PowerShell wrapper of C# function to retrieve system ARP table entries

Get-ArpEntry.ps1

Set-StrictMode -Version Latest

function Get-ArpEntry {
    <# .SYNOPSIS
    Retrieve system ARP table entries #>
    Param(
        # Retrieve all entries (not just learned)
        [switch]$All
    )

    $arpCode = @'
[StructLayout(LayoutKind.Sequential)]
struct MIB_IPNETROW
{
    [MarshalAs(UnmanagedType.U4)]
    public int dwIndex;
    [MarshalAs(UnmanagedType.U4)]
    public int dwPhysAddrLen;
    [MarshalAs(UnmanagedType.U1)]
    public byte mac0;
    [MarshalAs(UnmanagedType.U1)]
    public byte mac1;
    [MarshalAs(UnmanagedType.U1)]
    public byte mac2;
    [MarshalAs(UnmanagedType.U1)]
    public byte mac3;
    [MarshalAs(UnmanagedType.U1)]
    public byte mac4;
    [MarshalAs(UnmanagedType.U1)]
    public byte mac5;
    [MarshalAs(UnmanagedType.U1)]
    public byte mac6;
    [MarshalAs(UnmanagedType.U1)]
    public byte mac7;
    [MarshalAs(UnmanagedType.U4)]
    public int dwAddr;
    [MarshalAs(UnmanagedType.U4)]
    public int dwType;
}

[DllImport("IpHlpApi.dll")]
private static extern long GetIpNetTable(IntPtr pIpNetTable, ref int pdwSize, bool bOrder);

public class ArpEntry
{
    public string IPAddress { get; set; }
    public string MACAddress { get; set; }
}

public static System.Collections.Generic.List<ArpEntry> ArpCache()
{
    IntPtr buff;
    int requiredLen = 0;
    System.Collections.Generic.List<ArpEntry> set = new System.Collections.Generic.List<ArpEntry>();
    long result = GetIpNetTable(IntPtr.Zero, ref requiredLen, false);

    try
    {
        buff = Marshal.AllocCoTaskMem(requiredLen);
        result = GetIpNetTable(buff, ref requiredLen, false);

        int entries = Marshal.ReadInt32(buff);
        IntPtr entryBuffer = new IntPtr(buff.ToInt64() + Marshal.SizeOf(typeof(int)));

        for(int i = 0; i < entries; i++)
        {
            int currentIndex = i * Marshal.SizeOf(typeof(MIB_IPNETROW));
            IntPtr newStruct = new IntPtr(entryBuffer.ToInt64() + currentIndex);
            MIB_IPNETROW entry = (MIB_IPNETROW)Marshal.PtrToStructure(newStruct, typeof(MIB_IPNETROW));
            System.Net.IPAddress addr = new System.Net.IPAddress(BitConverter.GetBytes(entry.dwAddr));

            set.Add(new ArpEntry { IPAddress = addr.ToString(), MACAddress = String.Format("{0}-{1}-{2}-{3}-{4}-{5}",
                entry.mac0.ToString("X2"), entry.mac1.ToString("X2"), entry.mac2.ToString("X2"),
                entry.mac3.ToString("X2"), entry.mac4.ToString("X2"), entry.mac5.ToString("X2"))
            });
        }

    }
    catch(Exception e)
    {
        Console.WriteLine("Exception occurred: " + e.Message);
    }
    return set;
}
'@

    if (!('Win32.Arp+ArpEntry' -as [type])) { Add-Type -MemberDefinition $arpCode -Name 'Arp' -Namespace 'Win32' }

    if ($All) {
        return [Win32.Arp]::ArpCache()
    } else {
        return [Win32.Arp]::ArpCache().Where{
            $_.IPAddress -notmatch '^127\.|224\.|239\.|255\.' -and $_.MACAddress -notmatch '^[F-]+$'
        }
    }
}

This basically does the same thing as Get-NetNeighbor, but using C# to wrap GetIpNetTable. Inspired by this gist.