mixed stp version

[akanarya]

Hi,

I will lunch a bunch of SG series switches to my fabric.

These switches have rapid stp enabled by default.

In the same fabric i have a couple of older catalysts which support only pvst and rapid pvst.

sg350 has option for pvst and rapid pvst, but backbone sg550, which will be root, has classic/rapid/multiple stp modes

Since i have not enough knowledge to decide the correct conf, please guide me with your suggestions.

Regards,

[Reza Sharifi · Accepted solution]

Hi,

I am not familiar with SG series switches but in general, I would go with one flavor that works on all switches (new and old). So, rapid pvst should work just fine.

HTH

[balaji.bandi]

for MSTP Look at the admin guide :

https://www.cisco.com/c/dam/en/us/td/docs/switches/lan/csbms/350xg/admin_guide/AG_Tesla_350_550.pdf

[Joseph W. Doherty]

PVST variants are proprietary to Cisco and can have "issues" with non-per-VLAN STP variants as the former has a STP instance for every VLAN while the latter has only one STP instance for all VLANs.

Sometimes, with care, you can mix these STPs, but the "safest solution" is use MSTP, as already suggested by Balaji.

[akanarya]

thanks to all for your suggestions

There is an update.

Today i updated the firmware of sg550 (backbone), now it is identical to sg350 (edge).

Now i can enable rapid pvst on all switches including sg550.

However, manual says that, as Joseph suggested,

"The most common initial deployment of MSTP is in the backbone and distribution layers of a Layer 2 switched network"

So my mind goes such that

MSTP on sg550

rpvst on sg350s and catalysts.

do you agree on this configuration?

[Reza Sharifi]

That should work fine. Just document it well so, it is easy to understand where you run what flavor, where is the root and where is the backup root, etc... Using different STP flavors can get confusing for people who manage and operate the network on a daily basis especially when you run into an STP problem. Good Luck!

HTH

[Joseph W. Doherty]

Why do you feel the need to mix MSTP with another STP variant?

STP is (again) one instance (shared) by all VLANs.  (Supports additional redundant links that if not blocked would create L2 loops.)

PVST is one instance STP per VLAN.  (Allows having different blocked and non-blocked links, per VLAN.)

MSTP allow you to mix and match VLAN per STP instance.  (For using redundant links, often you only need two or maybe three STP instances regardless of number of VLANs.  I.e. less STP overhead than PVST.)

[akanarya]

No infact i dont feel a need to mix.

All endpoint switches will run rpvst. I have no other choice considering catalysts which support only pvst and rpvst.

Just for the backbone i had thought MSTP, because of the statement in the manual that i had quoted.

At this point, you are right, i think these two protocols wont match each other well.

So very first comment to topic made by Reza is the way to go.