https://forum.archive.openwrt.org/viewtopic.php?id=65671

By adding the following snippet to /etc/config/network and rebooting the router, the Switch config tab will be available in Luci:


config switch
        option name 'switch0'
        option reset '1'
        option enable_vlan '1'

config switch_vlan
        option device 'switch0'
        option vlan '1'
        option ports '0 1 2 3 6'

config switch_vlan
        option device 'switch0'
        option vlan '2'
        option ports '4 5'
				


Thanks sera, that did the trick!
I added your config to /etc/config/network and the Switch tab appeared in LuCI, also the router was not hanging anymore.

I figured the port mapping is as follows for the ACS:
Port0 - LAN Port 4
Port1 - LAN Port 3
Port2 - LAN Port 2
Port3 - LAN Port 1
Port4 - WAN
Port5 - CPU [WAN]
Port6 - CPU [LAN] - thanks sera!

I wanted to map my WAN interface to VLAN10, so I simply did the following:
Network -> Switch -> Add -> VLAN ID: 10, Port 4: tagged, CPU: tagged, Rest: off
Network -> Interfaces -> WAN -> Physical Settings -> Bridge interfaces: select eth0 and eth0.10

That's all. Finally my ACS was able to pick its IP via DHCP from my ISP's ONT (Optical Network Terminal).