fooling client DNS

Since this is a short term solution the easy thing to do is update the pool member of the LTM is the data center you are moving from with the IP address of the VIP in the new data center. This will force client with the old IP address through the old LTM which will LB to the new data center and to the application. There will be more latency but it will work and as DNS propagates through the internet less and less people will use it till all servers are updated. Once that happens you can remove the config from the old unit.