From: ccie2be (ccie2be@nyc.rr.com)
Date: Thu Dec 09 2004 - 18:41:59 GMT-3
James,
I think the issue you raise is the cause of great confusion to many people.
But, the issue I think is one primarily of terminology.
the native and default vlan's refer to different unrelated vlan's and have
different purposes for existing.
The native vlan is only relevant to 802.1q trunks and has nothing to do with
anything else. As you probably know, a packet crossing a 802.1q trunk will
have a vlan tag or it won't. If the packet doesn't have a vlan tag, how
does the switch know what to do with the packet? The answer is the switch
assume the packet is part of the native vlan and switches the packet
accordingly. Which vlan is the native vlan? Whichever vlan YOU make the
native vlan. If you don't explicitly make any vlan the native vlan, the
default vlan is the native vlan.
Now, the default vlan. This, by default, is vlan 1 and I don't think you
can change that. This is the vlan over which the vtp and stp messages
travel. And, from what I understand, even when this vlan isn't allowed over
a trunk, the vtp and stp traffic still goes over the trunk. Only the user
data from vlan 1 doesn't go over the trunk.
If I'm wrong with anything I've said, hopefully, someone will let us know.
HTH, Tim
----- Original Message -----
From: "Keane, James" <James.Keane@agriculture.gov.ie>
To: <ccielab@groupstudy.com>
Sent: Thursday, December 09, 2004 11:11 AM
Subject: 3550 - Default Vlan - Native Vlan & Trunks
> I was asked a fairly straightforward question yesterday
>
> quote
>
> 'let's say you are only allowed to send odd
> VLANs, 3,5,7,9,11, over a trunk, how about the default VLAN ? I think you
cannot disallow the default VLAN 1 unless you set the native VLAN to
> something else, is that right ?'
>
> unquote
>
> I responded with sure you cant disable the vlan you are trunking on .. but
I'll just verify that in the lab...
>
>
> To my astonishment I was able to completely remove vlan 1 from the trunk
while keeping my native vlan as 1..
>
> now the trunk mode on one side reads 'n-802.1q' and '802.1q' on the other.
Not quite sure what the n-802.1q is all about ??!
>
> What is going on ?
>
> One more final thing is buggin me - the default vlan is one and the native
vlan is one - you can change the native ...
>
> ... can you change the default ???
>
>
>
> I thought I understood this topic (grrrr)
>
>
> Any light on this would be greatly appreciated
>
>
> I am going back to practical studies II to revise the basics !!!
>
>
> Regards,
>
> James Keane
>
>
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