switchport trunk encapsulation dot1q vs switchport trunk allowed vlan

[varshenys]

Hi,

please someone tell me the difference of switchport trunk encapsulation dot1q vs switchport trunk allowed vlan

[marce1000]

- There is no difference between the two because both elements are unrelated, encapsulation specified the trunk-protocol as denoted , allowed vlan(s) specifies which vlans are allowed on the trunk.

 M.

[varshenys]

that means I can use both the commands together ?

[marce1000]

 - You can't use them together on the same command line, because they need to execute different things.

 M.

[MHM Cisco World]

there are two protocol tag the frame pass through the Trunk ISL and dot1Q
we use 
switchport trunk encapsulation dot1q 
to specific the protocol dot1q

to config the VLAN allow to pass through the trunk we use the command 

switchport trunk allowed vlan

Yes you can use both command under same port.

[Richard Burts]

The 2 commands are somewhat related but are quite different. If you want a switch port to operate as a trunk then the most important required command is switchport mode trunk. After defining the port as a trunk there are other commands that you might use.

switchport trunk encapsulation dot1q is an optional command that defines the encapsulation type of this trunk. dot1q is the default encapsulation type and the other type is isl. It has been a very long time since I have seen a switch configured to use isl, so the command to set encapsulation type is not used very frequently in live environments.

When a switch port is configured as a trunk, by default all vlans are carried on the trunk. If you want to specify that only certain vlans are to be carried on this trunk you would use the command switchport trunk allowed vlan.