GNS3 does not come with any Cisco IOS(router)/IOU(switch) firmware due to legal/licensing issues.
I will not cover how to get a hold of Cisco IOU.
This guide is a bit more complicated then integrating Cisco IOS router,
After you get a hold of a Cisco IOU bin file for a Cisco Switch, we can start!
You need to have VirtualBox installed. Then download Cisco IOU VM.ova and import it into VirtualBox.
[UPDATE] I switched to HYPER-V due to Windows 10 VirtualBox problems - Check out GNS3 IOU VM on Hyper-V
This should be already configured correctly, but check to confirm. Via "settings".
Fire up the VM and login via UNAME=root PWD=cisco >> ifconfig *confirm its 192.168.56.101*
Navigate to 192.168.56.101:8000 in your browser. You should see this >>
Click Uploads >> First we are going to upload the licensing file >> Dropdown list "IOU license (iourc) >> browse to file >> upload
If Successfull you will see >>
Now to Upload that IOU bin file!
If Successful you will see >>
Note both locations for use in GNS3!
Lets fire up GNS3 and import the IOU.
Lets add the "remote server" 1st (It should be ready to go, just hit "Add")
Now bind Local Server
Now lets add the Licencing file via IOS on UNIX >> Apply
FINALLY WE ARE READY TO ACTUALLY ADD THE IOU to GNS3!!
Go under IOS on UNIX >> IOU devices. *Leave it Remote, we added it earlier, and hit Yes to the prompt*
Now copy file path from Upload screen earlier >> *If L3 change manually, GNS3 does not auto-detect!*
Now Copy over your new switch and right click >> start
Now right click >> console
That's it you are ready to roll!
Note: VM needs to be running if using switch in GNS3. It is the IOU "server" for GNS3. It is not a resource hog though, so don't worry!
If you have issues, try disabling firewall to test, and then changing firewall rules if that is the problem!