I really wanted to cement my knowledge of MST and Port Priorities, and VIRL was perfect for this. All I did was use two switches connected with dual links. I defined 4 new vlans and then put two in MST 1 and two in MST 2.
What I noticed though was that both MST 1 and MST 2 were using Gi0/1 to forward, even though I had set SW1 as the root for MST1 and SW2 as the root for MST2. So I used port-priorities to configure MST1 to use Gi0/1 and MST2 to use Gi0/2.
The configuration of port-priorities is shown below:
VIRL was perfect to investigate and cement MST and port-priorities for me, and I didn't have to waste any of my INE rack rental time or purchase switches (which seem to be so much more expensive then routers for my CCIE lab)