Open the file /etc/xen/xend-config.sxp and make sure that the parameter network-script correspont to:

(network-script 'network-bridge-xhn0')

Add at the end of /etc/network/interfaces the following lines:

auto xenbr0

iface xenbr0 inet manual

then remove all the lines refering to xhn0 and add:

auto xhn0

iface xhn0 inet manual

Create the file /etc/xen/scripts/network-bridge-xhn0 and write the following lines into it:

#!/bin/bash
/etc/xen/scripts/network-bridge "$@" netdev=eth0 bridge=xenbr0
/sbin/ifconfig xhn0 up
/usr/sbin/brctl addif xenbr0 xhn0

and make it executable using the command chmod +x /etc/xen/scripts/network-bridge-xhn0

Reboot the machine. At the next startup eth0 and xhn0 will be linked together

Configure the domU associating a vif interface to the bridge xenbr0, by adding bridge=xenbr0 to the vif options. Example:

vif = [ 'bridge=xenbr0,mac=00:06:3E:1A:93:C3' ]

Start the virtual machine:

xm create <virtual_machine_name>

You can see the interfaces that are linked by the bridge executing the command brctl show

To connect the machines with the physical network you need to assign IP addresses that are in the same network class