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[2048];
    unsigned char *iphead, *ethhead;

    if ( (sock=socket(PF_PACKET, SOCK_RAW, htons(ETH_P_IP)))<0) ///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(1);
    }

    while (1)
    {
        printf("----------
");
        n = recvfrom(sock,buffer,2048,0,NULL,NULL);///接收数据包
        printf("%d bytes read
",n);
        /* Check to see if the packet contains at least
         *      * complete Ethernet (14), IP (20) and TCP/UDP
         *           * (8) headers.
         *                */
        if (n<42)
        {
            perror("recvfrom():");
            printf("Incomplete packet (errno is %d)
",errno);
            close(sock);
            exit(0);
        }
        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
",ethhead[6],ethhead[7],ethhead[8],ethhead[9],ethhead[10],ethhead[11]);
        printf("Destination MAC address: %02x:%02x:%02x:%02x:%02x:%02x
",ethhead[0],ethhead[1],ethhead[2],ethhead[3],ethhead[4],ethhead[5]);

        iphead = buffer+14; /* Skip Ethernet header */
        if (*iphead==0x45)
        {
            /* Double check for IPv4 and no options present */
            printf("Source host %d.%d.%d.%d
",iphead[12],iphead[13],iphead[14],iphead[15]);
            printf("Dest host %d.%d.%d.%d
",iphead[16],iphead[17],iphead[18],iphead[19]);
            ///这里只是取协议的前四个字节
            printf("Source %d ,Dest ports %d
",(iphead[20]<<8)+iphead[21],(iphead[22]<<8)+iphead[23]);///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
",iphead[9]);
        }
    }

}

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