The interface name of a network device increases if the mac address of the physical or virtual network card changes. A common case is if you made a clone of a virtual machine for example via VMware or KVM or replaced a physical network card in a non virtualized server.
If it’s a CentOS 6 machine you need to change 2 files to rename the interface for example from eth1 back to eth0.
One file is the udev rule for network devices which is located here:
/etc/udev/rules.d/70-persistent-net.rules
Copy the new mac address to the line of your eth0 rule and delete the new rule for eth1.
# PCI device 0x15ad:0x07b0 (vmxnet3)
SUBSYSTEM==”net”, ACTION==”add”, DRIVERS==”?*”, ATTR{address}==”00:50:56:b2:23:e0″, ATTR{type}==”1″, KERNEL==”eth*”, NAME=”eth0″
Modify the network configuration located under:
/etc/sysconfig/network-scripts/ifcfg-eth0
and replace the old ip with the new one and the old mac address with the new mac address.
To be sure everything works fine reboot your machine.