What best describes a fragment train in IPv4 fragmentation?

• A. Each fragment is treated independently
• B. All fragments belonging to the same original packet are included
• C. Fragments from different packets are grouped
• D. Only the first fragment is kept

Answer: (B)

Fragment train describes all fragments that come from a single original IP datagram. They share the same source, destination, protocol, and Identification value, and they travel as a set to be reassembled at the destination. The reassembly process waits until it has the complete collection of fragments for that datagram; only then can the original packet be reconstructed. This is why the correct description emphasizes that all fragments belonging to the same original packet are included. Treating fragments independently, grouping fragments from different packets, or keeping only the first fragment would prevent proper reassembly.