How do I obtain the physical (MAC) address of an IP address using C#?

Question

From C#, I want to do the equivalent of the following:

arp -a |findstr 192.168.1.254

Alternatively, the answer could call the SendARP function and get the results.

This will allow my application to do some other processing that requires the MAC address.

score 28 · Accepted Answer · edited Jun 19 '11 at 20:12

28

SendARP P/Invoke goes like this:

[DllImport("iphlpapi.dll", ExactSpelling=true)]
public static extern int SendARP( int destIp, int srcIP, byte[] macAddr, ref uint physicalAddrLen );

PInvoke.NET has this example:

IPAddress dst = IPAddress.Parse("192.168.2.1"); // the destination IP address

byte[] macAddr = new byte[6];
uint macAddrLen = (uint)macAddr.Length;

if (SendARP(BitConverter.ToInt32(dst.GetAddressBytes(), 0), 0, macAddr, ref macAddrLen) != 0)
     throw new InvalidOperationException("SendARP failed.");

string[] str = new string[(int)macAddrLen];
for (int i=0; i<macAddrLen; i++)
     str[i] = macAddr[i].ToString("x2");

Console.WriteLine(string.Join(":", str));

edited Jun 19 '11 at 20:12

Jon Seigel

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answered Oct 09 '08 at 15:54

jop

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3

Things to know about this answer that I discovered while testing on Windows XP using Wireshark: 1) If the IP/MAC Address pair is already in the ARP cache, the ARP request packet will NOT be sent out on the network, but SendARP will still return the (potentially stale) macAddress it has in its cache. 2) This method is potentially very slow if using only a single thread. Looping through a full subnet of IP addresses (eg. 192.168.1.x) using a single thread took 250+ seconds (1 second per IP address.) Making it massively multi-threaded took less than a second for all 250+ addresses. – Pretzel Jul 20 '09 at 18:23

score 4 · Answer 2 · answered May 11 '16 at 06:46

Here is my solution.

public static class MacResolver
{
    /// <summary>
    /// Convert a string into Int32  
    /// </summary>
    [DllImport("Ws2_32.dll")]
    private static extern Int32 inet_addr(string ip);

    /// <summary>
    /// The main funtion 
    /// </summary> 
    [DllImport("Iphlpapi.dll")]
    private static extern int SendARP(Int32 dest, Int32 host, ref Int64 mac, ref Int32 len);

    /// <summary>
    /// Returns the MACAddress by a string.
    /// </summary>
    public static Int64 GetRemoteMAC(string remoteIP)
    {   
        Int32 ldest = inet_addr(remoteIP);

        try
        {
            Int64 macinfo = 0;           
            Int32 len = 6;           

            int res = SendARP(ldest, 0, ref macinfo, ref len);

            return macinfo;    
        }
        catch (Exception e)
        {
            return 0;
        }
    }

    /// <summary>
    /// Format a long/Int64 into string.   
    /// </summary>
    public static string FormatMac(this Int64 mac, char separator)
    {
        if (mac <= 0)
            return "00-00-00-00-00-00";

        char[] oldmac = Convert.ToString(mac, 16).PadLeft(12, '0').ToCharArray();

        System.Text.StringBuilder newMac = new System.Text.StringBuilder(17);

        if (oldmac.Length < 12)
            return "00-00-00-00-00-00";

        newMac.Append(oldmac[10]);
        newMac.Append(oldmac[11]);
        newMac.Append(separator);
        newMac.Append(oldmac[8]);
        newMac.Append(oldmac[9]);
        newMac.Append(separator);
        newMac.Append(oldmac[6]);
        newMac.Append(oldmac[7]);
        newMac.Append(separator);
        newMac.Append(oldmac[4]);
        newMac.Append(oldmac[5]);
        newMac.Append(separator);
        newMac.Append(oldmac[2]);
        newMac.Append(oldmac[3]);
        newMac.Append(separator);
        newMac.Append(oldmac[0]);
        newMac.Append(oldmac[1]);

        return newMac.ToString();
    }
}

This returns valid Mac address only when using IP address, while using hostname the mac address is wrong. — Gopi, Mar 27 '17 at 06:28

score 1 · Answer 3 · answered Oct 09 '08 at 15:59

1

Hook into the WMI subsystem. Some VBScript code to get going in the right direction is here

answered Oct 09 '08 at 15:59

bugmagnet

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score 1 · Answer 4 · answered Oct 09 '08 at 16:06

To find your own:

Add a reference to System.Management

ManagementClass mc = new ManagementClass("Win32_NetworkAdapterConfiguration");

ManagementObjectCollection mcCol = mc.GetInstances();

foreach (ManagementObject mcObj in mcCol)
{
  Console.WriteLine(mcObj["Caption"].ToString());
  Console.WriteLine(mcObj["MacAddress"].ToString());
}

Not sure about finding that of another device.

How do I obtain the physical (MAC) address of an IP address using C#?

4 Answers4

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