You may use the following method to configure a Cisco Catalyst3560 switch port as a trunk. In this example we will use the FastEthernet 0/24 port.

Begin by entering global configuration mode and specifying the port, FastEthernet 0/24, that will be configured as a trunk port.

Next, we must specify the version of trunking we will implement. In this example we will implement IEEE 802.1q trunking which is specified by the switchport trunk encapsulation dot1q command.

Next, we enable the trunk with the switchport mode trunk command. Note that this command will automatically negotiates to convert the link on the other end to a trunk link.

Lastly, you may verify the trunk port with the show interface trunk command.

Enjoy!