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IP Addressing Fundamentals by Mark A. Sportack

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Symmetry of CIDR Notation

The binary mathematics of the IP address space creates a marvelous natural symmetry in CIDR-compliant addresses. What at first glance appears to be an unmanageable jumble of numbers is actually a remarkably logical system. The key is remembering that the binary number system works based on powers of 2. For each bit you move to the left, you double the bit's value. For each bit you move to the right, you halve the bit's value. These facts help you better appreciate CIDR's /number notation. For example, if you halve a bit's value by moving to the right, you can logically assume that the entire string of bits that follows the bit in question is also halved.

Look at Table 6-2 to see how this works. In this table, we'll look ...

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