Information about DNS
The Domain Name System (DNS) is the system that your computers use to translate alphanumeric domain names, such as www.adventure-works.com, to numerical Internet protocol (IP) addresses like 126.96.36.199. Because computers use IP addresses to communicate with each other, a query is made to DNS with every request that is made to a domain name.
A computer that runs a service to respond to DNS requests is called a DNS server. A DNS server serves requests for one or more zones, which are the components of a domain name. For instance, www.adventure-works.com has two zones as shown in the following diagram:
Figure 2 Zones of a domain name
In an environment where DNS is not integrated with AD DS, one DNS server is responsible for managing changes for each zone. Such DNS servers are called primary DNS servers for the zones that they manage. Zone data is stored in files that reside on the primary DNS server. A secondary DNS server for a zone will serve requests for that zone, but changes cannot be made on a secondary server (changes must be made on the primary server). Secondary servers are optional.
In a Windows environment where AD DS is present, a DNS server can host a zone that is integrated with AD DS. Instead of storing zone data in files, the data is stored in AD DS. If a zone is integrated with AD DS, changes can be made on any DNS server that hosts the zone. Changes made to the zone that is integrated with AD DS automatically replicate to other DNS servers that are integrated with AD DS. You can think of a zone that is integrated with AD DS as being hosted by multiple primary servers and no secondary servers.
When you introduced AD DS into your environment and configured your first domain controller, you were probably prompted to install DNS on the server. At that time, if you did not have a DNS server serving the zone for the domain that you created with your first domain controller, Windows probably installed DNS on the server and set the zone type for the domain to be integrated with AD DS (you can check by following the steps in How to Determine Where to Start Your Migration section later in this document).
If you already had another server acting as the primary DNS server for the domain that you told your domain controller to create, your environment probably does not have DNS integrated with AD DS. For example, you had a DNS server for adventure-works.com and then you set up your first domain controller on a different computer with a domain name of adventure-works.com. This is referred to as a stand-alone DNS server scenario.