Network 169 offers several routing troubleshooting challenges and configure 'how-to's' using GNS3 or VIRL platforms. Also offering great blog discussions around each platform differences.
Mininet is a great, quick way to spawn virtual networks for testing. The lightweight Ubuntu-based OS will create virtual servers and devices capable of communicating with the built-in SDN controller.
TechNet Virtual Labs
Microsoft's TechNet Virtual Labs is a powerful online environment that enables testing of new Microsoft products and technologies. Virtual Labs will walk you through, step-by-step, navigating multiple VM's to accomplish a complex technical task. It also explains each step using clear, simple terminology to help you learn quickly and efficiently.