A broadcast domain is a logical network segment in which any computer or other device connected to the network can directly transmit to any other on the domain without having to go through a routing device, provided that they share the same subnet address and are in the same VLAN, default or installed. More specifically, a broadcast domain is the area of the computer network composed of all the computers and networking devices that can be reached by sending a frame to the data link layer broadcast address. A very basic network that uses hubs rather than switches or routers is like a post office clerk checking the mail. One clerk looks at each letter to confirm that the mail is not for themselves. Broadcast domain is a restricted area in which information can be transmitted for all devices in the domain to receive. More specifically, Ethernet LANs are broadcast domains. Any devices attached to the LAN can transmit frames to any other device because the medium is a shared transmission system. Frames are normally addressed to a specific destination device on the network. While all devices detect the frame transmission on the network, only the device to which the frame is addressed actually receives it. A special broadcast address consisting of all 1s is used to send frames to all devices on the network. Media like Point-to-Point_Protocol do not have a broadcast domain. An ethernet repeater is a device that joins two LANs to extend the distance of the LAN. All network traffic is sent across the repeater unaltered. A bridge is a device that joins two LANs into a single broadcast domain, but isolates them so that problems on one LAN do not propagate to the other LAN. In addition, bridges maintain separate collision domains, so that computers on each segment only contend with other computers on the same segment for access.
