RADIUS

Name

Vendor-Specific

Synopsis

Attribute Number	26
Length	7 or more octets
Value	STRING
Allowed in	Access-Accept, Access-Request, Access-Challenge
Prohibited in	Access-Reject
Presence in Packet	Not required
Maximum Iterations	Unlimited

This attribute is used to carry attributes that are not specified in the RADIUS RFC. Vendors, NAS manufacturers, and others may want to transmit various implementation-specific information to the client and server and, thus, need a way to pass that information. However, this vendor information passed in addition to the standard global attributes absolutely cannot affect the operation of the base RADIUS protocol in any way. In Chapter 2, I discussed the format of a vendor-specific AVP and how one is carried inside this attribute.

Of particular interest is the type of this attribute. It is listed as a STRING type, but effectively it is seen as a pattern of undistinguished octets—this is to ensure the parts of the implementation that are not aware of the vendor-specific values do not misconfigure themselves or otherwise do detriment to the connection. Further, the value of the VSA within the vendor-specific AVP actually has several specification fields—think of them as “microfields” that further qualify the VSA. This eliminates any confusion and conflict between attributes specific to a vendor’s implementation and attributes generally available per the RADIUS RFC.