Spanning Tree Problem

[PinkLips]

I know this is a vast topic, but what is the quickest way to find out if your network has a spanning-tree problem and locate the switch that is causing it?

I have over 50 edge switches (2950) hanging off our two core switch (6500) in a spoke topology.

Thanks,
Nicole

 

[vipergg]

That is tough to say . I would hope all 50 switches are not in the same vlan . Start checking around the network and see what switch is the spanning tree root for each vlan , logically it should be the strongest switch which is the 6509 . If you have redundancy with a built in loop then somehere in the network you should see one port in each vlan in a blocking state . If you have a spanning tree problem then you would probably also higher than normal cpu usuage on each switch .

 

[wabob]

Vipergg, not to ask a dumb question, but doesn't a Spanning Tree problem (such as a loop) completely shut down your network, or at least the entire VLAN / broadcast domain in which it exists?

Is it possible for a network to operate with a Spanning Tree problem?

There are 10 kinds of people in the world.
Those who understand binary, and those who don't...

 

[vipergg]

It will still work "sometimes" usually in a severely degraded fashion . We have seen this many times when people bring in unmanaged hubs or switches and create a loop in the network . It can bring it to a crawl but it can still be used .

 

[chieftan]

The packet will double exponentially until the network (switches or routers...etc...) can no longer handle the amount of traffic. Then, PLOP, down goes the network.

1 packet becomes 2..... 2 packets become 4....4 packets become 8 and so on as shown:-

1
2
4
8
16
32
64
128
256

As can be seen, this soon becomes a major issue. If you do not have portfast enabled you will have to wait approximately 30 - 40 seconds for the ports to re-initialise with Spanning Tree.