dot1q trunk comes up, then goes down

Unanswered Question
Apr 9th, 2008
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have the following config on two 3750's

switchport trunk encapsulation dot1q

switchport trunk native vlan 900

switchport trunk allowed vlan 132-135,535,900

switchport mode trunk

when I no shut, link comes up, then down. vtp mode on core switch (one end) is server, other end is transparent. very strange. any help is appreciated.

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Istvan_Rabai Wed, 04/09/2008 - 22:28
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Hi Pete,

What is the speed and duplex config of the ports on both swiches?

They should be either auto on both sides, or they should have the same speed and duplex settings.

In addition, check if you are using a crossover cable, not straight-through cable.



Kevin Dorrell Thu, 04/10/2008 - 01:03
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In addition to Istvan's suggestions, check the native VLAN is 900 at both ends of the link, and that VLAN 900 exists both in the domain and in your VTP transparent switch.

Kevin Dorrell


dbroder Thu, 04/10/2008 - 21:03
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I'd also do a shut / no shut on both sides of that trunk just for good measure.



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