I spent far too long figuring this out, and wanted to share.
Simple task: Add a static IP address to the 2nd of 4 NICs on my server.
To start, I followed the instructions here under Static IP Address Assignment: https://help.ubuntu.com/14.04/serverguide/network-configuration.html
$ cat /etc/network/interfaces # This file describes the network interfaces available on your system # and how to activate them. For more information, see interfaces(5). # The loopback network interface auto lo iface lo inet loopback # The primary network interface auto em1 iface em1 inet dhcp auto em2 iface em2 inet static address 172.24.0.9 netmask 255.255.0.0
Then I run
sudo ifup em2, as per the instructions.
At first, it appeared to work.
ifconfig showed the interface properly, and I was able to ping devices on the network. HOWEVER, after about a minute or so, the assigned static IP address vanished. The address is lost and the machine is unreachable. This happens over and over no matter how often I bring the interface up or down. Why is this happening?