Behind-NAT-style Dynamic DNS script, designed to run on Ubiquiti EdgeRouter hardware

ddns.py

#!/usr/bin/python
import socket
import fcntl
import struct
import httplib
import json
import sys
from base64 import b64encode
from urllib import urlencode

def get_ip_address(ifname):
	s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
	return socket.inet_ntoa(fcntl.ioctl(s.fileno(), 0x8915, struct.pack('256s', ifname[:15]))[20:24])
	
config = json.load(open('/config/scripts/ddns.settings.json'))

for key in config:
	key = key.encode('ascii')
	try:
		params = config[key]
		
		try:
			lan_addr = get_ip_address(key)
		except:
			print 'No address defined on ' + key
			continue
			
		req = httplib.HTTPConnection('icanhazip.com', source_address=(lan_addr, 0))
		req.request('GET', '/')
		resp = req.getresponse()
		wan_addr = resp.read()
		wan_addr = wan_addr.rstrip('\n')	
		
		print key + ': ' + lan_addr + ' (IF address); ' + wan_addr + ' (Public address)'
			
		sys.stdout.write('Sending IP update for ' + key + ' to ' + params['server'] + '... ')
		
		req = httplib.HTTPConnection(params['server'], source_address=(lan_addr, 0))
		
		authData = b64encode(params['username'] + ':' + params['password'])
		headers = {"Authorization": "Basic " + authData}
		params = urlencode({'hostname': params['hostname'], 'myip': wan_addr, 'system': 'dyndns'})
		req.request('GET', '/nic/update?' + params, "", headers)	
		
		print req.getresponse().read();
	except:
		raise

ddns.settings.json

{
	"eth0": {
		"hostname": "a.domain.com",
		"username": "johndoe",
		"password": "1234",
		"server": "members.dyndns.com"
	},
	"eth1": {
		"hostname": "b.domain.com",
		"username": "johndoe",
		"password": "1234",
		"server": "members.dyndns.com"
	}
}