Active Directory and spanning subnets between sites
We are moving our a fairly big chuck of our servers to a remote data centre about 50 miles away from our main office. One of the options I want to consider is spanning the server IP subnet across the two sites. Probably layer 2 spanning using Cisco ASR's. It would make the migration, and DR easie (no reconfiguration of IP information on recovery). It would also mean much less configuration of firewalls at our different offices around the world.
One main concern is AD sites. If all of our servers are in 10.10.x.x (for arguments sake) and we span that subnet between the two sites, (the office and the DC), when a client in the office issues a call from a AD DC, given that DC's from both physical locations are in the same subnet, they will be in the same site. Will the clients rely on the first to respond? If so, how reliable is this? I know that clients will clear their cache of located DC's if the DC returned is in a different site from the client, but I guess I would rather make sure that it very rarely happens in the first place.
Has anyone done something like this with AD?