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I've set up OpenVPN on my Debian server and would like to add a rule to iptables. I already have a file that lists default filter rules that iptables reads from (pre-up). I tried adding the rule to the file like so:

*filter
# Default firewall rules are here
COMMIT

*mangle
-A POSTROUTING -s 10.8.0.0/24 -o wlan0 -j SNAT --to-source 192.168.1.230
COMMIT

I then try to apply the rules with:

sudo iptables-apply /etc/iptables.firewall.rules

and it fails.

For reference, I followed this tutorial but don't want to use the shell script because it also failed to apply the mangle rule.

1

You have to add the SNAT rule to the nat table and not mangle.

You could also add the rule directly to the active table using:

iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o wlan0 -j SNAT --to-source 192.168.1.230

And if everything is working save it to a file using:

iptables-save > file
  • 1
    Thanks, I don't know where the mangle/nat confusion happened. I also didn't know non-filter table rules don't show by default when you list them with iptables -S. I didn't see the rules until iptables -t nat -S. – cptncrnch Jun 14 '16 at 23:51
  • 1
    @cpt you're welcome, don't worry, happens to me as well. One more thing I learned while testing new iptables rules with iptables-restore is that error messages are not always very helpful. Using iptables directly will help you to find the mistake faster. Also try iptables -vnL – rda Jun 15 '16 at 0:20

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