Block a MAC Address ~BlackList !!

hi friends
a people Try to Connect or Like to try Connect to Internet. but Try Connect With N^time & Radius SomeTime Crash in 3Day!
RB1000 Log :

My ADSL Services is on a PPPoE Service.
Thats Connect From ADSL Links with a PPP, i How to Found That People ?
How to DisAllow That ?
My Idea : Block That MAC Address when who Say i NOT Connect to Internet i Found That ! but How ?

Any know ? :confused:

Use bridge filter to block that mac address, or add limit