12-13-2012 10:20 AM - edited 03-07-2019 10:35 AM
Hi everyone,
I wouldn't mind getting some clarification on this commant.
By default, a trunk carries ALL Vlans.
My basic question is, if I use the "switchport trunk allowed vlan 4" command, will the trunk DROP traffic from every Vlan except 3?
Eg,
interface GigabitEthernet5/34
description cisco
switchport trunk allowed vlan 109
switchport mode trunk
If I configure the above port in this manner, am I only allowing Vlan109 traffic through?
Thanks
12-13-2012 11:11 AM
Hi,
yes you only enable vlan 109 out the trunk port.
Regards.
Alain
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12-13-2012 11:19 AM
Hi Alain,
I appreciate the response because I read differently on other documents and websites. I read the following comman sets would be required in order to just allow Vlan 109 out of the trunked interface:
interface GigabitEthernet5/34
description cisco
switchport trunk allowed vlan remove 1-108, 110-4094
switchport trunk allowed vlan 109
switchport mode trunk
I assumed the allowed vlan xx command would automatically discard traffic traversing that given interface which does not reside in that specified vlan.
Dan
12-13-2012 11:23 AM
you are correct once you enter the command it will remove all vlans. Just remember if you need to add a 2 or 3 make sure you use the add commnad
interface GigabitEthernet5/34
switchport trunk allowed vlan ADD 110
This would add vlan 110 to the existing vlan 109.
Steve
12-13-2012 11:27 AM
Hi,
you don't need to remove the vlan first.
Regards.
Alain
Don't forget to rate helpful posts.
12-13-2012 01:54 PM
Thank you for the clarification.
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