Centos firewall blocking incoming connections

Question

After installing Centos 5.8 I could not pick up any open ports using nmap. So I ran the command #iptables --flush and all started working. However, after about 2 days I could not connect again and had to run the command.

1)How can I permanently ensure that my ports are open

2)What could be causing them to be shut in the first place since I did not touch the iptables?

Answer 1

Configure the firewall to open only the ports that you need to have open. Disabling the firewall entirely is very dangerous. You can use the system-config-firewall-tui command to configure it from a terminal.

Answer 2

I think you're running into the default firewall. Try these:

service iptables stop
chkconfig iptables off

Answer 3

The easiest way is to disable iptables:

service iptables save
service iptables stop
chkconfig iptables off

and for IPv6

service ip6tables save
service ip6tables stop
chkconfig ip6tables off