Different spanning tree protocols behavior

[zafarjankhan]

Hi,

This is my first time posting a question, so apologies if I missed something.

My question is...

I noticed a weird setup at my workplace and i'm unsure of how STP will interact. We have about 15 switches spread around the network, and I have noticed some run PVST and others run RSTP. I also noticed that there will two root bridges for a particular VLAN. However one root bridge will be running PVST and the other one will be running RSTP. What happens in that time of scenario?

Is it that only PVST switches will look at the root bridge running PVST and the ones running RSTP will look at the root switch running PVST.

[Reza Sharifi · Accepted solution]

Hi,

PVST and RSTP are compatible and can work together, but it is much simpler to just run one protocol (RSTP). Running multiple protocols make things complicated and harder to understand and manage. I recommend having a maintenance window and convert all your switches to RSTP..

HTH 

[zafarjankhan]

Thanks for your answer to my question. Appreciate it!

[devils_advocate · Accepted solution]

It usually happens when people add additional switches over time and configure them using RSTP.

You then end up with a mix of the two.

As Reza has said, schedule a maintenance window and get them all over to RSTP (or Per Vlan-RSTP). There could well be a blip during this time so I would avoid doing it unless you have advised users of potential down time.

You may find things improve after you change it, you could well have some sub optimal traffic flows if you have root bridges all over the place.