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TCP/IP Alternative Configuration: pt I The configuration

A question on the forum got me wondering about setting the Alternative Configuration on a TCP/IP properties of a network adapter. NICs are normally configured to either DHCP or a static address. If you use DHCP another tab “Alternative Configuration” appears on the IPv4 properties dialog. This can be set to APIPA (an address in the range 169.254.x.x/16 – ie DHCP failed) or a static address. DHCP will be tried first and if it fails the Alternative Configuration kicks in.

I had never seen anything on configuring this so started to dig.

It turns out that the information is held in the registry – big surprise! The data is a little difficult to track down

$index = 7            
$HKLM = 2147483650 #HKEY_LOCAL_MACHINE            
$data = @{}            
$nic = Get-WmiObject -Class Win32_NetworkAdapterConfiguration -Filter "Index=$index"            
$key = "SYSTEM\CurrentControlSet\services\Tcpip\Parameters\Interfaces\$($nic.SettingID)"            
$rc = Invoke-WmiMethod -Class StdRegProv -Name EnumValues -ArgumentList $hklm, $key            
if ($rc.ReturnValue -eq 0) {            
  $num = $rc.Types.count -1            
  for ($i=0; $i -le $num; $i++){            
     switch ($rc.Types[$i]) {            
       1 {$value = Invoke-WmiMethod -Class StdRegProv -Name GetStringValue -ArgumentList $hklm, $key, $($rc.sNames[$i]) |             
           select -ExpandProperty sValue}            
       2 {$value = Invoke-WmiMethod -Class StdRegProv -Name GetExpandedStringValue -ArgumentList $hklm, $key, $($rc.sNames[$i]) |             
           select -ExpandProperty sValue}            
       3 {$value = Invoke-WmiMethod -Class StdRegProv -Name GetBinaryValue -ArgumentList $hklm, $key, $($rc.sNames[$i]) |             
           select -ExpandProperty uValue}            
       4 {$value = Invoke-WmiMethod -Class StdRegProv -Name GetDWORDValue -ArgumentList $hklm, $key, $($rc.sNames[$i]) |             
          select -ExpandProperty uValue}            
       7 {$value = Invoke-WmiMethod -Class StdRegProv -Name GetMultiStringValue -ArgumentList $hklm, $key, $($rc.sNames[$i]) |             
         select -ExpandProperty sValue}            
       default {Write-Warning "Could not process $($rc.sNames[$i]) - type $($rc.Types[$i])"}            
     $data += @{$($rc.sNames[$i]) = $value}            
  }  ## end for            
else {            
 Write-Error "WMI call to registry provider failed"            
$data.GetEnumerator() | sort key

I’ve cheated for now and defined the NIC I’m interested in – Index =7 is my LAN connection.

I need to work with the HKLM hive so define the appropriate constant.

After getting the WMI object for the NIC – filter on Index I use the SettingID to define the registry key I need. The settingID looks like this - {01F4E3B7-5F1F-40BD-8252-DCC3331891C1}

The EnumValues method gives me the registry value names and types for that key. I can loop through them and call the appropriate method to read the registry value.

The data is output sorted by value name and looks like this

Name                           Value

----                           -----

AddressType                    0

DhcpConnForceBroadcastFlag     0

DhcpGatewayHardware            {192, 168, 1, 1...}

DhcpGatewayHardwareCount       1

DhcpInterfaceOptions           {6, 0, 0, 0...}


EnableDeadGWDetect             1

EnableDHCP                     0


IsServerNapAware               0

Lease                          0

LeaseObtainedTime              1336923004

LeaseTerminatesTime            2147483647


RegisterAdapterName            0   
RegistrationEnabled            1   

T1                             1336923004

T2                             1336923004

UseZeroBroadcast               0  


This shows we have a static address – the fact that IPAddress is set and that EnableDHCP=0

Next time we will look at enabling DHCP and then setting the alternative configuration

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