Which protocol operates primarily on Layer 3 of the OSI model?

The correct choice is IP because it is the primary protocol that operates at Layer 3, which is the Network layer of the OSI model. Layer 3 is responsible for packet forwarding, including routing through different routers in the network. The Internet Protocol (IP) is pivotal in defining how data packets are sent and routed across networks, providing addressing and routing capabilities that are essential for communication between devices on different networks.

Ethernet operates at Layer 2 (Data Link layer) and is concerned with the physical addressing and the transmission of frames over the same local area network. TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are both transport layer protocols, functioning at Layer 4 of the OSI model, and are responsible for end-to-end communication services, establishing connections and ensuring data integrity. Therefore, IP is distinctly the protocol designed for Layer 3 operations, encapsulating routing functionalities essential for network communication.