I keep getting these kinds of annoying messages running on the terminal (not a console in X). So I am unable to do anything in the command line. It keeps occurring every few seconds and obstructing whatever I'm doing.
I suspect it's something to do with iptables firewall. But how do I disable this? By the way, this doesn't happen within X. Only when I in the terminal (any virtual terminal, not just the first one).

Well...first thing I would do just to see if it is in fact iptables would be to turn iptables off and see what happens. If the messages go away, you know that it is iptables spewing all of that garbage, at which point you can start investigating iptables specifically to see if there is a way to either redirect that stuff to a log file somewhere or stop it altogether.

Reading the manpage for iptables, there is a big section on logging, which is what I suspect would be the first thing you might want to look at if you do determine that the problem is iptables.

I had the same problem a while back. Turning off logging in Guarddog made the problem go away. Not sure how to do it just using iptables.

man dmesg. Usually something like "dmesg -n 4" should do.

I have guarddog. So I think craigevil's post should help.

Ah! Good to know. I will keep that in mind if I ever see a question such as this again.