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Network Adapter speed and duplex

One thing that can cause problems on the network is the duplex setting on the network adapter.  If this doesn’t match the switch port then at best you will get performance issues and at worst no connectivity.

The speed of the connection can be obtained from Win32_NetworkAdapter but for the duplex setting we need to go to the registry.

function test-duplex {            
[CmdletBinding()]            
param (            
 [string]$computer="."            
)            
BEGIN {            
 $HKLM = 2147483650            
 $reg = [wmiclass]"\\$computer\root\default:StdRegprov"            
 $keyroot = "SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002BE10318}"            
}            
            
PROCESS {            
            
Get-WmiObject -Class Win32_NetworkAdapterConfiguration -ComputerName $computer -Filter "IPEnabled='$true'" |            
foreach {            
            
$data = $_.Caption -split "]"            
$suffix = $data[0].Substring(($data[0].length-4),4)            
$key = $keyroot + "\$suffix"            
            
$value = "*PhysicalMediaType"            
$pmt = $reg.GetDwordValue($HKLM, $key, $value)  ## REG_DWORD            
            
## 0=Unspecified, 9=Wireless, 14=Ethernet            
if ($pmt.uValue -eq 14){            
            
$nic = $_.GetRelated("Win32_NetworkAdapter") | select Speed, NetConnectionId            
            
$value = "*SpeedDuplex"            
$dup = $reg.GetStringValue($HKLM, $key, $value)  ## REG_SZ            
            
switch ($dup.sValue) {            
 "0" {$duplex = "Auto Detect"}            
 "1" {$duplex = "10Mbps \ Half Duplex"}            
 "2" {$duplex = "10Mbps \ Full Duplex"}            
 "3" {$duplex = "100Mbps \ Half Duplex"}            
 "4" {$duplex = "100Mbps \ Full Duplex"}            
}             
            
New-Object -TypeName PSObject -Property @{            
  NetworkConnector = $($nic.NetConnectionID )            
  DuplexSetting = $duplex            
  Speed = $($nic.Speed)            
}            
            
} #if            
} #foreach            
} #process            
} #function


Start by defining the information we need to read the registry



Get the Win32_NetworkAdapterConfiguration for those adapters that are IP enabled. We then test the physical media type and if its ethernet we get the duplex setting. The nework connectioid is retrieved to identify the card and an object is created to pull the output together

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