Ubuntu 9.10 Desktop Edition (and possibly previous versions as well, I haven't tested them) has no network connections after boot until at least 1 user logs in. This means any services that require networking (e.g. openssh-server) are not available until someone logs in locally either via gdm, kdm, or a TTY.
Ubuntu 9.10 Desktop Edition uses the NetworkManager service to take commands from the nm-applet in Gnome (or its equivalent in KDE). As I understand it, while NetworkManager is running at boot, it is not issued any commands to connect until you login for the first time because nm-applet isn't running until you login and your Gnome session starts (or similar for KDE). I'm not sure what prompts NetworkManager to connect to the network when you login via a TTY.
There are several relevant variables involved in starting up the network connections including:
- Wired vs Wireless (and the resulting drivers, SSID, passwords, and priorities)
- Static vs DHCP
- Multiple interfaces
- Support Ubuntu 9.10 Karmic Koala (bonus points for additional supported versions)
- Support wired eth0 interface
- Receive an IP address via DHCP
- Receive DNS information via DHCP (obviously the DHCP server must provide this information)
- Enable networking at the proper time (e.g. some time after file systems are loaded but before network services like ssh start)
- Switching distros or versions (e.g. to Server Edition) is not an acceptable solution
- Switching to a Static IP configuration is not an acceptable solution
- How to start networking on a wired interface before logon in Ubuntu Desktop Edition?