How to Calculate Subnetting Simply with Questions and Answers

One octet consists of 8 bits (11111111), 1 bit consists of different values, ordered from left to right.
Here we go : 128, 64, 32, 16, 8, 4, 2, 0.

I will not explain the fundamentals of subnetting here, because it is too long, and hopefully those who read this already understand the basics of subnetting, but still often forget 🗿.

OK, here are examples of questions and answers, along with explanations below.

Question

Find the answer below in IP 192.168.10.20/28 (Class C)

1. Total IP

2. Specify the Network IP

3. Specify the Broadcast IP

4. Range of hosts that can be used

5. Subnet Mask

6. Since he is at prefix 192.168.10.20/28, what is the total number of subnets to reach host 20?

Answer

1. 16

2. 192.168.10.16

3. 192.168.10.31

4. 192.168.10.17 - 192.168.10.30

5. 255.255.255.240

6. There are 2 = (192.168.10.0 - 192.168.10.15) and (192.168.10.16 - 192.168.10.31)

Explanation

1. Total IP, the formula for calculating the total IP is 2 ^ 4, why 2? because it is grouped between network and broadcast, and so it is 2, and why 4? we count the number of bits 0 in the host segment (4th octet). /28 if converted to binary is 11111111.11111111.11111111.11110000, okay means the number 0 is 4, then 2 ^ 4 the result is 16.

2. It is clear that the answer is 192.168.10.16, because if calculated from 0 then the range is 192.168.10.0 - 192.168.10.15, so it is fitting that 192.168.10.16 is used as an IP Network.

3. It is clear that the answer is 192.168.10.31, because the IP range itself is 192.168.10.16 - 192.168.10.31, where .31 is a broadcast.

4. The host range that can be used, 192.168.10.17 - 192.168.10.30, why is it only up to 30?, because .16 is as a network and .31 as a broadcast, so the host or client cannot use both ip.

5. Let's convert this /28 to binary numbers and look for the number 1 in the host segment (4th octet), 11111111.11111111.11111111.11110000, which means in arithmetic operations is 128+64+32+16 which results in 240. Then the answer is 255.255.255.240.

6. Because in this question the IP asked is 192.168.10.20/28, then we are actually in the second subnetting in this /28 prefix. Remember again because the total IP in the /28 prefix itself is 16, now it means that it is clear that we are in the second subnetting. Here's the information: Subnetting 1 = (192.168.10.0 - 192.168.10.15) Subnetting 2 = (192.168.10.16 - 192.168.10.31).

Have a good day mate! ☕.