Which of the following is not classified as a routable protocol in OSI Layer 3?

In the context of network protocols, routable protocols are those that can be routed through different networks based on their IP addresses, thus operating at OSI Layer 3 (The Network Layer). The primary function of Layer 3 is to manage device addressing, track the location of devices on the network, and determine the best way to move data.

The correct answer, HTTP, is a protocol that operates at OSI Layer 7 (The Application Layer). It is primarily responsible for allowing web servers and clients to communicate by transferring hypertext documents and does not inherently support routing of packets across networks.

In contrast, IPv4 is a fundamental network-layer protocol used for addressing and routing packets. ICMP operates at Layer 3, often used for error messages and operational queries. IPSec provides secure network communications by securing IP packets at the network layer but is still classified under Layer 3 protocols since it deals with IP traffic.

By recognizing where each protocol operates in the OSI model, you can see why HTTP is not classified as a routable protocol at Layer 3, focusing instead on application-level tasks.