Binary Calculations
To perform subnetting operations, you will need to be proficient at converting decimal and binary numbers. When working with IP addresses, work with each octet separately. The following table shows the decimal value for various binary values with a single 1 bit.
|
Binary Value |
10000000 |
01000000 |
00100000 |
00010000 |
00001000 |
00000100 |
00000010 |
00000001 |
|
Decimal Value |
128 |
64 |
32 |
16 |
8 |
4 |
2 |
1 |
To find the decimal value of a number with multiple 1 bits, simply add the decimal value of the bits together. For example, the decimal value of the binary number 10010101 is:
10000000 = 128
00010000 = 16
00000100 = 4
00000001 = 1
Total = 128 + 16 + 4 + 1 = 149
To calculate the number of valid subnets or the number of hosts per subnet, you will need to know how to find the exponential values of 2. Use the following chart to identify the exponent values and the final possible number (after subtracting 2 from each exponent).
|
# of bits |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
11 |
12 |
|
Exponent |
21 |
22 |
23 |
24 |
25 |
26 |
27 |
28 |
29 |
210 |
211 |
212 |
|
Exponent value |
2 |
4 |
8 |
16 |
32 |
64 |
128 |
256 |
512 |
1024 |
2048 |
4096 |
|
Total number (-2) |
0 |
2 |
6 |
14 |
30 |
62 |
128 |
254 |
510 |
1022 |
2046 |
4094 |
Tip: Memorize the shaded values. To find smaller or larger values, divide or multiply the exponent value by 2.
Credit: Testout 640-802 CCNA Notes
