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If UFW is actually not an application layer firewall but a "interface to iptables", how can it be if I have by DEFAULT INCOMING DENY and OUTGOING ALLOW setting that ANY internet application is working?

Especially Deluge and Transmission the torrent clients are working. Why?

I mean firefox does receive traffic on port 80 for example (INCOMING!).

To me that would prove that actually the UFW is not working at all?

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Your examples are all outgoing connections. No wonder they works, you allow that... (as is normally sane). Now, if I try to ssh to your PC or try to connect to your web server, my outgoing (which is your incoming) connection will be denied. – Rmano Mar 27 '14 at 3:13

Actually, incoming connections are only classified as connections that originate from without your network. Firefox starts a connection from within your network, so it doesn't count as an "incoming connection".

If you want to disable internet just take the interface you are using down:

sudo ifconfig <interface> down  

You can find <interface> from a plain ifconfig:


If you're using ethernet it will be something similar to eth followed by a number. If you're using wireless it is usually either wlan followed by a number.

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You can filter your outgoing traffic with ufw with destination on port 80

sudo ufw deny out to any port 80
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