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I want to block torrent and other file sharing apps from Airport Express. How could I achieve this?

I am not asking the port numbers.

Advanced > Port Mapping doesn't allow me to specify port ranges.

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up vote 3 down vote accepted

Incoming connections are naturally blocked by the NAT. AirPort Express does not provide a way for you to block outgoing connections.

Some Mac torrent clients such as Transmission use NAT-PMP to dynamically create port mappings so they can work. If you want to manually manage all incoming port mappings, disable NAT-PMP on the Express. Beware that you may have unwittingly been relying on NAT-PMP to work for other Mac and Windows software, so after you disable it there's a small possibility you may have to manually configure some port mappings for some of the protocols you've been using.

But as you probably know, even without NAT-PMP, many protocol implementations can get around the inbound connection blocking that is a natural side-effect of NAT.

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While there's no way to do it on AirPort Express, you can use Little Snitch to do it on your computer: – cregox Mar 26 '10 at 17:41

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