OpenVPN: Cannot open TUN/TAP dev

[^rooker]

[PROBLEM]
OpenVPN refused to start. In the logs I found this errormessage:

Thu Aug 31 22:01:25 2006 OpenVPN 2.1_beta14 i686-pc-linux [SSL] [LZO2] [EPOLL] built on Aug 31 2006
Thu Aug 31 22:01:25 2006 Diffie-Hellman initialized with 1024 bit key
Thu Aug 31 22:01:25 2006 TLS-Auth MTU parms [ L:1542 D:138 EF:38 EB:0 ET:0 EL:0 ]
Thu Aug 31 22:01:25 2006 Note: Cannot open TUN/TAP dev /dev/net/tun: No such file or directory (errno=2)
Thu Aug 31 22:01:25 2006 Note: Attempting fallback to kernel 2.2 TUN/TAP interface
Thu Aug 31 22:01:25 2006 Cannot allocate TUN/TAP dev dynamically
Thu Aug 31 22:01:25 2006 Exiting

Even "openvpn --mktun --dev tun0" didn't help any.

[SOLUTION]
The kernel was missing TUN/TAP device support.

Using "make menuconfig", you can find it in:

"Network device support" > "Universal TUN/TAP device driver support"

When compiling it as a module, it's in "/lib/modules/KERNELVERSION/kernel/drivers/net/tun.ko"

[^rooker]

[PROBLEM]

Cannot load certificate file D:/Apps/OpenVPN/config/client.crt: error:02001003:system library:fopen:No such process: error:20074002:BIO routines:FILE_CTRL:system lib: error:140AD002:SSL routines:SSL_CTX_use_certificate_file:system lib
Thu Aug 31 23:29:18 2006 Exiting

[SOLUTION]
The problem is "/" vs "\" in the path names.
Changing it to "D:\\Apps\\OpenVPN\\config\\" did the trick!