unicast

Unicast is a method of network communication where data is sent from a single source to a single destination. In IP networks, a unicast address identifies a single network interface, and packets with that address are routed to that specific host along a unicast path. Unicast can operate at both the network layer (IP) and the data link layer (Ethernet). At the link layer, frames are addressed to a single destination MAC; routers forward unicast frames toward the destination host.

Unicast is the default mode for most IP communications, such as retrieving a web page or transferring a file. It contrasts with broadcast, which delivers to all devices on a local network, and multicast, which delivers to a defined group of recipients. In multicast-enabled networks, routers replicate a single copy of the data only to networks that contain members of the group.

In IPv4 and IPv6, unicast addresses uniquely identify interfaces. IPv6 introduces several classes of unicast addresses, including global, link-local, and unique local addresses, while IPv4 uses address classes and subnetting. A related concept is anycast, in which multiple hosts share the same unicast address and packets are delivered to the nearest one according to routing metrics. Unicast remains the predominant mode for direct, point-to-point communication across wide and local area networks.