Do you find it hard to remember an IP address such as 192.168.1.10?  The challenge is networked computers use IP addresses to locate and connect to each other. 

DNS or Domain Name System is a hierarchical database system for locating computers and network services used in TCP/IP networks, such as the Internet.  It translates humanly meaningful names, called friendly names, to the numerical identifiers, an IP address, used by computers and other network devices when communicating with other networked equipment.

For example, www.ExampleDomain.com might translate to IP Address 192.168.1.10.   The process which associates a friendly name to an address is called name resolution, DNS-Resolution or DNS lookup.

Most computer networks have at least one server (called a name server) handling DNS queries.  That server keeps a list of all the IP addresses within its network, plus a cache of IP addresses for recently accessed computers outside the network.  Each computer or networked device on each network needs to know the location of only one name server.

When a program, such as a web-browser or mail-client, makes a request which requires a DNS lookup, the program sends a resolution request to the local computer DNS resolver which is part of the local operating system.  This resolver handles the communications required.

The local DNS resolver has a cache containing recent lookups.  If the local cache can provide the answer to the request, the resolver will return the address in the cache to the program that made the request.  If the cache does not contain the answer, the DNS resolver sends the request to one or more designated DNS name servers.  One of three things happens:

1. If the requested IP address is registered within the local network, you'll receive a response directly from one of the local name servers listed in the workstation configuration.  In this case, there usually is little or no wait for a response.

2. If the requested IP address is not registered locally (outside the local network– on the Internet), but a computer within the local network has recently requested the same IP address, then the local name server will retrieve the IP address from its cache.  Again, there should be little or no wait for a response.

3. If the requested IP address is not registered locally, and this is the first request for a lookup in a certain period of time (ranging from 12 hours to one week), then the local name server will perform a search on behalf of your computer.  This search may involve querying two or more other name servers at potentially very remote locations.  These queries can take anywhere from a second up to a minute (depending on the connection to the remote network and how many intermediate name servers must be contacted).  Sometimes, due to the protocol used for DNS, a response might not be received. In these cases, your workstation or client software may continue to repeat the query until a response is received, or you may receive an error message.

 Footnote: 

DNS databases hold many different record types.  The type of the record indicates what the format of the data is, and gives a hint of its intended use; for instance, an A record is used to translate from a domain name to an IPv4 address, the NS record lists which name servers can answer lookups on a DNS zone, and the MX record is used to translate from a name in the right-hand side of an e-mail address to the name of a machine able to handle mail for that address.  List of different DNS records