Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

A 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.

• A 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.


• If multiple LANs are connected with routers, the router forms the boundary of the broadcast domain. Broadcast traffic and collision signals do not cross routers, although most routers can be configured to forward specific broadcast traffic.

Note that virtual LAN (VLAN) technology can create "virtual" broadcast domains. A network built with switching devices can treat each workstation as an independent entity and groups of these workstations can be joined into a virtual broadcast domain, no matter where they are attached to the physical network. For more information, see "Switching and Switched Networks" and "VLAN (Virtual LAN)."

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