How to interface with the Linux tun driver

I'm having a hard time figuring this problem out - I am trying to write a program that will interact with the Linux tunnel driver. At a very basic level, I simply want to create an application that is able to transfer data over a network tunnel. However, I am completely at a loss as to how to properly set up the tunnel driver in order to accomplish this. I am developing on Ubuntu 9.04, and I have the tunnel driver kernel module loaded. There exists the device `/dev/net/tun`, however there are no `/dev/tunX` devices. I am unable to create these devices using `ifconfig` - whenever I run `/sbin/ifconfig tun0 up`, for example, I get the following error: tun0: ERROR while getting interface flags: No such device. If I attempt to look at the `/dev/net/tun` device, the following error is presented: cat: /dev/net/tun: File descriptor in bad state. Attempting to open `/dev/tunX` via a small program, basically, a simple ``` tun_fd = open( "/dev/tun0", O_RDWR ) ``` returns -1: the application is running as root and still cannot open this tunnel device. It is possible to open `/dev/net/tun`, however this does not appear to generate a new `/dev/tunX` device to use instead. So, in summary - how does one go about writing an application that wishes to use the Linux tunnel driver? Any insights would be greatly appreciated. Thanks; ~Robert