Iptables rules sometimes are reset automatically

Question

Can't figure out why iptables rules are dropped.

sudo iptables -A INPUT -s 89.111.3.48 -j DROP

Any suggestions are welcome.

Answer 1

sudo iptables -A INPUT -s 89.111.3.48 -j DROP

If you just run the above command, it just loads that rule into the kernel, not really changing the iptables file. This would be lost on a reboot or a restart of iptables.

service iptables save

would save the rules to /etc/sysconfig/iptables and the change would survive a reboot.

Answer 2

Your -A is adding the rule to the end of the INPUT rules. iptables works on first match wins. My guess is that some earlier rule is allowing the connections from the listed IP address and so your rule is never seeing them.

Solution: use -I

sudo iptables -I INPUT -s 89.111.3.48 -j DROP

This will insert your rule at the beginning of the INPUT table. For further information have a look at the iptables man pages.