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Stephen Shirodkar
Stephen Shirodkar

How to Master Network Simulation with GNS3 and Cisco IOS Images



Cisco IOS Images Free Download for GNS3


GNS3 is a graphical network simulator that allows you to create, configure, test and troubleshoot virtual and real networks. It is a powerful tool for network engineers, students, and enthusiasts who want to learn about different network technologies and prepare for certification exams such as Cisco CCNA, CCNP, or CCIE.




cisco ios images free download for gns3

But how do you get started with GNS3? And where do you find the Cisco IOS images that you need to run the routers and switches in your network topology? In this article, we will answer these questions and show you how to download Cisco IOS images for free and use them in GNS3. We will also discuss the advantages and disadvantages of using GNS3 for network simulation and give you some tips and recommendations to make the most out of it. What is GNS3 and why do you need it?


GNS3 stands for Graphical Network Simulator-3. It is an open source, free software that you can download from [39](http://gns3.com). It was originally developed as a tool for Cisco networking, but it has evolved and supports many devices from multiple network vendors, such as Juniper, Arista, Brocade, Cumulus, HPE, Palo Alto, MikroTik, and more. You can also integrate GNS3 with other software and platforms, such as Docker, VMware, VirtualBox, Wireshark, Ansible, etc. GNS3 allows you to create realistic network topologies by emulating or simulating network devices. Emulation means that GNS3 runs the actual software of the device (such as Cisco IOS) on a virtual machine or a hypervisor. Simulation means that GNS3 uses a simplified model of the device (such as Cisco Packet Tracer) that mimics its behavior and features. The main advantage of using GNS3 is that you can practice and experiment with different network scenarios without having to buy or rent expensive hardware equipment. You can also test new features, configurations, protocols, or applications before deploying them in a real network environment. You can also use GNS3 to study for certification exams or to demonstrate your skills and knowledge to potential employers or clients. How to install GNS3 on your computer


  • To use GNS3, you need to install two software components: the GNS3-all-in-one software (GUI) and the GNS3 virtual machine (VM). The GUI is the client part of GNS3 that provides the graphical user interface for creating and managing your network topologies. The VM is the server part of GNS3 that runs the network devices and provides the connectivity between them. You can install both components on your local PC (Windows, MAC, Linux) or you can install them on separate machines or even in the cloud. The recommended option is to install the GUI on your local PC and the VM on a remote server or in the cloud. This way, you can offload the CPU and memory resources required by the network devices to another machine and improve the performance and stability of your simulations. To install GNS3 on your computer, follow these steps: Download the latest version of GNS3-all-in-one software from [34](https://github.com/GNS3/gns3-gui/releases) and run the installer.

  • Select the components that you want to install (such as Dynamips, Qemu, VPCS) and follow the instructions on the screen.

  • Download the latest version of GNS3 VM from [41](https://www.gns3.com/software/download-vm) and import it into your preferred virtualization software (such as VMware Workstation or VirtualBox).

  • Start the GNS3 VM Start the GNS3 VM and make sure that it has the same version as the GNS3 GUI.

  • Open the GNS3 GUI and go to Edit > Preferences > Server. Select the Remote Servers tab and click Add.

  • Enter the IP address and port of the GNS3 VM and click OK. You should see a green dot indicating that the connection is successful.

  • Click Apply and OK to save the settings.

Congratulations, you have installed GNS3 on your computer. Now you are ready to download Cisco IOS images and use them in GNS3. How to download Cisco IOS images and use them in GNS3


  • Cisco IOS (Internetwork Operating System) is the software that runs on Cisco routers and switches. It provides the functionality and features that enable network communication and management. To use Cisco devices in GNS3, you need to have the Cisco IOS images that match the model and version of the device that you want to emulate. There are two ways to obtain Cisco IOS images: legally or illegally. The legal way is to have a valid Cisco account and a service contract that allows you to download the IOS images from the [40](https://software.cisco.com/download/home) website. The illegal way is to search for the IOS images on the internet and download them from unauthorized sources. We do not recommend or endorse the illegal way, as it may violate Cisco's terms of use and expose you to security risks and legal issues. Once you have downloaded the Cisco IOS images, you need to add them to GNS3. To do this, follow these steps: Go to Edit > Preferences > Dynamips > IOS Routers and click New.

  • Select New Image and browse to the location where you saved the IOS image file. Click Open.

  • GNS3 will scan the image and extract some information, such as the platform, model, and RAM requirements. Click Next.

  • Enter a name for the router (such as cisco-3725) and click Next.

  • Select the default RAM amount (128 MB) and click Next.

  • Select the number of network adapters (such as 2 FastEthernet) and click Next.

  • Select the WIC modules (such as WIC-1T) and click Next.

  • Select the Idle-PC value (such as 0x60aa1da4) and click Finish.

You have added a Cisco router to GNS3. You can repeat this process for other Cisco devices that you want to use in your network topology. You can also edit or delete the devices that you have added by going to Edit > Preferences > Dynamips > IOS Routers. Advantages and disadvantages of using GNS3 for network simulation


GNS3 is a powerful tool for network simulation, but it also has some limitations and drawbacks that you should be aware of. Here are some of the advantages and disadvantages of using GNS3 for network simulation:


Advantages Disadvantages ---------- ------------- It supports a wide range of network devices from multiple vendors, not only Cisco. It requires a lot of CPU and memory resources, especially when running multiple devices or complex topologies. It allows you to run real software (such as Cisco IOS) on virtual machines, which gives you more realism and accuracy than simulation software (such as Packet Tracer). It does not support all features or commands of the real devices, especially newer ones or those that depend on hardware components (such as switching ASICs). It enables you to integrate with other software and platforms, such as Docker, VMware, VirtualBox, Wireshark, Ansible, etc., which gives you more flexibility and functionality than standalone software. It can be difficult to set up and configure, especially for beginners or those who are not familiar with virtualization or networking concepts. It is free and open source, which means that you can download it, use it, modify it, or contribute to it without paying any fees or licenses. It may not be updated or supported regularly, which means that you may encounter bugs, errors, or compatibility issues with newer versions or platforms. Conclusion: Summary and recommendations




In this article, we have shown you how to download Cisco IOS images for free and use them in GNS3. We have also discussed the advantages and disadvantages of using GNS3 for network simulation and given you some tips and recommendations to make the most out of it.


GNS3 is a great tool for network engineers, students, and enthusiasts GNS3 is a great tool for network engineers, students, and enthusiasts who want to learn about different network technologies and prepare for certification exams such as Cisco CCNA, CCNP, or CCIE. It allows you to create realistic network topologies by emulating or simulating network devices without having to buy or rent expensive hardware equipment. It also enables you to integrate with other software and platforms, such as Docker, VMware, VirtualBox, Wireshark, Ansible, etc., to enhance your network simulation experience.


However, GNS3 also has some limitations and drawbacks that you should be aware of. It requires a lot of CPU and memory resources, especially when running multiple devices or complex topologies. It does not support all features or commands of the real devices, especially newer ones or those that depend on hardware components. It can be difficult to set up and configure, especially for beginners or those who are not familiar with virtualization or networking concepts. It may not be updated or supported regularly, which means that you may encounter bugs, errors, or compatibility issues with newer versions or platforms.


Therefore, we recommend that you use GNS3 as a complement to your network learning and testing activities, not as a substitute. You should always verify your results and configurations with real devices or official documentation before applying them in a real network environment. You should also keep your GNS3 software and Cisco IOS images up to date and follow the best practices and guidelines provided by the GNS3 community and Cisco support.


We hope that this article has helped you understand how to download Cisco IOS images for free and use them in GNS3. If you have any questions or feedback, please feel free to leave a comment below or contact us through our website. Thank you for reading and happy networking!


FAQs: Five common questions and answers about GNS3 and Cisco IOS images




  • What is the difference between emulation and simulation in GNS3?



Emulation means that GNS3 runs the actual software of the device (such as Cisco IOS) on a virtual machine or a hypervisor. Simulation means that GNS3 uses a simplified model of the device (such as Cisco Packet Tracer) that mimics its behavior and features.


  • What are the advantages and disadvantages of emulation and simulation in GNS3?



The advantages of emulation are that it provides more realism and accuracy than simulation, as it runs the real software of the device. The disadvantages of emulation are that it requires more CPU and memory resources than simulation, as it runs a full operating system on a virtual machine.


The advantages of simulation are that it requires less CPU and memory resources than emulation, as it runs a simplified model of the device. The disadvantages of simulation are that it does not support all features or commands of the real device, as it uses an approximation of its behavior and features.


  • How can I get Cisco IOS images legally?



The legal way to get Cisco IOS images is to have a valid Cisco account and a service contract that allows you to download the IOS images from the [38](https://software.cisco.com/download/home) website. You can also get Cisco IOS images from authorized resellers or partners.


  • How can I get Cisco IOS images illegally?



The illegal way to get Cisco IOS images is to search for them on the internet and download them from unauthorized sources. We do not recommend or endorse this way, as it may violate Cisco's terms of use and expose you to security risks and legal issues.


  • How can I update my Cisco IOS images in GNS3?



To update your Cisco IOS images in GNS3, you need to download the new version of the IOS image from the [37](https://software.cisco.com/download/home) website or another source. Then, you need to add the new image to GNS3 by going to Edit > Preferences > Dynamips > IOS Routers and clicking New. You can also edit or delete the old image by going to Edit > Preferences > Dynamips > IOS Routers.


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