Anycast Address

Anycast address is a special type of address that identifies multiple interfaces.  Any packets addressed to an anycast address are delivered to a single [any] interface - the nearest interface (that is configured with the anycast address) to the sending host in terms of routing distance.  While unicast address is used for one-to-one communication, and multicast address is used for one-to-many communication, an anycast address is used for one-to-one-of-many communication, which deliver data to one of the many available interfaces.

In order to facilitate delivery to the nearest anycast group member, the routing infrastructure must be aware of the interfaces that are assigned anycast addresses and their distances in terms of routing metrics.  Anycast addresses are assigned from the unicast address space.  The scope of an anycast address is the scope of the type of unicast address from which the anycast address is assigned.