Converting Between Binary and DDN Masks
By definition, a dotted-decimal number (DDN) used with IPv4 addressing contains four decimal numbers, separated by dots. Each decimal number represents 8 bits. So, a single DDN shows four decimal numbers that together represent some 32-bit binary number.
Conversion from a DDN mask to the binary equivalent is relatively simple to describe, but can be laborious to perform. First, to do the conversion, the process is as follows:
For each octet, perform a decimal-to-binary conversion.
However, depending on your comfort level with doing decimal-to-binary conversions, that process can be difficult or time-consuming. If you want to think about masks in binary for the exam, consider picking one of the following ...