IP forwarding with NetworkManager?

I want to share my WiFi internet connection over LAN, so I’m trying to set up IP forwarding. An old tutorial tells me to go to Network Settings in YaST to do this, but that applet says that NetworkManager is now handling all of that stuff.

How do I enable IP forwarding while NetworkManager handles my internet connections?

as root

echo 1 > /proc/sys/net/ipv4/ip_forward

When I connect the Ethernet cable to the computer that has WiFi capabilities, I lose internet connectivity. How come?