Reliable method to get machine's MAC address in C#

Question

Cleaner solution

var macAddr = 
    (
        from nic in NetworkInterface.GetAllNetworkInterfaces()
        where nic.OperationalStatus == OperationalStatus.Up
        select nic.GetPhysicalAddress().ToString()
    ).FirstOrDefault();

Or:

String firstMacAddress = NetworkInterface
    .GetAllNetworkInterfaces()
    .Where( nic => nic.OperationalStatus == OperationalStatus.Up && nic.NetworkInterfaceType != NetworkInterfaceType.Loopback )
    .Select( nic => nic.GetPhysicalAddress().ToString() )
    .FirstOrDefault();

Here's some C# code which returns the MAC address of the first operational network interface. Assuming the NetworkInterface assembly is implemented in the runtime (i.e. Mono) used on other operating systems then this would work on other operating systems.

New version: returns the NIC with the fastest speed that also has a valid MAC address.

/// <summary>
/// Finds the MAC address of the NIC with maximum speed.
/// </summary>
/// <returns>The MAC address.</returns>
private string GetMacAddress()
{
    const int MIN_MAC_ADDR_LENGTH = 12;
    string macAddress = string.Empty;
    long maxSpeed = -1;

    foreach (NetworkInterface nic in NetworkInterface.GetAllNetworkInterfaces())
    {
        log.Debug(
            "Found MAC Address: " + nic.GetPhysicalAddress() +
            " Type: " + nic.NetworkInterfaceType);

        string tempMac = nic.GetPhysicalAddress().ToString();
        if (nic.Speed > maxSpeed &&
            !string.IsNullOrEmpty(tempMac) &&
            tempMac.Length >= MIN_MAC_ADDR_LENGTH)
        {
            log.Debug("New Max Speed = " + nic.Speed + ", MAC: " + tempMac);
            maxSpeed = nic.Speed;
            macAddress = tempMac;
        }
    }

    return macAddress;
}

Original Version: just returns the first one.

/// <summary>
/// Finds the MAC address of the first operation NIC found.
/// </summary>
/// <returns>The MAC address.</returns>
private string GetMacAddress()
{
    string macAddresses = string.Empty;

    foreach (NetworkInterface nic in NetworkInterface.GetAllNetworkInterfaces())
    {
        if (nic.OperationalStatus == OperationalStatus.Up)
        {
            macAddresses += nic.GetPhysicalAddress().ToString();
            break;
        }
    }

    return macAddresses;
}

The only thing I don't like about this approach is if you have like a Nortel Packet Miniport or some type of VPN connection it has the potential of being chosen. As far as I can tell, there is no way to distinguish an actual physical device's MAC from some type of virtual network interface.

The MACAddress property of the Win32_NetworkAdapterConfiguration WMI class can provide you with an adapter's MAC address. (System.Management Namespace)

MACAddress

    Data type: string
    Access type: Read-only

    Media Access Control (MAC) address of the network adapter. A MAC address is assigned by the manufacturer to uniquely identify the network adapter.

    Example: "00:80:C7:8F:6C:96"

If you're not familiar with the WMI API (Windows Management Instrumentation), there's a good overview here for .NET apps.

WMI is available across all version of windows with the .Net runtime.

Here's a code example:

System.Management.ManagementClass mc = default(System.Management.ManagementClass);
ManagementObject mo = default(ManagementObject);
mc = new ManagementClass("Win32_NetworkAdapterConfiguration");

ManagementObjectCollection moc = mc.GetInstances();
    foreach (var mo in moc) {
        if (mo.Item("IPEnabled") == true) {
              Adapter.Items.Add("MAC " + mo.Item("MacAddress").ToString());
         }
     }

WMI is the best solution if the machine you are connecting to is a windows machine, but if you are looking at a linux, mac, or other type of network adapter, then you will need to use something else. Here are some options:

1. Use the DOS command nbtstat -a . Create a process, call this command, parse the output.
2. First Ping the IP to make sure your NIC caches the command in it's ARP table, then use the DOS command arp -a . Parse the output of the process like in option 1.
3. Use a dreaded unmanaged call to sendarp in the iphlpapi.dll

Heres a sample of item #3. This seems to be the best option if WMI isn't a viable solution:

using System.Runtime.InteropServices;
...
[DllImport("iphlpapi.dll", ExactSpelling = true)]
        public static extern int SendARP(int DestIP, int SrcIP, byte[] pMacAddr, ref uint PhyAddrLen);
...
private string GetMacUsingARP(string IPAddr)
{
    IPAddress IP = IPAddress.Parse(IPAddr);
    byte[] macAddr = new byte[6];
    uint macAddrLen = (uint)macAddr.Length;

    if (SendARP((int)IP.Address, 0, macAddr, ref macAddrLen) != 0)
        throw new Exception("ARP command failed");

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

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

To give credit where it is due, this is the basis for that code: http://www.pinvoke.net/default.aspx/iphlpapi.sendarp#

IMHO returning first mac address isn't good idea, especially when virtual machines are hosted. Therefore i check send/received bytes sum and select most used connection, that is not perfect, but should be correct 9/10 times.

public string GetDefaultMacAddress()
{
    Dictionary<string, long> macAddresses = new Dictionary<string, long>();
    foreach (NetworkInterface nic in NetworkInterface.GetAllNetworkInterfaces())
    {
        if (nic.OperationalStatus == OperationalStatus.Up)
            macAddresses[nic.GetPhysicalAddress().ToString()] = nic.GetIPStatistics().BytesSent + nic.GetIPStatistics().BytesReceived;
    }
    long maxValue = 0;
    string mac = "";
    foreach(KeyValuePair<string, long> pair in macAddresses)
    {
        if (pair.Value > maxValue)
        {
            mac = pair.Key;
            maxValue = pair.Value;
        }
    }
    return mac;
}

We use WMI to get the mac address of the interface with the lowest metric, e.g. the interface windows will prefer to use, like this:

public static string GetMACAddress()
{
    ManagementObjectSearcher searcher = new ManagementObjectSearcher("SELECT * FROM Win32_NetworkAdapterConfiguration where IPEnabled=true");
    IEnumerable<ManagementObject> objects = searcher.Get().Cast<ManagementObject>();
    string mac = (from o in objects orderby o["IPConnectionMetric"] select o["MACAddress"].ToString()).FirstOrDefault();
    return mac;
}

Or in Silverlight (needs elevated trust):

public static string GetMACAddress()
{
    string mac = null;
    if ((Application.Current.IsRunningOutOfBrowser) && (Application.Current.HasElevatedPermissions) && (AutomationFactory.IsAvailable))
    {
        dynamic sWbemLocator = AutomationFactory.CreateObject("WbemScripting.SWBemLocator");
        dynamic sWbemServices = sWbemLocator.ConnectServer(".");
        sWbemServices.Security_.ImpersonationLevel = 3; //impersonate

        string query = "SELECT * FROM Win32_NetworkAdapterConfiguration where IPEnabled=true";
        dynamic results = sWbemServices.ExecQuery(query);

        int mtu = int.MaxValue;
        foreach (dynamic result in results)
        {
            if (result.IPConnectionMetric < mtu)
            {
                mtu = result.IPConnectionMetric;
                mac = result.MACAddress;
            }
        }
    }
    return mac;
}