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Suppose I have a program which needs to connect to the Internet in order to work. Let's also say that I only want this program to communicate on private networks, so I add a firewall rule allowing it to communicate on private connections.

If I don't want it to work on public connections, should I explicitly add a new blocking firewall rule or would Windows Firewall automatically block the traffic on public networks for this program (i.e. following a whitelist approach, where everything is blocked by default)?

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Depends on the specific program. Most programs don't need a firewall rule to work. – Ramhound Apr 9 '13 at 11:07
@Ramhound I know, I was referring to programs which need a firewall rule to work – user1301428 Apr 9 '13 at 11:25
Are you talking about outbound connections, where the program connects to a server on the internet, or inbound connections, where a machine on the internet connects to the program? – Harry Johnston Apr 12 '13 at 5:00
@HarryJohnston both :) – user1301428 Apr 14 '13 at 12:21
By default, outbound connections are a blacklist, and inbound connections are a whitelist. But that's configurable. – Harry Johnston Apr 14 '13 at 22:53
up vote 1 down vote accepted

By default, outbound connections are a blacklist, and inbound connections are a whitelist.

However, you can configure this behaviour from the Windows Firewall with Advanced Security control panel (go to Windows Firewall and click on Advanced Settings).

To do this, right-click on the topmost node in the left-hand pane ("Windows Firewall with Advanced Security") and select Properties.

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