Centos firewall blocking incoming connections

Paddington asked:

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?

My answer:

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.

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