The guide you suggested turns the modem/router into a switch+AP, which is like saying: use a layer 3 device as a layer 2 device. It's a switch.
And, in fact, the device works perfectly in this configuration. PCs and peripherals connected to it obtain an IP address from the DHCP and reach other devices and the gateway to surf the internet.
As I said in my first post, the network is working well.
However, the device does not see that it is not connected to the Internet using the ADSL port or a LAN port configured as a WAN port, but through a simple LAN port. Again, everything works; the only drawback is that, for example, it does not search for firmware updates automatically, but you have to upload the file manually.
