Creating a Trunk Port and Enabling VLAN 20

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To create a trunk port and allow VLAN 20 on a Cisco switch, you would need to perform the following three steps:

1. Configure the trunk encapsulation protocol: The first step is to configure the trunk port to use the correct encapsulation protocol. This is done using the "switchport trunk encapsulation" command, followed by the desired protocol, which in this case is "dot1q". This command tells the switch to use IEEE 802.1Q encapsulation for the trunk port.

Example: switchport trunk encapsulation dot1q

2. Configure the port as a trunk: The next step is to configure the port as a trunk port using the "switchport mode" command. This command tells the switch to treat the port as a trunk port, and to use the encapsulation protocol specified in the previous step.

Example: switchport mode trunk

3. Allow VLAN 20 on the trunk port: Finally, you need to allow VLAN 20 on the trunk port using the "switchport trunk allowed vlan" command. This command tells the switch to allow traffic from VLAN 20 to pass through the trunk port. You can specify multiple VLANs by separating them with commas.

Example: switchport trunk allowed vlan 20

Note: The "switchport trunk native vlan" command is used to specify the VLAN that is used for untagged traffic on the trunk port. It is not necessary for allowing a specific VLAN on the trunk port, but it can be used to ensure that untagged traffic is assigned to the correct VLAN.