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 with. Even at a discount, each router and switch cost hundreds of US dollars, so to save money, I purchased some really outdated Cisco routers from the 1980s (search for Cisco AGS routers in your favorite search engine for a good chuckle), which significantly lacked features and horsepower, even for lab standards. As much as it made for 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, it was 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 different network scenarios. This was especially important when I tried to learn a new concept. All you need is the IOS images from Cisco, a few carefully constructed topology files, and you can easily construct a virtual network that you can test your knowledge on. I had a whole folder of network topologies, pre-saved 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. With GNS3, 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. The only thing that was lacking was the tool not being officially blessed by the vendor and the perceived lack of credibility because of it.
In 2015, the Cisco community decided to fulfill this need by releasing the Cisco VIRL. If you have a server that meets the requirements and you are willing to pay for the required annual license, this is my preferred method of developing and trying out much 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:
- Ease of use: All the images for IOSv, IOS-XRv, CSR100v, NX-OSv, and ASAv are included in a single download.
- Official (kind of): Although support is community-driven, it is a widely used tool internally at Cisco. Because of its popularity, the bugs get fixed quickly, new features are carefully documented, and useful knowledge is widely shared among its users.
- The cloud migration path: The project offers a 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/). This is an important feature that sometimes gets overlooked.
- The link and control-plane simulation: The tool can simulate latency, jitter, and packet loss on a per-link basis for real-world link characteristics. There is also a control-plane traffic generator for external route injection.
- Others: The tool offers some nice features, such as VM Maestro topology design and simulation control, AutoNetkit for automatic config generation, and user workspace management if the server is shared. There are also open source projects such as virlutils (https://github.com/CiscoDevNet/virlutils), which are actively worked on by the community to enhance the workability of the tool.
We will not use all of the features in VIRL 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, I want to offer some of the setups I used.