Computer Sciences > GATE 2025 SET-1 > IP Fragmentation
Suppose a message of size 15000 bytes is transmitted from a source to a destination using IPv4 protocol via two routers as shown in the figure. Each router has a defined maximum transmission unit (MTU) as shown in the figure, including IP header. The number of fragments that will be delivered to the destination is ______ (Answer in integer)
Correct : 7
IP header = 20 bytes. Original message = 15000 bytes total, so data payload = 14980 bytes.
At Router-1 (MTU = 5000 bytes):
Max data per fragment = 5000 - 20 = 4980 bytes. Rounded down to nearest multiple of 8 = 4976 bytes.
Fragments created: 4976 + 4976 + 4976 + 52 = 14980 bytes → 4 fragments
At Router-2 (MTU = 3000 bytes):
Max data per fragment = 3000 - 20 = 2980. Rounded down to multiple of 8 = 2976 bytes.
Each of the three 4976-byte fragments is split into 2 (2976 + 2000), and the 52-byte fragment passes through unchanged.
Total = 3 × 2 + 1 = 7 fragments delivered to the destination.
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