Which OSI layer does a router primarily operate at?

• A. Layer 3 - Network Layer
• B. Layer 2 - Data Link
• C. Layer 1 - Physical
• D. Layer 4 - Transport

Answer: (A)

Routers primarily operate at Layer 3, the Network Layer, because their main job is to move packets between different networks. They look at the destination IP address in each packet, consult their routing table (often learned through routing protocols), and forward the packet to the next hop that will bring it closer to the destination subnet. This routing decision based on IP addresses is the hallmark of the network layer.

In contrast, devices like switches work at Layer 2, forwarding frames based on MAC addresses within the same local network. Layer 1 is the physical transmission medium, and Layer 4 deals with transport protocols and ports (TCP/UDP), which aren’t used to route packets between networks. So the packet-forwarding behavior that underpins moving data across networks is a network-layer function.