还有一种可能——

请确保您尝试打开的IP地址与您正在收听的地址相同。我的服务器应用程序正在使用IPv6侦听主机的IP地址，但客户端试图在主机的IPv4地址上连接。

在我的例子中，有些域名可以使用，而有些则不行。在我的网页中添加对我的组织的代理Url的引用。配置修复了这个问题。

<system.net>
    <defaultProxy useDefaultCredentials="true">
      <proxy proxyaddress="http://proxy.my-org.com/" usesystemdefault="True"/>
    </defaultProxy>
</system.net>

I was facing this issue today. Mine was Asp.Net Core API and it uses Postgresql as the database. We have configured this database as a Docker container. So the first step I did was to check whether I am able to access the database or not. To do that I searched for PgAdmin in the start as I have configured the same. Clicking on the resulted application will redirect you to the http://127.0.0.1:23722/browser/. There you can try access your database on the left menu. For me I was getting an error as in the below image.

输入密码，并尝试是否能够访问它。对我来说，这行不通。因为它是一个Docker容器，我决定重新启动我的Docker桌面，右键单击任务栏中的Docker图标，然后单击重新启动。

在重新启动Docker后，我能够登录并看到数据库，并且当我在Visual Studio中重新启动应用程序时，错误也消失了。

希望能有所帮助。

我想分享我发现的这个答案，因为问题的原因不是防火墙或进程没有正确侦听，而是我使用的微软提供的代码示例。

https://msdn.microsoft.com/en-us/library/system.net.sockets.socket%28v=vs.110%29.aspx

我几乎完全按照所写的那样实现了这个函数，但发生的事情是我得到了这个错误:

2016-01-05 12:00:48075 [10] ERROR -错误是:System.Net.Sockets.SocketException (0x80004005): No connection could be made because The target machine actively refused it [fe80::caa:745:a1da:e6f1%11]:4080

这段代码将表示套接字已连接，但不是在正确通信实际所需的正确IP地址下。(微软提供)

private static Socket ConnectSocket(string server, int port)
    {
        Socket s = null;
        IPHostEntry hostEntry = null;

        // Get host related information.
        hostEntry = Dns.GetHostEntry(server);

        // Loop through the AddressList to obtain the supported AddressFamily. This is to avoid
        // an exception that occurs when the host IP Address is not compatible with the address family
        // (typical in the IPv6 case).
        foreach(IPAddress address in hostEntry.AddressList)
        {
            IPEndPoint ipe = new IPEndPoint(address, port);
            Socket tempSocket = 
                new Socket(ipe.AddressFamily, SocketType.Stream, ProtocolType.Tcp);

            tempSocket.Connect(ipe);

            if(tempSocket.Connected)
            {
                s = tempSocket;
                break;
            }
            else
            {
                continue;
            }
        }
        return s;
    }

我重写了代码，只使用它找到的第一个有效IP。我只关心使用IPV4，但它与localhost, 127.0.0.1，和您的网卡的实际IP地址，其中微软提供的例子失败了!

    private Socket ConnectSocket(string server, int port)
    {
        Socket s = null;

        try
        {
            // Get host related information.
            IPAddress[] ips;
            ips = Dns.GetHostAddresses(server);

            Socket tempSocket = null;
            IPEndPoint ipe = null;

            ipe = new IPEndPoint((IPAddress)ips.GetValue(0), port);
            tempSocket = new Socket(ipe.AddressFamily, SocketType.Stream, ProtocolType.Tcp);

            Platform.Log(LogLevel.Info, "Attempting socket connection to " + ips.GetValue(0).ToString() + " on port " + port.ToString());
            tempSocket.Connect(ipe);

            if (tempSocket.Connected)
            {
                s = tempSocket;
                s.SendTimeout = Coordinate.HL7SendTimeout;
                s.ReceiveTimeout = Coordinate.HL7ReceiveTimeout;
            }
            else
            {
                return null;
            }

            return s;
        }
        catch (Exception e)
        {
            Platform.Log(LogLevel.Error, "Error creating socket connection to " + server + " on port " + port.ToString());
            Platform.Log(LogLevel.Error, "The error is: " + e.ToString());
            if (g_NoOutputForThreading == false)
                rtbResponse.AppendText("Error creating socket connection to " + server + " on port " + port.ToString());
            return null;
        }
    }

这里还有一件事要检查，我犯这个错误的次数比我愿意承认的多:你是试图连接https还是http?我以为我有一些模糊的证书问题，但结果是我忘记了我的URL定义中的s。总是先检查基础!

最可能的原因是防火墙。

这篇文章包含了一组可能对您有用的原因。

从文章来看，可能的原因有:

FTP服务器设置 软件/个人防火墙设置 多种软件/个人防火墙 杀毒软件 LSP层 路由器固件 关闭电脑 电脑未插电 提琴手