Question

A network administrator wants to have the same network mask for all networks at a particular small site. The site has the following networks and number of devices:
IP phones - 22 addresses
PCs - 20 addresses needed
Printers - 2 addresses needed
Scanners - 2 addresses needed
The network administrator has deemed that 192.168.10.0/24 is to be the network used at this site. Which single subnet mask would make the most efficient use of the available addresses to use for the four subnetworks?

Answer 1

Answer:

The subnet mask for all networks in the site is = 255.255.255.224

Explanation:

IP version 4 addresses have three main classes, they are;

Class A : 0 - 126

Class B : 128 - 191

Class C : 192 - 223

And they are define in terms of host and network portion, by the subnet mask.

Class A: 10.0.0.0  , subnet mask: 255.0.0.0

Class B: 172.16.5.3 , subnet mask: 255.255.0.0

Class C: 192.168.2.4 , subnet mask: 255.255.255.0

The "255" on the mask represents the network portion on the ip address, while "0" represents the host.

IPv4 addresses  are 32 bits, with each for the four portions are 8 bits (or octet).

The highest number of host is; IP phones = 22 addresses

To get the mask, we have to get the number of possible host;

           host= 2$x^{n} - 2$

To get a little close to 22, we substitute 5;

                   =2$x^{5}-2$

                   =32 - 2   = 30 hosts

subnet mask;      255   .   255   .   255   .   255

                         11111111    11111111   11111111    1  1  1  00000

the 1s at the left of the last octet;

=2$x^{7}$ + 2$x^{6}$ + 2$x^{5}$

= 128 + 64 + 32       = 224

           The subnet mask for the site is = 255.255.255.224