Guys... I am giving up... after trying to hard, search on internet, etc I decide to post here.

I have a nagios server and some clients...

Port 5666 are opened and I can connect to it on both server and client machines (telnet localhost 5666 got me connected)

The server does not have any iptables rules. The client does.

But no matter what rules I put there it does not work.

Form the server I cannot telnet on port 5666

telnet localhost 5666

root@xx:/usr/local/nagios/etc/GroupMaster-1# telnet xx.xx.xx.xx 5666
Trying xx.xx.xx.xx...

I have used this rules:

# /sbin/iptables -A INPUT -p tcp --dport 5666 -j ACCEPT
# /sbin/iptables -A OUTPUT -p tcp --dport 5666 -j ACCEPT

But it does not work.

both server and client are running ubntu.

Thanks

look at output of iptables-save, it may explain, perhaps dropping packet elsewhere
line in mine looks like
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 5666 -j ACCEPT

What is the server/client software you're using? It may not be an iptables problem at all. Knowing what you're trying to do will help us accomplish what you want and even look at logs. There could be a configuration problem with the server software itself and not iptables at all. Without knowing your ultimate goal, you could potentially be asking the wrong questions and leading everyone into giving you the wrong answers. So what is your end game? What do you want to accomplish if we ignore the fact that you want iptables to "allow" port 5666?

What does say on the server system?

Also, why are you running iptables on just the client and not the server? That's a pretty big security risk.

Because I didn't setup it yet on the server. I am finishing configurations first.

fsainsbu, thanks for the help man but your iptables rules have me an error.

I was able though to bypass this issue with the following

-A net2fw -p tcp -m tcp --dport 5666 -j ACCEPT


Thanks for the help guys!

You still haven't given the output of this command...
It's best to know what you have before you start adding to it.