I don't believe that iptables (or other firewall) could cause an abnormal amount of collisions. I would think some kind of networking or hardware problems. Might want to swap in a new NIC or modem and see if that solves the problem.
Also you really should try to keep this all in one thread, so that anyone helping with your prob. can see all the related info in one place. Anyone wishing to contribute to this thread, please feel free to at the following link:
http://www.linuxquestions.org/questi...5&pagenumber=1
Thanks,
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