6500 missing the "switchport trunk encapsulation dot1q" command

Unanswered Question
Sep 17th, 2008

I was at a customer site yesteday trying to setup a etherchannel trunk between the 6500 and a WLAN controller. We setup the L2 port channel fine,but under the gig ports the command "switchport trunk encapsulation dot1q" was not available. We were able to do a "swithport mode trunk" and the trunk looked like it was up and fine but I could not pass traffic. Other ports on the other blades are in L2 portchannel trunks as well, and they have the command. And if we configured a port on one of the other blades we could type the command in. Just not on the blade the WLAN controller was plugged into. Not sure of the IOS version. Anyone ever see this?

I have this problem too.
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Edison Ortiz Wed, 09/17/2008 - 10:19

If the switchport does not support ISL, there isn't the need to specify 802.1q as the trunking encapsulation protocol as you only have one choice.

In other words, the trunk will only form by using 802.1q.

You can verify the trunk encapsulation with the command show interface gx/x switchport.

This behavior varies among modules and that's the reason you see it works in some modules and it does not in some others.

You can verify the module capabilities with the command:

show interface gx/x capabilities




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Mark Yeates Wed, 09/17/2008 - 10:23


What line card are you using? Some of the newer cards no longer use ISL trunking and are only capable of dotq. That's probably why it does not take the "switchport trunk encapsulation dot1q" command.



miwitte Wed, 09/17/2008 - 10:50

Nice. I'll ask the customer. That was really a weird one.


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