Sunday, 29 January 2012

Permanent iptables Configuration

You can save the configuration, and have it start up automatically. To save the configuration, you can use iptables-save and iptables-restore.

Save your firewall rules to a file:
sudo sh -c "iptables-save > /etc/iptables.rules"
At this point you have several options. You can make changes to /etc/network/interfaces or add scripts to /etc/network/if-pre-up.d/ and /etc/network/if-post-down.d/ to achieve similar ends. The script solution allows for slightly more flexibility.

Solution #1 - /etc/network/interfaces

Modify the /etc/network/interfaces configuration file to apply the rules automatically.
Open your /etc/network/interfaces file:
sudo vi /etc/network/interfaces
Add a single line (shown below) just after ‘iface lo inet loopback’:
pre-up iptables-restore < /etc/iptables.rules
You can also prepare a set of down rules, save them into second file /etc/iptables.downrules and apply it automatically using the above steps:
post-down iptables-restore < /etc/iptables.downrules
A fully working example using both from above:
auto eth0
iface eth0 inet dhcp
pre-up iptables-restore < /etc/iptables.rules
post-down iptables-restore < /etc/iptables.downrules
You may also want to keep information from byte and packet counters.
sudo sh -c "iptables-save -c > /etc/iptables.rules"
The above command will save the whole rule-set to a file called /etc/iptables.rules with byte and packet counters still intact.

Solution #2 /etc/network/if-pre-up.d and ../if-post-down.d

NOTE: This solution uses iptables-save -c to save the counters. Just remove the -c to only save the rules.

Alternatively you could add the iptables-restore and iptables-save to the if-pre-up.d and if-post-down.d directories in the /etc/network directory instead of modifying /etc/network/interface directly.

The script /etc/network/if-pre-up.d/iptablesload will contain:
iptables-restore < /etc/iptables.rules
exit 0
and /etc/network/if-post-down.d/iptablessave will contain:
iptables-save -c > /etc/iptables.rules
if [ -f /etc/iptables.downrules ]; then
iptables-restore < /etc/iptables.downrules
exit 0
Then be sure to give both scripts execute permissions:
sudo chmod +x /etc/network/if-post-down.d/iptablessave
sudo chmod +x /etc/network/if-pre-up.d/iptablesload
Solution #3 iptables-persistent

Install and use the iptables-persistent package.


If you manually edit iptables on a regular basis
The above steps go over how to setup your firewall rules and presume they will be relatively static (and for most people they should be). But if you do a lot of development work, you may want to have your iptables saved everytime you reboot. You could add a line like this one in /etc/network/interfaces:
pre-up iptables-restore < /etc/iptables.rules
post-down iptables-save > /etc/iptables.rules

The line "post-down iptables-save > /etc/iptables.rules" will save the rules to be used on the next boot.

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