Under IPv4 fragmentation, when does fragmentation occur?

Under IPv4 fragmentation, when does fragmentation occur?

• A. MTU is smaller than the packet size
• B. Packet size equals MTU
• C. IP ID changes during transmission
• D. Time to live expires

Answer: (A)

Fragmentation happens when a packet won’t fit on the next link because its MTU is smaller than the packet size. In IPv4, routers split such oversized packets into multiple fragments so each piece fits the MTU of that outbound link. If the packet size is equal to the MTU, it fits exactly and no fragmentation is needed. The IP identification value is used to reassemble fragments but doesn’t cause fragmentation, and a TTL expiring simply drops the packet rather than fragmenting it.

Fragmentation happens when a packet won’t fit on the next link because its MTU is smaller than the packet size. In IPv4, routers split such oversized packets into multiple fragments so each piece fits the MTU of that outbound link. If the packet size is equal to the MTU, it fits exactly and no fragmentation is needed. The IP identification value is used to reassemble fragments but doesn’t cause fragmentation, and a TTL expiring simply drops the packet rather than fragmenting it.