Cisco IOS – An interface whose trunk encapsulation is “Auto” can not be configured to “trunk” mode.
KB ID0001167 Problem If you try and change a ports status, to make it a trunk port, you may see this error; Petes-Switch(config-if)#switchport mode trunk Command rejected: An interface whose trunk encapsulation is “Auto” can not be configured to “trunk” mode. Trunk Settings I don’t know if this is a throwback to when we had ISL trunking and 802.1q, but you need to specify the encapsulation before you can...