CCNA Exam: Subnetting - Usable Host Calculation

Subnetting: with Subnet Mask

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How many usable host are there per subnet if you have the address of with a subnet mask of



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A. B. C. D.


The subnet mask is a Class C subnet mask, which means the first 3 octets (24 bits) are fixed and the last octet (8 bits) is used for defining the subnet and host addresses.

To determine the number of usable hosts per subnet, you need to calculate the number of valid host addresses within the subnet.

Given the IP address and a subnet mask of, we can analyze the subnet mask to determine the number of host bits.

The subnet mask can be represented in binary as:


Counting the number of zeros in the subnet mask, we find that there are four zeros. Each zero represents a bit that can be used for host addressing.

The number of usable host addresses can be calculated using the formula: 2^n - 2, where 'n' represents the number of host bits.

In this case, 'n' is equal to 4 (the number of zeros in the subnet mask).

Calculating: 2^4 - 2 = 16 - 2 = 14

So, there are 14 usable host addresses per subnet.

Therefore, the correct answer is D. 14.