You posted this just as I was adding my update to my original post.
The information I was referring to was from: http://www.howtoforge.com/forums/showthread.php?t=26737
I now see this is indeed ISPConfig 2 steps, but the same basic principals applied.
One question though. You wrote:
The change in ispconfig is straight forward, just add one IP after another under System > server IP. Thats all.
You dont have to set the gateway or nameservers of the additional IP block.
What about the IP in System->Server Config->server1.mydomain.com ?
Does that need
to be updated too? I noticed that before I changed IPs it had my old IP, so I put the new main IP there from eth0 and left the rest alone and it is working for me. Are you saying that even the IP here doesn't need to be changed?
Also, you do still have to go through the sites in ISPConfig 3 one by one and re-save each one after changing the IPs correct?