DNS System with Filtering

Hi,

I would like to know how the opendns handles filtering system.

I would like to setup a DNS server which will have filtering system
like DNS. It will have different configuration for different IPs.
For example, I will filter some websites for some IPs, those IPs will
see a forbidden page. This is very simple for proxy but I just want to
use DNS. Is there any module or software for this? DNS has this
system but I could not figure out how they do.

Thanks,

Beyza