Networking Issues 12.04
Networking Can Not Start on Boot
Sometimes networking is broken, characterized by a message that appears on boot:
Waiting for up to 60 more seconds for network configuration...
Network interfaces are defined in
/etc/udev/rules.d/70-persistent-net.rules. The system thinks it has eth0, but the network card is named eth1. You can safely rename this file and it will be recreated on boot, otherwise edit it so that network card present is name correctly. This file uses mac address to identify cards. Use ifconfig -a to identify them.
sudo dhclient eth1 will bring up networking in the mean time(and is a good test to identify this issue).
Network Manager Does Not Start
In addition it might be necessary to move/delete
/var/lib/NetworkManager/NetworkManager.state in order to get network manager to start correctly.