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@cmol cmol/natPMP.py
Last active Dec 16, 2015

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Script for requesting a port redirection via natPMP. Uses python3
"""
Script for requesting a port redirection via natPMP.
Follows the standart of:
http://tools.ietf.org/html/draft-cheshire-nat-pmp-07#section-3.3
with the exception of hold times. We are not going to wait a little
above 3 minutes to test for natPMP.
"""
import socket
import random
import errno
import os
from subprocess import check_output
from struct import pack, unpack
def create_payload(local_port, external_port, lifetime):
"""Create the natPMP payload for opening 'external_port'
(0 means that the GW will choose one randomly) and
redirecting the traffic to client machine.
int local_port
int external_port (optional)
return bytecode payload
"""
return pack('>2B3HI', 0, 1, 0, local_port, external_port, lifetime)
def send_payload(s, payload, gateway):
"""Encode and send the payload to the gateway of the network
socket s
int payload
string gateway
return bool success
"""
try:
s.sendto(payload, (gateway, 5351))
success = True
except socket.error as err:
if err.errno != errno.ECONNREFUSED:
raise err
success = False
return success
def parse_respons(payload):
"""Parse the respons from the natPMP device (if any).
string respons
return tuple (external_port, lifetime) or False
"""
values = unpack('>2BHI2HI', payload)
if values[2] != 0:
"""In this case, we get a status code back and can assume
that we are dealing with a natPMP capable gateway.
If the status code is anything other than 0, setting the
external port failed."""
return False
# Get lifetime and port
lifetime = values[6]
external_port = values[5]
return external_port, lifetime
def determine_gateway():
"""Determine the gateway of the network as it is
most likely here we will find a natPMP enabled device.
return string gatweay
"""
if os.name == 'posix':
if os.uname() == 'Linux':
default_gateway = check_output("ip route | awk '/default/ {print $3}'", shell=True).decode().strip()
elif os.uname() == 'Darwin':
default_gateway = check_output("/usr/sbin/netstat -nr | grep default | awk '{print $2}'", shell=True).decode().strip()
if os.name == 'nt':
"""Use WMI for finding the default gateway if we are on windows"""
import wmi
wmi_obj = wmi.WMI()
wmi_sql = "select DefaultIPGateway from Win32_NetworkAdapterConfiguration where IPEnabled=TRUE"
wmi_out = wmi_obj.query( wmi_sql )
for dev in wmi_out:
default_gateway = dev.DefaultIPGateway[0]
return default_gateway
def map_external_port(lport=random.randint(1025,65535), external_port=0, timeout=7200):
"""Try mapping an external port to an internal port via the natPMP spec
This will also test if the gateway is capable of doing natPMP (timeout based),
and determine the default gateway.
It is highly recommended that the lport is provided and bound in advance,
as this module will not test if the port is bindable, and will not return the lport.
If the timeout is set to 0 the mapping will be destroid. In this case the external
port must also be set to 0 and from the draft, is seems that the lport must be the
same as in the time of creation.
int lport
int external_port
int timeout
return tuple(external_port, timeout) or False"""
gateway = determine_gateway()
stimeout = .25
payload = create_payload(lport, external_port, timeout)
while stimeout < 6:
s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
s.bind(('',random.randint(1025, 65535)))
s.settimeout(stimeout)
if send_payload(s, payload, gateway):
try:
rpayload = s.recvfrom(4096)
except socket.error as err:
if (err.errno and err.errno != errno.ETIMEDOUT) or str(err) != 'timed out':
"""For some reason, the timed out error have no errno, although the
errno atrribute is existing (set to None). For this reason, we get this
weird error handeling. It might be a bug in python3.2.3"""
raise err
s = None
else:
if rpayload[1][0] == gateway:
return parse_respons(rpayload[0])
stimeout = stimeout * 2
return False
if __name__ == '__main__':
print(map_external_port())
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