Xen and mutiple unrelated IP’s

Xen is a powerful tool for virtualizing servers.

Recently I have been setting up servers for a new hosting company selling, well, virtual private servers.   We decided on Debian Etch (latest stable) as the main OS which would in turn host many other installations of Ubuntu.  Everything went very smoothly out of the box.   I updated Etch, installed LVM spanning four hard drives and installed xen and xen-tools using a compilation of the many tutorials available.

First sign of trouble was when our ISP gave us blocks of IP’s in a different subnets than the servers main IP.  My last ISP gave us a nice block all together and the default Xen bridge networking worked great.

In this case I was going to have to use routing.  After setting that up again according to a number of tutorials - it didn’t work.  My new ISP was less than helpful and newsgroups and searching the interweb for days  yielded nothing.  IRC was probably the most helpful place and really got me going in the right direction.

Finally the answer arrived.  In my /etc/xen/scripts/network-route i found this:

echo 1 >/proc/sys/net/ipv4/ip_forward

But I did not find:

echo 1 >/proc/sys/net/ipv4/conf/eth0/proxy_arp

Adding it caused everything to work  beautifully.