Domain Name Services
The Need for DNS
The Function of DNS
Examples of Name Resolution
Using the MMC
The Need for DNS
Domain Name Services (DNS) enable us to use human-friendly names for our computers. Even though the network uses numbers to identify each machine on a network, DNS enables people to think of computers in terms of names; the DNS service then maps those names to numeric addresses. DNS is used only with the Internet Protocol (IP).
DNS is critical to Active Directory (AD) because it is used to find Domain Controllers (DCs) and services on Domain Controllers such as Lightweight Directory Access Protocol (LDAP), Kerberos, and the Global Catalog. When a client needs to authenticate, it issues a DNS request for a nearby Active Directory Domain Controller. The DNS server then replies with the IP address and other information about the DC. In addition, when a DC needs to replicate with other DCs, it uses DNS to find the IP address of the DC. When we use Active Directory tools to add, subtract, or modify an Active Directory object, we use DNS to find an LDAP server running on a DC near us. Without DNS, Active Directory almost completely ceases to function.
The history of DNS began in the early 1980s. For the first few years, the Internet relied on a static text file called a hosts file, which was updated frequently and could be downloaded to an Internet-connected machine on a regular basis. Obviously, this did not scale beyond hundreds or thousands of hosts. The first DNS Request for Comments (RFC) appeared in 1984. Since then, DNS has been the standard methodology for name resolution on the Internet.
An enormous amount of public domain information about DNS can be found at http://www.ietf.org. Internet Request for Comments (RFCs) are considered the authoritative works on any Internet-related protocol or service.
DNS is conceptually a very simple service, akin to a phone directory. Just as a person with a phone directory can translate a name into a phone number, DNS accepts a fully qualified domain name (FQDN) and returns a 32-bit IP address. This is called a forward lookup. Or, it can accept an IP address and return an FQDN, which is called a reverse lookup. The entire process is known as name resolution.
The first step in installing DNS or Active Directory is planning. Do not begin implementation of production DNS servers until your DNS and Active Directory namespaces have been planned and decided on.