System.DirectoryServices 很慢？

当用户登录网站时，我使用下面的代码在活动目录中查找信息。针对本地域运行速度非常快，但通过 VPN 运行到远程受信任域时，速度非常慢（大约需要 7 或 8 秒）。从同一个机器到远程域运行 dsa.msc 几乎与在本地运行它一样快。

我正在使用属性过滤来检索尽可能少的数据，那么在这种情况下，System.DirectoryServices 是否存在本质上较慢的情况，或者是否有人对如何提高性能有任何提示？

VPN 上的网络连接良好，只是这段代码运行缓慢。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.DirectoryServices;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            using (var LDAPConnection = new DirectoryEntry("LDAP://domain/dc=domain,dc=com", "username", "password"))
            {
                LDAPConnection.AuthenticationType = AuthenticationTypes.Secure;
                using (DirectorySearcher Searcher = new DirectorySearcher(LDAPConnection))
                {
                    Searcher.Filter = "(&(&(objectclass=user)(objectcategory=person))sAMAccountName=username)";
                    Searcher.PropertiesToLoad.Add("mail");

                    SearchResult result = Searcher.FindOne(); //this line takes ages!

                    string EmailAddress = result.Properties["mail"][0].ToString();
                    Console.WriteLine(EmailAddress);
                }
            }
        }
    }
}

另一个建议是使用System.DirectoryServices.Protocols直接地;你的代码将如下所示：

string filter = "(&(&(objectclass=user)(objectcategory=person))" + 
                "sAMAccountName=username)";
NetworkCredential credentials = new NetworkCredential(...);
LdapDirectoryIdentifier directoryIdentifier = 
   new LdapDirectoryIdentifier("server", 389, false, false);
using (LdapConnection connection = 
   new LdapConnection(directoryIdentifier, credentials, AuthType.Basic))
{
    connection.Timeout = new TimeSpan(0, 0, 30);
    connection.SessionOptions.ProtocolVersion = 3;
    SearchRequest search = 
        new SearchRequest(query, filter, SearchScope.Base, "mail");
    SearchResponse response = connection.SendRequest(search) as SearchResponse;
    foreach(SearchResultEntry entry in response.Entries)
    {
        Console.WriteLine(entry.Attributes["mail"][0]);
    }
}