42

I add this rule:

sudo iptables -t nat -A OUTPUT -d a.b.c.d -p tcp \
       --dport 1723 -j DNAT --to-destination a.b.c.d:10000
  1. When restart computer rules are deleted. Why?
  2. What I can do to make the rules persist?
40

There is no option in iptables which will make your rules permanent. But you can use iptables-save and iptables-restore to fulfill your task.

First add the iptable rule using the command you gave.

Then save iptables rules to some file like /etc/iptables.conf using following command:

$  iptables-save > /etc/iptables.conf

Add the following command in /etc/rc.local to reload the rules in every reboot.

$  iptables-restore < /etc/iptables.conf
  • 14
    On Debian there is the iptables-persistent package which will do this. – bahamat Oct 20 '12 at 0:09
  • 6
    It's rather bad idea to place it in rc.local since there would be an open window gap between services start and firewall policy apply. I do prefer using pre-up hook for loopback interface in /etc/network/interfaces to overcome this. – poige Oct 20 '12 at 11:07
  • @poige: I agree 100%, rc.local might have the intended effect, but it's a kludge in this situation. – J. M. Becker Oct 20 '12 at 14:52
  • 3
    @bahamat: Installing that package is the best solution, It deserves it's own answer. – J. M. Becker Oct 20 '12 at 14:54
  • 1
    @TechZilla: Done. – bahamat Oct 22 '12 at 1:52
50

(Because it was suggested to make this an answer of its own...)

On debian install iptables-persistent.

The package will automatically load /etc/iptables/rules for you during boot.

Any time you modify your rules, run /sbin/iptables-save > /etc/iptables/rules to save them. You can also add that to the shutdown sequence if you like.

  • 12
    There are two different rule files: /etc/iptables/rules.v4 and /etc/iptables/rules.v6 for IPv4 and IPv6 respectively. If you want a table to apply to both kinds of connections you have to save it to both rule files. – PetaspeedBeaver Jan 23 '14 at 15:51
  • 11
    Don't add it to your shutdown sequence! If you botch your rules during changes/setup at least a good old reboot will get things back to the previously working state. – VertigoRay Feb 27 '17 at 23:03
1

After installing iptables-persistent above you can also save rules with the following shorter command on Ubuntu 16.04+: sudo netfilter-persistent save

And they can also be restored back to how they were last time you saved them with: sudo netfilter-persistent reload

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