Finding the Subnet ID: Binary
To start this section that uses binary, first consider a simple decimal math problem. The problem: Find the smallest three-digit decimal number that begins with 4. The answer, of course, is 400. And although most people would not have to break down the logic into steps, you know that 0 is the lowest-value digit you can use for any digit in a decimal number. You know that the first digit must be a 4, and the number is a three-digit number, so you just use the lowest value (0) for the last two digits, and find the answer: 400.
This same concept, applied to binary IP addresses, gives you the subnet ID. You have seen all the related concepts in other chapters, so if you already intuitively know how to find the subnet ...
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