QinQ termination and VPLS question

What happens after a frame gets QinQ terminated? Is it then assigned to vlan 1 by default?

If a frame is qinq tagged when it goes INTO interface 0/1, then what happens to another frame that goes OUT of fa0/1 ? Is it just going to pass through unaffected?

Does tagging occur when a frame enters or leave an interface?
I am confused.

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Comments

networker050184

Depends on what you mean by terminating. Usually the top level tag will be stripped off before passing onto whatever device is going to read the lower level VLAN. Sometimes it terminates into an L3 interface where both tags are stripped. It just all depends on the setup.

Usually you have the top level tag applied on ingress and stripped on egress. Again it just depends on what your end goal is.

Is there something specific you are trying to figure out?

hitmen

In my company qinq termination, both the tags are stripped off. However, I am not sure what happens after that and how it recovers its original Cvlan .

networker050184

It just depends on the setup. Hard to say without info on how this is setup.

Jackace

In the cisco switch world packets don't get tagged until they leave a trunk port.

phonic

Jackace wrote: »

In the cisco switch world packets don't get tagged until they leave a trunk port.

Technically, that's how all 'tagging' is handled. Tagged frames only exist on the wire. Once they come into the switch (or any VLAN aware interface), they are simply considered part of a particular VLAN. It doesn't matter whether they were originally tagged or native.

For QinQ, my understanding is that it is handled more or less like normal tagged traffic, albeit with an extra tag. Once the outer layer is stripped, the other VLAN information is processed however it is configured on the network. For example, one of our customers use a Metro-E that supports QinQ and we trunk a particular WAN circuit across the Metro-E using a VLAN to provide a public IP to a remote PBX system. When it comes out of the Metro-E on the far side, it goes into a switch that then has a designated port configured to be an access port on that VLAN where we plug the PBX into. So from a topology standpoint, it goes U40->T40->T40+T??->T40->U40, but that's just how we have it configured.

hitmen

I dont understand your U40 and T40.
Anyway does qinq termination strip off only the outer tag or both?
I have quite a hard time understanding this.

srg

hitmen wrote: »

I dont understand your U40 and T40.
Anyway does qinq termination strip off only the outer tag or both?
I have quite a hard time understanding this.

"QinQ termination" will generally strip both tags.