Routing a subnet from a data center to another

[Thomas Goirand <thomas@goirand.fr>]

Hi here!

We want to move all of our servers from one data center to another,
let's say from location A to location B. We have servers on both
location at the moment. The upstream network provider is the same on
both data center, so we can keep the keep the IPs of A when we move to B.

The issue is that the ISP is not capable of routing the IPs of A in both
locations at the same time, so we need to do the routing ourself for the
time of the migration (a server dedicated for the purpose will stay on
location A until the pools are routed in B).

In the data center A, we have 2 subnet of 64 IPs, one of the IPs of each
subnet being our network gateway. We do NOT control the gateway
(otherwise, it would be really easy for me: a simple iptables rule to
redirect to the VPN and a static route would have do, if I'm not
mistaking...).

I have tried already to setup OpenVPN on a VPS (running Xen), to do some
trials before going live on a real server. I tried to bridge tap0 and
eth0 of that VPS, but as soon as the bridge has both interfaces, the VPS
looses connectivity to the outside world.

I heard that I could use a proxyarp together with OpenVPN. That might
work, but I currently don't know how or what package to use.

Any suggestion?

Thomas