I want to block all internet connections to and from my windows 7 machine, but allow it to access everything on the local network. The local network is behind an Apple Airport Extreme.
What is the easiest way to do this?
If you disable DHCP then set an IP address and subnet mask but leave default gateway blank, then your computer will be unable to access outside the local network.
If someone is an administrator over the local machine, they would be able to reverse this if they were trying, but if that isn't a concern then this should work.
Option #1 (Windows Firewall rules)
You could create a firewall rule to block these connections. Follow these steps:
Change the default firewall behavior to block outbound network connections:
Create a firewall rule to allow local network outbound connections:
You're done configuring it!
Control via script
To block all outbound Internet traffic:
To allow all outbound Internet traffic
Option #2 (Specialized software)
If you are trying to block Internet access as a result of excessive Internet usage, there is specialized software that can block all Internet access when monthly or daily Internet traffic exceeds pre-defined maximum. Local network access is still allowed, though. One such program is DU Meter, which also has many other bells and whistles related to Internet bandwidth management on Windows computer.
Disclaimer: I'm the author of DU Meter.