Anetwork 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?

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

To get a little close to 22, we substitute 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 + 2 + 2

= 128 + 64 + 32       = 224

           The subnet mask for the site is = 255.255.255.224

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