ESP8266 / Arduino UDP Multicast example

esp8266-udp-multicast-hello-world.ino

#include <ESP8266WiFi.h>
#include <WiFiUdp.h>
#include <ESP8266WebServer.h>

// simple POC : send hello world string over UDP-multicast address every 2 seconds.
// a very simple way to connect IOT to local network without need of any server.
// author : Marc Quinton / feb 2019
// keywords : esp8266, arduino, multicast, IOT, example, POC

WiFiUDP udp;
const int port = 8266;

// IPAddress broadcast;
IPAddress broadcast=IPAddress(224, 0, 1, 3);

const char* ssid = "ssid";
const char* password = "password";

void setup(void)
{
  Serial.begin(115200);
  Serial.println("Startup");

  WiFi.mode(WIFI_STA);
  WiFi.begin(ssid, password);
  Serial.println("");

  // Wait for connection
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("");
  Serial.print("Connected to ");
  Serial.println(ssid);
  Serial.print("IP address: ");
  Serial.println(WiFi.localIP());

  Serial.print("broadcast address : ");
  Serial.print(broadcast);
  Serial.print(":");
  Serial.println(port);

}

void sendUDP(String string) {

  Serial.print("sendUDP : ");
  Serial.println(string);

  // convert string to char array
  char msg[255];
  string.toCharArray(msg,255);

  udp.beginPacketMulticast(broadcast, port, WiFi.localIP());
  udp.write(msg);
  udp.endPacket();
}

void loop(void)
{
  sendUDP((String)"hello world");
  delay(2000);
}

receive.rb

require 'socket'
require 'ipaddr'

MULTICAST_ADDR = "224.0.1.3" 
PORT = 8266

ip =  IPAddr.new(MULTICAST_ADDR).hton + IPAddr.new("0.0.0.0").hton
sock = UDPSocket.new
sock.setsockopt(Socket::IPPROTO_IP, Socket::IP_ADD_MEMBERSHIP, ip)
sock.bind(Socket::INADDR_ANY, PORT)
loop do
  msg, info = sock.recvfrom(1024)
  # puts "MSG: #{msg} from #{info[2]} (#{info[3]})/#{info[1]} len #{msg.size}" 
  puts msg
end

Very naughty, using a multicast address in the well-known service scope. Use the locally scoped address range 239.0.0.0 to 239.255.255.255

this is example i think so its no matter