Cisco Cisco IOS Software Release 12.4(15)T

To set the trunk characteristics when the interface is in trunking mode, use the switchport trunk 
commands in interface configuration mode. To reset all of the trunking characteristics back to the 
original defaults, use the no form of this command. 

switchport trunk {encapsulation dot1q | native vlan | allowed vlan}

no switchport trunk {encapsulation dot1q | native vlan | allowed vlan}

switchport trunk encapsulation {isl | dot1q [ethertype value] | negotiate} 

switchport trunk native vlan vlan-id 

switchport trunk allowed vlan vlan-list 

switchport trunk pruning vlan vlan-list 

no switchport trunk {encapsulation {isl | dot1q | negotiate} | native vlan | allowed vlan | 

pruning vlan} 

The default encapsulation type is dot1q.

The default access VLAN and trunk interface native VLAN is a default VLAN that corresponds to 
the platform or interface hardware.

The default for all VLAN lists is to include all VLANs.

Sets the trunk encapsulation format to 802.1Q. 

Sets the native VLAN for the trunk in 802.1Q trunking mode. 

Sets the list of allowed VLANs that transmit traffic from this interface in 
tagged format when in trunking mode.

Sets the trunk encapsulation format to Inter-Switch Link (ISL).

ethertype value

(Optional) Sets the EtherType value; valid values are from 0x0 to 
0x5EF-0xFFFF. 

Specifies that if the Dynamic Inter-Switch Link (DISL) protocol and 
Dynamic Packet Transport (DPT) negotiation do not resolve the 
encapsulation format, ISL is the selected format.

vlan-id

Identifies the particular native VLAN.

vlan-list

List of VLANs. See the “Usage Guidelines” section directions on formatting 
a vlan-list.

Sets the list of VLANs that are enabled for VLAN Trunking Protocol (VTP) 
pruning when in trunking mode. See the “Usage Guidelines” section for the 
vlan-list argument formatting guidelines.