Re: Native vlan from router to switch

What mechanism is responsible for such blocking ?

-Carlos

Narbik Kocharians @ 08/12/2011 13:34 -0300 dixit:
> 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
> <mailto: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
> <mailto: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 <mailto:tron_at_huapi.ba.ar>>
> LW7 EQI Argentina
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
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>
>
>
>
>
>
>
>
>
>
> --
> *Narbik Kocharians
> *CCSI#30832, CCIE# 12410 (R&S, SP, Security)
> *www.MicronicsTraining.com* <http://www.micronicstraining.com/>
> Sr. Technical Instructor
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>

-- 
Carlos G Mendioroz  <tron_at_huapi.ba.ar>  LW7 EQI  Argentina
Blogs and organic groups at http://www.ccie.net