代码如下：

using System;
using System.Net;
using System.Threading;

using System.Runtime.InteropServices;

namespace LocalIP {
  class LanSearch {

    /// <summary>
    /// 取MAC地址
    /// </summary>
    /// <param name="DestIP">目标IP</param>
    /// <param name="SrcIP">源IP</param>
    /// <param name="pMacAddr">MAC地址</param>
    /// <param name="PhyAddrLen">MAC地址的长度</param>
    /// <returns></returns>
    [DllImport("iphlpapi.dll", ExactSpelling = true)]
    private static unsafe extern int SendARP(int DestIP, int SrcIP, [Out] byte[] pMacAddr, ref int PhyAddrLen);

    /// <summary>
    /// 在线程中扫描
    /// </summary>
    private static void LanSearchThreadMethod() {
      int i = Convert.ToUInt16(Thread.CurrentThread.Name);
      Console.Write(".");

      string strIP = "192.168.1." + i.ToString();

      //IPHostEntry ip = null;
      IPAddress ip = null;
      try {
        //ip = Dns.GetHostEntry(strIP);
        ip = IPAddress.Parse(strIP);
      }
      catch {
        //Console.WriteLine("请勿输入非法IP地址");
        return;
      }

      byte[] b = new byte[6];
      int len = b.Length;
      //int r = SendARP(BitConverter.ToInt32(ip.AddressList[0].GetAddressBytes(), 0), 0, b, ref len);
      int r = SendARP(BitConverter.ToInt32(ip.GetAddressBytes(), 0), 0, b, ref len);
      int num = BitConverter.ToInt32(b, 0);
      string mac = BitConverter.ToString(b, 0, 6);

      if (num != 0) {//有效MAC
        //Console.WriteLine("\r\n{0}--{1}--{2}", ip.AddressList[0].ToString(), ip.HostName, mac);
        Console.WriteLine("\r\n{0}--{1}", ip.ToString(), mac);
      }
    }

    /// <summary>
    /// 程序主入口
    /// </summary>
    /// <param name="args"></param>
    [STAThread]
    static void Main(string[] args) {
      Thread[] thread = new Thread[255];
      ThreadStart threadMethod;

      for (int i = 0; i < 255; i++) {
        threadMethod = new ThreadStart(LanSearchThreadMethod);
        thread[i] = new Thread(threadMethod);
        thread[i].Name = i.ToString();
        thread[i].Start();
        if (!thread[i].Join(100)) {
          thread[i].Abort();
        }
      }

      Console.WriteLine("\r\n按任意键返回");
      Console.ReadLine();
    }

  }
}