Check ftp server is available or not

Add reference in your class:
using System.Net;
Then copy below mentioned method
/// <summary>
        /// GetServerAvailability to check ftp server is available or not
        /// </summary>
        /// <param name="userId">userId</param>
        /// <param name="password">password</param>
        /// <param name="ftpServerPath">ftpServerPath</param>
        /// <returns>status</returns>
        public static bool GetServerAvailability(string userId, string password, string ftpServerPath)
        {           
            FtpWebRequest reqFTP;
            bool isServerConnected = false;
            try
            {
                String serverUrl = String.Format("{0}{1}", @"ftp:", ftpServerPath);
                reqFTP = (FtpWebRequest)FtpWebRequest.Create(new Uri(serverUrl));
                reqFTP.UseBinary = true;
                reqFTP.Credentials = new NetworkCredential(userId, password);
                reqFTP.Method = WebRequestMethods.Ftp.ListDirectory;
                reqFTP.Proxy = null;
                reqFTP.KeepAlive = false;
                using (WebResponse response = reqFTP.GetResponse())
                {
                    isServerConnected = true;
                }
               
            }
            catch (Exception ex)
            { 
                if (string.Compare(ex.GetType().ToString(), "System.Net.Sockets.SocketException", true) == 0)
                {
                    System.Net.Sockets.SocketException socketError = (System.Net.Sockets.SocketException)ex;
                    if (socketError.ErrorCode == 11004)
                        isServerConnected = false;
                }
                else
                {                   
                    isServerConnected = false;
                }
            }
            finally
            {
                reqFTP = null;
            }
            return isServerConnected;
        }

Above mentioned code will return you true if server is available else false.