Anna,
You can daisy-chain switches that are connected with dot1q-tunnel ports, meaning that each subsequent device will push its own 802.1Q tag onto the existing frame and its tag stack. However, I am not sure if you can push multiple 802.1Q tags at once. Do you need anything like that? What types of switches are you using?
Do you really need to use Q-in-Q-in-Q, though? While possible, it is not a common scenario. Perhaps what you need to accomplish can be solved by other means. Can you be more specific why you need this? You also must be aware of the fact that with each 802.1Q tag, the frame gets bigger by 4 bytes, and you may start hitting the maximum supported frame size on your switches. Frames cannot be fragmented, meaning that if an additional 802.1Q tag causes the frame to become overly large, it will be dropped.
Best regards,
Peter
