Cisco 200-125 Exam

The network administrator is asked to configure 113 point-to-point links. Which IP addressing scheme defines the address range and subnet mask that meet the requirement and waste the fewest subnet and host addresses?

  • A. 10.10.0.0/16 subnetted with mask 255.255.255.252
  • B. 10.10.0.0/18 subnetted with mask 255.255.255.252
  • C. 10.10.1.0/24 subnetted with mask 255.255.255.252
  • D. 10.10.0.0/23 subnetted with mask 255.255.255.252
  • E. 10.10.1.0/25 subnetted with mask 255.255.255.252
Answer: Option D.
Explanation: 

We need 113 point-to-point links which equal to 113 sub-networks < 128 so we need to borrow 7 bits (because 2^7 = 128).
The network used for point-to-point connection should be /30.
So our initial network should be 30 ?7 = 23.
So 10.10.0.0/23 is the correct answer.
You can understand it more clearly when writing it in binary form:
/23 = 1111 1111.1111 1110.0000 0000
/30 = 1111 1111.1111 1111.1111 1100 (borrow 7 bits)

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