Example program for tap driver VPN
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simpletun.c Add Upstream Dec 11, 2012


simpletun, a (too) simple tunnelling program.


To compile the program, just do

$ gcc simpletun.c -o simpletun

If you have GNU make, you can also exploit implicit targets and do

$ make simpletun


simpletun -i <ifacename> [-s|-c <serverIP>] [-p <port>] [-u|-a] [-d]
simpletun -h

-i <ifacename>: Name of interface to use (mandatory)
-s|-c <serverIP>: run in server mode (-s), or specify server address (-c <serverIP>) (mandatory)
-p <port>: port to listen on (if run in server mode) or to connect to (in client mode), default 55555
-u|-a: use TUN (-u, default) or TAP (-a)
-d: outputs debug information while running
-h: prints this help text


Refer to http://backreference.org/2010/03/27/tuntap-interface-tutorial/ for 
more information on tun/tap interfaces in Linux in general, and on this 
program in particular.
The program must be run at one end as a server, and as client at the other 
end. The tun/tap interface must already exist, be up and configured with an IP 
address, and owned by the user who runs simpletun. That user must also have
read/write permission on /dev/net/tun. (Alternatively, you can run the
program as root, and configure the transient interfaces manually before
starting to exchange packets. This is not recommended)

Use is straightforward. On one end just run

[server]$ ./simpletun -i tun13 -s

at the other end run

[client]$ ./simpletun -i tun0 -c

where is the remote server's IP address, and tun13 and tun0 must be 
replaced with the names of the actual tun interfaces used on the computers.
By default it assumes a tun device is being used (use -u to be explicit), and
-a can be used to tell the program that the interface is tap. 
By default it uses TCP port 55555, but you can change that by using -p (the 
value you use must match on the client and the server, of course). Use -d to 
add some debug information. Press ctrl-c on either side to exit (the other end
will exit too).

The program is very limited, so expect to be disappointed.