Our ISP is Comcast and we have 5 static public IPs from them that we use for various services, including customers connecting to our network, VPN, web, DNS, etc...
We need more IP addresses from Comcast. Unfortunately, Comcast is telling us that they can't just simply give us 5 more addresses. They only give static IP addresses in blocks of 1, 5 or 13.
In order for us to get more static IPs, they have to take away our current 5 static IPs and give us 13 new ones.
How do we make this transition without causing all sorts of DNS chaos? We run public DNS servers, so we can make the DNS changes ourselves, but it will take some time obviously for those DNS changes to propagate throughout the internet.
Are there any easy ways to make this transition? Like create some type of fallback DNS entry or something? Surely there must be some sort of procedure for this kind of thing. The Comcast support guy was useless.