INTERNET-DRAFT Jari Arkko Internet Engineering Task Force Peter Hedman Gerben Kuijpers Hesham Soliman Ericsson John Loughney Pertti Suomela Juha Wiljakka Nokia Issued: February 22, 2002 Expires: August 22, 2002 Minimum IPv6 Functionality for a Cellular Host 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 an increasing number of cellular hosts are being connected to the Internet, IPv6 becomes necessary. Examples of such hosts are GPRS, UMTS, and CDMA2000 terminals. Standardization organizations are also making IPv6 mandatory in their newest specifications, such as the IP multimedia terminals specified for UMTS. However, the concept of IPv6 covers many aspects, numerous RFCs, a number of different situations, and is also partly still evolving. A rapid adoption of IPv6 is desired for cellular hosts. Yet these terminals vary greatly in terms of their processing capabilities and task orientation. Cellular host software often cannot be upgraded and must still meet tough demands for interoperability with other hosts, the cellular network, and the Internet. For these reasons it is necessary to understand how the IPv6 deployment starts and which parts of IPv6 are necessary under which situations. This document suggests basic IPv6 functionality for cellular hosts, and discusses when parts of the functionality is needed, and under which conditions. Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 Abstract............................................................1 1 Introduction......................................................3 1.1 Abbreviations..................................................5 1.2 Requirement Language...........................................5 1.3 Cellular Host IPv6 Features....................................6 2 Core IP...........................................................6 2.1 RFC1981 - Path MTU Discovery for IP Version 6..................6 2.2 RFC2373 - IP Version 6 Addressing Architecture.................6 2.3 RFC2374 - IPv6 Aggregatable Global Unicast Address Format......7 2.4 RFC2460 - Internet Protocol Version 6..........................7 2.5 RFC2461 - Neighbor Discovery for IPv6..........................8 2.6 RFC2462 - IPv6 Stateless Address Autoconfiguration.............8 2.7 RFC2463 - Internet Control Message Protocol for the IPv6.......9 2.8 RFC2472 - IP version 6 over PPP................................9 2.9 RFC2473 - Generic Packet Tunneling in IPv6 Specification.......9 2.10 RFC2710 - Multicast Listener Discovery (MLD) for IPv6.........9 2.11 RFC2711 - IPv6 Router Alert Option............................9 2.12 RFC2893 - Transition Mechanisms for IPv6 Hosts and Routers...10 2.13 RFC3041 - Privacy Extensions for Stateless AA in IPv6........10 2.14 RFC3056 - Connection of IPv6 Domains Via IPv4 Clouds.........10 2.15 Dynamic Host Configuration Protocol for IPv6 (DHCPv6)........10 2.16 Default Address Selection for IPv6...........................10 2.17 DNS..........................................................10 3 IP Security......................................................11 3.1 RFC2104 - HMAC: Keyed-Hashing for Message Authentication......12 3.2 RFC2401 - Security Architecture for the Internet Protocol.....12 3.3 RFC2402 - IP Authentication Header............................13 3.4 RFC2403 - The Use of HMAC-MD5-96 within ESP and AH............13 3.5 RFC2404 - The Use of HMAC-SHA-96 within ESP and AH............13 3.6 RFC2405 - The ESP DES-CBC Cipher Algorithm With Explicit IV...13 3.7 RFC2406 - IP Encapsulating Security Payload (ESP).............13 3.8 RFC2407 - The Internet IP Security DoI for ISAKMP.............13 3.9 RFC2408 û Internet Security Association and Key Mgmt Protocol.13 3.10 RFC2409 - The Internet Key Exchange (IKE)....................14 3.11 RFC2410 - The NULL Encryption Algorithm & its Use With IPsec.14 3.12 RFC2411 - IP Security Document Roadmap.......................14 3.13 RFC2451 - The ESP CBC-Mode Cipher Algorithms.................14 3.14 IP Security Remote Access....................................14 3.15 The AES Cipher Algorithm and Its Use With IPsec..............15 4 IP Mobility......................................................15 5 Security Considerations..........................................15 6 References.......................................................17 6.1 Normative.....................................................17 6.2 Non-Normative.................................................19 7 Acknowledgements.................................................20 8 Authors' Addresses...............................................20 Appendix A Revision History........................................22 Appendix B Cellular Host IPv6 Addressing in the 3GPP Model.........22 Appendix C Transition Issues.......................................23 Appendix D Mobility Issues.........................................23 Manyfolks [Page 2] Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 D.1 Mobility Support in IPv6.....................................23 D.2 Fast Handovers for Mobile IPv6...............................25 D.3 Hierarchical MIPv6 Mobility Management (HMIPv6)..............25 D.4 Mobile IP Security...........................................25 1 Introduction Technologies such as GPRS (General Packet Radio Service), UMTS (Universal Mobile Telecommunications System), and CDMA2000 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 newest specifications. One example of this is that 3GPP (Third Generation Partnership Project) specifies IPv6 support as mandatory for future UMTS IP multimedia terminals [3GPP-IMS]. The purpose of this draft is to propose a compact set of IPv6 specifications and functionality that cellular hosts must support. Such a specification is necessary in order to determine the optimal way to use IPv6 in a cellular environment. Important considerations are how to minimize footprint and implementation effort for a large number of consumer terminals, eliminate unnecessary user confusion with regards to configuration options, ensure interoperability and to provide an easy reference for those implementing IPv6 in a cellular host. The overarching desire is to ensure that cellular hosts are good citizens on the Internet. The main audiences of this document are the implementers who need guidance on what to implement, the IETF that wants to ensure a well- working global IPv6 network, and other standardization organizations that need a reference to how IPv6 can be mandated on their standards. For the purposes of this document, a cellular host is considered to be a terminal that uses an air interface to connect to a cellular access network (i.e. GPRS, UMTS, CDMA2000) in order to provide IPv6 connectivity to an IP network. The functionality to provide this connectivity is outlined in this draft. The description is made from a general cellular host point of view, and this document is intended to be applicable for many types of cellular network standards, or even multi-standard devices. The implementation of parts of the IPv6 specification in specific cellular networks (such as the UMTS) may differ from the general recommendation. Where this applies, additional information is given on how to make that part of IPv6 work in that specific cellular network. This information can also be used to provide standardization bodies insight in which issues it may be necessary to revise in future releases of the particular cellular network specifications. Manyfolks [Page 3] Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 Parts of this document may also be applicable in other, non-cellular contexts, such as small IPv6 appliances with similar size and cost restrictions. The scope of this document, however, is the cellular hosts and it may not cover all issues relevant in those other contexts. The use of IPv6 within cellular networks implies an implementation of the IPv6 stack within a wide range of terminals. Such terminals may vary significantly in terms of capacity, task orientation and processing power. For instance, the smallest handheld terminals can have a very limited amount of memory, computational power, and battery capacity. Cellular hosts operate over low bandwidth wireless links with limited throughput. As such, there are certain optimizations that would be required for these hosts in order to fit the largest possible amount of terminals within an area of spectrum. Tough demands are set for interoperability of cellular hosts towards other hosts, the cellular network, and the Internet. It is often hard or impossible to upgrade a large number of cellular hosts to a new software version. The long lifetime of the terminals sets a requirement for old equipment to still work in newer versions of the network and other hosts. The concept of IPv6 covers many aspects, numerous RFCs, a number of different situations, and is also partly still in evolution. For these reasons it is necessary to understand how the IPv6 deployment starts and which parts of IPv6 are necessary under which situations. This document reviews the IPv6 functionality, grouped under three categories: core IP, security, and mobility. For each category and each RFC in them, we discuss the following: - Is this part of functionality needed by cellular hosts and under which conditions? - In some cases individual parts of the RFCs are discussed in more detail and recommendations are given regarding their support. - In some other cases conflicts between some parts of functionality and the current cellular network protocols are identified. The aim of this work is to introduce a minimal set of IPv6 functionality û subject to the particular type of terminal and application û that would be required for cellular IPv6 hosts. As a general guideline, a cellular host should not appear any different from other IPv6 hosts. The set of requirements proposed should be suited to terminals with minimal capabilities, low cost and processing power. Interoperability can be achieved by listing needed IPv6 related IETF specifications according to chapter 1.3. The scope of the discussion in this document is the IPv6 functionality. The reader should be advised that other,non-IPv6 Manyfolks [Page 4] Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 specific 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]. The history of IPv6 in 3GPP specifications is briefly described in this paragraph. IPv6 was introduced as an option starting in 3GPP and ETSI Release 97 GSM / GPRS specifications. A wider support for IPv6 and the introduction of UMTS starts with 3GPP Release 99 networks and terminals. IPv6 is specified as the only IP version supported in Release 5 for IP Multimedia Subsystem (IMS). The authors used 3GPP Release 99 and Release 4 specifications as defined when this document was written as a base. Any possible changes to current IPv6 specifications shall be accommodated as they occur. The authors of this document seek feedback to ensure that the proposed functionality set is consistent, interoperable with the rest of the IPv6 Internet, complete, and does not open new security risks. 1.1 Abbreviations 3GPP Third Generation Partnership Project AH Authentication Header APN Access Point Name. The APN is a logical name referring to a GGSN and an external network. CDMA2000 Code Division Multiple Access 2000, the name identifying the third generation technology of IS-95 CDMA standard and ANSI-41 network. ESP Encapsulating Security Payload ETSI European Telecommunications Standards Institute IMS IP Multimedia Subsystem GGSN Gateway GPRS Support Node (a default router for cellular 3GPP IPv6 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 LAN 1.2 Requirement Language Manyfolks [Page 5] Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this document, are to be interpreted as described in [RFC-2119]. 1.3 Cellular Host IPv6 Features This specification defines IPv6 features for cellular hosts in three groups. Core IP In this group we describe the core parts of IPv6. IP Security In this group we discuss the security functionality suitable for cellular hosts. Chapter 3 defines the contents of this group, and discusses its usage in different contexts. IP Mobility In this group we discuss IP layer mobility functionality for cellular hosts. Basic functionality needed just to correspond with mobile nodes is a part of the Core IP group. Chapter 4 defines the contents of the IP Mobility group, and discusses its usage in different contexts. 2 Core IP This section describes the minimum needed IPv6 functionality of a cellular host in order to be able to communicate with other IPv6 hosts. 2.1 RFC1981 - Path MTU Discovery for IP Version 6 Path MTU Discovery [RFC-1981] MAY be supported. 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 uplink packet size MUST be limited to 1280 octets (standard limit in [RFC-2460]). However, the cellular host MUST be able to receive packets with size up to the link MTU before reassembly. 2.2 RFC2373 - IP Version 6 Addressing Architecture The IPv6 Addressing Architecture [RFC-2373] MUST be supported. IPX & NSAP addresses SHOULD NOT be used. Currently, this RFC is being Manyfolks [Page 6] Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 updated by [ADDRARCHv3], therefore this draft MUST be supported as well. 2.3 RFC2374 - IPv6 Aggregatable Global Unicast Address Format The IPv6 Aggregatable Global Unicast Address Format is described in [RFC-2374]. This RFC MUST be supported. 2.4 RFC2460 - Internet Protocol Version 6 The Internet Protocol Version 6 is specified in [RFC-2460]. This RFC MUST be supported. The cellular host is assumed to act as a host, not as a router. Implementation requirements for a cellular router are not defined in this document. 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 at least minimal processing of each extension header: - 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: In the case of the Core IP functionality only, AH and ESP headers are treated as if the Security Association had not existed, i.e. - packets with these headers are dropped. When the IP Security functionality is in use, they are processed as specified in RFCs 2401, 2402, and 2406. - 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. A cellular host implementing the Core IP functionality will typically send packets containing either no extension headers or the Fragment header. However, a cellular host MAY generate any of the extension headers. Cellular Hosts will act as the destination when processing the Routing Header. 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 terminal's addresses. If not, however, the terminal MUST implement Manyfolks [Page 7] Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 error checks as specified in section 4.4 of RFC 2460. There is no need for the terminal to send Routing Headers. 2.5 RFC2461 - Neighbor Discovery for IPv6 Neighbor Discovery is described in [RFC-2461] and, in general, MUST be supported. In cellular networks, some Neighbor Discovery messages can cause unnecessary traffic and consume valuable (limited) bandwidth. All current cellular links resemble a point-to-point link, hence, a mobile terminalÆs only neighbour on the cellular link is the default router which is already known through Router Discovery. This router most likely will not be a final destination for the hostÆs 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, Neighbor Solicitation and Advertisement messages MAY be implemented for the cellular interface. In addition, a cellular host SHOULD NOT send the link layer sub-option on its cellular interface, and SHOULD silently ignore it if received on the same interface. 2.5.1 Neighbor Discovery in 3GPP 3GPP terminals only need to support Router Solicitations and Router Advertisements for 3GPP IPv6 Address Autoconfiguration. Neighbor Solicitations and Advertisements MAY be used for Neighbor Unreachability Detection (NUD). They are not needed for 3GPP IPv6 Stateless Address Autoconfiguration, since Duplicate Address Detection is not needed in this address assignment mechanism (see section 2.6.1). 2.6 RFC2462 - IPv6 Stateless Address Autoconfiguration IPv6 Stateless Address Autoconfiguration [RFC-2462] MAY be supported. 2.6.1 Stateless Address Autoconfiguration in 3GPP A 3GPP cellular host MUST process a Router Advertisement as stated in chapter 5.5.3 of [RFC-2462]. A cellular host SHOULD NOT perform Duplicate Address Detection on its cellular interface, as each delegated prefix is unique within its scope when allocated using the 3GPP IPv6 Stateless Address Autoconfiguration. See appendix B for more details on 3GPP IPv6 Stateless Address Autoconfiguration. Manyfolks [Page 8] Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 2.7 RFC2463 - Internet Control Message Protocol for the IPv6 The Internet Control Message Protocol for the IPv6 [RFC-2463] MUST be supported. As per RFC 2463 section 2, ICMPv6 requirements MUST be fully implemented by every IPv6 node. However, references to the use of IP Security (sections 5.1 and 5.2) are not relevant for Core IP features. 2.8 RFC2472 - IP version 6 over PPP IPv6 over PPP [RFC-2472] MUST be supported for cellular hosts that implement PPP. 2.8.1 IP version 6 over PPP in 3GPP A 3GPP cellular host MUST support the IPv6CP interface identifier option. This option is needed to be able to connect other non-3GPP devices to the Internet using a PPP link between the 3GPP 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 to be 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. 2.9 RFC2473 - Generic Packet Tunneling in IPv6 Specification Generic Packet Tunneling [RFC-2473] MAY be supported if needed for transition mechanisms and MUST be supported if the Mobile Node functionality of Mobile IP is implemented, as specified in chapter 4. 2.10 RFC2710 - Multicast Listener Discovery (MLD) for IPv6 Multicast Listener Discovery [RFC-2710] MAY be supported, if the cellular host supports multicast functionality. There is no need for MLD if the host supports only the well-known multicast addresses, such as the All Nodes Address or Solicited Node Multicast Address. 2.11 RFC2711 - IPv6 Router Alert Option The Router Alert Option [RFC-2711] MAY be supported. Since the cellular host is not a router, the receiver side of the Router Alert Option may be omitted. Manyfolks [Page 9] Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 2.12 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 RFC. 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. 2.13 RFC3041 - Privacy Extensions for Stateless AA in IPv6 Privacy Extensions for Stateless Address Autoconfiguration [RFC- 3041] MAY be supported. Refer to section 5 for a discussion of the benefits of privacy extensions in a 3GPP environment. 2.14 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. Hence, 6to4 tunneling SHOULD be carried out by intermediate 6to4 routers rather than the cellular host. 2.15 Dynamic Host Configuration Protocol for IPv6 (DHCPv6) The Dynamic Host Configuration Protocol for IPv6 [DHCPv6] MAY be supported. DHCP is not needed when IPv6 stateless autoconfiguration is used, and no other functions of DHCP are used. 2.16 Default Address Selection for IPv6 Default Address Selection for IPv6 [DEFADDR] SHOULD be supported since cellular hosts can have more than one IPv6 address. 2.17 DNS Cellular hosts SHOULD support DNS, as described in [RFC-1034], [RFC- 1035] and [RFC-1886]. 2.17.1 RFC2874 - DNS Extensions to Support IPv6 Address Aggregation and Renumbering DNS Extensions to Support IPv6 Address Aggregation and Renumbering [RFC-2874] SHOULD NOT be supported. A6 can cause problems for cellular hosts operating over wireless links since several round trips may be needed to collect a complete DNS record, when a DNS resolver is implemented on a cellular host. 2.17.2 IPv6 Stateless DNS discovery Manyfolks [Page 10] Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 [DNS-DISC] shows a mechanism that allows hosts to discover a DNS in a stateless manner. When DNS is supported cellular hosts MUST have level 1 compliance. 2.17.3 Using DHCPv6 for DNS Configuration in Hosts A cellular host that supports both DHCPv6 and DNS SHOULD support [DNS-DHCP] for stateful configuration of DNS server addresses. 2.17.4 DNS use in 3GPP Some networks may provide DNS-proxy service for simple cellular hosts. Therefore, generally, DNS MAY be supported. A cellular host SHOULD perform DNS requests in the recursive mode, to limit signaling over the air interface. 3 IP Security The need for IP Security [RFC-2401] or other security mechanisms in cellular hosts depends on their intended use. The following services are discussed here: - End-to-end IPsec VPN service, e.g. to a corporate intranet - Web browsing service - IPv6 control message protection service, e.g. for ICMPv6 to the next hop router Recommendations are given on what security solution to employ for these services. We can not list all possible services here, and in general we expect application protocol RFCs to have requirements on what security services they MUST employ. For new applications, it is strongly suggested that some of the existing set of security mechanisms be used rather than new ones developed, adding to the amount of memory and implementation effort needed for a host supporting multiple services. We will now discuss the security mechanisms necessary for each service listed above. Note that if a recommended security mechanism has a wireless profile in the future, it SHOULD be supported. Cellular hosts that provide an end-to-end IPsec VPN service to a corporate intranet, for example, or to a transition-tunneling gateway MUST support IPsec and IKE. For this purpose an IPsec Remote Access solution SHOULD also be supported. This security set is defined in sections 3.1 to 3.15. Cellular hosts that provide a web browsing service SHOULD provide TLS [RFC-2246]. The use of security in a web browser is seen in most cases as very useful, as otherwise the user would be blocked from some of the sites - such as e-commerce sites - that do require security. The fact that just TLS should be the protocol to provide Manyfolks [Page 11] Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 web security relates to current deployment and the suitability of the single-side certificate trust model for this application. Even if a particular terminal does not support IP Security, it MUST be able to provide a clean indication to the other host that it is not willing to provide security associations. It is recommended that the terminal use ICMP Port Unreachable message for this. The use of IPsec, IKE, or other security services directly in the underlying IPv6 infrastructure communications (e.g. ICMPv6 or Neighbor Discovery) can also be discussed. The use of IPsec towards a specific home server in the context of a VPN service is easy. However, the use of any security service to local next hop routers (GGSNs) or other 3GPP nodes seems hard due to the difficulties in establishing a suitable trust infrastructure for creating the necessary Security Associations (SAs). In order for a terminal to create a SA with the next hop router for the purposes of securing the router and neighbor discovery tasks would mean the following. First, both the routers and all cellular hosts would have to be registered to a PKI system. Second, a trusted Certificate Authority (CA) would have to be found that encompasses both the visiting cellular host of an operator as well as the infrastructure of another operator. It is not clear if this is possible with today's technology. Furthermore, as [ICMPIKEv6] points out, dynamic SA negotiation can't be used for the protection of the first few connectivity establishment messages in ICMPv6. It may be possible to overcome these problems, however, the added security benefits of the protection in these cases would be minimal: encrypted radio communications exist at a lower layer, and the next hop router can always engage in any denial-of-service attacks (such as dropping all packets) regardless of the existence of any SAs. For these reasons, the 3GPP terminals will not be mandated to support any security for the pure IPv6 router and infrastructure protection purposes. The following subchapters are only applicable for those services where IPsec/IKE is recommended above. The below chapters define a simple wireless minimum profile for IPsec/IKE. What is recommended here for a specific service does not apply to other services, and use of a security service for some other service may imply a different set of protocols to be employed 3.1 RFC2104 - HMAC: Keyed-Hashing for Message Authentication This RFC [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 RFC [RFC-2401] MUST be supported. Manyfolks [Page 12] Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 3.3 RFC2402 - IP Authentication Header This RFC [RFC-2402] MAY be supported. The AH protocol is one of the alternative protocols in the IPsec protocol family, the other alternative being ESP. In the interest of minimizing implementation complexity and in particular configuration options, both protocols may not be needed in a cellular host. It is suggested that the ESP protocol be preferred for its confidentiality protection function. 3.4 RFC2403 - The Use of HMAC-MD5-96 within ESP and AH This RFC [RFC-2403] MUST be supported. 3.5 RFC2404 - The Use of HMAC-SHA-96 within ESP and AH This RFC [RFC-2404] MUST be supported. 3.6 RFC2405 - The ESP DES-CBC Cipher Algorithm With Explicit IV This RFC [RFC-2405] MAY be supported. It is, however, recommended that stronger algorithms than DES be supported. 3.7 RFC2406 - IP Encapsulating Security Payload (ESP) This RFC [RFC-2406] MUST be supported. 3.8 RFC2407 - The Internet IP Security DoI for ISAKMP This RFC [RFC-2407] MUST be supported. 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. 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. For instance, the use of pre-shared secrets as an authentication method in IKE is not feasible in practice in the context of a large number of hosts. Although work on such simplifications is useful, is not described here. 3.9 RFC2408 û Internet Security Association and Key Management Protocol This RFC [RFC-2408] MUST be supported. Manyfolks [Page 13] Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 3.10 RFC2409 - The Internet Key Exchange (IKE) This RFC [RFC-2409] MUST be supported. Note that a new version of the IKE protocol is being developed and is expected to replace it at a future time. 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, this specification recommends that 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. 3.11 RFC2410 - The NULL Encryption Algorithm & its Use With IPsec This RFC [RFC-2410] MUST be supported. 3.12 RFC2411 - IP Security Document Roadmap This RFC [RFC-2411] is of informational nature only. 3.13 RFC2451 - The ESP CBC-Mode Cipher Algorithms This RFC [RFC-2451] MUST be supported if encryption algorithms other than DES are implemented, e.g.: CAST-128, RC5, IDEA, Blowfish, 3DES. 3.14 IP Security Remote Access IPsec is often used in situations where legacy RADIUS or other authentication is desired instead of PKI-based authentication. Manyfolks [Page 14] Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 Cellular hosts offering VPN services to corporate intranets SHOULD support PIC [PIC]. 3.15 The AES Cipher Algorithm and Its Use With IPsec This specification [AESIPSEC] MUST be supported. We suggest here that in a new environment such as the cellular IPv6 older and insecure algorithms such as DES should not be used, and that the most secure and lightweight new ones should be used instead. Due to better efficiency we suggest the use of AES instead of 3DES. 4 IP Mobility Mobile IPv6 manages IP mobility resulting from the change in Care of Address (CoA) when a host moves within the Internet topology. However, at the time this is being written Mobile IPv6 specification is not yet an RFC and may change. Appendix D discusses the level of support of MIPv6 needed by cellular hosts and highlights the scenarios in which such support is useful. Some aspects of securing MIPv6 are also currently being debated. Yet at the same time the first cellular IPv6 hosts need to be produced. Implementors should therefore consider the implications of relying on preliminary information. We will also indicate certain functions that are particularly prone to modifications, and describe the tradeoffs involved. 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. In the following, we discuss such situations: - The suggested limitations (Section 2.4) 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, in most cases, assign new addresses to hosts in roaming situations and typically also when the cellular terminals 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 terminal is possible through its address. On the other hand, since a GGSNÆs coverage area is expected to be very large when compared to currently deployed default routers (no handovers between GGSNs are possible), a cellular host is likely to keep an address for a long time in Manyfolks [Page 15] Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 practise. Hence, IPv6 addressing privacy can be used for additional privacy during the time the terminal 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. Recommendations are given to support VPN-type tunneling to home networks, but to avoid the use of any security services in towards visited network nodes. This does not appear to open any new vulnerabilities, as ICMPv6 protection isnÆt possible in large scale today either. - Chapter 3 further discusses a specific profile of IPsec suitable for cellular implementations. Deviations from the standard RFCs are suggested mainly due to a desire to adopt the latest advances, such as the AES algorithm. On the other hand it is suggested to employ only the ESP protocol for reasons of reducing complexity. ESP provides a different protection than AH, which may have security implications. - As Chapter 4 mandates only the support of the Mobile IP Home Address option and not the full, optimized correspondent node behavior, the security problems related to Binding Updates are not relevant for nodes supporting only the Core IP features. However, security issues involving the Home Address Option MUST be solved before Chapter 2 recommendation of mandatory support can go forward. - The air-time 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 air-time is used correctly and no extra charges are applied to users due to misbehaving third parties. The wireless 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 QoS mechanisms mitigate these problems to an extent, it is still apparent that Denial-of- Service aspects may be highlighted in the cellular environment. It is possible for 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 Manyfolks [Page 16] Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 still an area of further study. It is also often easy to fill the wireless link and queues on both sides with additional or large packets. - In certain areas of the world it is possible to buy a prepaid cellular subscription without presenting personal identification. This could be leveraged by attackers that wish to remain unidentified. We 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, we recommend that any local network interface SHOULD have access controls to prevent bypassers from using the cellular host as an intermediary. 6 References 6.1 Normative [ADDRARCHv3] Hinden, R. and Deering, S. ôIP Version 6 Addressing Architectureö, Work in progress. [AESIPSEC] Frankel, S., Kelly, S. and Glenn, R., "The Candidate AES Cipher Algorithms and Their Use With IPsec", 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. [DNS-DHCP] Aboba, B., Droms R. and Narten T., ôUsing DHCPv6 for DNS Configuration in Hostsö, Work in progress. [DNS-DISC] Thaler, D. and Hagina, J., ôIPv6 Stateless DNS Discoveryö, Work in progress. [PIC] Sheffer, Y., Aboba, B. and Krawczyk, H., ôPIC, a Pre- IKE Credential Provisioning Protocolö, Work in progress. Manyfolks [Page 17] Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 [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. [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-2374] Hinden, R., O'Dell, M. and Deering, S., "An IPv6 Aggregatable Global Unicast Address Format", RFC 2374, 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. Manyfolks [Page 18] Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 [RFC-2410] Glenn, R. and Kent, S., "The NULL Encryption Algorithm and Its Use With IPsec", RFC 2410, November 1998 [RFC-2411] Thayer, R., Doraswamy, N., and R. Glenn, "IP Security Document Roadmap", RFC 2411, 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. [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-IMS] 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; IP Multimedia (IM) Subsystem - Stage 2; (3G TS 23.228 version 5.3.0) Manyfolks [Page 19] Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 [HMIPv6] Soliman, H., Castelluccia, C., ElMalki, K., Bellier, L., "Hierarchical MIPv6 mobility management (HMIPv6)" Work in progress. [ICMPIKEv6] Arkko, J., öEffects of ICMPv6 on IKE and IPsec Policiesö, Expired Internet Draft, Available at http://www.arkko.com/publications/draft-arkko-icmpv6- ike-effects-00.txt. [MIPv6] Johnson D. and Perkins, C., "Mobility Support in IPv6", Work in progress. [MIPv6-FH] Dommety, G., Editor, et al, "Fast Handovers for Mobile IPv6", Work in progress. [RFC-1034] Mockapetris, P., "Domain names û concepts and facilities", RFC 1034, November 1987 [RFC-2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC-2529] Carpenter, B. and Jung, C., "Transmission of IPv6 over IPv4 Domains without Explicit Tunnelsö, RFC 2529, March 1999. [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. [TCPWIRELESS] Inamura, H. et al. ôTCP over 2.5G and 3G Networksö. IETF, Work in progress. 7 Acknowledgements The authors would like to thank David DeCamp, Karim ElMalki, Markus Isom„ki, Petter Johnsen, Janne Rinne, Jonne Soininen and Shabnam Sultana for their comments and input. 8 Authors' Addresses Jari Arkko Ericsson 02420 Jorvas Finland Phone: +358 40 5079256 Fax: +358 40 2993401 Manyfolks [Page 20] Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 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 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 û 13 FIN-00180 HELSINKI FINLAND Phone: +358 7180 36242 Fax: +358 7180 36851 E-mail: john.loughney@nokia.com Pertti Suomela Nokia Mobile Phones Visiokatu 3 FIN-33720 TAMPERE Finland Phone: +358 7180 40546 Fax: +358 7180 48381 E-mail: pertti.suomela@nokia.com Manyfolks [Page 21] Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 Juha Wiljakka Nokia Mobile Phones Visiokatu 3 FIN-33720 TAMPERE Finland Phone: +358 7180 47562 Fax: +358 7180 48381 E-mail: juha.wiljakka@nokia.com Appendix A Revision History Changes from draft-manyfolks-ipv6-cellular-host-02.txt: - Added [ADDRARCHv3] to section 2.2. - Minor change to section 2.5. - Minor change to section 2.6 and 2.6.1. - Added section 2.8.1 on IPv6 over PPP in 3GPP. - Removed section 2.13.1 on privacy extensions to stateless address autoconfiguration in 3GPP. - Added recommendation on use of recursive mode DNS in section 2.17. - Changed recommendation on DNS extensions to support IPv6 from MAY to SHOULD NOT in section 2.17.1. - Added section 2.17.2 and 2.17.3 on DNS discovery. - Moved section 2.18 to the introduction of section 3. - Section 3: Minor revisions throughout this section. - Section 4: revised to reflect current situation of MIPv6, specific drafts moved to a new appendix, Appendix D. - Section 5: revised the discussion on IP address privacy. - Seperated references into Normative and Non-normative references. 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 û 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 defined 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 Manyfolks [Page 22] Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 avoids the necessity to perform Duplicate Address Detection at the network level for every address built by the mobile terminal. The GGSN always provides an Interface Identifier to the mobile terminal. The Mobile terminal 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 hostÆs). 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 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. It is recommended that the most transition mechanisms are provided by the network in order to save the limited resources of the cellular host. Tunneling (for example RFC 3056 - Connection of IPv6 Domains via IPv4 Clouds) should be carried out in the network. Also 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. Appendix D Mobility Issues D.1 Mobility Support in IPv6 Mobile IPv6 is specified in [MIPv6]. Manyfolks [Page 23] Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 Mobile IP is required for hosts moving within the Internet topology. At the highest level, the Mobile IPv6 functionality within Mobile Nodes can be divided to the following parts: - Correspondent Node (CN) functionality, defined by Mobile IPv6 specification [MIPv6], i.e. the basic functionality needed to correspond with mobile nodes. - Mobile Node (MN) functionality [MIPv6]. This includes the ability to configure Home and Care-of-Addresses (CoA) send Binding Updates (BUs) and receive Binding Acknowledgements and Requests. In addition, this function also includes the ability to maintain a Binding Update List. - Route optimization. The functionality needed to correspond with mobile nodes in an optimal manner. We will discuss the use of each part in turn. The basic functionality of a Correspondent Node, i.e. process the Home Address Option, must be supported by all hosts. However, at the time this is being written, the Home Address Option is defined only in preliminary form in [MIPv6]. Furthermore, at present it is unclear whether this option can be understood by all nodes or only in conjunction with Route Optimization. This is due to the possible use of the option in Denial-of-Service attacks that employ CNs as reflectors. Cellular host implementors are advised that leaving out Home Address Option support may prevent their hosts to communicate with future MIPv6 MNs. On the other hand, the inclusion of Home Address Option without Route Optimization being active for that host may present a threat that allows the cellular hosts to be used as reflectors in Denial-of-Service attacks. The mobile node functionality is needed when the host itself will move within the Internet topology i.e. changes its care-of address. This function is needed in cellular systems where MIPv6 is used for intra-access technology mobility. In other cellular systems where intra-access technology mobility is handled by other means (e.g. GTP in a 3GPP system), hosts with additional, non-cellular interfaces must have this functionality if they need to retain session or IP layer reachability while moving between different access technologies, i.e. - to use MIPv6 for inter-system IP handovers. For instance, when a hosts has both a Wireless LAN (WLAN) and an UMTS interface, MIPv6 MN functionality is needed to retain sessions when moving from UMTS area to a WLAN area. The UMTS network provides a basic mobility service (layer 2 mobility) to all hosts without requiring the implementation of IP layer mobility. Hosts that have interfaces only to networks providing such other mobility services, or hosts that do not require session mobility through interface handovers MAY have this functionality for reachability when the DNS is used to locate a host. That is, when roaming between different cellular operators. A host, in this case, would require a home address in the DNS and a Home agent. When connected to a default Manyfolks [Page 24] Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 router for the host, the host would update its Home Agent with its new address. Mobile node functionality is fully defined in the Mobile IPv6 specifications and should only be implemented according to an official RFC. The Route Optimization functionality for a CN, i.e. processing of Binding Updates, should be supported by all hosts supporting the Mobile Node functions and may be supported by all hosts. Route Optimization functionality should also only be implemented according to an official RFC. D.2 Fast Handovers for Mobile IPv6 Fast handovers for Mobile IPv6 is specified in [MIPv6-FH]. This draft should be supported. D.2.1 3GPP and Fast Handovers Within the current 3GPP architecture, a cellular host will always keep the connection to the same GGSN (default router) for a context. Movement between default routers is not permitted. The only scenario where a MN would change default routers is in the case of a handover between two different access technologies. In this case the MN will be simultaneously connected to both routers, which would eliminate the need for anticipation through the current router. Hence the Fast Handovers draft will not be required within the current 3GPP architecture. D.3 Hierarchical MIPv6 Mobility Management (HMIPv6) Hierarchical MIPv6 is specified in [HMIPv6]. HMIPv6 should be supported to run MIPv6 efficiently over the air. This aims at reducing the number of MIPv6 BUs sent over the air while moving within the topology. D.3.1 HMIPv6 in 3GPP As mentioned above, Inter-GGSN handovers are not allowed within the current 3GPP architecture. Hence, the benefit of implementing HMIPv6 in 3GPP will only appear during the inter-access technology handover, which may not be as common as intra-access technology ones. However the architecture can benefit from the per-flow movement explained in the draft that allows a MN to receive different traffic flows on different interfaces. D.4 Mobile IP Security Manyfolks [Page 25] Internet Draft Min. IPv6 Func. for a Cellular Host February 22, 2002 Hosts that implement MIPv6 must support the security features defined in [MIPv6]. Note that MNs and CNs may have different requirements. Manyfolks [Page 26]