udev: update map between MAC addresses and interface names

...Traditionally, Linux kernels look for ethernet cards and assign interface names based upon the order the cards are detected. Thus if you were to shift the network cards around, or replace them, you may end up with a different interface name for any given card. In recent Debian (and thus Ubuntu) releases, the Udev subsystem creates a map between MAC addresses and interface names, and when it finds a new MAC address it assigns a new ethernet interface name. Thus the first time you create an Ubuntu VM, the VM server assigns a MAC address, and your VM will map it to eth0. If you clone the VM, or move it, the VM server assigns a new MAC address, and your VM maps the new address to eth1. At this point, your network configuration (/etc/network/interfaces) no longer matches the hardware, and your VM no longer sees the network. Oops.

If this is the problem, you will see messages like this in your /var/log/kern.log file:

udev: renamed network interface eth0 to eth1

You can fix this in one of several ways:

1. Change your interface configuration (/etc/network/interfaces) to match the new ethernet interface.
2. Delete the Udev MAC address map (/etc/udev/rules.d/70-persistent-net.rules), reboot, and let Udev rebuild the map.
3. Edit the Udev MAC address map (/etc/udev/rules.d/70-persistent-net.rules) and map the current MAC address back to eth0. This is the preferred solution if you have multiple interfaces defined.

You'll probably need to reboot the VM after any of these changes...

source: http://stackoverflow.com/questions/175876/how-do-i-fix-my-vms-network-connection-if-it-seems-to-be-running-ok-from-the-hos/296274#296274
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