Three Mask Formats
Subnet masks can be written as 32-bit binary numbers, but not just any binary number. In particular, the binary subnet mask must follow these rules:
The value must not interleave 1s and 0s.
If 1s exist, they are on the left.
If 0s exist, they are on the right.
For example, the following values would be illegal. The first is illegal ...
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