From: Church, Chuck (cchurch@netcogov.com)
Date: Mon May 09 2005 - 11:52:45 GMT-3
I would believe it's for safety, since it makes it impossible to
accidentally bridge 2 VLANs together due to a native VLAN mismatch. But
keep in mind that the native VLAN carries important frames like CDP,
non-PVST BPDUs, PAGP, DTP, etc. A device that doesn't understand tagged
native VLAN might not interoperate correctly. I think the most
compatible method is going to be leaving the native VLAN as 1, not
tagging it, but never using it either. Just use the other
4090-something VLANs...
Chuck Church
Lead Design Engineer
CCIE #8776, MCNE, MCSE
Netco Government Services - Design & Implementation Team
1210 N. Parker Rd.
Greenville, SC 29609
Home office: 864-335-9473
Cell: 703-819-3495
cchurch@netcogov.com
PGP key: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x4371A48D
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Brant I. Stevens
Sent: Sunday, May 08, 2005 4:34 PM
To: James Ventre; ccielab@groupstudy.com
Subject: Re: Native vlan
I was under the impression that true 802.1q-compliant systems do not tag
the
native VLAN whatsoever, but Cisco provided that knob for vendors that
did
not exactly comply with the spec (or was it that they themselves didn't
adhere religiously to the spec on some of their gear? Or is it nostalgia
for
ISL?)
Thanks for the clarification regarding the use of dynamic trunking mode.
On 5/7/05 7:57 PM, "James Ventre" <messageboard@ventrefamily.com> wrote:
> That depends on your trunking configuration.
>
> Set you trunk to desirable, and you can have a native vlan if you're
> trunking, and a different vlan if it's not trunking. The native VLAN
on
> a trunk is just the VLAN that is untagged. If you hardcode the trunk
to
> "on" then your explaination applies.
>
> Here is an example:
>
> interface FastEthernet0/2
> switchport access vlan 5
> switchport mode dynamic desirable
> !
>
> If you're trunking, the native VLAN is 1. If you're not trunking, the
> access VLAN is 5.
>
>
> You don't have to have an "untagged" native vlan on 802.1Q trunks -
this
> command makes all vlans tagged:
> switch(config)#vlan dot1q tag native
>
>
>
> James
>
>
>
>
>
>
>
>
> Brant I. Stevens wrote:
>
>> The native VLAN of a trunk link is the port assignment of a given
>> port/interface should it not be trunking. With 802.1q, frames
originating
>> from the native vlan are not tagged with a VLAN assignment as they
cross the
>> trunk link; you don't really have a choice to not use a native VLAN.
If you
>> do not explicitly set the native VLAN of a trunk, it is left in the
default
>> VLAN (1).
>
>
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