To disable permanently all low level kernel messages (iptables etc.) from flooding the console in Debian do the following changes:
(you must be root for these changes)
To make the changes permanent:
Edit the file /etc/sysctl.conf
add the following line:
kernel.printk = 4 1 1 7
The above changes will be effective at reboot or immediately using the following command:
/sbin/sysctl -p /etc/sysctl.conf
To make the changes only temporarily
echo "4 1 1 7" > /proc/sys/kernel/printk
and you can check the setting with
cat /proc/sys/kernel/printk