Native Vlan

Hi,

Native vlan are a bit confusing.. i am trying to understand Native Vlans and untagged traffic.
I have been searching and im unable to find what exactly is a native vlan, all i find is that native vlan is used for untagged traffic and that you should not use Native vlan 1, because it leaves your network vulnerable to certain types of attacks (EX: Double tagging).

if all access ports are configured to access vlan x why do i need Native Vlan?
if trunk ports need a Native Vlan, than this means that all allowed Vlans in the trunk go through Native Vlan .

This is what is confusing me, and i dont understand why the need of Native Vlan if for example we dont have untagged traffic in a given network and we not use ip phones.

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Comments

Dieg0M

The concept of native VLAN only applies if the port operational state is set to be a trunk. In the case of access ports, the traffic will always be untagged. As for voice VLAN's, they will use a similar concept to trunk ports and the Data VLAN will be considered as native.

Gngogh

Dieg0M wrote: »

In the case of access ports, the traffic will always be untagged.

By default they are untagged because they belong to vlan 1 which is the native. but if they are in any other vlan that is not the native they are tagged with the vlan id, so the traffic will be tagged.

Now you are confusing me...

Dieg0M

No. An access port will only participate in the VLAN to which it has been assigned to and data will not be tagged. In the case of trunk ports they will use an 802.1q or ISL encapsulation to tag the packets between devices.

davenull

it looks like the 802.1q concept of native vlans was introduced to provide backward compatibility with devices that may not support vlan tagging

OfWolfAndMan

davenull wrote: »

it looks like the 802.1q concept of native vlans was introduced to provide backward compatibility with devices that may not support vlan tagging

Boom goes the dynamite.

Gngogh

Dieg0M wrote: »

No. An access port will only participate in the VLAN to which it has been assigned to and data will not be tagged. In the case of trunk ports they will use an 802.1q or ISL encapsulation to tag the packets between devices.

ok.. i understand now how tagging works. thanks for your help.

mikeybinec

Another example of untagged traffic is CDP