Retrieving IP and MAC addresses for a LAN

Introduction

Getting the IP and MAC for your PC is pretty simple, but what if you need those on your local network? It's not as simple as it sounds... in fact it's a complete pain, and most of the internet articles that Google finds return the MAC for the current PC only. This returns the network list. 

Using the code

// Get my PC IP address
Console.WriteLine("My IP : {0}", GetIPAddress());
// Get My PC MAC address
Console.WriteLine("My MAC: {0}", GetMacAddress());
// Get all devices on network
Dictionary<IPAddress, PhysicalAddress> all = GetAllDevicesOnLAN();
foreach (KeyValuePair<IPAddress, PhysicalAddress> kvp in all)
{
    Console.WriteLine("IP : {0}\n MAC {1}", kvp.Key, kvp.Value);
}

The code that does the work

/// <summary>
/// MIB_IPNETROW structure returned by GetIpNetTable
/// DO NOT MODIFY THIS STRUCTURE.
/// </summary>
[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;
}

/// <summary>
/// GetIpNetTable external method
/// </summary>
/// <param name="pIpNetTable"></param>
/// <param name="pdwSize"></param>
/// <param name="bOrder"></param>
/// <returns></returns>
[DllImport("IpHlpApi.dll")]
[return: MarshalAs(UnmanagedType.U4)]
static extern int GetIpNetTable(IntPtr pIpNetTable, 
      [MarshalAs(UnmanagedType.U4)] ref int pdwSize, bool bOrder);

/// <summary>
/// Error codes GetIpNetTable returns that we recognise
/// </summary>
const int ERROR_INSUFFICIENT_BUFFER = 122;
/// <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>
private static Dictionary<IPAddress, PhysicalAddress> GetAllDevicesOnLAN()
{
    Dictionary<IPAddress, PhysicalAddress> all = new Dictionary<IPAddress, PhysicalAddress>();
    // Add this PC to the list...
    all.Add(GetIPAddress(), GetMacAddress());
    int spaceForNetTable = 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, ref spaceForNetTable, false);
    // Allocate the space
    // We use a try-finally block to ensure release.
    IntPtr rawTable = IntPtr.Zero;
    try
    {
        rawTable = Marshal.AllocCoTaskMem(spaceForNetTable);
        // Get the actual data
        int errorCode = GetIpNetTable(rawTable, ref spaceForNetTable, false);
        if (errorCode != 0)
        {
            // Failed for some reason - can do no more here.
            throw new Exception(string.Format(
              "Unable to retrieve network table. Error code {0}", errorCode));
        }
        // Get the rows count
        int rowsCount = Marshal.ReadInt32(rawTable);
        IntPtr currentBuffer = new IntPtr(rawTable.ToInt64() + Marshal.SizeOf(typeof(Int32)));
        // Convert the raw table to individual entries
        MIB_IPNETROW[] rows = new MIB_IPNETROW[rowsCount];
        for (int index = 0; index < rowsCount; index++)
        {
            rows[index] = (MIB_IPNETROW)Marshal.PtrToStructure(new IntPtr(currentBuffer.ToInt64() +
                                        (index * Marshal.SizeOf(typeof(MIB_IPNETROW)))
                                       ),
                                        typeof(MIB_IPNETROW));
        }
        // Define the dummy entries list (we can discard these)
        PhysicalAddress virtualMAC = new PhysicalAddress(new byte[] { 0, 0, 0, 0, 0, 0 });
        PhysicalAddress broadcastMAC = new PhysicalAddress(new byte[] { 255, 255, 255, 255, 255, 255 });
        foreach (MIB_IPNETROW row in rows)
        {
            IPAddress ip = new IPAddress(BitConverter.GetBytes(row.dwAddr));
            byte[] rawMAC = new byte[] { row.mac0, row.mac1, row.mac2, row.mac3, row.mac4, row.mac5 };
            PhysicalAddress pa = new PhysicalAddress(rawMAC);
            if (!pa.Equals(virtualMAC) && !pa.Equals(broadcastMAC) && !IsMulticast(ip))
            {
                //Console.WriteLine("IP: {0}\t\tMAC: {1}", ip.ToString(), pa.ToString());
                if (!all.ContainsKey(ip))
                {
                    all.Add(ip, pa);
                }
            }
        }
    }
    finally
    {
        // Release the memory.
        Marshal.FreeCoTaskMem(rawTable);
    }
    return all;
}

/// <summary>
/// Gets the IP address of the current PC
/// </summary>
/// <returns></returns>
private static IPAddress GetIPAddress()
{
    String strHostName = Dns.GetHostName();
    IPHostEntry ipEntry = Dns.GetHostEntry(strHostName);
    IPAddress[] addr = ipEntry.AddressList;
    foreach (IPAddress ip in addr)
    {
        if (!ip.IsIPv6LinkLocal)
        {
            return (ip);
        }
    }
    return addr.Length > 0 ? addr[0] : null;
}

/// <summary>
/// Gets the MAC address of the current PC.
/// </summary>
/// <returns></returns>
private static PhysicalAddress GetMacAddress()
{
    foreach (NetworkInterface nic in NetworkInterface.GetAllNetworkInterfaces())
    {
        // Only consider Ethernet network interfaces
        if (nic.NetworkInterfaceType == NetworkInterfaceType.Ethernet &&
            nic.OperationalStatus == OperationalStatus.Up)
        {
            return nic.GetPhysicalAddress();
        }
    }
    return null;
}

/// <summary>
/// Returns true if the specified IP address is a multicast address
/// </summary>
/// <param name="ip"></param>
/// <returns></returns>
private static bool IsMulticast(IPAddress ip)
{
    bool result = true;
    if (!ip.IsIPv6Multicast)
    {
        byte highIP = ip.GetAddressBytes()[0];
        if (highIP < 224 || highIP > 239)
        {
            result = false;
        }
    }
    return result;
}

History

Original version.