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DNS Definition and Basics

What is DNS? 

This article applies to: DNS

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DNS Overview

DNS, which stands for Domain Name System, provides translation of a networked machine's (host's) name to a machine-readable IP address so that packets are routed over the network correctly. Conversely, for security reasons, a server on the network may use "reverse lookup" in order to assure its administrators that the proper people are connecting to it. Some Web or ftp servers will not allow a connection unless they can reverse-map the IP address to a registered hostname. A lookup on a domain name looks like this:



In the example above, the command 'nslookup' is used to ask for information about the host name The DNS server CUDNS returns the information that is an alias for the machine CUINFOB and has an IP address of Next, a reverse lookup on the IP address,, returns the "official" name of the machine:

> nslookup


Register the Hosts on Your Subnet(s) to Ease Administration

Naming the machines on your subnet is a standard practice that makes administration much simpler. It provides:

  • Easy tracking and inventory of IP addresses

  • Easier problem tracking and resolution when network trouble occurs

  • The only way to give your machines a name on the Internet

Basics for Registering a Host

If you are not the network administrator, contact your department's network administrator with your request. If you don't know who your network administrator is, you can look it up by finding your subnet (the first three numbers in your IP address) on the Subnet Administration page.

If you are the network administrator, you can make your own host changes on the DNSDB main page. If you can't get access to your subnet's pages, another network administrator in your unit who does have access can add you to the list of administrators , or you may send email to hostmaster, asking to be added to the list of network administrators for your subnet.

Criteria for Host Names

The host name should be in lowercase, should start with a letter, and can consist of alphanumeric characters and dashes. Underscores and special characters should be avoided. The host name must be unique within the subdomain. The network administrator should use common sense in assigning names.

About Subdomains

Reading from right to left, the subdomain is the third part of the fully qualified domain name. In the example, is the full subdomain name. Creating a subdomain with a meaningful name, such as for Cornell Information Technologies, assists the Cornell Hostmaster in locating the responsible party should there be a problem with the subnet or any host(s) on that subnet.


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