PVST - MSTP interop : Error

Hi All

As far as I know (from readings etc) :

1) In case of MSTP - PVSTP inter-op scenarios ; we should either have
     [A] root for all vlans (all instances) in MST region
     [B] root for all vlans on PVST switch

2) Having root for half vlans in MST region and half on PVST switch is not a
valid scenario and we will see PVST_Inc error in this .

3) Best practice suggest having root in MSTP region

4) However there is no stopping having root on PVST switch as well .

Now My problem is following (My intent is to get SW2 PVST switch as root):

SW-1 (MSTP) g1/1---------------------g1/1- SW-2(PVST)
                     g1/2---------------------g1/2

SW1 config
===========
spanning-tree mode mst
spanning-tree extend system-id
!
spanning-tree mst configuration
 name aa
 revision 10
 instance 1 vlan 1-5
 instance 2 vlan 6-10
!
spanning-tree mst 1 priority 8192
spanning-tree mst 2 config 32768

SW2 config
========
!
spanning-tree mode pvst
spanning-tree extend system-id
spanning-tree vlan 1-4094 priority 4096
!

At SW1 ; I am getting following error :
C4924(config)#
*Mar 26 06:39:35.735: %SPANTREE-2-PVSTSIM_FAIL: Blocking root port Gi1/1:
Inconsitent inferior PVST BPDU received on VLAN 2, claiming root
2:0024.1430.2f00

C4924#sh span mst 1

##### MST1 vlans mapped: 1-5
Bridge address 001d.450d.0700 priority 8193 (8192 sysid 1)
Root this switch for MST1

Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- --------
--------------------------------
Gi1/1 Mstr BKN*20000 144.1 P2p Bound(PVST) *PVST_Inc
Gi1/2 Altn BLK 20000 128.2 P2p Bound(PVST)

C4924#sh span mst 2

##### MST2 vlans mapped: 6-10
Bridge address 001d.450d.0700 priority 32770 (32768 sysid 2)
Root this switch for MST2

Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- --------
--------------------------------
Gi1/1 Mstr BKN*20000 128.1 P2p Bound(PVST) *PVST_Inc
Gi1/2 Altn BLK 20000 128.2 P2p Bound(PVST)

Please let me know where am i wrong ?

Thanks
Gaurav Madan

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Received on Sat Mar 26 2011 - 13:15:41 ART