STP mode choice

[thermseeker]

Hello all, happy new year!

I'm posting this here as OS6900 is our core switch and I didn't find a more specific forum for this subject.

Please, I'd like to hear some advice on configuring STP. My doubt is about which mode to use, flat or per VLAN. I currently use the default which is per VLAN RSTP. We're about to move from 20 to 35 VLANs based on directives coming from our central administration and I think this is an opportunity to reevaluate the current setup.

We have around 45 switches here. Our topology is very straighforward, I only have one ring in an energy substation for the protection devices and a few link aggregations between the administrative office and the core switch. No other redundant links, both because we don't need the extra bandwith and because all cables are internal to our site, so no trucks ripping cables off poles, and no excavators digging them off the ground. Even tho, if necessity arises the topology allows to easily create redundant link interconnecting a few fibers around the site.

So, STP for us has the main function of avoiding accidental loops in the network, which may happen when adding a new switch or something like.

The question being, is there any major downside on using flat STP in this scenario? In my limited knowledge of STP I think flat mode would ease configuration and maintenance. Am I wrong?

Thank you in advance for sharing your experience.

Regards,
Tales Maschio

[Gleylancer]

The question you should ask yourself, is, do you need STP per VLAN or not? The advantage is that you can define a priority in each vlan seperately instead of doing it for all of them at once.

[thermseeker]

Your answer called my attention to a fact. I don't really need STP per VLAN, as I want the core switch to be the root bridge for all VLANs. But, being able to disable STP in a few VLANs will allow me to do a cleaner setup. For example, I don't need STP on the backup traffic VLANs as they only exist in the core switch and have a basically immutable topology. There are other VLANs with similar characteristics for which STP can be disabled.

Thanks for your contribution.
Tales