I posted an article recently on how to download and run a FREE Cisco router emulator (see Practice Cisco Router Configuartion using a free emulator). I want to tell you up front, the only real catch is that you have to have a copy of the Cisco IOS that will run in the emulator. However, the emulator supports a number of different types of routers.
The cool thing about the emulator is that, on a single PC, you can run multiple routers and switches. You can design the network topology and connect all the devices together. Then, you can configure each of the routers in the LAN or WAN network.
It is a very powerful tool for creating & testing configurations as well as just learning about Cisco routers. The cost and trouble of purchasing and setting up a number of physical Cisco routers makes running an emulator on your PC a “no-brainer”.
Yes, there are simulators but emulators are much better because you are running the REAL IOS so you have 100% compatibility with the “real thing”.
I hope you will check out my article and try this very cool emulator out for yourself!