Service Selection for Mobile IPv4
RFC 5446

Network Working Group                                        J. Korhonen
Request for Comments: 5446                        Nokia Siemens Networks
Category: Informational                                       U. Nilsson
                                                             TeliaSonera
                                                           February 2009

                   Service Selection for Mobile IPv4

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (c) 2009 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.

Abstract

   In some Mobile IPv4 deployments, identifying the mobile node or the
   mobility service subscriber is not enough to distinguish among the
   multiple services possibly provisioned to the mobile node.  The
   capability to specify different services in addition to the mobile
   node's identity can be leveraged to provide flexibility for mobility
   service providers to provide multiple services within a single
   mobility service subscription.  This document describes a Service
   Selection extension for Mobile IPv4 that is intended to assist home
   agents to make specific service selections for their mobility service
   subscriptions during the registration procedure.

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Table of Contents

   1. Introduction ....................................................2
   2. Requirements ....................................................3
   3. Service Selection Extension .....................................3
   4. Processing Considerations .......................................5
      4.1. Mobile Node Considerations .................................5
      4.2. Home Agent Considerations ..................................5
      4.3. Foreign Agent Considerations ...............................6
   5. Security Considerations .........................................7
   6. IANA Considerations .............................................7
   7. Acknowledgments .................................................7
   8. References ......................................................8
      8.1. Normative References .......................................8
      8.2. Informative References .....................................8

1.  Introduction

   Mobile IPv4 [RFC3344] can identify mobile nodes in various ways,
   including home addresses [RFC3344] and Network Access Identifiers
   (NAIs) [RFC4282] [RFC2794].  In some Mobile IPv4 deployments,
   identifying the mobile node (MN) or the mobility service subscriber
   via a Proxy Mobile IPv4 client [LEUNG] (hereafter, the mobile node
   and the Proxy Mobile IPv4 client are used interchangeably) is not
   enough to distinguish among the multiple services possibly
   provisioned to the mobile node.

   The capability to specify different services in addition to the
   mobile node's identity can be leveraged to provide flexibility for
   mobility service providers to provide multiple services within the
   same mobility service subscription.  For example:

   o  Provide an enterprise data access for which the mobility service
      provider hosts connectivity and mobility services on behalf of the
      enterprise.

   o  Provide access to service domains that are otherwise not
      accessible from public networks because of some mobility service
      providers' business reasons.

   o  Provide simultaneous access to different service domains that are
      separated based on policies of the mobility service provider.

   o  Enable easier policy assignment for mobility service providers
      based on the subscribed services.

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   This document describes a Service Selection extension for Mobile IPv4
   that is intended to assist home agents to make specific service
   selections for their mobility service subscriptions during the
   registration procedure.  A Mobile IPv6-equivalent Service Selection
   Mobility Option has been described in [RFC5149].  The service
   selection may affect home agent routing decisions, Home Address
   assignment policies, firewall settings, and security policies.  When
   the service selection is used, every Registration Request must
   contain the Service Selection extension.  The Service Selection
   extension from the Registration Request may be echoed back in the
   Registration Reply.

   In absence of a specifically indicated service, the home agent must
   act as if the default service, plain Internet access, had been
   requested.  There is no absolute requirement that this default
   service would be allowed to all subscribers, but it is highly
   recommended in order to avoid having normal subscribers employ
   operator-specific configuration values in order to get basic service.

   Some of the potential use cases were listed earlier in this section.
   The general aim is better manageability of services and service
   provisioning, from both operators' and service providers' points of
   view.  However, it should be understood that there are potential
   deployment possibilities where selecting a certain service may
   restrict simultaneous access to other services from a user point of
   view (e.g., a "walled garden").  For example, services may be located
   in different administrative domains or external customer networks
   that practice excessive filtering of inbound and outbound traffic.

2.  Requirements

   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 [RFC2119].

3.  Service Selection Extension

   At most one Service Selection extension MAY be included in any Mobile
   IPv4 Registration Request message.  When the service selection is
   used, the Service Selection extension MUST be included in every
   Registration Request message.  In absence of a specifically indicated
   service in the Registration Request for the initial registration or
   re-registration, the home agent MUST act as if the default service,
   such as plain Internet access, had been requested.  The Service
   Selection extension MUST be placed in the Registration Request
   message as follows:

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   o  When present, the extension MUST appear after the MN-NAI
      extension, if the MN-NAI is also present in the message.

   o  If the extension was added by the mobile node to a Registration
      Request, it MUST appear prior to any authentication-enabling
      extensions [RFC3344] [RFC4721].

   o  In the event the foreign agent adds the Service Selection
      extension to a Registration Request, the extension MUST appear
      prior to any Foreign-Home authentication-enabling extensions
      [RFC3344].

   The home agent MAY echo the received Service Selection extension
   option back in a Mobile IPv4 Registration Reply message.  The echoed
   Service Selection extension MUST be an unchanged copy of the Service
   Selection extension received in the corresponding Registration
   Request message.  The Service Selection extension MUST be placed in
   the Registration Reply message as follows:

   o  If the extension was originally added by the mobile node to a
      Registration Request, it MUST appear in the Registration Reply
      prior to any authentication-enabling extensions [RFC3344]
      [RFC4721].

   o  If the foreign agent added the Service Selection extension to a
      Registration Request, the extension MUST appear in the
      Registration Reply prior to any Foreign-Home authentication-
      enabling extensions [RFC3344].

   The Service Selection extension has the following format:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Type = 151   |   Length      | Identifier...                 ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Service Selection Extension

   o  Type: 8-bit identifier set to 151 (the type of this skippable
      extension).

   o  Length: 8-bit unsigned integer, representing the length of the
      Service Selection extension in octets, excluding the Type and
      Length fields.  A value of zero (0) is not allowed.

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   o  Identifier: A variable-length, encoded service-identifier string
      used to identify the requested service.  The identifier string
      length is between 1 and 255 octets.  This specification allows
      international identifier strings that are based on the use of
      Unicode characters, encoded as UTF-8 [RFC3629] and formatted using
      Normalization Form KC (NFKC) as specified in [NFKC].

      'ims', 'voip', and 'voip.companyxyz.example.com' are valid
      examples of Service Selection extension Identifiers.  At minimum
      the Identifier MUST be unique among the home agents to which the
      mobile node is authorized to register.

4.  Processing Considerations

4.1.  Mobile Node Considerations

   A mobile node or its proxy representative MAY include the Service
   Selection extension into any Registration Request message.  The
   Service Selection extension can be used with any mobile node
   identification method.  The extension is used to identify the service
   to be associated with the mobility session; if the service selection
   is used, the Service Selection extension MUST be included into every
   Registration Request message sent to a home agent.  If the mobile
   node wishes to change the selected service, it is RECOMMENDED that
   the mobile node de-register the existing binding with the home agent
   before proceeding with a binding registration for a different
   service.  The provisioning of the service identifiers to the mobile
   node or its proxy representative is out of the scope of this
   specification.

   If the mobile node receives a Registration Reply message with a Code
   set to SERVICE_AUTHORIZATION_FAILED and the mobile node has an
   existing binding with the Home Address used in the failed
   Registration Request message, the mobile node MUST delete the
   existing binding.  If there is no existing binding, the mobile node
   proceeds as with any failed initial registration.

4.2.  Home Agent Considerations

   Upon receiving the Service Selection extension, the home agent
   authenticates and authorizes the mobile node.  If the home agent
   supports the Service Selection, it MUST also verify that the mobile
   node is authorized to the service identified by the Service Selection
   extension.  The services the mobile node is authorized to SHOULD be
   part of the general mobile node subscription data.  If the mobile
   node is not authorized to the service, or the home agent does not

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   recognize the identified service, the home agent MUST deny the
   registration and send a Registration Reply with a Code
   SERVICE_AUTHORIZATION_FAILED (error code 151).

   The Service Selection extension is used to assist the mobile node
   authorization phase and identifies a specific service that is to be
   authorized.  The Service Selection extension MAY also affect the Home
   Address allocation when, for example, used with the MN-NAI extension.
   For example, for the same NAI, there MAY be different Home Addresses,
   depending on the identified service.  Furthermore, the Service
   Selection extension MAY also affect the routing of the outbound IP
   packets in the home agent depending on the selected service.  The
   home agent MAY also apply different policy or quality of service
   treatment to traffic flows based on the selected service.

   If the newly arrived Registration Request message with a Service
   Selection extension indicates a change in the selected service, then
   the home agent MUST re-authorize the mobile node.  The absence of the
   Service Selection extension MUST be treated as a request for the
   default service, which may also cause the re-authorization of the
   mobile node.  Depending on the home agent's policies, the services
   policies, the Home Address allocation policies, and the subscription
   policies, the home agent may or may not be able to authorize the
   mobile node to the new service.  For example the existing service and
   the new service could require different Home Addresses.  If the
   authorization fails, then the home agent MUST deny the registration,
   delete any binding with the existing Home Address, and send a
   Registration Reply with a Code set to SERVICE_AUTHORIZATION_FAILED
   (error code 151).

   Depending on the local home agent's policy, the home agent MAY echo
   the Service Selection extension in the corresponding Registration
   Reply message towards the mobile node or the foreign agent.  The home
   agent MUST NOT change the content of the echoed Service Selection
   extension.

4.3.  Foreign Agent Considerations

   A foreign agent MUST skip the Service Selection extension if the
   Registration Request already contains the Service Selection
   extension.  If the Registration Request does not contain the Service
   Selection extension, the foreign agent MAY add the Service Selection
   extension to the Registration Request message.  How the foreign agent
   learns the service that the mobile node needs to authorize is outside
   the scope of this document.

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   In the case a foreign agent added the Service Selection extension to
   the Registration Request on behalf of the mobile node, it MUST verify
   whether the corresponding Registration Reply message from a home
   agent also contains an echoed Service Selection extension.  If the
   received Registration Reply message contains the echoed Service
   Selection extension, the foreign agent MUST NOT include the extension
   to the Registration Reply message that gets forwarded to the mobile
   node.

5.  Security Considerations

   The protection for the Service Selection extension depends on the
   service that is being identified and eventually selected.  If the
   service selection information should not be revealed on the wire, it
   should be protected in a manner similar to Registration Requests and
   Registration Replies.  The Service Selection extension is protected
   by the same authentication-enabling extension as the rest of the
   Registration Request message.

   The home agent MUST verify that the mobile node is authorized to the
   service included in the Service Selection extension.  The Service
   Selection extension authorization is part of the normal mobile node
   registration and authentication procedure.  Both registration
   authentication and service authorization MUST succeed before the
   mobile node is allowed to register to the home agent.

6.  IANA Considerations

   A new Mobile IPv4 Extension type has been assigned in the "Extensions
   appearing in Mobile IP control messages" registry for the extension
   described in Section 3.  The Extension type has been allocated from
   the 'skippable' range (128-255):

       Service Selection Extension       is set to 151

   A new Mobile IPv4 error code has been assigned in the "Registration
   denied by the home agent" section of the "Code Values for Mobile IP
   Registration Reply Messages" registry.  The error code has been
   allocated from the 'Error Codes from the Home Agent' range (128-192):

       SERVICE_AUTHORIZATION_FAILED      is set to 151

7.  Acknowledgments

   The authors would like to thank Henrik Levkowetz, Kent Leung, Spencer
   Dawkins, and Jari Arkko for their comments.  Jouni Korhonen also
   acknowledges TeliaSonera and the TEKES MERCoNe project, where most of
   the work was conducted.

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8.  References

8.1.  Normative References

   [NFKC]     Davis, M. and M. Durst, "Unicode Standard Annex #15;
              Unicode Normalization Forms", Unicode 5.0.0, October 2006.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3344]  Perkins, C., "IP Mobility Support for IPv4", RFC 3344,
              August 2002.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

8.2.  Informative References

   [LEUNG]    Leung, K., "WiMAX Forum/3GPP2 Proxy Mobile IPv4", Work
              in Progress, December 2008.

   [RFC2794]  Calhoun, P. and C. Perkins, "Mobile IP Network Access
              Identifier Extension for IPv4", RFC 2794, March 2000.

   [RFC4282]  Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The
              Network Access Identifier", RFC 4282, December 2005.

   [RFC4721]  Perkins, C., Calhoun, P., and J. Bharatia, "Mobile IPv4
              Challenge/Response Extensions (Revised)", RFC 4721,
              January 2007.

   [RFC5149]  Korhonen, J., Nilsson, U., and V. Devarapalli, "Service
              Selection for Mobile IPv6", RFC 5149, February 2008.

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Authors' Addresses

   Jouni Korhonen
   Nokia Siemens Networks
   Linnoitustie 6
   FIN-02600 Espoo
   FINLAND

   EMail: jouni.nospam@gmail.com

   Ulf Nilsson
   TeliaSonera Corporation
   Marbackagatan 11
   S-123 86 Farsta
   SWEDEN

   EMail: ulf.s.nilsson@teliasonera.com

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