Which OSI layer is responsible for routing and the IP, ICMP, and ARP protocols?

• A. Physical layer
• B. Transport layer
• C. Network layer
• D. Application layer

Answer: (C)

Routing and inter-network addressing are handled at the Network layer. This layer is responsible for path selection and forwarding packets from one network to another, which is the job IP performs as a network-layer protocol. ICMP sits with IP in supporting network-layer functions, providing diagnostic and control messages about network operations and errors. ARP operates to connect IP addresses to the actual hardware addresses on a local link, enabling the network-layer packets to be delivered on the appropriate local segment. In short, routing, logical addressing, and the mechanisms that support delivering packets between networks come from the Network layer, while the other layers focus on different responsibilities: Physical handles the actual transmission medium, Transport ensures end-to-end delivery and reliability, and Application provides the user-facing services.