Re: Native vlan from router to switch

May be depending on the equipment, the trunk will "form" just fine,
if VLAN hopping is not considered to be a problem :)
CDP may barf. If VLAN 1 is involved, other griefs will pop.

Different problems:
-framing: no problem, but "native VLAN" frames do not signal which VLAN
they belong to, so if they do not match, frames will hop from one VLAN
to the other.

-signalling (DTP): AFAIK, VLANs are not part of the info interchanged,
so the trunk will form even if native is not the same.

-control: (CDP/VTP/STP/...): well, you may have a problem here.
In particular, CDP/VTP go on VLAN 1, so if this is one of the VLANs
involved in the crossing, it won't work.

-Others ?

-Carlos

David Bass @ 08/12/2011 08:25 -0300 dixit:
> The trunk will come up fine, but you won't have IP connectivity between the 2 devices on the VLANs/subnets you are expecting because the 2 native VLANs are being bridged. Do some research on how dot1q trunks work and you should be able to figure it out.
>
>
>
> On Dec 7, 2011, at 11:40 PM, CCIE KID <eliteccie_at_gmail.com> wrote:
>
>> Hi fellas,
>>
>> I tested a scenario where the Native vlan differs from the router port to
>> the switch port. I understood that if the NAtive vlan mismatches on a trunk
>> port , then appropriate trunking wont be formed.
>> But when i connect my router to a switch and in the router subinterface . I
>> am having a native vlan of 20 and in the switch port it is having a native
>> vlan of 10 , but still the trunk is forming perfectly
>>
>> Can someone correct me
>> fa0/1.1 fa0/1
>> Router1-----------------------------------------------Switch 1
>>
>> Router 1
>>
>> inter fa 0/1.1
>> encap dot1q 20 native
>> ip add 10.1.1.1 255.255.255.0
>> no sh
>>
>>
>> Switch 1
>>
>> int fa 0/1
>> enc dot1q 10 native
>> swi trunk enc dot
>> swi mo trunk
>> no sh
>>
>>
>> But s
>>
>> --
>> With Warmest Regards,
>>
>> CCIE KID
>> CCIE#29992 (Security)
>>
>>
>> Blogs and organic groups at http://www.ccie.net
>>
>> _______________________________________________________________________
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>
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-- 
Carlos G Mendioroz  <tron_at_huapi.ba.ar>  LW7 EQI  Argentina
Blogs and organic groups at http://www.ccie.net