The terms multicast and broadcast describe communication where data is sent from a single sender to multiple recipients. Multicast emphasizes delivering to a subset of available recipients, whereas broadcast emphasizes delivering to all available recipients.

The advantage of multicast when compared to a series of unicasts to the same recipients is in that the network hardware can send a single data packet that is received by multiple nodes connected to the same network segment. Using multicast instead of unicast to deliver the same data to multiple recipients can therefore save network bandwidth.

Given that the network hardware can only communicate directly with other nodes connected to the same network segment, addressing and routing mechanisms must be added by the unreliable unicast layer.