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If a LAN is large or is connected to the
Internet, it is often challenging to remember the numeric addresses
(IP addresses) of hosts. Most hosts are identified on the Internet by
friendly computer names known as domain names. The Domain Name System (DNS) is used to translate computer names such as cisco.com to their
corresponding unique IP address. The DNS software runs on a computer
that acts as a network server for handling the address translations. DNS
software may be hosted on the network itself or by an Internet Service
Provider (ISP). Address translations are used each time the Internet
is accessed. The process of translating names to addresses is known as
name resolution.
The DNS server keeps records that map computer (host) names and their corresponding IP address. These record types are all combined in the DNS table. When a hostname needs to be translated to its IP address, the client contacts the DNS server. A hierarchy of DNS servers exists on the Internet with different servers maintaining DNS information for their own areas of authority, called zones. If the DNS server consulted by a computer does not have an IP mapping for the hostname sought, it will pass the query to another DNS server until the information is obtained. DNS is not an absolute requirement to communicate on the Internet, but without it, all communications must use IP addresses instead of hostnames. It is much easier for most people to remember "cisco.com" than 198.133.219.25. In order for the computers on the LAN to access and make use of the DNS services, the DNS server IP address must be entered into the Internet TCP/IP Properties Dialog Box as well as the IP address/subnet mask.
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