Root Spanning Tree Question

[steverob]

On one of our core siwtches that is running spanning tree I have noticed the following for the root for a spanning tree

VLAN 47

Spanning tree mode PVST+

Spanning tree type ieee

Spanning tree enabled

Designated Root 00-00-00-00-00-00

Designated Root Priority 0

Designated Root Cost 0

Designated Root Port 1/0

Does anybody know what the all zeros mean? I would expect to see a valid mac address here

[Prashanth Krishnappa]

Probably it is because STP is not running in that VLAN on the switch. Do you have any active ports in VLAN 47 in the switch?

[steverob]

No on that switch there is no ports in that VLAN. What I find confusing is on our access switches the following shows up for that VLAN. All of the access switches have 2 GIG uplinks to the core switch.

VLAN47

Spanning tree enabled protocol ieee

Root ID Priority 49954

Address 000c.ce76.be40

This bridge is the root

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

Bridge ID Priority 49954 (priority 49152 sys-id-ext 802)

Address 000c.ce76.be40

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

Aging Time 300

Uplinkfast enabled

Interface Role Sts Cost Prio.Nbr Type

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

Gi1/1 Desg FWD 3004 128.1 P2p

Gi1/2 Desg FWD 3004 128.2 P2p

On all of our access switches in the closets there are no ports assigned to VLAN 47.

[milan.kulik]

Hi,

is VLAN47 allowed on trunks between the core and access?

I'd guess it's allowed on the access trunk side but disabled on the core side.

Regards,

Milan

[steverob]

VLAN 47 has been cleared on the trunk on the core switch. I am assuming VLAN 47 is then still being passed by VTP and since VLAN 47 has been cleared off the trunk ports all of the access switches think they are the root switch for that VLAN. Makes it really confusing to look at 14 access switches who all think they are the root bridge for the VLAN