deny unknown clients in dhcpv6

[shafi at bbnl.co.in]

Hi,

    I have installed & configure the isc-dhcp-server(dhcpv6) in ubuntu 
12.04,currently every one is getting ip from my server.So i am planning 
to allow only the authorized clients and deny the unknown clients,but i 
don't know how to configure it,please any one help me to fix this 
problem.


Regards
shafi