"IP addresses are just 32-bit binary numbers, but they're
important binary numbers: you need to how to work with them. When
working with subnet masks, new network administrators generally get
confused with the ones they haven't memorized. All the subnet mask
amounts to is moving the boundary between the part of the address
that represents a "network" and the part that represents a "host."
Once you're comfortable with this method of thinking about IP
addresses and masks, you've mastered IP addressing."