I found this problem in a textbook, and I do not understand the solution:

Find the subnet which the IP: `192.168.1.25`

belongs to.

Here is what they did:

`255.255.255.224`

for`192.168.1.25`

and do a binary`AND`

operation.- Then take the subnet mask because of postfix
`/27`

CIDR postfix in the IP.

But why? In the problem definition, the number `/27`

was not given. How did they come up with that?

`192.168.1.25/27`

means 27 mask bits; this corresponds to the subnet mask`255.255.255.224`

. – John Willemse May 3 '13 at 14:55