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2.1 Attributes

Information carried by RADIUS requests is stored as a list of attribute-value pairs. Each pair consists of an attribute number and an attribute value. The attribute number identifies the type of information the pair carries, and the attribute value keeps the actual data.

The value part of an attribute can contain data of one of the following types:


A 32-bit unsigned integer value.


An IPv4 IP-number.


A character string up to 253 characters long.

For convenience, the attributes and the values of some frequently used integer attributes are given symbolic names. These names are assigned to attributes and values in the dictionary file (see section Dictionary of Attributes — ‘raddb/dictionary).

Attribute numbers range from 1 to 255. Attributes with numbers greater than 255 are used internally by the server and cannot be sent to the NAS.

The vendor-specific attribute number 26 is special, allowing vendors of the NAS hardware or software to support their own extended attributes. vendor-specific attribute.

Each attribute has a set of properties associated with it. The properties are:

Usage flags

These flags determine the usage of the attribute in the configuration files ‘huntgroups’, ‘hints’, and ‘users’.


When a RADIUS server functions in proxy mode, it uses the propagation flag to determine which attributes from the reply packet should be passed back to the requesting NAS (see section Proxy Service).


Some configuration rules may cause the addition of new A/V pairs to the incoming request. Before the addition of a new pair, radiusd scans the request to see if it already contains a pair with the same attribute. If it does, the value of the additivity determines the following additional actions:


The old pair is retained in the request; the new pair is not added to it.


The old pair is retained in the request, but its value is replaced with that of the new pair.


The new pair is appended to the end of the pair list.

Attributes are declared in the ‘raddb/dictionary’ file. For a detailed description, see ATTRIBUTE statement. For information about particular attributes, see Attribute List.

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