Question 554 of 952 from exam 200-125: Cisco Certified Network Associate Exam

D

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)

To configure 113 point-to-point links, we need to use a subnet mask that can provide at least 113 usable IP addresses, since each point-to-point link will need two IP addresses, one for each end of the link.

Option A: 10.10.0.0/16 subnetted with mask 255.255.255.252 This option creates 65,534 subnets with 2 usable IP addresses each. However, since we only need 113 usable IP addresses, this option is wasteful and will result in unused IP addresses.

Option B: 10.10.0.0/18 subnetted with mask 255.255.255.252 This option creates 4,096 subnets with 2 usable IP addresses each. This provides enough IP addresses for the required 113 point-to-point links, but also results in a large number of unused IP addresses.

Option C: 10.10.1.0/24 subnetted with mask 255.255.255.252 This option creates 256 subnets with 2 usable IP addresses each. This provides enough IP addresses for the required 113 point-to-point links, but also results in a large number of unused IP addresses.

Option D: 10.10.0.0/23 subnetted with mask 255.255.255.252 This option creates 512 subnets with 2 usable IP addresses each. This provides enough IP addresses for the required 113 point-to-point links, with a smaller number of unused IP addresses compared to the previous options.

Option E: 10.10.1.0/25 subnetted with mask 255.255.255.252 This option creates 128 subnets with 2 usable IP addresses each. This provides enough IP addresses for the required 113 point-to-point links, with a smaller number of unused IP addresses compared to the previous options.

Therefore, the best option that meets the requirement and wastes the fewest subnet and host addresses is Option E: 10.10.1.0/25 subnetted with mask 255.255.255.252.