After my upgrade to Ubuntu 8.10 (Intrepid Ibex) I had been experiencing a number of network-related problems. Yesterday I was able to fix them.

The symptoms:

• When I booted without network connectivity the machine would hang (approximately 90 seconds) while doing "Configuring network interfaces".
• The Network Manager icon was not shown even though nm-applet was running.
• New wireless networks were not detected but existing wireless networks did work.

Fortunately these two bugs helped me to diagnose and solve the problem. I still had some old entries in my /etc/network/interfaces file which were conflicting with the new Network Manager. Apparently the file was not cleaned up during the upgrade.

I removed all lines in /etc/network/interfaces except the following two and all problems disappeared:

auto lo
iface lo inet loopback