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GATE | GATE CS Mock 2018 | Set 2 | Question 55

  • Last Updated : 08 Mar, 2018
Geek Week

Consider the given network implementation scenario. For the given classful NID, the requirement is to create 13 subnets. With given details, find the range of first and last valid IP in 15th subnet.

(A) to
(B) to
(C) to
(D) Not of these

Answer: (B)

Explanation: Default mask :
We are supposed to create 13 subnets, which is not possible becuase subnets can be created only in powers of 2. Subnet leads to wastage of IP, that’s the reason we moved to VLSM.
No of subnets = 2^4 = 16 subnets

means, 4 host bits are borrowed. Which makes subnet mask

199     .10      .20      .240

Block size = 256-240 = 16
Valid IP per subnet ID = 2^n – 2 , where n = no of host bits left 2^4-2 = 14

First Subnet :
1st IP :
1st valid IP :
Last valid IP :
Last IP :

In 2nd Subnet, 1st IP : and last IP :
In 3rd Subnet, 1st IP : and last IP :
In 15th subnet, 1st IP : , 1st Valid IP :
Last IP: , Last Valid IP:

Answer : Option (b)

Quiz of this Question

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