Consolidated Platform Configuration Guide, Cisco Ios Release 15.2(4)E (Catalyst 2960-X Switches - Cisco Catalyst 2960 series Configuration Manual

How to Configure VLAN Trunks
If a packet has a VLAN ID that is the same as the outgoing port native VLAN ID, the packet is sent untagged;
otherwise, the switch sends the packet with a tag.
SUMMARY STEPS
1. enable
2. configure terminal
3. interface interface-id
4. switchport trunk native vlan vlan-id
5. end
6. show interfaces interface-id switchport
7. copy running-config startup-config
DETAILED STEPS
Command or Action
Step 1
enable
Example:
Switch> enable
Step 2 configure terminal
Example:
Switch# configure terminal
Step 3
interface interface-id
Example:
Switch(config)# interface gigabitethernet1/0/2
Step 4 switchport trunk native vlan vlan-id
Example:
Switch(config-if)# switchport trunk native vlan
12
Step 5
end
Example:
Switch(config-if)# end

Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)

2140
Purpose
Enables privileged EXEC mode. Enter your password if
prompted.
Enters the global configuration mode.
Defines the interface that is configured as the IEEE 802.1Q
trunk, and enters interface configuration mode.
Configures the VLAN that is sending and receiving
untagged traffic on the trunk port.
For vlan-id, the range is 1 to 4094.
Returns to privileged EXEC mode.