网络唤醒原理浅析(Wake On LAN)

之前我的一篇文章《网络唤醒全攻略(Wake On Lan)》介绍过如何设置远程唤醒电脑，着重于使用，这篇主要从原理方面解析一下当中的奥妙；

原理

将唤醒魔术包发送的被唤醒机器的网卡上，魔术包指AMD公司开发的唤醒数据包，具有远程唤醒的网卡都支持这个标准，用16进制表示如下：

6对“FF”前缀+16次重复MAC地址,举个例子假如我的网卡MAC地址是：AA:BB:CC:DD:EE:FF:11

那么魔术包就是:

0xFFFFFFFFFFAABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11

但是传送的时候必须封包成二进制格式才可以传送，简单来说，我们抽2个区段分析：

FFFFFFFFFFF 转成： 11111111 11111111 11111111 11111111 11111111 11111111

AABBCCDDEEFF11 转成：‭10101010 10111011 11001100 11011101 11101110 11111111 00010001‬

那么封包后就是把每个字节连接在一起：

11111111 11111111 11111111 11111111 11111111  11111111 10101010 10111011 11001100 11011101 11101110 11111111 00010001‬
……..10101010 10111011 11001100 11011101 11101110 11111111 00010001‬（第16次）

开发实现

关键代码（Java）:

	private String Wake(String name, String host, String mac, int port) {
        try {
            byte[] macBytes = getMacBytes(mac);//转成字节类型
            byte[] bytes = new byte[6 + 16 * macBytes.length];
            for (int i = 0; i < 6; i++) {
                bytes[i] = (byte) 0xff;
            }
            for (int i = 6; i < bytes.length; i += macBytes.length) {
                System.arraycopy(macBytes, 0, bytes, i, macBytes.length); //放入16个MAC地址
            }
            InetAddress address = InetAddress.getByName(host);
            DatagramPacket packet = new DatagramPacket(bytes, bytes.length, address, port);
            DatagramSocket socket = new DatagramSocket();
            socket.send(packet);
            socket.close();
            return "wol_package_sent_success";
        } catch (Exception e) {
            return "wol_package_sent_fail";
        }
    }

private static byte[] getMacBytes(String mac) throws IllegalArgumentException {
        byte[] bytes = new byte[6];
        String[] hex = mac.split("(\\:|\\-)");
        if (hex.length != 6) {
            throw new IllegalArgumentException("Invalid MAC address.");
        }
        try {
            for (int i = 0; i < 6; i++) {
                bytes[i] = (byte) Integer.parseInt(hex[i], 16);
            }
        } catch (NumberFormatException e) {
            throw new IllegalArgumentException("Invalid hex digit in MAC address.");
        }
        return bytes;
    }

更多细节请 阅读原文