[CentOS] CentOS 4.4 blocking outbound connections?

[Jed Reynolds]

Neil Aggarwal wrote:
> Fabian:
>
> I rebooted the machine to see what would happen.
> It went back to not accepting the connections again.
>
> If I turn off the firewall, everything works fine.
>
> I believe there is something flaky in the iptables
> implementation of CentOS 4.4 from what I am seeing.
>
> Any ideas?
>
>   

I often write my rules as chains that end in a -j LOG --prefix "chainX" 
then a -j REJECT, and this helps identify where my traffic is failing. I 
can then later switch off the logging and turn the rejecting to 
dropping. Below is a particularly lean example, but it shows a method by 
which you can get detailed feedback on how your chains match certain 
packets that you pass to them.


#!/bin/bash
#fail=DROP
fail=REJECT
log=1
...

[ $log -eq 1 ] && iptables -A INPUT -j LOG --log-prefix 'start:'
iptables -N my0ssh
iptables -A my0ssh -p tcp -m tcp --m state --state NEW -j RETURN
[ $log -eq 1 ] && iptables -A my0ssh -j LOG --log-prefix "my0ssh no match"
...
iptables -A INPUT -j my0ssh
iptables -J LOG --log-prefix 'fall-thru-failure:'
iptables -A INPUT -j $fail