After we started dan make sure it configured correcty. we can then move to the next step. adding IOS image in our GNS to run the simulation of Cisco IOS. Adding the IOS image can be done by these steps :
1. Run GNS3
2. In menu bar, choose edit , choose IOS Images and hypervisors
3. In IOS images and hypervisors window, choose image file
4. New window to locate/select your image file will appear, choose image file with .bin extension
5. Choose save
Now if you drag and drop router icon according to you IOS image for example : router C7200, GNS will not display any warning, and you can start configuring your router simulation.
To download image file you can search via google 🙂