What is Anycast

Anycast is a type of Network Topology just like its predecessors, Unicast, Multicast and Broadcast. This article provides an insight with this new network scheme, its advantages and compares it with other existing network schemes.

The following different network schemes show a schematic representation of each traditional type. It would be easier to understand Anycast after a basic understanding of other topologies.

The Unicast Network topology involves one to one association with the source and destination.

In multicast there is a one to many associations between the source and the destination.

Broadcast signifies a one to All relation between the source and the destination. Broadcasts are however mostly confined to the local subnet and need special rules to travel beyond the router.

Anycast is the new player on the block. Anycast is based on IPV6 (Internet Protocol Version 6), the communication typically happens between a single sender and several nearest receivers in a group. The routing tables on the router are updated using IP V6 to give the packets the path to the nearest destination, making the transfer much faster. IP V6 determines automatically as to which destination end points are closest, and sends them the packets like a Unicast. The destination then carries on relays the packets to its nearest hosts until all destinations are addressed.

Anycast is generally used for load balancing and high availability services. For example a lot of music streaming, logging on to your nearest (geographically and network wise) servers when you connect to Yahoo or Google etc. DNS is another application where the resolution can be much faster if you hit a server that is much closer to you and in effect it also provides load balaning and redundancy (high availability). In future we would find more and more applications for Anycasting!

For a detailed and in depth look, you can visit the WiKi at http://en.wikipedia.org/wiki/Anycast