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Catalyst 2960 Switch SoftwareConfiguration Guide
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Chapter12 Configuring VLANs
Configuring VLAN Trunks
•If you try to enable IEEE 802.1x on a trunk port, an error message appears, and IEEE 802 .1x is not
enabled. If you try to change the mode of an IEEE 802.1x-enabled port to trunk, the po rt mode is
not changed.
•A port in dynamic mode can negotiate with its neighbor to become a trunk port. If you try to enable
IEEE 802.1x on a dynamic port, an error message appears, and I EEE 802.1x is not enabled. If you
try to change the mode of an IEEE 802.1x-enabled port to dynamic, the port mode is not change d.
Configuring a Trunk Port
Beginning in privileged EXEC mode, follow these steps to configure a port as a tr unk port:
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, us e
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 IEEE 802.1Q trunk. The exa mple assumes that the
neighbor interface is configured to support IEEE 802.1Q trunking.
Switch# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)# interface gigabitethernet0/2
Switch(config-if)# switchport mode dynamic desirable
Switch(config-if)# end
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 interface interface-id Specify the port to be configured for trunking, and enter interface
configuration mode.
Step3 switchport mode {dynamic {auto |
desirable} | trunk}
Configure the interface as a Layer 2 trunk (required only if the interface
is a Layer 2 access 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.
Step4 switchport access vlan vlan-id (Optional) Specify the default VLAN, which is used if the interface stops
trunking.
Step5 switchport trunk native vlan vlan-id Specify the native VLAN for IEEE 802.1Q trunks.
Step6 end Return to privileged EXEC mode.
Step7 show interfaces interface-id switchport Display the switchport configuration of the interface in the
Administrative Mode and the Administrative Trunking Encapsulation
fields of the display.
Step8 show interfaces interface-id trunk Display the trunk configuration of the interface.
Step9 copy running-config startup-config (Optional) Save your entries in the configuration file.