Determine IP address of CONNECTED interface (linux) in python

Question

On my linux machine, 1 of 3 network interfaces may be actually connected to the internet. I need to get the IP address of the currently connected interface, keeping in mind that my other 2 interfaces may be assigned IP addresses, just not be connected.

I can just ping a website through each of my interfaces to determine which one has connectivity, but I'd like to get this faster than waiting for a ping time out. And I'd like to not have to rely on an external website being up.

Update:

All my interfaces may have ip addresses and gateways. This is for an embedded device. So we allow the user to choose between say eth0 and eth1 . But if there's no connection on the interface that the user tells us to use, we fall back to say eth2 which (in theory) will always work.

So what I need to do is first check if the user's selection is connected and if so return that IP. Otherwise I need to get the ip of eth2 . I can get the IPs of the interfaces just fine, it's just determining which one is actually connected.

Answer 1

如果系统的默认网关是可靠的，请从route -n的输出中获取，其中包含" UG " （请注意空格）还将包含网关的IP和活动接口的接口名称。

Answer 2

the solution is here : http://code.activestate.com/recipes/439093-get-names-of-all-up-network-interfaces-linux-only/

import fcntl
import array
import struct
import socket
import platform
"""
global constants.  If you don't like 'em here,
move 'em inside the function definition.
"""
SIOCGIFCONF = 0x8912
MAXBYTES = 8096

def localifs():
    """
    Used to get a list of the up interfaces and associated IP addresses
    on this machine (linux only).

    Returns:
    List of interface tuples.  Each tuple consists of
    (interface name, interface IP)
    """
    global SIOCGIFCONF
    global MAXBYTES

    arch = platform.architecture()[0]

    # I really don't know what to call these right now
    var1 = -1
    var2 = -1
    if arch == '32bit':
        var1 = 32
        var2 = 32
    elif arch == '64bit':
        var1 = 16
        var2 = 40
    else:
        raise OSError("Unknown architecture: %s" % arch)

    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    names = array.array('B', '\0' * MAXBYTES)
    outbytes = struct.unpack('iL', fcntl.ioctl(
        sock.fileno(),
        SIOCGIFCONF,
        struct.pack('iL', MAXBYTES, names.buffer_info()[0])
        ))[0]

    namestr = names.tostring()
    return [(namestr[i:i+var1].split('\0', 1)[0], socket.inet_ntoa(namestr[i+20:i+24])) \
            for i in xrange(0, outbytes, var2)]


print localifs()