如何查看当前开放的端口？

在C#中，要查看当前开放的端口，可以通过调用Windows API来实现。一种方法是使用`System.Diagnostics`命名空间下的`Process`类，结合`TcpListener`和`Socket`类来枚举正在监听的端口。以下是使用C#代码来查看本地计算机上开放端口的示例：

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Net;
using System.Net.NetworkInformation;
using System.Net.Sockets;

class Program
{
    static void Main()
    {
        List<IPAddress> localIPs = new List<IPAddress>();
        
        // Add the loopback IP address.
        localIPs.Add(IPAddress.Loopback);

        // Add IP addresses for all network interfaces on the local machine.
        IPHostEntry host = Dns.GetHostEntry(Dns.GetHostName());
        foreach (IPAddress ip in host.AddressList)
        {
            if (ip.AddressFamily == AddressFamily.InterNetwork)
            {
                localIPs.Add(ip);
            }
        }

        foreach (IPAddress localIP in localIPs)
        {
            Console.WriteLine("Interface IP Address: " + localIP.ToString());

            IPGlobalProperties properties = IPGlobalProperties.GetIPGlobalProperties();

            // Retrieve TCP connections.
           TcpConnectionInformation[] tcpConnInfoArray = properties.GetTcpConnections();
            foreach (TcpConnectionInformation tcpConnInfo in tcpConnInfoArray)
            {
                // Print out the state of the connection.
                Console.WriteLine("TCP State: " + tcpConnInfo.State.ToString());
                
                // Print out the local endpoint.
                IPEndPoint localEndPoint = tcpConnInfo.LocalEndPoint as IPEndPoint;
                if (localEndPoint != null && localEndPoint.Address.Equals(localIP))
                {
                    Console.WriteLine("Local EndPoint: " + localEndPoint.ToString());
                }
            }

            // Retrieve UDP connections.
            IPEndPoint[] udpListeners = properties.GetActiveUdpListeners();
            foreach (IPEndPoint udpEndPoint in udpListeners)
            {
                if (udpEndPoint.Address.Equals(localIP))
                {
                    Console.WriteLine("UDP Listener EndPoint: " + udpEndPoint.ToString());
                }
            }
        }
    }
}

上面的代码会显示所有本地接口的IP地址，并列出每个IP地址上的TCP和UDP监听端口。请注意，这需要在具有管理员权限的环境中运行，因为某些端口信息可能受到安全限制。