I have a question about STP on a Cisco Nexus 7000

[cristianre1316]

Hello.

I have a question about one problem that I have in the production environment, 

The Switch has the below configuration:

spanning-tree mode mst
spanning-tree mst 0-1 priority 12288
spanning-tree mst configuration
name Instancia1q
instance 1 vlan 1-5,7-9,11-21,29-31,37,39,50,52,99,303,305-306,400-404,406-407,410-446,448-459,461-480,482-494,496-501
hardware forwarding interface statistics mode invalid

yesterday we had one problem with the STP, I revised logs and noted the belonging log:

%STP-6-MST_DIGEST: MST digest changed to 0x46f9e9593d6e0efcdba8ef398603f5d2, pre-std digest changed to 0xab440184b14c08846369e5ee8855c638”

When I revised the startup-config I noticed the configuration STP was changed, I noticed that the first line was missing or It looked like someone deleted it.

spanning-tree mst 0-1 priority 12288
spanning-tree mst configuration
name Instancia1q
instance 1 vlan 1-5,7-9,11-21,29-31,37,39,50,52,99,303,305-306,400-404,406-407,410-446,448-459,461-480,482-494,496-501

When I introduced the command spanning-tree mode most of the production environment came to line again.

So, we have doubts about what caused that line to be missed, I questioned to people in charge of the network, but they only told me that they deleted one vlan (496) that Vlan is in the pool instance 1.

I have one question, Is there anything STP doesn't like and can remove the spanning-tree mode mst command by modifying something? Or do you have to apply a ´´no spanning-tree mode mst´´?

I appreciate the help with the response because we don´t know what happened.

[marce1000]

 - Because a vlan was removed from the instance, the mst instance was no longer valid  and needed to be enabled again with the new vlan list ; you may want to consider spanning tree protocols other then mst , 

 M.

[MHM Cisco World]

You remove vlan from instance' the mst will not do anything. It will stable.

That powerful of mst you can include many vlan in one instance and then add remove vlan ftom database and mst will be stable.

[Gopinath_Pigili]

MST "deals" with MSTI Instaces and not directly with VLANs.

Each VLAN is mapped with an instance => By default, all VLANs are mapped to the IST (MSTI 0) instance. You can explicitly map them to other instances, if needed.

That is the reason why I do not think we can disable MST on a vlan basis like pvst/rstp as MST operates with instances.

Hello Sebastian, I think in fact "no instance instance_id [vlan vlan_range] " will return to the default VLAN-to-instance map

For example if vlan 10 is mapped to instance 1, the command no instance 1 vlan 10 will return vlan 10 to his default instance MSTI0 (IST).

Best regards
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