ether1 is used as IP-passthrough (LTE) and connected to a WAN port of my Ubiquiti router.
There is also a management vlan on that ether1 interface.
Now I wanted to use ether2 and ether3 in the same IP range as my other devices managed by my Ubiquiti Router (with the dhcp server).
So I assume I will need A second VLAN on ether1 for this purposes, but how should I do it?
Should I simply modified the default vlan id of the ports? How could I bridge (is it the right word?) them to the ether1 interface???
The hardware VLAN support in the MT7621 switch chips is not compatible with RouterOS, so you’ll have to use bridging in software. As you want ether2, ether3 to be access ports to the VLAN which has to be tagged on ether1, you have to use a bridge with vlan-filtering=yes (the name of the feature is slightly misleading).
The exact configuration steps required depend on the current configuration of the device, so if you need a step-by-step guide, you’ll have to follow the hint in my automatic signature here below. In any case, it is easy to lock yourself out of the device, so use safe mode, or configure and verify management access via one of (ether2, ether3) before touching the ether1 & vlan configuration, or configure and verify access via serial console (using an usb to serial converter).