Native VLAN

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May 19th, 2008
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I understand that Native VLAN which is 1 by default for Cisco, is where the packets are sent untagged. I know that Native VLAN can be changed to other than VLAN 1 for example VLAN 23 or something.

But, what is the purpose of the Native VLAN in the first place? Doesnt the packet get to its appropriate vlan over the trunked link regardless?

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gpulos Mon, 05/19/2008 - 08:38
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Not necessarily.

A native vlan is used, as you've mentioned, to forward packets that do not have a tag when they get to the ingress of the port.

A trunk will forward untagged packets to the native vlan configured.

If a trunk gets a packet that does not have a tag, and there was no native vlan, it would not know how to forward it. This is what the native vlan provides; a way for the trunk to know where to forward the packet if the packet were not tagged.

When the trunk receives a packet without a tag, it forwards it to the native vlan.

Native vlan is defined in a clause in the 802.1Q standard for interoperability with older devices that do not understand 802.1Q.


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