When you add a new network card in your linux box and remove the old one, the new card will be named eth1. If you want to change it back to eth0, you can edit the file “70-persistent-net.rules” to remove the old eth0 card line and also remove the new eth1 line:
vi /etc/udev/rules.d/70-persistent-net.rules
Then you just need to reboot and the file will be updated with the new network card as eth0.