Skip to content
GATEiit

GATE CSE 2025 Session 1 Q57: IPv4 fragments through routers with MTU 5000 and 3000

Question

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)

Source sends to Router-1 (MTU = 5000 bytes), which forwards to Router-2 (MTU = 3000 bytes), which forwards to the Destination
Tap the figure to enlarge

Try it: numerical answer: type the value

Numerical answer. No negative marking.
Show answer and explanation

Answer: 7 (official GATE 2025 final answer key)

Concept used: IPv4 fragmentation: each fragment carries a 20-byte header, and data per fragment (except the last) must be a multiple of 8 bytes; fragments are not reassembled at routers.

First step: At MTU 5000 each fragment carries at most 4976 data bytes (a multiple of 8), so 15000 bytes become 4976 + 4976 + 4976 + 72; then refragment each for MTU 3000.

Full step-by-step solution

Detailed working, common mistakes and linked mock tests will be available with a free GATEiit account. Log-in is coming soon.

Share this question

WhatsAppDownload image

Source: official GATE 2025 Session 1 CS question paper and final answer key, organised by IIT Roorkee. Question paper · Answer key

More Computer Networks PYQs

PracticePractise Computer Networks questions →Full paperAll GATE CSE 2025 Session 1 questions →