CCNA Routing and Switching Portable Command Guide, Third Edition

Chapter 1. How to Subnet

Class A–E Addresses

Converting Between Decimal Numbers and Binary

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

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 ...