RSTP root bridge selection is taking 12 seconds

[anthonymurphy586]

I have 5 switches with links going to each other in a star topology. Now, Switch 3 is the root bridge but when i power it off it takes about 12 seconds to switch over to switch 2 which is configured to be the next root bridge if a failure occurs. Does 12 seconds sound to long? There are no specific times online indicating how long this should take. 

[M02@rt37]

Hello @anthonymurphy586,

The total transition time from Listening to Forwarding state is about 30 seconds. Considering some additional processing time and network latency, a 12-second transition from one switch to another as the root bridge is reasonable.

[anthonymurphy586]

30 seconds? I thought that was for STP not RSTP?

[M02@rt37]

Sorry @anthonymurphy586 lol I dont read the title. Shame on me.

Please share configurations.

[wesleyj84]

Would you share your rstp and port configs for those switches?

[paul driver]

Hello

• What stp mode are you running and is it the same mode consistent on all switches < if not suggest you apply this if applicable>
• Assumption is you stp diameter is default (7)? < depending the stp mode this can be change automatically to decrease your stp timers>
• Do you also have portfast enabled on ALL edge ports? <---- if not suggest you apply this

[Joseph W. Doherty]

"RSTP operational details:  Detection of root switch failure is done in 3 hello times, which is 6 seconds if the default hello times have not been changed."

Forgoing found in Wiki STP article.

If electing a new root also takes 6 seconds, that would account for your 12 seconds.

[Martin L]

what is topology? (below is example of it);  what are ports roles and where?   how exactly did u measure your 12 sec delay?

Regards, ML
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