Python: get default gateway for a local interface/ip address in linux

Question

On Linux, how can I find the default gateway for a local ip address/interface using python?

I saw the question "How to get internal IP, external IP and default gateway for UPnP", but the accepted solution only shows how to get the local IP address for a network interface on windows.

Thanks.

Answer 1

For those people who don't want an extra dependency and don't like calling subprocesses, here's how you do it yourself by reading /proc/net/route directly:

import socket, struct

def get_default_gateway_linux():
    """Read the default gateway directly from /proc."""
    with open("/proc/net/route") as fh:
        for line in fh:
            fields = line.strip().split()
            if fields[1] != '00000000' or not int(fields[3], 16) & 2:
                continue

            return socket.inet_ntoa(struct.pack("<L", int(fields[2], 16)))

I don't have a big-endian machine to test on, so I'm not sure whether the endianness is dependent on your processor architecture, but if it is, replace the < in struct.pack('<L', ... with = so the code will use the machine's native endianness.

Answer 2

For completeness (and to expand on alastair's answer), here is an example that uses "netifaces" (tested under Ubuntu 10.04, but this should be portable):

$ sudo easy_install netifaces
Python 2.6.5 (r265:79063, Oct  1 2012, 22:04:36)
...
$ ipython
...
In [8]: import netifaces
In [9]: gws=netifaces.gateways()
In [10]: gws
Out[10]:
{2: [('192.168.0.254', 'eth0', True)],
 'default': {2: ('192.168.0.254', 'eth0')}}
In [11]: gws['default'][netifaces.AF_INET][0]
Out[11]: '192.168.0.254'

Documentation for 'netifaces': https://pypi.python.org/pypi/netifaces/

Answer 3

It seems http://pypi.python.org/pypi/pynetinfo/0.1.9 can do this, but I haven't tested it.

Answer 4

The latest version of netifaces can do this too, but unlike pynetinfo, it will work on systems other than Linux (including Windows, OS X, FreeBSD and Solaris).

Answer 5

def get_ip():
    file=os.popen("ifconfig | grep 'addr:'")
    data=file.read()
    file.close()
    bits=data.strip().split('\n')
    addresses=[]
    for bit in bits:
        if bit.strip().startswith("inet "):
            other_bits=bit.replace(':', ' ').strip().split(' ')
            for obit in other_bits:
                if (obit.count('.')==3):
                    if not obit.startswith("127."):
                        addresses.append(obit)
                    break
    return addresses

Answer 6

You can get it like this (Tested with python 2.7 and Mac OS X Capitain but should work on GNU/Linux too): import subprocess

def system_call(command):
    p = subprocess.Popen([command], stdout=subprocess.PIPE, shell=True)
    return p.stdout.read()


def get_gateway_address():
    return system_call("route -n get default | grep 'gateway' | awk '{print $2}'")

print get_gateway_address()

Answer 7

here my solution to get default gateway for Mac and Linux with python:

import subprocess
import re
import platform

def get_default_gateway_and_interface():
    if platform.system() == "Darwin":
        route_default_result = subprocess.check_output(["route", "get", "default"])
        gateway = re.search(r"\d{1,3}.\d{1,3}.\d{1,3}.\d{1,3}", route_default_result).group(0)
        default_interface = re.search(r"(?:interface:.)(.*)", route_default_result).group(1)

    elif platform.system() == "Linux":
        route_default_result = re.findall(r"([\w.][\w.]*'?\w?)", subprocess.check_output(["ip", "route"]))
        gateway = route_default_result[2]
        default_interface = route_default_result[4]

    if route_default_result:
        return(gateway, default_interface)
    else:
        print("(x) Could not read default routes.")

gateway, default_interface = get_default_gateway_and_interface()
print(gateway)