Just a little tip for those of you using vif-route for your networking in Xen. I needed to do this recently for a server at OVH as bridging cannot be used.

Set up multiple IPs by separating them with a space like follows in the domU config:

vif = [ 'ip=78.129.140.250 78.129.140.251' ]

You can also add more IPs to the domU without having to restart it using the following syntax replacing 78.129.140.1 with your gateway and vif101.0 with the interface name associated with the domU in your dom0:

ip route add 78.129.140.251 dev vif101.0 src 78.129.140.1

Your domU should now be able to use the extra IP!

In my case, I was trying to forward the IP to an OpenVZ VE within a domU -- this works perfectly fine with the above and no further configuration is required within the domU (other than obviously adding the IP to the OpenVZ container).