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.

Asked By: GnP

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Source

Answer 1

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

Answered By: Florian Diesch

Answer 2

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

Answered By: jldupont

Answer 3

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:
                # If not default route or not RTF_GATEWAY, skip it
                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.

Answered By: ssokolow

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).

Answered By: al45tair

Answer 5

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/

Answered By: theartofrain

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()

Answered By: throws_exceptions_at_you

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)

Answered By: Helton Wernik

Answer 8

for Mac:

import subprocess

def get_default_gateway():
    route_default_result = str(subprocess.check_output(["route", "get", "default"]))
    start = 'gateway: '
    end = '\n'
    if 'gateway' in route_default_result:
        return (route_default_result.split(start))[1].split(end)[0]

print(get_default_gateway())

Answered By: Sepehr Rafiei

Answer 9

Here a solution if you have multiple default gateways.

import socket, struct
from pprint import pprint as pp

with open("/proc/net/route") as fh:
    # skip header
    next(fh)
    route_list = []
    for line in fh:
        routes = line.strip().split()
        destination = socket.inet_ntoa(struct.pack("<L", int(routes[1], 16)))
        if destination != "0.0.0.0":
            continue
        gateway = socket.inet_ntoa(struct.pack("<L", int(routes[2], 16)))
        mask = socket.inet_ntoa(struct.pack("<L", int(routes[7], 16)))
        metric = routes[6]
        interface = routes[0]
        route_table = (destination, gateway, mask, metric, interface)
        route_list.append(route_table)
    pp(route_list)

#[('0.0.0.0', '0.0.0.0', '0.0.0.0', '0', 'wlan0'),
# ('0.0.0.0', '192.168.225.1', '0.0.0.0', '1024', 'usb0')]

Answered By: delijati

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

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