Get MAC from IP address in .NET

After dealing with several options, most of them involving a call to a command line tool and parsing the output, which is not really elegant. Other solutions were based on obsolete VBScript client code and ActiveX, even worse.

Finally I found in the excellent pinvoke.net site a very nice and simple example using a simple call to iphlpapi.dll’s SendARP method. The trick was to use ARP to get the MAC from the IP.

Note that this has it’s limitations, as I will only work if the remote machine is in the same network and the packet does not need to go through a router. I was enough for our needs.

Here’s the code I adapted from the example:

public static string GetMAC(IPAddress ipAddr)
{
    var mac = new byte[6];
    var len = (uint)mac.Length;

    var result = SendARP((int)ipAddr.Address, 0, mac, ref len);

    if (result != 0)
    {
        return "MAC not found!";
    }

    var str = new string[(int)len];

    for (var i = 0; i < len; i++)
    {
        str[i] = mac[i].ToString("x2");
    }

    return string.Join(":", str);
}

[DllImport("iphlpapi.dll", ExactSpelling = true)]
private static extern int SendARP(int destIP, int srcIP, byte[] pMacAddr, ref uint phyAddrLen);

Enjoy!