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

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

Step-by-step 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