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IPv4, CIDR and NAT

GATE CSE 2014 Set 3 · Q28

MCQ2 marksMedium

Time

An IP router with a Maximum Transmission Unit (MTU) of 1500 bytes has received an IP packet of size 4404 bytes with an IP header of length 20 bytes. The values of the relevant fields in the header of the third IP fragment generated by the router for this packet are

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Solution

Step-by-step verified solution

Official answer: A) MF bit: 0, Datagram Length: 1444; Offset: 370

IPv4, CIDR and NAT

Given:

  • Total IP packet size = 44044404 bytes

  • IP header size = 2020 bytes

  • Payload data size = 4404−20=43844404 - 20 = 4384 bytes

  • MTU = 15001500 bytes

The maximum payload capacity per fragment is 1500−20=14801500 - 20 = 1480 bytes (which is a multiple of 88, as required for fragmentation offset: 1480/8=1851480 / 8 = 185).

Let us trace the fragments:

  1. Fragment 1:

    • Data bytes: 00 to 14791479 (14801480 bytes)

    • Datagram length = 1480+20=15001480 + 20 = 1500 bytes

    • Fragment Offset = 0/8=00 / 8 = 0

    • MF=1\text{MF} = 1

  2. Fragment 2:

    • Data bytes: 14801480 to 29592959 (14801480 bytes)

    • Datagram length = 1480+20=15001480 + 20 = 1500 bytes

    • Fragment Offset = 1480/8=1851480 / 8 = 185

    • MF=1\text{MF} = 1

  3. Fragment 3:

    • Remaining data: 4384−2960=14244384 - 2960 = 1424 bytes (bytes 29602960 to 43834383)

    • Datagram length = 1424+20=14441424 + 20 = 1444 bytes

    • Fragment Offset = 2960/8=3702960 / 8 = 370

    • MF=0\text{MF} = 0 (last fragment)

Thus, the third fragment has MF bit: 0, Datagram Length: 1444, Offset: 370, which matches (A).

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This IPv4, CIDR and NAT previous year question is Q28 of the GATE CSE 2014 Set 3 paper. Find more GATE CSE PYQs on IPv4, CIDR and NAT in Computer Networks, or browse all GATE CSE PYQs.

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IPv4, CIDR and NAT in GATE CSE

IPv4, CIDR and NAT has 14 GATE CSE PYQs across 10 papers from 2012 to 2025. 4 of them are 2-mark MCQs like this one, and GATE CSE 2014 Set 3 has 4.

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GateAI solution cardGATE CSE 2014 Set 3 · Q28 · MCQ

An IP router with a Maximum Transmission Unit (MTU) of 1500 bytes has received an IP packet of size 4404 bytes with an IP header of length 20 bytes. The values of the relevant fields in the header of the third IP fragment generated by the router for this packet are

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