If you want to specify a default gateway or ip address for your Ubuntu installation, try the following steps.
Open SSH and type this command
sudo nano /etc/network/interfaces
You can edit everything there as shown in the screenshot below (click to enlarge)
auto eth0 iface eth0 inet static address 192.168.1.231 netmask 255.255.255.0 network 192.168.1.0 broadcast 192.168.1.255 gateway 192.168.1.77 # dns-* options are implemented by the resolvconf package, if installed dns-nameservers 192.168.1.253 192.168.1.226 dns-search nextbridge.org