Question

As the network administrator for a growing ISP, you want to make efficient use of your network addresses. One of the networks addresses IANA assigned to you is a Class C network of 192.168.88.0. You have decided to use the addresses in this Class C network to satisfy the IP address requirements of 18 corporate customers who need between 20 and 24 addresses each. calculate a subnet mask that meets their needs. List the subnet mask and the first four subnetwork addresses the mask will create. [5 marks]

please answer fast in 30 minutes and the subject is data commniucations and network.

Answer 1

The Class C network (lets say 192.168.1.0) has the ability to have 254 hosts (192.168.1.1 - 192.168.1.254, due to the fact that the 192.168.1.0 is the network address and 192.168.1.255 is the network address).

If you break down the subnet mask in to binary (11111111.11111111.11111111.00000000)
you will see that there are 8 spots here. To break this down you will go like this
|128|64|32|16|8|4|2|1|
so you can see that the proper mask will end up being 11111111.11111111.11111111.|1|1|1|1|0|0|0|0| in binary. As this spot will allow 16 addresses per network. It also allows for 16 networks.
To calculate that in decimal it would be 128+64+32+16 = 240 giving a 255.255.255.240 mask. End result 16 networks with 16 addresses per network with upto 14 usable addresses per network. Meeting the requirements for your 16 customers, each having 10-14 addresses needed per network.

The networks will be
192.168.1.0
192.168.1.16
192.168.1.32
192.168.1.48

Each network will be able to exactly hold 14 address (because of the first and last being the network and broadcast addresses) and your mask will be 255.255.255.240.