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Cisco 3750g Stack - to - Xtrem 3804 trunk config

Posted on 2008-10-01
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Last Modified: 2012-05-05
Have an existing 2960G Cisco switch that the VLAN1 interface is setup with an IP and the next line is the trunk command:
switchport mode trunk
There is no Dot1Q encapsulation for this interface on the existing 2960 when I look at the config and it works fine.  When I try to do this on a new 3750G stack I get the following error:

Command rejected: An interface whose trunk encapsulation is "Auto" can not be configured to "trunk" mode.

I have seen where I may need to add the dot1q encap but want to make sure especially since I am connecting to an older Extreme 3804 Switch and it either did not have to be done on the existing 2960G or is it possibly transparent to me?  Any help much appreciated.
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Question by:TTNSTC
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by:Don Johnston
Don Johnston earned 45 total points
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2950's and 2960's support 802.1q trunking only. The "switchport trunk encapsulation" command is not recognized since there's only one trunking protocol.


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Soulja earned 30 total points
ID: 22618706
The reason you get that error on the 3750 is because you have to enter the switchport encapsulation dot1q command first then the switchport mode trunk command.
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by:Soulja
ID: 22618719
Correction switchport trunk encapsulation command.
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by:Don Johnston
Don Johnston earned 45 total points
ID: 22619362
The "switchport trunk encapsulation" cannot be used on a switch that supports only one trunking protocol.
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by:Soulja
ID: 22620140
I am referring to the 3750 switches, not the 2960.
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by:kdearing
ID: 22620295
Make sure you use dot1q trunking and not Cisco's old ISL, it is proprietary
Dot1q is the standard to be used between devices from different manufacturers.
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Author Closing Comment

by:TTNSTC
ID: 31502086
Thanks guys.  The 3750 came up by default and recognized the dot1q protocol and adapted.  I was just a little confused because this had to be hard coded on the 2960 about a year ago to work.  Because of your responses I have a better understanding and everything is good.  Thanks again.
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by:TTNSTC
ID: 22620705
Thanks everyone
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