Which method is used to direct communications to the IP address that is closest to the source?

Anycast is a way of allowing the same IP address on multiple machines in different geographical areas. The routing protocol is used to advertise in routing tables the closest IP by the use of metrics. Currently this is how DNS root servers work. A unicast address is a single valid IP address for direct communications purposes between two hosts. A broadcast will forward a message to all computers in the same subnet. A multicast address is a single address that is selectively sent to a multicast group of hosts.