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CCNA Routing and Switching Portable Command Guide, Third Edition by Scott Empson

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Chapter 1. How to Subnet

Class A–E Addresses

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Converting Between Decimal Numbers and Binary

In any given octet of an IP address, the 8 bits can be defined as follows:

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To convert a decimal number into binary, you must turn on the bits (make them a 1) that would add up to that number, as follows:

187 = 10111011 = 128+32+16+8+2+1

224 = 11100000 = 128+64+32

To convert a binary number into decimal, you must add the bits that have been turned on (the 1s), as follows:

10101010 = 128+32+8+2 = 170

11110000 = 128+64+32+16 = 240

The IP address 138.101.114.250 ...

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