Native Vlan

[Bruin2781]

Hi,

Hope that someone can help me out, i want to be sure on something

When configuring a trunk between a switch and a router and you are not routing the native vlan in your network. Do you still need to configure the native vlan (physical interface or subinterface with the "native" command ) on the router side of the trunk. If not, is de router then simply dropping the untagged frames.

Edwin

[Peter Paluch · Accepted solution]

Hi Edwin,

When configuring a trunk between a switch and a router and you are not routing the native vlan in your network. Do you still need to configure the native vlan (physical interface or subinterface with the "native" command )

If you are not using the native VLAN in your network, then no - you do not need to configure the physical interface or the subinterface with the encapsulation dot1q vlan-id native command. The only thing you obviously need to do is no shutdown on the physical interface.

If not, is de router then simply dropping the untagged frames.

That is correct.

Best regards,
Peter

[Bruin2781]

Thanks all

[Joseph W. Doherty]

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Posting

On a router, the main interface is the "native", and if you don't define an IP for it, it wouldn't accept IP packets.  (Basically the same behavior when there's no tagged frames at all.)

[JDGranger]

Okay, going to take a shot at explaining the native VLAN to you and maybe it will clear things up, if not ask away and I'll do my best.

Native VLAN is for untagged VLAN traffic so lets say you have a host that is on VLAN 20 and your native VLAN was set to 10. Anything that was not tagged for VLAN 20 will be assumed to be on native VLAN10.

As to your question, when you configure a trunk remember that it carries all VLAN traffic unless you tell it otherwise. In our case since we changed the native VLAN to 10 (default is 1) we would need to set both sides of the trunk to native VLAN 10, otherwise you will get syslog messages saying that there is a native VLAN mismatch.

HTH

Jon