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13May/100

GNS3, my new best friend

I've just been in a Cisco training for the last few days.  The facility is very clean, nice, and the training was very well laid out and valuable.

As I suspect is often the case with these types of environments there were a few technical issues with our lab equipment.  These classrooms are not dedicated to any one class so keeping the gear in the class is impractical.  There are a lot of moving parts and keeping everything straight and running is surely no small task.  The actual hardware is somewhere else and connected to the classroom via the network.  In our class there were issues with the connection to our gear and it was slowing down our progress.

The instructor very thoughtfully had already prepared an environment that would better facilitate the labs.  In comes GNS3.  I had not used, or even heard of, this little gem and I am sorry for it.  GNS3 is an open source "Graphical Network Simulator" that allows you to model network devices virtually. 

One of the primary differences between this and other 'simulator' software packages is that GNS3 simulates the hardware layer of the network devices. This allows you to run an actual Cisco IOS on the virtual gear.  With this new virtual network you can interact with the CLI, run SDM, and model pretty much any aspect of your network that you need or want to.  In a classroom environment this is particularly useful as every student can have the same setup with identical IP information and rules without conflicting with each other.  In a work environment the system allows you to model proposed architecture or changes to your production environment without impacting the real world.

To improve things farther, you can also bridge the network connection on your PC and have it interact with actual devices on your true network if you chose.  The other option would be to run VMWare Workstation or other virtualization software and interact with the virtual network thus farther extending the lab into the client/server side.  My friend and colleague Robert Patton has written a great article on this topic.

The software even has some built in integration with WireShark so that you can run packet captures on the virtual network interfaces and see what packets are going back and forth for troubleshooting or learning.

There are some quirks that I wont go into here, but there is a wealth of information on their website as well as a ton of stuff on their  GNS3 Blog.  This is one tool that I know will come in handy whenever I need to make a change to our corporate network.

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