There are a few other virtual labs that I use for this book and other purposes. The GNS3 tool is one of them:

As mentioned previously in this chapter, GNS3 is what a lot of us used to study for certification tests and to practice for labs. The tool has really grown up from the early days of the simple frontend for Dynamips into a viable commercial product. Cisco-made tools, such as VIRL, DevNet, and dCloud, only contain Cisco technologies. Even though they provide ways for virtual lab devices to communicate with the outside world, they are not as easy as just having multi-vendor virtualized appliances living directly in the simulation environment. GNS3 is vendor-neutral and can include a multi-vendor virtualized platform directly in the lab. This is typically done either by making a clone of the image (such as Arista vEOS) or by directly launching the network device image via other hypervisors (such as Juniper Olive emulation). Some might argue that GNS3 does not have the breadth and depth of the Cisco VIRL project, but since they can run different variation Cisco technologies, I often use it when I need to incorporate other vendor technologies into the lab. 

Another multi-vendor network emulation environment that has gotten a lot of great reviews is the Emulated Virtual Environment Next Generation (EVE-NG), http://www.eve-ng.net/. I personally do not have much experience with the tool, but many of my colleagues and friends in the industry use it for their network labs. 

There are also other virtualized platforms, such as Arista vEOS (https://eos.arista.com/tag/veos/), Juniper vMX (http://www.juniper.net/us/en/products-services/routing/mx-series/vmx/), and vSRX (http://www.juniper.net/us/en/products-services/security/srx-series/vsrx/), which you can use as a standalone virtual appliance during testing. They are great complementary tools for testing platform-specific features, such as the differences between the API versions on the platform. Many of them are offered as paid products on public cloud provider marketplaces for easier access. They are often offered the identical feature as their physical counterpart.