Router-on-Stick 802.1Q - VLAN Configuration

[snarayanaraju]

Hello Friends.

I know how Router-on-Stick 802.1Q configuration works and how to configure it as well.

But i am wondering how it works without i am creating a VLAN Database or VLAN. I am just configuring the interfaces with command  "encapsulation dot1Q 12", But i have not created VLAN 12 in the router.

How does router differentiate between VLAN if the VLAN information is not there in the VLAN database or Configuration.

Can you help me in understanding this basics. Thanks in advance

regards,

SAIRAM

[Jan Hrnko · Accepted solution]

Hi Sairam,

You don't need the VLANs configured in any way. In fact, it doesn't make any sense as with routed interface, all VLANs are terminated on that very interface - all VLAN information is removed (decapsulated and encapsulated in a completely new frame). After all, router is a L3 device, it can't switch frames on its routed interfaces.

But i am wondering how it works without i am creating a VLAN Database or  VLAN. I am just configuring the interfaces with command  
"encapsulation dot1Q 12", 
But i have not created VLAN 12 in the router.

By issuing this command, you are saying that on that very interface all incoming frames with VLAN tag 12 present will be processed by that subinterface. In addition, any correspoding frames leaving that subinterface will have VLAN tag 12 applied to them. You don't need a database for that. You are simply marking sent frames with VLAN tag 12... and all frames received with VLAN tag 12 are processed on matching subinterface.

If you have any further questions, or I didn't make it clear enough, please feel free to ask!

Best regards,

Jan

[snarayanaraju]

Thank you Jan for your prompr response.

[Jan Hrnko]

Sairam,

you are welcome! Please, if you have any more thoughts or questions, don't hesitate to ask!

Best regards,

Jan