Typically, you configure 802.1Q trunks with a native VLAN ID, which strips tagging from all packets on that VLAN. This configuration allows all untagged traffic and control traffic to transit the Cisco Nexus 5000 Series switch. Packets that enter the switch with 802.1Q tags that match the native VLAN ID value are similarly stripped of tagging.
To maintain the tagging on the native VLAN and drop untagged traffic, enter the vlan dot1q tag native command. The switch will tag the traffic received on the native VLAN and admit only 802.1Q-tagged frames, dropping any untagged traffic, including untagged traffic in the native VLAN.
Control traffic continues to be accepted untagged on the native VLAN on a trunked port, even when the vlan dot1q tag native command is enabled.
The vlan dot1q tag native command is enabled on global basis.
The following example shows how to enable 802.1Q tagging on the switch:
switch# configure terminal
switch(config)# vlan dot1q tag native
switch# show vlan dot1q tag native
vlan dot1q native tag is enabled