PC to Router Internet sharing, unable to establish ethernet connection

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http://askubuntu.com – Laptop gets the Internet through wifi. I'm trying to plug a router to the laptop to create a new wifi network. Laptop would bridge. What I want: INTERNET ((( wifi ))) LAPTOP <--- ethernet ---> router ((( wifi ))) Network Manager of laptop: eth0 is set to IPv4 "Shared to other computers". Web interface of router: WLAN is set to "Dynamic IP (via DHCP)". When I plug the Ethernet cable (cat5e) from the router (WLAN port) to my laptop, eth0 keeps flickering ("connected"/"disconnected") every 0.5 sec. Is it because I'm using a crossover cable or would it be because of some misconfiguratio (HowTos)