Domain Name System

The Domain Name System (DNS) overcomes both major weaknesses of the host table:

  • DNS scales well. It doesn’t rely on a single large table; it is a distributed database system that doesn’t bog down as the database grows. DNS currently provides information on approximately 16,000,000 hosts, while fewer than 10,000 were ever listed in the host table.

  • DNS guarantees that new host information will be disseminated to the rest of the network as it is needed.

Information is automatically disseminated, and only to those who are interested. Here’s how it works. If a DNS server receives a request for information about a host for which it has no information, it passes on the request to an authoritative server. An authoritative server is any server responsible for maintaining accurate information about the domain being queried. When the authoritative server answers, the local server saves (caches) the answer for future use. The next time the local server receives a request for this information, it answers the request itself. The ability to control host information from an authoritative source and to automatically disseminate accurate information makes DNS superior to the host table, even for networks not connected to the Internet.

The Domain Hierarchy

DNS is a distributed hierarchical system for resolving host names into IP addresses. Under DNS, there is no central database with all of the Internet host information. The information is distributed among thousands of name servers ...

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