This post gives an overview of GNS3 software and shows how to install it. It is a part of GNS3 Tutorial series.
What is GNS3?
GNS3 is a free network emulation software with GUI that can be used to run real network OS (for example, Cisco IOS) images, and build various network topologies in a virtual environment on your PC. It is supported on all major operating systems: Linux, Windows and Mac OS. GNS3 is very popular among those preparing for Cisco certification exams, though it supports other vendors as well.
There are two ways you can use GNS3 platform:
GNS3-all-in-one: Both GNS3 GUI and GNS3 Server run as processes on your PC. The appliances listed on the marketplace are not supported with this option. You can use only older versions of Cisco IOS (up to 12.4)
GNS3-all-in-one + GNS3 VM: GNS3 GUI runs on your PC, but GNS3 server runs on a separate VM. This option is recommended for more complex deployments.
Note, that GNS3 itself does not provide any network OS images, that is, for example, if you want to emulate a Cisco IOS or any other router, you will have to provide your own image files.
The recommended hardware requirements for running GNS3 on Windows are below:
CPU: 4 and more logical cores. CPU should support virtualization.
Memory: 8GB of RAM
Storage: 35GB on SSD storage
The following Windows OS are supported:
Windows 7 SP1 (64 bit)
Windows 8 (64 bit)
Windows 10 (64 bit)
Windows Server 2012 (64 bit)
Windows Server 2016 (64 bit)
Installation on Windows
We will now install GNS3 as a standalone software without GNS3 VM. This will allow you to use platform for emulating Cisco IOS without building complex environment. Later, when you are more comfortable with the platform, you are encouraged to switch to the deployment with GNS3 VM.
Step 1. Install GNS3
Go to GNS3 website and download the installation file. You will have to create an account to be able to download it.
Choose the one for Windows OS.
Once the file is downloaded launch the installation file and click Next,Next, Next… The installation wizard will download the required packages and finish the installation.
Step 2. Create a new project in GNS3
Now, that we have finished the installation, let’s run the GNS3. You will see the following window:
Click Cancel to close it.
Click File => New Blank Project to create a new project. Enter the name of the project and click OK:
The new project will be created. If you want to look at the settings of the project, go to Edit => Preferences. There you will find the location directory for the project and other useful information. We are using Local server for emulating network OS and therefore we can create only routers with legacy Cisco IOS 12.4. The screenshot below shows that the Local server is enabled:
Step 3. Add a new template
Before we continue, make sure you have a Cisco IOS, because GNS3 won’t provide you one. I will use c3725-adventerprisek9-mz.124-25d.bin. You can find the list of recommended IOS image versions on the GNS3 website:
Note the Minimum RAM and Idle-PCvalue, you will need them later.
Go to Edit=>Preferences=>IOS routers and click New.
Browse to the location of your IOS file and click Next:
Provide the correct values for RAM and Idle-PC value:
Click Finish and you will see the overview of the new template. Then Click Apply.
Now, if you go back to the workspace, you will see that the Cisco 3725 router is now available.
Step 4. Add a new router to the workspace.
Drag and Drop the new template to the workspace. The new router symbol will be added with R1 label. Then right-click it and select Start.
To access the console of the new router right-click it again and select Console. The console window will open up:
Here you can make any configuration changes, don’t forget to save the config of the router before you shut it down, just like on a real hardware.
Step 5. Add a second router to the workspace.
Drag and drop the second router. Then use the Link tool to connect them to each other. Click on the Link button and then on the 1st router to select the interface, then click on the 2nd router to select its interface. You will end up with a connection like this:
Step 6. Verify the connectivity.
I have configured the IP addresses on the routers and made sure they had basic connectivity and could ping each other:
Now, that everything works, we can save routers configuration and shut them down. You can use Stop All button to do this:
After this you can close the GNS3.
You have successfully built your first GNS3 topology. There will be another post, where I will show you how to emulate Cisco routers running newer IOS 15 images.