The Domain Name System, or DNS for short, is something like the telephone directory for the Internet: if you type in a domain name such as posadis.org in, for example, your browser, it will be looked up and converted to an Internet IP number, the Internet equivalent of a telephone number, which is used by your computer to make a connection. See the following diagram:

Apart from converting domain names to IP numbers, DNS also plays an important role in delivering e-mail and blocking spam. A DNS server is a program that answers DNS requests from clients. Whether you need a DNS server depends on your particular situation.

• You need a Domain Name Server if you want to serve information about an Internet domain name (this task is called authoritative DNS). You can, for a small or bigger fee, let somebody else do DNS, but you can do it yourself by running your own DNS server as well.
• You can use a Domain Name Server if you want to connect a local network to the Internet. Setting up a DNS server will speed up the domain name lookup process for your local network (caching DNS). Additionally, you can give names to computers on your local network. The latter goal van also be achieved by using a file called hosts on your client PCs. Using hosts instead of DNS can safe you time if you have a relatively small and static network, though it is not as scalable and doesn’t have as much applications as setting up a local DNS zone.

There is a DNS overview that provides, well, an overview of what makes the Domain Name System tick. You can also learn how to use DNS for naming hosts, how to use DNS for e-mail, and how to map IP numbers to domain names.

For Authoritative DNS: DNS data is stored in zones; you can see What makes up a zone. The fundamental pieces of data in the Domain Name System are Resource records, which are stored by authoritative DNS servers in Master files.

For caching DNS, refer to the article about Caching. If you run a caching DNS server, you’ll also want to know about Setting the DNS server on workstations.

Communicating to DNS servers happens with the standard DNS ports. A technical overview of the lower-level operation of DNS is provided in the article about DNS Messages.

Also, check out the links to other websites about the Domain Name System, and the DNS in the News section to find out what’s happening in the DNS world.

• Article about DNS cache spoofing
• Article about using DNS for phishing
• DNS cache snooping
• Custom root nameservers