DNS System

The Internet Protocol address is a 32- bit integer. If somebody wants to send a message it is necessary to include the destination address, but people prefer to assign machines pronounceable, easily remembered names (host names). For this reason the Domain Name System is used. These logical names also allow independence from knowing the physical location of a host. A host may be moved to a different network, while the users continue to use the same logical name.

The Domain Name System (DNS) is a distributed database used by TCP/IP applications to map between hostnames and IP addresses, and to provide electronic mail routing information. Each site (university department, campus, company, or department within a company, for example) maintains its own database of information and runs a server program that other systems across the Internet can query. The DNS provides the protocol which allows clients and servers to communicate with each other.

The system accesses the DNS through a resolver. The resolver gets the hostname and returns the IP address or gets an IP address and looks up a hostname. The resolver returns the IP address before asking the TCP to open a connection or sending a datagram using UDP.