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

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

Answer: (B)

Switching is performed at the Data Link layer in the OSI model, and at the Link layer in the TCP/IP model. A switch forwards frames based on destination MAC addresses and learns which devices are reachable on which ports by inspecting the source MAC address of every frame it sees. Over time it builds a MAC address table that maps each device to a specific port. When a frame arrives, the switch uses that table to forward the frame only to the port where the destination device is connected; if the destination MAC isn’t yet known, the switch floods the frame to all ports in the same network segment until it learns where the device is. This is why switches are considered layer-2 devices. Routers, operating at the Network/Internet layer, move packets between different networks using IP addresses, not MACs. Some devices can perform higher-layer switching, but the fundamental switching inside a local network is a Data Link/Link layer function.