Network Working Group P. Congdon

Network Working Group P. Congdon
Request for Comments: 4849 M. Sanchez
Category: Standards Track ProCurve Networking by HP
B. Aboba
Microsoft Corporation
April 2007

RADIUS Filter Rule Attribute

Status of This Memo

This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The IETF Trust (2007).

Abstract

While RFC 2865 defines the Filter-Id attribute, it requires that the
Network Access Server (NAS) be pre-populated with the desired
filters. However, in situations where the server operator does not
know which filters have been pre-populated, it is useful to specify
filter rules explicitly. This document defines the NAS-Filter-Rule
attribute within the Remote Authentication Dial In User Service
(RADIUS). This attribute is based on the Diameter NAS-Filter-Rule
Attribute Value Pair (AVP) described in RFC 4005, and the
IPFilterRule syntax defined in RFC 3588.

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RFC 4849 Filter Rule Attribute April 2007

Table of Contents

1. Introduction ....................................................2
1.1. Terminology ................................................2
1.2. Requirements Language ......................................3
1.3. Attribute Interpretation ...................................3
2. NAS-Filter-Rule Attribute .......................................3
3. Table of Attributes .............................................5
4. Diameter Considerations .........................................5
5. IANA Considerations .............................................6
6. Security Considerations .........................................6
7. References ......................................................7
7.1. Normative References .......................................7
7.2. Informative References .....................................7
8. Acknowledgments .................................................7

1. Introduction

This document defines the NAS-Filter-Rule attribute within the Remote
Authentication Dial In User Service (RADIUS). This attribute has the
same functionality as the Diameter NAS-Filter-Rule AVP (400) defined
in [RFC4005], Section 6.6, and the same syntax as an IPFilterRule
defined in [RFC3588], Section 4.3. This attribute may prove useful
for provisioning of filter rules.

While [RFC2865], Section 5.11, defines the Filter-Id attribute (11),
it requires that the Network Access Server (NAS) be pre-populated
with the desired filters. However, in situations where the server
operator does not know which filters have been pre-populated, it is
useful to specify filter rules explicitly.

1.1. Terminology

This document uses the following terms:

Network Access Server (NAS)
A device that provides an access service for a user to a network.

RADIUS server
A RADIUS authentication server is an entity that provides an
authentication service to a NAS.

RADIUS proxy
A RADIUS proxy acts as an authentication server to the NAS, and a
RADIUS client to the RADIUS server.

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1.2. Requirements Language

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].

1.3. Attribute Interpretation

If a NAS conforming to this specification receives an Access-Accept
packet containing a NAS-Filter-Rule attribute that it cannot apply,
it MUST act as though it had received an Access-Reject. [RFC3576]
requires that a NAS receiving a Change of Authorization Request
(CoA-Request) reply with a CoA-NAK if the Request contains an
unsupported attribute. It is RECOMMENDED that an Error-Cause
attribute with value set to "Unsupported Attribute" (401) be included
in the CoA-NAK. As noted in [RFC3576], authorization changes are
atomic so that this situation does not result in session termination,
and the pre-existing configuration remains unchanged. As a result,
no accounting packets should be generated because of the CoA-Request.

2. NAS-Filter-Rule Attribute

Description

This attribute indicates filter rules to be applied for this user.
Zero or more NAS-Filter-Rule attributes MAY be sent in Access-Accept,
CoA-Request, or Accounting-Request packets.

The NAS-Filter-Rule attribute is not intended to be used concurrently
with any other filter rule attribute, including Filter-Id (11) and
NAS-Traffic-Rule [Traffic] attributes. NAS-Filter-Rule and NAS-
Traffic-Rule attributes MUST NOT appear in the same RADIUS packet.
If a NAS-Traffic-Rule attribute is present, a NAS implementing this
specification MUST silently discard any NAS-Filter-Rule attributes
that are present. Filter-Id and NAS-Filter-Rule attributes SHOULD
NOT appear in the same RADIUS packet. Given the absence in [RFC4005]
of well-defined precedence rules for combining Filter-Id and NAS-
Filter-Rule attributes into a single rule set, the behavior of NASes
receiving both attributes is undefined, and therefore a RADIUS server
implementation cannot assume a consistent behavior.

Where multiple NAS-Filter-Rule attributes are included in a RADIUS
packet, the String field of the attributes are to be concatenated to
form a set of filter rules. As noted in [RFC2865], Section 2.3, "the
forwarding server MUST NOT change the order of any attributes of the
same type", so that RADIUS proxies will not reorder NAS-Filter-Rule
attributes.

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RFC 4849 Filter Rule Attribute April 2007

A summary of the NAS-Filter-Rule Attribute format is shown below.
The fields are transmitted from left to right.

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 | Length | String...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type

92

Length

>=3

String

The String field is one or more octets. It contains filter rules
in the IPFilterRule syntax defined in [RFC3588], Section 4.3, with
individual filter rules separated by a NUL (0x00). A NAS-Filter-
Rule attribute may contain a partial rule, one rule, or more than
one rule. Filter rules may be continued across attribute
boundaries, so implementations cannot assume that individual
filter rules begin or end on attribute boundaries.

The set of NAS-Filter-Rule attributes SHOULD be created by
concatenating the individual filter rules, separated by a NUL
(0x00) octet. The resulting data should be split on 253-octet
boundaries to obtain a set of NAS-Filter-Rule attributes. On
reception, the individual filter rules are determined by
concatenating the contents of all NAS-Filter-Rule attributes, and
then splitting individual filter rules with the NUL octet (0x00)
as a delimiter.

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RFC 4849 Filter Rule Attribute April 2007

3. Table of Attributes

The following table provides a guide to which attributes may be found
in which kinds of packets, and in what quantity.

Access- Access- Access- Access- CoA- Acct-
Request Accept Reject Challenge Req Req # Attribute
0 0+ 0 0 0+ 0+ 92 NAS-Filter-Rule

The following table defines the meaning of the above table entries.

0 This attribute MUST NOT be present in the packet.
0+ Zero or more instances of this attribute MAY be
present in the packet.
0-1 Zero or one instance of this attribute MAY be
present in the packet.

4. Diameter Considerations

[RFC4005], Section 6.6, defines the NAS-Filter-Rule AVP (400) with
the same functionality as the RADIUS NAS-Filter-Rule attribute. In
order to support interoperability, Diameter/RADIUS gateways will need
to be configured to translate RADIUS attribute 92 to Diameter NAS-
Filter-Rule AVP (400) and vice versa.

When translating Diameter NAS-Filter-Rule AVPs to RADIUS NAS-Filter-
Rule attributes, the set of NAS-Filter-Rule attributes is created by
concatenating the individual filter rules, separated by a NUL octet.
The resulting data SHOULD then be split on 253-octet boundaries.

When translating RADIUS NAS-Filter-Rule attributes to Diameter NAS-
Filter-Rule AVPs, the individual rules are determined by
concatenating the contents of all NAS-Filter-Rule attributes, and
then splitting individual filter rules with the NUL octet as a
delimiter. Each rule is then encoded as a single Diameter NAS-
Filter-Rule AVP.

Note that a translated Diameter message can be larger than the
maximum RADIUS packet size (4096 bytes). Where a Diameter/RADIUS
gateway receives a Diameter message containing a NAS-Filter-Rule AVP
that is too large to fit into a RADIUS packet, the Diameter/RADIUS
gateway will respond to the originating Diameter peer with a Result-
Code AVP with the value DIAMETER_RADIUS_AVP_UNTRANSLATABLE (5018),
and with a Failed-AVP AVP containing the NAS-Filter-Rule AVP. Since
repairing the error will probably require re-working the filter
rules, the originating peer should treat the combination of a
Result-Code AVP with value DIAMETER_RADIUS_AVP_UNTRANSLATABLE and a
Failed-AVP AVP containing a NAS-Filter-Rule AVP as a terminal error.

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RFC 4849 Filter Rule Attribute April 2007

5. IANA Considerations

This specification does not create any new registries.

This document uses the RADIUS [RFC2865] namespace, see
<http://www.iana.org/assignments/radius-types>. One value has been
allocated in the section "RADIUS Attribute Types". The RADIUS
attribute for which a value has been assigned is:

92 - NAS-Filter-Rule

This document also utilizes the Diameter [RFC3588] namespace. A
Diameter Result-Code AVP value for the
DIAMETER_RADIUS_AVP_UNTRANSLATABLE error has been allocated. Since
this is a permanent failure, the allocation (5018) is in the 5xxx
range.

6. Security Considerations

This specification describes the use of RADIUS for purposes of
authentication, authorization and accounting. Threats and security
issues for this application are described in [RFC3579] and [RFC3580];
security issues encountered in roaming are described in [RFC2607].

This document specifies a new attribute that can be included in
existing RADIUS packets, which are protected as described in
[RFC3579] and [RFC3576]. See those documents for a more detailed
description.

The security mechanisms supported in RADIUS and Diameter are focused
on preventing an attacker from spoofing packets or modifying packets
in transit. They do not prevent an authorized RADIUS/Diameter server
or proxy from modifying, inserting, or removing attributes with
malicious intent. Filter attributes modified or removed by a
RADIUS/Diameter proxy may enable a user to obtain network access
without the appropriate filters; if the proxy were also to modify
accounting packets, then the modification would not be reflected in
the accounting server logs.

Since the RADIUS protocol currently does not support capability
negotiation, a RADIUS server cannot automatically discover whether a
NAS supports the NAS-Filter-Rule attribute. A legacy NAS not
compliant with this specification may silently discard the NAS-
Filter-Rule attribute while permitting the user to access the
network. This can cause users to improperly receive unfiltered
access to the network. As a result, the NAS-Filter-Rule attribute
SHOULD only be sent to a NAS that is known to support it.

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RFC 4849 Filter Rule Attribute April 2007

7. References

7.1. Normative References

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

[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)", RFC
2865, June 2000.

[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
Arkko, "Diameter Base Protocol", RFC 3588, September 2003.

[RFC4005] Calhoun, P., Zorn, G., Spence, D., and D. Mitton, "Diameter
Network Access Server Application", RFC 4005, August 2005.

7.2. Informative References

[RFC2607] Aboba, B. and J. Vollbrecht, "Proxy Chaining and Policy
Implementation in Roaming", RFC 2607, June 1999.

[RFC3576] Chiba, M., Dommety, G., Eklund, M., Mitton, D., and B.
Aboba, "Dynamic Authorization Extensions to Remote
Authentication Dial In User Service (RADIUS)", RFC 3576,
July 2003.

[RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication
Dial In User Service) Support For Extensible Authentication
Protocol (EAP)", RFC 3579, September 2003.

[RFC3580] Congdon, P., Aboba, B., Smith, A., Zorn, G., and J. Roese,
"IEEE 802.1X Remote Authentication Dial In User Service
(RADIUS) Usage Guidelines", RFC 3580, September 2003.

[Traffic] Congdon, P., Sanchez, M., Lior, A., Adrangi, F., and B.
Aboba, "RADIUS Attributes for Filtering and Redirection",
Work in Progress, March 2007.

8. Acknowledgments

The authors would like to acknowledge Emile Bergen, Alan DeKok, Greg
Weber, Glen Zorn, Pasi Eronen, David Mitton, and David Nelson for
contributions to this document.

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RFC 4849 Filter Rule Attribute April 2007

Authors' Addresses

Paul Congdon
Hewlett Packard Company
ProCurve Networking by HP
8000 Foothills Blvd, M/S 5662
Roseville, CA 95747

EMail: [email protected]
Phone: +1 916 785 5753
Fax: +1 916 785 8478

Mauricio Sanchez
Hewlett Packard Company
ProCurve Networking by HP
8000 Foothills Blvd, M/S 5559
Roseville, CA 95747

EMail: [email protected]
Phone: +1 916 785 1910
Fax: +1 916 785 1815

Bernard Aboba
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052

EMail: [email protected]
Phone: +1 425 706 6605
Fax: +1 425 936 7329

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RFC 4849 Filter Rule Attribute April 2007

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Internet Society.

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