原始套接字-TCP/IP下三层数据显示

 #include <stdio.h>
 #include <errno.h>
 #include <unistd.h>
 #include <sys/socket.h>
 #include <sys/types.h>
 #include <linux/in.h>
 #include <linux/if_ether.h>

 int main(int argc, char **argv)
 {
     int sock, n;
     char buffer[];
     unsigned char *iphead, *ethhead;

     if ( (sock=socket(PF_PACKET, SOCK_RAW, htons(ETH_P_IP)))<) ///建立套接字。PF_PACKET：底层包访问协议;SOCK_RAW：提供原始网络协议访问;
     {
         perror("socket");
         exit();
     }

     while ()
     {
         printf("----------\n");
         n = recvfrom(sock,buffer,,,NULL,NULL);///接收数据包
         printf("%d bytes read\n",n);
         /* Check to see if the packet contains at least
          *      * complete Ethernet (14), IP (20) and TCP/UDP
          *           * (8) headers.
          *                */
         if (n<)
         {
             perror("recvfrom():");
             printf("Incomplete packet (errno is %d)\n",errno);
             close(sock);
             exit();
         }
         ethhead = buffer;
         ///打印顺序可以通过wireshark包分析出来！！！
         printf("Source MAC address:%02x:%02x:%02x:%02x:%02x:%02x\n",ethhead[],ethhead[],ethhead[],ethhead[],ethhead[],ethhead[]);
         printf("Destination MAC address: %02x:%02x:%02x:%02x:%02x:%02x\n",ethhead[],ethhead[],ethhead[],ethhead[],ethhead[],ethhead[]);

         iphead = buffer+; /* Skip Ethernet header */
         if (*iphead==0x45)
         {
             /* Double check for IPv4 and no options present */
             printf("Source host %d.%d.%d.%d\n",iphead[],iphead[],iphead[],iphead[]);
             printf("Dest host %d.%d.%d.%d\n",iphead[],iphead[],iphead[],iphead[]);
             ///这里只是取协议的前四个字节
             printf("Source %d ,Dest ports %d\n",(iphead[]<<)+iphead[],(iphead[]<<)+iphead[]);///端口占两个字节所以要使高位左移8位然后再加上低位值
             printf("Layer-4 protocol %d\n",iphead[]);
         }
     }

 }

输出：

----------
74 bytes read
Source MAC address:48:8a:d2:12:59:ec
Destination MAC address: 00:21:6a:85:2c:8c
Source host 220.181.57.232
Dest host 192.168.0.118
Souce port front:80 ,Dest port front:80 ----
Source 80 ,Dest ports 59472
Layer-4 protocol 6