From: Erick Bergquist (ebergquist@ameritech.net)
Date: Sat Feb 18 2006 - 15:51:58 GMT-3
Do you have the global command configured below?
vlan dot1q tag native
Use the vlan dot1q tag native global configuration
command to enable tagging of native VLAN frames on all
IEEE 802.1Q trunk ports. Use the no form of this
command to return to the default setting.
vlan dot1q tag native
no vlan dot1q tag native
--- Hiro Eiji <hpnkpn103@yahoo.co.jp> wrote:
> Hi,
>
> I have a question about how native vlan works on
> cisco catalyst switches.
>
> My understanding about native vlan was that the
> native vlan packets are
> always sent untagged on the 802.1Q trunk link.
>
> I had a chance to capture native vlan packets on a
> 802.1Q trunk link the
> other day.
> To my surprise, the captured data showed the result
> otherwise.
> The native vlan packets were in fact tagged with the
> native vlan ID.
>
> Here is the topology that I used.
>
> Cat3550 - Damn Hub - Cat3550
> |
> My PC
>
> When I changed the native vlan ID to 50 at both
> ends, the native vlan
> packets were tagged with vlan ID 50.
>
> Those native tagged vlan packets included the STP
> BPDUs, CDP frames
> and ICMP packets between native vlan segments.
>
> Has anyone experienced similar phenomena or have any
> idea why those native
> vlan packets are tagged?
> Or if someone could possibly run a quick test on the
> equipment and see if
> native vlan packets are tagged,
> that would be highly appreciated. ( and if you do,
> pls make sure you use
> non-intel NIC to capture the packets.
> Otherwise you cannot see the vlan tags ).
>
> Thanks,
>
> Hiro Eiji
>
>
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