Sharing /64 3GPP Mobile Interface Subnet to a LAN

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Document Type Active Internet-Draft (v6ops WG)
Authors Cameron Byrne  , Dan Drown
Last updated 2012-12-17
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V6OPS Working Group                                             C. Byrne
Internet-Draft                                              T-Mobile USA
Intended Status: Informational                                  D. Drown
Expires: June 17, 2013                                 December 14, 2012

           Sharing /64 3GPP Mobile Interface Subnet to a LAN 


   This document describes a known and implemented method of sharing a
   /64 IPv6 prefix from a User Equipment 3GPP radio interface to a
   tethered LAN.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on June 17, 2013.

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Table of Contents

   1. Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2. The Challenge of Providing IPv6 Addresses to a 3GPP Tethered 
      LAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3. Method for Sharing the 3GPP Interface /64 to the Tethered LAN .  3
   4. Security Considerations . . . . . . . . . . . . . . . . . . . .  5
   5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . .  5
   6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . .  5
   7. Informative References  . . . . . . . . . . . . . . . . . . . .  5


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1. Introduction

   3GPP mobile cellular networks such as GSM, UMTS, and LTE have
   architectural support for IPv6 [RFC6459], but only 3GPP Release-10
   and onwards of the 3GPP specification supports DHCPv6 [RFC3633] for
   delegating IPv6 addresses to a tethered LAN.  To facilitate the use
   of IPv6 in a tethered LAN prior to deployment of DHCPv6 in a 3GPP
   network and in User Equipment (UE), this document describes how the
   3GPP UE interface assigned /64 subnet may be shared from the 3GPP
   interface to a tethered LAN.  This is achieved by specifying the UE
   3GPP interface as an IPv6 /128 subnet taken from the 3GPP interface's
   network assigned /64 subnet.  Then, assign the same address to the
   tethered LAN interface with the full /64 subnet.  The /64 tethered
   LAN subnet will then be advertised to the tethered LAN via Router
   Advertisements (RA) [RFC4861]. 

   The end result is that all UE interfaces have link-local IPv6
   addresses, the UE's 3GPP interface has a /128 address from the 3GPP
   network assigned /64, and the same address that is assigned to the
   3GPP interface is assigned to the tethered LAN interface with a /64
   subnet and advertised to the LAN via RA.  This approach only impacts
   the UE configuration and does not require any changes to the 3GPP

2. The Challenge of Providing IPv6 Addresses to a 3GPP Tethered LAN

   As described in [RFC6459], 3GPP networks assign a /64 subnet to each
   UE with RA.  IPv6 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 sharing the assigned /64 from the 3GPP interface to
   the LAN, 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 tethered LAN.  The
   method described in this document should only be applied when
   deploying DHCPv6 is not achievable in the 3GPP network and the UE.

3. Method for Sharing the 3GPP Interface /64 to the Tethered LAN

   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 Network 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 use the 3GPP network assigned /64 to assign itself a /128

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   address to the 3GPP radio interface for consistent network connection
   formation and the same address with a /64 to the tethered LAN
   interface.  The tethered LAN interface may then advertise the /64 to
   the LAN with RA.  The LAN interface RA configuration must be tightly
   coupled with the 3GPP interface state.  If the 3GPP interface goes
   down or changes address, that state should be reflected in the LAN
   IPv6 configuration.  Just as in a standard IPv6 router, the packet
   TTL will be decremented when passing packets between interfaces.

   The procedure may also be described in terms of the following usage

   1.  The user activates tethering on the wireless LAN of the UE.

   2.  The UE checks to make sure the 3GPP interfaces is active and has
       an IPv6 address.  If the interface does not have an IPv6 address,
       an attempt will be made to acquire one, or else the procedure
       will terminate.

   3.  In this example, the UE finds the 3GPP interface has the IPv6
       address 2001:db8:ac10:f002:1234:4567:0:9/128 assigned and active.

   4.  The UE copies the address 2001:db8:ac10:f002:1234:4567:0:9 with a
       64 bit mask from the 3GPP interfaces to the wireless LAN
       interfaces and begins announcing the prefix
       2001:db8:ac10:f002::/64 via RA to the wireless LAN.

   5.  The gateway in the 3GPP network routes all packets for
       2001:db8:ac10:f002::/64 to the UE using the link-local address as
       the next hop.  The gateway does not perform Neighbor Discover or
       Network Unreachability Detection on 3GPP wireless link segment
       towards the UE.

   6.  The UE directly processes all packets destine to itself at

   7.  The UE, acting as a router running NDP on the LAN, will route
       packet to and from the LAN.  IPv6 packets passing between
       interfaces will have the TTL decremented.

   8.  If the 3GPP interface state changes, the LAN will immediately
       update to reflect the change and ensure that the LAN IPv6 prefix
       remains a valid extension of the 3GPP network.

   9.  Since the address 2001:db8:ac10:f002:1234:4567:0:9/128 is the
       only instance of the assigned /64 on the 3GPP interface, there is
       no chance of an address conflict on that interface.  On the LAN
       interface, there is no chance of address conflict since the

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       address is defended using Duplicate Address Detection (DAD).

       The UE should be compliant with the relevant requirements in [I-

4. Security Considerations

   Security considerations identified in [I-D.draft-binet-v6ops-
   cellular-host-requirement] are to be taken into account.

5. IANA Considerations

   This document does not require any action from IANA.

6. Acknowledgments

   Many thanks for review and discussion from Masanobu Kawashima, Teemu
   Savolainen, Mikael Abrahamsson, Eric Vyncke, Alexandru Petrescu,
   Jouni Korhonen, Julien Laganier, and Ales Vizdal.

7. Informative References

   [I-D.draft-binet-v6ops-cellular-host-requirement] Binet, D.,
              Boucadair, M., A. Vizdal, C. Byrne, G. Chen, "Internet
              Protocol Version 6 (IPv6) for Cellular Hosts", draft-
              draft-binet-v6ops-cellular-host-requirement (work in
              progress), October 2012.

   [RFC3633]  Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
              Host Configuration Protocol (DHCP) version 6", RFC 3633,
              December 2003.

   [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.

   [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.

   Authors' Addresses

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   Cameron Byrne
   T-Mobile USA
   Bellevue, Washington, USA


   Dan Drown

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