Unicast vs Multicast vs Broadcast vs Anycast

4 major routing schemes: Unicast, Multicast, Broadcast, and Anycast.

Multicast and Broadcast are one-to-many routing schemes. Unicast and Anycast are one-to-one routing schemes (there is one sender and one recipient of the packet).

• Broadcast: one node sends packets that hit all recipient nodes. Broadcast is not widely used any longer and was not implemented in IPv6.
• Multicast: one node sends packets that hit multiple (but not all) recipient nodes that have opted into a group.
• Unicast: there is only one possible destination on the entire network for a packet sent over Unicast
• Anycast: there are multiple possible destinations and the network itself picks the route that is most preferential. Anycast has been used widely to load balance DNS for some time. (Load Balancing without Load Balancers)