Users Guide

Layer 2 Switching Commands 885
VLAN 1 is the default native VLAN on a trunk port. The default allowed
VLAN membership on a trunk port is all VLANs.
Command Mode
Interface Configuration (gigabitethernet, port-channel, tengigabitethernet,
fortygigabitethernet) mode
Interface Range mode
Port-Channel Range mode
User Guidelines
Untagged traffic received on a trunk port is forwarded on the native VLAN, if
configured.
To drop untagged traffic on a trunk port, remove the native VLAN from the
trunk port. (Ex. switchport trunk allowed vlan remove 1.) Management
traffic is still allowed on the trunk port in this configuration.
The no form of the command sets the allowed or native VLAN membership
back to the defaults.
It is possible to exclude VLANs that have not yet been created from trunk
port membership. For example, it is possible to exclude VLANs learned
dynamically via GVRP from being configured on a trunk port using this
command.
Example
console(config)#interface gigabitethernet 1/0/1
console(config-if-Gi1/0/1)#switchport trunk allowed vlan 1-1024
console(config-if-Gi1/0/1)#switchport trunk allowed vlan except
1,2,3,5,7,11,13
switchport trunk encapsulation dot1q
Use this command for compatibility. This command performs no action.
Syntax
switchport trunk encapsulation dot1q