no, there's no router or switch. I gave the addresses to it. and the arduino is connected directly..
well, in the mean time, I tried another thing. I turned my Android phone into a portable Wi-Fi hotspot.
the laptop has gained Internet access. the Wi-Fi Connection has dhcp, Dns, gateway: 192.168.43.1, the Android has got: 192.168.43.60
so I gave my laptop ethernet interface an address in the same network, 192.168.43.170.
now forArduino I let it use DHCP. it worked partially, the error comes not any more "0", but "-2". which according to Arduino cookbook means, "no DNS records found.".
by tring the IP Address of google instead, it gave "0"..