Re: Native vlan from router to switch

Between any two switch if the Native VLAN is mismatched the trunk will come
up but you won't be able to pass any traffic through it, and you can see
that with a "Show spanning block".

On Thu, Dec 8, 2011 at 4:31 AM, David Bass <davidbass570_at_gmail.com> wrote:

> We are talking about CCIE lab, so best practice and "working" status all
> go out the window :). In his scenario he's talking about router to switch
> trunk, so no VTP or STP (if you do this switch to switch you'll definitely
> have issues though, so very good to know)...CDP will definitely bark
> non-stop though which is very irritating.
>
>
>
> On Dec 8, 2011, at 6:08 AM, Carlos G Mendioroz wrote:
>
> > 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
> >>>
> >>> _______________________________________________________________________
> >>> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
> >> Blogs and organic groups at http://www.ccie.net
> >> _______________________________________________________________________
> >> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
> >
> > --
> > Carlos G Mendioroz <tron_at_huapi.ba.ar> LW7 EQI Argentina
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
>
>
>
>
>
>
>
>

-- 
*Narbik Kocharians
*CCSI#30832, CCIE# 12410 (R&S, SP, Security)
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