Does freeradius as a proxy pass along everything?

Dumb question that I'm hoping is easy to answer. If I configure freeradius to proxy all requests, and the client (and ultimate RADIUS server) uses some vendor specific attributes, will freeradius as a proxy forward the requests and responses without dropping any of the VSAs? In other words, when freeradius is acting as a proxy, does it basically ignore the contents of the request and response? Or, does it need to be able to speak the vendor-specific language, so to speak, to be able to proxy the request/response? Thanks, Mitch Gerdisch