**This is more of a networking question, but I am applying it to FileMaker Server directly

I've got two virtual single machine FM 14 servers under different subnets/buildings that I want to setup to be a hot/cold availability situation.  The backup VM is synced from the production every 15 minutes (one of the great reasons to use ZFS filesystem).  This server does have a static IP address assigned, but I forgot that I can't use the same IP address under a different subnet.  So when the backup server is turned on, it will broadcast to a different IP address.  Which isn't ideal, considering it will confuse end users to switch to a different server/IP - I wanted to make this transparent.  Unless I move the backup hardware to the same building/subnet, this is going to be an issue that I need help with.

Can I use a DNS round robin technique for this situation?  I know it's more for load balancing, but if I change the IP address of the backup to something appropriate to that subnet, then I believe it'll work so the end user only deals with one IP.  I do also have to consider WebDirect/IIS and an installed certificate.  

If anyone has experience with this and/or can give me some ideas, I would be very grateful!

Not sure about a round-robin but you can certainly do a quick-switch of the DNS name from one to the other if needed.

Given FMI's big push on security and SSL certs; you should avoid letting users connect through IP addresses and always use DNS names, so that would fit it nicely.