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Cisco™ CCNA : Subnetting

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Subnetting Scenario Question 2

How many subnet bits are required for X number of hosts ? (Assume X value to be 5 in this case)

Tip : Convert X (for the subnets) to binary, determine the number of bits needed for the host portion, additionally determine the subnet mask from the remaining bits, using formula 2ⁿ, find the

relevant number of subnets in this scenario.

Solution :

Step 1: Consider the Class C address N.N.N.H, where H is the host portion whose binary and decimal representation is as shown ---->

Convert 5 to binary. Binary equivalent of 5 is as shown --------->

Step 2: As shown in the figure above, the number of bits needed for the host portion are 3. Therefore, 2

bits

-2=2

-2=6 (6>5)

3 bits are required for the host portion for 5 hosts.

Step 3 (Additional): To know the subnet mask , add the decimal value of the remaining 5 bits i.e, (128+64+32+16+8) = 248

Subnet Mask is 255.255.255.248 (11111111.11111111.11111111.11111000)

Number of subnet bits: 29, here 5 bits are used from the host portion of our subnet mask

Therefore number of subnets required is (2n), where 'n' is the number of bits being used from the host portion of our subnet mask i.e. 5

Therefore, 2

=32 is the number of subnets