Stop P2P traffic with xServe

Hello all

I’m a real newbie sysadmin (wanna be actually) and have a xServe accting as the router on my network, but I must lockdown P2P that the students had set up. I was looking to L7-filter or something like that, but that tool is for linux, it’s possible to do that on xServe. The server provides NAT, Firewall and DHCP to all clients.

How do I shut off all that damned traffic?

Thanks in advance