NAS-Filter-Rule: RADIUS Filter Rule Attribute
A RADIUS attribute that carries actual packet filter rules to an access server instead of just naming a preconfigured filter.
Congdon, P., Sanchez, M., and B. Aboba, "RADIUS Filter Rule Attribute", RFC 4849, DOI 10.17487/RFC4849, April 2007, <https://www.rfc-editor.org/info/rfc4849>.
@misc{rfc4849,
series = {Request for Comments},
number = 4849,
howpublished = {RFC 4849},
publisher = {RFC Editor},
doi = {10.17487/RFC4849},
url = {https://www.rfc-editor.org/info/rfc4849},
author = {P. Congdon and M. Sanchez and B. Aboba},
title = {{RADIUS Filter Rule Attribute}},
pagetotal = 9,
year = 2007,
month = apr,
} RFC text
Contents
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.
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.
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.
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.
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.
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.
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.
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
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.
This document and the information contained herein are provided on an
"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
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
AI ELI5
On this page
§1Introduction and Terms
RFC 4849 defines the NAS-Filter-Rule attribute for RADIUS. It has the same functionality as the Diameter NAS-Filter-Rule AVP (400) from RFC 4005 and the same syntax as an IPFilterRule from RFC 3588, Section 4.3.
The motivation is a limit in RFC 2865. Its Filter-Id attribute (11) requires the Network Access Server (NAS) to be pre-populated with the desired filters. When the server operator does not know which filters are preloaded, it is more useful to specify the filter rules explicitly.
The document uses three terms. A NAS is a device that provides an access service for a user to a network. A RADIUS server provides an authentication service to a NAS. A RADIUS proxy acts as an authentication server to the NAS and as a RADIUS client to the RADIUS server.
Before, the boss could only say "use rule list number 5", which works only if the guard has a list number 5. Now the boss can write the rules out.
§2The Attribute Format
The attribute has three fields: Type is 92, Length is at least 3, and String is one or more octets.
The String holds filter rules in IPFilterRule syntax, with individual rules separated by a NUL octet (0x00). One attribute may hold a partial rule, one rule or several rules. Rules can continue across attribute boundaries, so an implementation cannot assume that a rule begins or ends where an attribute does.
A sender SHOULD concatenate all the rules, separated by NUL octets, and split the result on 253-octet boundaries to get the set of attributes. A receiver concatenates the contents of all NAS-Filter-Rule attributes and then splits on NUL to recover the rules.
If the list of rules is too long for one envelope, you cut it into pieces and use several envelopes. The reader tapes the pieces back together and reads the rules in order.
§3Where and How It Is Used
Zero or more NAS-Filter-Rule attributes MAY be sent in Access-Accept, CoA-Request or Accounting-Request packets. The attribute table marks them as 0+ in those three packet types and 0 (MUST NOT be present) in Access-Request, Access-Reject and Access-Challenge.
Where several attributes appear, their String fields are concatenated to form one set of rules. RFC 2865 forbids a forwarding server from changing the order of attributes of the same type, so proxies will not reorder them.
The attribute is not meant to be used with other filter attributes. NAS-Filter-Rule and NAS-Traffic-Rule MUST NOT appear in the same packet, and if a NAS-Traffic-Rule is present, a NAS implementing this RFC MUST silently discard the NAS-Filter-Rule attributes. Filter-Id and NAS-Filter-Rule SHOULD NOT appear together, because without defined precedence rules the NAS behavior is undefined.
If a conforming NAS gets an Access-Accept with a NAS-Filter-Rule it cannot apply, it MUST act as though it had received an Access-Reject. For a CoA-Request with an unsupported attribute, the NAS replies with a CoA-NAK, and an Error-Cause attribute of 401 (Unsupported Attribute) is RECOMMENDED. Authorization changes are atomic, so the session continues with its existing configuration.
The rules slip can ride along with the "you may come in" message. If the guard cannot understand a rule, the guard acts as if the answer was no, rather than letting someone in with the wrong rules.
| Packet | NAS-Filter-Rule (92) |
|---|---|
| Access-Request | 0 (MUST NOT be present) |
| Access-Accept THIS RFC | 0+ (zero or more) |
| Access-Reject | 0 (MUST NOT be present) |
| Access-Challenge | 0 (MUST NOT be present) |
| CoA-Request THIS RFC | 0+ (zero or more) |
| Accounting-Request THIS RFC | 0+ (zero or more) |
§4Diameter Considerations
RFC 4005 defines the Diameter NAS-Filter-Rule AVP (400). Diameter/RADIUS gateways need to be configured to translate RADIUS attribute 92 to that AVP and back.
Going from Diameter to RADIUS, the gateway concatenates the individual rules with NUL separators and SHOULD split the data at 253-octet boundaries. Going from RADIUS to Diameter, it joins all attributes, splits on NUL, and encodes each rule as its own Diameter AVP.
A translated Diameter message can exceed the maximum RADIUS packet size of 4096 bytes. In that case the gateway answers the Diameter peer with a Result-Code of DIAMETER_RADIUS_AVP_UNTRANSLATABLE (5018) and a Failed-AVP containing the NAS-Filter-Rule AVP. Repairing this probably needs the filter rules reworked, so the originating peer should treat it as a terminal error.
Two offices speak slightly different languages. A translator at the border turns one long rule list into pieces, or pieces into a list. If the list is too big for the other side's envelopes, the translator sends it back saying it cannot be done.
§5Security Considerations
The attribute rides in existing RADIUS packets, which are protected as described in RFC 3579 and RFC 3576. RADIUS and Diameter security aims to stop spoofing and modification in transit. It does not stop an authorized server or proxy from changing, inserting or removing attributes with bad intent. If a proxy strips filters, a user could get network access without the right filters, and if it also alters accounting packets, the accounting logs would not show it.
RADIUS has no capability negotiation, so a server cannot discover on its own whether a NAS supports this attribute. A legacy NAS may silently discard it and still let the user in, giving unfiltered access. Therefore NAS-Filter-Rule SHOULD only be sent to a NAS that is known to support it.
If a middleman tears up the rules slip, the guard lets people in without the rules. And an old guard who does not know about slips may just ignore them, so only hand slips to guards you know can read them.
§6IANA Considerations
The RFC creates no new registries. It uses the RADIUS namespace, where one value was allocated in the RADIUS Attribute Types registry: 92 for NAS-Filter-Rule.
It also uses the Diameter namespace, where a Result-Code value for DIAMETER_RADIUS_AVP_UNTRANSLATABLE was allocated. Because this is a permanent failure, the value 5018 is in the 5xxx range.
The number 92 was reserved for this new kind of slip, and 5018 for the "cannot translate this" answer, so nobody else uses them.