I remember when I first started to study for my Cisco Certified Internetwork Expert (CCIE) lab exam, I purchased some used Cisco equipment from eBay to study. Even at a discount, each router and switch are hundreds of US dollars, so to save money, I even purchased some really outdated Cisco routers from the 1980s (search for Cisco AGS routers in your favorite search engine for a good chuckle) that significantly lacked in feature and horsepower even for lab standards. As much as it makes an interesting conversation with family members when I turned them on (they were really loud), putting the physical devices together was not fun. They were heavy and clunky, a pain to connect all the cables, and to introduce link failure, I would literally unplug a cable.

Fast forward a few years, Dynamip was created and I fell in love with how easy it was to create network scenarios. All you need is the iOS images from Cisco, a few carefully constructed topology file, and you can easily construct a virtual network that you can test your knowledge on. I had a whole folder of network topologies, presaved configurations, and different version of images, as called for by the scenario. The addition of a GNS3 frontend gives the whole setup a beautiful GUI facelift. Now, you can just click and drop your links and devices; you can even just print out the network topology for your manager right out of the GNS3 design panel.

In 2015, the Cisco community decided to fill this need by releasing the Cisco VIRL. If you have hardware machines that meet the hardware requirements and you are willing to pay for the required annual license, this is my preferred method of developing and try out many of the Python code both for this book and my own production use.

Even at a monetary cost, in my opinion, the VIRL platform offers a few advantages over other alternatives:

• An ease of use: All the images for IOSv, IOS-XRv, CSR100v, NX-OSv, ASAv are included in the single download.
• Official (kind of): Although the support is community driven, it is an internally widely used tool at Cisco. It is also the popular kid on the bock that increases bug fix, documentation, and tribal knowledge.
• The cloud migration path: The project offers logical migration path when your emulation grows out of the hardware power you have, such as Cisco dCloud (https://dcloud.cisco.com/), VIRL on Packet (http://virl.cisco.com/cloud/), and Cisco DevNet (https://developer.cisco.com/).
• The link and control-plane simulation: The tool can simulate latency and jitter and packet-loss on a per-link basis for real-world link characteristics. There is also control-plane traffic generator for the external route injection.
• Others: The tool also offers some nice features such as VM Maestro topology design and simulation control, AutoNetkit for automatic config generation, and the user workspace management if the server is shared.

We will not use all of the features in this book. But since this is a relatively new tool that is worth your consideration, if you do decide this is the tool you would like to use as well, I want to offer some of the setups I used.