The networking tools cannot identify the Xen Virtual Ethernet networking card inside the guest operation system you should execute cat /etc/modprobe.conf(in Red Hat Enterprise Linux 4 and Red Hat Enterprise Linux 5) or cat /etc/modules.conf(in Red Hat Enterprise Linux 3). The output should contain the line “alias eth0 xen-vnif” and a similar line for each additional interface. To fix this problem you will need to add the aliasing lines (for example, alias eth0 xen-vnif) for every para-virtualized interface for the guest.