Cisco MSTP - PVSTP question

Unanswered Question
May 13th, 2010

I saw some previous topics  regarding MSTP and  PVSTP interaction but I still have some uncertainties.
Also I've read the "understanding MSTP article" from cisco's website.

my setup i:

c1 -----c2

c1 needs to be root for vlan 1-20

c2 root for rest of the vlans

c1 pvst

c2 mst

trunk conf

switchport trunk enca dot1q

sw mode trunk

sw trunk allowed vlan 1,3,6

c2 mst config

instance 0 vlan 1,3,6

instance 1 vlan all except above

and when i enable the trunk i got error and link goes to blocking mode

%SPANTREE-2-PVSTSIM_FAIL: Blocking root port Gi0/24: Inconsitent inferior PVST BPDU received on VLAN 4, claiming root 24580:0022.55bb.1500

anything i am missing in my config ?

I understand that mst needs to be root bridge for all the rstp vlans but is there any alternative way around it ?

I have this problem too.
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briangormley Tue, 09/02/2014 - 04:50

Did you ever get a resolution for this?

I have a situation whereby in a predominantly HP network (comware) I have a handful of Cisco switches. All running MST. The Root for all VLANs is a L3 HP Core chassis switch. Everythign is fine until you plug a new Cisco switch into the network configured with the default PVST. All the Cisco switches running MST shutdown their up-link to the Core with an error 

SPANTREE-2-PVSTSIM_FAIL: Blocking root port Po1: Inconsistent Inferior PVST BPDU received on VLAN 4, claiming to be root 32772:mac address.

It is is an inferior BPDU why is the Cisco switch shutting down the port. I need to remove PVSTSIM I think?

InayathUlla Sharieff Tue, 09/02/2014 - 09:15

PVST simulation is run on boundary ports and works in two ways:

  • If the MST region has the root bridge for CIST, PVST simulation is required in order to replicate instance 0 information, and create one BPDU for every VLAN that is allowed across the trunk and tag it with the appropriate VLAN information.
  • If the root bridge for CIST is outside of the MST region, then PVST simulation is required to process VLAN 1 information only. The other BPDUs (VLANs 2 and above) are used for consistency checks and information from these VLANs is never copied as root bridge information.

For PVST simulation to work without failures, these two conditions must be met:

  • If the root bridge for CIST is within a non-MST region, the spanning-tree priority of VLANs 2 and above within that domain must be better (lesser) than that of VLAN 1.
  • If the root bridge for CIST is within a MST region, VLANs 2 and above defined in the non-MST domains must have their spanning-tree priorities worse (greater) than that of the CIST root.

If these conditions are not met, the boundary port is put into a PVST simulation inconsistent state until the problem is corrected.





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