rlm_attr_filter - FreeRADIUS Module

The rlm_attr_filter module exists for filtering certain attributes and values in received ( or transmitted ) radius packets from ( or to ) remote proxy servers. It gives the proxier ( us ) a flexible framework to filter the attributes we send to or receive from these remote proxies. This makes sense, for example, in an out-sourced dialup situation to various policy decisions, such as restricting a client to certain ranges of Idle-Timeout or Session-Timeout.

Filter rules are defined and applied on a per-realm basis, where the realm is anything that is defined and matched based on the configuration of the rlm_realm module.

The file that defines the attribute filtering rules follows a similar syntax to the users file. There are a few differences however:

There are no check-items allowed other than the realm.

There can only be a single DEFAULT entry.

The rules for each entry are parsed to top to bottom, and an attribute must pass *all* the rules which affect it in order to make it past the filter. Order of the rules is important. The operators and their purpose in defining the rules are as follows:

=

THIS OPERATOR IS NOT ALLOWED. If used, and warning message is printed and it is treated as ==

:=

Set, this attribute and value will always be placed in the output A/V Pairs. If the attribute exists, it is overwritten.

==

Equal, value must match exactly.

=*

Always Equal, allow all values for the specified attribute.

!*

Never Equal, disallow all values for the specified attribute. ( This is redundant, as any A/V Pair not explicitly permitted will be dropped ).

!=

Not Equal, value must not match.

>=

Greater Than or Equal

<=

Less Than or Equal

>

Greather Than

<

Less Than

If regular expressions are enabled the following operators are also possible. ( Regular Expressions are included by default unless your system doesn't support them, which should be rare ). The value field uses standard regular expression syntax.

=~

Regular Expression Equal

!~

Regular Expression Not Equal

See the default /etc/raddb/attrs for working examples of sample rule ordering and how to use the different operators.

The main configuration item is:

attrsfile

This specifies the location of the file used to load the filter rules.

authorization, accounting, preproxy, postproxy

/etc/raddb/radiusd.conf /etc/raddb/attrs

radiusd(8), radiusd.conf(5)

Chris Parker, cparker@segv.org