Which of the following protocols operates at Layer 4

IPsec operates at Layer 4 (Transport Layer) in the OSI model, providing secure communication via protocols like ESP and AH, which work with TCP or UDP. BGP and OSPF are Layer 3 (Network Layer) routing protocols, and ARP operates at Layer 2 (Data Link Layer). Fortinet’s FortiGate uses IPsec for VPNs at Layer 4. Exact extract: "IPsec operates at the Transport Layer (Layer 4) to secure communications, encapsulating TCP or UDP packets... BGP and OSPF function at the Network Layer, while ARP resolves IP to MAC addresses at the Data Link Layer."