AZ-802: Administering Windows Server

Active Directory site awareness works because a client (or a domain controller registering its own service records) is matched to a site by comparing its IP address against Subnet objects that are each associated with a specific site in AD Sites and Services; a domain controller's own site membership is not recalculated automatically just because its physical network location or IP address changes, so an administrator must ensure the domain controller's new IP range is mapped to the destination site so that Netlogon registers the DC's SRV records under that site and clients there can discover it. Associating the 10.41.0.0/16 subnet with Site2 creates that mapping for the network DC2 will use after the move, letting Site2 clients locate DC2 through normal site-aware DC location, while leaving the existing 10.40.0.0/16-to-Site1 mapping untouched so Site1's client computers and DC1 continue resolving to their own site exactly as before.