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native vlan not in database

scottmanzie1
Level 1
Level 1

Hi

 

After a fairly serious spanning-tree issue for a customer, a review is being done around trunk link configrations etc for inconsistencies. Some switches have been found with a native vlan that isnt prese database, not sure if this is an issue or not, seems to be there on a lot of others so far

 

Thanks

1 Accepted Solution

Accepted Solutions

Hello

 


@scottmanzie1 wrote:

Hi

 

After a fairly serious spanning-tree issue for a customer, a review is being done around trunk link configrations etc for inconsistencies. Some switches have been found with a native vlan that isnt prese database, not sure if this is an issue or not, seems to be there on a lot of others so far

 

Thanks


Note - : The native vlan is not switch based, Its link based meaning you can have many native vlans on one switch, it between either side of a trunk, Now if you have a native vlan mismatch on a trunk not only will the switch complain about it stp would probably block due to inconstant vlans ids in their respective received bpdu's ONLY  that is if the mismatch vlan it blocks is traversing the trunk at that time and those same vlans are in the vtp d/b

 

Lastly even in a mismatch control protocols like vtp/dtp/cdp are still able to traverse the trunk.

.

 

 

 

 


Please rate and mark as an accepted solution if you have found any of the information provided useful.
This then could assist others on these forums to find a valuable answer and broadens the community’s global network.

Kind Regards
Paul

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6 Replies 6

balaji.bandi
Hall of Fame
Hall of Fame

yes you need to have native VLAN created in the Database, if you are not using VLAN1 as native VLAN.(this is not best practice to use VLAN1 as native VLAN).

 

 

BB

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Hello

 


@balaji.bandi wrote:

yes you need to have native VLAN created in the Database, if you are not using VLAN1 as native VLAN.(this is not best practice to use VLAN1 as native VLAN).


@balaji.bandi 
I dont think you do, You can successfully establish a trunk without having the specified native vlan on a trunk being actually present it the vtp d/b , it isn't needed to be created unless you actually want an untagged vlan active on your switch access ports for users connect to.


Please rate and mark as an accepted solution if you have found any of the information provided useful.
This then could assist others on these forums to find a valuable answer and broadens the community’s global network.

Kind Regards
Paul

@paul driver , thank you for the headsup . (check my PM)

 

 

BB

***** Rate All Helpful Responses *****

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Hello

 


@scottmanzie1 wrote:

Hi

 

After a fairly serious spanning-tree issue for a customer, a review is being done around trunk link configrations etc for inconsistencies. Some switches have been found with a native vlan that isnt prese database, not sure if this is an issue or not, seems to be there on a lot of others so far

 

Thanks


Note - : The native vlan is not switch based, Its link based meaning you can have many native vlans on one switch, it between either side of a trunk, Now if you have a native vlan mismatch on a trunk not only will the switch complain about it stp would probably block due to inconstant vlans ids in their respective received bpdu's ONLY  that is if the mismatch vlan it blocks is traversing the trunk at that time and those same vlans are in the vtp d/b

 

Lastly even in a mismatch control protocols like vtp/dtp/cdp are still able to traverse the trunk.

.

 

 

 

 


Please rate and mark as an accepted solution if you have found any of the information provided useful.
This then could assist others on these forums to find a valuable answer and broadens the community’s global network.

Kind Regards
Paul

thanks Paul

 

Interesting you mention the inconstent vlan ID, that was what happened during the fault that has led to this config review for the partiular customer.

 

During the fault the core 3850 blocked the port-channel linked to a stack of 2960's, it wasnt due to bad config of the native vlan on the interfaces though, it was because the native vlan was in a shutdown state at L2 on the 3850.Strangely it had always been that way, but opening it stopped the issue immediately

 

 

Hello

That's interesting to hear, I have just replicated a SW-SW PC and shutdown the L2 native vlan I specified and it didn't error the way you mention.

 

But what i did noticed is on creation of the port-channel and specifying a native vlan NOT in to vtp d/b  it reports an error to say the vlan is not created, However on a normal trunk it allows you to specify a native vlan without it being it the vtp d/b

 

Lastly after creation of the PC I first shutdown the vlan and all was fine and then  i removed it entirely from the vtp d/b and it still didn't error even after i shutdown /restarted both the physical and logical interfaces.

 

So going back to what i first stated that you dont really need to have vlan in the D/B to specify the native vlan isn't quite correct, you may require it on first creation of L2 PC but after that you dont which was my understanding.

 

I wonder if anyone else has any thoughts on this?

 

 

 


Please rate and mark as an accepted solution if you have found any of the information provided useful.
This then could assist others on these forums to find a valuable answer and broadens the community’s global network.

Kind Regards
Paul
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