指定哪些DNS服務器用來解決在.NET

Question

主機名，我想知道是否有任何方式強迫System.Net.Dns類解決您在使用一組自定義DNS服務器，而不是使用那些主機名是與主網絡連接相關聯。

我懷疑這隻能用像DnDns這樣的自定義庫（http://dndns.codeplex.com），但我希望這可以在.NET中完成。

Answer 1

不能用.Net框架來完成。 Dns.Resolve方法依賴於內部的Win32 API，而這些API依次通過與網絡連接關聯的DNS服務器。

爲了得到這個工作，你必須改變與網絡適配器的地址相關聯的DNS服務器。

Answer 2

您可以使用「JH Software的.NET的DNS客戶端」來完成此操作 - 無需更改DNS本地服務器。 看到http://www.simpledns.com/dns-client-lib.aspx

Answer 3

在.NET標準測試的第二個代碼示例：

public static async Task<IPHostEntry> GetHostEntryAsync(string host, string dns = null) 
    { 
     if (string.IsNullOrEmpty(host)) 
     { 
      return null; 
     } 

     //Check if any cached result exists 
     Tuple<string, string> key = new Tuple<string, string>(host, dns); 
     if (NetHelper._dnsCache.TryGetValue(key, out Tuple<IPHostEntry, DateTime> record) && record.Item2 > DateTime.Now) 
     { 
      return record.Item1; 
     } 

     //Check dns server's address or port 
     IPHostEntry result = null; 
     int dnsPort; 
     if (dns != null) 
     { 
      string[] blocks = dns.Split(':'); 
      if (blocks.Length == 2 && int.TryParse(blocks[1], out dnsPort))//dns is ip v4 
      { 
       dns = blocks[0]; 
      } 
      else if (blocks.Length == 9 && int.TryParse(blocks[8], out dnsPort))//dns is ip v6 
      { 
       blocks[0] = blocks[0].TrimStart('['); 
       blocks[7] = blocks[7].TrimStart(']'); 
       dns = string.Format("{0}:{1}:{2}:{3}:{4}:{5}:{6}:{7}", blocks); 
      } 
      else 
      { 
       dnsPort = 53; 
      } 
     } 
     else 
     { 
      dnsPort = 53; 
     } 

     //Check if host is ip address 
     if (host[0] == '[' && host[host.Length - 1] == ']')//IPV6 address 
     { 
      host = host.Substring(1, host.Length - 2); 
     } 
     if (IPAddress.TryParse(host, out IPAddress address)) 
     { 
      result = new IPHostEntry { AddressList = new IPAddress[] { address } }; 
     } 
     else if (string.IsNullOrEmpty(dns)) 
     { 
      result = await Dns.GetHostEntryAsync(host); 
     } 
     else 
     { 
      #region Resolve with customized dns server 
      IPAddress dnsAddr; 
      if (!IPAddress.TryParse(dns, out dnsAddr)) 
      { 
       throw new ArgumentException("The dns host must be ip address.", nameof(dns)); 
      } 
      using (MemoryStream ms = new MemoryStream()) 
      { 
       Random rnd = new Random(); 
       //About the dns message:http://www.ietf.org/rfc/rfc1035.txt 

       //Write message header. 
       ms.Write(new byte[] { 
        (byte)rnd.Next(0, 0xFF),(byte)rnd.Next(0, 0xFF), 
        0x01, 
        0x00, 
        0x00,0x01, 
        0x00,0x00, 
        0x00,0x00, 
        0x00,0x00 
       }, 0, 12); 

       //Write the host to query. 
       foreach (string block in host.Split('.')) 
       { 
        byte[] data = Encoding.UTF8.GetBytes(block); 
        ms.WriteByte((byte)data.Length); 
        ms.Write(data, 0, data.Length); 
       } 
       ms.WriteByte(0);//The end of query, muest 0(null string) 

       //Query type:A 
       ms.WriteByte(0x00); 
       ms.WriteByte(0x01); 

       //Query class:IN 
       ms.WriteByte(0x00); 
       ms.WriteByte(0x01); 

       Socket socket = new Socket(SocketType.Dgram, ProtocolType.Udp); 
       try 
       { 
        //send to dns server 
        byte[] buffer = ms.ToArray(); 
        while (socket.SendTo(buffer, 0, buffer.Length, SocketFlags.None, new IPEndPoint(dnsAddr, dnsPort)) < buffer.Length) ; 
        buffer = new byte[0x100]; 
        EndPoint ep = socket.LocalEndPoint; 
        int num = socket.ReceiveFrom(buffer, 0, buffer.Length, SocketFlags.None, ref ep); 

        //The response message has the same header and question structure, so we move index to the answer part directly. 
        int index = (int)ms.Length; 
        //Parse response records. 
        void SkipName() 
        { 
         while (index < num) 
         { 
          int length = buffer[index++]; 
          if (length == 0) 
          { 
           break; 
          } 
          else if (length > 191) 
          { 
           return; 
          } 
          index += length; 
         } 
        } 

        List<IPAddress> addresses = new List<IPAddress>(); 
        while (index < num) 
        { 
         SkipName();//Seems the name of record is useless in this scense, so we just needs to get the next index after name. 
         byte type = buffer[index += 2]; 
         index += 7;//Skip class and ttl 

         int length = buffer[index++] << 8 | buffer[index++];//Get record data's length 

         if (type == 0x01)//A record 
         { 
          if (length == 4)//Parse record data to ip v4, this is what we need. 
          { 
           addresses.Add(new IPAddress(new byte[] { buffer[index], buffer[index + 1], buffer[index + 2], buffer[index + 3] })); 
          } 
         } 
         index += length; 
        } 
        result = new IPHostEntry { AddressList = addresses.ToArray() }; 
       } 
       finally 
       { 
        socket.Dispose(); 
       } 
      } 
      #endregion 
     } 

     //Cache and return result 
     NetHelper._dnsCache[key] = new Tuple<IPHostEntry, DateTime>(result, DateTime.Now.AddMinutes(15)); 

     #pragma warning disable CS4014 
     Task.Run(async() => 
     { 
      await Task.Delay((int)TimeSpan.FromMinutes(15).TotalMilliseconds); 
      NetHelper._dnsCache.Remove(key); 
     }); 
     #pragma warning restore CS4014 
     return result; 

    }