In Routeros，The characteristics of QinQ，Not in accordance with the IEEE802.1ad，Hope can provide modified outer Ethernet TPID options，Almost all manufacturers QinQ protocol number is 0x8100,However, you can modify the QinQ outer TPID，I want to change into 0x88a8，Hope Routers can also provide the option。thanks！
You can do this on RouterOS.
Simply set the “use-service-tag” option on the outer vlan.
See http://wiki.mikrotik.com/wiki/Manual:Interface/VLAN#Q-in-Q
Thanks！！！
If you can provide a custom is better? A few manufacturers is 0x9100