Cisco Support Community
Community Member

spanning tree and pruning

I have a 6 switch network (cat 6000's), with the following vlans: 1, 10, 20, 30, 40.

I want to create two "domains" say Outside and Internal and I want to put 2 switch's in Outside and 2 in Internal.

I also want only vlan's 1, 10, and 20 to be physically accessible on "domain--Outside" and have only vlan's 1,20,30,and 40 accessible on the "domain---Internal"

Here's what I've done:

I have created a VTP domain and enable pruning, I have 2 ISL trunks between the "domain's" and have cleared the appropriate vlan's on the trunks at the ingress and egress.

From what I understand, there is now 2 instances of spanning tree for the cleared (pruned) vlan's.

I also understand that under some circumstances, the pruned (cleared) vlans, under a failure situation, might stop pruning for x seconds. With this, I believe there will be layer 2 wide spanning-tree war for cleared (pruned) vlan's, and then once the pruning re-enables, there will be an additional spanning tree war for the disparate instances of the vlans.

Under what failure situations will pruning "disable" itself?

Additionally, if a switch is powered on, how soon will the pruning take effect?

Can anyone suggest a more graceful way to do this?


Community Member

Re: spanning tree and pruning

Before I make any suggestions, I was wondering what the reason is for turning on pruning on the switches. My understanding is that it is always turned off by default.


CreatePlease to create content