Configuring A Trunk Port - Cisco Catalyst 2950 Software Configuration Manual

Configuring VLAN Trunks
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Configuring a Trunk Port

Beginning in privileged EXEC mode, follow these steps to configure a port as an IEEE 802.1Q
trunk port:
Command
Step 1 configure terminal
Step 2 interface interface-id
Step 3
switchport mode {dynamic {auto |
desirable} | trunk}
Step 4 switchport access vlan vlan-id
Step 5
switchport trunk native vlan vlan-id
Step 6 end
Step 7 show interfaces interface-id switchport Display the switchport configuration of the interface in the Administrative
Step 8 show interfaces interface-id trunk
Step 9 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 IEEE 802.1Q trunk. The example assumes that the
neighbor interface is configured to support IEEE 802.1Q trunking.
Switch# configure terminal
Enter configuration commands, one per line.
Switch(config)# interface fastethernet0/4
Switch(config-if)# switchport mode dynamic desirable
Switch(config-if)# end
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
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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 IEEE 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 changed.
Protected ports are supported on IEEE 802.1Q trunks.
Purpose
Enter global configuration mode.
Enter the interface configuration mode and the port to be configured for
trunking.
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).
(Optional) Specify the default VLAN, which is used if the interface stops
trunking.
Specify the native VLAN.
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.
• dynamic auto—Set the interface to a trunk link if the neighboring
interface is set to trunk or desirable mode.
dynamic desirable—Set the interface to a trunk link if the
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neighboring interface is set to trunk, desirable, or auto mode.
trunk—Set the interface in permanent trunking mode and negotiate
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to convert the link to a trunk link even if the neighboring interface is
not a trunk interface.
End with CNTL/Z.
Chapter 16 Configuring VLANs
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