Is there a method to get default network interface on local using python3?

Question

Hi I want to get the default network interface using Python. After google, I got pynetinfo can do this. But pynetinfo seems not work on Python3. Is there another method to instead pynetinfo?

Answer 1

If you are using Linux you can examining the route table directly on /proc/net/route. This file contains the routing parameters of your system, here is an example:

Iface   Destination Gateway     Flags   RefCnt  Use Metric  Mask        MTU Window  IRTT
eth1    0009C80A    00000000    0001    0       0   0       00FFFFFF    0   0       0
eth2    0000790A    00000000    0001    0       0   0       0080FFFF    0   0       0
eth3    00007A0A    00000000    0001    0       0   0       0080FFFF    0   0       0
eth0    00000000    FE09C80A    0003    0       0   0       00000000    0   0       0

In this example all traffic to networks 10.200.9.0/24, 10.121.0.0/25 and 10.122.0.0/25 is broadcasted via eth1, eth2 and eth3 respectively, the rest of packages are sent using eth0 interface to the gateway 10.200.9.254. So the question is how to get this programatically using Python?

def get_default_iface_name_linux():
    route = "/proc/net/route"
    with open(route) as f:
        for line in f.readlines():
            try:
                iface, dest, _, flags, _, _, _, _, _, _, _, =  line.strip().split()
                if dest != '00000000' or not int(flags, 16) & 2:
                    continue
                return iface
            except:
                continue

get_default_iface_name_linux() # will return eth0 in our example

Answer 2

with pyroute2:

from pyroute2 import IPDB
ip = IPDB()
# interface index:
print(ip.routes['default']['oif'])
# interface details:
print(ip.interfaces[ip.routes['default']['oif']])
# release DB
ip.release()