The Last Octet

Again, this is one of those simple configs once you've seen it, but it is a bear to track down and find this info. Basically what I want to do here is tell the OS to bring up the interface regardless of it not having an IP assigned to it. Typically linux systems only bring up their interfaces if they have addresses configured for them. Bringing up an address free interface can be handy for network sniffing, virtualization projects, and various bridging configs.

Here's what you need to place in /etc/network/interfaces for the interface you need to bring up (X = your interface number):

auto ethX
iface ethX inet manual
up ifconfig ethX up