Networking Arithmetic

Example 14

Given the address 23.56.7.91 and the default class A mask, find the beginning address (network address).

Solution

The default mask is 255.0.0.0, which means that only the first byte is preserved

and the other 3 bytes are set to 0s. The network address is 23.0.0.0.

Example 15

Given the address 132.6.17.85 and the default class B mask, find the beginning address (network address).

Solution

The default mask is 255.255.0.0, which means that the first 2 bytes are preserved

 and the other 2 bytes are set to 0s. The network address is 132.6.0.0.

Example 16

Given the address 201.180.56.5 and the class C default mask, find the beginning address (network address).

Solution

The default mask is 255.255.255.0, which means that the first 3 bytes are

preserved and the last byte is set to 0. The network address is 201.180.56.0.

We must not apply the default mask of one class to an address belonging
to another class.