Changing STP priority on root bridge

[Andras Dosztal]

Hi guys,

I know that lowering the STP priority on the root bridge (like from 4096 to 2048) not causes convergence, but does it have any temporary effects on data traffic? I'm using PVST+.

I'm asking this just to be sure. I think issues might only occur on overloaded devices, where there's no computing resources for recalculation.

Thanks for the help.

[Andras Dosztal]

I made a test in a lab environment, using the following devices:

I started an extended ping from R5 (ping ip SW1 si 1500 tim 1 re 5000), then I changed STP priority on SW1 to 4096. This is the debug log on SW2:

47w0d: STP: VLAN0001 heard root  4097-8cb6.4ff2.d000 on Gi3/1

47w0d:     supersedes  8193-8cb6.4ff2.d000

No recalculation, no Topology Change Notice, no packet loss during the ping. The answer to the question is no, it doesn't have any effects on traffic. (Or at least no effect on lab traffic. )