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round robin DNS

A load balancing technique in which balance power is placed in the DNS server instead of a strictly dedicated machine as other load techniques do.

Round robin works on a rotating basis in that one server IP address is handed out, then moves to the back of the list; the next server IP address is handed out, and then it moves to the end of the list; and so on, depending on the number of servers being used. This works in a looping fashion.

Round robin DNS is usually used for balancing the load of geographically distributed Web servers. For example, a company has one domain name and three identical home pages residing on three servers with three different IP addresses. When one user accesses the home page it will be sent to the first IP address. The second user who accesses the home page will be sent to the next IP address, and the third user will be sent to the third IP address. In each case, once the IP address is given out, it goes to the end of the list. The fourth user, therefore, will be sent to the first IP address, and so forth.

Although very easy to implement, round robin DNS has important drawbacks, such as those inherited from the DNS hierarchy itself and TTL times, which causes undesired address caching to be very difficult to manage. Moreover, its simplicity makes that remote servers that go unpredictably down inconsistent in the DNS tables. However, this technique, together with other load balancing and clustering methods, can produce good solutions for some situations.

(Special thanks to Tom��s S��nchez L��pez for providing the updated definition for this term.)

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