ServerAndClient.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Net;
using System.Net.Sockets;

namespace ReverseStringServer2
{
    class Program
    {
        static void Main(string[] args)
        {
            // address to bind
            IPEndPoint endPoint = new IPEndPoint(IPAddress.Any, 9999);
            // create the the socket
            Socket socket = new Socket(SocketType.Dgram, ProtocolType.Udp);
            // bind to endpoint
            socket.Bind(endPoint);

            while (true)
            {
                byte[] data = new byte[4096];
                EndPoint sender = new IPEndPoint(0, 0);
                int rlen = socket.ReceiveFrom(data, ref sender);
                // transform to utf8
                string message = Encoding.UTF8.GetString(data, 0, rlen);
                char[] chars = message.ToCharArray();
                Array.Reverse(chars);
                byte[] response = Encoding.UTF8.GetBytes(chars);
                socket.SendTo(response, sender);
            }
        }

        static void Client()
        {
            IPEndPoint serverEndPoint = new IPEndPoint(IPAddress.Parse("192.168.22.223"), 9999);
            // create the the socket
            Socket socket = new Socket(SocketType.Dgram, ProtocolType.Udp);

            while (true)
            {
                string message = Console.ReadLine();
                byte[] data = Encoding.UTF8.GetBytes(message);
                socket.SendTo(data, serverEndPoint);
                byte[] response = new byte[4096];
                int rlen = socket.Receive(response);
                Console.WriteLine(Encoding.UTF8.GetString(response, 0, rlen));
            }
        }
    }
}