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Versions: 00 01 RFC 3314
Internet-Draft M. Wasserman, Editor
Document: draft-ietf-ipv6-3gpp-recommend-01.txt Wind River
Expires: October 2002 April 2002
Recommendations for IPv6 in 3GPP Standards
1 Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [RFC2026].
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other
documents at any time. It is inappropriate to use Internet-Drafts
as reference material or to cite them other than as "work in
progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
2 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:
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.
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.
3 Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
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4 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 RFC 2119
[KEYWORD].
5 Table of Contents
1 Status of this Memo.......................................1
2 Abstract..................................................1
3 Copyright Notice..........................................1
4 Conventions Used In This Document.........................2
5 Table of Contents.........................................2
6 Introduction..............................................3
6.1 What is the 3GPP?.........................................3
6.2 What is the IETF?.........................................4
6.3 Terminology...............................................4
6.3.1 3GPP Terminology..........................................5
6.3.2 IETF Terminology..........................................5
6.4 Overview of the IPv6 Addressing Architecture..............6
6.5 An IP-Centric View of the 3GPP System.....................7
6.5.1 Overview of the UMTS Architecture.........................7
6.5.2 The PDP Context...........................................9
6.5.3 IPv6 Address Autoconfiguration in GPRS...................11
7 Recommendations to the 3GPP..............................13
7.1 Limitations of 3GPP Address Assignment...................13
7.2 Advertising Multiple Prefixes............................14
7.3 Assigning a Prefix to Only One Primary PDP Context.......14
7.3.1 Is a /64 per PDP Context Too Much?.......................14
7.3.2 Prefix Information in the SGSN...........................15
7.4 Multiple Identifiers per PDP Context.....................15
8 Additional IPv6 Work Items...............................17
9 Security Considerations..................................17
10 Appendix A: Analysis of Findings........................18
10.1 Address Assignment Solutions.............................18
11 References...............................................20
12 Authors and Acknowledgements.............................22
13 Editor's Contact Information.............................22
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6 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.
An architectural overview of 3GPP was presented, and there was much
discussion regarding the use of IPv6 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 7.
3. Further work items that should be considered by the IPv6 WG.
These items are discussed in section 8.
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 to allow 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].
6.1 What is the 3GPP?
The Third Generation Partnership Project (3GPP) is a global
standardization partnership founded in late 1998. Its
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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 major part 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].
6.2 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,
which are 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.
6.3 Terminology
This section defines the 3GPP and IETF terminology used in this
document. The 3GPP terms and their meanings have been taken from
[TR21905].
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6.3.1 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
6.3.2 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]
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SIIT Stateless IP/ICMP Transition Mechanism [SIIT]
6.4 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
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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.
6.5 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.
6.5.1 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
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------
| |
| 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
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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 is 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].
6.5.2 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.
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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
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6.5.3 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 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
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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.
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7 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 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.
7.1 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.
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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 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.
7.2 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).
7.3 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.
7.3.1 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?
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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].
7.3.2 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.
7.4 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
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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.
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8 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.
9 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.
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10 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.
10.1 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
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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.
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11 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]
S. Bradner, "The Internet Standards Process -- Revision 3",
RFC 2026, BCP9, October 1996
[KEYWORD]
S. Bradner, "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, BCP14, March 1999.
[TR21905]
3GPP TR 21.905, "Vocabulary for 3GPP Specifications", V5.0.0
[IPV6]
S. Deering, R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998.
[NAT-PT]
G. Tsirtsis, P. Shrisuresh, "Network Address Translation -
Protocol Translation (NAT-PT)", RFC2766, February 2000.
[PPP]
Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51, RFC
1661, July 1994.
[SIIT]
E. Nordmark, "Stateless IP/ICMP Translation Algorithm", RFC
2765, February 2000.
[ADDRARCH]
R. Hinden, S. Deering, "IP Version 6 Addressing Architecture",
RFC 2373, July 1998
[IPV6ND]
T. Narten, E. Nordmark, W. Simpson, "Neighbor Discovery for IP
Version 6 (IPv6)", RFC 2461, December 1998
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[AUTOCONF]
S. Thomson, T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998
[PRIVADDR]
T. Narten, R. Draves, "Privacy Extensions for Stateless
Address Autoconfiguration in IPv6", RFC 3041, January 2001
[IPV6ETH]
M. Crawford, "Transmission of IPv6 Packets over Ethernet
Networks", RFC 2464, December 1998
[PPPv6]
D. Haskin, E. Allen, "IP Version 6 over PPP", RFC2472,
December 1998.
[MULTLINK]
C. Huitema, D. Thaler, "Multi-link Subnet Support in IPv6",
draft-thaler-ipngwg-multilink-subnets-01.txt, July 2001
[SITEREN]
C. Huitema, "IPv6 Site Renumbering", draft-huitema-ipv6-
renumber-00.txt, July 2001
[HD]
C. Huitema, A. Durand, "The Host-Density Ratio for Address
Assignment Efficiency: An update on the H ratio", draft-
durand-huitema-h-density-ratio-02.txt, August 2001
[IABAA]
IAB, IESG, "IAB/IESG Recommendations on IPv6 Address
Allocations to Sites", RFC3177, September 2001.
[AAPOL]
APNIC, ARIN, RIPE-NCC, "IPv6 Address Allocation and Assignment
Global Policy". Draft of December, 22 2001, Version 2001-12-
22 [ftp://ftp.cs.duke.edu/pub/narten/global-ipv6-assign-2001-
12-22.txt]
[SCOPARCH]
S. Deering, et. al, "IPv6 Scoped Address Architecture", draft-
ietf-ipngwg-scoping-arch-02.txt, March 2001
[CELLREQ]
J. Arkko, et. al, "Minimum IPv6 Functionality for a Cellular
Host", draft-manyfolks-ipv6-cellular-host-01.txt, September
2001
[PREFDEL]
J. Martin, B. Haberman, "Automatic Prefix Delegation Protocol
for Internet Protocol Version 6 (IPv6)", draft-haberman-
ipngwg-auto-prefix-01.txt, July 2001
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12 Authors and Acknowledgements
This document was written by the IPv6 3GPP design team:
Steve Deering, Cisco Systems
<deering@cisco.com>
Karim El-Malki, Ericsson Radio Systems
<Karim.El-Malki@era.ericsson.se>
Paul Francis, Tahoe Networks
<francis@tahoenetworks.com>
Bob Hinden, Nokia
<hinden@iprg.nokia.com>
Christian Huitema, Microsoft
<huitema@windows.microsoft.com>
Niall Richard Murphy, Hutchison 3G
<niallm@enigma.ie>
Markku Savela, Technical Research Centre of Finland
<Markku.Savela@vtt.fi>
Jonne Soininen, Nokia
<Jonne.Soininen@nokia.com>
Margaret Wasserman, Wind River
<mrw@windriver.com>
Information was incorporated from a presentation co-authored by:
Juan-Antonio Ibanez, Ericsson Eurolab
13 Editor's Contact Information
Comments or questions regarding this document should be sent to:
Margaret Wasserman
Wind River
10 Tara Blvd., Suite 330 Phone: (603) 897-2067
Nashua, NH 03062 USA Email: mrw@windriver.com
Wasserman, Editor Expires May 2002 22
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