How do I Split the below method in 3-tier as BOL/DAL/BLL

protected void CmdLogin_Click(object sender, EventArgs e)
        {

            _path = "LDAP://#";
            //lblerrormsg.Text = string.Empty;
            try
            {
                if (!IsAuthenticated(Convert.ToString(ConfigurationManager.AppSettings["domain"]), Login1.UserName, Login1.Password))
                {
                    return;
                }
                SqlCommand cmd = new SqlCommand("#");
                cmd.CommandType = CommandType.StoredProcedure;
                cmd.Parameters.Add("@UserID", SqlDbType.NVarChar, 50).Value = Login1.UserName;
                LMS dal = new LMS();
                DataSet ds = dal.DisconectedMethod(cmd);
                if (ds != null && ds.Tables.Count > 0 && ds.Tables[0].Rows.Count > 0)
                {
                    Session["Authorization"] = Convert.ToString(ds.Tables[0].Rows[0]["ROLE"]);
                    Session["UserID"] = Convert.ToString(ds.Tables[0].Rows[0]["UserID"]);
                    Session["EMPLOYEE_NAME"] = Convert.ToString(ds.Tables[0].Rows[0]["EMPLOYEE_NAME"]);
                    Response.Redirect("index.aspx");
                }
            }
            catch (Exception ex)
            {
                Login1.FailureText = ex.Message;
            }

        }


        private bool IsAuthenticated(string domain, string username, string pwd)
        {
            string domainAndUsername = domain + @"\" + username;
            DirectoryEntry entry = new DirectoryEntry(_path, domainAndUsername, pwd);

            try
            {
                //Bind to the native AdsObject to force authentication.
                object obj = entry.NativeObject;

                DirectorySearcher search = new DirectorySearcher(entry);

                search.Filter = "(SAMAccountName=" + username + ")";
                search.PropertiesToLoad.Add("cn");
                SearchResult result = search.FindOne();

                if (null == result)
                {
                    return false;
                }

                //Update the new path to the user in the directory.
                _path = result.Path;
                _filterAttribute = (string)result.Properties["cn"][0];
            }
            catch (Exception ex)
            {
                Login1.FailureText = ex.Message;
            }

            return true;
        }