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How to subnet a network

Understanding subnetting is very important not only for those preparing for CCNA exam but also network administrators. Today, I am going to teach you how to create a subnet in a network. For this, I will use Packet Tracer software. To know what is subnetting and why we need it go here. So let’s start.

Imagine I formed a small software company named shunya whose network looks like below. I hired one Java developer, one software tester, one HR and one network administrator. I have been assigned the IP address range from 192.168.10.1 to 192.168.10.255.

I have enabled DHCP on my router as below.

After one year, imagine my company has received Abrahamic blessings from GOD and has seen rapid growth. Now the company has three Java developers, three software testers and  a dedicated HR team. Not only that, my company now has moved into Remote Infrastructure Management(RIM) and has a Network Operation Center(NOC) and Security Operation Center(SOC).  Total I have 15 computers in my network which looks like below.

Now see the image below. Here the machine “JD1″ sends a packet to machine “Testing3″. We can see here that for communication between machines “JD1: and “Testing3″ other machines have also been disturbed.

So for this reason, I decided to subnet the network. I decide to divide the network into three subnets as shown below.

To create a subnet, first we need to have proper planning as to how many subnets we need and how many we may need in the future. Presently, I need three subnets. The number of subnets should always be calculated in the powers of 2.

2 to the power of 1 = 2

This doesn’t satisfy our requirement as we need three subnets.

2 to the power of 2 = 4

This satisfies our requirement. So we need to take two bits from the host portion of the IP address. 192.168.10.1 to 192.168.10.255 is the address range available to us with subnet mask 255.255.255.0,  Writing the subnet mask in the binary notation, it is

11111111 11111111 11111111 00000000

 255            255          255             0  

The first 24 bits are network bits and the last eight bits are host bits. To create three subnets, we need to take two bits from the host portion of the address as explained above.

11111111 111111111 11111111 11000000

   255              255            255         192

Four subnets which can be created from the above subnet mask are,

192.168.10.0 to 192.168.10.63 ( with host bits 00000000 )

192.168.10.64 to 192.168.10.127 ( with host bits 01000000 )

192.168.10.128 to 192.168.10.191 ( with host bits 10000000 )

192.168.10.192 to 192.168.10.255 ( with host bits 11000000 )

Since we require only three subnets, we will create the first three subnets. The first subnet ( 192.168.10.1 to 192.168.10.63 ) comprises of Java Developers and Software testers. The commands are as below on the interface.

If you go to any machine on this subnet and look at its IP address, it will be like below.

Now the subnet for the Human Resource Department ( 192.168.10.128 to 192.168.10.191 ) . This will be like below.

The third subnet ( 192.168.10.64 to 192.168.10.127 ) comprises of NOC and SOC.

Now our network has been successfully sub netted into three subnets and we still have another subnet to use for future use.

Hope this was helpful. If you have any doubts regarding this article please comment below. Thank you.

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Install Packet Tracer in Windows and Linux

Cisco Certified Network Associate certification has become must for anybody who wishes to start  a career in networking. This certification validates that you have the ability to install, configure and troubleshoot a network. You need  lot of practice for achieving success in this exam. Apart from the labs where you are getting trained for CCNA what if you had a chance to practice at home. Or what if you want to self learn for CCNA? Well for both of the questions above, Cisco Packet Tracer is the perfect answer. To quote from Cisco’s official website, Packet tracer is

“a powerful network simulation program that allows students to experiment with network behavior and ask “what if” questions.”

It further says,

“The simulation-based learning environment helps students develop 21st century skills such as decision making, creative and critical thinking, and problem solving. Packet Tracer complements the Networking Academy curricula, allowing instructors to easily teach and demonstrate complex technical concepts and networking systems design.”

Nothing could have defined that better. This software is available for free from Cisco’s website provided you are a registered Networking Academy student, alumni, instructor, or administrator. Even if you are not one among the above you could still get hold of this software, just google it.

Now I’m gonna show you how to install packet tracer in Windows and Linux.

1.Windows

Any installation in Windows is just clicks and mouse and the same applies to Packet tracer. Click on the exe file downloaded. The below screen appears. Select “I accept the agreement” and click on “Next”.

Setup will show the folder in which the program’s shortcuts will be created. If you want to change the folder, you can change it. Click on “Next”.

Then the program will ask whether to create a Desktop icon and create a Quick Launch icon. Make your own choice and click on “Next”.

Then the summary of the settings we selected is displayed. Click on “Install”.

The installation starts as shown below.

In seconds, installation gets completed and the below screen is shown. Click on “Finish”.

Then the below popup appears asking you to close or restart your computer. Click on “OK”.

As we selected Launch option, Packet tracer is automatically launched.

2. Linux

To install Packet Tracer in Linux, we need a .deb package of Packet tracer which can be downloaded from here. Now I am going to install it in Ubuntu Precise Pangolin (12.04). Download the above file to the desktop.

Start the terminal and see your current working directory by typing “pwd”. If the current directory is not desktop move to the Desktop directory using “cd”. After reaching the Desktop directory, type “ls” to see if the packet tracer binary is there.

Left click on the packet tracer .bin file displayed after typing “ls” above, the entire word will be selected. Then right click and select copy. Now type “chmod +x” and then hit “CTRL+SHIFT+V “to paste the text we copied above. Our command should look like this.

                       chmod +x  PacketTracer533_i386_installer-deb.bin

What chmod +x command does is that it gives all users permission to execute.

Then type “./PacketTracer533_i386_installer-deb.bin” in the terminal. This will start extracting the binary package.

Then terminal prompts us to hit Enter to read the End User License Agreement.  Enter.

After displaying a rather long EULA, terminal asks us if we accept the terms of EULA. Type “Y”.

Then system asks us for the sudo password. Type the password and hit Enter.

When the installation is finished, close the terminal, go to Dashboard, if packet tracer is not seen, type ‘pac’ in the search box. When Packet Tracer is shown, click on it.

A message box shows up saying that we are starting packet tracer for the first time and our files will be stored in a specific folder. Click on “OK”.

Another message box pops up. Click on OK”.

Packet tracer is started.