I generally use NetworkManager (the applet in Karmic) for managing network connections, but I would like the ability to close a VPN connection from the command line. How do I do this? I have been searching and am quite surprised that there isn't (as far as I have been able to tell) a simple command.

If there is not in fact a simple command, can someone perhaps provide a link or resource that explains network manager and its relationship to other networking software such as wpa_supplicant?