native vlan

Hi experts,

Advice please if native vlan on cisco switches are relevnat to only interface level?

can i define any vlan as native vlan in interface level?

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Yes it is only relevant to an interface. You can configure any available vlan as native vlan but it is not a nice configuration. Any device which needs a trunk port could be configured to the desired vlan anyway.

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phoenix26Author Commented:
Hi expert neuba,

yes neuba for trunking only iam asking.

So for trunking any vlan can be configured as native vlan right ?


Yes. For example:

interface GigabitEthernet6/5
 description foobar
 switchport access vlan 42
 switchport trunk encapsulation dot1q
 switchport trunk native vlan 42
 switchport mode trunk
 spanning-tree portfast

This server gets all avaiable vlans with the trunk and without any special configuration it would be in the vlan 42. The config is obsolete since we configured the vlan 42 as an extra interface on the server (which is nicer anyway).
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phoenix26Author Commented:
Hi Neuba expert/ experts,

When is the possible scenarios when native vlan mismatch occurs?

Significance of Native VLAN
When you use an IEEE 802.1Q trunk port, all frames are tagged except those on the VLAN configured as the "native VLAN" for the port. Frames on the native VLAN are always transmitted untagged and are normally received untagged. Therefore, when an AP is connected to the switchport, the native VLAN configured on the AP must match the native VLAN configured on the switchport.

Note:  If there is a mismatch in the native VLANs, the frames are dropped.

This scenario is better explained with an example. If the native VLAN on the Switch1 port is configured as VLAN 12 and on the other Switch2, the native VLAN is configured as VLAN 1, then when the Switch2 sends a frame on its native VLAN to the switch1, the switch considers the frame as belonging to VLAN 12 since the frames from the native VLAN of the SW1 are untagged. This causes confusion in the network and results in connectivity problems. The same happens when the switch1 forwards a frame from its native VLAN to the SW2.

Also, when you configure the switch port, ensure that all the VLANs that are configured on the SWitches  are allowed on the switchport. For example, if VLANs 6, 7, and 8 exist on the  switch have to be allowed on the switchport. This can be done using this command in the switch:

switchport trunk allowed vlan add 6,7,8
By default, a switchport configured as a trunk allows all VLANs to pass through the trunk port. Refer to Interaction with Related Switches for more information on how to configure the switchport.
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