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rfc:rfc4849

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.

Congdon, et al. Standards Track [Page 1] 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.

Congdon, et al. Standards Track [Page 2] RFC 4849 Filter Rule Attribute April 2007

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.

Congdon, et al. Standards Track [Page 3] 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.

Congdon, et al. Standards Track [Page 4] 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.

Congdon, et al. Standards Track [Page 5] 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.

Congdon, et al. Standards Track [Page 6] 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.

Congdon, et al. Standards Track [Page 7] 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: paul.congdon@hp.com
 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: mauricio.sanchez@hp.com
 Phone: +1 916 785 1910
 Fax:   +1 916 785 1815
 Bernard Aboba
 Microsoft Corporation
 One Microsoft Way
 Redmond, WA 98052
 EMail: bernarda@microsoft.com
 Phone: +1 425 706 6605
 Fax:   +1 425 936 7329

Congdon, et al. Standards Track [Page 8] RFC 4849 Filter Rule Attribute April 2007

Full Copyright Statement

 Copyright (C) The IETF Trust (2007).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
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 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
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 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Congdon, et al. Standards Track [Page 9]

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