You can catch UDP packet as specified port and IP address

UDP Client Program

using System;
using System.Text;
using System.Net;
using System.Net.Sockets;


namespace Server
{
    class Program
    {
        static void Main(string[] args)
        {
            byte[] data = new byte[1024];

           IPEndPoint ipep = new IPEndPoint(IPAddress.Any, 600);
            UdpClient newsock = new UdpClient(ipep);

            Console.WriteLine("Waiting for a client...");

            IPEndPoint sender = new IPEndPoint(IPAddress.Any, 0);

            data = newsock.Receive(ref sender);

            Console.WriteLine("Message received from {0}:", sender.ToString());
            Console.WriteLine(Encoding.ASCII.GetString(data, 0, data.Length));



            string welcome = "Welcome to my test server";
            data = Encoding.ASCII.GetBytes(welcome);
            newsock.Send(data, data.Length, sender);

            int serino = 1;
            int serino2 = 1;
            while (true)
            {
                data = newsock.Receive(ref sender);
                string[] words = Encoding.ASCII.GetString(data, 0, data.Length).Split(',');
                if (serino.ToString()== words[0] && words[1]=="192.168.85.1")
                { Console.WriteLine("Errorrrrrrrrrrrrrrrrrrrrrrrrrrrrrr");
                    serino++;

                }
                if(serino2.ToString()==words[0] && words[1] == "192.168.1.61")
                {
                    serino2++;
                    Console.WriteLine("XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX");
                }
                 Console.WriteLine(Encoding.ASCII.GetString(data, 0, data.Length));
             //   Console.WriteLine(words[0]);
                newsock.Send(data, data.Length, sender);
                
                
            }

        }  


    }
}