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STP path cost not changing when link speed changed back to auto

I start out with three VIRL switches connected together in a triangle configuration by trunk links.  All links are 1 Gbps links, set to auto.  STP performs as expected. 

 

I then change the link speed between one of the switches by turning off auto negotiation, and then forcing the link speed to 10 Mbps.  STP again performs as expected, changing the path cost to 100 for that link, and changing the location of the blocking port. 

 

Then I remove the link speed (no speed 10) on both switch interfaces for the link, and turn auto back on (no speed 10; negotiation auto).  I verify the change back to speed auto has occurred on each interface.  At this point STP behaves unexpectedly.  Show spanning-tree vlan 1 still shows the path cost at 100.  The BLK port does not move back. 

 

I have tried:

waiting

removing the physical cable and putting a new on in

 

Not quite understanding why STP is not automatically updating itself in this situation.  Any ideas?

 

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VIP Collaborator

Re: STP path cost not changing when link speed changed back to auto

Hello

It is not normally. I use VIRL and i had no problem with issue like this.

I will suggest you to check somethings below;

1. Versions of STP in use; Make sure that you are using the lastest STP version, normally on VIRL the oldest STP is used.
2. Check spanning-tree root cost; show spanning-tre root cost, this will help you with information about cost for each interface.
3. Check if your vlan database is consistent.

Regards,
Jaderson Pessoa
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