misconfigured adsl modems hammering my freeradius

[Tom De Wispelaere]

Hello,

we are using freeradius (with mysql backend) in an isp environment for
authentication and accounting of adsl modems.
Some of these modems are misconfigured with a wrong password and  try
to authenticate every 5 secs or so, so i was wondering if there is a
simple way to tell radius not to do a lookup every 5 secs for these
particular modems...
As the number of modems is growing, it seems that these misconfigured
modems are putting more and more strain on the radius.....

Any advice greatly appreciated,

Tom