STP problem with stacked 3750

Unanswered Question
Feb 27th, 2007


I have a STP problem in a wiring closet in one of my building. The network as been upgraded last Saturday from 3500XL to 3750G. My network topology is :

Aggregation (L2) (4 3750G stacked)STP Root

15 wiring closet with 1 to 7 stacked 3750

In my wiring closet 7, my STP topology keep changing. The topology change originate from stackport1. How is this possible ?

Keep in mind that the config of the switch stack is the same in all the 15 wiring closet and this is the only place I have a problem. I can't change to RPVST, I still have 1 3500XL switch in my building. (to be changed over next weekend)

VLAN0150 is executing the ieee compatible Spanning Tree protocol

Bridge Identifier has priority 32768, sysid 150, address 0019.aa54.3280

Configured hello time 1, max age 8, forward delay 6

Current root has priority 150, address 0018.197f.e200

Root port is 616 (Port-channel1), cost of root path is 3

Topology change flag not set, detected flag not set

Number of topology changes 10 last change occurred 00:10:31 ago

from StackPort1

Times: hold 1, topology change 14, notification 1

hello 1, max age 8, forward delay 6

Timers: hello 0, topology change 0, notification 0, aging 300

I have this problem too.
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glen.grant Wed, 02/28/2007 - 15:14

That is just telling you that the device that caused it is somewhere down the stack . TCN's are not necessarily bad as long as they aren't constant . In a well configured network they should be minimal though . Look for things like user ports that do not have spanning tree portfast turned which will cause TCN's across the network everytime some user pc comes on line . Portfast stops tcn's from user ports . Do not use portfast on any network device attached interfaces .


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