Re: Allowed vlan's in Trunk

From: Paul Cosgrove (paul.cosgrove@heanet.ie)
Date: Mon Jun 23 2008 - 18:45:52 ART

Hi Sadiq,

You mentioned vlan 1, but not what happens when the native vlan is
changed to something else and neither of these vlans are in the allowed
list (this is what CCIE3000 referred to).

Layer 2 control protocols are permitted on vlan 1 and the native vlan,
even if you do not add the native vlan in the allowed list.

DTP (both tagged and untagged as I recall) and VTP will be sent on the
native vlan of the interface. STP is sent on vlan 1, the native vlan
and any other permitted vlans.

Paul

Sadiq Yakasai wrote:
> Sorry CCIE3000,
>
> LOL!! So what exactly are you saying here? I have read this 3 times and
> still cant figure out what your conclusion/question/concern/confusion (if
> any) is... :)
>
> Please can you clarify a little bit more?
>
> Thanks
>
> Sadiq
>
>
CCIE3000 wrote:
> Yep, this is true...but even when you use another vlan as native and remove
> that vlan it still works okay.
>
> I've been reading through the docs but haven't found anything to explain why
> yet.
>
> Stop the press........
>
> Reading Sadiq's post got me thinking.
>
> Okay, I've got a SVI for vlan 3 on both switches, with trunk between them,
> no etherchannel
>
> Native vlan is 3, but only 4 and 5 are permitted.
>
> Okay, trunk stays up but you are unable to ping between the two SVI's.
>
> I'm in uncharted territory here so I hope the following isn't complete bull.
> So the switch trunk allowed vlan stops the data traffic but doesn't stop the
> control traffic for the trunk.
>
> As I said, Sadiq's post caused the light bulb to switch on.
>
> How's that sound?
>
>
> On 6/23/08, A.G. Ananth Sarma (GMail) <ananth.sarma@gmail.com> wrote:
>> Hi,
>>
>> it is not the question of permitting. In the first place, you cannot remove
>> VLAN 1.
>>
>> See note below:
>>
>>
>> ------------------------------
>> *Note *VLANs 1 and 1002 to 1005 are reserved and cannot be removed.
>>
>>
>> http://www.cisco.com/en/US/docs/switches/lan/catalyst2900xl_3500xl/releasesa4/eesoftconfig/masctrnk.html
>>
>> *Section: Defining the Allowed VLANs on a Trunk*
>>
>>
>> HTH,
>>
>> Ananth
>>
>>
>> On Mon, Jun 23, 2008 at 5:46 PM, CCIE3000 <ccie3000@googlemail.com>
>> wrote:
>>
>>> Hi Guys,
>>>
>>> If you have a question that states to only allow the necessary vlans
>>> across
>>> the trunk and the native vlan is vlan 1 would you permit vlan 1 as well as
>>> the other necessary vlan's?
>>>
>>> I'm just about to play on the switches now but I thought I'd throw it up
>>> for
>>> discussion.
>>>
>>> Cheers.
>>>
>>>
>>> _______________________________________________________________________
>>> Subscription information may be found at:
>>> http://www.groupstudy.com/list/CCIELab.html
>
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
>
>
>
>
> 

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