运行PowerShell UDP端口测试脚本报错：UdpClient无BeginConnect方法

问题背景 #

运行基于System.Net.Sockets.UdpClient的PowerShell UDP端口测试脚本时，触发以下错误：

Method invocation failed because [System.Net.Sockets.UdpClient] does not contain a method named 'BeginConnect'.
At line:12 char:9
+         $connect = $obj.BeginConnect($target,$port,$null,$null)
+         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [], RuntimeException
    + FullyQualifiedErrorId : MethodNotFound

原始脚本 #

$targetservers = "192.168.2.2"
$ports = "53"

$result = @()

foreach ($target in $targetservers) {

    foreach ($port in $ports) {

        $obj = new-Object System.Net.Sockets.UdpClient

        $connect = $obj.BeginConnect($target,$port,$null,$null)

        $Wait = $connect.AsyncWaitHandle.WaitOne(100,$false)

        If (-Not $Wait) {

            write-host $target ‘port’ $port ‘Closed – Timeout’

        }

        else {

            $value = “Open”

            write-host $target ‘port’ $port $value

            $r = new-object -type psobject

            $r | add-member -membertype noteproperty -name host -value $target

            $r | add-member -membertype noteproperty -name port -value $port

            $r | add-member -membertype noteproperty -name state -value $value

            $result += $r

        }

    }

}

UPDATE 1脚本 #

$targetservers = "192.168.200.11"
$ports = "53"

$result = @()

foreach ($target in $targetservers) {

    foreach ($port in $ports) {

        $obj = new-Object System.Net.Sockets.UdpClient

        $connect = $obj.Connect($target,$port)

        $Wait = $connect.AsyncWaitHandle.WaitOne(100,$false)

        If (-Not $Wait) {

            write-host $target ‘port’ $port ‘Closed – Timeout’

        }

        else {

            $value = “Open”

            write-host $target ‘port’ $port $value

            $r = new-object -type psobject

            $r | add-member -membertype noteproperty -name host -value $target

            $r | add-member -membertype noteproperty -name port -value $port

            $r | add-member -membertype noteproperty -name state -value $value

            $result += $r

        }

    }

}

问题根源 #

1. UdpClient类没有BeginConnect方法：这个异步方法属于TCP协议的TcpClient，UDP是无连接协议，不存在“建立连接”的概念。
2. UPDATE 1脚本的错误：UdpClient.Connect()是无返回值的void方法，执行后$connect为$null，调用$connect.AsyncWaitHandle会直接报错。而且Connect()只是设置后续发送/接收的默认远程端点，不会发起任何实际的网络请求，根本无法用来判断端口状态。

正确解决方案 #

UDP端口测试的核心是发送测试数据包并等待响应，因为UDP没有连接握手，只能通过目标是否返回响应来判断端口是否开放（或服务是否存活）。以下是修正后的脚本（以DNS服务为例）：

$targetservers = "192.168.2.2"
$ports = "53"
$result = @()

foreach ($target in $targetservers) {
    foreach ($port in $ports) {
        $state = "Closed/Unresponsive"
        $udpClient = $null
        try {
            $udpClient = New-Object System.Net.Sockets.UdpClient
            # 设置发送和接收超时（单位：毫秒）
            $udpClient.Client.ReceiveTimeout = 1000
            $udpClient.Client.SendTimeout = 1000

            # 发送符合DNS协议的测试查询包（查询www.example.com的A记录）
            $dnsTestPacket = [byte[]]@(
                0x00, 0x01, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x03, 0x77, 0x77, 0x77,
                0x07, 0x65, 0x78, 0x61, 0x6D, 0x70, 0x6C, 0x65,
                0x03, 0x63, 0x6F, 0x6D, 0x00, 0x00, 0x01, 0x00, 0x01
            )
            $udpClient.Send($dnsTestPacket, $dnsTestPacket.Length, $target, $port) | Out-Null

            # 尝试接收响应
            $remoteEndpoint = New-Object System.Net.IPEndPoint([System.Net.IPAddress]::Any, 0)
            $response = $udpClient.Receive([ref]$remoteEndpoint)
            
            if ($response -ne $null) {
                $state = "Open/Responsive"
            }
        }
        catch [System.Net.Sockets.SocketException] {
            # 根据错误码区分不同情况
            switch ($_.Exception.ErrorCode) {
                10060 { $state = "Closed – Timeout" }
                10049 { $state = "Target Unreachable" }
                default { $state = "Error: $($_.Exception.Message)" }
            }
        }
        finally {
            # 确保释放资源
            if ($udpClient) { $udpClient.Close() }
        }

        Write-Host "$target port $port $state"
        # 添加结果到集合
        $result += [PSCustomObject]@{
            Host  = $target
            Port  = $port
            State = $state
        }
    }
}

# 输出最终结果
$result

脚本关键说明 #

• 协议适配：测试不同UDP服务时，需要发送对应协议的测试包（比如SNMP用GetRequest包），否则目标服务可能不会返回响应。
• 超时控制：通过ReceiveTimeout和SendTimeout避免脚本长时间等待。
• 异常处理：捕获SocketException来处理超时、不可达等网络异常，更准确判断端口状态。

内容的提问来源于stack exchange，提问作者Arbelac