Newb VLAN question...

Answered Question
Apr 5th, 2009
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Going over some other questions this morning, I ran into one I had myself but forgot to ask...say we have:


interface FastEthernet1/0/1

switchport trunk encapsulation dot1q

switchport trunk allowed vlan 3,4,6-9,300

switchport mode trunk


---

When you have the cmd

sw mo tr

doesnt that mean all VLANs are allowed? By having the line

switchport trunk allowed vlan 3,4,6-9,300

Is this config not allowing all other VLANs?


Thanks

Correct Answer by lamav about 8 years 3 months ago

Hello:


By default, a dot1q trunk configured on a Cisco device will allow all vlans that are configured on the switch.


You can prune some vlans off the trunk by using the "allowed" keyword.


"doesnt that mean all VLANs are allowed?"

Yes.


"By having the line switchport trunk allowed vlan 3,4,6-9,300 Is this config not allowing all other VLANs?"


Correct. Only vlans 3,4,6,7,8,9 and 300 will be allowed on that trunk.


HTH


Victor

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Correct Answer
lamav Sun, 04/05/2009 - 08:16
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Hello:


By default, a dot1q trunk configured on a Cisco device will allow all vlans that are configured on the switch.


You can prune some vlans off the trunk by using the "allowed" keyword.


"doesnt that mean all VLANs are allowed?"

Yes.


"By having the line switchport trunk allowed vlan 3,4,6-9,300 Is this config not allowing all other VLANs?"


Correct. Only vlans 3,4,6,7,8,9 and 300 will be allowed on that trunk.


HTH


Victor

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