Attribute Number: 25
Value: String

The Class attribute mainly exists to funnel identification and
property information to the accounting systems of RADIUS
implementations.

From RFC2865:
"This Attribute is available to be sent by the server to the client
in an Access-Accept and SHOULD be sent unmodified by the client to
the accounting server as part of the Accounting-Request packet if
accounting is supported.  The client MUST NOT interpret the
attribute locally."