How to block all Internet traffic, but keep LAN connection open?

Hello,

 

I have NIS 2014 installed. For a period of time, I need to block all Internet traffic, but keep LAN connection open. How do I do that in NIS?

 

I know that NIS has a setting called Block All Network Traffic, but that's not what I want as it blocks everything, including LAN connections.

 

I want to block Internet, but keep LAN connections open.

 

Thanks in advance.

 

David