Configure VLANs on Asus RT-AC65P

[Technocrat]

I'm trying to setup VLANs on the router. I have two ISP lines and would like to use both of them with mwan3 module.
For that I need to make an additional WAN port from one of LAN ports. The problem here is that the Switch tab is not available in Network section of Luci.
I tried to add the Switch section in /etc/config/network like below, but after that LAN stopped to work, so I removed it.

config 'switch' 'eth0'
        option 'enable' '0'
        option 'enable_vlan' '0'
        option 'reset' '1'

Available interfaces on the router:

ls -l /sys/class/net

lrwxrwxrwx    1 root     root             0 May 13 19:55 br-lan -> ../../devices/virtual/net/br-lan
lrwxrwxrwx    1 root     root             0 Jan  1  1970 eth0 -> ../../devices/platform/1e100000.ethernet/net/eth0
lrwxrwxrwx    1 root     root             0 Jan  1  1970 lan1 -> ../../devices/platform/1e100000.ethernet/mdio_bus/mdio-bus/mdio-bus:1f/net/lan1
lrwxrwxrwx    1 root     root             0 Jan  1  1970 lan2 -> ../../devices/platform/1e100000.ethernet/mdio_bus/mdio-bus/mdio-bus:1f/net/lan2
lrwxrwxrwx    1 root     root             0 Jan  1  1970 lan3 -> ../../devices/platform/1e100000.ethernet/mdio_bus/mdio-bus/mdio-bus:1f/net/lan3
lrwxrwxrwx    1 root     root             0 Jan  1  1970 lan4 -> ../../devices/platform/1e100000.ethernet/mdio_bus/mdio-bus/mdio-bus:1f/net/lan4
lrwxrwxrwx    1 root     root             0 Jan  1  1970 lo -> ../../devices/virtual/net/lo
lrwxrwxrwx    1 root     root             0 Jan  1  1970 wan -> ../../devices/platform/1e100000.ethernet/mdio_bus/mdio-bus/mdio-bus:1f/net/wan
lrwxrwxrwx    1 root     root             0 May 13 19:55 wlan0 -> ../../devices/platform/1e140000.pcie/pci0000:00/0000:00:00.0/0000:01:00.0/net/wlan0
lrwxrwxrwx    1 root     root             0 May 13 19:55 wlan1 -> ../../devices/platform/1e140000.pcie/pci0000:00/0000:00:01.0/0000:02:00.0/net/wlan1

[mk24]

It has DSA, so you don't need to configure the switch directly. DSA is supposed to look to the user like there isn't even a switch, though of course it is still active behind the scenes.

Simply remove one of the lanX ports from the lan bridge and build a second wan network for it.

config interface 'wan2'
   option ifname 'lan4'
   ...

[Technocrat]

Thank you for the reply! I already did that yesterday, but didn't restart the router. Internet was not reachable, so I thought that this is not a working approach. Today I did the same and after restart it started to work.