Look up the IP addresses and source interface for each given host.

lookup.py

#!/usr/bin/env python3

from collections import OrderedDict
import socket
import sys


def print_route_lookup(host, addrinfo):
    endpoints = set()
    for info in addrinfo:
        if int(info[1]) == socket.SOCK_DGRAM:
            endpoints.add((info[0], info[4]))
    for endpoint in endpoints:
        af = int(endpoint[0])
        sock = socket.socket(int(endpoint[0]), socket.SOCK_DGRAM)
        endpoint_address = endpoint[1]
        peername = endpoint_address[0]
        description = peername
        local_address = "0.0.0.0" if af == socket.AF_INET else "::"
        try:
            sock.bind((local_address, 0))
            sock.connect((peername, 7))
            sockname = sock.getsockname()
            own_ip = sockname[0]
            if host != peername:
                description = "%s at %s" % (host, peername)
            print("%s via %s" % (description, own_ip))
        except OSError as e:
            # Probably "can't assign requested address", which probably means
            # we tried to connect to an IPv6 address, but IPv6 is not
            # configured.
            print("%s - no route to host" % description, file=sys.stderr)


if __name__ == "__main__":
    lookups = OrderedDict()
    for arg in sys.argv[1:]:
        try:
            lookups[arg] = socket.getaddrinfo(arg, 443)
        except socket.gaierror:
            print("%s - name lookup failed" % arg, file=sys.stderr)
    for host in lookups:
        print_route_lookup(host, lookups[host])