原始套接字编程(1)

Linux下原始套接字的原理

创建原始套接字：
socket(AF_NET, SOCK_RAW, protocol);

1. 参数protocol用来致命所接收的协议包，如果是像IPPROTO_TCP(6)这种非0、非255的协议，能接收ip头为protocol域的数据包，包括IP头，协议头以及数据；发送数据时，默认只需构建protocol协议头及数据，不需构建IP头。可以通过设置原始套接字的IP_HDRINCL属性，使用户自己构建IP头。
setsockopt (rawsock, IP, IP_HDRINCL, “1”, sizeof (“1”));
2. 如果protocol为IPPROTO_RAW，创建的原始套接字只能用来发送IP数据包，且默认开启IP_HDRINCL属性，需要用户自己构建IP包头，计算校验和。
3. 对于protocol为IPPROTO_IP的原始套接字，可以接收任何的IP数据包。其中的校验和验证和协议分析由程序自己完成。
4. 若要监测所有输入与输出的数据包，而且不仅限制于IP包(tcp/udp/icmp)，监测 arp/rarp包，以及以太网头部，需要通过以下语句建立原始套接字：
sock_raw = socket( AF_PACKET , SOCK_RAW , htons(ETH_P_ALL)) ;

原始套接字在windows下的局限

Limitations on Raw Sockets
On Windows 7, Windows Vista, Windows XP with Service Pack 2 (SP2), and Windows XP with Service Pack 3 (SP3), the ability to send traffic over raw sockets has been restricted in several ways:

TCP data cannot be sent over raw sockets.
UDP datagrams with an invalid source address cannot be sent over raw sockets. The IP source address for any outgoing UDP datagram must exist on a network interface or the datagram is dropped. This change was made to limit the ability of malicious code to create distributed denial-of-service attacks and limits the ability to send spoofed packets (TCP/IP packets with a forged source IP address).
A call to the bind function with a raw socket for the IPPROTO_TCP protocol is not allowed.

Note The bind function with a raw socket is allowed for other protocols (IPPROTO_IP, IPPROTO_UDP, or IPPROTO_SCTP, for example).

These above restrictions do not apply to Windows Server 2008 R2, Windows Server 2008 , Windows Server 2003, or to versions of the operating system earlier than Windows XP with SP2.

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