Active Directory relies heavily on DNS and various problems can arise from an incorrectly configured DNS. The DNS configuration for Active Directory is slightly unusual, so refer to the How to configure DNS for Active Directory within the Oxford University Environment pages for details.
If you're familiar with the ways in which DNS is configured for Active Directory within the University you can skip directly to the recommended configuration: Configuring DNS to Support Active Directory using an Existing DNS Name (Option 1).
It is also possible to configure DNS slightly differently, to use a different domain name to the usual DNS domain name in use. This is documented in the Alternative configuration: Configuring DNS to support Active Directory using a Private Internal Name (Option 2).