Question

You are planning to redesign a Classful 172.31.0.0 network to accommodate 3540 subnets with 10 hosts per subnet. In your own words, explain what subnet masks you could use to satisfy this new requirement. You must use concepts such as host bits, hosts and subnets to justify your answer. Simply listing out subnet masks won’t be awarded any marks.

Answer 1

Solution:

Given,

=>Network address = 172.31.0.0

=>Number of subnets = 3540

=>Number of hosts/subnet = 10

Explanation:

=>We know that address range for class B is 128 to 191 so the given network address comes under class B.

=>In class B, 16 bits are given to net ID part and 16 bits are given to host ID part.

Subnetting:

Calculating number of bits for bits for subnets:

=>Number of bits required for 3540 subnets = ceil(log₂(3540))

=>Number of bits required for 3540 subnets = ceil(11.79)

=>Number of bits required for 3540 subnets = 12 bits

Calculating number of bits for hosts:

=>Number of bits for 10 hosts = ceil(log₂(10))

=>Number of bits for 10 hosts = ceil(3.32)

=>Number of bits for 10 hosts = 4 bits

Calculating subnet mask:

=>As 12 bits are borrowed from the 16 bits host ID part of class B, so finally 28 bits will be given to the net ID as well as subnet ID part and remaining 4 bits will be given to the host ID part.

=>Put all 1's in net ID as well subnet ID part and all 0's in host ID part to calculate the subnet mask.

=>Subnet mask = 11111111.11111111.11111111.11110000 in binary

=>Subnet mask = 255.255.255.240 in decimal

I have explained each and every part with the help of statements attached to the answer above.