Answer by telcoM for New network interface created after reboot - OEL 6

The important thing is that this is a Xen virtual machine.

Apparently the virtualization host does not assign persistent MAC addresses to the virtual NICs. Every time the VM is powered on, the host may assign a new MAC address for its virtual NIC. And as the MAC address changes, OEL 6 will "think" the NIC is not the same as before.

The instructions for optimizing the VM's operating system for virtualization should have included the steps to avoid this problem. However, the generic way to do this for OEL/RHEL 6.x is:

1.) Create an empty file /etc/udev/rules.d/75-persistent-net-generator.rules. This will override the corresponding file in /lib/udev/rules.d/ and so will disable udev's MAC address memory function:

touch /etc/udev/rules.d/75-persistent-net-generator.rules

2.) Delete the existing record of MAC addresses previously seen by udev:

rm /etc/udev/rules.d/70-persistent-net.rules

3.) Delete any HWADDR= lines from any existing network configuration files:

sed -i -e '/^HWADDR=/d' /etc/sysconfig/network-scripts/ifcfg-eth*

4.) Reboot the VM. Now it should accept the first NIC as eth0, the second as eth1 etc. and ignore any future MAC address changes on them.