Networking looks OK, but does not work at all

I am trying to get networking to work on Sabayon X KDE Edition. I have configured wireless networking using the NetworkManager applet and networking looks OK. However, I can't connect to the Internet, I cannot ping my gateway and I cannot even ping localhost. I have never seen this behaviour on Linux. I am using a manually-configured kernel because I have to boot using UEFI. If you suspect any specific Kernel options, I can check them against the config. Also, networking worked fine in the Sabayon live environment. Does anybody have an idea what is going on here? # ifconfig lo: flags=73 mtu 65536 inet 127.0.0.1 netmask 255.0.0.0 inet6 ::1 prefixlen 128 scopeid 0x10 loop txqueuelen 0 (Lokale Schleife) RX packets 66 bytes 5208 (5.0 KiB) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 66 bytes 5208 (5.0 KiB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0 wlan0: flags=4163 mtu 1500 inet 192.168.178.36 netmask 255.255.255.0 broadcast 192.168. 178.255 inet6 fe80::c685:8ff:fe30:b77c prefixlen 64 scopeid 0x20 ether c4:85:08:30:b7:7c txqueuelen 1000 (Ethernet) RX packets 402 bytes 44048 (43.0 KiB) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 169 bytes 73070 (71.3 KiB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0 # netstat -r Kernel IP Routentabelle Ziel Router Genmask Flags MSS Fenster irtt Iface default 192.168.178.1 0.0.0.0 UG 0 0 0 wlan0 loopback localhost 255.0.0.0 UG 0 0 0 lo 192.168.178.0 * 255.255.255.0 U 0 0 0 wlan0 # ping -c3 192.168.178.36 PING 192.168.178.36 (192.168.178.36) 56(84) bytes of data. --- 192.168.178.36 ping statistics --- 3 packets transmitted, 0 received, 100% packet loss, time 2007ms # ping -c3 localhost PING localhost (127.0.0.1) 56(84) bytes of data. --- localhost ping statistics --- 3 packets transmitted, 0 received, 100% packet loss, time 2005ms