Which of the following is not a transport layer protocol?

The transport layer is responsible for providing end-to-end communication services for applications, and it includes protocols such as Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). Both TCP and UDP are integral to facilitating the transmission of data between applications over a network, each with its own unique set of features.

Open Shortest Path First (OSPF), on the other hand, is not a transport layer protocol. Instead, it operates at the network layer and is primarily concerned with routing. OSPF is a link-state routing protocol that helps routers exchange information about the state of the links in their network, enabling them to make informed routing decisions.

Internet Control Message Protocol (ICMP) also does not belong to the transport layer; it is used for network diagnostics and error reporting, making it part of the network layer as well.

This distinction is significant, as understanding the specific layers of the OSI model and the functions of each protocol is essential for networking concepts studied in the CCNA curriculum.