





Internet Engineering Task Force (IETF)                  J. Korhonen, Ed.
Request for Comments: 7066                                      Broadcom
Obsoletes: 3316                                            J. Arkko, Ed.
Category: Informational                                         Ericsson
ISSN: 2070-1721                                            T. Savolainen
                                                                   Nokia
                                                             S. Krishnan
                                                                Ericsson
                                                           November 2013


  IPv6 for Third Generation Partnership Project (3GPP) Cellular Hosts

Abstract

   As the deployment of third and fourth generation cellular networks
   progresses, a large number of cellular hosts are being connected to
   the Internet.  Standardization organizations have made the Internet
   Protocol version 6 (IPv6) mandatory in their specifications.
   However, the concept of IPv6 covers many aspects and numerous
   specifications.  In addition, the characteristics of cellular links
   in terms of bandwidth, cost, and delay put special requirements on
   how IPv6 is used.  This document considers IPv6 for cellular hosts
   that attach to the General Packet Radio Service (GPRS), Universal
   Mobile Telecommunications System (UMTS), or Evolved Packet System
   (EPS) networks (hereafter collectively referred to as Third
   Generation Partnership Project (3GPP) networks).  This document also
   lists specific IPv6 functionalities that need to be implemented in
   addition to what is already prescribed in the IPv6 Node Requirements
   document (RFC 6434).  It also discusses some issues related to the
   use of these components when operating in these networks.  This
   document obsoletes RFC 3316.

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/rfc7066.



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Copyright Notice

   Copyright (c) 2013 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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................3
      1.1. Scope of This Document .....................................3
      1.2. Abbreviations ..............................................5
      1.3. Cellular Host IPv6 Features ................................6
   2. Basic IP ........................................................6
      2.1. Internet Protocol Version 6 ................................6
      2.2. Neighbor Discovery in 3GPP Networks ........................6
      2.3. Stateless Address Autoconfiguration ........................8
      2.4. IP Version 6 over PPP ......................................8
      2.5. Multicast Listener Discovery (MLD) for IPv6 ................9
      2.6. Privacy Extensions for Address Configuration in IPv6 .......9
      2.7. Dynamic Host Configuration Protocol for IPv6 (DHCPv6) ......9
      2.8. DHCPv6 Prefix Delegation ..................................10
      2.9. Router Preferences and More-Specific Routes ...............10
      2.10. Neighbor Discovery and Additional Host Configuration .....10
   3. IP Security ....................................................11
      3.1. Extension Header Considerations ...........................11
   4. Mobility .......................................................11
   5. Acknowledgements ...............................................11
   6. Security Considerations ........................................12
   7. References .....................................................14
      7.1. Normative References ......................................14
      7.2. Informative References ....................................15
   Appendix A. Cellular Host IPv6 Addressing in the 3GPP Model .......17
   Appendix B. Changes from RFC 3316 .................................18









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1.  Introduction

   Technologies such as GPRS (General Packet Radio Service), UMTS
   (Universal Mobile Telecommunications System), Evolved Packet System
   (EPS), CDMA2000 (Code Division Multiple Access 2000), and eHRPD
   (Enhanced High Rate Packet Data) are making it possible for cellular
   hosts to have an always-on connection to the Internet.  IPv6
   [RFC2460] has become essential to such networks as the number of
   cellular hosts is increasing rapidly.  Standardization organizations
   working with cellular technologies have recognized this and made IPv6
   mandatory in their specifications.

   Support for IPv6 and the introduction of UMTS started with 3GPP
   Release-99 networks and hosts.  For a detailed description of IPv6 in
   3GPP networks, including the Evolved Packet System, see [RFC6459].

1.1.  Scope of This Document

   For the purpose of this document, a cellular interface is considered
   to be the interface to a cellular access network based on the
   following standards: 3GPP GPRS and UMTS Release-99 and Release-4 to
   Release-11; EPS Release-8 to Release-11; and future UMTS or EPS
   releases.  A cellular host is considered to be a host with such a
   cellular interface.

   This document complements the IPv6 Node Requirements [RFC6434] in
   places where clarifications are needed with discussion on the use of
   these selected IPv6 specifications when operating over a cellular
   interface.  Such a specification is necessary in order to enable the
   optimal use of IPv6 in a cellular network environment.  The
   description is made from the point of view of a cellular host.
   Complementary access technologies may be supported by the cellular
   host, but those are not discussed in detail.  Important
   considerations are given in order to eliminate unnecessary user
   confusion over configuration options, ensure interoperability, and
   provide an easy reference for those who are implementing IPv6 in a
   cellular host.  It is necessary to ensure that cellular hosts are
   good citizens of the Internet.

   This document is informational in its nature, and it is not intended
   to replace, update, or contradict any IPv6 standards documents or the
   IPv6 Node Requirements [RFC6434].

   This document is primarily targeted to the implementers of cellular
   hosts that will be used with the cellular networks listed in this
   document.  This document provides guidance on which IPv6-related
   specifications are to be implemented in such cellular hosts.  Parts
   of this document may also apply to other cellular link types, but



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   this document does not provide any detailed analysis on other link
   types.  This document should not be used as a definitive list of IPv6
   functionalities for cellular links other than those listed above.
   Future changes in 3GPP networks that impact host implementations may
   result in updates to this document.

   There are different ways to implement cellular hosts:

   o  The host can be a "closed" device with optimized built-in
      applications, with no possibility to add or download applications
      that can have IP communications.  An example of such a host is a
      very simple form of a mobile phone.

   o  The host can be an open device, e.g., a "smart phone" where it is
      possible to download applications to expand the functionality of
      the device.

   o  The cellular radio modem part can be separated from the host IP
      stack with an interface.  One example of such a host is a laptop
      computer that uses a USB cellular modem for cellular access.

   If a cellular host has additional IP-capable interfaces (such as
   Ethernet, WLAN, Bluetooth, etc.), then there may be additional
   requirements for the device, beyond what is discussed in this
   document.  Additionally, this document does not make any
   recommendations on the functionality required on laptop computers
   having a cellular interface such as an embedded modem or a USB modem
   stick, other than recommending link-specific behavior on the cellular
   link.

   This document discusses IPv6 functionality as of the time when this
   document was written.  Ongoing work on IPv6 may affect what is
   required of future hosts.

   Transition mechanisms used by cellular hosts are not in the scope of
   this document and are left for further study.  The primary transition
   mechanism supported by 3GPP is dual-stack [RFC4213].  Dual-stack-
   capable bearer support has been added to GPRS starting from 3GPP
   Release-9 and to EPS starting from Release-8 [RFC6459], whereas the
   earlier 3GPP releases required multiple single IP version bearers to
   support dual-stack.










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1.2.  Abbreviations

   2G    Second Generation Mobile Telecommunications, such as Global
         System for Mobile Communications (GSM) and GPRS technologies.

   3G    Third Generation Mobile Telecommunications, such as UMTS
         technology.

   4G    Fourth Generation Mobile Telecommunications, such as LTE
         technology.

   3GPP  Third Generation Partnership Project.  Throughout the document,
         the term "3GPP networks" refers to architectures standardized
         by 3GPP, in Second, Third, and Fourth Generation releases: 99,
         4, and 5, as well as future releases.

   EPS   Evolved Packet System.

   GGSN  Gateway GPRS Support Node (a default router for 3GPP IPv6
         cellular hosts in GPRS).

   GPRS  General Packet Radio Service.

   LTE   Long Term Evolution.

   MT    Mobile Terminal, for example, a mobile phone handset.

   MTU   Maximum Transmission Unit.

   PDN   Packet Data Network.

   PDP   Packet Data Protocol.

   PGW   Packet Data Network Gateway (the default router for 3GPP IPv6
         cellular hosts in EPS).

   SGW   Serving Gateway (the user plane equivalent of a Serving GPRS
         Support Node (SGSN) in EPS (and the default router for 3GPP
         IPv6 cellular hosts when using Proxy Mobile IPv6 (PMIPv6))).

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

   UMTS  Universal Mobile Telecommunications System.

   WLAN  Wireless Local Area Network.





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1.3.  Cellular Host IPv6 Features

   This document lists IPv6 features for cellular hosts; these features
   are split into three groups and are discussed below.

   Basic IP

      In this group, the basic IPv6 features essential for cellular
      hosts are listed and described.

   IP Security

      In this group, the parts related to IP Security are described.

   Mobility

      In this group, IP-layer mobility issues are described.

2.  Basic IP

   For most parts, refer to the IPv6 Node Requirements document
   [RFC6434].

2.1.  Internet Protocol Version 6

   The Internet Protocol version 6 (IPv6) is specified in [RFC2460].
   This specification is a mandatory part of IPv6.  A cellular host must
   conform to the generic IPv6 host requirements [RFC6434], unless
   specifically pointed out otherwise in this document.

2.2.  Neighbor Discovery in 3GPP Networks

   A cellular host must support Neighbor Solicitation and Neighbor
   Advertisement messages [RFC4861].  Some further notes on how Neighbor
   Discovery is applied in the particular type of an interface can be
   useful.

   In 3GPP networks, some Neighbor Discovery messages can be unnecessary
   in certain cases.  GPRS, UMTS, and EPS links resemble a point-to-
   point link; hence, the cellular host's only neighbor on the cellular
   link is the default router that is already known through Router
   Discovery.  The cellular host always solicits for routers when the
   cellular interface is brought up (as described in [RFC4861],
   Section 6.3.7).

   There are no link-layer addresses on the 3GPP cellular link
   technology.  Therefore, address resolution and next-hop determination
   are not needed.  If the cellular host still attempts to do address



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   resolution, e.g., for the default router, it must be understood that
   the GGSN/PGW may not even answer the address resolution Neighbor
   Solicitations.  And even if it does, the Neighbor Advertisement is
   unlikely to contain the Target link-layer address option as there are
   no link-layer addresses on the 3GPP cellular link technology.

   The cellular host must support Neighbor Unreachability Detection
   (NUD) as specified in [RFC4861].  Note that the link-layer address
   considerations above also apply to NUD.  The NUD-triggered Neighbor
   Advertisement is also unlikely to contain the Target link-layer
   address option as there are no link-layer addresses.  The cellular
   host should also be prepared for NUD initiated by a router (i.e.,
   GGSN/PGW).  However, it is unlikely a router-to-host NUD would ever
   take place on GPRS, UMTS, or EPS links.  See Appendix A for more
   discussion on the router-to-host NUD.

   In 3GPP networks, it is desirable to reduce any additional periodic
   signaling.  Therefore, the cellular host should include a mechanism
   in upper-layer protocols to provide reachability confirmations when
   two-way IP-layer reachability can be confirmed (see [RFC4861],
   Section 7.3.1).  These confirmations would allow the suppression of
   NUD-related messages in most cases.

   Host TCP implementation should provide reachability confirmation in
   the manner explained in [RFC4861], Section 7.3.1.

   The widespread use of UDP in 3GPP networks poses a problem for
   providing reachability confirmation.  As UDP itself is unable to
   provide such confirmation, applications running on top of UDP should
   provide the confirmation where possible.  In particular, when UDP is
   used for transporting DNS, the DNS response should be used as a basis
   for reachability confirmation.  Similarly, when UDP is used to
   transport RTP [RFC3550], the RTP Control Protocol (RTCP) [RFC3550]
   feedback should be used as a basis for the reachability confirmation.
   If an RTCP packet is received with a reception report block
   indicating some packets have gone through, then packets are reaching
   the peer.  If they have reached the peer, they have also reached the
   neighbor.

   When UDP is used for transporting SIP [RFC3261], responses to SIP
   requests should be used as the confirmation that packets sent to the
   peer are reaching it.  When the cellular host is acting as the
   server-side SIP node, no such confirmation is generally available.
   However, a host may interpret the receipt of a SIP ACK request as
   confirmation that the previously sent response to a SIP INVITE
   request has reached the peer.





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2.3.  Stateless Address Autoconfiguration

   IPv6 Stateless Address Autoconfiguration is defined in [RFC4862].
   This specification is a mandatory part of IPv6 and also the only
   mandatory method to configure an IPv6 address in a 3GPP cellular
   host.

   A cellular host in a 3GPP network must process a Router Advertisement
   as stated in [RFC4862].  The Router Advertisement contains a maximum
   of one prefix information option with lifetimes set to infinite (both
   valid and preferred lifetimes).  The advertised prefix cannot ever be
   used for on-link determination (see [RFC6459], Section 5.2), and the
   lifetime of the advertised prefix is tied to the PDP Context/PDN
   Connection lifetime.  Keeping the forward compatibility in mind,
   there is no reason for the 3GPP cellular host to have 3GPP-specific
   handling of the prefix information option(s) although 3GPP
   specifications state that the Router Advertisement may contain a
   maximum of one prefix information option and the lifetimes are set to
   infinite.

   Hosts in 3GPP networks can set DupAddrDetectTransmits equal to zero,
   as each assigned prefix is unique within its scope when advertised
   using 3GPP IPv6 Stateless Address Autoconfiguration.  In addition,
   the default router (GGSN/PGW) will not configure any addresses on its
   interfaces based on prefixes advertised to IPv6 cellular hosts on
   those interfaces.  Thus, the host is not required to perform
   Duplicate Address Detection on the cellular interface.

   Furthermore, the GGSN/PGW will provide the cellular host with an
   interface identifier that must be used for link-local address
   configuration.  The link-local address configured from this interface
   identifier is guaranteed not to collide with the link-local address
   that the GGSN/PGW uses.  Thus, the cellular host is not required to
   perform Duplicate Address Detection for the link-local address on the
   cellular interface.

   See Appendix A for more details on 3GPP IPv6 Stateless Address
   Autoconfiguration.

2.4.  IP Version 6 over PPP

   A cellular host in a 3GPP network that supports PPP [RFC1661] on the
   interface between the MT and the TE must support the IPv6 Control
   Protocol (IPV6CP) [RFC5072] interface identifier option.  This option
   is needed to be able to connect other devices to the Internet using a
   PPP link between the cellular device (MT, e.g., a USB dongle) and
   other devices (TE, e.g., a laptop).  The MT performs the PDP Context
   activation based on a request from the TE.  This results in an



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   interface identifier being suggested by the MT to the TE, using the
   IPV6CP option.  To avoid any duplication in link-local addresses
   between the TE and the GGSN/PGW, the MT must always reject other
   suggested interface identifiers by the TE.  This results in the TE
   always using the interface identifier suggested by the GGSN/PGW for
   its link-local address.

   The rejection of interface identifiers suggested by the TE is only
   done for creation of link-local addresses, according to 3GPP
   specifications.  The use of privacy addresses [RFC4941] or similar
   technologies for unique local IPv6 unicast addresses [RFC4193] and
   global addresses is not affected by the above procedure.

2.5.  Multicast Listener Discovery (MLD) for IPv6

   Within 3GPP networks, hosts connect to their default routers
   (GGSN/PGW) via point-to-point links.  Moreover, there are exactly two
   IP devices connected to the point-to-point link, and no attempt is
   made (at the link layer) to suppress the forwarding of multicast
   traffic.  Consequently, sending MLD reports for link-local addresses
   in a 3GPP environment is not necessary, although sending them causes
   no harm or interoperability issues.  Refer to Section 5.10 of
   [RFC6434] for MLD usage for multicast group knowledge that is not
   link-local.

2.6.  Privacy Extensions for Address Configuration in IPv6

   Privacy Extensions for Stateless Address Autoconfiguration [RFC4941]
   or other similar technologies may be supported by a cellular host.
   Privacy, in general, is important for the Internet.  In 3GPP
   networks, the lifetime of an address assignment depends on many
   factors such as radio coverage, device status, and user preferences.
   As a result, the prefix the cellular host uses is also subject to
   frequent changes.

   Refer to Section 6 for a discussion of the benefits of Privacy
   Extensions in a 3GPP network.

2.7.  Dynamic Host Configuration Protocol for IPv6 (DHCPv6)

   As of 3GPP Release-11, the Dynamic Host Configuration Protocol for
   IPv6 (DHCPv6) [RFC3315] is neither required nor supported for address
   autoconfiguration.  IPv6 Stateless Address Autoconfiguration still
   remains the only mandatory address configuration method.  However,
   DHCPv6 may be useful for other configuration needs on a cellular
   host, e.g., Stateless DHCPv6 [RFC3736] may be used to configure DNS





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   and SIP server addresses, and DHCPv6 Prefix Delegation [RFC3633] may
   be used to delegate a prefix to the cellular host for use on its
   downstream non-cellular links.

2.8.  DHCPv6 Prefix Delegation

   Starting from Release-10, DHCPv6 Prefix Delegation was added as an
   optional feature to the 3GPP system architecture [RFC3633].  The
   Prefix Delegation model defined for Release-10 requires that the /64
   IPv6 prefix assigned to the cellular host on the 3GPP link must
   aggregate with the shorter delegated IPv6 prefix.  The cellular host
   should implement the Prefix Exclude Option for DHCPv6 Prefix
   Delegation [RFC6603] (see [RFC6459], Section 5.3 for further
   discussion).

2.9.  Router Preferences and More-Specific Routes

   The cellular host should implement the Default Router Preferences and
   More-Specific Routes extension to Router Advertisement messages
   [RFC4191].  These options may be useful for cellular hosts that also
   have additional interfaces on which IPv6 is used.

2.10.  Neighbor Discovery and Additional Host Configuration

   The DNS server configuration is learned from the 3GPP link-layer
   signaling.  However, the cellular host should also implement the IPv6
   Router Advertisement Options for DNS Configuration [RFC6106].  DHCPv6
   is still optional for cellular hosts, and learning the DNS server
   addresses from the link-layer signaling can be cumbersome when the MT
   and the TE are separated using techniques other than the PPP
   interface.

   The cellular host should also honor the MTU option in the Router
   Advertisement (see [RFC4861], Section 4.6.4).  The 3GPP system
   architecture uses extensive tunneling in its packet core network
   below the 3GPP link, and this may lead to packet fragmentation
   issues.  Therefore, the GGSN/PGW may propose to the cellular host an
   MTU that takes the additional tunneling overhead into account.













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3.  IP Security

   IPsec [RFC4301] is a fundamental, but not mandatory, part of IPv6.
   Refer to the IPv6 Node Requirements (Section 11 of [RFC6434]) for the
   security requirements that also apply to cellular hosts.

3.1.  Extension Header Considerations

   Support for the Routing Header Type 0 (RH0) has been deprecated
   [RFC5095].  Therefore, the cellular host should by default follow the
   RH0 processing described in Section 3 of [RFC5095].

   IPv6 packet fragmentation has known security concerns.  The cellular
   host must follow the handling of overlapping fragments as described
   in [RFC5722], and the cellular host must not fragment any Neighbor
   Discovery messages as described in [RFC6980].

4.  Mobility

   For the purposes of this document, IP mobility is not relevant.  The
   movement of cellular hosts within 3GPP networks is handled by link-
   layer mechanisms in the majority of cases.  3GPP Release-8 introduced
   Dual-Stack Mobile IPv6 (DSMIPv6) for client-based mobility [RFC5555].
   Client-based IP mobility is optional in the 3GPP architecture.

5.  Acknowledgements

   The authors would like to thank the original authors for their
   groundwork for this document: Gerben Kuijpers, John Loughney, Hesham
   Soliman, and Juha Wiljakka.

   The original [RFC3316] document was based on the results of a team
   that included Peter Hedman and Pertti Suomela in addition to the
   authors.  Peter and Pertti have contributed both text and their IPv6
   experience to this document.

   The authors would like to thank Jim Bound, Brian Carpenter, Steve
   Deering, Bob Hinden, Keith Moore, Thomas Narten, Erik Nordmark,
   Michael Thomas, Margaret Wasserman, and others on the IPv6 WG mailing
   list for their comments and input.

   We would also like to thank David DeCamp, Karim El Malki, Markus
   Isomaki, Petter Johnsen, Janne Rinne, Jonne Soininen, Vlad Stirbu,
   and Shabnam Sultana for their comments and input in preparation of
   this document.






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   For this revised version of [RFC3316] the authors would like to thank
   Dave Thaler, Ales Vizdal, Gang Chen, Ray Hunter, Charlie Kaufman,
   Owen DeLong, and Alexey Melnikov for their comments, reviews, and
   input.

6.  Security Considerations

   This document does not specify any new protocols or functionalities,
   and as such, it does not introduce any new security vulnerabilities.
   However, specific profiles of IPv6 functionality are proposed for
   different situations, and vulnerabilities may open or close depending
   on which functionality is included and what is not.  There are also
   aspects of the cellular environment that make certain types of
   vulnerabilities more severe.  The following issues are discussed:

   o  The suggested limitations (Section 3.1) in the processing of
      extension headers also limits exposure to Denial-of-Service (DoS)
      attacks through cellular hosts.

   o  IPv6 addressing privacy [RFC4941] or similar technology may be
      used in cellular hosts.  However, it should be noted that in the
      3GPP model, the network would assign a new prefix, in most cases,
      to hosts in roaming situations; the network would also typically
      assign a new prefix when the cellular hosts activate a PDP Context
      or a PDN Connection. 3GPP devices must not use interface
      identifiers that are unique to the device, so the only difference
      in address between 3GPP devices using Stateless Address
      Autoconfiguration is in the prefix.  This means that 3GPP networks
      will already provide a limited form of addressing privacy, and no
      global tracking of a single host is possible through its address.
      On the other hand, since a GGSN/PGW's coverage area is expected to
      be very large when compared to currently deployed default routers
      (no handovers between GGSN/PGWs are possible), a cellular host can
      keep a prefix for a long time.  Hence, IPv6 addressing privacy can
      be used for additional privacy during the time the host is on and
      in the same area.  The privacy features can also be used to, e.g.,
      make different transport sessions appear to come from different IP
      addresses.  However, it is not clear that these additional efforts
      confuse potential observers any further, as they could monitor
      only the network prefix part.

   o  The use and recommendations of various security services such as
      IPsec or Transport Layer Security (TLS) [RFC5246] in the
      connection of typical applications that also apply to cellular
      hosts are discussed in Section 11 of [RFC6434].






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   o  The airtime used by cellular hosts is expensive.  In some cases,
      users are billed according to the amount of data they transfer to
      and from their host.  It is crucial for both the network and the
      users that the airtime is used correctly and no extra charges are
      applied to users due to misbehaving third parties.  The cellular
      links also have a limited capacity, which means that they may not
      necessarily be able to accommodate more traffic than what the user
      selected, such as a multimedia call.  Additional traffic might
      interfere with the service level experienced by the user.  While
      Quality-of-Service mechanisms mitigate these problems to an
      extent, it is still apparent that DoS aspects may be highlighted
      in the cellular environment.  It is possible for existing DoS
      attacks that use, for instance, packet amplification, to be
      substantially more damaging in this environment.  How these
      attacks can be protected against is still an area for further
      study.  It is also often easy to fill the cellular link and queues
      on both sides with additional or large packets.

   o  Within some service provider networks, it is possible to buy a
      prepaid cellular subscription without presenting personal
      identification.  Attackers that wish to remain unidentified could
      leverage this.  Note that while the user hasn't been identified,
      the equipment still is; the operators can follow the identity of
      the device and block it from further use.  The operators must have
      procedures in place to take notice of third party complaints
      regarding the use of their customers' devices.  It may also be
      necessary for the operators to have attack detection tools that
      enable them to efficiently detect attacks launched from the
      cellular hosts.

   o  Cellular devices that have local network interfaces (such as WLAN
      or Bluetooth) may be used to launch attacks through them, unless
      the local interfaces are secured in an appropriate manner.
      Therefore, local network interfaces should have access control to
      prevent others from using the cellular host as an intermediary.

   o  The 3GPP link model mitigates most of the known IPv6 on-link and
      neighbor cache targeted attacks (see Section 2.2 and Appendix A).

   o  Advice for implementations in the face of Neighbor Discovery DoS
      attacks may be useful in some environments [RFC6583].

   o  Section 9 of [RFC6459] further discusses some recent concerns
      related to the security of cellular hosts.







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7.  References

7.1.  Normative References

   [RFC2460]   Deering, S. and R. Hinden, "Internet Protocol, Version 6
               (IPv6) Specification", RFC 2460, December 1998.

   [RFC4213]   Nordmark, E. and R. Gilligan, "Basic Transition
               Mechanisms for IPv6 Hosts and Routers", RFC 4213,
               October 2005.

   [RFC4301]   Kent, S. and K. Seo, "Security Architecture for the
               Internet Protocol", RFC 4301, December 2005.

   [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.

   [RFC5095]   Abley, J., Savola, P., and G. Neville-Neil, "Deprecation
               of Type 0 Routing Headers in IPv6", RFC 5095,
               December 2007.

   [RFC5722]   Krishnan, S., "Handling of Overlapping IPv6 Fragments",
               RFC 5722, December 2009.

   [RFC6434]   Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node
               Requirements", RFC 6434, December 2011.

   [RFC6980]   Gont, F., "Security Implications of IPv6 Fragmentation
               with IPv6 Neighbor Discovery", RFC 6980, August 2013.














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7.2.  Informative References

   [RFC1661]   Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51,
               RFC 1661, July 1994.

   [RFC3261]   Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
               A., Peterson, J., Sparks, R., Handley, M., and E.
               Schooler, "SIP: Session Initiation Protocol", RFC 3261,
               June 2002.

   [RFC3315]   Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
               and M. Carney, "Dynamic Host Configuration Protocol for
               IPv6 (DHCPv6)", RFC 3315, July 2003.

   [RFC3316]   Arkko, J., Kuijpers, G., Soliman, H., Loughney, J., and
               J.  Wiljakka, "Internet Protocol Version 6 (IPv6) for
               Some Second and Third Generation Cellular Hosts",
               RFC 3316, April 2003.

   [RFC3550]   Schulzrinne, H., Casner, S., Frederick, R., and V.
               Jacobson, "RTP: A Transport Protocol for Real-Time
               Applications", STD 64, RFC 3550, July 2003.

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

   [RFC3736]   Droms, R., "Stateless Dynamic Host Configuration Protocol
               (DHCP) Service for IPv6", RFC 3736, April 2004.

   [RFC4191]   Draves, R. and D. Thaler, "Default Router Preferences and
               More-Specific Routes", RFC 4191, November 2005.

   [RFC4193]   Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
               Addresses", RFC 4193, October 2005.

   [RFC5072]   Varada, S., Haskins, D., and E. Allen, "IP Version 6 over
               PPP", RFC 5072, September 2007.

   [RFC5246]   Dierks, T. and E. Rescorla, "The Transport Layer Security
               (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC5555]   Soliman, H., "Mobile IPv6 Support for Dual Stack Hosts
               and Routers", RFC 5555, June 2009.

   [RFC6106]   Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
               "IPv6 Router Advertisement Options for DNS
               Configuration", RFC 6106, November 2010.



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   [RFC6459]   Korhonen, J., 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.

   [RFC6583]   Gashinsky, I., Jaeggli, J., and W. Kumari, "Operational
               Neighbor Discovery Problems", RFC 6583, March 2012.

   [RFC6603]   Korhonen, J., Savolainen, T., Krishnan, S., and O. Troan,
               "Prefix Exclude Option for DHCPv6-based Prefix
               Delegation", RFC 6603, May 2012.

   [TS.23060]  3GPP, "General Packet Radio Service (GPRS); Service
               description; Stage 2", 3GPP TS 23.060 11.5.0, March 2013.

   [TS.23401]  3GPP, "General Packet Radio Service (GPRS) enhancements
               for Evolved Universal Terrestrial Radio Access Network
               (E-UTRAN) access", 3GPP TS 23.401 11.5.0, March 2013.

   [TS.23402]  3GPP, "Architectural enhancements for non-3GPP accesses",
               3GPP TS 23.402 11.6.0, March 2013.

   [TS.29061]  3GPP, "Interworking between the Public Land Mobile
               Network (PLMN) supporting packet based services and
               Packet Data Networks (PDN)", 3GPP TS 29.061 11.4.0,
               March 2013.

























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Appendix A.  Cellular Host IPv6 Addressing in the 3GPP Model

   This appendix aims to very briefly describe the 3GPP IPv6 addressing
   model for 2G (GPRS), 3G (UMTS), and 4G (EPS) cellular networks from
   Release-99 onwards.  More information for 2G and 3G can be found in
   3GPP Technical Specifications [TS.23060] and [TS.29061].  The
   equivalent documentation for 4G can be found in 3GPP Technical
   Specifications [TS.23401], [TS.23402], and [TS.29061].

   There are two possibilities to allocate the address for an IPv6 node:
   stateless and stateful autoconfiguration.  The stateful address
   allocation mechanism needs a DHCP server to allocate the address for
   the IPv6 node.  On the other hand, the Stateless Address
   Autoconfiguration procedure does not need any external entity
   involved in the address autoconfiguration (apart from the GGSN/PGW).
   At the time of writing this document, the IPv6 Stateless Address
   Autoconfiguration mechanism is still the only mandatory and supported
   address configuration method for the cellular 3GPP link.

   In order to support the standard IPv6 Stateless Address
   Autoconfiguration mechanism as recommended by the IETF, the GGSN/PGW
   shall assign a single /64 IPv6 prefix that is unique within its scope
   to each primary PDP Context or PDN Connection that uses IPv6
   Stateless Address Autoconfiguration.  This avoids the necessity to
   perform Duplicate Address Detection (DAD) at the network level for
   any address built by the mobile host.  The GGSN/PGW always provides
   an interface identifier to the mobile host.  The mobile host uses the
   interface identifier provided by the GGSN/PGW to generate its link-
   local address.  The GGSN/PGW provides the cellular host with the
   interface identifier, usually in a random manner.  It must ensure the
   uniqueness of such an identifier on the link (i.e., no collisions
   between its own link-local address and the cellular host's).

   In addition, the GGSN/PGW will not use any of the prefixes assigned
   to cellular hosts to generate any of its own addresses.  This use of
   the interface identifier, combined with the fact that each PDP
   Context or PDN Connection is allocated a unique prefix, will
   eliminate the need for DAD messages over the air interface and
   consequently reduces inefficient use of radio resources.
   Furthermore, the allocation of a prefix to each PDP Context or PDN
   Connection will allow hosts to implement the Privacy Extensions in
   [RFC4941] without the need for further DAD messages.

   In practice, the GGSN/PGW only needs to route all traffic destined to
   the cellular host that falls under the prefix assigned to it.  This
   implies the GGSN/PGW may implement a minimal Neighbor Discovery
   protocol subset since, due to the point-to-point link model and the
   absence of link-layer addressing, the address resolution can be



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   entirely statically configured per PDP Context or PDN Connection, and
   there is no need to defend any addresses other than the link-local
   addresses for very unlikely duplicates.  This also has an additional
   effect on a router-to-host NUD.  There is really no need for the NUD,
   since from the point of view of GGSN/PGW, GGSN/PGW does not need to
   care for a single address but just routes the whole prefix to the
   cellular host.  However, the cellular host must be prepared for the
   unlikely event of receiving a NUD against its link-local address.  It
   should be noted that the 3GPP specifications at the time of writing
   this document are silent about what should happen if the router-to-
   host NUD fails.

   See Section 5 of [RFC6459] for further discussion on 3GPP address
   allocation and the 3GPP link model.

Appendix B.  Changes from RFC 3316

   o  Clarified that [RFC4941] or similar technologies may be used for
      privacy purposes (as stated in [RFC6459]).

   o  Clarified that MLD for link-local addresses is not necessary, but
      doing it causes no harm (instead of saying it may not be needed in
      some cases).

   o  Clarified that a cellular host should not do any changes in its
      stack to meet the 3GPP link restriction on the Router
      Advertisement Prefix Information Options (PIOs).

   o  Clarified that a cellular host should not do any changes in its
      stack to meet the infinite prefix lifetime requirement the 3GPP
      link has.

   o  Clarified that the prefix lifetime is tied to the PDP Context/PDN
      Connection lifetime.

   o  Clarified explicitly that a NUD from the gateway side to the User
      Equipment's link-local address is possible.

   o  Added references to 3GPP specifications.

   o  Provided additional clarification on NUD on 3GPP cellular links.

   o  Added an explicit note that the prefix on the link is /64.

   o  Clarified that DHCPv6 ([RFC3315]) is not used at all for address
      autoconfiguration.

   o  Removed all sections that can be directly found in [RFC6434].



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   o  Added clarifications to 3GPP link model and how Neighbor Discovery
      works on it.

   o  Added [RFC4191] recommendations.

   o  Added DHCPv6-based Prefix Delegation recommendations.

   o  Added [RFC6106] recommendations.

   o  Added reference to [RFC5555] regarding client-based mobility.

   o  Added text regarding Router Advertisement MTU option handling.

   o  Added Evolved Packet System text.

   o  Added clarification on the primary 3GPP IPv6 transition mechanism.

   o  Added reference to [RFC5095], which deprecates the RH0.

   o  Added references to [RFC5722] and [RFC6980] regarding IPv6
      fragmentation handling.

   o  Added reference to [RFC6583] for Neighbor Discovery denial-of-
      service attack considerations.

   o  Made the PPP IPV6CP [RFC5072] support text conditional.

























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Authors' Addresses

   Jouni Korhonen (editor)
   Broadcom
   Porkkalankatu 24
   FIN-00180 Helsinki
   Finland

   EMail: jouni.nospam@gmail.com


   Jari Arkko (editor)
   Ericsson
   Jorvas  02420
   Finland

   EMail: jari.arkko@piuha.net


   Teemu Savolainen
   Nokia
   Hermiankatu 12 D
   FI-33720 Tampere
   Finland

   EMail: teemu.savolainen@nokia.com


   Suresh Krishnan
   Ericsson
   8400 Decarie Blvd.
   Town of Mount Royal, QC
   Canada

   Phone: +1 514 345 7900 x42871
   EMail: suresh.krishnan@ericsson.com















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