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RPVST/MST

luke sawyer
Level 1
Level 1

‎12-21-2015 08:40 PM - edited ‎03-08-2019 03:11 AM

I'm looking for an explanation into MST and RPVST interoperability. I've been using the below document as a guide as to what I should expect  but I'm not seeing what it seems I should expect. 

http://www.cisco.com/c/en/us/support/docs/lan-switching/multiple-instance-stp-mistp-8021s/116464-configure-pvst-00.html

In the below configuration, SW4 becomes the root for MST0 and AS1's uplink into the MST region is becomes root as expected. 

AS1 (VLAN1/32769)

 +

 +

SW1 + + ++ SW2

   +                  +

   +                  +

   +                  +

SW3 + + + +  SW4 (Root MST0/32768)

What I'm having trouble understanding is why, when I change vlan 150 to have a lower priority than the MST0 root, does SW1 display the expect "%SPANTREE-2-PVSTSIM_FAIL: Blocking designated port Gi1/0/1: Inconsistent superior PVST BPDU received on VLAN 150" but all ports remain designated/forwarding for MST0. You can see that the although the port as marked as "PVST Sim. Inconsistent", the port is still forwarding and SW1 is learning MAC addresses on that interface. 

SW1#sh spanning-tree int g1/0/1

Mst Instance Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
MST0 Desg FWD 20000 128.1 P2p Bound(PVST) *PVST_Inc
MST1 Desg FWD 20000 128.1 P2p Bound(PVST) *PVST_Inc
MST2 Desg FWD 20000 128.1 P2p Bound(PVST) *PVST_Inc

SW1#sh spanning-tree mst 0 detail

GigabitEthernet1/0/1 of MST0 is forwarding (PVST Sim. Inconsistent)
Port info port id 128.1 priority 128 cost 20000
Designated root address 0017.9426.e900 priority 32768 cost 0
Design. regional root address 0017.9426.e900 priority 32768 cost 400000
Designated bridge address 0021.d747.d400 priority 32768 port id 128.1
Timers: message expires in 0 sec, forward delay 0, forward transitions 2
pvst inconsistency timer expires in 19 sec
Bpdus sent 139260, received 157514

SW1#sh mac address-table dynamic int g1/0/1
Mac Address Table
-------------------------------------------

Vlan Mac Address Type Ports
---- ----------- -------- -----
1 001e.be4e.ec81 DYNAMIC Gi1/0/1
150 001e.be4e.ec81 DYNAMIC Gi1/0/1
Total Mac Addresses for this criterion: 2

Any input would be much appreciated.

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5 Replies 5

Philip D'Ath
VIP Alumni
VIP Alumni

‎12-29-2015 07:25 PM

What model switches are they?  If they are all the same model, what version software are you running on them?

I've had an issue like this before when Cisco and HP switches were both used in the same environment.  The HP switches were calculating the path weights differently than the Cisco's and caused all sorts of nightmares.

0 Helpful

luke sawyer
Level 1
Level 1
In response to Philip D'Ath

‎12-30-2015 02:05 PM

All Cisco. A 3560 and 3750

0 Helpful

Peter Paluch
Cisco Employee
Cisco Employee

‎12-30-2015 12:00 AM

Hi Luke,

The occurrence of PVST Simulation Inconsistent state is logical, because in MST/PVST interoperation, only two scenarios are allowed (a simplified explanation; it is better to talk about superior/inferior BPDUs on boundary ports rather than priorities but this is how it turns out on Cisco switches):

  • Either the priority of the IST Root Bridge (MST0 Root Bridge) is lower than the priorities of all PVST root bridges in all VLANs. In this case, the MST region becomes the root bridge for all VLANs in the PVST region.
  • Or the priority of the IST Root Bridge is higher than the priority of the VLAN1 root bridge, and successively, the priority of the VLAN1 root bridge is higher than the priorities of all root bridges in remaining VLANs. In this case, the PVST region will keep its per-VLAN root bridges and the MST region will choose a single "Root" port (properly called the Master port) toward these roots.

However, after the PVST Simulation Inconsistency has been declared, the port should definitely be blocked. Your observations are extremely surprising and confusing.

Do you have an option of testing a different IOS version? I would not be surprised at all if this was a bug.

Best regards,
Peter

0 Helpful

luke sawyer
Level 1
Level 1
In response to Peter Paluch

‎12-30-2015 02:04 PM

I will attempt another version of IOS but because the hardware is old, I'm relatively limited on options. I'm going to see if I can get something newer on these and try it again.

In my example above-

AS1: WS-C3560E-48PD-SF with 12.2.55 SE9

SW1: WS-C3750G-24TS-1U with 12.2.40

--------

Upgraded all switches to the latest code but mst0 is still forwarding and AS1 sees itself as root while switch 1 has an MST regional root.

AS1: 12.2(55)SE10

SW1: 15.0(2)SE9

SW1:

SW1#sh spanning-tree mst 0

##### MST0 vlans mapped: 201-4094
Bridge address 0021.d747.d400 priority 32768 (32768 sysid 0)
Root address 0017.9426.e900 priority 32768 (32768 sysid 0)
port Gi1/0/19 path cost 200000
Regional Root address 001d.456f.3a00 priority 32768 (32768 sysid 0)
internal cost 200000 rem hops 19
Operational hello time 2 , forward delay 15, max age 20, txholdcount 6
Configured hello time 2 , forward delay 15, max age 20, max hops 20

Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Gi1/0/1 Desg FWD 20000 128.1 P2p Bound(PVST) *PVST_Inc
Gi1/0/19 Root FWD 200000 128.19 P2p
Gi1/0/20 Altn BLK 200000 128.20 P2p
Gi1/0/23 Desg FWD 20000 128.23 P2p
Gi1/0/24 Desg FWD 20000 128.24 P2p

SW1:
%SPANTREE-2-PVSTSIM_FAIL: Blocking designated port Gi1/0/1: Inconsitent superior PVST BPDU received on VLAN 150, claiming root 4246:001e.be4e.ec80

SW1#sh spanning-tree mst 0 detail

##### MST0 vlans mapped: 201-4094
Bridge address 0021.d747.d400 priority 32768 (32768 sysid 0)
Root address 0017.9426.e900 priority 32768 (32768 sysid 0)
port Gi1/0/19 path cost 200000
Regional Root address 001d.456f.3a00 priority 32768 (32768 sysid 0)
internal cost 200000 rem hops 19
Operational hello time 2 , forward delay 15, max age 20, txholdcount 6
Configured hello time 2 , forward delay 15, max age 20, max hops 20

GigabitEthernet1/0/1 of MST0 is forwarding (PVST Sim. Inconsistent)
Port info port id 128.1 priority 128 cost 20000
Designated root address 0017.9426.e900 priority 32768 cost 200000
Design. regional root address 001d.456f.3a00 priority 32768 cost 200000
Designated bridge address 0021.d747.d400 priority 32768 port id 128.1
Timers: message expires in 0 sec, forward delay 0, forward transitions 2
pvst inconsistency timer expires in 19 sec
Bpdus sent 1609, received 229

SW1:

SW1#sh mac address-table dynamic vlan 150
Mac Address Table
-------------------------------------------

Vlan Mac Address Type Ports
---- ----------- -------- -----
150 001e.be4e.ec81 DYNAMIC Gi1/0/1

AS1

VLAN0150
Spanning tree enabled protocol rstp
Root ID Priority 4246
Address 001e.be4e.ec80
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 4246 (priority 4096 sys-id-ext 150)
Address 001e.be4e.ec80
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/1 Desg FWD 4 128.1 P2p Peer(STP)

0 Helpful

Peter Paluch
Cisco Employee
Cisco Employee
In response to luke sawyer

‎01-07-2016 12:25 AM

Luke,

Unfortunately, I won't have access to real lab till tomorrow so only then I can test what is going on.

Would you mind posting the exact configs of all 5 switches so I could replicate your setup in my lab?

Best regards,
Peter

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