Cisco Certified Network Professional 2025 – 400 Free Practice Questions to Pass the Exam

The correct answer involves the concept of encapsulation, which refers to the process of wrapping data with protocol information that allows for its proper transmission across a network. In the context of ISL (Inter-Switch Link) operations, encapsulation specifically adds a header and trailer to frames. This is crucial for maintaining the integrity and identification of the frames as they traverse different networks or VLANs.

Encapsulation is central to how data moves through network interfaces, as it injects necessary metadata—like source and destination information—into the frames, ensuring they are appropriately routed and understood by receiving devices.

While trunking and frame tagging also relate to switches and VLANs, they do not explicitly describe the action of adding a header and trailer to data frames in the way encapsulation does. Trunking refers to the configuration that allows multiple VLANs to be carried over a single link, and frame tagging refers specifically to the process of marking frames with VLAN information, but without necessarily invoking the concept of adding a full header and trailer. Frame routing, on the other hand, concerns itself with the direction the frames take rather than the modification of their structure.

Thus, encapsulation is the most fitting answer, as it encompasses the idea of adding headers and trailers to