Graphical Network Simulator 3, GNS3 Review
// January 8th, 2010 // No Comments » // Technical Know-It-All
A few weeks back, I was tasked to skill up on IP at work. It seems like ages since I completed my Cisco Training Academy, so I decided the easiest way to get back into it is through Cisco simulators out there. In all honesty, I would much prefer having the physical boxes to play with but I have sold them all when I moved to Singapore 2 years back.
The popular simulators out there would be Boson and RouterSim, which (I honestly think) is fairly buggy at best. The problem with simulators like Boson & RS are manly due to the fact that it is usually re-engineered code made to look and feel like Cisco’s IOS. Not all commands are available (though visible on the “?”, doesn’t mean it’s usable), abbreviated commands (sh run, cop run st, etc.) doesn’t always work, output might or might not be what is expected and the list goes on. It’s not as bad as it sounds, because people do get away passing CCNA’s and CCNP’s from it. (Maybe it’s just me).
Anyway, I came across GNS3 as an open source alternative to the other “paid” sims out there. From experience, open source goodies are generally difficult to setup at best. But I was truly surprised with the setup for GNS on Windows. Unfortunately, I can’t say the same for the Mac OSX though. Still struggling to get it to work on my Mac.
GNS is basically a GUI version of Dynamips if you are truly interested in what’s happening in the backend. (I’m not, so no elaborating here 
)
Like all things FREE, there is always a catch! The catch with GNS is that it requires a Cisco IOS binary file in order to work and it only supports router codes (no switches). If you really really need a switch, you can potentially configure a 36xx and put in an Ethernet card slot to make it into a switch. I remember seeing a tutorial on this on the GNS Documentation site. Officially, you have to be a Cisco Partner or Customer to be able to download these images, but surely I’m sure you can find some floating around on the web.
So how does it work?
What it actually does is emulate a Cisco Router with the original IOS on your workstation. It’s pretty much VmWare for Cisco Routers if you like. Once you sort out the IOS installation and tell it where Dynamips (which is installed as part of the GNS3 package) is located, you are ready to go. Building the virtual network if as simple as drawing a Visio diagram. You can also add in additional WIC’s or line cards, and RAM (just like VmWare can for Servers). And the best part… no limitation on CLI and output. What you see if what you get on the real thing! Same IOS code like the real deal, only difference its that you don’t have the equipment physically. If y0u can get hold of Cisco 36xx series router binaries, you can potentially setup a virtual lab to do your CCIE (a little far fetch, but not totally impossible). Based on the options available, the latest version is capable of taking Cisco PIX & ASA binaries, and JunOS. I have yet to try it because I do not have access to any of those code. Maybe you guys can let me know when you try it out.
So if you are an aspiring CCNA or CCNP or even CCIE on a budget, give this a go.
