Anycast addressing is a useful technique for providing redundancy and load sharing to specific types of network services on the Internet. Anycast addressing is nothing more than assigning a common IP address to multiple instances of the same service, which are located at strategic points in the overal network topology. By utilizing the underlying routing infrastructure of the Internet, IP packets are forwarded to the nearest instance of an anycast service. Common network services that can most easily take advantage of anycast addressing include DNS, multicast rendezvous points (RPs), syslog, network flow export, IPv6 to IPv4 relay routers and sink hole networks.
This article will briefly examine what anycast addressing is all about, where it is used and some of the technical considerations involved in an anycast deployment. The focus here is on anycast addressing as used by the IPv4 Internet. IPv6 provides a similar, but operationally unique service called anycast that will not be discussed here. The author's area of expertise is with internetworking and information security. He has experience in anycast addressing for RPs in multicast-enabled networks and has just begun to embark on a trial anycast DNS deployment
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