Is "switchport trunk allowed vlan all" necessary?

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May 14th, 2007
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What is is purpose of "switchport trunk allowed vlan all" command?


If the port was set to "switchport mode trunk", is it still necessary to use "switchport trunk allowed vlan all" in order to allow all vlans?


Thanks,


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mohammedmahmoud Mon, 05/14/2007 - 06:07
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Hi,


No, all VLANs are allowed by default you don't need this command by default, this command is used to manipulate some design consideration when defining the VLANs that are not allowed to transmit and receive on the trunk port:


This example shows how to define the allowed VLANs list for trunk port Fa0/1 to allow VLANs 1 to 100, VLAN 250, and VLANs 500 to 1005, and how to verify the allowed VLAN list for the trunk:


Switch(config)# interface fa0/1

Switch(config-if)# switchport mode trunk

Switch(config-if)# switchport trunk allowed vlan remove 101-499

Switch(config-if)# switchport trunk allowed vlan add 250

Switch(config-if)# end



HTH, please do rate all helpful replies,

Mohammed Mahmoud.

glen.grant Mon, 05/14/2007 - 06:48
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I think the only reason it is there is if you happened to have a current trunk pruned only to allow a few vlans and then for some reason want to allow them all . By default they are all allowed.

tunemore1 Mon, 05/14/2007 - 08:35
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I think you are right. "Add" and "Remove" are needed but "all" seems a bit redundant.


Hey, I am still hoping somebody will come up with suprise answer. ;)


mohammedmahmoud Mon, 05/14/2007 - 10:47
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Hi,


When configuring a port as trunk, all VLANs are allowed by default, you don't need this command, you'll need it to reset allowed VLANs if for any reason you have formerly removed any.


HTH, please do rate all helpful replies,

Mohammed Mahmoud.

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