Diameter Maintenance and J. Korhonen (ed.)
Extensions (DIME) TeliaSonera
Internet-Draft M. Jones
Intended status: Standards Track Bridgewater Systems
Expires: April 30, 2009 L. Morand
Orange Labs
T. Tsou
Huawei
October 27, 2008
Diameter User-Name and Realm Based Request Routing Clarifications
draft-korhonen-dime-nai-routing-02.txt
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Abstract
This specification clarifies the Diameter realm based request
routing. We focus on the case where a Network Access Identifier in
the User-Name AVP is used to populate the Destination-Realm AVP and
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the Network Access Identifier contains more than one realm. This
particular case is possible when the Network Access Identifier
decoration is used to force a routing of request messages through a
predefined list of realms. However, this functionality is not
unambiguously specified in the Diameter Base Protocol specification.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology and Abbreviations . . . . . . . . . . . . . . . . 3
3. Problem Overview . . . . . . . . . . . . . . . . . . . . . . . 4
4. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Interpretation of Decorated NAIs . . . . . . . . . . . . . 6
4.2. Enhanced Request Routing Solution . . . . . . . . . . . . 6
4.3. Backwards Compatibility Considerations . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . . . . 11
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1. Introduction
This specification clarifies the Diameter realm based request routing
defined in RFC 3588 [1]. We focus on the case where the Network
Access Identifier (NAI) [2] in the User-Name AVP is used to populate
the Destination-Realm AVP and the NAI contains more than one realm.
This particular case is possible when the NAI decoration is used to
force a routing of request messages through a predefined list of
realms.
According to the Diameter request routing processing rules in RFC
3588, the request originator may populate the Destination-Realm AVP
with the realm part of the NAI available in the User-Name AVP.
Unfortunately, there is no unambiguous mandatory language in RFC 3588
how Diameter agents participating to the request routing should
update the Destination-Realm AVP at each realm.
This specification presents both the issue regarding to the Diameter
realm based request routing with NAI decoration and also a solution
for the problem. The solution would only apply to Diameter Base
Protocol implementations that take the solution presented in this
specification into account. The solution, however, is fully
backwards compatible with the RFC 3588 Diameter Base Protocol.
2. Terminology and Abbreviations
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].
Network Access Identifier (NAI):
The Network Access Identifier (NAI) is the user identity submitted
by the client during access authentication. In roaming, the
purpose of the NAI is to identify the user as well as to assist in
the routing of the authentication request.
Decorated NAI:
A NAI specifying a source route. See Section 2.7 of RFC 4282 for
more information.
Network Access Provider (NAP):
A business entity that provides network access infrastructure to
one or more realms. A NAP infrastructure constitutes of one or
more NASes.
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Network Access Server (NAS):
The device that peers connect to in order to obtain access to the
network.
3. Problem Overview
The Diameter Base Protocol RFC 3588 Section 6.1 defines the request
routing in detail. This specification concerns only those cases
where a Destination-Realm AVP is included in a request message. A
Diameter peer originating a request message MAY retrieve the realm
information from the User-Name AVP and use that realm to populate the
Destination-Realm AVP. The User-Name AVP is in form of a NAI (in
this case a NAI with the realm part). The realm based request
routing, as described in RFC 3588, does not discuss how to handle
Decorated NAIs. The original NAI RFC 2486 [4] that RFC 3588
references to, does not defined how to construct a NAI with multiple
realms. Since then RFC 2486 has been obsoleted by RFC 4282 which in
turn defines how to construct Decorated NAIs.
Decorated NAIs are used to force routing of messages through a
predefined list of realms and in that way force certain inter-realm
roaming arrangements, see Section 2.7. of RFC 4282 [2]. For example,
a terminal (e.g., a mobile host) may learn based on some application
or implementation specific manner that its network access
authentication signaling must traverse through certain realms in
order to reach the home realm. In this case the terminal would
decorate its NAI during the network access authentication with the
list of intermediating realms and the home realm. As a result, the
network access server (NAS) and intermediating Diameter agents would
make sure that all subsequent request messages traverse through the
desired realms as long as the request messages contain the User-Name
AVP with a Decorated NAI.
NAI Decoration has previously been used, for example, in RADIUS [5]
based roaming networks using RFC 2486 NAIs in a proprietary manner.
There is a need to replicate the same NAI based routing enforcement
functionality also in Diameter based roaming networks. There are
also publicly available specifications (e.g., see [6], [7] and [8])
that assume NAI Decoration based request routing enforcement is fully
supported by RFC 3588. The same assumption is carried over to NASREQ
[9] and EAP [10] Diameter applications.
Figure 1 illustrates an example deployment scenario where Decorated
NAIs would be used to force a certain route through desired realms.
A roaming terminal (e.g., a mobile host) discovers a number of
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Network Access Providers (NAP): NAP A and NAP B. None of the NAPs are
able to provide direct connectivity to roaming terminals home realm
(i.e. Realm-H). However, the roaming terminal learns, somehow, that
NAP B is able to provide connectivity to the Realm-H through the
Realm-X (i.e. the visited realm from the roaming terminal point of
view). During the network access authentication, the roaming
terminal would decorate its NAI as Realm-H!username@Realm-X. The
roaming terminal has also an alternative route to its home realm
through NAP A, Realm-Z and Realm-X. If the roaming terminal were to
choose to use NAP A, then it would decorate its NAI as Realm-X!Realm-
H!username@Realm-Z. Diameter agents should now be able to route the
request message through desired realms using the Decorated NAI
originally found in the User-Name AVP.
.--. .--. .--.
_(. `) _(. `) _(. `)
_(Visited`)_ _(Visited`)_ _( Home `)_
( Realm-Z `)<---->( Realm-X `)<------>( Realm-H `)
( ` . ) ) ( ` . ) ) ( ` . ) )
`--(_______)--' `--(_______)--' `--(_______)--'
| __ /
| /
.--. .--.
_( `. _( `.
( NAP A ) ( NAP B )
( ` . ) ) ( ` . ) )
`--(___.-' `--(___.-'
)
( ( )
( |
+-+
|M|
+-+
Figure 1: Example roaming scenario with intermediating realms. The
mobile host authenticates to the home realm through one or more
visited realms.
NAI Decoration is not limited to the network access authentication
and authorization procedures. It can be used with any Diameter
application whose commands are proxiable and include the User-Name
AVP with a NAI. Generally NAI Decoration can be used to force a
certain route for all request messages at a realm granularity.
As a problem summary we have two main issues:
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o Updating both Destination-Realm and User-Name AVPs based on the
Decorated NAI extracted from the User-Name AVP. The update would
be done by intermediating Diameter agents that participate to
realm based request routing. Specifically, this would concern
Diameter proxies.
o How Diameter agents could implement the handling of the NAI
Decoration based routing enforcement in a way that is still
backwards compatible with RFC 3588.
RFC 5113 [11] Section 2.3 also discusses NAI decoration related
issues with EAP [12] in general.
4. Solution Overview
This specification defines a solution for Diameter realm based
request routing with routing enforcement using the User-Name AVP NAI
Decoration. Diameter proxy agent implementations can claim
compliance using the solution described in this specification.
4.1. Interpretation of Decorated NAIs
Implementations compliant to this specification MUST have an uniform
way of interpreting decorated NAIs. That is, in the case of
decoration, the character '!' is used to separate realms in the list
of decorated realms in the NAI (as shown in examples in [2]).
4.2. Enhanced Request Routing Solution
When a Diameter agent receives a request message containing a
Destination-Realm AVP with a realm that the agent is configured to
process locally (and in the case of proxies the Diameter application
is locally supported), it MUST do the following further processing
before handling the message locally:
o If the User-Name AVP is available in the request message, then the
Diameter agent MUST inspect whether the User-Name AVP contains a
Decorated NAI. If the NAI is not decorated then the Diameter
agent proceeds with a normal RFC 3588 message processing.
o If the User-Name AVP contains a Decorated NAI, then the Diameter
agent MUST process the NAI as defined in RFC 4282 and update the
value of the User-Name AVP accordingly. Furthermore, the Diameter
agent MUST update the Destination-Realm AVP to match the new realm
in the User-Name AVP.
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o The request message is then sent to the next hop using the normal
request routing rules as defined in RFC 3588.
Figure 2 illustrates an example of a roaming terminal originated
signaling with the home realm (Realm-H) through a NAP and two
intermediating realms (Realm-Z, Realm-X) before reaching the home
realm (Realm-H). The example shows how the User-Name AVP and the
Destination-Realm AVP change at each realm before reaching the final
destination. If the signaling were originated from the NAS/NAP only,
then the step 1) can be omitted.
1) Roaming Terminal -> NAS/NAP
Identity/NAI = realm-X!realm-H!username@realm-Z
2) NAS/NAP -> Realm-Z
User-Name = realm-X!realm-H!username@realm-Z
Destination-Realm = realm-Z
3) Realm-Z -> realm-X
User-Name = realm-H!username@realm-X
Destination-Realm = realm-X
4) Realm-X -> Realm-H
User-Name = username@realm-H
Destination-Realm = realm-H
Figure 2: The roaming terminal decides that the Diameter messages
must be routed via Realm-Z, Realm- X and Realm-H.
4.3. Backwards Compatibility Considerations
Obviously, the functionality described in Section 4.2 cannot be
guaranteed to work with the existing implementations of RFC 3588 or
any other strictly RFC 3588 compliant existing application (such as
NASREQ and EAP). An incompliant implementation would automatically
fall back to the normal RFC 3588 request routing behavior that,
unfortunately, cannot offer desired enhanced request routing
functionality. Therefore, it is RECOMMENDED that the solution
defined in this specification is only applied to newly specified
Diameter applications. A Diameter agent MAY implement the solution
defined in this specification also for the existing application. A
Diameter client SHOULD NOT assume the functionality described in
Section 4.2 from Diameter applications that do not comply with this
specification.
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5. IANA Considerations
This specification has no actions to IANA.
6. Security Considerations
A malicious node initiating (or indirectly causing initiation of)
Diameter request may purposely create malformed list of realms in the
NAI. This may cause the routing of requests through realms that
would normally have nothing to do with the initiated Diameter message
exchange. Furthermore, a malformed list of realms may contain non-
existing realms causing the routing of Diameter messages that cannot
ultimately be routed anywhere. However, the request message might
get routed several hops before such non-existent realms are
discovered and thus creating unnecessary overhead to the routing
system in general.
The NAI decoration is used in AAA infrastructures where the Diameter
messages are transported between the NAS and the Diameter server via
one or more AAA brokers or Diameter proxies. In this case the NAS to
the Diameter server AAA communication rely on the security properties
of the intermediate AAA brokers and Diameter proxies.
7. Acknowledgements
The authors would like to thank Victor Fajardo and Stefan Winter for
their comments on this draft.
Jouni Korhonen would like to thank TEKES WISEciti project for
providing funding to work on this document.
8. References
8.1. Normative References
[1] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko,
"Diameter Base Protocol", RFC 3588, September 2003.
[2] Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The Network
Access Identifier", RFC 4282, December 2005.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
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8.2. Informative References
[4] Aboba, B. and M. Beadles, "The Network Access Identifier",
RFC 2486, January 1999.
[5] Rigney, C., Willens, S., Rubens, A., and W. Simpson, "Remote
Authentication Dial In User Service (RADIUS)", RFC 2865,
June 2000.
[6] 3GPP, "3GPP system to Wireless Local Area Network (WLAN)
interworking; System description", 3GPP TS 23.234 6.10.0,
October 2006.
[7] 3GPP, "3GPP system to Wireless Local Area Network (WLAN)
interworking; WLAN User Equipment (WLAN UE) to network
protocols; Stage 3", 3GPP TS 24.234 6.7.0, October 2006.
[8] 3GPP, "Numbering, addressing and identification", 3GPP
TS 23.003 3.15.0, October 2006.
[9] Calhoun, P., Zorn, G., Spence, D., and D. Mitton, "Diameter
Network Access Server Application", RFC 4005, August 2005.
[10] Eronen, P., Hiller, T., and G. Zorn, "Diameter Extensible
Authentication Protocol (EAP) Application", RFC 4072,
August 2005.
[11] Arkko, J., Aboba, B., Korhonen, J., and F. Bari, "Network
Discovery and Selection Problem", RFC 5113, January 2008.
[12] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, "Extensible Authentication Protocol (EAP)",
RFC 3748, June 2004.
Authors' Addresses
Jouni Korhonen
TeliaSonera
Email: jouni.nospam@gmail.com
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Mark Jones
Bridgewater Systems
303 Terry Fox Drive
Ottawa, Ontario K2K 3J1
Canada
Email: Mark.Jones@bridgewatersystems.com
Lionel Morand
Orange Labs
38-40 rue du general Leclerc
Issy-moulineaux Cedex 9, 92794
France
Email: Lionel.morand@orange-ftgroup.com
Tina Tsou
Huawei
R&D Center, Huawei Technologies Co., Ltd
Bantian, Shenzhen
P.R. China
Email: tena@huawei.com
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