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Subnetting without using binary numbers

When you are working on a network environment or plan to take a ccna exam or any networking exam, time is very important. With this method, subnetting networks is just a matter of three special steps.

Steps for subnetting:

1. Identify the subnet mask

2. Get the increment

3.  Identify the network range


Now lets try to solve the problem below.

Supposing there are two network hubs each in different rooms and each hubs has clients with the following ip addresses. What networking device shall be used in this network setup?

subnet diagram

subnet diagram


We can solve this using the three special steps.

Step 1. Identify the network subnet

In this problem the network has a subnet mask of both in different rooms. Default subnet mask for Class C ip address is With this the borrowed subnet is 248.


Step 2. Get the increment

There are several ways to get the increment but we will exclude decimal to binary conversion. To perform this we will subtract the borrowed subnet from 256. Why 256? 256 is number of ip address in an octet. That is from 0 -255.

By the given formula: 256 – “borrowed subnet”, it shows that:

256 – 248 = 8

8 is the increment for the subnet.


Step 4. Identify the network range

From the increment, we can identify the different subnetworks by adding 8 starting from 0. To make it short do only until the highest ip address in the problem and that is .28.





32 <- we stop here.


We can already identify the network range as until until until until


We can  identify the network id, first usable ip address, last usable ip address, and broadcast id of the network.

From the problem above, given ip addresses are,, 192.168.1. 26 and

network id is the beginning ip address of the network

first usable ip address is the ip address next to network id ( network id + 1 )

broadcast id is the last ip address of the network

last usable ip address is the ip address before the broadcast id ( broadcast id – 1 )


Hence, we can come up with the following: and belongs to network

network id:

first usable ip address:

last usable ip address:

broadcast id: and belongs to network

network id:

first usable ip address:

last usable ip address:

broadcast id:


The problem shows that there are two different networks existing. To connect two different networks, a router is to be used.

7 Responses to “Subnetting without using binary numbers”

  1. Lassaad says:


  2. isaac akelendola says:

    very nice, i was confused when i applied your formula to class B ip addresses.

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