30 December 2007

Ubuntu firewall

This post offers a way of telling your Ubuntu system to set up a simple firewall at boot time. It assumes that you have a single network adapter called eth0.

I saved my firewall rules (in iptables-save format) to /etc/network/fwrules. My firewall rules are fairly specific to my setup, but the following might serve as a good starting point if you want to try this:

-A INPUT -i lo -j ACCEPT
-A INPUT -p tcp -m tcp --dport 22 -j ACCEPT
-A INPUT -i eth0 -m state --state RELATED,ESTABLISHED -j ACCEPT

And then I just saved the following to /etc/network/if-pre-up.d/fw:


iptables-restore < /etc/network/fwrules

(Be sure to make this file executable: sudo chmod 755 /etc/network/if-pre-up.d/fw).

This loads the firewall rules prior to bringing up the network interface, so that the firewall is in place by the time the network connection is active.

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