At which layer of the OSI model does fragmentation occur?

• A. Layer 2
• B. Layer 3 only
• C. Layer 4
• D. Layer 5

Answer: (B)

Fragmentation occurs at Layer 3 of the OSI model, which is the Network layer. This layer is responsible for packet forwarding, including routing through different routers in a network. When packets are too large to be transmitted over a particular network segment, they must be fragmented into smaller units to fit within the constraints of the physical layer.

At Layer 3, protocols like Internet Protocol (IP) take care of this fragmentation process. It breaks down larger packets into smaller fragments that can be transmitted over the network. Each fragment is sent separately and reassembled at the destination. This functionality is crucial for effective network communication, especially in varied network environments where maximum transmission unit (MTU) sizes can differ.

The other layers mentioned do not handle fragmentation in the same way. Layer 2 (Data Link layer) deals with frames and may have its own form of data encapsulation, but it does not manage fragmentation for routing. Layer 4 (Transport layer) is focused on end-to-end communication and reliability, typically managing flow control and error correction, rather than packet fragmentation. Finally, Layer 5 (Session layer) is more concerned with session establishment, management, and termination, rather than the structure and format of data packets themselves. Thus, the correct