MultiServer.java

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.InetAddress;
import java.net.MulticastSocket;

/**
 * @author cristian
 */
public class MultiServer {
    public static void main(String[] args) throws IOException {
        byte[] buf = new byte[256];
        DatagramPacket packet = new DatagramPacket(buf, buf.length);
        MulticastSocket socket = new MulticastSocket(4445);
        // las direcciones multicast rango: 224.0.0.1 a 239.255.255.255
        socket.joinGroup(InetAddress.getByName("239.255.255.255"));

        socket.receive(packet);
        String recibido = new String(packet.getData());

        System.out.println("llego paquete: " + recibido);

        InetAddress address = packet.getAddress();
        int port = packet.getPort();
        packet = new DatagramPacket(buf, buf.length, address, port);
        socket.send(packet);


        socket.close();
    }
}