C#

The only values for a custom command that you can define in your application or use in OnCustomCommand are those between 128 and 256. Integers below 128 correspond to system-reserved values.

server:-
int recv;
byte[] data = new byte[1024];
IPEndPoint ipep = new IPEndPoint(IPAddress.Any, 10294);
Socket newsock = new Socket(AddressFamily.InterNetwork,
SocketType.Dgram, ProtocolType.Udp);
newsock.Bind(ipep);
newsock.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.AddMembership, new MulticastOption(IPAddress.Any, IPAddress.Parse("127.0.0.1")));

while (true)
{
   IPEndPoint sender2 = new IPEndPoint(IPAddress.Any, 0);
   IPEndPoint sender1 = new IPEndPoint(IPAddress.Parse("192.168.1.35") , 0);
   EndPoint tmpRemote = (EndPoint)(sender2);
   EndPoint tmpRemote1 = (EndPoint)(sender1);
   data = new byte[1024];
   recv = newsock.ReceiveFrom(data, ref tmpRemote);
   Console.WriteLine(Encoding.ASCII.GetString(data, 0, recv));
   string welcome = "7010";
   data = Encoding.ASCII.GetBytes(welcome);
   newsock.SendTo(data, data.Length, SocketFlags.None, tmpRemote1 );
} 


client:-
IPEndPoint ipep = new IPEndPoint(IPAddress.Parse("192.168.1.35"), 10294);
byte[] data = new byte[1024];
Socket client = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);

private void Form1_Load(object sender, EventArgs e)
        {
           client.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.MulticastTimeToLive, 10);
        }
 private void button1_Click(object sender, EventArgs e)
        {           
            string welcome = "What's your IP?";
	    data = Encoding.ASCII.GetBytes(welcome);
	    client.SendTo(data, data.Length, SocketFlags.None, ipep);
        }

 private void timer1_Tick(object sender, EventArgs e)
        {
           IPEndPoint server = new IPEndPoint(IPAddress.Any, 0);
	   EndPoint tmpRemote = (EndPoint)server;
           data = new byte[1024];
	   int recv = client.ReceiveFrom(data, ref tmpRemote);
	   this.richTextBox1.Text = Encoding.ASCII.GetString(data, 0, recv); 
        }

 private void Form1_FormClosing(object sender, FormClosingEventArgs e)
        {
            client.Close(); 
        }