1。用C#调用DOS命令获取本机网卡的MAC地址
System.Diagnostics.Process p=new System.Diagnostics.Process();
p.StartInfo.CreateNoWindow=true;
p.StartInfo.UseShellExecute=false;
p.StartInfo.RedirectStandardOutput=true;
p.StartInfo.FileName="ipconfig";
p.StartInfo.Arguments="/all";
p.Start();
p.WaitForExit();
string s=p.StandardOutput.ReadToEnd();
MessageBox.Show(s.Substring(s.IndexOf("Physical Address. . . . . . . . . :")+36,17));

2。使用API，利用ARP协议，只能获得同网段计算机的MAC


     #region By ARP

        [DllImport("Iphlpapi.dll")]
        private static extern int SendARP(Int32 dest, Int32 host, ref Int64 mac, ref Int32 length);

        [DllImport("Ws2_32.dll")]
        private static extern Int32 inet_addr(string ip);

        public static string GetMacByARP(string clientIP)
        {
            string ip = clientIP;
            Int32 ldest = inet_addr(ip);
            Int64 macinfo = new Int64();
            Int32 len = 6;
            try
            {
                SendARP(ldest, 0, ref macinfo, ref len);
            }
            catch
            {
                return "";
            }
            string originalMACAddress = Convert.ToString(macinfo, 16);
            if (originalMACAddress.Length < 12)
            {
                originalMACAddress = originalMACAddress.PadLeft(12, '0');
            }
            string macAddress;
            if (originalMACAddress != "0000" && originalMACAddress.Length == 12)
            {
                string mac1, mac2, mac3, mac4, mac5, mac6;
                mac1 = originalMACAddress.Substring(10, 2);
                mac2 = originalMACAddress.Substring(8, 2);
                mac3 = originalMACAddress.Substring(6, 2);
                mac4 = originalMACAddress.Substring(4, 2);
                mac5 = originalMACAddress.Substring(2, 2);
                mac6 = originalMACAddress.Substring(0, 2);
                macAddress = mac1 + "-" + mac2 + "-" + mac3 + "-" + mac4 + "-" + mac5 + "-" + mac6;
            }
            else
            {
                macAddress = "";
            }
            return macAddress.ToUpper();
        }

        public static IPAddress[] GetLocalIP()
        {
            string hostName = Dns.GetHostName();
            IPHostEntry ipEntry = Dns.GetHostByName(hostName);
            return ipEntry.AddressList;
        }

        #endregion