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.
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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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