Cisco Systems N3KC3048TP1GE Configuring Native 802.1Q VLANs, switch# configure terminal, Purpose

Configuring Access and Trunk Interfaces

Configuring Native 802.1Q VLANs

Procedure

Command or Action

Step 1 switch# configure terminal

Step 2 switch(config)# interface {type slot/port port-channelnumber}

Step 3 switch(config-if)# switchport trunk

allowed vlan {vlan-listall none [add except none remove {vlan-list}]}

Purpose

Enters configuration mode.

Specifies an interface to configure, and enters interface configuration mode.

Sets allowed VLANs for the trunk interface. The default is to allow all VLANs on the trunk interface: 1 to 3967 and 4048 to 4094. VLANs 3968 to 4047 are the default VLANs reserved for internal use by default; this group of VLANs is configurable. By default, all VLANs are allowed on all trunk interfaces.

Note You cannot add internally allocated VLANs as allowed VLANs on trunk ports. The system returns a message if you attempt to list an internally allocated VLAN as an allowed VLAN.

This example shows how to add VLANs to the list of allowed VLANs on an Ethernet trunk port:

switch# configure terminal switch(config)# interface ethernet 1/3 switch(config-if)# switchport trunk allow vlan 15-20

Configuring Native 802.1Q VLANs

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 3000 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.

Note The vlan dot1q tag native command is enabled on global basis.

Procedure

	Command or Action	Purpose
Step 1	switch# configure terminal	Enters configuration mode.

	Cisco Nexus 3000 NX-OS Layer 2 Switching Configuration Guide, Release 5.0(3)U3(1)
56	OL-26590-01