Important: Never configure your network card as bridge. You may broadcast a virtual MAC address on the network, causing the emergency shutdown of your network port and the suspension of your server. Configure only NAT or routed mode!

Change the file xend-config.sxp for the usage of the “route” scripts of Xen

(network-script network-route) 
(vif-script     vif-route)

add to the script

echo  'echo 1 > /proc/sys/net/ipv4/conf/eth0/proxy_arp' >> /etc/xen/scripts/network-route

in the XEN configuration of the VM:

vif  = [ 'ip=my_ip_failover' ]
netmask = "255.255.255.0" 
gateway = "ADDR_IP_MACHINE_HOST" 

in the configuration of the VM

auto eth0
iface eth0 inet static address my_ip_failover
netmask 255.255.255.255
post-up /sbin/ip route add ADDR_IP_MACHINE_HOST/32 dev eth0
post-up /sbin/ip route add default via ADDR_IP_MACHINE_HOST