Re: Native VLAN

Muzammil,

My understanding is that we are not to run native VLAN on trunks unless
absolutely required to. Or to explicitly tag the native VLAN using 3vlan
dot1q tag native2 from global config as a security precaution against VLAN
hopping. Check this out:
http://www.cisco.com/en/US/products/hw/switches/ps708/products_white_paper09
186a008013159f.shtml#wp39211

This behavior can be tested in a lab pretty easily. In fact, I will do it
myself now because you got me wondering about dynamic trunk negotiation and
how the interface behaves when trunk negotiation fails and 3tag native2 is
configured....will native network traffic still flow across the segment? My
pat answer is 3no2...so VLAN information is completely irrelevant (native or
not, the interfaces will be shut or flapping maybe). But I should verify
before claiming...

John

On 5/18/10 1:44 PM, "Muzammil Malick" <malickmuz_at_gmail.com> wrote:

> Hi guys
>
> So I know many people will have asked this already and i have read some
> posts int he archive.
> However I am still not clear.
>
> My understanding is that the native vlan is used over a trunk link to sent
> traffic untagged.
>
> 1)Can somebody provide a practical example of why you would want to send
> untagged traffic across the trunk.
>
> 2) I have also read in the archives that one of the reasons for using a
> native vlan is to send management traffic
> across a trunk, and if the trunk loses its trunk status the traffic will
> continue to flow because it is untagged.
> What does this statement mean when it says "the trunk loses its trunk
> status?"
>
> Thanks in advance
>
>
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Received on Tue May 18 2010 - 14:01:02 ART