Should native VLAN be allowed on trunk?

Unanswered Question
Oct 20th, 2009
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Hi,


We use a dedicated VLAN as the native VLAN for trunk ports on our Catalyst switches. This VLAN is not used on any access ports. Is there any advantage of allowing this VLAN over the trunk or could we only allow the VLANs used by hosts?


In other words, in the example below, is there a reason to add VLAN 82 to the "switchport trunk allowed vlan" list?


interface GigabitEthernet0/1

description Trunk to XXXXX

switchport mode trunk

switchport nonegotiate

switchport trunk native vlan 82

switchport trunk allowed vlan 16,18,20,22,24


Thanks in advance for your help!


Best regards,


Harry


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Jon Marshall Tue, 10/20/2009 - 04:42
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Harry


No there isn't really any reason as no traffic should be untagged across the trunk.


Jon

Jon Marshall Tue, 10/20/2009 - 05:27
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Harry


Just as a side note to this - DTP uses the native vlan but as you have disabled DTP this shouldn't be a problem.


Jon

jbrenesj Tue, 10/20/2009 - 09:31
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Agree, but two more things to add.

UDLD causes issues if the native VLAN is not allowed and I remember something when you combine PVST+ and MST between two switches via trunks not having the native VLAN allowed. They are backwards compatible but I have seen weird issues due to this and the native VLAN not being allowed.

Since you are not in these corner cases they are good.

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