In the OSI and TCP/IP models, which layer is responsible for bridging?

• A. Layer 1
• B. Layer 2
• C. Layer 3
• D. Layer 4

Answer: (B)

Bridging is a Data Link layer function. This layer handles how frames are placed on the medium and uses MAC addresses to decide where a frame should go. A bridge (or switch) learns which devices live on which network segment by watching source MAC addresses, builds a forwarding table, and then forwards frames toward the destination segment when the destination MAC is known. If the destination isn’t known yet, the bridge broadcasts the frame to all other segments, then learns from the responses. This layer-level decision making is what connects separate LAN segments into a larger network while keeping collision domains separate and reducing unnecessary traffic. It isn’t done at the Physical layer, which is just electrical signaling; nor at the Network layer, which uses IP addresses for routing between networks; nor at the Transport layer, which deals with end-to-end communication and ports.