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The biggest rapid-pvst diameter

Hello, I would like to know what is the biggest possible rapid-pvst diameter and how to set it up? Do I need to set timers on primary and secondary root switch only or it must be set on every switch? How do I count timers for specific diameter? Thanks.

paul driver
VIP Expert

The recommendation is stp max diameter is 7 meaning 7 hops between the farthest end points in the local network however i would say it can be higher but not much higher.

Along with the 3 known stp timers ( hello- forward delay and max-age) in an stp bpdu there is another timer called message age (default 0) which increases by 1 as an stp bpdu traverses each switch through the lan

This message age field timer is subtracted from the defined max age timer as such the further way the switches are the less time the bpdu has to refresh until a point stp becomes unstable as such cisco does recommend certain timer limits to be appended to a lan

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Thanks for your reply.

I found somewhere that max-age value is in fact max count of hops when using rapid-pvst. Is it true? Is it possible to have a correctly working circle with let´s say 20 or 30 switches running rapid-pvst? I know that such a big network should be separated and routed, but is it possible to keep it on L2?