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iroperto1
Beginner

Command rejected: A port which is configured to "trunk" mode can not be configured to negotiate the encapsulation

I deployed a new cisco 9500 to be trunk to cisco WS-C3560-24PS. However, on the WS-C3560-24PS when I tried to remove the switchport trunk encapsulation dot1q. I get Command rejected: A port which is configured to "trunk" mode can not be configured to negotiate the encapsulation. Please if any one can share some light. 

11 REPLIES 11
Martin L
VIP Advocate

 

I don't think you can use encapsulation ISL anymore; so only one left is encapsulation dot1q along with switchport mode trunk - which i think you must have it on trunk port.  You can try command switchport nonegotiate. 

you must remove switchport mode trunk first - worked for me but not the same switch

why you want to remove that command ?

 

Regards, ML
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I want to remove the command because it doesn't work since is connect to cisco 9500 and I had deployed 5 other switches to the same cisco 9500 just with the switchport mode trunk is only this switch that refuse to connect to the cisco 9500. The other switches are working fine. They don't have that dot1q at the interface level.

Well I don't want to encapsulate. I know we can only use sot1q, but that's the thing I want to remove that statement. I have other switches connect to the same cisco 9500 just as trunk and vlan allowed. However, if I remove switchport mode trunk first I may lose the trunk I'm not local to the switch, but I also tried to console to the switch without success. I think I will try what you are recommending.

 

 

Thanks! 

Another option if not a production one - you have console access, default the interface and start configuring as per the requirement.

 

BB

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I tried that already this without success. Thanks everyone for your help!

not sure what kind of IOS Code running here :

 

check this example :

 

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst9500/software/release/16-6/configuration_guide/vlan/b_166_vlan_9500_cg/b_166_vlan_9500_cg_chapter_010.html

 

it would be nice to see the configuration and explain - how the other side configured, what is not working exactly.

 

BB

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Switch   Ports  Model              SW Version              SW Image           
------   -----  -----              ----------              ----------         
*    1   26     WS-C3560-24PS      12.2(20)SE4             C3560-I9-M         


Configuration register is 0xF

Thanks man. I tried the to use dynamic auto no success. However, when I connected the switch to another switch same model I could trunk with no problem. but I replace the switch to 3650 this switch I can trunk to Cisco 9500 with no problem.

on the beginning. I wasn't able to console, but I rebooted the switch I default int gig 0/1, However, the switch keep forcing me to use dot1q. All I need is switchport trunk allowed vlan xxx, xxx,xxx and switchport mode trunk. because the cisco 9500 which is connect doesn't have choice for dot1q at the interface level. but I replace the switch with 3650 and that fixed the issue.

 

Thanks all.

not sure what IOS, some old IOS may have defaults some latest have different options.  you can see show interface g x/x capabilities or show run all give you full configuration.

 

BB

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But my question was never about dot1q or ISL. my questions was about why the switch doesn't let me just trunk.  

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