UDP hole punching library

Usage no npm install needed!

<script type="module">
  import udpHolePuncher from 'https://cdn.skypack.dev/udp-hole-puncher';


CircleCI npm

UDP Hole Puncher


JS library implementing a UDP hole punching protocol to connect two peers located behind NAT devices. Will not work when one or both peers are located behind a symmetric NAT box. In that case, you may need a relay server + a TURN lib (like this one) to facilitate communication between both peers.


  • no rendez-vous server lock in
  • verifies if bidirectional communication is possible
  • can be browserified (to be used in chrome and cordova apps)


npm install udp-hole-puncher


const dgram = require('dgram');
const UdpHolePuncher = require('udp-hole-puncher');

// peer's public port and address
const peer = {
  port: 1234,
  addr: '',
// local port
const myPort = 5678;

// socket config
const socket = dgram.createSocket('udp4');
socket.on('error', (error) => {...} );
socket.on('message', (message, rinfo) => {...} );
socket.on('listening', () => {
  // puncher config
  const puncher = new UdpHolePuncher(socket);
  // when connection is established, send dummy message
  puncher.on('connected', () => {
    const message = new Buffer('hello');
    socket.send(message, 0, message.length, peer.port, peer.addr);
  // error handling code
  puncher.on('error', (error) => {
  // connect to peer (using its public address and port)
  puncher.connect(peer.addr, peer.port);

// bind socket


var puncher = new UdpHolePuncher(socket, args)

Create a new udp-hole-puncher.

socket must be an operational datagram socket.

args specifies some optional config settings, including the maximum request attempts + timeout between every request attempt (ms). Default settings are { maxRequestAttempts: 10, requestTimeout: 500 }

puncher.connect(addr, port)

Try to establish a connection with a peer using its public address and port. Note that to setup bidirectional communication, both peers must simultaneously execute a connect operation (initiating the punching protocol).


End execution of the hole punching protocol.


puncher.on('connected', () => {})

Fired when the hole punching protocol completes and both peers can reach each other.

puncher.on('reachable', () => {})

Called when the other peer was able to reach this peer. No guarantee yet that bidirectional communication can be established.

puncher.on('timeout', () => {})

Fired when the hole punching protocol timeouts.

puncher.on('error', (error) => {})

Fired when a fatal error occurs.

Chrome and cordova apps

gulp browserify [--production]

Puts udp-hole-puncher.debug.js and udp-hole-puncher.min.js in build folder. Can be used in chrome and cordova app. When integrating udp-hole-puncher in a cordova app, use cordova-plugin-chrome-apps-sockets-udp:

cordova plugin add https://github.com/MobileChromeApps/cordova-plugin-chrome-apps-sockets-udp


See examples directory. Note that both peers should not be located behind the same NAT device. To test this lib, deploy one peer on your home network and another one outside of that network -- for instance on a public cloud infrastructure.

To run this test example, execute the following cmd on two machines A and B:

server-A$ npm run-script peer -- --bind=12345 --addr=<PUBLIC ADDR OF B> --port=23456
server-B$ npm run-script peer -- --bind=23456 --addr=<PUBLIC ADDR OF A> --port=12345