Re: Spanning tree root changed

farhan.javed · ‎10-08-2006

Hi every1 ,

Actually I am using 3548 switch and on its interface g0/1 which is connecting to anoth 3548 switch..

I am getting an alert in HP-OV, that Spanning tree root has changed for Vlan5..

As I found the topology isa changed from g0/1..

Will anyone of you help me..

I am pasting little informations below..

Thanks

============

VLAN0005

Spanning tree enabled protocol ieee

Root ID Priority 8197

Address 000a.f4fa.3480

This bridge is the root

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

Bridge ID Priority 8197 (priority 8192 sys-id-ext 5)

Address 000a.f4fa.3480

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

Aging Time 300

Interface Port ID Designated Port

ID

Name Prio.Nbr Cost Sts Cost Bridge ID Prio

.Nbr

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

----

Fa0/1 128.1 19 FWD 0 8197 000a.f4fa.3480 128.

1

Fa0/5 128.5 19 FWD 0 8197 000a.f4fa.3480 128.

5

Fa0/9 128.9 19 FWD 0 8197 000a.f4fa.3480 128.

9

Interface Port ID Designated Port

ID

Name Prio.Nbr Cost Sts Cost Bridge ID Prio

.Nbr

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

----

Fa0/10 128.10 19 FWD 0 8197 000a.f4fa.3480 128.

10

Fa0/44 128.44 19 FWD 0 8197 000a.f4fa.3480 128.

44

Fa0/46 128.46 19 FWD 0 8197 000a.f4fa.3480 128.

46

Fa0/47 128.47 19 FWD 0 8197 000a.f4fa.3480 128.

47

Gi0/1 128.49 4 FWD 0 8197 000a.f4fa.3480 128.

49

Gi0/2 128.50 4 FWD 0 8197 000a.f4fa.3480 128.

50

SW18#

=========================

THis is the Neighbor switch 3550...

=======

SW18#sh spanning-tree int g0/2

Vlan Port ID Designated Port

ID

Name Prio.Nbr Cost Sts Cost Bridge ID Prio

.Nbr

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

----

VLAN0005 128.50 4 FWD 0 8197 000a.f4fa.3480 128.

50

=========================================

Is there any command which can help me to troubleshoot spanning tree related problems...

globalnettech · ‎10-08-2006

Hello Farhan,

did the root change occur randomly, or after you connected the second to the first switch ? In order to make sure that the root switch doesn't change, use the global command 'spanning-tree vlan 5 priority 0' or 'spanning-tree vlan 5 root primary' command.

The ' show spanning-tree vlan 5' command you are already using should give you the necessary information needed to determine your STP topology. In addition, the 'debug spanning-tree' command has numerous options to debug spanning tree problems, check this link to the command reference for details:

debug spanning-tree

http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124tcr/tdb_r/dbg_s2ht.htm#wp1104543

HTH,

GNT

Francois Tallet · ‎10-09-2006

What do you mean by "topology isa changed from g0/1."? Was this switch seeing the root bridge on this interface earlier?

Right now, g0/1 is designated, which is consistent with the fact that this bridge Sw18 is currently the root for vlan 5. There is nothing much more anyone will be able to tell you on this forum with the information you provide. If order to know if there is a problem or not, we would need to know what you would expect this switch to be and why.

Regards,

Francois