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INFORMATIONAL

Independent Submission                                     A. Dodd-Noble
Request for Comments: 7651                                 S. Gundavelli
Category: Informational                                            Cisco
ISSN: 2070-1721                                              J. Korhonen
                                                             F. Baboescu
                                                    Broadcom Corporation
                                                                 B. Weis
                                                                   Cisco
                                                          September 2015


               3GPP IP Multimedia Subsystems (IMS) Option
        for the Internet Key Exchange Protocol Version 2 (IKEv2)

Abstract

   This document defines two new configuration attributes for the
   Internet Key Exchange Protocol version 2 (IKEv2).  These attributes
   can be used for carrying the IPv4 address and IPv6 address of the
   Proxy-Call Session Control Function (P-CSCF).  When an IPsec gateway
   delivers these attributes to an IPsec client, the IPsec client can
   obtain the IPv4 and/or IPv6 address of the P-CSCF server located in
   the 3GPP network.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This is a contribution to the RFC Series, independently of any other
   RFC stream.  The RFC Editor has chosen to publish this document at
   its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not 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/rfc7651.












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Copyright Notice

   Copyright (c) 2015 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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions and Terminology . . . . . . . . . . . . . . . . .   4
     2.1.  Conventions . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  P_CSCF_IP4_ADDRESS Configuration Attribute  . . . . . . . . .   4
   4.  P_CSCF_IP6_ADDRESS Configuration Attribute  . . . . . . . . .   5
   5.  Example Scenario  . . . . . . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   The Third Generation Partnership Project (3GPP) S2b reference point
   [TS23402], specified by the 3GPP system architecture, defines a
   mechanism for allowing a mobile node (MN) attached in an untrusted,
   non-3GPP IP access network to securely connect to a 3GPP network and
   access IP services.  In this scenario, the mobile node establishes an
   IPsec Encapsulating Security Payload (ESP) tunnel [RFC4303]  to the
   security gateway called the Evolved Packet Data Gateway (ePDG) that
   in turn establishes a Proxy Mobile IPv6 (PMIPv6) [RFC5213] or GPRS
   Tunneling Protocol (GTP) [TS23402] tunnel to the Packet Data Network
   Gateway (PGW) [TS23402] where the mobile node's session is anchored.

   The below figure shows the interworking option for non-3GPP access
   over an untrusted access network.  The Mobile Access Gateway (MAG)
   and the Local Mobility Anchor (LMA) functions are defined in
   [RFC5213].  The ePDG and PGW functions are defined in [TS23402].  The
   IPsec ESP tunnel is used between the MN and the ePDG; either a PMIP
   or GTP tunnel is used between the ePDG and PGW.



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                                 +------------+
                                 |    ePDG    |
                                 | +--------+ |
   +------+        _----_        | | IPsec  | |      _----_      +-----+
   |  MN  |      _(      )_      | | Module | |    _(      )_    | LMA |
   |      |<====( Internet )=====| +--------+ |===( Operator )===|(PGW)|
   +------+      (_      _)      |      :     |    (_Network_)   +-----+
                   '----'        | +--------+ |      '----'
                  IPsec Tunnel   | | PMIPv6 | |  PMIPv6/GTP Tunnel
                                 | |   MAG  | |
                                 | +--------+ |
                                 +------------+

      |<------------ IKEv2/IPsec ------> | <------ PMIPv6/GTP ----->|


           Figure 1: Exchange of IPv4 Traffic Offload Selectors

   A mobile node in this scenario may potentially need to access the IP
   Multimedia Subsystem (IMS) services in the 3GPP network.  The 3GPP
   IMS architecture is described in [TS23228] and [TS24229].  Currently,
   there are no attributes in IKEv2 [RFC7296] that can be used for
   carrying these information elements.  In the absence of these
   attributes, the mobile node needs to be statically configured with
   this information and this is proving to be an operational challenge.
   Any other approaches for discovering these functions (such as using
   DNS or DHCP) would result in obtaining configuration from the access
   network and not from the home network.  Given that the above
   referenced 3GPP interface is primarily for allowing the mobile node
   to connect to the 3GPP network through an untrusted access network,
   the access network may not have any relation with the home network
   provider and may be unable to deliver the mobile node's home network
   configuration.

   This specification therefore defines two new IKEv2 attributes
   [RFC7296] that allow an IPsec gateway to provide the IPv4 and/or IPv6
   address of the P-CSCF server.  These attributes can be exchanged by
   IKEv2 peers as part of the configuration payload exchange.  The
   attributes follow the configuration attribute format defined in
   Section 3.15.1 of [RFC7296].  Furthermore, providing the P-CSCF
   server address(es) in IKEv2 as a standard attribute(s) enables
   clients to directly access IMS services behind a VPN gateway without
   going through the 3GPP-specific interfaces.








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2.  Conventions and Terminology

2.1.  Conventions

   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].

2.2.  Terminology

   All the IKEv2-related terms used in this document are to be
   interpreted as defined in [RFC7296] and [RFC5739].  All the mobility-
   related terms are to be interpreted as defined in [RFC5213] and
   [RFC5844].  Additionally, this document uses the following terms:

   Proxy-Call Session Control Function (P-CSCF)

      The P-CSCF is the entry point to the 3GPP IMS and serves as the
      SIP outbound proxy for the mobile node.  The mobile node performs
      SIP registration to 3GPP IMS and initiates SIP sessions via a
      P-CSCF.

   Evolved Packet Data Gateway (ePDG)

      This is a security gateway defined by the 3GPP system
      architecture.  The protocol interfaces it supports include IKEv2
      [RFC7296].

3.  P_CSCF_IP4_ADDRESS Configuration Attribute

   The P_CSCF_IP4_ADDRESS configuration attribute is formatted as
   follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |R|        Attribute Type       |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         IPv4 Address                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                     Figure 2: IPv4 Address of P-CSCF

   Reserved (1 bit)
      Refer to the IKEv2 specification [RFC7296]





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   Attribute Type (15 bits)
      20

   Length (2 octets)
      Length of the IPv4 address field that follows.  Possible values
      are (0) and (4).  A value of (4) indicates the size of the 4-octet
      IPv4 address that follows.  A value of (0) indicates that it's an
      empty attribute with a zero-length IPv4 address field primarily
      used as a request indicator.

   IPv4 Address (4 octets)
      An IPv4 address of the P-CSCF server.

   The P_CSCF_IP4_ADDRESS configuration attribute provides an IPv4
   address of a P-CSCF server within the network.  If an instance of an
   empty P_CSCF_IP4_ADDRESS attribute with a zero-length IPv4 Address
   field is included by the mobile node, the responder MAY respond with
   zero, one, or more P_CSCF_IP4_ADDRESS attributes.  If several
   P_CSCF_IP4_ADDRESS attributes are provided in one IKEv2 message,
   there is no implied order among the P_CSCF_IP4_ADDRESS attributes.
   However, a system architecture using this specification may be able
   to enforce some order at both the peers.

4.  P_CSCF_IP6_ADDRESS Configuration Attribute

   The P_CSCF_IP6_ADDRESS configuration attribute is formatted as
   follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |R|        Attribute Type       |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                                                               |
   |                          IPv6 Address                         |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                     Figure 3: IPv6 Address of P-CSCF

   Reserved (1 bit)
      Refer to the IKEv2 specification [RFC7296]

   Attribute Type (15 bits)
      21




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   Length (2 octets)
      Length of the IPv6 address field that follows.  Possible values
      are (0) and (16).  A value of (16) indicates the size of the
      16-octet IPv6 address that follows.  A value of (0) indicates that
      it's an empty attribute with a zero-length IPv6 address field
      primarily used as a request indicator.

   IPv6 Address (16 octets)
      An IPv6 address of the P-CSCF server.

   The P_CSCF_IP6_ADDRESS configuration attribute provides an IPv6
   address of a P-CSCF server within the network.  If an instance of an
   empty P_CSCF_IP6_ADDRESS attribute with a zero-length IPv6 Address
   field is included by the mobile node, the responder MAY respond with
   zero, one, or more P_CSCF_IP6_ADDRESS attributes.  If several
   P_CSCF_IP6_ADDRESS attributes are provided in one IKEv2 message,
   there is no implied order among the P_CSCF_IP6_ADDRESS attributes.
   However, a system architecture using this specification may be able
   to enforce some order at both the peers.
































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5.  Example Scenario

   The mobile node MAY request the IP address of an P-CSCF server as
   shown below.

         Client      Gateway
        --------    ---------

         HDR(IKE_SA_INIT), SAi1, KEi, Ni  -->

                  <--  HDR(IKE_SA_INIT), SAr1, KEr, Nr, [CERTREQ]

         HDR(IKE_AUTH),
         SK { IDi, CERT, [CERTREQ], AUTH, [IDr],
              CP(CFG_REQUEST) =
                 { INTERNAL_IP4_ADDRESS(),
                   INTERNAL_IP4_DNS(),
                   P_CSCF_IP4_ADDRESS() }, SAi2,
              TSi = (0, 0-65535, 0.0.0.0-255.255.255.255),
              TSr = (0, 0-65535, 0.0.0.0-255.255.255.255) }  -->

                <--  HDR(IKE_AUTH),
                     SK { IDr, CERT, AUTH,
                          CP(CFG_REPLY) =
                             { INTERNAL_IP4_ADDRESS(192.0.2.234),
                               P_CSCF_IP4_ADDRESS(192.0.2.1),
                               P_CSCF_IP4_ADDRESS(192.0.2.4),
                               INTERNAL_IP4_DNS(198.51.100.33) },
                          SAr2,
                          TSi = (0, 0-65535, 192.0.2.234-192.0.2.234),
                          TSr = (0, 0-65535, 0.0.0.0-255.255.255.255) }


                    Figure 4: P-CSCF Attribute Exchange

6.  IANA Considerations

   Per this document, the following IANA actions have been completed.

   o  Action 1: This specification defines a new IKEv2 attribute for
      carrying the IPv4 address of the P-CSCF server.  This attribute is
      defined in Section 3.  It has been assigned value 20 from the
      "IKEv2 Configuration Payload Attribute Types" namespace defined in
      [RFC7296].







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   o  Action 2: This specification defines a new IKEv2 attribute for
      carrying the IPv6 address of the P-CSCF server.  This attribute is
      defined in Section 4.  It has been assigned value 21 from the
      "IKEv2 Configuration Payload Attribute Types" namespace defined in
      [RFC7296].

7.  Security Considerations

   This document is an extension to IKEv2 [RFC7296] and therefore it
   inherits all the security properties of IKEv2.

   The two new IKEv2 attributes defined in this specification are for
   carrying the IPv4 and IPv6 address of the P-CSCF server.  These
   attributes can be exchanged by IKE peers as part of the configuration
   payload, and the currently defined IKEv2 security framework provides
   the needed integrity and privacy protection for these attributes.
   Therefore, this specification does not introduce any new security
   vulnerabilities.

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, DOI 10.17487/RFC4303, December 2005,
              <http://www.rfc-editor.org/info/rfc4303>.

   [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
              Kivinen, "Internet Key Exchange Protocol Version 2
              (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
              2014, <http://www.rfc-editor.org/info/rfc7296>.

8.2.  Informative References

   [RFC5213]  Gundavelli, S., Ed., Leung, K., Devarapalli, V.,
              Chowdhury, K., and B. Patil, "Proxy Mobile IPv6",
              RFC 5213, DOI 10.17487/RFC5213, August 2008,
              <http://www.rfc-editor.org/info/rfc5213>.

   [RFC5739]  Eronen, P., Laganier, J., and C. Madson, "IPv6
              Configuration in Internet Key Exchange Protocol Version 2
              (IKEv2)", RFC 5739, DOI 10.17487/RFC5739, February 2010,
              <http://www.rfc-editor.org/info/rfc5739>.



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   [RFC5844]  Wakikawa, R. and S. Gundavelli, "IPv4 Support for Proxy
              Mobile IPv6", RFC 5844, DOI 10.17487/RFC5844, May 2010,
              <http://www.rfc-editor.org/info/rfc5844>.

   [TS23228]  3GPP, "IP Multimedia Subsystem (IMS); Stage 2", 3GPP TS
              23.228, Version 13.3.0, June 2015.

   [TS23402]  3GPP, "Architecture enhancements for non-3GPP accesses",
              3GPP TS 23.402, Version 13.2.0, June 2015.

   [TS24229]  3GPP, "IP multimedia call control protocol based on
              Session Initiation Protocol (SIP) and Session Description
              Protocol (SDP); Stage 3", 3GPP TS 24.229, Version 13.2.1,
              June 2015.

Acknowledgements

   The authors would like to specially thank Tero Kivinen for the
   detailed reviews.  The authors would also like to thank Vojislav
   Vucetic, Heather Sze, Sebastian Speicher, Maulik Vaidya, Ivo
   Sedlacek, Pierrick Siete, and Hui Deng for all the discussions
   related to this topic.





























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Authors' Addresses

   Aeneas Noble
   Cisco
   30 International Pl
   Tewksbury, MA  95134
   United States

   Email: noblea@cisco.com


   Sri Gundavelli
   Cisco
   170 West Tasman Drive
   San Jose, CA  95134
   United States

   Email: sgundave@cisco.com


   Jouni Korhonen
   Broadcom Corporation
   3151 Zanker Road
   San Jose, CA  95134
   United States

   Email: jouni.nospam@gmail.com


   Florin Baboescu
   Broadcom Corporation
   100 Mathilda Place
   Sunnyvale, CA  94086
   United States

   Email: baboescu@broadcom.com


   Brian Weis
   Cisco
   170 West Tasman Drive
   San Jose, CA  95134
   United States

   Email: bew@cisco.com






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