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Vlan Trunking Configurations

Posted on 2011-09-22
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Last Modified: 2012-05-12
It is my understanding that a switch port can be either access or trunk port and not both at the same time.  When you configure a port as "switchport mode trunk", the configuration on the same port of "swithport ccess vlan xx" will be ignored because it has no consequence or noeffect

Looking at the configuration below, I notice the port in question is in trunk mode even though the command did not explicitly set the port to trunk

sh run int g0/2
Building configuration...

Current configuration : 109 bytes
!
interface GigabitEthernet0/2
 switchport access vlan 5
 switchport trunk native vlan 5
 no ip address
!

sh int status
Gi0/2  connected    trunk      a-full a-1000 10/100/1000BaseTX

My question is; does the command " switchport trunk native vlan" turn trunking to on just as the command "switchport mode trun"?

Thanks
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Question by:donemore2003
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Soulja earned 500 total points
ID: 36582489
No. When you don't use either of the mode commands the port is essentially dynamic. It the port above connects to another trunk port, it will negotiate into a trunk and have vlan 5 as its native. Otherwise, it is an access port in vlan 5. This is why is it best to put ports in a certain mode to insure they remain that way.
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by:Soulja
ID: 36582500
You can confirm what I am saying by entering:

sh interface gig0/2 switchport
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by:Soulja
ID: 36582620
Just to add:

switchport mode trunk or switchport mode access sets to port to a static access or trunk port. In the case of switchport mode trunk, it is still possible for it to try to negotiate with other dynamic ports so you add the command switchport trunk nonnegotiate to keep it from sent DTP packets.
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by:donemore2003
ID: 36582810
Thank you Soulja.  Thanks for pointing out that by not specifying the mode, the port can either be access or trunk depending on what is connecting to that port.
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