Trunk Encapsulation

Unanswered Question
Jul 15th, 2008

We have a Cisco 3640 and Catalyst 3500's adn are using ISL encap for our Trunking Encapsulation. I want to change our encapsulation from ISL to 801.2Q and want to know the steps to complete this. Can I simply change the encapsulation type on the switches and the router or must I recreate all the VLAN's from scratch with the new 802.1Q

I have this problem too.
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Mark Yeates Tue, 07/15/2008 - 12:15

This should just be as easy as changing the encapsulation from isl to dot1q.


switchport trunk encapsulation dot1q


encapsulation dot1q (vlan#)


bmtcisco Tue, 07/15/2008 - 12:56


Thanks for your quick response, I suspected this was what was needed but wanted to be sure

Giuseppe Larosa Tue, 07/15/2008 - 12:40

Hello Chris,

you just need to change the trunk encapsulation protocol on the switch side and router subif configuration (encapsulation command)

Be aware that on the router side you need to go under each subif and use the command encapsulation dot1q

You need to do this for all subifs. If you don't do for one your subif that subif will be isolated.

You can check you are receiving and sending frames on vlans of interest with show vlan on the router shell.

Hope to help



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