6.3 Bridge

Bridges are relatively simple devices that connect LANs of the same architecture (e.g. Ethernet to Ethernet). Bridges operate at the lower two layers of the OSI Reference Model, providing Physical Layer and Data Link Layer connectivity. A bridge, at the most basic level, acts simply to extend the physical reach of a LAN, passing traffic from one LAN segment to another based on the destination MAC address. In other words, bridges act as LAN repeaters where specified distance limitations are exceeded. Bridges have buffers so they can store and forward frames in the event that the destination link is congested with traffic. Two-port bridges are the most common configuration.

A key advantage of bridges is their inherent simplicity. As protocol-dependent devices, they don't perform complex processes on the data frames traveling through them, neither do they attempt to evaluate the network as a whole to make end-to-end routing decisions. Bridges simply read the destination MAC address of the incoming frame and forward it along its way to the next link. Bridges can be cascaded, or connected in series, link by link. As bridges are so simple, they are inexpensive and fast. Such bridges can support multiple LANs and LAN segments connected by multiple media.

In contemporary networking a switch generally would be used instead of bridge.

Hub Networking devices Switch