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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   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

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.

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.

   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.

   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.

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.

   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.

   [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.

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