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!

To see all numbers in binary, please click here.

P.S. This sample is for Class C Subnet. (255.255.xxx.0)