Internet Engineering Task Force (IETF) C. Byrne
Request for Comments: 7278 T-Mobile USA
Category: Informational D. Drown
ISSN: 2070-1721 A. Vizdal
Deutsche Telekom AG
June 2014
Extending an IPv6 /64 Prefix from a
Third Generation Partnership Project (3GPP)
Mobile Interface to a LAN Link
Abstract
This document describes requirements for extending an IPv6 /64 prefix
from a User Equipment Third Generation Partnership Project (3GPP)
radio interface to a LAN link and describes two implementation
examples.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7278.
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Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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described in the Simplified BSD License.
Table of Contents
1. Introduction ....................................................3
2. The Challenge of Providing IPv6 Addresses to a LAN Link via a
3GPP UE .........................................................4
3. Requirements for Extending the 3GPP Interface /64 IPv6
Prefix to a LAN Link ............................................4
4. Example Methods for Extending the 3GPP Interface /64
IPv6 Prefix to a LAN Link .......................................5
4.1. General Behavior for All Example Scenarios .................5
4.2. Example Scenario 1: Global Address Only Assigned to
LAN Link ...................................................5
4.3. Example Scenario 2: A Single Global Address Assigned to a
3GPP Radio and LAN Link ....................................7
5. Security Considerations .........................................8
6. Acknowledgments .................................................8
7. Informative References ..........................................8
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1. Introduction
3GPP mobile cellular networks such as Global System for Mobile
Communications (GSM), Universal Mobile Telecommunications System
(UMTS), and Long Term Evolution (LTE) have architectural support for
IPv6 [RFC6459], but only 3GPP Release-10 and onwards of the 3GPP
specification [TS.23401] supports DHCPv6 Prefix Delegation [RFC3633]
for delegating IPv6 prefixes to a single LAN link.
To facilitate the use of IPv6 in a LAN prior to the deployment of
DHCPv6 Prefix Delegation in 3GPP networks and in User Equipment (UE),
this document describes requirements and provides examples on how the
3GPP UE radio interface assigned global /64 prefix may be extended
from the 3GPP radio interface to a LAN link.
There are two scenarios where this might be done. The first is where
the 3GPP node sets up and manages its own LAN (e.g., an IEEE 802.11
Service Set Identifier (SSID)) and provides single-homed service to
hosts that connect to this LAN. A second scenario is where the 3GPP
node connects to an existing LAN and acts as a router in order to
provide redundant or multi-homed IPv6 service.
This document is intended to address the first scenario; it is not
applicable to the second scenario, because the operational
complexities of the second scenario are not addressed.
This can be achieved by receiving the Router Advertisement (RA)
[RFC4861] announced globally unique /64 IPv6 prefix from the 3GPP
radio interface by the UE and then advertising the same IPv6 prefix
to the LAN link with RA. For all of the cases in the scope of this
document, the UE may be any device that functions as an IPv6 router
between the 3GPP network and a LAN.
This document describes requirements for achieving an IPv6 prefix
extension from a 3GPP radio interface to a LAN link including two
practical implementation examples:
1) The 3GPP UE only has a global-scope address on the LAN link.
2) The 3GPP UE maintains the same consistent 128-bit global-scope
IPv6 anycast address [RFC4291] on the 3GPP radio interface and the
LAN link. The LAN link is configured as a /64 and the 3GPP radio
interface is configured as a /128.
Section 4 describes the characteristics of each of the two example
approaches.
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1.2. Special Language
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 [RFC2119].
Note that this document is not a Standard, and conformance with it is
not required in order to claim conformance with IETF Standards for
IPv6.
This document uses the normative keywords only for precision.
2. The Challenge of Providing IPv6 Addresses to a LAN Link via a
3GPP UE
As described in [RFC6459], 3GPP networks assign a /64 global-scope
prefix to each UE using RA. DHCPv6 Prefix Delegation is an optional
part of 3GPP Release-10 and is not covered by any earlier releases.
Neighbor Discovery Proxy (ND Proxy) [RFC4389] functionality has been
suggested as an option for extending the assigned /64 from the 3GPP
radio interface to the LAN link, but ND Proxy is an Experimental
protocol and has some limitations with loop avoidance.
DHCPv6 is the best way to delegate a prefix to a LAN link. The
methods described in this document SHOULD only be applied when
deploying DHCPv6 Prefix Delegation is not achievable in the 3GPP
network and the UE. The methods described in this document are at
various stages of implementation and deployment planning. The goal
of this memo is to document the available methods that may be used
prior to DHCPv6 deployment.
3. Requirements for Extending the 3GPP Interface /64 IPv6 Prefix to a
LAN Link
R-1: The 3GPP network provided /64 prefix MUST be made available on
the LAN link.
LAN attached devices shall be able to use the 3GPP network
assigned IPv6 prefix (e.g. using IPv6 Stateless Address
Autoconfiguration - SLAAC [RFC4862]).
R-2: The UE MUST defend all of its IPv6 addresses on the LAN link.
In case a LAN attached node will, for example, autoconfigure the
same global IPv6 address as used on the 3GPP interface, the UE
must fail the Duplicate Address Detection (DAD) [RFC4862] process
run by the LAN node.
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R-3: The LAN link configuration MUST be tightly coupled with the 3GPP
link state.
R-4: The UE MUST decrement the time to live (TTL) when passing
packets between IPv6 links across the UE.
4. Example Methods for Extending the 3GPP Interface /64 IPv6 Prefix to
a LAN Link
4.1. General Behavior for All Example Scenarios
As [RFC6459] describes, the 3GPP-network-assigned /64 is completely
dedicated to the UE and the gateway does not consume any of the /64
addresses. The gateway routes the entire /64 to the UE and does not
perform ND or Neighbor Unreachability Detection (NUD) [RFC4861].
Communication between the UE and the gateway is only done using
link-local addresses and the link is point-to-point. This allows
for the UE to reliably manipulate the /64 from the 3GPP radio
interface without negatively impacting the point-to-point 3GPP radio
link interface. The LAN link RA configuration must be tightly
coupled with the 3GPP link state. If the 3GPP link goes down or
changes the IPv6 prefix, that state should be reflected in the LAN
link IPv6 configuration. Just as in a standard IPv6 router, the
packet TTL will be decremented when passing packets between IPv6
links across the UE. The UE is employing the weak host model
[RFC1122]. The RA function on the UE is exclusively run on the LAN
link.
The LAN-link-originated RA message carries a copy of the following
3GPP radio-link-received RA message option fields:
o MTU (if not provided by the 3GPP network, the UE will provide its
3GPP link MTU size)
o Prefix Information
4.2. Example Scenario 1: Global Address Only Assigned to LAN Link
For this case, the UE receives the RA from the 3GPP network but does
not use a global address on the 3GPP interface. The 3GPP-interface-
received RA /64 prefix information is used to configure the Neighbor
Discovery Protocol (NDP) on the LAN. The UE assigns itself an IPv6
address on the LAN link from the 3GPP-interface-received RA. The LAN
link uses RA to announce the prefix to the LAN. The UE LAN link
interface defends its LAN IPv6 address with DAD. The UE shall not
run SLAAC to assign a global address on the 3GPP radio interface
while routing is enabled.
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This method allows the UE to originate and terminate IPv6
communications as a host while acting as an IPv6 router. The
movement of the IPv6 prefix from the 3GPP radio interface to the LAN
link may result in long-lived data connections being terminated
during the transition from a host-only mode to router-and-host mode.
Connections that are likely to be affected are ones that have been
specifically bound to the 3GPP radio interface. This method is
appropriate if the UE or software on the UE cannot support multiple
interfaces with the same anycast IPv6 address and the UE requires
global connectivity while acting as a router.
Below is the general procedure for this scenario:
1. The user activates router functionality for a LAN on the UE.
2. The UE checks to make sure the 3GPP interface is active and has
an IPv6 address. If the interface does not have an IPv6 address,
an attempt will be made to acquire one; otherwise, the procedure
will terminate.
3. In this example, the UE finds the 3GPP interface is active and
has the IPv6 address 2001:db8:ac10:f002:1234:4567:0:9 assigned.
4. The UE moves the address 2001:db8:ac10:f002:1234:4567:0:9 as a
/64 from the 3GPP interfaces to the LAN link interface, disables
the IPv6 SLAAC feature on the 3GPP radio interface to avoid
address autoconfiguration, and begins announcing the prefix
2001:db8:ac10:f002::/64 via RA to the LAN. For this example, the
LAN has 2001:db8:ac10:f002:1234:4567:0:9/64 and the 3GPP radio
only has a link-local address.
5. The UE directly processes all packets destined to itself at
2001:db8:ac10:f002:1234:4567:0:9.
6. The UE, acting as a router running NDP on the LAN, will route
packets to and from the LAN. IPv6 packets passing between
interfaces will have the TTL decremented.
7. On the LAN link interface, there is no chance of address conflict
since the address is defended using DAD. The 3GPP radio
interface only has a link-local address.
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4.3. Example Scenario 2: A Single Global Address Assigned to a
3GPP Radio and LAN Link
In this method, the UE assigns itself one address from the 3GPP-
network RA-announced /64. This one address is configured as anycast
[RFC4291] on both the 3GPP radio link as a /128 and on the LAN link
as a /64. This allows the UE to maintain long-lived data connections
since the 3GPP radio interface address does not change when the
router function is activated. This method may cause complications
for certain software that may not support multiple interfaces with
the same anycast IPv6 address, or are sensitive to prefix length
changes. This method also creates complications for ensuring
uniqueness for Privacy Extensions [RFC4941]. When Privacy Extensions
are in use, all temporary addresses will be copied from the 3GPP
radio interface to the LAN link. The preferred and valid lifetimes
will be synchronized, such that the temporary anycast addresses on
both interfaces expire simultaneously.
There might also be more complex scenarios in which the prefix length
is not changed and privacy extensions are supported by having the
subnet span multiple interfaces, as ND Proxy does [RFC4389]. Further
elaboration is out of scope of the present document.
Below is the general procedure for this scenario:
1. The user activates router functionality for a LAN on the UE.
2. The UE checks to make sure the 3GPP interface is active and has
an IPv6 address. If the interface does not have an IPv6 address,
an attempt will be made to acquire one; otherwise, the procedure
will terminate.
3. In this example, the UE finds the 3GPP interface is active and
has the IPv6 address 2001:db8:ac10:f002:1234:4567:0:9 assigned.
4. The UE moves the address 2001:db8:ac10:f002:1234:4567:0:9 as an
anycast /64 from the 3GPP interface to the LAN interface and
begins announcing the prefix 2001:db8:ac10:f002::/64 via RA to
the LAN. The 3GPP interface maintains the same IPv6 anycast
address with a /128. For this example, the LAN has
2001:db8:ac10:f002:1234:4567:0:9/64 and the 3GPP radio interface
has 2001:db8:ac10:f002:1234:4567:0:9/128.
5. The UE directly processes all packets destined to itself at
2001:db8:ac10:f002:1234:4567:0:9.
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6. On the LAN interface, there is no chance of address conflict
since the address is defended using DAD. The 3GPP radio
interface only has a /128 and no other systems on the 3GPP radio
point-to-point link may use the global /64.
5. Security Considerations
Since the UE will be switched from an IPv6 host mode to an IPv6
router-and-host mode, basic IPv6 Customer Premises Equipment (CPE)
security functions [RFC6092] SHOULD be applied.
Despite the use of temporary IPv6 addresses, the mobile-network-
provided /64 prefix is common to all the LAN-attached devices
potentially concerning privacy. An IPv6 prefix provided by a nomadic
device (e.g., a smartphone) is not a long-lived one due to
re-attaches caused by a device reload, traveling through loosely
covered areas, etc. The network will provide a new IPv6 prefix after
a successful re-attach.
3GPP-mobile-network-capable CPEs (e.g., a router) are likely to keep
the mobile network data connection up for a longer time. Some mobile
networks may be re-setting the mobile network connection regularly
(e.g., every 24 hours), others may not. Privacy-concerned users
shall take appropriate measures to not keep their IPv6 prefixes long
lived.
6. Acknowledgments
Many thanks for review and discussion from Dave Thaler, Sylvain
Decremps, Mark Smith, Dmitry Anipko, Masanobu Kawashima, Teemu
Savolainen, Mikael Abrahamsson, Eric Vyncke, Alexandru Petrescu,
Jouni Korhonen, Lorenzo Colitti, Julien Laganier, Owen DeLong, Holger
Metschulat, Yaron Sheffer, and Victor Kuarsingh. Special thanks to
Ann Cerveny for her language review.
7. Informative References
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, October 1989.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
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[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
Proxies (ND Proxy)", RFC 4389, April 2006.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, September 2007.
[RFC6092] Woodyatt, J., Ed., "Recommended Simple Security
Capabilities in Customer Premises Equipment (CPE) for
Providing Residential IPv6 Internet Service", RFC 6092,
January 2011.
[RFC6459] Korhonen, J., Ed., Soininen, J., Patil, B., Savolainen,
T., Bajko, G., and K. Iisakkila, "IPv6 in 3rd Generation
Partnership Project (3GPP) Evolved Packet System (EPS)",
RFC 6459, January 2012.
[TS.23401] 3GPP, "General Packet Radio Service (GPRS) enhancements
for Evolved Universal Terrestrial Radio Access Network
(E-UTRAN) access", 3GPP TS 23.401 10.0.0, June 2010.
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Authors' Addresses
Cameron Byrne
T-Mobile USA
Bellevue, Washington, USA
EMail: Cameron.Byrne@T-Mobile.com
Dan Drown
EMail: Dan@Drown.org
Ales Vizdal
Deutsche Telekom AG
Tomickova 2144/1
Prague, 149 00
Czech Republic
EMail: Ales.Vizdal@T-Mobile.cz
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