The GATE Grind

GATE 2014 CS (CS3) – Question 38

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

An IP router with MTU 1500 bytes receives a 4404-byte IP packet with 20-byte header. What are the relevant header fields of the third fragment?

  1. MF = 0; Datagram Length = 1444; Offset = 370
  2. MF = 1; Datagram Length = 1424; Offset = 185
  3. MF = 1; Datagram Length = 1500; Offset = 370
  4. MF = 0; Datagram Length = 1424; Offset = 2960

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Correct answer: (A) MF = 0; Datagram Length = 1444; Offset = 370

Explanation

Original payload is4404−20=4384bytes. Each full fragment carries1480payload bytes, divisible by8. After two,1424payload bytes remain; the last fragment length is1444including its20byteheader, offset2960/8=370andMF=0. Thus **A**.