10.4 IP Address Classes
10.4.3 Binary and decimal conversion review
Instructor Note
  In chapter 1, students were taught the binary number system. Review the techniques for converting between the two systems. Use of calculators is discouraged for two reasons. First, practitioners of networking often need to make quick, "back-of-the-envelope" conversions between decimal and binary numbers. Second, no calculators are allowed on the CCNA exam.

This TI is related to CCNA Certification Exam Objectives #29, #30, and #36.
Each place in an octet represents a different power of 2. As in the Base 10 number system, the powers increase from right to left.

Figure   illustrates a method for converting binary numbers to decimal numbers. Figure allows you to practice your conversion skills.

Figure   illustrates a method for converting decimal numbers to binary numbers. Figure allows you to practice your conversion skills.

Example:
10010000 (Work from right to left).

0 x 20 = 0
0 x 21 = 0
0 x 22 = 0
0 x 23 = 0
1 x 24 = 16
0 x 25 = 0
0 x 26 = 0
1 x 27 = 128
__________
Total = 144

In this example, there are 0 values of 20; 0 values of 21; 0 values of 22; 0 values of 23; 1 value of 24; 0 values of 25; 0 values of 26; and 1 value of 27. There are no 1s, no 2s, no 4s, no 8s, one 16s, no 32s, no 64, and one 128. Added together, the values total 144, therefore, the binary number 10010000 equals the decimal number 144.