We currently have 11 Dell PowerEdge servers running CentOS 5.6 in a cabinet at a colo facility. Our colo provider recently informed us that they want to move us to a new VLAN, and give us all new IPs on a new subnet in a contiguous block. I want to be able to migrate the servers to the new IPs with no (or at least minimum) downtime.
Each of the Dell servers has at least two NICs, so let's say existing NIC A of each server is plugged into existing switch A, which connects to our provider's existing subnet A.
My plan is to: 1) turn the DNS TTLs down for our domain names, 2) connect a second switch (switch B) to our new subnet (subnet B), 3) configure each server's second NIC (NIC B) with the IP, netmask, and gateway information for subnet B, 4) plug each server's NIC B into switch B.
But after that, I'm lost (I'm a routing n00b). I don't know how to configure the routing so that all servers will be reachable on BOTH IPs while we transfer DNS. Then, after the DNS is moved over, how do I modify the routing again so that only the new IPs and subnet are used?
Thanks in advance!