Re: Native vlan from router to switch

Your question was answered. A few times.

CCIE # 23962 (SP)

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On 09 Dec 2011, at 7:40 AM, CCIE KID <eliteccie_at_gmail.com> wrote:

> Hi all,
>
> Still my question has not been answered. What will happen if a router
> connected to a switch is placed in two different native Vlans. U guys are
> all talking about connecting two switches and incorporating two different
> native vlans.
>
> My scenario is simple. R1-----------------------Sw1
>
> I m using two different native vlans from R1 to Sw1 . Whether trunk will
> form.? Or if the trunk forms, whether user traffic will be able to pass
> through or not.
>
> Please reply to my questions
>
> Thank You
>
> On Fri, Dec 9, 2011 at 4:23 AM, George J. Sanchez <marco207p_at_gmail.com>wrote:
>
>> I've seen plenty of customers networks with native vlan mismatches,
>> traffic will pass. With that being said, newer code may fix different
>> "features" that previous codes had issues with.
>>
>> Regards,
>> Joe Sanchez
>>
>> On Dec 8, 2011, at 1:28 PM, Narbik Kocharians <narbikk_at_gmail.com> wrote:
>>
>>> This is what i was referring to:
>>>
>>>
>>> R1 s F0/0 is connected to SW1 s port F0/1
>>>
>>> R2 s F0/1 is connected to SW2 s port F0/2
>>>
>>>
>>> SW1 s F0/19 is connected to SW2 s F0/19
>>>
>>>
>>> *SW1#sh run int f0/19 | B inter*
>>>
>>> interface FastEthernet0/19
>>>
>>> switchport trunk encapsulation dot1q
>>>
>>> switchport trunk native vlan 10
>>>
>>> switchport mode trunk
>>>
>>> end
>>>
>>> *
>>> *
>>>
>>> *SW2#sh run int f0/19 | B inter*
>>>
>>> interface FastEthernet0/19
>>>
>>> switchport trunk encapsulation dot1q
>>>
>>> switchport mode trunk
>>>
>>> end
>>>
>>>
>>> *NOTE: The trunk is UP*
>>>
>>>
>>> *SW1#Show int trunk*
>>>
>>>
>>> Port Mode Encapsulation Status Native vlan
>>>
>>> Fa0/19 on 802.1q trunking 10
>>>
>>>
>>> Port Vlans allowed on trunk
>>>
>>> Fa0/19 1-4094
>>>
>>>
>>> Port Vlans allowed and active in management domain
>>>
>>> Fa0/19 1,10,80
>>>
>>>
>>> Port Vlans in spanning tree forwarding state and not pruned
>>>
>>> Fa0/19 1,10,80
>>>
>>>
>>>
>>> *SW2#sh spanning-tree blockedports *
>>>
>>>
>>> Name Blocked Interfaces List
>>>
>>> -------------------- ------------------------------------
>>>
>>> VLAN0001 Fa0/19
>>>
>>> VLAN0010 Fa0/19
>>>
>>>
>>> Number of blocked ports (segments) in the system : 2
>>>
>>>
>>> *All Traffic is blocked for the two Vlans.*
>>>
>>> *And sure you can get around it, and one way to do this is to filter
>> BPDUs
>>> that carry the VLANs as you mentioned:*
>>>
>>>
>>> SW1(config)#int f0/19
>>>
>>> SW1(config-if)#spanning-tree bpdufilter en
>>>
>>>
>>> *SW1#sh spannin blockedports *
>>>
>>>
>>> Name Blocked Interfaces List
>>>
>>> -------------------- ------------------------------------
>>>
>>>
>>> Number of blocked ports (segments) in the system : 0
>>>
>>>
>>> *And I am sure there are other ways. But remember this is the default
>>> behavior BUT not on all IOSes, on some IOSes, it will complain that there
>>> is a Native VLAN mismatch, but it will NOT block the VLANs configured as
>>> Native*
>>>
>>>
>>> On Thu, Dec 8, 2011 at 10:35 AM, Narbik Kocharians <narbikk_at_gmail.com
>>> wrote:
>>>
>>>> Yes, you are correct, you can get around it, i was referring to the
>>>> default behavior.
>>>>
>>>>
>>>> On Thu, Dec 8, 2011 at 9:23 AM, Paul Cocker <paul.cocker_at_gmx.com>
>> wrote:
>>>>
>>>>> Spanning-tree...
>>>>>
>>>>> I'm guessing the vlan is in the bpdu.
>>>>>
>>>>> with this config...
>>>>>
>>>>> SW1
>>>>> interface FastEthernet0/13
>>>>> switchport trunk encapsulation dot1q
>>>>> switchport trunk native vlan 10
>>>>> switchport mode trunk
>>>>> switchport nonegotiate
>>>>>
>>>>> SW2
>>>>> interface FastEthernet0/13
>>>>> switchport access vlan 20
>>>>> switchport trunk encapsulation dot1q
>>>>> switchport trunk native vlan 20
>>>>> switchport mode trunk
>>>>> switchport nonegotiate
>>>>> no cdp enable
>>>>>
>>>>>
>>>>> you get this...
>>>>>
>>>>> *Mar 1 00:18:26.994: %SPANTREE-2-RECV_PVID_ERR: Received BPDU with
>>>>> inconsistent peer vlan id 10 on FastEthernet0/13 VLAN20.
>>>>> *Mar 1 00:18:26.994: %SPANTREE-2-BLOCK_PVID_LOCAL: Blocking
>>>>> FastEthernet0/13 on VLAN0020. Inconsistent local vlan.
>>>>>
>>>>> You can disable spanning tree, or use bpdufilter to get around it.
>>>>>
>>>>>
>>>>> On 08/12/2011 16:58, Carlos G Mendioroz 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
>>>>>>>>>>
>>>>>>>>>>
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>>>>>>>>
>>>>>>>> --
>>>>>>>> Carlos G Mendioroz <tron_at_huapi.ba.ar <mailto:tron_at_huapi.ba.ar>>
>>>>>>> LW7 EQI Argentina
>>>>>>>
>>>>>>>
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>>> CCIELab.html>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>> *Narbik Kocharians
>>>>>>> *CCSI#30832, CCIE# 12410 (R&S, SP, Security)
>>>>>>> *www.MicronicsTraining.com*
>>> <http://www.micronicstraining.**com/<http://www.micronicstraining.com/>
>>>>>>>>
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>>>>>>> YES! We take Cisco Learning Credits!
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>>>>>>
>>>>>
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>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>> *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
>>>>
>>>>
>>>
>>>
>>> --
>>> *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
>>>
>>>
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>
>
> --
> With Warmest Regards,
>
> CCIE KID
> CCIE#29992 (Security)
>
>
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Received on Fri Dec 09 2011 - 07:55:56 ART