XEN with routed DomUs
Configure /etc/xen/xend-config.sxp for routing:
(network-script network-route) (vif-script vif-route)
and enable arp proxy with sysctl -w net.ipv4.conf.eth0.proxy_arp=1 for runtime and by adding
net.ipv4.conf.eth0.proxy_arp=1
to /etc/sysctl.conf permanently.