eth0 interface in VirtualBox (Backtrack 5 VM)

After generating a new MAC address for a virtual NIC, I had two interfaces: the loopback interface (lo) and eth3. eth0 had disappeared, and eth3 wasn’t getting assigned an IP.

It turns out that udev on Debian assigns a new eth number for each new MAC address. Deleting the file /etc/udev/rules.d/70-persistent-cd.rules solved this problem.