STP issue

Unanswered Question
Jun 17th, 2010

Hi all,

We are having an issue configuring the Spanning protocol on the topology shown in the attached picture. I will try to explain the situation:

     - The 4510 of the old building is forced to be the root bridge of the topology (spanning-tree vlan 1-1001 priority 4096)

     - The 10 Gb optical fiber is redundant

     - The wifi bridge should only be used in case of the 10Gb optical fiber stops working.

In order to configure this we have configured the following:

     - The cost of the interfaces of the two switch stacks where the wifi bridge is connected has been modified:

               spanning-tree vlan 1-1001 cost 100

In this situation we can see the following:

     - The port on the switch stack of the old building gets Blocked (BLK) --> OK, all the traffic goes through the optical fiber

     - On the 4507 of the new building we can see one of the TenGigabit interface blocked for all the vlans, while the other is forwarding --> OK

      - If we make a shutdown on the TenGibabit interface which is forwarding:

               - The interface of the wifi bridge is still blocked --> OK

               - On the 4507 the TenGigabit interface which was blocked goes to forwarding status --> OK

     - If we make a no shutdown, everything recovers OK.

     - If we make a shutdown on both TenGigabit interface:

               - The interface where the wifi bridge is connected gets unblocked (Role Root, Status forwarding) --> OK

     - If we make a no shutdown on both TenGigabit interface:

               - On the 4507 of the new building one of the TenGigabit interfaces gets blocked and the other one forwarding -->OK

               - On the switch of the new building where the wifi bridge is connected: designated and forwarding --> OK

               - The interface of the switch of the old building where the wifi bridge is connected does not get blocked --> WRONG!!

In this last situation, we cannot see it by making "show spanning-tree blockedports". We have to make a "shutdown" and a "no shutdown" on this interface in order to see it again as blocked, by making the "show spanning-tree blockedports" command. Shouldn't this be automatic when go make a "no shutdown" on the TenGigabit interfaces?

Where could be the problem? The 4510 has an older IOS, 12.2(25)SG2.

Any help will be appreciated!!

Thanks in advance!!



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