommunications System (UMTS) networks. The document lists basic components of IPv6 functionality and discusses some issues relating to the use of these components when operating in these networks. Internet Draft IPv6 for Some 2G and 3G Cellular Hosts May 17, 2002 Abstract.............................................................1 1 Introduction.......................................................3 1.1 Scope of this Document..........................................3 1.2 Abbreviations...................................................4 1.4 Cellular Host IPv6 Features.....................................5 2 Basic IP...........................................................5 2.1 RFC1981 - Path MTU Discovery for IP Version 6...................5 2.2 RFC2373 - IP Version 6 Addressing Architecture..................5 2.3 RFC2460 - Internet Protocol Version 6...........................6 2.4 RFC2461 - Neighbor Discovery for IPv6...........................6 2.5 RFC2462 - IPv6 Stateless Address Autoconfiguration..............7 2.6 RFC2463 - Internet Control Message Protocol for the IPv6........7 2.7 RFC2472 - IP version 6 over PPP.................................8 2.8 RFC2473 - Generic Packet Tunneling in IPv6 Specification........8 2.9 RFC2710 - Multicast Listener Discovery (MLD) for IPv6...........8 2.10 RFC2711 - IPv6 Router Alert Option.............................9 2.11 RFC2893 - Transition Mechanisms for IPv6 Hosts and Routers.....9 2.12 RFC3041 - Privacy Extensions for Address Configuration in IPv6.9 2.13 RFC3056 - Connection of IPv6 Domains via IPv4 Clouds...........9 2.14 Dynamic Host Configuration Protocol for IPv6 (DHCPv6)..........9 2.15 Default Address Selection for IPv6.............................9 2.16 DNS............................................................9 3 IP Security.......................................................10 3.1 RFC2104 - HMAC: Keyed-Hashing for Message Authentication.......10 3.2 RFC2401 - Security Architecture for the Internet Protocol......10 3.3 RFC2402 - IP Authentication Header.............................10 3.4 RFC2403 - The Use of HMAC-MD5-96 within ESP and AH.............11 3.5 RFC2404 - The Use of HMAC-SHA-96 within ESP and AH.............11 3.6 RFC2405 - The ESP DES-CBC Cipher Algorithm With Explicit IV....11 3.7 RFC2406 - IP Encapsulating Security Payload (ESP)..............11 3.8 RFC2407 - The Internet IP Security DoI for ISAKMP..............11 3.9 RFC2408 - The Internet Security Association and Key Management 11 Protocol...........................................................11 3.10 RFC2409 - The Internet Key Exchange (IKE).....................11 3.11 RFC2410 - The NULL Encryption Algorithm & its Use With IPsec..12 3.12 RFC2451 - The ESP CBC-Mode Cipher Algorithms..................12 4. Mobility.........................................................12 5. Security Considerations..........................................13 6. References.......................................................14 6.1. Normative.....................................................14 6.2. Non-Normative.................................................16 7. Acknowledgements.................................................17 8. Authors' Addresses...............................................17 Appendix A Revision History.........................................19 Appendix B Cellular Host IPv6 Addressing in the 3GPP Model..........19 Appendix C Transition Issues........................................20 Manyfolks [Page 2] Internet Draft IPv6 for Some 2G and 3G Cellular Hosts May 17, 2002 1 Introduction Technologies such as GPRS (General Packet Radio Service), UMTS (Universal Mobile Telecommunications System) and CDMA2000 (Code Division Multiple Access 2000) are making it possible for cellular hosts to have an always-on connection to the Internet. IPv6 becomes necessary, as it is expected that the number of such cellular hosts will increase rapidly. Standardization organizations working with cellular technologies have recognized this and are making IPv6 mandatory in their specifications. Support for IPv6 and the introduction of UMTS starts with 3GPP Release 99 networks and hosts. IPv6 is specified as the only IP version supported in Release 5 for IP Multimedia Subsystem (IMS). 1.1 Scope of this Document For the purposes of this document, a cellular interface is considered to be the interface to a cellular access network based on the following standards: 3GPP GPRS and UMTS Release 99, Release 4, Release 5, as well as future UMTS releases. A cellular host is considered to be a host with such a cellular interface. This document lists IPv6 specifications and discusses some issues relating to the use of these specifications when operating over cellular interfaces. Such a specification is necessary in order for the optimal use of IPv6 in a cellular environment. The description is made from a cellular host point of view. Important considerations are given in order to eliminate unnecessary user confusion over configuration options, ensure interoperability and to provide an easy reference for those implementing IPv6 in a cellular host. It is necessary to ensure that cellular hosts are good citizens of the Internet. The main audience of this document are the implementers of cellular hosts that will be used with GPRS, 3GPP UMTS Release 99, Release 4, Release 5, or future releases of UMTS. The document provides guidance on which parts of IPv6 to implement in such cellular hosts. Parts of this document may also apply to other cellular link types, but no such detailed analysis has been done yet and is a topic of future work. This document should not be used as a definitive list of IPv6 functionality for cellular links other than those listed above. Future changes in 3GPP networks that require changes in host implementations may result in updates to this document. There are different ways to implement cellular hosts: - The host can be a "closed 2G or 3G host" with a very compact size and optimized applications, with no possibility to add or download applications that can have IP communications. An example of such a host is a very simple form of a mobile phone. Manyfolks [Page 3] Internet Draft IPv6 for Some 2G and 3G Cellular Hosts May 17, 2002 - The host can be an "open 2G or 3G host" with a compact size, but where it is possible to download applications; such as a PDA-type of phone. If a cellular host has additional interfaces on which IP is used, (such as Ethernet, WLAN, Bluetooth, etc.) then there may be additional requirements for the device, beyond what is discussed in this document. Additionally, this document does not make any recommendations on the functionality required on laptop computers having a cellular interface such as a PC card, other than recommending link specific behavior on the cellular link. This document discusses IPv6 functionality as specified when this draft is written. Ongoing work on IPv6 may affect what is needed from future hosts. The reader should also be advised other relevant work exists for various other layers. Examples of this include the header compression work done in the IETF ROHC group, or the TCP work in [TCPWIRELESS]. 1.2 Abbreviations 2G Second Generation Mobile Telecommunications, such as GSM and GPRS technologies. 3G Third Generation Mobile Telecommunications, such as UMTS technology. 3GPP 3rd Generation Partnership Project. Throughout the document, the term 3GPP (3rd Generation Partnership Project) networks refers to architectures standardized by 3GPP, in Second and Third Generation releases: 99, 4, and 5, as well as future releases. AH Authentication Header APN Access Point Name. The APN is a logical name referring to a GGSN and an external network. ESP Encapsulating Security Payload ETSI European Telecommunications Standards Institute IMS IP Multimedia Subsystem GGSN Gateway GPRS Support Node (a default router for 3GPP IPv6 cellular hosts) GPRS General Packet Radio Service GSM Global System for Mobile Communications IKE Internet Key Exchange ISAKMP Internet Security Association and Key Management Protocol MT Mobile Terminal, for example, a mobile phone handset. MTU Maximum Transmission Unit PDP Packet Data Protocol SGSN Serving GPRS Support Node TE Terminal Equipment, for example, a laptop attached through a 3GPP handset. UMTS Universal Mobile Telecommunications System WLAN Wireless Local Area Network Manyfolks [Page 4] Internet Draft IPv6 for Some 2G and 3G Cellular Hosts May 17, 2002 1.4 Cellular Host IPv6 Features This specification defines IPv6 features for cellular hosts in three groups. Basic IP In this group, basic parts of IPv6 are described. IP Security In this group, the IP Security parts, as well as, the suitability of various security functions to different applications in cellular hosts are discussed. Mobility In this group, IP layer mobility issues are discussed. 2 Basic IP 2.1 RFC1981 - Path MTU Discovery for IP Version 6 Path MTU Discovery [RFC-1981] may be used. Cellular hosts with a link MTU larger than the minimum IPv6 link MTU (1280 octets) can use Path MTU Discovery in order to discover the real path MTU. The relative overhead of IPv6 headers is minimized through the use of longer packets, thus making better use of the available bandwidth. The IPv6 specification [RFC-2460] states in chapter 5 that "a minimal IPv6 implementation (e.g., in a boot ROM) may simply restrict itself to sending packets no larger than 1280 octets, and omit implementation of Path MTU Discovery." If Path MTU Discovery is not implemented then the sending packet size is limited to 1280 octets (standard limit in [RFC-2460]). However, if this is done, the cellular host must be able to receive packets with size up to the link MTU before reassembly. This is because the node at the other side of the link has no way of knowing less than the MTU is accepted. 2.2 RFC2373 - IP Version 6 Addressing Architecture The IPv6 Addressing Architecture [RFC-2373] is a mandatory part of IPv6. Currently, this specification is being updated by [ADDRARCHv3]; therefore, this specification may be made obsolete by the new one, in which case the new specification must be supported. Manyfolks [Page 5] Internet Draft IPv6 for Some 2G and 3G Cellular Hosts May 17, 2002 2.3 RFC2460 - Internet Protocol Version 6 The Internet Protocol Version 6 is specified in [RFC-2460]. This specification is a mandatory part of IPv6. By definition, a cellular host acts as a host, not as a router. Implementation requirements for a cellular router are not defined in this document. Consequently, the cellular host must implement all non-router packet receive processing as described in RFC 2460. This includes the generation of ICMPv6 error reports, and the processing of at least the following extension headers: - Hop-by-Hop Options header: at least the Pad1 and PadN options - Destination Options header: at least the Pad1 and PadN options - Routing (Type 0) header: final destination (host) processing only - Fragment header - AH and ESP headers (see also a discussion on the use of IPsec for various purposes in Section 3) - The No Next Header value Unrecognized options in Hop-by-Hop Options or Destination Options extensions must be processed as described in RFC 2460. The cellular host must follow the packet transmission rules in RFC 2460. The cellular host must always be able to receive and reassemble fragment headers. It will also need to be able to send a fragment header in cases where it communicates with an IPv4 host through a translator. Cellular hosts should only process routing headers when they are the final destination and return errors if the processing of the routing header requires them to forward the packet to another node. This will also ensure that the cellular hosts will not be inappropriately used as relays or components in Denial-of-Service attacks. Acting as the destination involves the following: the cellular hosts must check the Segments Left field in the header, and proceed if it is zero or one and the next address is one of the host's addresses. If not, however, the host must implement error checks as specified in section 4.4 of RFC 2460. There is no need for the host to send Routing Headers. 2.4 RFC2461 - Neighbor Discovery for IPv6 Neighbor Discovery is described in [RFC-2461]. This specification is a mandatory part of IPv6. Manyfolks [Page 6] Internet Draft IPv6 for Some 2G and 3G Cellular Hosts May 17, 2002 2.4.1 Neighbor Discovery in 3GPP Networks In GPRS and UMTS networks, some Neighbor Discovery messages can cause unnecessary traffic and consume valuable (limited) bandwidth. GPRS and UMTS links resemble a point-to-point link; hence, the host's only neighbor on the cellular link is the default router that is already known through Router Discovery. This router is typically not the final destination for the host's traffic. Additionally, due to special characteristics of the cellular link, lower layer connectivity information should make it unnecessary to track the reachability of the router. Therefore, while the host must support Neighbor Solicitation and Advertisement messages, their use is not necessary and the host may choose to not initiate them. In addition, a cellular host should not send the link layer option on its cellular interface, and should silently ignore it when received on the same interface. Hosts in a UMTS network, only need to use Router Solicitations and Router Advertisements for 3GPP IPv6 Address Autoconfiguration (see appendix B). Neighbor Solicitations and Advertisements may be used for Neighbor Unreachability Detection (NUD). They are not required for 3GPP IPv6 Stateless Address Autoconfiguration, since address duplication is not possible in this address assignment mechanism (see section 2.5.1). 2.5 RFC2462 - IPv6 Stateless Address Autoconfiguration IPv6 Stateless Address Autoconfiguration is defined in [RFC-2462]. This specification is a mandatory part of IPv6. 2.5.1 Stateless Address Autoconfiguration in 3GPP Networks A cellular host in a 3GPP network must process a Router Advertisement as stated in section 2.4. Hosts in 3GPP networks can set DupAddrDetectTransmits equal to zero, as each delegated prefix is unique within its scope when allocated using the 3GPP IPv6 Stateless Address Autoconfiguration. Thus, Duplicate Address Detection is not required on the cellular interface. DAD messages will not be sent or received by the IPv6 cellular host on the cellular interface. See appendix B for more details on 3GPP IPv6 Stateless Address Autoconfiguration. 2.6 RFC2463 - Internet Control Message Protocol for the IPv6 The Internet Control Message Protocol for the IPv6 is defined [RFC- 2463]. This specification is a mandatory part of IPv6. Currently, this work is being updated. Manyfolks [Page 7] Internet Draft IPv6 for Some 2G and 3G Cellular Hosts May 17, 2002 As per RFC 2463 section 2, ICMPv6 requirements must be fully implemented by every IPv6 node. See also Section 3 for an explanation of the use of IPsec for protecting ICMPv6 communications. 2.7 RFC2472 - IP version 6 over PPP IPv6 over PPP [RFC-2472] must be supported for cellular hosts that implement PPP. 2.7.1 IP version 6 over PPP in 3GPP Networks A cellular host in a 3GPP network must support the IPv6CP interface identifier option. This option is needed to be able to connect other devices to the Internet using a PPP link between the cellular device (MT) and other devices (TE, e.g. a laptop). The MT performs the PDP Context activation based on a request from the TE. This results in an interface identifier being suggested by the MT to the TE, using the IPv6CP option. To avoid any duplication in link-local addresses between the TE and the GGSN, the MT must always reject other suggested interface identifiers by the TE. This results in the TE always using the interface identifier suggested by the GGSN for its link-local address. The rejection of interface identifiers suggested by the TE is only done for creation of link local addresses, according to 3GPP specifications. The use of privacy addresses [RFC-3041] for site- local and global addresses is not affected by the above procedure. The above procedure is only concerned with assigning the interface identifier used for forming link-local addresses, and does not preclude TE from using other interface identifiers for addresses with larger scopes (i.e. site-local and global). 2.8 RFC2473 - Generic Packet Tunneling in IPv6 Specification Generic Packet Tunneling [RFC-2473] may be supported if needed for transition mechanisms. 2.9 RFC2710 - Multicast Listener Discovery (MLD) for IPv6 Multicast Listener Discovery [RFC-2710] may be supported, if the cellular host is supporting applications that require the use of multicast services. There is no need for MLD if the host only supports the well-known (hard coded in IPv6 implementations) link local multicast addresses. MLD is not used for listening on such addresses. Manyfolks [Page 8] Internet Draft IPv6 for Some 2G and 3G Cellular Hosts May 17, 2002 2.10 RFC2711 - IPv6 Router Alert Option The Router Alert Option [RFC-2711] may be supported. Currently, this option is needed for MLD implementations (see section 2.9) or when RSVP [RFC-2205] is used. 2.11 RFC2893 - Transition Mechanisms for IPv6 Hosts and Routers [RFC-2893] specifies a number of transition mechanisms for IPv6 hosts. Cellular hosts may support the dual stack mechanism mentioned in this specification. This also includes resolving addresses from the DNS and selecting the type of address for the correspondent host (IPv4 vs. IPv6). Cellular hosts should not support configured or automatic tunnels to avoid unnecessary tunneling over the air interface, unless there are no other mechanisms available. Tunneling can lead to poor usage of available bandwidth. 2.12 RFC3041 - Privacy Extensions for Address Configuration in IPv6 Privacy Extensions for Stateless Address Autoconfiguration [RFC- 3041] may be used. Refer to section 5 for a discussion of the benefits of privacy extensions in a 3GPP network. 2.13 RFC3056 - Connection of IPv6 Domains via IPv4 Clouds Connection of IPv6 domains via IPv4 clouds [RFC-3056] should not be supported to avoid unnecessary tunneling over the air interface. For a cellular host, this specification would mean capability to create 6to4 tunnels starting from the cellular host itself. In a cellular environment, tunneling over the air interface should be minimized as tunneling can lead to poor usage of available bandwidth. Hence, intermediate 6to4 routers should carry out 6to4 tunneling, instead of cellular hosts. 2.14 Dynamic Host Configuration Protocol for IPv6 (DHCPv6) The Dynamic Host Configuration Protocol for IPv6 [DHCPv6] may be used. DHCPv6 is not required for address autoconfiguration when IPv6 stateless autoconfiguration is used. However, DHCPv6 may be useful for other configuration needs on a cellular host. 2.15 Default Address Selection for IPv6 Default Address Selection for IPv6 [DEFADDR] is needed for cellular hosts with more than one address. 2.16 DNS Cellular hosts should support DNS, as described in [RFC-1034], [RFC- 1035] and [RFC-1886]. Manyfolks [Page 9] Internet Draft IPv6 for Some 2G and 3G Cellular Hosts May 17, 2002 If DNS is used, a cellular host should perform DNS requests in the recursive mode, to limit signaling over the air interface. 3 IP Security IPsec [RFC-2401] is a fundamental part of IPv6, and support for AH and ESP is described as mandatory in the specifications. The first part of this section discusses the applicability of IP Security and other security mechanisms for common tasks in cellular hosts. The second part, subsections 3.1 to 3.13, lists the RFCs related to IPsec and discusses the use of these parts of IPsec in a cellular context. In general, the need to use a security mechanism depends on the intended application for it. Different security mechanisms are useful in different contexts, and have different limitations. Some applications require the use of TLS [RFC-2246], in some situations IPsec is used. It is not realistic to list all possible services here, and it is expected that application protocol specifications have requirements on what security services they require. Note that cellular hosts able to download applications must be prepared to offer sufficient security services for these applications regardless of the needs of the initial set of applications in those hosts. The following sections list specifications related to the IPsec functionality, and discuss their applicability in a cellular context. In some applications, a different set of protocols may need a different set of protocols may need to be employed. In particular, the below discussion is not relevant for applications that use other security services than IPsec. 3.1 RFC2104 - HMAC: Keyed-Hashing for Message Authentication This specification [RFC-2104] must be supported. It is referenced by RFC 2403 that describes how IPsec protects the integrity of packets. 3.2 RFC2401 - Security Architecture for the Internet Protocol This specification [RFC-2401] must be supported. 3.3 RFC2402 - IP Authentication Header This specification [RFC-2402] must be supported. The IPsec WG has discussed the role of AH in the future, and it is possible that it will be made optional in the future versions of the IPsec protocol set. Implementers are recommended to take this in account. Manyfolks [Page 10] Internet Draft IPv6 for Some 2G and 3G Cellular Hosts May 17, 2002 3.4 RFC2403 - The Use of HMAC-MD5-96 within ESP and AH This specification [RFC-2403] must be supported. 3.5 RFC2404 - The Use of HMAC-SHA-96 within ESP and AH This specification [RFC-2404] must be supported. 3.6 RFC2405 - The ESP DES-CBC Cipher Algorithm With Explicit IV This specification [RFC-2405] may be supported. It is, however, recommended that stronger algorithms than DES be used. Algorithms, such as AES, are undergoing work in the IPsec working group. 3.7 RFC2406 - IP Encapsulating Security Payload (ESP) This specification [RFC-2406] must be supported. 3.8 RFC2407 - The Internet IP Security DoI for ISAKMP Automatic key management, [RFC-2408] and [RFC-2409], is not a mandatory part of the IP Security Architecture. Note, however, that in the cellular environment the IP addresses of a host may change dynamically. For this reason the use of manually configured Security Associations is not practical, as the newest host address would have to be updated to the SA database of the peer as well. Even so, it is not clear that all applications would use IKE for key management. For instance, hosts may use IPsec ESP [RFC-2406] for protecting SIP signaling in the IMS [3GPP-ACC] but provide authentication and key management through another mechanism such as UMTS AKA (Authentication and Key Agreement) [UMTS-AKA]. It is likely that several simplifying assumptions can be made in the cellular environment, with respect to the mandated parts of the IP Security DoI, ISAKMP, and IKE. Although work on such simplifications would be useful, is not described here. 3.9 RFC2408 - The Internet Security Association and Key Management Protocol This specification [RFC-2408] is optional according to the IPv6 specifications, but may be necessary in some applications, as described in Section 3.8. 3.10 RFC2409 - The Internet Key Exchange (IKE) This specification [RFC-2409] is optional according to the IPv6 specifications, but may be necessary in some applications, as described in Section 3.8. Manyfolks [Page 11] Internet Draft IPv6 for Some 2G and 3G Cellular Hosts May 17, 2002 Interactions with the ICMPv6 packets and IPsec policies may cause unexpected behavior for IKE-based SA negotiation unless some special handling is performed in the implementations. The ICMPv6 protocol provides many functions, which in IPv4 were either non-existent or provided by lower layers. For instance, IPv6 implements address resolution using an IP packet, ICMPv6 Neighbor Solicitation message. In contrast, IPv4 uses an ARP message at a lower layer. The IPsec architecture has a Security Policy Database that specifies which traffic is protected, and how. It turns out that the specification of policies in the presence of ICMPv6 traffic is not easy. For instance, a simple policy of protecting all traffic between two hosts on the same network would trap even address resolution messages, leading to a situation where IKE can't establish a Security Association since in order to send the IKE UDP packets one would have had to send the Neighbor Solicitation Message, which would have required an SA. In order to avoid this problem, Neighbor Solicitation, Neighbor Advertisement, Router Solicitation, and Router Advertisement messages must not lead to the use of IKE-based SA negotiation. The Redirect message should not lead to the use of IKE-based SA negotiation. Other ICMPv6 messages may use IKE-based SA negotiation as is desired in the Security Policy Data Base. Note that the above limits the usefulness of IPsec in protecting all ICMPv6 communications. For instance, it may not be possible to protect the ICMPv6 traffic between a cellular host and its next hop router. (Which may be hard in any case due to the need to establish a suitable public key infrastructure. Since roaming is allowed, this infrastructure would have to authenticate all hosts to all routers.) 3.11 RFC2410 - The NULL Encryption Algorithm & its Use With IPsec This specification [RFC-2410] must be supported. 3.12 RFC2451 - The ESP CBC-Mode Cipher Algorithms This specification [RFC-2451] must be supported if encryption algorithms other than DES are implemented, e.g.: CAST-128, RC5, IDEA, Blowfish, 3DES. 4. Mobility For the purposes of this document, IP mobility is not relevant. When Mobile IPv6 specification is approved, a future update to this document may address these issues, as there may be some effects on IPv6 hosts due to Mobile IP. The movement of cellular hosts within 3GPP networks is handled by link layer mechanisms. Manyfolks [Page 12] Internet Draft IPv6 for Some 2G and 3G Cellular Hosts May 17, 2002 5. Security Considerations This document does not specify any new protocols or functionality, and as such, it does not introduce any new security vulnerabilities. However, specific profiles of IPv6 functionality are proposed for different situations, and vulnerabilities may open or close depending on which functionality is included and what is not. There are also aspects of the cellular environment that make certain types of vulnerabilities more severe. The following issues are discussed: - The suggested limitations (Section 2.3) in the processing of routing headers limits also exposure to Denial-of-Service attacks through cellular hosts. - IPv6 addressing privacy [RFC3041] may be used in cellular hosts. However, it should be noted that in the 3GPP model, the network would assign new addresses, in most cases, to hosts in roaming situations and typically, also when the cellular hosts activate a PDP context. This means that 3GPP networks will already provide a limited form of addressing privacy, and no global tracking of a single host is possible through its address. On the other hand, since a GGSN's coverage area is expected to be very large when compared to currently deployed default routers (no handovers between GGSNs are possible), a cellular host can keep an address for a long time. Hence, IPv6 addressing privacy can be used for additional privacy during the time the host is on and in the same area. The privacy features can also be used to e.g. make different transport sessions appear to come from different IP addresses. However, it is not clear that these additional efforts confuse potential observers any further, as they could monitor only the network prefix part. - The use of various security services such as IPsec or TLS in the connection of typical applications in cellular hosts is discussed in Chapter 3 and recommendations are given there. - Chapter 3 also discusses under what conditions it is possible to provide IPsec protection of e.g. ICMPv6 communications - The airtime used by cellular hosts is expensive. In some cases, users are billed according to the amount of data they transfer to and from their host. It is crucial for both the network and the users that the airtime is used correctly and no extra charges are applied to users due to misbehaving third parties. The cellular links also have a limited capacity, which means that they may not necessarily be able to accommodate more traffic than what the user selected, such as a multimedia call. Additional traffic might interfere with the service level experienced by the user. While Quality of Service mechanisms mitigates these problems to an extent, it is still apparent that Denial-of-Service (DoS) aspects may be highlighted in the cellular environment. It is possible for Manyfolks [Page 13] Internet Draft IPv6 for Some 2G and 3G Cellular Hosts May 17, 2002 existing DoS attacks that use for instance packet amplification to be substantially more damaging in this environment. How these attacks can be protected against is still an area of further study. It is also often easy to fill the cellular link and queues on both sides with additional or large packets. - Within some service provider networks, it is possible to buy a prepaid cellular subscription without presenting personal identification. Attackers that wish to remain unidentified could leverage this. Note that while the user hasn't been identified, the equipment still is; the operators can follow the identity of the device and block it from further use. The operators must have procedures in place to take notice of third party complaints regarding the use of their customers' devices. It may also be necessary for the operators to have attack detection tools that enable them to efficiently detect attacks launched from the cellular hosts. - Cellular devices that have local network interfaces (such as IrDA or Bluetooth) may be used to launch attacks through them, unless the local interfaces are secured in an appropriate manner. Therefore, local network interfaces should have access control to prevent others from using the cellular host as an intermediary. 6. References 6.1. Normative [ADDRARCHv3] Hinden, R. and Deering, S. "IP Version 6 Addressing Architecture", Work in progress. [DEFADDR] Draves, R., "Default Address Selection for IPv6", Work in progress. [DHCPv6] Bound, J. et al., "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", Work in progress. [RFC-1981] McCann, J., Mogul, J. and Deering, S., "Path MTU Discovery for IP version 6", RFC 1981, August 1996. [RFC-1035] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, November 1987. [RFC-1886] Thomson, S. and Huitema, C., "DNS Extensions to support IP version 6, RFC 1886, December 1995. [RFC-2104] Krawczyk, K., Bellare, M., and Canetti, R., "HMAC: Keyed-Hashing for Message Authentication", RFC 2104, February 1997. Manyfolks [Page 14] Internet Draft IPv6 for Some 2G and 3G Cellular Hosts May 17, 2002 [RFC-2246] Dierks, T. and Allen, C., "The TLS Protocol Version 1.0", RFC 2246, January 1999 [RFC-2373] Hinden, R. and Deering, S., "IP Version 6 Addressing Architecture", RFC 2373, July 1998. [RFC-2401] Kent, S. and Atkinson, R., "Security Architecture for the Internet Protocol", RFC 2401, November 1998. [RFC-2402] Kent, S. and Atkinson, R., "IP Authentication Header", RFC 2402, November 1998. [RFC-2403] Madson, C., and Glenn, R., "The Use of HMAC-MD5 within ESP and AH", RFC 2403, November 1998. [RFC-2404] Madson, C., and Glenn, R., "The Use of HMAC-SHA-1 within ESP and AH", RFC 2404, November 1998. [RFC-2405] Madson, C. and Doraswamy, N., "The ESP DES-CBC Cipher Algorithm With Explicit IV", RFC 2405, November 1998. [RFC-2406] Kent, S. and Atkinson, R., "IP Encapsulating Security Protocol (ESP)", RFC 2406, November 1998. [RFC-2407] Piper, D., "The Internet IP Security Domain of Interpretation for ISAKMP", RFC 2407, November 1998. [RFC-2408] Maughan, D., Schertler, M., Schneider, M., and Turner, J., "Internet Security Association and Key Management Protocol (ISAKMP)", RFC 2408, November 1998. [RFC-2409] Harkins, D., and Carrel, D., "The Internet Key Exchange (IKE)", RFC 2409, November 1998. [RFC-2410] Glenn, R. and Kent, S., "The NULL Encryption Algorithm and Its Use With IPsec", RFC 2410, November 1998 [RFC-2451] Pereira, R. and Adams, R., "The ESP CBC-Mode Cipher Algorithms", RFC 2451, November 1998 [RFC-2460] Deering, S. and Hinden, R., "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [RFC-2461] Narten, T., Nordmark, E. and Simpson, W., "Neighbor Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998. Manyfolks [Page 15] Internet Draft IPv6 for Some 2G and 3G Cellular Hosts May 17, 2002 [RFC-2462] Thomson, S. and Narten, T., "IPv6 Stateless Address Autoconfiguration", RFC 2462. [RFC-2463] Conta, A. and Deering, S., "ICMP for the Internet Protocol Version 6 (IPv6)", RFC 2463, December 1998. [RFC-2473] Conta, A. and Deering, S., "Generic Packet Tunneling in IPv6 Specification", RFC 2473, December 1998. [RFC-2710] Deering, S., Fenner, W. and Haberman, B., "Multicast Listener Discovery (MLD) for IPv6", RFC 2710, October 1999. [RFC-2711] Partridge, C. and Jackson, A., "IPv6 Router Alert Option", RFC 2711, October 1999. [RFC-2874] Crawford, M. and Huitema, C., "DNS Extensions to Support IPv6 Address Aggregation and Renumbering", RFC 2874, July 2000. [RFC-3041] Narten, T. and Draves, R., "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 3041, January 2001. 6.2. Non-Normative [3GPP-ACC] 3GPP Technical Specification 3GPP TS 33.203, "Technical Specification Group Services and System Aspects; 3G Security; Access security for IP-based services (Release 5)", 3rd Generation Partnership Project, March 2002. [3GPP-IMS] 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; IP Multimedia (IM) Subsystem - Stage 2; (3G TS 23.228) [3GPP-IPv6] 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects "Architectural requirements" (TS 23.221) [IPv6-3GPP] Wasserman, M (editor), "Recommendations for IPv6 in 3GPP Standards" Work in Progress. [RFC-1034] Mockapetris, P., "Domain names - concepts and facilities", RFC 1034, November 1987 [RFC-2529] Carpenter, B. and Jung, C., "Transmission of IPv6 over IPv4 Domains without Explicit Tunnels", RFC 2529, March 1999. Manyfolks [Page 16] Internet Draft IPv6 for Some 2G and 3G Cellular Hosts May 17, 2002 [RFC-2893] Gilligan, R. and Nordmark, E., "Transition Mechanisms for IPv6 Hosts and Routers", RFC 2893, August 2000. [RFC-3056] Carpenter, B. and Moore, K., "Connection of IPv6 domains via IPv4 clouds", RFC 3056, February 2001. [RFC-2205] Resource ReSerVation Protocol (RSVP) -- Version 1 Functional Specification. R. Braden, Ed., L. Zhang, S. Berson, S. Herzog, S. Jamin, RFC 2205September 1997. [TCPWIRELESS] Inamura, H. et al. "TCP over 2.5G and 3G Networks". IETF, Work in progress. [UMTS-AKA] 3GPP Technical Specification 3GPP TS 33.102, "Technical Specification Group Services and System Aspects; 3G Security; Security Architecture (Release 4)", 3rd Generation Partnership Project, December 2001. 7. Acknowledgements The authors would like to thank Jim Bound, Brian Carpenter, Steve Deering, Bob Hinden, Keith Moore, Thomas Narten, Erik Nordmark, Michael Thomas, Margaret Wasserman and others at the IPv6 WG mailing list for their comments and input. We would also like to thank David DeCamp, Karim El Malki, Markus Isom„ki, Petter Johnsen, Janne Rinne, Jonne Soininen, Vlad Stirbu and Shabnam Sultana for their comments and input in preparation of this document. 8. Authors' Addresses Jari Arkko Ericsson 02420 Jorvas Finland Phone: +358 40 5079256 Fax: +358 40 2993401 E-Mail: Jari.Arkko@ericsson.com Peter Hedman Ericsson SE-221 83 LUND SWEDEN Phone: +46 46 231760 Fax: +46 46 231650 E-mail: peter.hedman@emp.ericsson.se Manyfolks [Page 17] Internet Draft IPv6 for Some 2G and 3G Cellular Hosts May 17, 2002 Gerben Kuijpers Ericsson Skanderborgvej 232 DK-8260 Viby J DENMARK Phone: +45 89385100 Fax: +45 89385101 E-mail: gerben.a.kuijpers@ted.ericsson.se Hesham Soliman Ericsson Radio Systems AB Torshamnsgatan 23, Kista, Stockholm SWEDEN Phone: +46 8 4046619 Fax: +46 8 4047020 E-mail: Hesham.Soliman@era.ericsson.se John Loughney Nokia Research Center It„merenkatu 11 ű 13 FIN-00180 HELSINKI FINLAND Phone: +358 7180 36242 Fax: +358 7180 36851 E-mail: john.loughney@nokia.com Pertti Suomela Nokia Mobile Phones Sinitaival 5 FIN-33720 TAMPERE Finland Phone: +358 7180 40546 Fax: +358 7180 47518 E-mail: pertti.suomela@nokia.com Juha Wiljakka Nokia Mobile Phones Sinitaival 5 FIN-33720 TAMPERE Finland Phone: +358 7180 47562 Fax: +358 7180 47518 E-mail: juha.wiljakka@nokia.com Manyfolks [Page 18] Internet Draft IPv6 for Some 2G and 3G Cellular Hosts May 17, 2002 Appendix A Revision History Changes from draft-ietf-ipv6-cellular-host-01.txt: - Additional clarification to the scope of the document. - Additional text on Path MTU added. - Additional explanation in section 2.5.1 - Additional text (chapter 2.3) to show that hosts need to be able to send the fragmentation header. - Discussion on the use of Privacy addresses added. - Clarification on the use of DHCPv6 added. - Additional text to clarify the use of DAD - Removed some references to application-specific security mechanisms in chapter 3. - Removed the reference to MIPv6 from 2.8 - Clarified when MLD was needed in chapter 2.9 - Removed Appendix D and references to MIPv6 - Several editorial changes. Appendix B Cellular Host IPv6 Addressing in the 3GPP Model The appendix aims to very briefly describe the 3GPP IPv6 addressing model for 2G (GPRS) and 3G (UMTS) cellular networks from Release 99 onwards. More information can be found from 3GPP Technical Specification 23.060. There are two possibilities to allocate the address for an IPv6 node: stateless and stateful autoconfiguration. The stateful address allocation mechanism needs a DHCP server to allocate the address for the IPv6 node. On the other hand, the stateless autoconfiguration procedure does not need any external entity involved in the address autoconfiguration (apart from the GGSN). In order to support the standard IPv6 stateless address autoconfiguration mechanism, as recommended by the IETF, the GGSN shall assign a prefix that is unique within its scope to each primary PDP context that uses IPv6 stateless address autoconfiguration. This avoids the necessity to perform Duplicate Address Detection at the network level for every address built by the mobile host. The GGSN always provides an Interface Identifier to the mobile host. The Mobile host uses the interface identifier provided by the GGSN to generate its link-local address. Since the GGSN provides the cellular host with the interface identifier, it must ensure the uniqueness of such identifier on the link (I.e. no collisions between its own link local address and the cellular host's). In addition, the GGSN will not use any of the prefixes assigned to cellular hosts to generate any of its own addresses. This use of the interface identifier, combined with the fact that each PDP context is allocated a unique prefix, will eliminate the Manyfolks [Page 19] Internet Draft IPv6 for Some 2G and 3G Cellular Hosts May 17, 2002 need for DAD messages over the air interface, and consequently allows an efficient use of bandwidth. Furthermore, the allocation of a prefix to each PDP context will allow hosts to implement the privacy extensions in RFC 3041 without the need for further DAD messages. Appendix C Transition Issues IETF has specified a number of IPv4 / IPv6 transition mechanisms [RFC-2893] to ensure smooth transition from IPv4 to IPv6 and interoperability between IPv4 and IPv6 during the transition period. The three main transition methods from a cellular network point of view are dual IPv4 / IPv6 stacks, tunneling and protocol translators, such as NAT-PT or SIIT. It is recommended that cellular hosts have dual IPv4 / IPv6 stacks to be able to interoperate with both IPv4 and IPv6 domains and use both IPv6 and IPv4 applications / services. Tunneling (for example RFC 3056 - Connection of IPv6 Domains via IPv4 Clouds) should be carried out in the network. In addition, any protocol translation function, such as NAT-PT, should be implemented in the network, not in the cellular host. The tunneling mechanism specified by [RFC-2529] is not relevant for a cellular host. [RFC-2529] allows isolated IPv6-only hosts to connect to an IPv6 router via an IPv4 domain. The scenario of an IPv6-only host in an IPv4-only cellular network is considered unlikely. Manyfolks [Page 20]