root inconsistent error on boundary port mstp to pvstp

[riccardo_romani]

hi all , could you me help to undertand why boundary port of my region MSTP go to error inconsistent status? these ports are connected to PVSTP swithes and the error occours i switch the rrot bridge inside region (root for mstp and cst). thanks in advance

[Georg Pauwen]

Hello Riccardo,

the first thing I would check is if one of the PVST bridges is attempting to become the root for one or more of the VLANs. Keep in mind that, if the MSTP bridge is the root, it must be the root for all VLANs...

Have a look as the document below is well, it describes various situations in which a port would go into ´error inconsistent´:

Understanding Multiple Spanning Tree Protocol (802.1s)

http://www.cisco.com/warp/public/473/147.html

HTH,

GP

[riccardo_romani]

hi GP thanks for your reply , i red the document you suggest me and i confirm that MSTP bridge is the root for all vlan , i attach our environment for your better comprension.

P.S. it seems , viewing the log of lower mstp switches , that they receive superior root bpdu from ports connected to PVST switches referring to mac address of mstp root bridge.

bye Riccardo

[Georg Pauwen]

Hello Riccardo,

can you try and set the spanning-tree priority value on both PVST switches to the highest possible value ?

spanning-tree vlan X priority 65535

and see if that makes a difference ?

Regards,

GP

[riccardo_romani]

we'll try it. The strange thing is that from PVST switches to MST switches go a bpdu invoking root bridge referred to root bridge in mst region that has been switched off! The superior bpdu is sent from PVST switches but it refers to mac address of mst (powered off).

[Francois Tallet]

Hi Riccardo,

The interaction between MST and PVST is not straightforward indeed. Could you tell me what IOS version you are running on the MST switches (there have been a slight change with the IEEE standard MST implementation).

At the boundary of a PVST region, the MST switch is going to replicate the information of MST 0 (the CIST) to all the vlans that are configured on the port. That means that for all the vlans configured on this port, the root bridge will be the root of MST 0.

The MST region only accept the BPDUs from vlan 1 (which is the CST in our PVST implementation).

If you are sure that MST0 has a better information than all the vlans configured on the PVST switches, maybe you have a mismatch in the list of allowed vlans on the trunks between the MST and PVST switches.

The error message displayed when the port goes to inconsistent state mention a vlan: please, forward the STP information for this one as well as for vlan 1 on the PVST switches and MST0 on the MST switches.

Regards,

Francois

PS: unfortunately, I don't really understand what is depicted in your diagram:-(