AirPort Express as range extender together with AirPort Extreme over wired Ethernet
I need to extend the range of my wireless network operated primarily by an AirPort Extreme 802.11n (5th gen). So I bought an AirPort Express 802.11n (2nd gen) and configured it as an range extender to existing network. For the configuration matter I used my iPhone. Now, the problem is that the range between the AirPort Extreme and the desired location for the AirPort Express is a bit too far for optimal connection. But I also have a wired Ethernet cable network in my house and therefore I wish to connect the AirPort Express to the AirPort Extreme through cable. I use one of the common Ethernet ports on the AirPort Extreme and the WAN-port on the AirPort Express.
But – when I do this – the whole network goes down! Both wireless units disappear from my AirPort tool app (iPhone/iPad) or at least seems to be inactive. I get error messages. I loose my Internet connection and the only way to make it work again is to disconnect the Ethernet cable from the two units. Then after reboot, the network works fine again. I should add that the network including the AirPort Express works fine when the AirPort Express is connected wireless to the AirPort Extreme, however, speed could be higher.
What do I do wrong and how shall I do instead?