Native VLAN

Unanswered Question
Jan 1st, 2009
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Hi Everybody,


Can anybody explain the why native VLAN in necessary and what for it is used.


I have gone through various articles and i am literally confused the actual need of Native VLAN.


Everybody is saying the same explanation that Native VLAN is untagged VLAN. Why this traffic has to be sent in trunk link with untagged.


regards,


R.B.Kumar

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Giuseppe Larosa Thu, 01/01/2009 - 06:36
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Hello R.B. Kumar,

in the IEEE 802.1Q standard the untagged native vlan is provided for compatibility with NICs that doesn't support vlan tagging.


In this way connecting a non vlan tagging capable device to a 802.1Q trunk port the device is still able to communicate over the native vlan.


802.1Q introduces a vlan tag just after the source mac address: from ethernet point of view a vlan tagged PDU is not an IPv4 packet but has a different ethertype that of 802.1Q


da|sa|802.1Q ethertype|vlanid!CoS|ip ethertype


an old device that is not able to handle the 802.1Q ethertype (0x8100) just discards tagged frames




Hope to help

Giuseppe



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