What is the reason for ip domain name in the router, even though active directory service provides DNS for the network?
"ip domain name" specifies the domain name of the cisco device itself. One of the things this is used for is security certificate generation for IPSEC, SSH or HTTPS access. The certificate will be generated using the entries you put in for hostname and domain name.
ip name-server specifies the dns servers used for resolving dns names to ip addresses.