原始套接字简单应用

/***************SimpelSniffer.c*************/
//auther:duanjigang@2006s
//add by wenhao
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <sys/types.h>
#include <linux/if_ether.h>


#define BUFFER_MAX 2048

int main(int argc, char *argv[])
{       
int sock, n_read, proto;        
char buffer[BUFFER_MAX];
//char  *ethhead, *iphead, *tcphead, 
//                 *udphead, *icmphead, *p;
    char *ethhead,*iphead,*p;

//创建原始套接字        
if( (sock = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_IP))) < 0)
    {
        fprintf(stdout, "create socket error\n");
        exit(-1);
    }

while(1) 
{
//将接收到的数据都存放在buffer中,接收到字节大小n_read
//这里接收到的数据应该是数据链路层的数据
     n_read = recvfrom(sock, buffer, 2048, 0, NULL, NULL);
/*
        14   6(dest)+6(source)+2(type or length)
        +
        20   ip header 
        +
        8   icmp,tcp or udp header
        = 42
*/
//如果小于42表示我们的数据有问题,重新接收
    if(n_read < 42) 
    {
      fprintf(stdout, "Incomplete header, packet corrupt\n");
continue;
    }

        ethhead = buffer;
        p = ethhead;
int n = 0XFF;
                printf("MAC: %.2X:%02X:%02X:%02X:%02X:%02X==>"
"%.2X:%.2X:%.2X:%.2X:%.2X:%.2X\n",
        p[6]&n, p[7]&n, p[8]&n, p[9]&n, p[10]&n, p[11]&n,
        p[0]&n, p[1]&n, p[2]&n,p[3]&n, p[4]&n, p[5]&n);

                   iphead = ethhead + 14;  
                   p = iphead + 12;

           printf("IP: %d.%d.%d.%d => %d.%d.%d.%d\n",
           p[0]&0XFF, p[1]&0XFF, p[2]&0XFF, p[3]&0XFF,
           p[4]&0XFF, p[5]&0XFF, p[6]&0XFF, p[7]&0XFF);
            proto = (iphead + 9)[0];
            p = iphead + 20;
             printf("Protocol: ");
switch(proto)
              {
case IPPROTO_ICMP: printf("ICMP\n");break;
case IPPROTO_IGMP: printf("IGMP\n");break;
case IPPROTO_IPIP: printf("IPIP\n");break;
case IPPROTO_TCP :
case IPPROTO_UDP : 
    printf("%s,", proto == IPPROTO_TCP ? "TCP": "UDP"); 
    printf("source port: %u,",((p[0]<<8)&0XFF00) |  (p[1]&0XFF));
    printf("dest port: %u\n", ((p[2]<<8)&0XFF00) | (p[3]&0XFF));
break;
case IPPROTO_RAW : printf("RAW\n");break;
default:printf("Unkown, please query in include /netinet/in.h\n");
        }
   }
}