The GATE Grind

GATE 2010 CS (CS1) – Question 57

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

10.105.1.113 and 10.105.1.91 belong to the same IP network. Which subnet mask is NOT possible?

  1. 255.255.255.0
  2. 255.255.255.128
  3. 255.255.255.192
  4. 255.255.255.224

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Correct answer: (D) 255.255.255.224

Explanation

The final octets are 01110001 and 01011011. Their first two bits agree, so masks /24, /25 and /26 place them together. The /27 mask 11100000 produces network octets 96 and 64 respectively, separating them. Hence D is impossible.

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