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Trunk issue

foresthome asked
Medium Priority
Last Modified: 2012-05-06
I'm trying to create a trunk connection between a 2924 Cisco switch and a 2960. I can set the mode to trunk on the 2960 just fine. I connect the the two switches with a cross-over cable and the connection goes down. The port on the 2924 goes green/yellow. If I leave the port on the 2924 as "mode access" the two switches can see each other but the VLAN database does not update on the 2960.(2924 is the vlan server).

What am I doing wrong?

Thank you!
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Can you should use the config of the ports on each side? Have you tried another cable?

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Shut both ports down on each switch then plugin the cable.
Hard set the port speeds and duplex.
Set the trunk encapsulation.
No shut the ports.

Also double check your spanning tree configuration.

Let us know how this goes.
Don JohnstonInstructor
Top Expert 2015

2900XL switches do not support DTP. You will need to manually define and create the trunk on each switch.

switchport trunk encap dot1q
switchport mode trunk

This is due to encapsulation mismatch between the switches over the trunk. Force both ends to use dot1q encapsulation


I tried to do the same thing with two 2900 switches and worked like a charm. I tried with a 3550 switch and I get the same problem as with the 2960.

Here is how I setup the ports on the switches:

3550 Switch

interface FastEthernet0/6
 switchport trunk encapsulation dot1q
 switchport mode trunk
 no ip address
 duplex full
 speed 100

2900 switch

interface FastEthernet0/9
 duplex full
 speed 100
 switchport trunk encapsulation dot1q
 switchport mode trunk

Thank you for your help!
Don JohnstonInstructor
Top Expert 2015

What is the status of the ports with this configuration?

Can you get the link to come up with it configured as access ports?

Please post the output of a "show int f0/6 switchport" and "show int f0/9 switchport".
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