需要调用 win32 API，参考 Send directly to MAC address over Ethernet：

To communicate at the ethernet/ARP level you need to P/Invoke to the win32 IPHelper APIs. Ie. to send an ARP:

using System;
using System.Collections.Generic;
using System.Text;
using System.Net;
using System.Net.Sockets;
using System.Net.Mail;
using System.IO;

namespace ConsoleApplication3
{
    class Program
    {
        
        [System.Runtime.InteropServices.DllImport("iphlpapi.dll", ExactSpelling=true)]
        public static extern int SendARP(int DestIP, int SrcIP, byte[] pMacAddr, ref int PhyAddrLen);

        static void Main(string[] args)
        {
            IPAddress ipAddress = IPAddress.Parse("x.x.x.x");
            byte[] macBytes = new byte[6];
            int length = 6;
            SendARP(BitConverter.ToInt32(ipAddress.GetAddressBytes(), 0), 0, macBytes, ref length);
            Console.WriteLine( BitConverter.ToString(macBytes, 0, 6));          

            Console.WriteLine("PROGRAM END....");
            Console.ReadKey();
        }
    }
}