This is a fun one. I never used to have this problem with RHEL 5 but RHEL 6 and debian based distros have had this issue all along. You clone from a Linux template and you get a new mac address. But the new interface comes in as ETH1 or perhaps if you have multiple generations you might have eth6 or eth7. How do you clear this up? Well it’s all about the fact that the operating system keeps track of the mac address in it’s udev rules. So open up /etc/udev/rules.d/70-persistent-net.rules and delete all the mac address entries. Once you reboot the machine you should have your interface come in as eth0 again.
In Debian it is normally named: /etc/udev/rules.d/z25_persistent-net.rules.