Which layer of the OSI model does a bridge operate at?

A bridge operates at Layer 2 of the OSI model, which is the Data Link layer. This layer is responsible for node-to-node data transfer and for detecting and correcting errors that may occur at the physical layer. Bridges are used to segment networks and filter traffic, which enhances the efficiency of the network by reducing collision domains.

By functioning at Layer 2, a bridge is able to understand and manage MAC (Media Access Control) addresses, enabling it to make decisions based on the source and destination addresses contained within data frames. This capability allows bridges to maintain a MAC address table, effectively learning which devices are connected to which segments of the network, thereby reducing unnecessary traffic.

Other layers of the OSI model like Layer 1 (Physical) deal with the transmission of raw bit streams over a physical medium, Layer 3 (Network) is concerned with logical addressing (like IP addresses) and routing between different networks, while Layer 4 (Transport) provides end-to-end communication services and manages session control and error recovery. These functions are outside the scope of a bridge's capabilities, solidifying its operation specifically at Layer 2.