How to add, install or import IOS in GNS3

This tutorial explains how to download and import Cisco IOS image files to GNS3. Learn how to add or install Cisco IOS images to GNS3.

GNS3 is free network simulator software. It emulates and simulates 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 its default installation. It only provides a platform to use Cisco IOS, but it does not provide any Cisco IOS itself. To use a Cisco device in GNS3, you need to download and import its IOS to GNS3.

How to download Cisco IOS image files for GNS3

You can obtain Cisco IOS image files from many sources. You can get them from a Cisco device or download them from Cisco’s official site (it required an active subscription plan). Many sites store and offer Cisco IOS images for educational purposes. The following site provides the largest collection of the Cisco IOS image files.

https://tfr.org/cisco-ios/

If it does not work, you can use the following search term on Google to find other sites.

intitle:index.of cisco ios parent directory bin

You can use any working site from the result to download the Cisco IOS image files.

Installing and importing Cisco IOS in GNS3

After downloading the IOS image file, open GNS3, click Edit and click Preferences.

Navigate to the Dynamips -> IOS routersoption in the left pane and click the New button in the right pane.

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

By default, IOS files are compressed. GNS3 supports both compressed and decompressed formats. Compressed files not only consume less space but are 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.

Verify the file path again and click the Next button.

If the selected IOS belongs to an outdated device, the wizard displays a warning message.

In real life, using an outdated device is not recommended. Since GNS3 uses a real Cisco IOS, it also follows the same recommendation and warns us about the outdated IOS.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.

In 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 necessary, you can also adjust the device name.

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

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.

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

Select appropriate interfaces and click the Next button.

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 the desired WIC interfaces and click the Next button.

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.

Click the Finish button to close the wizard.

Managing IOS files

All installed IOS image 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.

Video version

This tutorial is also available in video format on our YouTube channel.

That’s all for this tutorial, in this tutorial, we learned how to download, install, and manage Cisco IOS image files on GNS3.