I cloned a machine to one that was physically identical, changed the name of the new machine, and everything appeared good except that eth0 is gone and has been replaced by eth3. (I think the machines have two NICs but only one is brought out.)
I used Network Manager to fix a static IP address for the new machine and have not attempted to edit /etc/network/interfaces (having learned my lesson on that!).
Too keep every thing the same I'd like to use eth0 for the first port but don't understand which file needs editing or what command to give. I suspect that somewhere there is a file with the device eth0 associated with the MAC address for the old machine.