GNS3 is a virtual network software. You add nodes to a virtual network and find out about their interfaces in real time.
Run the AIO (All-in-one) installer from their website on the computer of your choice. I chose a Server 2012 Standard VM, but it should work on a client OS as well. NOTE: This installs over ten programs. Make sure to download binaries for the routers you plan to virtualize by downloading using Google “cisco binaries for gns3” or “index of ios parent directory bin”.
Before starting, make sure to open up the guide here. When you start GNS3, the first thing you want to do is go to Edit => Preferences => Dynamips => IOS Routers => and add the router files there.
Once that is completed you should see a router icon on your left navigation pane. From there, you drag and drop it into the center stage area for you to work with it. I usually just “start” the router and then “console” into it.
Now comes the fun part, learning how to use each of these! This is as far as I will go for now as I haven’t gotten to focus too much into this just yet :
See more details by following this guide here: http://www.petenetlive.com/KB/Article/0001079.htm