VB.NET code to get all machine names with their IP from network

''' <summary>
''' GetIpNetTable external method
''' </summary>
''' <param name="pIpNetTable"></param>
''' <param name="pdwSize"></param>
''' <param name="bOrder"></param>
''' <returns></returns>
<DllImport("IpHlpApi.dll")> _
Private Shared Function GetIpNetTable(pIpNetTable As IntPtr, <MarshalAs(UnmanagedType.U4)> ByRef pdwSize As Integer, bOrder As Boolean) As <MarshalAs(UnmanagedType.U4)> Integer
End Function

''' <summary>
''' Error codes GetIpNetTable returns that we recognise
''' </summary>
Const ERROR_INSUFFICIENT_BUFFER As Integer = 122
''' <summary>
''' MIB_IPNETROW structure returned by GetIpNetTable
''' DO NOT MODIFY THIS STRUCTURE.
''' </summary>
<StructLayout(LayoutKind.Sequential)> _
Private Structure MIB_IPNETROW
    <MarshalAs(UnmanagedType.U4)> _
    Public dwIndex As Integer
    <MarshalAs(UnmanagedType.U4)> _
    Public dwPhysAddrLen As Integer
    <MarshalAs(UnmanagedType.U1)> _
    Public mac0 As Byte
    <MarshalAs(UnmanagedType.U1)> _
    Public mac1 As Byte
    <MarshalAs(UnmanagedType.U1)> _
    Public mac2 As Byte
    <MarshalAs(UnmanagedType.U1)> _
    Public mac3 As Byte
    <MarshalAs(UnmanagedType.U1)> _
    Public mac4 As Byte
    <MarshalAs(UnmanagedType.U1)> _
    Public mac5 As Byte
    <MarshalAs(UnmanagedType.U1)> _
    Public mac6 As Byte
    <MarshalAs(UnmanagedType.U1)> _
    Public mac7 As Byte
    <MarshalAs(UnmanagedType.U4)> _
    Public dwAddr As Integer
    <MarshalAs(UnmanagedType.U4)> _
    Public dwType As Integer
End Structure

''' <summary>
''' Get the IP and MAC addresses of all known devices on the LAN
''' </summary>
''' <remarks>
''' 1) This table is not updated often - it can take some human-scale time
'''    to notice that a device has dropped off the network, or a new device
'''    has connected.
''' 2) This discards non-local devices if they are found - these are multicast
'''    and can be discarded by IP address range.
''' </remarks>
''' <returns></returns>
Public Shared Function GetAllDevicesOnLAN() As Dictionary(Of IPAddress, PhysicalAddress)
    Dim all As New Dictionary(Of IPAddress, PhysicalAddress)()
    ' Add this PC to the list...
    all.Add(GetIPAddress(), GetMacAddress())
    Dim spaceForNetTable As Integer = 0
    ' Get the space needed
    ' We do that by requesting the table, but not giving any space at all.
    ' The return value will tell us how much we actually need.
    GetIpNetTable(IntPtr.Zero, spaceForNetTable, False)
    ' Allocate the space
    ' We use a try-finally block to ensure release.
    Dim rawTable As IntPtr = IntPtr.Zero
    Try
        rawTable = Marshal.AllocCoTaskMem(spaceForNetTable)
        ' Get the actual data
        Dim errorCode As Integer = GetIpNetTable(rawTable, spaceForNetTable, False)
        If errorCode <> 0 Then
            ' Failed for some reason - can do no more here.
            Throw New Exception(String.Format("Unable to retrieve network table. Error code {0}", errorCode))
        End If
        ' Get the rows count
        Dim rowsCount As Integer = Marshal.ReadInt32(rawTable)
        Dim currentBuffer As New IntPtr(rawTable.ToInt64() + Marshal.SizeOf(GetType(Int32)))
        ' Convert the raw table to individual entries
        Dim rows As MIB_IPNETROW() = New MIB_IPNETROW(rowsCount - 1) {}
        For index As Integer = 0 To rowsCount - 1
            rows(index) = CType(Marshal.PtrToStructure(New IntPtr(currentBuffer.ToInt64() + (index * Marshal.SizeOf(GetType(MIB_IPNETROW)))), GetType(MIB_IPNETROW)), MIB_IPNETROW)
        Next
        ' Define the dummy entries list (we can discard these)
        Dim virtualMAC As New PhysicalAddress(New Byte() {0, 0, 0, 0, 0, 0})
        Dim broadcastMAC As New PhysicalAddress(New Byte() {255, 255, 255, 255, 255, 255})
        For Each row As MIB_IPNETROW In rows
            Dim ip As New IPAddress(BitConverter.GetBytes(row.dwAddr))
            Dim rawMAC As Byte() = New Byte() {row.mac0, row.mac1, row.mac2, row.mac3, row.mac4, row.mac5}
            Dim pa As New PhysicalAddress(rawMAC)
            If Not pa.Equals(virtualMAC) AndAlso Not pa.Equals(broadcastMAC) AndAlso Not IsMulticast(ip) Then
                'Console.WriteLine("IP: {0}\t\tMAC: {1}", ip.ToString(), pa.ToString());
                If Not all.ContainsKey(ip) Then
                    all.Add(ip, pa)
                End If
            End If
        Next
    Finally
        ' Release the memory.
        Marshal.FreeCoTaskMem(rawTable)
    End Try
    Return all
End Function