I have an MP70 and a Cisco switch.
On the MP70 Gateway, I use the LAN > WAN configuration to add my two VLANs, with Id’s of 20 and 199.
I enter the Device IP for each VLAN (10.192.20.1 and 10.199.192.6 and the correct masks.
I hit apply and save, and reload.
There is a good cable connecting eth1 of the MP70 to fa/21 of the Cisco router.
The Cisco switch has a trunked(Tagged) port fa/21 with VLANs20 and 199 allowed. The port mode is set to “trunk”
Neither the Cisco or the MP70 can see each others MAC address.
I have read the VLAN sectionn in the official manual for these devices (41112975_ALEOS 4.11.2 Software Configuration User Guide for AirLink MP70_r1.pdf) and it should be possible according to that.