From: George Goglidze (goglidze@gmail.com)
Date: Wed Jan 23 2008 - 20:32:32 ARST
Hi there,
Having native vlan tagging, does not mean when the switch receives untagged
frame it will not understand it is for native vlan.
also, when another switch receives tagged traffic for vlan 1, it will just
untag it and it will still work.
the only problem would be if you had different native vlan's on both sides.
Regards,
On Jan 23, 2008 10:10 AM, YourPal <dearprudence28@gmail.com> wrote:
> Dear Group,
>
> I have a scenario relating to the implication of "vlan dot1q tag native"
> command. My simple setup is as follows:
>
> SW3 (Gi0/19) -------------802.1Q------------- (Gi0/19) SW4
>
> 1. The native VLAN of the 802.1Q trunk between SW3 and SW4 is VLAN 1.
> 2. SW3 has dot1q native vlan tagging disabled by default. SW4 has it
> explicitly enabled.
> 3. Question is, why SW3's Vlan1 SVI can still ping to SW4's Vlan1 SVI?
>
>
> Please see outputs below:
>
> SW3
> ---
> SW3#sh int tru
>
> Port Mode Encapsulation Status Native vlan
> Gi0/19 on 802.1q trunking 1
>
> SW3#sh vlan dot1q tag native
> dot1q native vlan tagging is disabled
>
> SW3#sh run int vl1
> Building configuration...
>
> Current configuration : 53 bytes
> !
> interface Vlan1
> ip address 1.1.1.3 255.0.0.0
> end
>
> SW3#pi 1.1.1.4
>
> Type escape sequence to abort.
> Sending 5, 100-byte ICMP Echos to 1.1.1.4, timeout is 2 seconds:
> !!!!!
> Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms
>
>
> SW4
> ---
> SW4#sh int tru
>
> Port Mode Encapsulation Status Native vlan
> Gi0/19 on 802.1q trunking 1
>
> SW4#sh vla dot tag native
> dot1q native vlan tagging is enabled
>
> SW4#sh run int vl1
> Building configuration...
>
> Current configuration : 53 bytes
> !
> interface Vlan1
> ip address 1.1.1.4 255.0.0.0
> end
>
> SW4#pi 1.1.1.3
>
> Type escape sequence to abort.
> Sending 5, 100-byte ICMP Echos to 1.1.1.3, timeout is 2 seconds:
> !!!!!
> Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms
>
>
>
>
> I was under the impression that SW4, with native vlan tagging enabled,
> will
> drop any untagged frames that it receives on a 802.1Q trunk. In this case,
> SW3 sends untagged frames (belonging to VLAN 1) to SW4. SW4 should be
> expecting ingress VLAN 1 frames to be tagged. Hmm...I must be missing some
> obvious points.
>
> Kindly enlighten.
>
>
> Thank you.
>
> BR,
> Emil
>
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