blocks|key|1334365|text|您自己的MTU在registry中是可用的，但实际上MTU将到达您的计算机和目的地之间的路径中最小的MTU。它既是可变的，也只能通过经验来确定。有许多RFCs展示了如何确定它。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1334366|LAN内部可以有非常大的MTU值，因为网络硬件通常是同构的，或者至少是集中管理的。|1334367|entityMap|0|LINK|mutability|MUTABLE|url|http://www.pctools.com/guides/registry/detail/280/|1|http://en.wikipedia.org/wiki/Path_MTU_discovery^0|8|8|0|23|4|1|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@$A|Q|B|R|1|S]|$A|T|B|U|1|V]]|C|$]]|$1|D|3|E|5|6|7|W|8|@]|9|@]|C|$]]|$1|F|3|-4|5|6|7|X|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]|N|$5|I|J|K|C|$L|O]]]]

Your own MTU is available in the <a href="http://www.pctools.com/guides/registry/detail/280/" rel="nofollow noreferrer">registry</a>, but the MTU in practice is going to the smallest MTU in the path between your machine and the destination. Its both variable and can only be determined empirically. There are a number of <a href="http://en.wikipedia.org/wiki/Path_MTU_discovery" rel="nofollow noreferrer">RFCs</a> showing how to determine it.

LAN's can internally have very large MTU values, since the network hardware is typically homogeneous or at least centrally administrated.

blocks|key|1334454|text|这对我来说是一个有趣的话题。当通过UDP在现实世界的互联网上传送大块的UDP数据时，可能会对一些实际结果感兴趣，并且在每秒1个包的传输速率下，数据继续以最小的包丢失出现，直到大约2K。在这上面，你开始遇到问题，但我们定期发送1600%2B字节数据包没有痛苦-这是在GPRS移动网络以及广域网全球范围内。在~1K假设信号是稳定的(其实不然！)您可以获得低丢包率。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1334455|有趣的是，这不是奇怪的数据包，而是几秒钟的狂暴数据包-这可能就是为什么VoIP调用偶尔崩溃的原因。|1334456|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

This is an interesting topic for me. Perhaps some practical results might be of interest when delivering chunky UDP data around the real world internet via UDP, and with a transmission rate of 1 packet a second, data continues to turn up with minimal packet loss up to about 2K. Over this and you start running into issues, but regularly we delivered 1600+ bytes packets without distress - this is over GPRS mobile networks as well as WAN world wide. At ~1K assuming the signal is stable (its not!) you get low packet loss. 

Interestingly its not the odd packet, but often a squall of packets for a few seconds - which presumably is why VoIP calls just collapse occasionally.

blocks|key|1334514|text|这是我用来检查Path+PowerShell问题的一小段Windows。(一般的技术在其他编程语言中实现起来并不困难。)许多防火墙和路由器被配置为丢弃所有ICMP，这是由不了解情况的人所做的。路径MTU发现取决于是否能够接收设置了需要分段的ICMP目标不可达消息，以响应发送设置了不分段的数据包。Resolve+IPv4+Fragmentation,+MTU,+MSS,+and+PMTUD+Issues+with+GRE+and+IPsec实际上很好地解释了discovery是如何工作的。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1334515|function+Test-IPAddressOrName($ipAddressOrName)
{
++++$ipaddress+=+$null
++++$isValidIPAddressOrName+=+[ipaddress]::TryParse($ipAddressOrName,+[ref]+$ipaddress)

++++if+($isValidIPAddressOrName+-eq+$false)
++++{
++++++++$hasResolveDnsCommand+=+$null+-ne+(Get-Command+Resolve-DnsName+-ErrorAction+SilentlyContinue)
++++++++if+($hasResolveDnsCommand+-eq+$true)
++++++++{
++++++++++++$dnsResult+=+Resolve-DnsName+-DnsOnly+-Name+$ipAddressOrName+-ErrorAction+SilentlyContinue
++++++++++++$isValidIPAddressOrName+=+$null+-ne+$dnsResult
++++++++}
++++}

++++return+$isValidIPAddressOrName
}

function+Get-NameAndIPAddress($ipAddressOrName)
{
++++$hasResolveDnsCommand+=+$null+-ne+(Get-Command+Resolve-DnsName+-ErrorAction+SilentlyContinue)

++++$ipAddress+=+$null
++++$validIPAddress+=+[ipaddress]::TryParse($ipAddressOrName,+[ref]+$ipAddress)
++++$nameAndIp+=+[PSCustomObject]+@{+'Name'+=+$null;+'IPAddress'+=+$null+}

++++if+($validIPAddress+-eq+$false)
++++{
++++++++if+($hasResolveDnsCommand+-eq+$true)
++++++++{
++++++++++++$dnsResult+=+Resolve-DnsName+-DnsOnly+$ipAddressOrName+-Type+A+-ErrorAction+SilentlyContinue

++++++++++++if+($null+-ne+$dnsResult+-and+$dnsResult.QueryType+-eq+'A')
++++++++++++{
++++++++++++++++$nameAndIp.Name+=+$dnsResult.Name
++++++++++++++++$nameAndIp.IPAddress+=+$dnsResult.IPAddress
++++++++++++}
++++++++++++else
++++++++++++{
++++++++++++++++Write-Error+"The+name+$($ipAddressOrName)+could+not+be+resolved."
++++++++++++++++$nameAndIp+=+$null
++++++++++++}
++++++++}
++++++++else
++++++++{
++++++++++++Write-Warning+"Resolve-DnsName+not+present.+DNS+resolution+check+skipped."
++++++++}
++++}
++++else
++++{
++++++++$nameAndIp.IPAddress+=+$ipAddress

++++++++if+($hasResolveDnsCommand+-eq+$true)
++++++++{
++++++++++++$dnsResult+=+Resolve-DnsName+-DnsOnly+$ipAddress+-Type+PTR+-ErrorAction+SilentlyContinue

++++++++++++if+($null+-ne+$dnsResult+-and+$dnsResult.QueryType+-eq+'PTR')
++++++++++++{
++++++++++++++++$nameAndIp.Name+=+$dnsResult.NameHost
++++++++++++}
++++++++}
++++}

++++return+$nameAndIp
}

<#
++++.Synopsis
++++Performs+a+series+of+pings+(ICMP+echo+requests)+with+Don't+Fragment+specified+to+discover+the+path+MTU+(Maximum+Transmission+Unit).

++++.Description
++++Performs+a+series+of+pings+with+Don't+Fragment+specified+to+discover+the+path+MTU+(Maximum+Transmission+Unit).+An+ICMP+echo+request+
++++is+sent+with+a+random+payload+with+a+payload+length+specified+by+the+PayloadBytesMinimun.+ICMP+echo+requests+of+increasing+size+are+
++++sent+until+a+ping+response+status+other+than+Success+is+received.+If+the+response+status+is+PackeTooBig,+the+last+successful+packet+
++++length+is+returned+as+a+reliable+MTU;+otherwise,+if+the+respone+status+is+TimedOut,+the+same+size+packet+is+retried+up+to+the+number+
++++of+retries+specified.+If+all+of+the+retries+have+been+exhausted+with+a+response+status+of+TimedOut,+the+last+successful+packet+
++++length+is+returned+as+the+assumed+MTU.

++++.Parameter+UseDefaultGateway
++++If+UseDefaultGateway+is+specified+the+default+gateway+reported+by+the+network+interface+is+used+as+the+destination+host.

++++.Parameter+DestinationHost
++++The+IP+Address+or+valid+fully+qualified+DNS+name+of+the+destination+host.

++++.Parameter+InitialTimeout
++++The+number+of+milliseconds+to+wait+for+an+ICMP+echo+reply.+Internally,+this+is+doubled+each+time+a+retry+occurs.

++++.Parameter+Retries
++++The+number+of+times+to+try+the+ping+in+the+event+that+no+reply+is+recieved+before+the+timeout.

++++.Parameter+PayloadBytesMinimum
++++The+minimum+number+of+bytes+in+the+payload+to+use.+The+minimum+MTU+for+IPv4+is+68+bytes;+however,+in+practice,+it's+extremely+rare+
++++to+see+an+MTU+size+less+than+576+bytes+so+the+default+value+is+548+bytes+(576+bytes+total+packet+size+minus+an+ICMP+header+of+28+
++++bytes).

++++.Parameter+PayloadBytesMaximum
++++The+maximum+number+of+bytes+in+the+payload+to+use.+An+IPv4+MTU+for+jumbo+frames+is+9000+bytes.+The+default+value+is+8973+bytes+(9001+
++++bytes+total+packet+size,+which+is+1+byte+larger+than+the+maximum+IPv4+MTU+for+a+jumbo+frame,+minus+an+ICMP+header+of+28+bytes).

++++.Example
++++Discover-PathMTU+-UseDefaultGateway

++++.Example
++++Discover-PathMTU+-DestinationHost+'192.168.1.1'

++++.Example
++++Discover-PathMTU+-DestinationHost+'www.google.com'
#>
function+Discover-PathMtu
{
++++[CmdletBinding(SupportsShouldProcess+=+$false)]
++++param
++++(
++++++++[Parameter(Mandatory+=+$true,+ParameterSetName+=+'DefaultGateway')]
++++++++[switch]+$UseDefaultGateway,

++++++++[Parameter(Mandatory+=+$true,+Position+=+0,+ValueFromPipeline+=+$true,+ParameterSetName+=+'IPAddressOrName')]
++++++++[ValidateScript({+Test-IPAddressOrName+$_+})]
++++++++[string]+$DestinationHost,

++++++++[Parameter(ParameterSetName+=+'IPAddressOrName')]
++++++++[Parameter(ParameterSetName+=+'DefaultGateway')]
++++++++[int]+$InitialTimeout+=+3000,

++++++++[Parameter(ParameterSetName+=+'IPAddressOrName')]
++++++++[Parameter(ParameterSetName+=+'DefaultGateway')]
++++++++[int]+$Retries+=+3,

++++++++[Parameter(ParameterSetName+=+'IPAddressOrName')]
++++++++[Parameter(ParameterSetName+=+'DefaultGateway')]
++++++++$PayloadBytesMinimum+=+548,

++++++++[Parameter(ParameterSetName+=+'IPAddressOrName')]
++++++++[Parameter(ParameterSetName+=+'DefaultGateway')]
++++++++$PayloadBytesMaximum+=+8973
++++)

++++begin
++++{
++++++++$ipConfiguration+=+Get-NetIPConfiguration+-Detailed+%7C+?{+$_.NetProfile.Ipv4Connectivity+-eq+'Internet'+-and+$_.NetAdapter.Status+-eq+'Up'+}+%7C+Sort+{+$_.IPv4DefaultGateway.InterfaceMetric+}+%7C+Select+-First+1
++++++++$gatewayIPAddress+=+$ipConfiguration.IPv4DefaultGateway.NextHop

++++++++$pingOptions+=+New-Object+System.Net.NetworkInformation.PingOptions
++++++++$pingOptions.DontFragment+=+$true
++++++++$pinger+=+New-Object+System.Net.NetworkInformation.Ping

++++++++$rng+=+New-Object+System.Security.Cryptography.RNGCryptoServiceProvider
++++}

++++process
++++{
++++++++$pingIpAddress+=+$null

++++++++if+($UseDefaultGateway+-eq+$true)
++++++++{
++++++++++++$DestinationHost+=+$gatewayIPAddress
++++++++}

++++++++$nameAndIP+=+Get-NameAndIPAddress+$DestinationHost

++++++++if+($null+-ne+$nameAndIP)
++++++++{
++++++++++++Write-Host+"Performing+Path+MTU+discovery+for+$($nameAndIP.Name)+$($nameAndIP.IPAddress)..."

++++++++++++$pingReply+=+$null
++++++++++++$payloadLength+=+$PayloadBytesMinimum
++++++++++++$workingPingTimeout+=+$InitialTimeout

++++++++++++do
++++++++++++{
++++++++++++++++$payloadLength%2B%2B

++++++++++++++++#+Use+a+random+payload+to+prevent+compression+in+the+path+from+potentially+causing+a+false+MTU+report.
++++++++++++++++[byte[]]+$payloadBuffer+=+(,0x00+*+$payloadLength)
++++++++++++++++$rng.GetBytes($payloadBuffer)

++++++++++++++++$pingCount+=+1

++++++++++++++++do
++++++++++++++++{
++++++++++++++++++++$pingReply+=+$pinger.Send($nameAndIP.IPAddress,+$workingPingTimeout,+$payloadBuffer,+$pingOptions)

++++++++++++++++++++if+($pingReply.Status+-notin+'Success',+'PacketTooBig',+'TimedOut')
++++++++++++++++++++{
++++++++++++++++++++++++Write-Warning+"An+unexpected+ping+reply+status,+$($pingReply.Status),+was+received+in+$($pingReply.RoundtripTime)+milliseconds+on+attempt+$($pingCount)."
++++++++++++++++++++}
++++++++++++++++++++elseif+($pingReply.Status+-eq+'TimedOut')
++++++++++++++++++++{
++++++++++++++++++++++++Write-Warning+"The+ping+request+timed+out+while+testing+a+packet+of+size+$($payloadLength+%2B+28)+using+a+timeout+value+of+$($workingPingTimeout)+milliseconds+on+attempt+$($pingCount)."
++++++++++++++++++++++++$workingPingTimeout+=+$workingPingTimeout+*+2
++++++++++++++++++++}
++++++++++++++++++++else
++++++++++++++++++++{
++++++++++++++++++++++++Write-Verbose+"Testing+packet+of+size+$($payloadLength+%2B+28).+The+reply+was+$($pingReply.Status)+and+was+received+in+$($pingReply.RoundtripTime)+milliseconds+on+attempt+$($pingCount)."
++++++++++++++++++++++++$workingPingTimeout+=+$InitialTimeout
++++++++++++++++++++}

++++++++++++++++++++Sleep+-Milliseconds+10

++++++++++++++++++++$pingCount%2B%2B
++++++++++++++++}+while+($pingReply.Status+-eq+'TimedOut'+-and+$pingCount+-le+$Retries)
++++++++++++}+while+($payloadLength+-lt+$PayloadBytesMaximum+-and+$pingReply+-ne+$null+-and+$pingReply.Status+-eq+'Success')

++++++++++++if+($pingReply.Status+-eq+'PacketTooBig')
++++++++++++{
++++++++++++++++Write-Host+"Reported+IPv4+MTU+is+$($ipConfiguration.NetIPv4Interface.NlMtu).+The+discovered+IPv4+MTU+is+$($payloadLength+%2B+27)."
++++++++++++}
++++++++++++elseif+($pingReply.Status+-eq+'TimedOut')
++++++++++++{
++++++++++++++++Write-Host+"Reported+IPv4+MTU+is+$($ipConfiguration.NetIPv4Interface.NlMtu).+The+discovered+IPv4+MTU+is+$($payloadLength+%2B+27),+but+may+not+be+reliable+because+the+packet+appears+to+have+been+discarded."++++
++++++++++++}
++++++++++++else
++++++++++++{
++++++++++++++++Write-Host+"Reported+IPv4+MTU+is+$($ipConfiguration.NetIPv4Interface.NlMtu).+The+discovered+IPv4+MTU+is+$($payloadLength+%2B+27),+but+may+not+be+reliable,+due+to+an+unexpected+ping+reply+status."++++
++++++++++++}

++++++++++++return+$payloadLength+%2B+27
++++++++}
++++++++else
++++++++{
++++++++++++Write-Error+"The+name+$($DestinationHost)+could+not+be+resolved.+No+Path+MTU+discovery+will+be+performed."
++++++++}
++++}

++++end
++++{
++++++++if+($null+-ne+$pinger)
++++++++{
++++++++++++$pinger.Dispose()
++++++++}

++++++++if+($null+-ne+$rng)
++++++++{
++++++++++++$rng.Dispose()
++++++++}
++++}
}|code-block|syntax|javascript|1334516|entityMap|0|LINK|mutability|MUTABLE|url|https://www.cisco.com/c/en/us/support/docs/ip/generic-routing-encapsulation-gre/25885-pmtud-ipfrag.html^0|44|21|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

Here's a bit of Windows PowerShell that I wrote to check for Path MTU issues. (The general technique is not too hard to implement in other programming languages.) A lot of firewalls and routers are configured to drop all ICMP by people who don't know any better. Path MTU Discovery depends on being able to receive an ICMP Destination Unreachable message with Fragementation Needed set in response to sending a packet with Don't Fragment set. The <a href="https://www.cisco.com/c/en/us/support/docs/ip/generic-routing-encapsulation-gre/25885-pmtud-ipfrag.html" rel="nofollow noreferrer">Resolve IPv4 Fragmentation, MTU, MSS, and PMTUD Issues with GRE and IPsec</a> actually does a really good job of explaining how discovery works.

<pre><code>function Test-IPAddressOrName($ipAddressOrName)
{
 $ipaddress = $null
 $isValidIPAddressOrName = [ipaddress]::TryParse($ipAddressOrName, [ref] $ipaddress)

 if ($isValidIPAddressOrName -eq $false)
 {
 $hasResolveDnsCommand = $null -ne (Get-Command Resolve-DnsName -ErrorAction SilentlyContinue)
 if ($hasResolveDnsCommand -eq $true)
 {
 $dnsResult = Resolve-DnsName -DnsOnly -Name $ipAddressOrName -ErrorAction SilentlyContinue
 $isValidIPAddressOrName = $null -ne $dnsResult
 }
 }

 return $isValidIPAddressOrName
}

function Get-NameAndIPAddress($ipAddressOrName)
{
 $hasResolveDnsCommand = $null -ne (Get-Command Resolve-DnsName -ErrorAction SilentlyContinue)

 $ipAddress = $null
 $validIPAddress = [ipaddress]::TryParse($ipAddressOrName, [ref] $ipAddress)
 $nameAndIp = [PSCustomObject] @{ 'Name' = $null; 'IPAddress' = $null }

 if ($validIPAddress -eq $false)
 {
 if ($hasResolveDnsCommand -eq $true)
 {
 $dnsResult = Resolve-DnsName -DnsOnly $ipAddressOrName -Type A -ErrorAction SilentlyContinue

 if ($null -ne $dnsResult -and $dnsResult.QueryType -eq 'A')
 {
 $nameAndIp.Name = $dnsResult.Name
 $nameAndIp.IPAddress = $dnsResult.IPAddress
 }
 else
 {
 Write-Error "The name $($ipAddressOrName) could not be resolved."
 $nameAndIp = $null
 }
 }
 else
 {
 Write-Warning "Resolve-DnsName not present. DNS resolution check skipped."
 }
 }
 else
 {
 $nameAndIp.IPAddress = $ipAddress

 if ($hasResolveDnsCommand -eq $true)
 {
 $dnsResult = Resolve-DnsName -DnsOnly $ipAddress -Type PTR -ErrorAction SilentlyContinue

 if ($null -ne $dnsResult -and $dnsResult.QueryType -eq 'PTR')
 {
 $nameAndIp.Name = $dnsResult.NameHost
 }
 }
 }

 return $nameAndIp
}

&lt;#
 .Synopsis
 Performs a series of pings (ICMP echo requests) with Don't Fragment specified to discover the path MTU (Maximum Transmission Unit).

 .Description
 Performs a series of pings with Don't Fragment specified to discover the path MTU (Maximum Transmission Unit). An ICMP echo request 
 is sent with a random payload with a payload length specified by the PayloadBytesMinimun. ICMP echo requests of increasing size are 
 sent until a ping response status other than Success is received. If the response status is PackeTooBig, the last successful packet 
 length is returned as a reliable MTU; otherwise, if the respone status is TimedOut, the same size packet is retried up to the number 
 of retries specified. If all of the retries have been exhausted with a response status of TimedOut, the last successful packet 
 length is returned as the assumed MTU.

 .Parameter UseDefaultGateway
 If UseDefaultGateway is specified the default gateway reported by the network interface is used as the destination host.

 .Parameter DestinationHost
 The IP Address or valid fully qualified DNS name of the destination host.

 .Parameter InitialTimeout
 The number of milliseconds to wait for an ICMP echo reply. Internally, this is doubled each time a retry occurs.

 .Parameter Retries
 The number of times to try the ping in the event that no reply is recieved before the timeout.

 .Parameter PayloadBytesMinimum
 The minimum number of bytes in the payload to use. The minimum MTU for IPv4 is 68 bytes; however, in practice, it's extremely rare 
 to see an MTU size less than 576 bytes so the default value is 548 bytes (576 bytes total packet size minus an ICMP header of 28 
 bytes).

 .Parameter PayloadBytesMaximum
 The maximum number of bytes in the payload to use. An IPv4 MTU for jumbo frames is 9000 bytes. The default value is 8973 bytes (9001 
 bytes total packet size, which is 1 byte larger than the maximum IPv4 MTU for a jumbo frame, minus an ICMP header of 28 bytes).

 .Example
 Discover-PathMTU -UseDefaultGateway

 .Example
 Discover-PathMTU -DestinationHost '192.168.1.1'

 .Example
 Discover-PathMTU -DestinationHost 'www.google.com'
#&gt;
function Discover-PathMtu
{
 [CmdletBinding(SupportsShouldProcess = $false)]
 param
 (
 [Parameter(Mandatory = $true, ParameterSetName = 'DefaultGateway')]
 [switch] $UseDefaultGateway,

 [Parameter(Mandatory = $true, Position = 0, ValueFromPipeline = $true, ParameterSetName = 'IPAddressOrName')]
 [ValidateScript({ Test-IPAddressOrName $_ })]
 [string] $DestinationHost,

 [Parameter(ParameterSetName = 'IPAddressOrName')]
 [Parameter(ParameterSetName = 'DefaultGateway')]
 [int] $InitialTimeout = 3000,

 [Parameter(ParameterSetName = 'IPAddressOrName')]
 [Parameter(ParameterSetName = 'DefaultGateway')]
 [int] $Retries = 3,

 [Parameter(ParameterSetName = 'IPAddressOrName')]
 [Parameter(ParameterSetName = 'DefaultGateway')]
 $PayloadBytesMinimum = 548,

 [Parameter(ParameterSetName = 'IPAddressOrName')]
 [Parameter(ParameterSetName = 'DefaultGateway')]
 $PayloadBytesMaximum = 8973
 )

 begin
 {
 $ipConfiguration = Get-NetIPConfiguration -Detailed | ?{ $_.NetProfile.Ipv4Connectivity -eq 'Internet' -and $_.NetAdapter.Status -eq 'Up' } | Sort { $_.IPv4DefaultGateway.InterfaceMetric } | Select -First 1
 $gatewayIPAddress = $ipConfiguration.IPv4DefaultGateway.NextHop

 $pingOptions = New-Object System.Net.NetworkInformation.PingOptions
 $pingOptions.DontFragment = $true
 $pinger = New-Object System.Net.NetworkInformation.Ping

 $rng = New-Object System.Security.Cryptography.RNGCryptoServiceProvider
 }

 process
 {
 $pingIpAddress = $null

 if ($UseDefaultGateway -eq $true)
 {
 $DestinationHost = $gatewayIPAddress
 }

 $nameAndIP = Get-NameAndIPAddress $DestinationHost

 if ($null -ne $nameAndIP)
 {
 Write-Host "Performing Path MTU discovery for $($nameAndIP.Name) $($nameAndIP.IPAddress)..."

 $pingReply = $null
 $payloadLength = $PayloadBytesMinimum
 $workingPingTimeout = $InitialTimeout

 do
 {
 $payloadLength++

 # Use a random payload to prevent compression in the path from potentially causing a false MTU report.
 [byte[]] $payloadBuffer = (,0x00 * $payloadLength)
 $rng.GetBytes($payloadBuffer)

 $pingCount = 1

 do
 {
 $pingReply = $pinger.Send($nameAndIP.IPAddress, $workingPingTimeout, $payloadBuffer, $pingOptions)

 if ($pingReply.Status -notin 'Success', 'PacketTooBig', 'TimedOut')
 {
 Write-Warning "An unexpected ping reply status, $($pingReply.Status), was received in $($pingReply.RoundtripTime) milliseconds on attempt $($pingCount)."
 }
 elseif ($pingReply.Status -eq 'TimedOut')
 {
 Write-Warning "The ping request timed out while testing a packet of size $($payloadLength + 28) using a timeout value of $($workingPingTimeout) milliseconds on attempt $($pingCount)."
 $workingPingTimeout = $workingPingTimeout * 2
 }
 else
 {
 Write-Verbose "Testing packet of size $($payloadLength + 28). The reply was $($pingReply.Status) and was received in $($pingReply.RoundtripTime) milliseconds on attempt $($pingCount)."
 $workingPingTimeout = $InitialTimeout
 }

 Sleep -Milliseconds 10

 $pingCount++
 } while ($pingReply.Status -eq 'TimedOut' -and $pingCount -le $Retries)
 } while ($payloadLength -lt $PayloadBytesMaximum -and $pingReply -ne $null -and $pingReply.Status -eq 'Success')

 if ($pingReply.Status -eq 'PacketTooBig')
 {
 Write-Host "Reported IPv4 MTU is $($ipConfiguration.NetIPv4Interface.NlMtu). The discovered IPv4 MTU is $($payloadLength + 27)."
 }
 elseif ($pingReply.Status -eq 'TimedOut')
 {
 Write-Host "Reported IPv4 MTU is $($ipConfiguration.NetIPv4Interface.NlMtu). The discovered IPv4 MTU is $($payloadLength + 27), but may not be reliable because the packet appears to have been discarded." 
 }
 else
 {
 Write-Host "Reported IPv4 MTU is $($ipConfiguration.NetIPv4Interface.NlMtu). The discovered IPv4 MTU is $($payloadLength + 27), but may not be reliable, due to an unexpected ping reply status." 
 }

 return $payloadLength + 27
 }
 else
 {
 Write-Error "The name $($DestinationHost) could not be resolved. No Path MTU discovery will be performed."
 }
 }

 end
 {
 if ($null -ne $pinger)
 {
 $pinger.Dispose()
 }

 if ($null -ne $rng)
 {
 $rng.Dispose()
 }
 }
}
</code></pre>

I need to know what the largest UDP packet I can send to another computer is without fragmentation.

This size is commonly known as the MTU (Maximum Transmission Unit). Supposedly, between 2 computers, will be many routers and modems that may have different MTUs. 

I read that the TCP implementation in windows automatically finds the maximum MTU in a path.

I was also experimenting, and I found out that the maximum MTU from my computer to a server was 57712 bytes+header. Anything above that was discarded. My computer is on a LAN, isn't the MTU supposed to be around 1500 bytes?

How to find the largest UDP packet I can send without fragmenting?

我需要知道在没有碎片的情况下可以发送给另一台计算机的最大UDP数据包是什么。此大小通常称为MTU (最大传输单位)。据推测，在两台计算机之间，将有许多路由器和调制解调器可能具有不同的MTU。我读到windows中的TCP实现会自动查找路径中的最大MTU。我也在做实验，我发现从我的计算机到服务器的最大MTU是57712 ...

问如何在不分段的情况下找到可以发送的最大UDP数据包？
EN

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问如何在不分段的情况下找到可以发送的最大UDP数据包？EN

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