I updated my 10.04 LTS servers recently to 12.04 LTS. One of the issues I have is that when I upgraded my iptables script failed. I decided that I would, try and fix my iptables, but iptables changed so much from 10.04 to 12.04. After many days of screwing around, I gave up and looked at alternatives to get my firewall working again. I found ubuntu had a product called Ubuntu Firewall. To get ufw and working, is not a hard task. Howto is shown below.
You need to enable ufw
Now if you want to allow ssh port open, so you can make a remote connection to the server.
To see the the current status and list of what ports are open
If your like me and running the server also as you gateway, you may only want to block the interface to the outside world and open all ports on the internal interface.
This does not do any nat traversal/masquerading. I will blog about this later.