Scanning network for open ports with nmap command

Whenever you are configuring a firewall, you want to make sure afterwards that the firewall really is configured properly and to do that is to scan it. Below follows two great links that helped me.

http://www.cyberciti.biz/tips/linux-scanning-network-for-open-ports.html
 
http://www.cyberciti.biz/networking/nmap-command-examples-tutorials/