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2950 spanning tree issue

Here is the problem we are having , we have a 2950 hooked to a 6509 hybrid dist box with approx 90 vlans on it . We hook up a new 2950 and we get the following message, Dec 21 19:47:45.116: %SPANTREE_VLAN_SW-2-MAX_INSTANCE: Platform limit of 64 STP instances exceeded. No instance created. Ok , I know about the spanning tree issues with the 2950 only having limited PVST instances . But up at the dist side we have "manually pruned off all but 5 vlans on the trunk feeding this 2950 with the "clear trunk" command . I thought manually pruning off the vlans from the trunk would eliminate this problem , maybe i have a misunderstanding of how this works. Also the message on the 2950 complains about it only having 64 instances of spanning tree yet when you do a "show vtp status it says it supports 250 instances locally so whats up with that , 2950 running 12.1.22EA4 . So I guess I'm asking is there any way around this for the 2950 . Also in client/server mode do you have to manually prune off the vlans on both the server side and the client side ??

VIP Purple

Re: 2950 spanning tree issue

Hello Glen,

I guess instead of manually pruning the VLANs off the trunk, you could also try and enable VTP pruning globally on the 6509 (set vtp pruning enable). I assume you have the 6509 configured as the VTP server (set vtp mode server) ?

I am not sure if CatOS and IOS defaults to the same VTP version, can you check this (with 'show vtp domain' for CatOS and 'show vtp status' for the IOS switch) ?

Also, in a purely IOS environment, manually pruning VLANs off a trunk requires doing that only on the server side, but with a mix of CatOS and IOS, it might have to be done on both sides, you might want to give it a try and use the 'switchport trunk allowed' command on the 2950 as well...




Re: 2950 spanning tree issue

Hi vtp pruning is already enabled on the distr. 6509 . Both are running vtp version 2. That was my understanding as well about only manually pruning the server side so that is the way it is right now . I'll probably try manually pruning the 2950 side and see what happens . Still wonder about the log message saying there is 64 instances where the "show vtp status" says it supports 250 instances locally. Maybe i'll do a bug search.

Community Member

Re: 2950 spanning tree issue

You have done everything right except to namually prune the VLANs off of the trunk on the 2950.

What happens at the 2950 is it learns all of the VLANs via VTP and because it's trunk has not been manually pruned, it tries to run an instance of STP for each VLAN that it has learned. The switchport tunk allowed command is all you need on the 2950's uplink port.



Re: 2950 spanning tree issue

Thanks , I guess I thought because it had been manually pruned on the server (6509) side that the vlans would not be propagated across the link .

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