Network Working Group                                           J. Arkko
Request for Comments: 3316                                   G. Kuijpers
Category: Informational                                       H. Soliman
                                                                Ericsson
                                                             J. Loughney
                                                             J. Wiljakka
                                                                   Nokia
                                                              April 2003

Internet Protocol Version 6 (IPv6)
for Some Second and Third Generation Cellular Hosts

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

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 Internet
   Protocol version 6 (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.  This document also
   lists basic components of IPv6 functionality and discusses some
   issues relating to the use of these components when operating in
   these networks.

   1. Introduction.....................................................3
      1.1  Scope of this Document......................................3
      1.2  Abbreviations...............................................4
      1.3  Cellular Host IPv6 Features.................................5
   2. Basic IP.........................................................5
      2.1  RFC1981 - Path MTU Discovery for IP Version 6...............5
      2.2  RFC3513 - IP Version 6 Addressing Architecture..............6
      2.3  RFC2460 - Internet Protocol Version 6.......................6
      2.4  RFC2461 - Neighbor Discovery for IPv6.......................7
      2.5  RFC2462 - IPv6 Stateless Address Autoconfiguration..........8
      2.6  RFC2463 - Internet Control Message Protocol for the IPv6....8
      2.7  RFC2472 - IP version 6 over PPP.............................9
      2.8  RFC2473 - Generic Packet Tunneling in IPv6 Specification....9
      2.9  RFC2710 - Multicast Listener Discovery (MLD) for IPv6.......9
      2.10 RFC2711 - IPv6 Router Alert Option.........................10
      2.11 RFC3041 - Privacy Extensions for Address Configuration
                     in IPv6 .........................................10
      2.12 Dynamic Host Configuration Protocol for IPv6 (DHCPv6)......10
      2.13 RFC3484 - Default Address Selection for IPv6...............11
      2.14 DNS........................................................11
   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.........................12
      3.4  RFC2403 - The Use of HMAC-MD5-96 within ESP and AH.........12
      3.5  RFC2404 - The Use of HMAC-SHA-96 within ESP and AH.........12
      3.6  RFC2405 - The ESP DES-CBC Cipher Algorithm With
                     Explicit IV......................................12
      3.7  RFC2406 - IP Encapsulating Security Payload (ESP)..........12
      3.8  RFC2407 - The Internet IP Security DoI for ISAKMP..........12
      3.9  RFC2408 - The Internet Security Association and Key
                     Management Protocol..............................13
      3.10 RFC2409 - The Internet Key Exchange (IKE)..................13
      3.11 RFC2410 - The NULL Encryption Algorithm & its Use
                     With IPsec.......................................14
      3.12 RFC2451 - The ESP CBC-Mode Cipher Algorithms...............14
   4. Mobility........................................................14
   5. Security Considerations.........................................14
   6. References......................................................16
      6.1  Normative..................................................16
      6.2  Informative................................................18
   7. Contributors....................................................19
   8. Acknowledgements................................................19
   Appendix A - Cellular Host IPv6 Addressing in the 3GPP Model.......20
   Authors' Addresses.................................................21
   Full Copyright Statement...........................................22

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 for IP Multimedia Subsystem (IMS) starting from
   Release 5.

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 with discussion on 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.

   This document is informational in nature, and it is not intended to
   replace, update, or contradict any IPv6 standards documents [RFC-
   2026].

   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.

   - 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
   document has been 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, the
   analysis of the effects of error-prone links to performance in [RFC-
   3155], or the TCP work in [RFC-3481].

   Transition mechanisms used by cellular hosts are not described in
   this document and are left for further study.

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

1.3 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 are described.

     Mobility

          In this group, IP layer mobility issues are described.

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 Section 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 RFC3513 - IP Version 6 Addressing Architecture

The IPv6 Addressing Architecture [RFC-3513] is a mandatory part of
IPv6.

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 (see Section 5 of RFC2460).

   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 (DoS) 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.

2.4.1 Neighbor Discovery in 3GPP Networks

   A cellular host must support Neighbor Solicitation and Advertisement
   messages.

   In GPRS and UMTS networks, some Neighbor Discovery messages can be
   unnecessary in certain cases.  GPRS and UMTS links resemble a point-
   to-point link; hence, the cellular host's only neighbor on the
   cellular link is the default router that is already known through
   Router Discovery.  There are no link layer addresses.  Therefore,
   address resolution and next-hop determination are not needed.

   The cellular host must support neighbor unreachability detection as
   specified in [RFC-2461].

   In GPRS and UMTS networks, it is very desirable to conserve
   bandwidth.  Therefore, the cellular host should include a mechanism
   in upper layer protocols to provide reachability confirmation when
   two-way IP layer reachability can be confirmed (see RFC-2461, Section
   7.3.1).  These confirmations will allow the suppression of most NUD-
   related messages in most cases.

   Host TCP implementation should provide reachability confirmation in
   the manner explained in RFC 2461, Section 7.3.1.

   The common use of UDP in 3GPP networks poses a problem for providing
   reachability confirmation.  UDP itself is unable to provide such
   confirmation.  Applications running over UDP should provide the
   confirmation where possible.  In particular, when UDP is used for
   transporting RTP, the RTCP protocol feedback should be used as a
   basis for the reachability confirmation.  If an RTCP packet is
   received with a reception report block indicating some packets have
   gone through, then packets are reaching the peer.  If they have
   reached the peer, they have also reached the neighbor.

   When UDP is used for transporting SIP, responses to SIP requests
   should be used as the confirmation that packets sent to the peer are
   reaching it.  When the cellular host is acting as the server side SIP
   node, no such confirmation is generally available.  However, a host
   may interpret the receipt of a SIP ACK request as confirmation that
   the previously sent response to a SIP INVITE request has reached the
   peer.

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.  In
   addition, the default router (GGSN) will not configure or assign to
   its interfaces, any addresses based on prefixes delegated to IPv6
   hosts.  Thus, the host is not required to perform Duplicate Address
   Detection on the cellular interface.

   See Appendix A 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.

   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] must be supported by cellular
   hosts.

   MLD requires that MLD messages be sent for link-local multicast
   addresses (excluding the all-nodes address).  The requirement that
   MLD be run even for link-local addresses aids layer-two devices
   (e.g., Ethernet bridges) that attempt to suppress the forwarding of
   link-layer multicast packets to portions of the layer-two network
   where there are no listeners.  If MLD is used to announce the

   presence of listeners for all IP multicast addresses (including
   link-local multicast addresses), layer 2 devices can snoop MLD
   messages to reliably determine which portions of a network IP
   multicast messages need to be forwarded to.

2.9.1 MLD in 3GPP Networks

   Within 3GPP networks, hosts connect to their default routers (GGSN)
   via point-to-point links.  Moreover, there are exactly two IP devices
   connected to the point-to-point link, and no attempt is made (at the
   link-layer) to suppress the forwarding of multicast traffic.
   Consequently, sending MLD reports for link-local addresses in a 3GPP
   environment may not always be necessary.

   MLD is needed for multicast group knowledge that is not link-local.

2.10 RFC2711 - IPv6 Router Alert Option

   The Router Alert Option [RFC-2711] must be supported, and its use is
   required when MLD is used (see Section 2.9) or when RSVP [RFC-2205]
   is used.

2.11 RFC3041 - Privacy Extensions for Address Configuration in IPv6

   Privacy Extensions for Stateless Address Autoconfiguration [RFC-3041]
   should be supported.  RFC 3041, and privacy in general, is important
   for the Internet.  Cellular hosts may use the temporary addresses as
   described in RFC 3041.  However, the use of the Privacy Extension in
   an environment where IPv6 addresses are short-lived may not be
   necessary.  At the time this document has been written, there is no
   experience on how long-lived cellular network address assignments
   (i.e., attachments to the network) are.  The length of the address
   assignments depends upon many factors such as radio coverage, device
   status and user preferences.  Additionally, the use of temporary
   address with IPsec may lead to more frequent renegotiation for the
   Security Associations.

   Refer to Section 5 for a discussion of the benefits of privacy
   extensions in a 3GPP network.

2.12 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.

2.13 RFC3484 - Default Address Selection for IPv6

Default Address Selection [RFC-3484] is needed for cellular hosts.

2.14 DNS

   Cellular hosts should support DNS, as described in [RFC-1034], [RFC-
   1035], [RFC-1886], and [RFC-3152].

   If DNS is used, a cellular host can perform DNS requests in the
   recursive mode, to limit signaling over the air interface.  Both the
   iterative and the recursive approach should be supported, however, as
   the specifications require implementation of the iterative approach,
   and allow the recursive approach as an option.  Furthermore, all DNS
   servers may not support recursive queries, and the security benefits
   of DNS Security cannot always be achieved with them.

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, Sections 3.1 to 3.13, lists the
   specifications 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.
   This discussion focuses on the use of IPsec.  In some applications, 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.

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.  These
   new algorithms are useful, and should be supported as soon as their
   standardization is ready.

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.  Work on such simplifications would be
   useful, but is outside the scope of this document.

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.

   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
   all IPv6 hosts due to Mobile IP.  The movement of cellular hosts
   within 3GPP networks is handled by link layer mechanisms.

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 DoS 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 Section 3 and recommendations are given there.

   - Section 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 mitigate these problems to an extent,
     it is still apparent that DoS 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 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

   [RFC-1035]  Mockapetris, P., "Domain names - implementation and
               specification", STD 13, RFC 1035, November 1987.

   [RFC-1886]  Thomson, S. and C. Huitema, "DNS Extensions to support IP
               version 6, RFC 1886, December 1995.

   [RFC-1981]  McCann, J., Mogul, J. and S. Deering, "Path MTU Discovery
               for IP version 6", RFC 1981, August 1996.

   [RFC-2026]  Bradner, S., "The Internet Standards Process -- Revision
               3", BCP 9, RFC 2026, October 1996.

   [RFC-2104]  Krawczyk, K., Bellare, M. and R. Canetti, "HMAC:  Keyed-
               Hashing for Message Authentication", RFC 2104, February
               1997.

   [RFC-2246]  Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
               RFC 2246, January 1999.

   [RFC-2401]  Kent, S. and R. Atkinson, "Security Architecture for the
               Internet Protocol", RFC 2401, November 1998.

   [RFC-2402]  Kent, S. and R. Atkinson,  "IP Authentication Header",
               RFC 2402, November 1998.

   [RFC-2403]  Madson, C., and R. Glenn, "The Use of HMAC-MD5 within ESP
               and AH", RFC 2403, November 1998.

   [RFC-2404]  Madson, C., and R. Glenn, "The Use of HMAC-SHA-1 within
               ESP and AH", RFC 2404, November 1998.

   [RFC-2405]  Madson, C. and N. Doraswamy, "The ESP DES-CBC Cipher
               Algorithm With Explicit IV", RFC 2405, November 1998.

   [RFC-2406]  Kent, S. and R. Atkinson, "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 J. Turner,
               "Internet Security Association and Key Management
               Protocol (ISAKMP)", RFC 2408, November 1998.

   [RFC-2409]  Harkins, D. and D. Carrel, "The Internet Key Exchange
               (IKE)", RFC 2409, November 1998.

   [RFC-2410]  Glenn, R. and S. Kent, "The NULL Encryption Algorithm and
               Its Use With IPsec", RFC 2410, November 1998.

   [RFC-2451]  Pereira, R. and R. Adams, "The ESP CBC-Mode Cipher
               Algorithms", RFC 2451, November 1998.

   [RFC-2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
               (IPv6) Specification", RFC 2460, December 1998.

   [RFC-2461]  Narten, T., Nordmark, E. and W. Simpson, "Neighbor
               Discovery for IP Version 6 (IPv6)", RFC 2461, December
               1998.

   [RFC-2462]  Thomson, S. and T. Narten, "IPv6 Stateless Address
               Autoconfiguration", RFC 2462, December 1998.

   [RFC-2463]  Conta, A. and S. Deering, "ICMP for the Internet Protocol
               Version 6 (IPv6)", RFC 2463, December 1998.

   [RFC-2473]  Conta, A. and S. Deering, "Generic Packet Tunneling in
               IPv6 Specification", RFC 2473, December 1998.

   [RFC-2710]  Deering, S., Fenner, W. and B. Haberman, "Multicast
               Listener Discovery (MLD) for IPv6", RFC 2710, October
               1999.

   [RFC-2711]  Partridge, C. and A. Jackson, "IPv6 Router Alert Option",
               RFC 2711, October 1999.

   [RFC-2874]  Crawford, M. and C. Huitema, "DNS Extensions to Support
               IPv6 Address Aggregation and Renumbering", RFC 2874, July
               2000.

   [RFC-3041]  Narten, T. and R. Draves, "Privacy Extensions for
               Stateless Address Autoconfiguration in IPv6", RFC 3041,
               January 2001.

   [RFC-3152]  Bush, R., "Delegation of IP6.ARPA", BCP 49, RFC 3152,
               August 2001.

   [RFC-3155]  Dawkins, S., Montenegro, G., Kojo, M., Magret, V. and N.
               Vaidya, "End-to-end Performance Implications of Links
               with Errors", BCP 50, RFC 3155, August 2001.

   [RFC-3484]  Draves, R., "Default Address Selection for Internet
               Protocol version 6 (IPv6)", RFC 3484, February 2003.

   [RFC-3513]  Hinden, R. and S. Deering, "Internet Protocol Version 6
               (IPv6) Addressing Architecture", RFC 3513, April 2003.

6.2. Informative

   [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)

   [DHCPv6]    Bound, J., et al., "Dynamic Host Configuration Protocol
               for IPv6 (DHCPv6)", Work in progress.

   [RFC-1034]  Mockapetris, P., "Domain names - concepts and
               facilities", STD 13, RFC 1034, November 1987.

   [RFC-2529]  Carpenter, B. and C. Jung, "Transmission of IPv6 over
               IPv4 Domains without Explicit Tunnels", RFC 2529, March
               1999.

   [RFC-2205]  Braden, R., Zhang, L., Berson, S., Herzog, S. and S.
               Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
               Functional Specification", RFC 2205, September 1997.

   [RFC-3314]  Wasserman, M., Editor, "Recommendations for IPv6 in Third
               Generation Partnership Project (3GPP) Standards, RFC
               3314, September 2002.

   [RFC-3481]  Inamura, H., Montenegro, G., Ludwig, R., Gurtov, A. and
               F. Khafizov, "TCP over Second (2.5G) and Third (3G)
               Generation Wireless Networks", BCP 71, RFC 3481, February
               2003.

   [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. Contributors

   This document is based on the results of a team that included Peter
   Hedman and Pertti Suomela in addition to the authors.  Peter and
   Pertti have contributed both text and their IPv6 experience to this
   document.

8. 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
   Isomaki, Petter Johnsen, Janne Rinne, Jonne Soininen, Vlad Stirbu and
   Shabnam Sultana for their comments and input in preparation of this
   document.

Appendix A - 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.  The GGSN provides the cellular host
   with the interface identifier, usually in a random manner.  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 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.

Authors' Addresses

   Jari Arkko
   Ericsson
   02420 Jorvas
   Finland

   EMail: jari.arkko@ericsson.com

   Gerben Kuijpers
   Ericsson
   Skanderborgvej 232
   DK-8260 Viby J
   Denmark

   EMail: gerben.a.kuijpers@ted.ericsson.se

   John Loughney
   Nokia Research Center
   Itamerenkatu 11 - 13
   FIN-00180 HELSINKI
   Finland

   EMail: john.loughney@nokia.com

   Hesham Soliman
   Ericsson Radio Systems AB
   Torshamnsgatan 23, Kista, Stockholm
   Sweden

   EMail: hesham.soliman@era.ericsson.se

   Juha Wiljakka
   Nokia Mobile Phones
   Sinitaival 5
   FIN-33720 TAMPERE
   Finland

   EMail: juha.wiljakka@nokia.com

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