CONNECT P2P THROUGH UDP HOLE PUNCHING

Summary

UDP Hole Punching is a technique used to establish a direct peer-to-peer (P2P) connection between devices behind a NAT (Network Address Translation). This method allows peers to communicate directly with each other without needing to go through any intermediary servers.

Server Usage

• Signaling Server: broker.emqx.io:1883
• STUN Server: stun.l.google.com:19302

Description

1. Signaling by MQTT

• MQTT is used for the signaling mechanism to exchange Candidates between devices..

2. STUN Protocol

• Obtains the PUBLIC_IP and opens the PUBLIC_PORT by sending a query to the STUN SERVER. The router temporarily holds this PUBLIC_PORT for a short time.
• Using STUN is crucial for punching a hole, a device behind NAT will map its LOCAL_PORT to this PUBLIC_PORT to send messages to another device behind NAT.

3. Gathering Candidate

• The connection setup process depends on:
  • Case 1: Both devices are behind the same NAT and on the same machine.
  • Case 2: Both devices are behind the same NAT but on different machines in the same local network.
  • Case 3: Both devices are behind different NATs, requiring each device to map its LOCAL_PORT to a PUBLIC_PORT.

4. UDP Hole Punching

• Devices will start sending/receiving messages based on the Candidates received from the other side.

How to use ?

To run the application, simply execute the following steps:

• Install dependency

  sudo apt update
  sudo apt install libmosquitto-dev
  

• Build

  make

The program after building includes two applications Peer1 and Peer2. Test the connection with 3 different cases:

• Run both peers on the same Linux machine using two terminals..
• Run the peers on two Linux machines connected to the same network.
• Run the peers on two Linux machines located on different Internet service providers.

Reference

• P2P-NAT