11-06-2018 05:07 AM - edited 03-08-2019 04:33 PM
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
Solved! Go to Solution.
11-06-2018 06:10 AM - edited 11-06-2018 06:57 AM
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.
.
11-06-2018 05:44 AM
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).
11-06-2018 07:04 AM - edited 11-06-2018 07:06 AM
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.
11-06-2018 07:45 AM
11-06-2018 06:10 AM - edited 11-06-2018 06:57 AM
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.
.
11-07-2018 04:44 AM
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
11-07-2018 06:25 AM - edited 11-07-2018 06:26 AM
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?
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