请解释一下这个 LAN 唤醒脚本的工作原理

Question

几个月前，我在博客上发现了这段 PowerShell 代码。它无需使用外部程序即可将 LAN 唤醒信号发送到您选择的 MAC 地址。我对这篇博文发表了评论，并要求作者描述一下脚本背后的逻辑，因为我对此感到好奇。稍后我又回到博客文章，看看作者是否回复了我的评论。我很惊讶地发现我被重定向到一个页面，作者说他由于崩溃而丢失了他的博客。我不记得它的细节，但我想我不再为那个博客添加书签了。

所以现在我想请求 Stack Overflow 上的聪明人看看这段代码并向我解释它的逻辑。每行都有评论就太好了。我很好奇这是如何运作的。它似乎比我发现的其他脚本更强大，因为它可以跨子网工作。不过我对网络了解不多。

我最好奇的事情之一是最后的 for 循环。为什么要多次发送信号？为什么在不同的端口上？但我真的很想知道整个脚本背后的逻辑。

代码：

param (
    $targetMac,
    $network = [net.ipaddress]::Broadcast,
    $subnet = [net.ipaddress]::Broadcast
)
try {
    if($network.gettype().equals([string])) {
        $network = [net.ipaddress]::Parse($network);
    }
    if($subnet.gettype().equals([string])) {
        $subnet = [net.ipaddress]::Parse($subnet);
    }
    $broadcast = new-object net.ipaddress (([system.net.ipaddress]::parse("255.255.255.255").address -bxor $subnet.address -bor $network.address))

    $mac = [Net.NetworkInformation.PhysicalAddress]::Parse($targetMac.toupper().replace(".",""))

    $u = New-Object net.sockets.udpclient
    $ep = New-Object net.ipendpoint $broadcast, 0
    $ep2 = New-Object net.ipendpoint $broadcast, 7
    $ep3 = New-Object net.ipendpoint $broadcast, 9

    $payload = [byte[]]@(255,255,255, 255,255,255);
    $payload += ($mac.GetAddressBytes()*16)

    for($i = 0; $i -lt 10; $i++) {
        $u.Send($payload, $payload.Length, $ep) | Out-Null
        $u.Send($payload, $payload.Length, $ep2) | Out-Null
        $u.Send($payload, $payload.Length, $ep3) | Out-Null
        sleep 1;
    }
} catch {
    $Error | Write-Error;
}

Answer 1

#These are the parameters to the script. The only mandatory param here is the mac address
#[net.ipaddress]::Broadcast will resolve to something like 255.255.255.255
param (
    $targetMac,
    $network = [net.ipaddress]::Broadcast,
    $subnet = [net.ipaddress]::Broadcast
)

#We start the try, catch error handling here.
#if something in try block fails, the catch block will write the error
try {

#This will evaludate to False. Hence, $network will have whatever was passed through params or the default value
#in this case the default value is 255.255.255.255
    if($network.gettype().equals([string])) {
        $network = [net.ipaddress]::Parse($network);
    }

#This will evaludate to False. Hence, $network will have whatever was passed through params or the default value
#in this case the default value is 255.255.255.255    
    if($subnet.gettype().equals([string])) {
        $subnet = [net.ipaddress]::Parse($subnet);
    }

    #Not sure if this is really required here. But, assuming that the default value for both $network and $subet is 255.255.255.255,
    #this will result in $broadcast set to 255.255.255.255
    $broadcast = new-object net.ipaddress (([system.net.ipaddress]::parse("255.255.255.255").address -bxor $subnet.address -bor $network.address))

#This again assumes that you had given . as the delimeter in MAC address and removes that from MAC address    
    $mac = [Net.NetworkInformation.PhysicalAddress]::Parse($targetMac.toupper().replace(".",""))

#Create a new object of type net.sockets.udpclient
    $u = New-Object net.sockets.udpclient

#WOL magic packet can be sent on port 0, 7, or 9    
#Create a end point for the broadcast address at port 0    
    $ep = New-Object net.ipendpoint $broadcast, 0

#Create a end point for the broadcast address at port 7    
    $ep2 = New-Object net.ipendpoint $broadcast, 7

#Create a end point for the broadcast address at port 9    
    $ep3 = New-Object net.ipendpoint $broadcast, 9

#Create a payload packet
#First, create a byte array
    $payload = [byte[]]@(255,255,255, 255,255,255);

#add the mac address to the above byte array    
    $payload += ($mac.GetAddressBytes()*16)

#Send 10 magic packets for each port number or end point created above.
#one is more than enough. If everything is congfigured properly
    for($i = 0; $i -lt 10; $i++) {
        $u.Send($payload, $payload.Length, $ep) | Out-Null
        $u.Send($payload, $payload.Length, $ep2) | Out-Null
        $u.Send($payload, $payload.Length, $ep3) | Out-Null
        sleep 1;
    }
} catch {
#catch block catches any error from try block
    $Error | Write-Error;
}

Answer 2

维基百科对 LAN 唤醒有很好的解释：

http://en.wikipedia.org /wiki/Wake-on-LAN

摘自该文章：

[The Magic Packet] is typically sent as a UDP datagram to port 7 or 9, but actually it can be 
sent on any port.

我猜测多次发送数据包的原因是为了解决偶尔的网络冲突。如果发生冲突，则必须重新发送数据包。