networking - Interfacing with TUNTAP for MAC OSX (Lion) using Python

Question

I found the following tunap example program and can not get it to work:

http://www.secdev.org/projects/tuntap_udp/files/tunproxy.py

I have modified the following lines:

f = os.open("/dev/tun0", os.O_RDWR)
ifs = ioctl(f, TUNSETIFF, struct.pack("16sH", "toto%d", TUNMODE))
ifname = ifs[:16].strip("x00")

The first line was modified to reflect the real location of the driver. It was originally

f = os.open("/dev/net/tun", os.O_RDWR)

Upon running I get the following error:

 sudo ./tuntap.py -s 9000
 Password:
 Traceback (most recent call last):
   File "./tuntap.py", line 65, in <module>
     ifs = ioctl(f, TUNSETIFF, struct.pack("16sH", "toto%d", TUNMODE))
 IOError: [Errno 25] Inappropriate ioctl for device

I am using the latest tunap drivers installed from http://tuntaposx.sourceforge.net/download.xhtml

Answer 1

The OSX tun/tap driver seems to work a bit different. The Linux example dynamically allocates a tun interface, which does not work in OSX, at least not in the same way.

I stripped the code to create a basic example of how tun can be used on OSX using a self-selected tun device, printing each packet to the console. I added Scapy as a dependency for pretty printing, but you can replace it by a raw packet dump if you want:

import os, sys
from select import select
from scapy.all import IP

f = os.open("/dev/tun12", os.O_RDWR)
try:
    while 1:
        r = select([f],[],[])[0][0]
        if r == f:
            packet = os.read(f, 4000)
            # print len(packet), packet
            ip = IP(packet)
            ip.show()
except KeyboardInterrupt:
    print "Stopped by user."

You will either have to run this as root, or do a sudo chown your_username /dev/tun12 to be allowed to open the device.

To configure it as a point-to-point interface, type:

$ sudo ifconfig tun12 10.12.0.2 10.12.0.1

Note that the tun12 interface will only be available while /dev/tun12 is open, i.e. while the program is running. If you interrupt the program, your tun interface will disappear, and you will need to configure it again next time you run the program.

If you now ping your endpoint, your packets will be printed to the console:

$ ping 10.12.0.1

Ping itself will print request timeouts, because there is no tunnel endpoint responding to your ping requests.