远程唤醒技术原理

远程唤醒技术（Wake On LAN）是通过给支持WOL标准的网卡，广播一个特定格式的数据包，由网卡唤醒停机状态中的计算机的这么一种技术。常用于远程唤醒网络服务器。

数据包格式：6个0xFF字节+16次目标机器的MAC地址

如需要唤醒MAC地址为00:1E:67:03:35:BD的计算机，数据包数据如下（十六进制）：
0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0x00 0x1E 0x67 0x03 0x35 0xBD 0x00 0x1E 0x67 0x03 0x35 0xBD 0x00 0x1E 0x67 0x03 0x35 0xBD 0x00 0x1E 0x67 0x03 0x35 0xBD 0x00 0x1E 0x67 0x03 0x35 0xBD 0x00 0x1E 0x67 0x03 0x35 0xBD 0x00 0x1E 0x67 0x03 0x35 0xBD 0x00 0x1E 0x67 0x03 0x35 0xBD 0x00 0x1E 0x67 0x03 0x35 0xBD 0x00 0x1E 0x67 0x03 0x35 0xBD 0x00 0x1E 0x67 0x03 0x35 0xBD 0x00 0x1E 0x67 0x03 0x35 0xBD 0x00 0x1E 0x67 0x03 0x35 0xBD 0x00 0x1E 0x67 0x03 0x35 0xBD 0x00 0x1E 0x67 0x03 0x35 0xBD 0x00 0x1E 0x67 0x03 0x35 0xBD

附一段简单的C代码：

#include 
#include 
#include 
#include 
#include 
#include 

#define PORT 12345

int main(int argc, char **argv) {
	if (argc < 2) {
		printf("Usage: wake mac1 mac2 mac3 ...\n");
		exit(1);
	}
	int s = socket(AF_INET, SOCK_DGRAM, 0);
	if (s == -1) {
		perror("socket");
		exit(1);
	}
	int optval = 1;
	int ret = setsockopt(s, SOL_SOCKET, SO_BROADCAST, &optval, sizeof(int)); 
	if (ret == -1) {
		perror("setsockopt");
		exit(1);
	}
	struct sockaddr_in addr;
	bzero(&addr, sizeof(addr));
	addr.sin_family = AF_INET;
	//addr.sin_addr.s_addr = inet_addr("192.168.0.23");
	addr.sin_addr.s_addr = htonl(INADDR_BROADCAST);
	addr.sin_port = htons(PORT);
	int i, j, k;
	char buf[6 + 16 * 6] = {0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF};
	char dst[2];
	for (i = 1; i < argc; ++i) {
		if (strlen(argv[i]) != 17) {
			printf("Invalid mac address %s!\n", argv[i]);
			continue;
		}
		j = 5;
		buf[++j] = (char)strtol(strncpy(dst, argv[i]     , 2), NULL, 16);
		buf[++j] = (char)strtol(strncpy(dst, argv[i] +  3, 2), NULL, 16);
		buf[++j] = (char)strtol(strncpy(dst, argv[i] +  6, 2), NULL, 16);
		buf[++j] = (char)strtol(strncpy(dst, argv[i] +  9, 2), NULL, 16);
		buf[++j] = (char)strtol(strncpy(dst, argv[i] + 12, 2), NULL, 16);
		buf[++j] = (char)strtol(strncpy(dst, argv[i] + 15, 2), NULL, 16);
		k = 2;
		do {
			memcpy(buf + k * 6, buf + 6, 6);
		} while (++k < 18);
		int len = sendto(s, buf, sizeof(buf), 0, (struct sockaddr*)&addr, sizeof(addr));
		if (len == -1) {
			perror("sendto");
		} else {
			printf("Wake %s OK!\n", argv[i]);
		}
	}
	return 0;
}

参考资料：

http://en.wikipedia.org/wiki/Wake-on-LAN