iptables logging (the good way) in Debian Etch

When using iptables to log, you generally make a ‘LOG’ chain, and then

iptables -A INPUT -j LOG

iptables -A INPUT -j DROP

To log and then drop.

LOG has some disadvantages though. Using LOG, information will fill up the output of the ‘dmesg’ command as well as the kern.log file. Using Debian Etch, I was unable to get iptables to log to any other file but kern.log.

A better solution is ULOG.

You can clear your dmesg output with ‘dmesg -c’

apt-get install ulogd

iptables -N DROPLOG
iptables -A DROPLOG -j ULOG -m limit –limit 2/hour –ulog-nlgroup 1 –ulog-qthreshold 20

iptables -A DROPLOG -j REJECT
iptables -A INPUT -p tcp -i eth0 –dport 22 -j ACCEPT
iptables -A INPUT -i eth0 -j DROPLOG

This will drop and log all incoming traffic except for port 22.

You shouldn’t need to edit /etc/ulogd.conf, but you might want to check it out.

All information should get logged to /var/log/ulog/syslogemu.log