How to add, install or import IOS in GNS3

This tutorial explains how to install or import Cisco IOS files in GNS3. Learn how to install, configure and use Cisco IOS files in GNS3 in detail.

GNS3 is a network simulator software. It is used to simulate routers, switches, and other networking devices. Cisco uses proprietary software for its routers and switches. This software is known as Cisco IOS. GNS3 can run Cisco IOS. Since Cisco IOS is protected by copyright laws, GNS3 does not include any Cisco IOS in the default installation. It only provides a platform to use Cisco IOS but it does not provide any Cisco IOS itself. It means, to use any Cisco device in GNS3, you have to install that device’s IOS first.

Downloading Cisco IOS

To install a Cisco device in GNS3, you have to obtain its IOS file. There are several sources from where you can obtain a Cisco IOS file. You can get it from a Cisco device or download it from Cisco’s official site (it requires a valid Cisco account and license agreement) or download it from educational sites. If none of these work, you can search the following term on Google.

intitle:index.of cisco ios parent directory bin

You may check the following site.
It contains the largest collection of Cisco IOS files. I found this site through a Google search. It may be may not be working at this moment.

Installing and importing Cisco IOS in GNS3

Download or obtain the IOS file that you want to use on GNS3.

gns3 file

Open GNS3, and click the Edit file menu, and from the sub-menu, click the Preferences option.

file menu gns3

On the opened window, navigate to the Dynamips -> IOS routers option in the left pane and click the New button in the right pane.

Dynamips  options

Select the New Image option and click the Browse button and select the downloaded IOS image file.

new image

By default, IOS files are compressed. GNS3 supports both compressed and decompressed formats. Compressed files not only consume less space but also easier to manage. Unless you have a particular reason to keep IOS files in their original form, click the No option to keep them in compressed format.

file format

Verify the file path again and click the Next button.

verify file path

If the selected IOS belongs to an outdated device, the wizard may display a warning message.

In real life, using an outdated device is not recommended. Since GNS3 uses a real Cisco IOS, it also follows the same recommendation and warns us about the outdated IOS. If you only want to use this device for exam preparation or to get some hands-on experience on Cisco IOS, you can ignore this message.

ignore notice

On the next step, the wizard extracts the hardware information (platform and chassis number) from the selected IOS file and lists the information on the next screen along with an automatically populated device name.

If the extracted information is incorrect, select the correct platform and chassis number from the drop-down. If required, you may adjust the device name as well.

Verify or adjust the information and Click the Next button to continue.

select hardware platform

The next screen allows us to set the RAM size for this device. By default, the wizard automatically allocates the minimum recommended memory (RAM) for the device. But if required, you can adjust it.

set ram size

If the selected IOS belongs to a modular device, the next screen allows us to install the interfaces in available slots.

select interfaces

Select appropriate interfaces and click the Next button.

interface selected

If the selected IOS belongs to a device that has WIC modules, the next screen allows us to install WIC interfaces in WIC slots.

select wic

Select the desired WIC interfaces and click the Next button.

wic selected

The next screen allows us to define how much CPU this IOS can use. You should always specify this value. This value prevents a faulty or buggy IOS from consuming all CPU cycles. Once this value is configured, GNS3 does not allow the IOS to consume the CPU beyond this limit.

Click the Idle-PC finder button and use the suggested value in this field.

limit cpu usages

Click the Finish button to close the wizard.

cpu limit

Managing IOS files

All installed files are listed in the right pane of the Dynamips -> IOS routers option. Select the file which you want to manage. Once the IOS file is selected, control options will be highlighted in the bottom section. Control options are the following.

New: -

this option is used to install the new IOS file. If no installed IOS file is selected, only this option will be highlighted.

Decompress: -

This option allows us to decompress the selected IOS file.

Edit: -

This option allows us to update the configuration values that were configured during the installation process. All configuration values are listed in the right section of the pane.

Delete: -

This option allows us to delete the selected IOS file.

managing IOS

How to use the installed device?

Once the IOS file has been successfully installed or imported in GNS3, the belonging device will be available in the "Installed appliances" box. For example, in this tutorial, we installed an IOS file that belongs to a c2600 series router. To use this router, click the Routers icon from the left pane and select the "Installed appliances" option from the drop-down box. The box will list all installed devices. Select the router and drag it into the workspace.

using installed IOS

That’s all for this tutorial. If you like this tutorial, share it with your friends through your social network.

ComputerNetworkingNotes CCNA Study Guide How to add, install or import IOS in GNS3