Implementing and Administering DNS
Terms you'll need to understand:
Domain Name System (DNS)
Fully qualified domain name (FQDN)
Relative distinguished name
Active Directory (AD) integrated zone
Resource records (RR)
Techniques you'll need to master:
Installing and configuring DNS for AD
Integrating AD DNS zones with non-AD DNS zones
Configuring zones for dynamic update
Managing replication of DNS data
The Domain Name System (DNS) is a name-resolution database most commonly associated with the Internet. It was first defined as a way to replace the aging HOSTS file system, which is explained in the next section. With Windows 2000, Microsoft has made DNS the primary method of name resolution for Active Directory (AD) networks. In fact, DNS is a required element for installing ADso much so that the process of upgrading a member or standalone server to an AD domain controller (DC) automatically installs the DNS server service if you do not have a valid DNS server for AD to use.
We'll briefly touch on how and why DNS was created, because without that background, troubleshooting DNS by testing with alternative name-resolution methods won't fully make sense.
You will need to know how to install, configure, and troubleshoot the DNS server service.
Brief History of DNS
As mentioned previously, DNS has its origins in the Internet. When the Internet was small, every single TCP/IP (Transmission Control Protocol/Internet Protocol) host on the Internet had a file called HOSTS that contained mappings of every other host on the Internet and its IP address (hence, the name). Whenever a new host (such as a workstation or server) was added to the Internet, a new master HOSTS file was created and posted, and everyone on the Internet would download the updated file. This was fine when the Internet was small and changes were infrequent. However, as the Internet grew, the process of updating HOSTS files on every system became increasingly unmanageable. Enter DNS. DNS was conceived as a hierarchical namespace that allows the management of the Internet namespace to be partitioned and distributed. As such, not every system needs to know the name and IP address of every other system on the Internet. Conceptually, the DNS hierarchy looks like a tree. At the very top is what is known as the root domain, which is represented by a period (.). Below the root domain are the top-level domains, which are the .com, .net, .edu, .org, and so on that we are all familiar with.
Below the top-level domains are the second-level domains, which are what we work with every day when sending email or visiting a Web site. Microsoft.com is a second-level domain, as is Army.mil and Harvard.edu. When you visit http://www.Inside-Corner.com, you are accessing a host computer called www in the Inside-Corner.com second-level domain.
Fully Qualified Domain Names (FQDNs)
With DNS, another important term to understand is the fully qualified domain name (FQDN). This refers to the complete, unambiguous name of a host. The FQDN contains everything from the host name through the root domain. An example is the http://www.microsoft.com. FQDN. In this example, www is the host, microsoft.com is the second-level domain, com is the top-level domain, and the trailing period represents the root domain. This FQDN is said to be "unambiguous" because it uniquely defines a single host on the Internet.
Relative Distinguished Names (RDNs)
Unlike an FQDN, a relative distinguished name (RDN) is just the part of the host name that represents the host system. In the previous example, www would be the RDN. These types of names are not used on the Internet because of the likelihood the name would be ambiguous and unable to be resolved to an IP address. However, RDNs are common on internal networks, because corporate DNS servers check their local zones first to resolve a name (more on zones later).
Now that we have explored some background information, let's examine DNS as it relates to Windows 2000 and AD.