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RFC 3314 - Recommendations for IPv6 in Third Generation Partners


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Network Working Group                                  M. Wasserman, Ed.
Request for Comments: 3314                                    Wind River
Category: Informational                                   September 2002

                      Recommendations for IPv6 in
         Third Generation Partnership Project (3GPP) Standards

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

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

   This document contains recommendations from the Internet Engineering
   Task Force (IETF) IPv6 Working Group to the Third Generation
   Partnership Project (3GPP) community regarding the use of IPv6 in the
   3GPP standards.  Specifically, this document recommends that the 3GPP
   specify that multiple prefixes may be assigned to each primary PDP
   context, require that a given prefix must not be assigned to more
   than one primary PDP context, and allow 3GPP nodes to use multiple
   identifiers within those prefixes, including randomly generated
   identifiers.

   The IPv6 Working Group supports the use of IPv6 within 3GPP and
   offers these recommendations in a spirit of open cooperation between
   the IPv6 Working Group and the 3GPP community.  Since the original
   publication of this document as an Internet-Draft, the 3GPP has
   adopted the primary recommendations of this document.

Conventions Used In This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in BCP 14, RFC 2119
   [KEYWORD].

Table of Contents

   1       Introduction.............................................  2
   1.1     What is the 3GPP?........................................  3
   1.2     What is the IETF?........................................  4
   1.3     Terminology..............................................  4
   1.3.1   3GPP Terminology.........................................  4
   1.3.2   IETF Terminology.........................................  5
   1.4     Overview of the IPv6 Addressing Architecture.............  6
   1.5     An IP-Centric View of the 3GPP System....................  7
   1.5.1   Overview of the UMTS Architecture........................  7
   1.5.2   The PDP Context.......................................... 10
   1.5.3   IPv6 Address Autoconfiguration in GPRS................... 11
   2       Recommendations to the 3GPP.............................. 13
   2.1     Limitations of 3GPP Address Assignment................... 13
   2.2     Advertising Multiple Prefixes............................ 14
   2.3     Assigning a Prefix to Only One Primary PDP Context....... 14
   2.3.1   Is a /64 per PDP Context Too Much?....................... 15
   2.3.2   Prefix Information in the SGSN........................... 16
   2.4     Multiple Identifiers per PDP Context..................... 16
   3       Additional IPv6 Work Items............................... 16
   4       Security Considerations.................................. 17
   Appendix A:  Analysis of Findings................................ 18
   Address Assignment Solutions..................................... 18
   References....................................................... 19
   Authors and Acknowledgements..................................... 22
   Editor's Address................................................. 22
   Full Copyright Statement......................................... 23

1. Introduction

   In May 2001, the IPv6 Working Group (WG) held an interim meeting in
   Redmond, WA to discuss the use of IPv6 within the 3GPP standards.
   The first day of the meeting was a joint discussion with 3GPP, during
   which an architectural overview of 3GPP's usage of IPv6 was
   presented, and there was much discussion regarding particular aspects
   of IPv6 usage within 3GPP.  At that meeting, a decision was made to
   form a design team to write a document offering advice from the IPv6
   WG to the 3GPP community, regarding their use of IPv6.  This document
   is the result of that effort.

   This document offers recommendations to the 3GPP community from the
   IETF IPv6 Working Group.  It is organized into three main sections:

      1. An introduction (this section) that provides background
         information regarding the IETF IPv6 WG and the 3GPP and
         includes a high-level overview of the technologies discussed in
         this document.

      2. Recommendations from the IPv6 WG to the 3GPP community.  These
         can be found in section 2.

      3. Further work items that should be considered by the IPv6 WG.
         These items are discussed in section 3.

   It is the purpose of this document to provide advice from the IPv6
   Working Group to the 3GPP community.  We have limited the contents of
   this document to items that are directly related to the use of IPv6
   within 3GPP.  This document defines no standards, and it is not a
   definitive source of information regarding IPv6 or 3GPP.  We have not
   chosen to explore 3GPP-related issues with other IETF protocols
   (i.e., SIP, IPv4, etc.), as they are outside the scope of the IPv6
   Working Group.

   The IPv6 Working Group fully supports the use of IPv6 within 3GPP,
   and we encourage 3GPP implementers and operators to participate in
   the IETF process.  We are offering these suggestions in a spirit of
   open cooperation between the IPv6 Working Group and the 3GPP
   community, and we hope that our ongoing cooperation will help to
   strengthen both sets of standards.

   The 3GPP address allocation information in this document is based on
   the 3GPP document TS 23.060 version 4.1.0 [OLD-TS23060].  At the 3GPP
   plenary meeting TSG #15 in March 2002, the 3GPP adopted the two
   primary recommendations contained in this document, allocating a
   unique prefix to each primary PDP context when IPv6 stateless address
   autoconfiguration is used, and allowing the terminals to use multiple
   interface identifiers.  These changes were retroactively applied from
   3GPP release 99 onwards, in TS23.060 versions 3.11.0, 4.4.0 and 5.1.0
   [NEW-TS23060].

1.1 What is the 3GPP?

   The Third Generation Partnership Project (3GPP) is a global
   standardization partnership founded in late 1998.  Its Organizational
   Partners have agreed to co-operate in the production of technical
   specifications for a Third Generation Mobile System, based on the
   evolved GSM core networks.

   The 3GPP Organizational Partners consist of several different
   standardization organizations: ETSI from Europe, Standards Committee
   T1 Telecommunications (T1) in the USA, China Wireless
   Telecommunication Standard Group (CWTS), Korean Telecommunications
   Technology Association (TTA), the Association of Radio Industries and
   Businesses (ARIB), and the Telecommunication Technology
   Committee(TTC) in Japan.

   The work is coordinated by a Project Co-ordination Group (PCG), and
   structured into Technical Specification Groups (TSGs).  There are
   five TSGs: Core Network (TSG CN), Radio Access Networks (TSG RAN),
   Services and System Aspects (TSG SA), GSM/EDGE Radio Access Network
   (GERAN), and the Terminals (TSG T).  The TSGs are further divided
   into Working Groups (WGs).  The technical work is done in the working
   groups, and later approved in the TSGs.

   3GPP working methods are different from IETF working methods.  The
   major difference is where the majority of the work is done.  In 3GPP,
   the work is done in face-to-face meetings, and the mailing list is
   used mainly for distributing contributions, and for handling
   documents that were not handled in the meeting, due to lack of time.
   Decisions are usually made by consensus, though voting does exist.
   However, it is rather rare to vote.  3GPP documents are public and
   can be accessed via the 3GPP web site [3GPP-URL].

1.2 What is the IETF?

   The Internet Engineering Task Force (IETF) is a large, open,
   international community of network designers, operators, vendors, and
   researchers, concerned with the evolution of the Internet
   architecture and the smooth operation of the Internet.  The IETF is
   also the primary standards body developing Internet protocols and
   standards.  It is open to any interested individual.  More
   information about the IETF can be found at the IETF web site [IETF-
   URL].

   The actual technical work of the IETF is done in working groups,
   organized by topic into several areas (e.g., routing, transport,
   security, etc.).  The IPv6 Working Group is chartered within the
   Internet area of the IETF.  Much of the work is handled via mailing
   lists, and the IETF holds meetings three times per year.

1.3 Terminology

   This section defines the 3GPP and IETF terminology used in this
   document.  The 3GPP terms and their meanings have been taken from
   [TR21905].

1.3.1   3GPP Terminology

   APN          Access Point Name.  The APN is a logical name referring
                to a GGSN and an external network.

   CS           Circuit Switched

   GERAN        GSM/EDGE Radio Access Network

   GGSN         Gateway GPRS Support Node.  A router between the GPRS
                network and an external network (i.e., the Internet).

   GPRS         General Packet Radio Services

   GTP-U        General Tunneling Protocol - User Plane

   MT           Mobile Termination.  For example, a mobile phone
                handset.

   PDP          Packet Data Protocol

   PDP Context  A PDP connection between the UE and the GGSN.

   PS           Packet Switched

   SGSN         Serving GPRS Support Node

   TE           Terminal Equipment.  For example, a laptop attached
                through a 3GPP handset.

   UE           User Equipment (TE + MT + USIM).  An example would be
                a mobile handset with a USIM card inserted and a
                laptop attached.

   UMTS         Universal Mobile Telecommunications System

   USIM         Universal Subscriber Identity Module.  Typically, a
                card that is inserted into a mobile phone handset.

   UTRAN        Universal Terrestrial Radio Access Network

1.3.2   IETF Terminology

   IPv6         Internet Protocol version 6 [RFC 2460]

   NAS          Network Access Server

   NAT          Network Address Translator

   NAT-PT       Network Address Translation with Protocol Translation.
                An IPv6 transition mechanism. [NAT-PT]

   PPP          Point-to-Point Protocol [PPP]

   SIIT         Stateless IP/ICMP Transition Mechanism [SIIT]

1.4 Overview of the IPv6 Addressing Architecture

   The recommendations in this document are primarily related to IPv6
   address assignment.  To fully understand the recommended changes, it
   is necessary to understand the IPv6 addressing architecture, and
   current IPv6 address assignment mechanisms.

   The IPv6 addressing architecture represents a significant evolution
   from IPv4 addressing [ADDRARCH].  It is required that all IPv6 nodes
   be able to assemble their own addresses from interface identifiers
   and prefix information.  This mechanism is called IPv6 Host
   Autoconfiguration [AUTOCONF], and it allows IPv6 nodes to configure
   themselves without the need for stateful configuration servers (i.e.,
   DHCPv6) or statically configured addresses.

   Interface identifiers can be globally unique, such as modified EUI-64
   addresses [ADDRARCH], or non-unique, such as randomly generated
   identifiers.  Hosts that have a globally unique identifier available
   may also choose to use randomly generated addresses for privacy
   [PRIVADDR] or for other reasons.  IPv6 hosts are free to generate new
   identifiers at any time, and Duplicate Address Detection (DAD) is
   used to protect against the use of duplicate identifiers on a single
   link [IPV6ND].

   A constant link-local prefix can be combined with any interface
   identifier to build an address for communication on a locally
   attached link.  IPv6 routers may advertise additional prefixes
   (site-local and/or global prefixes)[IPV6ND].  Hosts can combine
   advertised prefixes with their own interface identifiers to create
   addresses for site-local and global communication.

   IPv6 introduces architectural support for scoped unicast addressing
   [SCOPARCH].  A single interface will typically have multiple
   addresses for communication within different scopes: link-local,
   site-local and/or global [ADDRARCH].  Link-local addresses allow for
   local communication, even when an IPv6 router is not present.  Some
   IPv6 protocols (i.e., routing protocols) require the use of link-
   local addresses.  Site-local addressing allows communication to be
   administratively contained within a single site.  Link-local or
   site-local connections may also survive changes to global prefix
   information (e.g., site renumbering).

   IPv6 explicitly associates each address with an interface.
   Multiple-interface hosts may have interfaces on more than one link or
   in more than one site.  Links and sites are internally identified
   using zone identifiers.  Proper routing of non-global traffic and
   proper address selection are ensured by the IPv6 scoped addressing
   architecture [SCOPARCH].

   IPv6 introduces the concept of privacy addresses [PRIVADDR].  These
   addresses are generated from an advertised global prefix and a
   randomly generated identifier, and are used for anonymous access to
   Internet services.  Applications control the generation of privacy
   addresses, and new addresses can be generated at any time.

   The IPv6 site renumbering specification [SITEREN] relies upon the
   fact that IPv6 nodes will generate new addresses when new prefixes
   are advertised on the link, and that they will deprecate addresses
   that use deprecated prefixes.

   In the future, additional IPv6 specifications may rely upon the
   ability of IPv6 nodes to use multiple prefixes and/or multiple
   identifiers to dynamically create new addresses.

1.5 An IP-Centric View of the 3GPP System

   The 3GPP specifications define a Third Generation Mobile System.  An
   overview of the packet switched (PS) domain of the 3GPP Release 99
   system is described in the following sections.  The authors hope that
   this description is sufficient for the reader who is unfamiliar with
   the UMTS packet switched service, to understand how the UMTS system
   works, and how IPv6 is currently defined to be used within it.

1.5.1   Overview of the UMTS Architecture

   The UMTS architecture can be divided into two main domains -- the
   packet switched (PS) domain, and the circuit switched (CS) domain.
   In this document, we will concentrate on the PS domain, or General
   Packet Radio Services (GPRS).

  ------
 |  TE  |
  ------
    |
    +R
    |
  ------   Uu  -----------   Iu  -----------   Gn  -----------   Gi
 |  MT  |--+--|   UTRAN   |--+--|   SGSN    |--+--|   GGSN    |--+--
  ------       -----------       -----------       -----------
   (UE)

                   Figure 1:  Simplified GPRS Architecture

  ------
 |      |
 |  App |- - - - - - - - - - - - - - - - - - - - - - - - -(to app peer)
 |      |
 |------|                                              -------------
 |  IP  |- - - - - - - - - - - - - - - - - - - - - - -|      IP     |->
 | v4/6 |                                             |     v4/6    |
 |------|      -------------       -------------      |------       |
 |      |     |  \ Relay /  |     |  \ Relay /  |     |      |      |
 |      |     |   \     /   |     |   \     /   |     |      |      |
 |      |     |    \   /    |     |    \   /    |     |      |      |
 | PDCP |- - -| PDCP\ /GTP_U|- - -|GTP_U\ /GTP_U|- - -|GTP_U |      |
 |      |     |      |      |     |      |      |     |      |      |
 |------|     |------|------|     |------|------|     |------|      |
 |      |     |      |  UDP |- - -|  UDP |  UDP |- - -| UDP  |      |
 |      |     |      |------|     |------|------|     |------|      |
 |  RLC |- - -|  RLC |  IP  |- - -|  IP  |  IP  |- - -| IP   |      |
 |      |     |      | v4/6 |     | v4/6 | v4/6 |     |v4/6  |      |
 |------|     |------|------|     |------|------|     |------|------|
 |  MAC |     |  MAC | AAL5 |- - -| AAL5 |  L2  |- - -| L2   |  L2  |
 |------|     |------|------|     |------|------|     |------|------|
 |  L1  |- - -|  L1  |  ATM |- - -|  ATM |  L1  |- - -| L1   |  L1  |
  ------       -------------       -------------       -------------

    UE             UTRAN                SGSN                GGSN
 (handset)

                       Figure 2:  GPRS Protocol Stacks

     ------
    |      |
    | App. |- - - - - - - - - - - - - - - - - - - - - - (to app peer)
    |      |
    |------|
    |      |
    |  IP  |- - - - - - - - - - - - - - - - - - - - - - (to GGSN)
    | v4/6 |
    |      |     |             |
    |------|     |-------------|
    |      |     |  \ Relay /  |
    |      |     |   \     /   |
    |      |     |    \   /    |
    |      |     |     \ / PDCP|- - - (to UTRAN)
    |      |     |      |      |
    |  PPP |- - -|  PPP |------|
    |      |     |      |  RLC |- - - (to UTRAN)
    |      |     |      |------|
    |      |     |      |  MAC |
    |------|     |------|------|
    |  L1a |- - -|  L1a |  L1b |- - - (to UTRAN)
     ------       -------------
       TE              MT
    (laptop)        (handset)

                 Figure 3:  Laptop Attached to 3GPP Handset

   The GPRS core network elements, shown in Figures 1 and 2, are the
   User Equipment (UE), Serving GPRS Support Node (SGSN), and Gateway
   GPRS Support Node (GGSN).  The UTRAN comprises Radio Access Network
   Controllers (RNC) and the UTRAN base stations.

   GGSN:  A specialized router that functions as the gateway between the
          GPRS network and the external networks, e.g., Internet.  It
          also gathers charging information about the connections.  In
          many ways, the GGSN is similar to a Network Access Server
          (NAS).

   SGSN:  The SGSN's main functions include authentication,
          authorization, mobility management, and collection of billing
          information.  The SGSN is connected to the SS7 network and
          through that, to the Home Location Register (HLR), so that it
          can perform user profile handling, authentication, and
          authorization.

   GTP-U: A simple tunnelling protocol running over UDP/IP and used to
          route packets between RNC, SGSN and GGSN within the same, or
          between different, UMTS backbone(s).  A GTP-U tunnel is
          identified at each end by a Tunnel Endpoint Identifier (TEID).

   Only the most significant elements of the GPRS system are discussed
   in this document.  More information about the GPRS system can be
   found in [OLD-TS23060].

1.5.2   The PDP Context

   The most important 3GPP concept in this context is a PDP Context.  A
   PDP Context is a connection between the UE and the GGSN, over which
   the packets are transferred.  There are two kinds of PDP Contexts --
   primary, and secondary.

   The primary PDP Context initially defines the link to the GGSN.  For
   instance, an IP address is assigned to each primary PDP Context.  In
   addition, one or more secondary PDP Contexts can be added to a
   primary PDP Context, sharing the same IP address.  These secondary
   PDP Contexts can have different Quality of Service characteristics
   than the primary PDP Context.

   Together, a primary PDP Context and zero or more secondary PDP
   Contexts define, in IETF terms, a link.  GPRS links are point-to-
   point.  Once activated, all PDP contexts have equal status, meaning
   that a primary PDP context can be deleted while keeping the link
   between the UE and the GGSN, as long as there are other (secondary)
   PDP contexts active for the same IP address.

   There are currently three PDP Types supported in GPRS -- IPv4, IPv6,
   and PPP.  This document will only discuss the IPv6 PDP Type.

   There are three basic actions that can be performed on a PDP Context:
   PDP Context Activation, Modification, and Deactivation.  These
   actions are described in the following.

   Activate PDP Context

         Opens a new PDP Context to a GGSN.  If a new primary PDP
         Context is activated, there is a new link created between a UE
         and a GGSN.  A UE can open multiple primary PDP Contexts to one
         or more GGSNs.

   Modify PDP Context

         Changes the characteristics of a PDP Context, for example QoS
         attributes.

   Deactivate PDP Context

         Deactivates a PDP Context.  If a primary PDP Context and all
         secondary PDP contexts associated with it are deactivated, a
         link between the UE and the GGSN is removed.

   The APN is a name which is logically linked to a GGSN.  The APN may
   identify a service or an external network.  The syntax of the APN
   corresponds to a fully qualified domain name.  At PDP context
   activation, the SGSN performs a DNS query to find out the GGSN(s)
   serving the APN requested by the terminal.  The DNS response contains
   a list of GGSN addresses from which the SGSN selects one (in a
   round-robin fashion).

                 ---------                           --------
                |         |                         |  GGSN  |
                |         |           LINK 1        |        |
                |      -======== PDP Context A ========-   - - -> ISP X
                |         |                         |        |
                |         |                         |        |
                |         |                         |        |
                |       /======= PDP Context B =======\      |
                |      -  |           LINK 2        |  -   - - -> ISP Y
                |       \======= PDP Context C =======/      |
                |         |                         |        |
                |   MT    |                          --------
                |(handset)|
                |         |                          --------
  --------      |         |                         |  GGSN  |
 |        |     |         |           LINK 3        |        |
 |        |     |      -======== PDP Context D ========-     |
 |   TE   |     |         |                         |        |
 |(laptop)|     |         |                         |      - - -> ISP Z
 |        |     |         |           LINK 4        |        |
 |     -====PPP====-----======== PDP Context E ========-     |
 |        |     |         |                         |        |
 |        |     |         |                         |        |
  --------       ---------                           --------

           Figure 3:  Correspondence of PDP Contexts to IPv6 Links

1.5.3   IPv6 Address Autoconfiguration in GPRS

   GPRS supports static and dynamic address allocation.  Two types of
   dynamic address allocation are supported -- stateless, and stateful.
   Stateful address configuration uses an external protocol to connect
   to a server that gives the IP address, e.g., DHCP.

   The stateless IPv6 autoconfiguration works differently in GPRS than
   in Ethernet networks.  GPRS nodes have no unique identifier, whereas
   Ethernet nodes can create an identifier from their EUI-48 address.
   Because GPRS networks are similar to dialup networks, the stateless
   address autoconfiguration in GPRS was based on PPPv6 [PPPV6].

   3GPP address autoconfiguration has the following steps:

      1. The Activate PDP Context message is sent to the SGSN (PDP
         Type=IPv6, PDP Address = 0, etc.).

      2. The SGSN sends a Create PDP Context message to the GGSN with
         the above parameters.

      3. GGSN chooses an interface identifier for the PDP Context and
         creates the link-local address.  It answers the SGSN with a
         Create PDP Context response (PDP Address = link-local address).

      4. The SGSN sends an Activate PDP Context accept message to the UE
         (PDP Address = link-local address).

      5. The UE keeps the link-local address, and extracts the interface
         identifier for later use.  The UE may send a Router
         Solicitation message to the GGSN (first hop router).

      6. After the PDP Context Activation, the GGSN sends a Router
         Advertisement to the UE.

      7. The UE should be configured not to send a Neighbor Solicitation
         message.  However, if one is sent, the GGSN will silently
         discard it.

      8. The GGSN updates the SGSN with the whole IPv6 address.

   Each connected handset or laptop will create a primary PDP context
   for communication on the Internet.  A handset may create many primary
   and/or secondary PDP contexts throughout the life of its connection
   with a GGSN.

   Within 3GPP, the GGSN assigns a single 64-bit identifier to each
   primary PDP context.  The GGSN also advertises a single /64 prefix to
   the handset, and these two items are assembled into a single IPv6
   address.  Later, the GGSN modifies the PDP context entry in the SGSN
   to include the whole IPv6 address, so that the SGSN can know the
   single address of each 3GPP node (e.g., for billing purposes).  This
   address is also used in the GGSN to identify the PDP context
   associated with each packet.  It is assumed that 3GPP nodes will not

   generate any addresses, except for the single identifier/prefix
   combination assigned by the GGSN.  DAD is not performed, as the GGSN
   will not assign the same address to multiple nodes.

2  Recommendations to the 3GPP

   In the spirit of productive cooperation, the IPv6 Working Group
   recommends that the 3GPP consider three changes regarding the use of
   IPv6 within GPRS.  Specifically, we recommend that the 3GPP:

      1. Specify that multiple prefixes may be assigned to each primary
         PDP context,

      2. Require that a given prefix must not be assigned to more than
         one primary PDP context, and

      3. Allow 3GPP nodes to use multiple identifiers within those
         prefixes, including randomly generated identifiers.

   Making these changes would provide several advantages for 3GPP
   implementers and users:

      Laptops that connect to 3GPP handsets will work without any
      software changes.  Their implementation of the standard IPv6 over
      PPP, address assignment, and autoconfiguration mechanisms will
      work without any modification.  This will eliminate the need for
      vendors and operators to build and test special 3GPP drivers and
      related software.  As currently specified, the 3GPP standards will
      be incompatible with laptop implementations that generate their
      own identifiers for privacy or other purposes.

      IPv6 software implementations could be used in 3GPP handsets
      without any modifications to the IPv6 protocol mechanisms.  This
      will make it easier to build and test 3GPP handsets.

      Applications in 3GPP handsets will be able to take advantage of
      different types of IPv6 addresses (e.g., static addresses,
      temporary addresses for privacy, site-scoped addresses for site
      only communication, etc.)

      The GPRS system will be better positioned to take advantage of new
      IPv6 features that are built around the current addressing
      architecture.

2.1 Limitations of 3GPP Address Assignment

   The current 3GPP address assignment mechanism has the following
   limitations:

      The GGSN only advertises a single /64 prefix, rather than a set of
      prefixes.  This will prevent the participation of 3GPP nodes
      (e.g., handsets or 3GPP-attached laptops) in IPv6 site
      renumbering, or in other mechanisms that expect IPv6 hosts to
      create addresses based on multiple advertised prefixes.

      A 3GPP node is assigned a single identifier and is not allowed to
      generate additional identifiers.  This will prevent the use of
      privacy addresses by 3GPP nodes.  This also makes 3GPP mechanisms
      not fully compliant with the expected behavior of IPv6 nodes,
      which will result in incompatibility with popular laptop IPv6
      stacks.  For example, a laptop that uses privacy addresses for web
      browser connections could not currently establish a web browser
      connection over a 3GPP link.

   These limitations could be avoided by enabling the standard IPv6
   address allocation mechanisms in 3GPP nodes.  The GGSN could
   advertise one or more prefixes for the local link in standard IPv6
   Router Advertisements, and IPv6 addresses could be assembled, as
   needed, by the IPv6 stack on the handset or laptop.  An interface
   identifier could still be assigned by the GGSN, as is currently
   specified in the 3GPP standards.  However, the handset or laptop
   could generate additional identifiers, as needed for privacy or other
   reasons.

2.2 Advertising Multiple Prefixes

   For compliance with current and future IPv6 standards, the IPv6 WG
   recommends that the 3GPP allow multiple prefixes to be advertised for
   each primary PDP context.  This would have several advantages,
   including:

      3GPP nodes could participate in site renumbering and future IPv6
      mechanisms that rely on the use of multiple global prefixes on a
      single link.

      Site-local prefixes could be advertised on 3GPP links, if desired,
      allowing for site-constrained communication that could survive
      changes to global prefix information (e.g., site renumbering).

2.3 Assigning a Prefix to Only One Primary PDP Context

   The IPv6 WG recommends that the 3GPP treat a primary PDP context,
   along with its secondary PDP contexts, as a single IPv6 link, and
   that the GGSN view each primary PDP context as a single subnet.
   Accordingly, a given global (or site-local) prefix should not be
   assigned to more than one PDP context.

   Because multiple IPv6 hosts may attach through a 3GPP handset, the
   IPv6 WG recommends that one or more /64 prefixes should be assigned
   to each primary PDP context.  This will allow sufficient address
   space for a 3GPP-attached node to allocate privacy addresses and/or
   route to a multi-link subnet [MULTLINK], and will discourage the use
   of NAT within 3GPP-attached devices.

2.3.1   Is a /64 per PDP Context Too Much?

   If an operator assigns a /64 per PDP context, can we be assured that
   there is enough address space for millions of mobile devices?  This
   question can be answered in the positive using the Host Density (HD)
   Ratio for address assignment efficiency [HD].  This is a measure of
   the number of addresses that can practically and easily be assigned
   to hosts, taking into consideration the inefficiencies in usage
   resulting from the various address assignment processes.  The HD
   ratio was empirically derived from actual telephone number and data
   network address assignment cases.

   We can calculate the number of easily assignable /64's making the
   following assumptions:

      An HD ratio of 0.8 (representing the efficiency that can be
      achieved with no particular difficulty).

      Only addresses with the 3-bit prefix 001 (the Aggregatable Global
      Unicast Addresses defined by RFC 2373) are used, resulting in 61
      bits of assignable address space.

   Using these assumptions, a total of 490 trillion (490x10^12) /64
   prefixes can be assigned.  This translates into around 80,000 PDP
   Contexts per person on the earth today.  Even assuming that a
   majority of these IPv6 /64 prefixes will be used by non-3GPP
   networks, there is still clearly a sufficient number of /64 prefixes.

   Given this, it can be safely concluded that the IPv6 address space
   will not be exhausted if /64 prefixes are allocated to primary PDP
   contexts.

   For more information regarding policies for IPv6 address assignment,
   refer to the IAB/IESG recommendations regarding address assignment
   [IABAA], and the APNIC, ARIN and RIPE address allocation policy
   [AAPOL].

2.3.2   Prefix Information in the SGSN

   Currently, the 3GPP standards allow only one prefix and one
   identifier for each PDP context.  So, the GGSN can send a single IPv6
   address to the SGSN, to be used for billing purposes, etc.

   Instead of using the full IPv6 address to identify a PDP context, the
   IPv6 WG recommends that the SGSN be informed of each prefix that is
   currently assigned to a PDP context.  By assigning a prefix to only
   one primary PDP context, the SGSN can associate a prefix list with
   each PDP context.

2.4 Multiple Identifiers per PDP Context

   The IPv6 WG also recommends that the 3GPP standards be modified to
   allow multiple identifiers, including randomly generated identifiers,
   to be used within each assigned prefix.  This would allow 3GPP nodes
   to generate and use privacy addresses, and would be compatible with
   future IPv6 standards that may depend on the ability of IPv6 nodes to
   generate new interface identifiers for communication.

   This is a vital change, necessary to allow standards-compliant IPv6
   nodes to connect to the Internet through 3GPP handsets, without
   modification.  It is expected that most IPv6 nodes, including the
   most popular laptop stacks, will generate privacy addresses.  The
   current 3GPP specifications will not be compatible with those
   implementations.

3  Additional IPv6 Work Items

   During our work on this document, we have discovered several areas
   that could benefit from further informational or standards-track work
   within the IPv6 Working Group.

   The IPv6 WG should work to define a point-to-point architecture and
   specify how the standard IPv6 address assignment mechanisms are
   applicable to IPv6 over point-to-point links.  We should also review
   and clarify the IPv6 over PPP specification [PPP] to match the
   current IPv6 addressing architecture [ADDRARCH].

   The IPv6 WG should consider publishing an "IPv6 over PDP Contexts"
   (or similar) document.  This document would be useful for developers
   writing drivers for IPv6 stacks to work over 3GPP PDP Contexts.

   The IPv6 working group should undertake an effort to define the
   minimal requirements for all IPv6 nodes.

4  Security Considerations

   This document contains recommendations on the use of the IPv6
   protocol in 3GPP standards.  It does not specify a protocol, and it
   introduces no new security considerations.

Appendix A:  Analysis of Findings

   This section includes some analysis that may be useful to
   understanding why the IPv6 working group is making the above
   recommendations.  It also includes some other options that were
   explored, and the reasons why those options were less suitable than
   the recommendations outlined above.

A.1 Address Assignment Solutions

   In order to allow for the configuration and use of multiple IPv6
   addresses per primary PDP Context having different interface
   identifiers, some modifications to the current 3GPP specifications
   would be required.

   The solutions to achieve this were evaluated against the following
   factors:

      -  Scarcity and high cost of wireless spectrum
      -  Complexity of implementation and state maintenance
      -  Stability of the relevant IETF standards
      -  Impact on current 3GPP standards

   Two solutions to allow autoconfiguration of multiple addresses on the
   same primary PDP Context were considered:

      1. Assign one or more entire prefixes (/64s) to a PDP Context upon
         PDP Context activation and allow the autoconfiguration of
         multiple addresses.

         a) The assignment may be performed by having the GGSN advertise
            one or more /64 prefixes to the mobile device.

         b) The assignment may be performed by building "prefix
            delegation" functionality into the PDP Context messages or
            by using layer 3 mechanisms such as [PREFDEL].  In this way,
            the prefix is not assigned to the link between the GGSN and
            the mobile device (as in 1a), but it is assigned to the
            mobile device itself.  Note that [PREFDEL] cannot be
            considered stable and has not, at this stage, been adopted
            by the IPv6 WG as a WG document.

      2. Share the same prefix between multiple PDP Contexts connected
         to the same GGSN (and APN).  Given that mobile devices may
         generate multiple addresses using more than one interface
         identifier, this would require DAD for the newly generated
         addresses over the air interface, and a proxy DAD, function
         which would increase the complexity and the amount of state to

         be kept in the GGSN.  Also, the GGSN would need to determine
         when the temporary addresses are no longer in use, which would
         be difficult.  One possible solution could be using periodic
         unicast neighbor solicitations for the temporary addresses
         [IPV6ND].

   Considering all the factors when evaluating the solutions, the
   recommendation is to use Solution 1a.  This solution requires the
   least modification to the current 3GPP standards and maintains all
   the advantages of the other solutions.

   Effectively, this would mean that each APN in a GGSN would have a
   certain number of /64 prefixes that can be handed out at PDP context
   Activation, through Router Advertisements.  Therefore, instead of
   using the full IPv6 address to identify a primary PDP context, the
   IPv6 WG recommends that the GGSN use the entire prefix (together with
   other 3GPP specific information) and that the SGSN be informed of the
   prefixes that are assigned to a PDP context.  By assigning a given
   prefix to only one primary PDP context, the GGSN and SGSN can
   associate a prefix list with each PDP context, as needed.

   Note that the recommended solution does not imply or assume that the
   mobile device is a router.  The MT is expected to use the /64 for
   itself and may also use this prefix for devices attached to it.
   However, this is not necessary if each device behind the MT is
   connected to a separate primary PDP Context and therefore can use a
   /64, which is not shared with other devices.  The MT is also expected
   to handle DAD locally for devices attached to it (e.g., laptops)
   without forwarding Neighbor Solicitations over the air to the GGSN.

References

   [OLD-TS23060] TS 23.060, "General Packet Radio Service (GPRS);
                 Service description; Stage 2", V4.1.0

   [NEW-TS23060] TS 23.060 version 3.11.0 (release 99), 4.4.0 (release
                 4) and 5.1.0 (release 5).

   [3GPP-URL]    http://www.3gpp.org

   [IETF-URL]    http://www.ietf.org

   [RFC2026]     Bradner, S., "The Internet Standards Process --
                 Revision 3", BCP 9, RFC 2026, October 1996

   [KEYWORD]     Bradner, S., "Key words for use in RFCs to Indicate
                 Requirement Levels", BCP 14, RFC 2119, March 1999.

   [TR21905]     3GPP TR 21.905, "Vocabulary for 3GPP Specifications",
                 V5.0.0

   [IPV6]        Deering, S. and R. Hinden, "Internet Protocol, Version
                 6 (IPv6) Specification", RFC 2460, December 1998.

   [NAT-PT]      Tsirtsis, G. and P. Shrisuresh, "Network Address
                 Translation - Protocol Translation (NAT-PT)", RFC 2766,
                 February 2000.

   [PPP]         Simpson, W., "The Point-to-Point Protocol (PPP)", STD
                 51, RFC 1661, July 1994.

   [SIIT]        Nordmark, N., "Stateless IP/ICMP Translation
                 Algorithm", RFC 2765, February 2000.

   [ADDRARCH]    Hinden, R. and S. Deering, "IP Version 6 Addressing
                 Architecture", RFC 2373, July 1998.

   [IPV6ND]      Narten, T., Nordmark, E. and W. Simpson, "Neighbor
                 Discovery for IP Version 6 (IPv6)", RFC 2461, December
                 1998.

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

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

   [IPV6ETH]     Crawford, M., "Transmission of IPv6 Packets over
                 Ethernet Networks", RFC 2464, December 1998.

   [PPPv6]       Haskin, D. and E. Allen, "IP Version 6 over PPP", RFC
                 2472, December 1998.

   [MULTLINK]    C. Huitema, D. Thaler, "Multi-link Subnet Support in
                 IPv6", Work in Progress.

   [SITEREN]     C. Huitema, "IPv6 Site Renumbering", Work in Progress.

   [HD]          Durand, A. and C. Huitema, "The Host-Density Ratio for
                 Address Assignment Efficiency: An update on the H
                 ratio", RFC 3194, November 2001.

   [IABAA]       IAB, IESG, "IAB/IESG Recommendations on IPv6 Address
                 Allocations to Sites", RFC 3177, September 2001.

   [AAPOL]       APNIC, ARIN, RIPE-NCC, "IPv6 Address Allocation and
                 Assignment Global Policy", Work in Progress.

   [SCOPARCH]    S. Deering, et. al., "IPv6 Scoped Address
                 Architecture", Work in Progress.

   [CELLREQ]     J. Arkko, et. al., "Minimum IPv6 Functionality for a
                 Cellular Host", Work in Progress.

   [PREFDEL]     J. Martin, B. Haberman, "Automatic Prefix Delegation
                 Protocol for Internet Protocol Version 6 (IPv6)", Work
                 in Progress.

Authors and Acknowledgements

   This document was written by the IPv6 3GPP design team:

   Steve Deering, Cisco Systems
   EMail: deering@cisco.com

   Karim El-Malki, Ericsson Radio Systems
   EMail: Karim.El-Malki@era.ericsson.se

   Paul Francis, Tahoe Networks
   EMail: francis@tahoenetworks.com

   Bob Hinden, Nokia
   EMail: hinden@iprg.nokia.com

   Christian Huitema, Microsoft
   EMail: huitema@windows.microsoft.com

   Niall Richard Murphy, Hutchison 3G
   EMail: niallm@enigma.ie

   Markku Savela, Technical Research Centre of Finland
   Email: Markku.Savela@vtt.fi

   Jonne Soininen, Nokia
   EMail: Jonne.Soininen@nokia.com

   Margaret Wasserman, Wind River
   EMail: mrw@windriver.com

   Information was incorporated from a presentation co-authored by:

         Juan-Antonio Ibanez, Ericsson Eurolab

Editor's Address

   Comments or questions regarding this document should be sent to:

   Margaret Wasserman
   Wind River
   10 Tara Blvd., Suite 330
   Nashua, NH  03062  USA

   Phone:  (603) 897-2067
   EMail:  mrw@windriver.com

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