I am using ubuntu 12.04 with unity and I wanted to have static ip on my network, as I am sharing my local with other computers. I had a bad failure with the network manager, I learned some tricks so I wanted to write about them.
I wanted to use static ip, so I've tried firstly the network manager, but for some reason, even though it worked locally, I didn't have internet. I've tried to add a DNS 184.108.40.206 but it wasn't listen. I think it is a bug regarding the network manager, so I've went to the nicer solution of command line. I've typed sudo nano /etc/network/interfaces and I've added the following:
The first line configures the localhost and the 127.0.0.1 the auto eth0 was the configuration for the static ip for the ethernet device. The problem was that I had to add dns-nameservers option otherwise I still didn't have connection to the internet.
It was a strange bug because I had connection with the other machines of my local network. Keep that in mind if you have additional problem with the internet connection and you have setup static ip.