udp_forwarder.js

var dgram = require('dgram');
var config = {
  1194: 'openvpn.example.com:1194',
  1195: 'anothervpn.example.com:1194'
};

var listenSockets = {};
var natTable = {};
Object.keys(config).forEach(function(port) {
  var forwardHost = config[port].split(':')[0];
  var forwardPort = config[port].split(':')[1];
  var listenSocket = listenSockets[port] = dgram.createSocket('udp4');

  console.log('Listening on UDP port %d', port);
  listenSocket.bind(port);
  listenSocket.on('message', function(msg, rinfo) {
    var natTableKey = [port, rinfo.addres, rinfo.port].join(':');
    var socket = natTable[natTableKey];
    if (!socket) {
      socket = dgram.createSocket('udp4');
      socket.bind();
      socket.on('message', function(msg, rinfo2) {
        console.log('Received %d bytes from %s:%d and forwarded to %s:%d', msg.length, rinfo2.address, rinfo2.port, rinfo.address, rinfo.port);
        listenSocket.send(msg, 0, msg.length, rinfo.port, rinfo.address);
      });
    }

    console.log('Received %d bytes from %s:%d and forwarded to %s:%d', msg.length, rinfo.address, rinfo.port, forwardHost, forwardPort);
    socket.send(msg, 0, msg.length, forwardPort, forwardHost);

    natTable[natTableKey] = socket;
  });
});