Re: Native vlan from router to switch

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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> >>>>>
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> > CCIELab.html>
> >>>>>>
> >>>>>> --
> >>>>>> Carlos G Mendioroz <tron_at_huapi.ba.ar <mailto:tron_at_huapi.ba.ar>>
> >>>>> LW7 EQI Argentina
> >>>>>
> >>>>>
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> 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!
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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
> >
> >
> > Blogs and organic groups at http://www.ccie.net
> >
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-- 
With Warmest Regards,
CCIE KID
CCIE#29992 (Security)
Blogs and organic groups at http://www.ccie.net