2 router network setup. Why does ping only work in one direction?

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http://serverfault.com – So the setup looks like this: There is a main WLAN-router/modem which is connected to the internet and serves the lower floor with WLAN. Now upstairs I have a second WLAN-router/modem (I will call it router two from now on). A normal ethernet cable is plugged in in router two in one of the four ethernet ports and also in one of the four ethernet ports in router one. Since I don't want router two to act as a router but rather as an WLAN access point I set the routing mode to bridge in the admin interface. I did also disable it's dhcp server. Now when I connect to router two via WLAN I get a (HowTos)