Which layer of the OSI model does a router primarily operate on?

A router primarily operates at the Network Layer of the OSI model, which is responsible for data routing, packet forwarding, and addressing. The Network Layer enables devices on different networks to communicate with one another by determining the best path for data packets to travel from the source to the destination. This layer uses logical addressing, typically IP addresses, which allow routers to make decisions based on the destination IP address of each packet.

The Network Layer's primary function includes managing traffic between different subnets, handling packet fragmentation and reassembly, and routing protocols such as OSPF and BGP that assist in finding optimal routes for data. Essentially, routers examine the destination address in the packets they receive, make forwarding decisions based on their routing tables, and direct the packets to the appropriate next hop toward their final destination.

While other layers, such as the Physical Layer and Data Link Layer, are important for establishing actual data connections and managing physical hardware, the primary intelligence and functionality that allow for dynamic routing of packets occur at the Network Layer. The Transport Layer focuses on end-to-end communication and session management, which lies above the Network Layer and does not involve the routing functions that are crucial for a router's operation.