|  | 10.3 | IP Addresses within the IP Header
| 10.3.4 | IP address as a 32-bit binary number

An IP address is represented by a 32 bit binary number. As a quick review, remember that each binary digit can be only 0 or 1. In a binary number, the value of the right-most bit (also called the least significant bit) is either 0 or 1. The corresponding decimal value of each bit doubles as you move left in the binary number. So the decimal value of the 2nd bit from the right is either 0 or 2. The third bit is either 0 or 4, the fourth bit 0 or 8, etc ...

IP addresses are expressed as dotted-decimal numbers - we break up the 32 bits of the address into four octets (an octet is a group of 8 bits). The maximum decimal value of each octet is 255. The largest 8 bit binary number is 11111111. Those bits, from left to right, have decimal values of 128, 64, 32, 16, 8, 4, 2, and 1. Added together, they total 255.

What is the decimal value of the highlighted octet in the graphic? What is the value of the bit on the far left side? The next bit? Since those are the only 2 bits on (or set), then the decimal value is 128+64=192!

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