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How would one go about retrieving a network device's netmask (In Linux preferably, but if it's cross-platform then cool)? I know how in C on Linux but I can't find a way in Python -- minus ctypes perhaps. That or parsing ifconfig. Any other way?
ioctl(socknr, SIOCGIFNETMASK, &ifreq) // C version
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Use the ifconfig command to confirm that the IP address and netmask are correct. Invoke ifconfig with the name of the network interface that you want to examine. If the interface does not come up, replace the interface cable and try again. If it still fails, use the diag command to check the device.
In order to find the subnet mask for your host, use the “ifconfig” command with the interface name and pipe it with the “grep” command to isolate the “mask” string. In this case, you are presented with subnet masks for every network interface (loopback interface included).
This works for me in Python 2.2 on Linux:
iface = "eth0"
socket.inet_ntoa(fcntl.ioctl(socket.socket(socket.AF_INET, socket.SOCK_DGRAM), 35099, struct.pack('256s', iface))[20:24])
The netifaces module deserves a mention here. Straight from the docs:
>>> netifaces.interfaces()
['lo0', 'gif0', 'stf0', 'en0', 'en1', 'fw0']
>>> addrs = netifaces.ifaddresses('en0')
>>> addrs[netifaces.AF_INET]
[{'broadcast': '10.15.255.255', 'netmask': '255.240.0.0', 'addr': '10.0.1.4'}, {'broadcast': '192.168.0.255', 'addr': '192.168.0.47'}]
Works on Windows, Linux, OS X, and probably other UNIXes.
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