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RSTP, TCN and Convergence

Let's say I have a server plugged into a switchport not configured for Portfast (which it should be)...If I reboot the server, and the port goes DOWN/UP therefore triggering a TCN, will that TCN cause a SpanningTree re-convergence AKA network outage? I presume the answer would be 'No' since the server would not be sending a superior BPDU or any BPDU at all therefore the topology would not recalculate. If I remember correctly TCN's don't necessarily mean that the Spanning-tree topology has re-converged, they just signify that a non-edge port went into a forwarding state. Is my understanding correct?

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Cisco Employee

Yes failrly true.When edge

Yes failrly true.


When edge port goes up/down, there is no significant topology change. meaning root switch and any STP ports do not change their roles;  the only thing that change is MAC is no longer reachable out off edge port;MAC will be gone after 300 sec of inactivity.
when switch learns same MAC is now on new port, it will remove prevoius entry and keep new one without waiting 300 sec.  
 
regarding TC of nonedge port moving to fowarding, take a look at p.18-19 in http://blog.ine.com/wp-content/uploads/2011/11/understanding-stp-rstp-convergence.pdf

 

HTH

 

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