Subnetting?! You can do it!

Subnetting can be confusing until it is broken into steps and followed logically. Practicing these steps on a regular basis will enable one to understand subnetting.

Before attempting subnetting, one must understand how to work with binary and decimal number conversions. Let's review this first.

2⁰=1
2¹=2
2²=4
2³=8
2⁴=16
2⁵=32
2⁶=64
2⁷=128

The following pattern for solving binary numbers to decimal numbers and decimal numbers to binary numbers should be used. Always remember to read from right to left instead of left to right. Also notice that each place doubles in value from right to left.

27	26	25	24	23	22	21	20
128	64	32	16	8	4	2	1

The above should be memorized. Later this will be important to remember when figuring out the number of subnets and hosts per subnets. Therefore, this skill must be practiced and reinforced as often as possible. Here are a few sample problems.

Example 1 (binary to decimal)
11001011 = 203 or

27	26	25	24	23	22	21	20
128	64	32	16	8	4	2	1
1	1	0	0	1	0	1	1

Example 2 (binary to decimal)
01011110 = 94 or

27	26	25	24	23	22	21	20
128	64	32	16	8	4	2	1
0	1	0	1	1	1	1	0

By writing out the chart and placing the 1's and 0's under the proper place in the chart, all that is left is to add up the place values that have 1's under them and the total will be the decimal number value.

To convert decimal numbers to binary numbers, place 1's in the place values until all the place values with 1's add up to the total. If any numbered place adds a value that is larger than the decimal number, 0's should be placed in those place values.

Subnetting Review

When you are creating subnets,you must determine the optimal number of subnets and host.
To identify subnets, you will "borrow" bits from host ID portion of the IP address:

The number of subnets available depends on the number of bits borrowed.

• The available nmber of subnets =2s, I which s is the number of bits borrowed.

The number of hosts per subnet available depends upon yhe number of host ID bits not borrowed.

• The available number of hosts per subnet=2h-2, in which h is the number of host bits not borrowed.
• One address is reserved as the network address.
• One address is reserved as the broadcast address.