Why am I seeing "P2p Bound(PVST)" in MST?

[jlixfeld]

I have a 3550 (c3550-ipservicesk9-mz.122-35.SE5.bin), an ME3400 (me340x-metroaccess-mz.122-40.SE.bin) and two MRV 912 switches. All three support MST, which (by all indications) I think I have setup correctly.

- 3550 F0/1 connects to 3400 F0/1

- 3550 F0/2 connects to MRV1 Port 2

- 3400 F0/2 connects to MRV2 Port 2

- MRV1 Port 1 connects to MRV2 Port 1.

On both the 3550 and the 3400, it shows F0/2 for all MST instances as "P2p Bound(PVST)". What does that mean? Does it mean that it thinks the MRVs are talking PVST to it? The MRVs don't even speak PVST.

Is that "P2p Bound(PVST)" a misnomer, and does it actually mean something else?

3550>show spanning-tree

MST0

Spanning tree enabled protocol mstp

Root ID Priority 24576

Address 0011.bbfb.4180

This bridge is the root

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 24576 (priority 24576 sys-id-ext 0)

Address 0011.bbfb.4180

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/1 Desg FWD 200000 128.1 P2p

Fa0/2 Desg FWD 200000 128.2 P2p Bound(PVST)

Fa0/23 Desg FWD 2000000 128.23 Shr

Fa0/24 Desg FWD 200000 128.24 P2p Bound(STP)

MST1

Spanning tree enabled protocol mstp

Root ID Priority 24577

Address 0011.bbfb.4180

This bridge is the root

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 24577 (priority 24576 sys-id-ext 1)

Address 0011.bbfb.4180

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/1 Desg FWD 200000 128.1 P2p

Fa0/2 Desg FWD 200000 128.2 P2p Bound(PVST)

Fa0/23 Desg FWD 2000000 128.23 Shr

Fa0/24 Desg FWD 200000 128.24 P2p Bound(STP)

3400>show span

MST0

Spanning tree enabled protocol mstp

Root ID Priority 24576

Address 0011.bbfb.4180

Cost 0

Port 3 (FastEthernet0/1)

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 28672 (priority 28672 sys-id-ext 0)

Address 001d.e53b.4280

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Interface Role Sts Cost Prio.Nbr Type

------------------- ---- --- --------- -------- --------------------------------

Fa0/1 Root FWD 200000 128.3 P2p

Fa0/2 Desg FWD 200000 128.4 P2p Bound(PVST)

MST1

Spanning tree enabled protocol mstp

Root ID Priority 24577

Address 0011.bbfb.4180

Cost 200000

Port 3 (FastEthernet0/1)

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 28673 (priority 28672 sys-id-ext 1)

Address 001d.e53b.4280

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Interface Role Sts Cost Prio.Nbr Type

------------------- ---- --- --------- -------- --------------------------------

Fa0/1 Root FWD 200000 128.3 P2p

Fa0/2 Desg FWD 200000 128.4 P2p Bound(PVST)

On the MRV side, it thinks the Droot is via port 2, which is correct so it's certainly speaking MST.

# show spanning-tree instance 0

...

BridgeId: 8000-000fbd0170cf Bridge Priority: 32768 (0x8000)

Designated Root: 6000-0011bbfb4180 Root Port: 8002 (2 )

...

Any thoughts?

[Giuseppe Larosa]

Hello Jason,

have you verified that the MST region name and MST revision number are equal on all devices ?

because bound should mean boundary and this is means the devices treat each other as in different regions.

I may be wrong but this is my understanding

Hope to help

Giuseppe

[Francois Tallet]

This flag means that the port is boundary because it is (or at least thinks it is) connected to a PVST switch. Cisco's MST includes a PVST simulation component that is triggered as soon as you receive a PVST+ BPDU on a port.

PVST+ are treated like BPDUs by Cisco switch, but third party boxes just see them as user data and forward them. So your problem is probably that there might be some PVST+ devices behind your MRV switches that can still flood their BPDUs toward the 3550/3400. You need to check on that.

Also, once a port is declared boundary PVST, it stick to this mode. A single BPDU is enough to switch to this state. You can flap the link or (simpler) do a "clear spanning-tree detect" from the exec prompt in order to clear the flag, once you got rid of the source of the PVST+ BPDUs.

Regards,

Francois