Anycast is an addressing mode in computer nets, with which one can address an individual computer from a whole group of computers via an address. It answers that, which is attainable over the shortest route.

Of view of a Clients no difference consists between Unicast and Anycast. The Client sends a IP package to one "„normal "“IP address and receives from this an answer. Which server is addressed, alone the Routing determines. With unstable Routing successive IP packages can be led to different servers. Therefore Anycast is preferably inserted with connectingless minutes such as UDP. In stable environments Anycast can be used in addition, with TCP.

Anycast is used for example with the root servers of the Domain Name of system and with the IPv6-in-IPv4-Tunnelmechanismus 6to4.

Anycast is realized by a distribution several homogeneous servers on spatially separated IP nets. Each computer receives the same IP address and publicises these by host route over Routing minutes as for instance to OSPF or RIP and/or BGP for global Setups). In case of failure or unattainableness disappears the host route and all following packages to another server is led. The desired service can be furnished thus also in case of failure one or several servers. Thus the availability increases. For administration a server must be able to be addressed also directly. Anycast servers possess therefore in nearly all cases additionally an Unicast address.

See also

• Multicast, Unicast

Related links

• RFC 1546

Articles in category "Anycast"

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• anycast - a definition from Whatis.com
  In Internet Protocol Version 6 (IPv6), anycast is communication between a single sender and the nearest.


• Anycast - Wikipedia, the free encyclopedia
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• Anycast Addressing on the Internet || kuro5hin.org
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• INTERNET PROTOCOL VERSION 6 ANYCAST ADDRESSES [last updated 1999 ...
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