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

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();