Yep. http://www.cistron.nl/~miquels/radius/ You're looking for "portslave".
> In that case I could test ISDN & modem auth. & logging
> of various detail files ...
>
> When those tests satisfy I could switch over to this new
> radius version "on the fly" ...
>
> Any suggestions ?
On the above mentioned WWW site you can also find my own version of
radiusd, that does a lot of things like radius-2.0 (and more). It
includes a program called "radtest" with which you can test the
RADIUS daemon. There's not much documentation included though.
Mike.