Configuring A Trunk Port - Cisco Catalyst 3750 Software Configuration Manual

Chapter 10 Configuring VLANs

Configuring a Trunk Port

Beginning in privileged EXEC mode, follow these steps to configure a port as an ISL or 802.1Q
trunk port:
Command
Step 1
configure terminal
Step 2 interface interface-id
Step 3 switchport trunk encapsulation {isl |
dot1q | negotiate}
Step 4
switchport mode {dynamic {auto |
desirable} | trunk}
Step 5
switchport access vlan vlan-id
Step 6
switchport trunk native vlan vlan-id
Step 7
end
Step 8 show interfaces interface-id switchport Display the switchport configuration of the interface in the Administrative
Step 9 show interfaces interface-id trunk
Step 10 copy running-config startup-config
To return an interface to its default configuration, use the default interface interface-id interface
configuration command. To reset all trunking characteristics of a trunking interface to the defaults, use
the no switchport trunk interface configuration command. To disable trunking, use the switchport
mode access interface configuration command to configure the port as a static-access port.
This example shows how to configure a port as an 802.1Q trunk. The example assumes that the neighbor
interface is configured to support 802.1Q trunking.
Switch# configure terminal
Enter configuration commands, one per line.
Switch(config)# interface gigabitethernet1/0/2
Switch(config-if)# switchport mode dynamic desirable
Switch(config-if)# switchport trunk encapsulation dot1q
Switch(config-if)# end
78-15870-01
Purpose
Enter global configuration mode.
Enter the interface configuration mode and the port to be configured for
trunking.
Configure the port to support ISL or 802.1Q encapsulation or to negotiate
(the default) with the neighboring interface for encapsulation type.
You must configure each end of the link with the same encapsulation type.
Configure the interface as a Layer 2 trunk (required only if the interface
is a Layer 2 access port or tunnel port or to specify the trunking mode).
• dynamic auto—Set the interface to a trunk link if the neighboring
interface is set to trunk or desirable mode. This is the default.
• dynamic desirable—Set the interface to a trunk link if the
neighboring interface is set to trunk, desirable, or auto mode.
trunk—Set the interface in permanent trunking mode and negotiate
•
to convert the link to a trunk link even if the neighboring interface is
not a trunk interface.
(Optional) Specify the default VLAN, which is used if the interface stops
trunking.
Specify the native VLAN for 802.1Q trunks.
Return to privileged EXEC mode.
Mode and the Administrative Trunking Encapsulation fields of the
display.
Display the trunk configuration of the interface.
(Optional) Save your entries in the configuration file.
End with CNTL/Z.
Catalyst 3750 Metro Switch Software Configuration Guide
Configuring VLAN Trunks
10-21