STP confusion :(

[vijay kumar]

Hi all ,

We have configured this switch as root for vlan a and vlan b(example) . But in one vlan i am able to see this switch is the root . whereas other vlan is not showing. But both BID and RID mac address denoting the same switch ...

Logs as below .

Switch# show spanning-tree vlan a

VLAN0258

  Spanning tree enabled protocol rstp

  Root ID    Priority    4354

             Address     64a0.e743.82c1

             This bridge is the root

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

  Bridge ID  Priority    4354   (priority 4096 sys-id-ext 258)

             Address     64a0.e743.82c1

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

Interface        Role Sts Cost      Prio.Nbr Type

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

interface             Desg FWD 1         128.4115 P2p

switch# show spanning-tree vlan y

VLAN0259

  Spanning tree enabled protocol rstp

  Root ID    Priority    4354

             Address     64a0.e743.82c1

             Cost        14

             Port        4115

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

  Bridge ID  Priority    4355   (priority 4096 sys-id-ext 259)

             Address     64a0.e743.82c1

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

Interface        Role Sts Cost      Prio.Nbr Type

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

interface     Root FWD 1         128.4115 P2p

Any idea on this....

[chandra_rc16]

I believe the root priority in Vlan0259 should be 4355 whereas it is 4354.

Try configuring the Root priority in Vlan0259 again.

And if it is in PT try rebboting the switch.

Please don't mind if my suggestion doen't help. Even i'm still learning.

Regards,

Chandu

[Steve Krause]

Somewhere in your infrastructure there is another switch advertising better BPDUs for vlan259. Track that switch down and figure out what it's STP configuration is. Could be it's priority is 0 or it's priority is also 4096 with a lower MAC

[JohnTylerPearce]

vijay,

What you can do, is do a 'show span vlan 259', and then do a 'show cdp neighbor' and you should be able to track the switch down.

Just follow the root port.