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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter 14 Co n figuring VLANs
Configur ing VLAN Trunks
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STP Port Fast setting
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trunk s tat us: i f o ne po rt i n a po rt g rou p ce as es t o b e a t runk, a ll por t s ce ase t o be t runk s.
•If you try to enable 802.1X on a trunk port, an error message appears, and 802.1X is not enabled. If
you try to c han ge t he mod e of an 8 02. 1X -ena ble d p or t to tr unk , th e port m ode i s not ch an ged.
•A port in dynamic mode can negotiate with its neighbor to become a trunk port. If you try to enable
802.1X on a dynamic port, an error message appears, and 802.1X is not enabled. If you try to change
the m ode o f a n 80 2.1 X-e nab led po rt t o dyna mic , the por t m ode is not ch an ge d.

Configuring a Trunk Port

Beginning i n privileged EX EC mode , follow th ese s teps t o con figure a por t as 80 2. 1Q t runk port:
To return an interface to its default configuration, use the default interface interface-id in terfa ce
configurat ion com mand. To re set al l trunki ng char ac ter istic s of a trunk ing i nte rfac e to the de faults, us e
the no switchport trunk interface configurat ion com mand. To disa ble trunking , use the switchport
mode access interface configuration command to configure the port as a static-access port.
Command Purpose
Step 1 configure terminal Enter glob al co nfigur atio n mo de .
Step 2 interface interface-id Enter the interface configuration mode and the port to be configured for
trunking.
Step 3 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 in terface to a trunk li nk if the neig hboring
interface is set to trunk or desirable mode.
•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 in terface.
Step 4 switchport access vlan vlan-id (Optional) Sp ecify the d ef ault VLAN , whi ch is used if the inter fa ce stops
trunking.
Step 5 switchport trunk native vlan vlan-id Specify the native VLAN.
Step 6 end Return to privileged EXEC mode.
Step 7 show interfaces interface-id switchport Display the swi tchpor t configu ratio n o f th e inter face in th e
Administrative Mode and the Administrative Trunking Encapsulation
fields of the display.
Step 8 show interfaces interface-id trunk Display the trunk configuration of the interface.
Step 9 copy running-config startup-config (Optional) Save your entries in the configuration file.