I have a strange requirement for a client who has a pre-existing environment that we don't want to mess with too much. Currently there are two physical offices with this client, they have essentially two domains with one office being their main location (site A) and the second being a Satellite office (Site B.) Site A has an AD domain of a.domain.com (10.0.0.x) and site b is b.domain.com (10.0.1.x). The original configuration was a single server at each site, each the domain controller and file server for the locations. These two domains have a simple trust setup between them About 3 years ago, Site A decided they wanted to implement Exchange server so we installed an Exchange sever into the environment and people at Site A loved it so much, a couple people in Site B started to want to use it. So we would create a separate AD account for the Site B user so they could authenticate Exchange across the VPN, no problem. So here we are a couple years later and now they want to put an Exchange server in Site B in order to accommodate increased storage and LAN performance that is becoming restrained over the VPN of the two sites.
Our approach at this point is to implement the Exchange server in Site B, give it a local Site B ip address and assign it a Site A DNS address, join it to the domain and move forward with an Exchange installation. People will have separate credentials for their local computer login vs. the Exchange account which is kind of a pain but I dont see a more streamlined approach. Being they are both using the same external domain address and they want a common GAL is there a way to create a new Exchange instance on Site Bs environment, transfer users already created in Site A? If we do it the way we are proposing, is the trust between the two domains and subsequent subnets going to be disruptive to the configuration or should I give site Bs Exchange server an IP in Site As subnet and configure a static route?