Re: Native vlan from router to switch

Spanning-tree will block traffic for every VLAN.

On Thu, Dec 8, 2011 at 8:58 AM, Carlos G Mendioroz <tron_at_huapi.ba.ar> wrote:

> 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
>> >>>
>> >>>
>> ______________________________**______________________________**
>> ___________
>> >>> Subscription information may be found at:
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>> >>
>> ______________________________**______________________________**
>> ___________
>> >> Subscription information may be found at:
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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
>>
>> ______________________________**______________________________**
>> ___________
>> Subscription information may be found at:
>> http://www.groupstudy.com/**list/CCIELab.html<http://www.groupstudy.com/list/CCIELab.html>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> --
>> *Narbik Kocharians
>> *CCSI#30832, CCIE# 12410 (R&S, SP, Security)
>> *www.MicronicsTraining.com* <http://www.micronicstraining.**com/<http://www.micronicstraining.com/>
>> >
>>
>> Sr. Technical Instructor
>> YES! We take Cisco Learning Credits!
>> Training & Remote Racks available
>>
>>
> --
> Carlos G Mendioroz <tron_at_huapi.ba.ar> LW7 EQI Argentina
>

-- 
*Narbik Kocharians
*CCSI#30832, CCIE# 12410 (R&S, SP, Security)
*www.MicronicsTraining.com* <http://www.micronicstraining.com/>
Sr. Technical Instructor
YES! We take Cisco Learning Credits!
Training & Remote Racks available
Blogs and organic groups at http://www.ccie.net