Don't do this from within SQL Server. Instead, use an IPSEC policy at the OS level.

How to block specific network protocols and ports by using IPSec

This talks about how to do it from the command-line. You can use the GUI to do so. In that case, execute mmc from Start | Run and then add the IPSEC policy add-in. Specifically restrict the TCP ports the SQL Servers are listening on to the IP addresses that should be able to connect.