The GATE Grind

GATE 2013 CS (CS1) – Question 47

Computer Networks · IPv4: Addressing, CIDR, Fragmentation and NAT · 2 marks · Multiple choice

An IPv4 datagram has M=0, HLEN=10, total length 400 and fragment offset 300. Identify fragment position and zero-based first/last payload-byte numbers.

  1. Last,2400,2789
  2. First,2400,2759
  3. Last,2400,2759
  4. Middle,300,689

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Correct answer: (C) Last,2400,2759

Explanation

Offset units are eight bytes, so the first payload byte is 300×8=2400. Header length is 10×4=40 bytes; payload length is 400−40=360. Its final byte is 2400+360−1=2759. M=0 and nonzero offset identify the last fragment. Thus C.

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