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IPv4 Fragmentation

GATE CSE 2025 Set 2 · Q23

MCQ1 markMedium

Time

Consider a network that uses Ethernet and IPv4. Assume that IPv4 headers do not use any options field. Each Ethernet frame can carry a maximum of 1500 bytes in its data field. A UDP segment is transmitted. The payload (data) in the UDP segment is 7488 bytes. Which ONE of the following choices has the CORRECT total number of fragments transmitted and the size of the last fragment including IPv4 header?

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Solution

Step-by-step verified solution

Official answer: D) 6 fragments, 116 bytes

IPv4 Fragmentation
  1. Determine the total IP payload size:

    • UDP payload =7488 bytes= 7488\text{ bytes}

    • UDP header size =8 bytes= 8\text{ bytes}

    • Total UDP segment size (which forms the IPv4 payload) =7488+8=7496 bytes= 7488 + 8 = 7496\text{ bytes}

  2. Determine maximum data payload per fragment:

    • Ethernet Maximum Transmission Unit (MTU) =1500 bytes= 1500\text{ bytes}

    • Standard IPv4 header size (without options) =20 bytes= 20\text{ bytes}

    • Maximum IPv4 payload per fragment =1500−20=1480 bytes= 1500 - 20 = 1480\text{ bytes}

    • Since 14801480 is a multiple of 88 (1480/8=1851480 / 8 = 185), each full fragment can carry 1480 bytes1480\text{ bytes} of data.

  3. Calculate number of fragments and remaining bytes:

    • Fragment 1 to 5: Each carries 1480 bytes1480\text{ bytes} of payload   ⟹  5×1480=7400 bytes\implies 5 \times 1480 = 7400\text{ bytes}.

    • Fragment 6 (the last fragment): Carries the remaining 7496−7400=96 bytes7496 - 7400 = 96\text{ bytes} of payload.

    • Total number of fragments =6= 6.

  4. Size of the last fragment including IPv4 header:

    • Size =96 bytes (payload)+20 bytes (IPv4 header)=116 bytes= 96\text{ bytes (payload)} + 20\text{ bytes (IPv4 header)} = 116\text{ bytes}.

Thus, the total number of fragments is 6 and the size of the last fragment is 116 bytes, corresponding to Option (D).

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This IPv4 Fragmentation previous year question is Q23 of the GATE CSE 2025 Set 2 paper. Find more GATE CSE PYQs on IPv4 Fragmentation in Computer Networks, or browse all GATE CSE PYQs.

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IPv4 Fragmentation in GATE CSE

IPv4 Fragmentation has 8 GATE CSE PYQs across 8 papers from 2014 to 2025. 2 of them are 1-mark MCQs like this one, and it is the only one in GATE CSE 2025 Set 2.

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GateAI solution cardGATE CSE 2025 Set 2 · Q23 · MCQ

Consider a network that uses Ethernet and IPv4. Assume that IPv4 headers do not use any options field. Each Ethernet frame can carry a maximum of 1500 bytes in its data field. A UDP segment is transmitted. The payload (data) in the UDP segment is 7488 bytes. Which ONE of the following choices has the CORRECT total number of fragments transmitted and the size of the last fragment including IPv4 header?

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Independent practice explanation verified by the GateAI team. GATE is conducted by the IITs; question text follows the official paper.