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Nexus spanning tree pseudo configuration

eagles-nest
Level 1
Level 1

Hi

 

I am trying to understand the pseudo configuration commands in a Nexus hybrid topology.

 

I have vlans a, b and c only in the vPC side of the topology.  I have peer switch configured and the same stp priority on both switches.

In the standard Spaning-tree topology I have completely seperate vlans x, y and z.

 

What should I be configuring in the pseudo config section ?  Do I define a pseudo root priority for all vlans a, b, c and x, y, z or just for the standard spanning tree vlans x, y and z.  I need to avoid and, even short, spanning tree outages if I take one Nexus out of service for a short time.

 

My thinking is that if one Nexus is out of service the physical mac will be used and potentially reduce the root priority of the vPC vlans causing a TCN and STP recalculation in vlans a, b and c.  This can be avoided by configuring a pseudo root priority for all Vlans lower than the current spanning tree priority shared by the vPC peers.  Is this correct ?  However, since I have a shared priority of 8192 on current vPC vlans will configuring, for example, a pseudo root priority of 4096 on those vPC vlans won't this also cause the TCN and recalculation I am trying to avoid ?  Is the benefit of the pseudo root config only obtained if it is configured at the start when the vPC is formed and prior to the peer switch command being issued ?

 

Thanks, Stuart.

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