Switch Not Pruning Trunk

Unanswered Question
Sep 18th, 2007
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Here's a short version of the question:

If VTP pruning appears to be "pruning" on all of your trunk links to other switches except for one -- what could be a possible cause?

Far-end switch is in the same VTP domain with adequate code level and only a few ports not in the native vlan (with the exception of a trunk port to a Cat2950)?

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Kevin Dorrell Tue, 09/18/2007 - 22:33
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Is CDP working corrrectly on that link?

Is the trunk statically on, or dynamic?

Kevin Dorrell


sometechguy Wed, 09/19/2007 - 12:24
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It appears that the culprits were non-Cisco IP phones that were trunked on a far-end switch.

I'm now assuming that trunks to non-Cisco devices from a downstream switch will cause all upstream trunks not prune (which kind of makes sense).

Kevin Dorrell Wed, 09/19/2007 - 13:11
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Oh right, that does make sense. If you have a downstream trunk and you cannot find out what VLANs it wants, then you cannot justify pruning any VLANs on the upstream trunks.

Now, if you had restricted the allowed VLANs on those non-Cisco trunks by configuring an allowed vlan list, would it have pruned the rest?

Thanks for that ... it's a good one to remember.

Kevin Dorrell



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