At which OSI layer do routers operate?

Routers operate at the Network Layer of the OSI (Open Systems Interconnection) model, which is the fourth layer. This layer is responsible for the routing of data packets between devices across different networks. It manages logical addressing, typically using IP addresses, to determine the best path for data to travel through the network.

By functioning at this layer, routers can analyze traffic and make decisions based on the content of the packets, rather than just forwarding them as some lower-layer devices do. They can also perform tasks like fragmenting packets when necessary and managing packet forwarding among various subnets.

The other layers do not serve the same purpose as the Network Layer. The Application Layer deals with high-level protocols and user interface concerns, the Data Link Layer manages local network data transfer between directly connected devices, and the Physical Layer involves the actual hardware transmission of data over physical mediums. Each layer has its defined functions and responsibilities, which is why understanding their roles is crucial in networking.