- The technical information in this article may not be 100% accurate because the details have been summarized.
The Domain Name System (DNS) is responsible for translating a human-readable host name such as "www.google.com" into an IP address that the networking software and hardware need to communicate.
There is no central repository that stores the names and addresses of all the computers on the Internet. The Domain Name System distributes the responsibility among a large set of DNS servers. There is one authoritative server for each domain, and that server is responsible for managing the IP addresses and other technical characteristics of the domain and the hosts defined in that domain. All the other servers follow a standard protocol to find and contact the authoritative server.
In order to minimize communication overhead and time, a non-authoritative DNS server will not contact the authoritative server every time it needs to know the address of a particular computer. After it contacts the authoritative server, it will keep a local copy of the result in its cache. After a configurable period of time elapses, usually 24 to 48 hours, the non-authoritative server will destroy its local copy and fetch a new copy.
The process of managing the local copies is called caching.
Caching dramatically reduces overhead, but there is one negative consequence: changes to host addresses do not take effect immediately and globally. After a change at the authoritative server, the old information will be used until all the other servers have updated the out of date information in their cache.