I have two NICs within my Ubuntu server. One being the internet, the other being an internal network.
I have the following configuration whereas eth0 is the internet, eth1 is the internal network
auto lo eth0 eth1 iface lo inet loopback iface eth0 inet dhcp iface eth1 inet static address 192.168.1.21 netmask 255.255.255.0
Eth0 works correctly and I cannot connect via the internal IP. Both eth's are up.