leupi: Iptables is something you just have to read about once. What the rules do is conceptually simple, but writing rules that work takes a little practice.
Online, look through the tutorials at http://www.netfilter.org/documentati...entation-howto
(scroll down to Tutorials) and specifically look at http://iptables-tutorial.frozentux.n...tutorial.html,
which includes numerous examples. Then add rules to /etc/sysconfig/iptables, restart the iptables services and see if the new rule(s) fix the problem.
Also, if you don’t mind spending a few $$$, these books would make a good addition to your library:
Running Linux, Fourth Edition (Matt Welsh, et al): US$29.67 (amazon.com)
Linux in a Nutshell, Fourth Edition (Ellen Siever, et al): US$26.37 (amazon.com)