### Supernetting and Binary System

Today, I want to show you how to change decimal to binary and SUPERNETTING.

## How to Change Decimal to Binary

It is so simple! You just need to divide decimal number by 2. The most important point is remainder. Let's do a sample. Find 12 in binary system.
12:2=6+0   As you see, the remainder is 0.
6:2=3+0     As you see, the remainder is 0.
3:2=1+1     As you see, the remainder is 1.
1:2=0+1     As you see, the remainder is 1.
Then lets write them down to up. (It is like Arabic.) So, it is 1100 in binary system.

## Understanding SUPERNETTING

Once I try to setup my Cisco Meraki, I had some problems with CIDR. If I put x.x.8.0/22, it works. However, it doesn't work for x.x.2.0/22. But x.x.2.0/23 works.
Then, I learned the supernetting.
Explanation 1:  The important point is where you catch the 1 for all subnetting. (When you AND them, it should be 1. Once you reached 1, you reach the max CIDR.) Please see below picture to understand easily.

Explanation 2:
If you thinking for x.x.x.x/24; you need to check the number at rank#24. If the ranges are 1, it is OK.
• For /24 CIDR, it is only 1 subnet; so every /24 CIDR will be fine.
• For /23 CIDR, there are 2 subnet (510 host); so you need to check the number at rank#23 for each subnet, they should be 1.
Let me explain with an example:
10.1.1.0/23: It has 2 subnet which are 10.1.1.1-10.1.1.254 and 10.1.2.1-10.1.2.254
10.1.1.0: 00000110.00000001.00000001.00000000 =>Rank#23 is 0.
10.1.2.0: 00000110.00000001.00000010.00000000
=>Rank#23 is 1.
So, 10.1.1.0/23 can't be. Both rank#23 must be 1.
• For /22 CIDR, there are 4 subnet (1022 host); so you need to check the number at rank#22 for each subnet, they should be 1.
Explanation 3: (Best Explanation:) Take the first 1 (number 1) from right side. And check below subnets on the same rank. You only can add as much as it is!