GNS3 is a network simulator that allows you to create and test complex network topologies using virtual devices. You can use GNS3 to emulate Cisco routers and switches, as well as other vendors' devices. To emulate Cisco devices, you need to use GNS3 IOS images, which are the software files that run on the virtual devices. In this article, we will show you how to download and use GNS3 IOS images for your network simulations.
What are GNS3 IOS images?
GNS3 IOS images are the files that contain the operating system of the Cisco devices that you want to emulate. They are usually copied from real Cisco devices or downloaded from Cisco's website if you have a service contract. GNS3 supports both emulated and simulated devices. Emulation means that GNS3 mimics or emulates the hardware of a device and you run actual images on the virtual device. Simulation means that GNS3 uses a simplified model of the device and does not require an image file.
For emulation, GNS3 uses an emulator called Dynamips, which can run unmodified IOS images for some Cisco platforms, such as the c7200 series. For simulation, GNS3 uses a simulator called IOU (IOS on Unix), which can run IOS images for some Cisco switches and routers. However, IOU images are not publicly available and require a license to use.
There are different ways to download GNS3 IOS images, depending on your source and your license. Here are some options:
From Cisco's website
If you have a service contract with Cisco, you can download IOS images directly from Cisco's website: https://software.cisco.com/download/navigator.html. You will need to log in with your credentials and enter your serial number. You can then select the platform and the version of the IOS that you want to download.
Note that only the c7200 series images are still available for download from Cisco's website, as they are the only ones that still support Dynamips emulation. The images for all other platforms have reached end of support status and have been removed.
If you don't have a service contract with Cisco, you can purchase a VIRL license to get access to multiple IOS images that are very useful for GNS3 simulations. VIRL is a network simulation platform developed by Cisco that allows you to create virtual network topologies using various Cisco devices. The price starts at $199.99 per year for the Personal Edition: http://virl.cisco.com/.
You can use VIRL images without license authentication. You can therefore download the VIRL images, integrate them with GNS3 and use them offline if needed. VIRL images support both Dynamips and IOU emulation.
From physical Cisco devices
If you own a physical router or switch like a Cisco 3725 router or a Cisco 3560 switch, you can copy the IOS image from the device and import it into GNS3. You will need to connect to the device using a console cable or a telnet session and use commands such as show flash or show version to find out the name and location of the image file. You will then need to use commands such as copy flash tftp or copy flash ftp to transfer the image file to your computer. 06063cd7f5