GetAdapterAddresses in PowerShell. Turned out NetworkGuid wasn't what I needed. Took me long enough to figure out that I couldn't bring myself to throw the code away.

GetAdaptersAddresses.ps1

$MethodDefinition = @'

[DllImport("iphlpapi.dll")]
public static extern uint GetAdaptersAddresses(uint Family, uint Flags, IntPtr Reserved, IntPtr pAdapterAddresses, ref uint pOutBufLen);

'@

$iphlpapi = Add-Type -MemberDefinition $MethodDefinition -Name 'IPHelper' -Namespace 'Pinvoke' -PassThru


# This typedef just captures the NetworkGuid and pointer to the next struct.
$TypeDefinition = @'

namespace Pinvoke {
using System;
using System.Runtime.InteropServices;

[StructLayout(LayoutKind.Sequential)]
public struct GUID {
    public uint Data1;
    public ushort Data2;
    public ushort Data3;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 8)] public byte[] Data4;
}

[StructLayout(LayoutKind.Explicit)]
public struct IP_ADAPTER_ADDRESSES {
    [FieldOffset(8)] public IntPtr Next;
    [FieldOffset(252)] public GUID NetworkGuid;
    // // Alternative, struct-less offsets.
    // [FieldOffset(252)] public uint NetworkGuid1;
    // [FieldOffset(256)] public ushort NetworkGuid2;
    // [FieldOffset(258)] public ushort NetworkGuid3;
    // [FieldOffset(260)] public [MarshalAs(UnmanagedType.ByValArray, SizeConst = 8)] byte[] NetworkGuid4;
}
}

'@

# This typedef captures all the adapter info.
$TypeDefinition = @'

namespace Pinvoke {
using System;
using System.Runtime.InteropServices;

[StructLayout(LayoutKind.Sequential)]
public struct SOCKET_ADDRESS
{
    public IntPtr lpSockAddr;
    public int iSockaddrLength;
}

[StructLayout(LayoutKind.Sequential)]
public struct GUID {
    public uint Data1;
    public ushort Data2;
    public ushort Data3;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 8)]
    public byte[] Data4;
}

[StructLayout(LayoutKind.Sequential)]
public struct IP_ADAPTER_ADDRESSES
{
    public UInt64 Alignment;
    public IntPtr Next;
    public IntPtr AdapterName;
    public IntPtr FirstUnicastAddress;
    public IntPtr FirstAnycastAddress;
    public IntPtr FirstMulticastAddress;
    public IntPtr FirstDnsServerAddress;
    [MarshalAs(UnmanagedType.LPWStr)]
    public string DnsSuffix;
    [System.Runtime.InteropServices.MarshalAs(UnmanagedType.LPWStr)]
    public string Description;
    [System.Runtime.InteropServices.MarshalAs(UnmanagedType.LPWStr)]
    public string FriendlyName;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 8)]
    public byte[] PhysicalAddress;
    public uint PhysicalAddressLength;
    public uint Flags;
    public uint Mtu;
    public uint IfType;
    public uint OperStatus;
    uint Ipv6IfIndex;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
    public uint[] ZoneIndices;
    public IntPtr FirstPrefix;
    public UInt64 TrasmitLinkSpeed;
    public UInt64 ReceiveLinkSpeed;
    public IntPtr FirstWinsServerAddress;
    public IntPtr FirstGatewayAddress;
    public uint Ipv4Metric;
    public uint Ipv6Metric;
    public UInt64 Luid;
    public SOCKET_ADDRESS Dhcpv4Server;
    public uint CompartmentId;
    public GUID NetworkGuid;
    public uint ConnectionType;
    public uint TunnelType;
    public SOCKET_ADDRESS Dhcpv6Server;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 130)]
    public byte[] Dhcpv6ClientDuid;
    public uint Dhcpv6ClientDuidLength;
    public uint Dhcpv6Iaid;
    public uint FirstDnsSuffix;
}
}

'@

Add-Type -TypeDefinition $TypeDefinition -PassThru

$bufptr = [System.IntPtr]::Zero
$bufsize = 0
$iphlpapi::GetAdaptersAddresses(0, 0, [System.IntPtr]::Zero, $bufptr, [ref]$bufsize)
$bufptr = [System.Runtime.InteropServices.Marshal]::AllocHGlobal($bufsize)
$iphlpapi::GetAdaptersAddresses(0, 0, [System.IntPtr]::Zero, $bufptr, [ref]$bufsize)

$adapter = [System.Runtime.InteropServices.Marshal]::PtrToStructure($bufptr, [System.Type][Pinvoke.IP_ADAPTER_ADDRESSES])