轉發網址：https://blog.csdn.net/eqiang8271/article/details/8489769

//Example 1.
#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>
#include <unistd.h>
#include 
 
<stdlib.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) {
    perror("socket");
    exit(1);
  }
 
  while (1) {
    printf("----------\n");
    n = recvfrom(sock,buffer,2048
 
,0,NULL,NULL);
    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<42) {
      perror("recvfrom():");
      printf("Incomplete packet (errno is %d)\n", errno);
      close(sock);
      exit(
 
0);
    }
 
    ethhead = buffer;
    printf("Source MAC address: %02x:%02x:%02x:%02x:%02x:%02x\n",
           ethhead[0],ethhead[1],ethhead[2],ethhead[3],ethhead[4],ethhead[5]);
    printf("Destination MAC address: %02x:%02x:%02x:%02x:%02x:%02x\n",
           ethhead[6],ethhead[7],ethhead[8],ethhead[9],ethhead[10],ethhead[11]);
 
    iphead = buffer+14; /* Skip Ethernet header */
    if (*iphead==0x45) { /* Double check for IPv4 and no options present */
        printf("Source host: %d.%d.%d.%d\n", iphead[12], iphead[13], iphead[14], iphead[15]);
        printf("Dest host: %d.%d.%d.%d\n", iphead[16], iphead[17], iphead[18], iphead[19]);
        printf("Source,Dest ports %d,%d\n", (iphead[20]<<8)+iphead[21], (iphead[22]<<8)+iphead[23]);
        printf("Layer-4 protocol %d\n",iphead[9]);
    }
  }
}

//Example 2.

#include <stdio.h>
#include <string.h>
#include <errno.h> 
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h> 
#include <linux/in.h>
#include <linux/if_ether.h>
#include <net/if.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <stdlib.h>

int main(int argc, char **argv) {
  int sock, n;
  char buffer[2048];
  unsigned char *iphead, *ethhead;
  struct ifreq ethreq;
   
  if ( (sock=socket(PF_PACKET, SOCK_RAW, htons(ETH_P_IP)))<0) {
    perror("socket");
    exit(1);
  }
 
  /* Set the network card in promiscuos mode */
  strncpy(ethreq.ifr_name,"eth0",IFNAMSIZ);
  if (ioctl(sock,SIOCGIFFLAGS,&ethreq)==-1) {
    perror("ioctl");
    close(sock);
    exit(1);
  }
  ethreq.ifr_flags|=IFF_PROMISC;
  if (ioctl(sock,SIOCSIFFLAGS,&ethreq)==-1) {
    perror("ioctl");
    close(sock);
    exit(1);
  }
   
  while (1) {
    printf("----------\n");
    n = recvfrom(sock,buffer,2048,0,NULL,NULL);
    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<42) {
      perror("recvfrom():");
      printf("Incomplete packet (errno is %d)\n", errno);
      close(sock);
      exit(0);
    }
 
    ethhead = buffer;
    printf("Source MAC address: %02x:%02x:%02x:%02x:%02x:%02x\n",
           ethhead[0],ethhead[1],ethhead[2],ethhead[3],ethhead[4],ethhead[5]);
    printf("Destination MAC address: %02x:%02x:%02x:%02x:%02x:%02x\n",
           ethhead[6],ethhead[7],ethhead[8],ethhead[9],ethhead[10],ethhead[11]);
 
    iphead = buffer+14; /* Skip Ethernet header */
    if (*iphead==0x45) { /* Double check for IPv4 and no options present */
      printf("Source host %d.%d.%d.%d\n", iphead[12],iphead[13],iphead[14],iphead[15]);
      printf("Dest host %d.%d.%d.%d\n",iphead[16],iphead[17],iphead[18],iphead[19]);
      printf("Source,Dest ports %d,%d\n",(iphead[20]<<8)+iphead[21],(iphead[22]<<8)+iphead[23]);
      printf("Layer-4 protocol %d\n",iphead[9]);
    }
  }
   
}

使用BPF的這個可能有問題：

#include <stdio.h>
#include <string.h>
#include <errno.h> 
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h> 
#include <linux/in.h>
#include <linux/if_ether.h>
#include <net/if.h>
#include <linux/filter.h>
#include <sys/ioctl.h>
 
int main(int argc, char **argv) {
  int sock, n;
  char buffer[2048];
  unsigned char *iphead, *ethhead;
  struct ifreq ethreq;
  
  /*my ip: 10.219.119.23 == 0x0adb7716*/
  /*
    udp and host 192.168.13.41 and src port 5000
    (000) ldh      [12]
    (001) jeq      #0x800           jt 2        jf 14
    (002) ldb      [23]
    (003) jeq      #0x11            jt 4        jf 14
    (004) ld       [26]
    (005) jeq      #0x0adb7716      jt 8        jf 6
    (006) ld       [30]
    (007) jeq      #0x0adb7716      jt 8        jf 14
    (008) ldh      [20]
    (009) jset     #0x1fff          jt 14       jf 10
    (010) ldxb     4*([14]&0xf)
    (011) ldh      [x + 14]
    (012) jeq      #0x1388          jt 13       jf 14
    (013) ret      #68
    (014) ret      #0
  */
  struct sock_filter BPF_code[]= {
    { 0x28, 0, 0, 0x0000000c },
    { 0x15, 0, 12, 0x00000800 },
    { 0x30, 0, 0, 0x00000017 },
    { 0x15, 0, 10, 0x00000011 },
    { 0x20, 0, 0, 0x0000001a },
    { 0x15, 2, 0, 0x0adb7716 },
    { 0x20, 0, 0, 0x0000001e },
    { 0x15, 0, 6, 0x0adb7716 },
    { 0x28, 0, 0, 0x00000014 },
    { 0x45, 4, 0, 0x00001fff },
    { 0xb1, 0, 0, 0x0000000e },
    { 0x48, 0, 0, 0x0000000e },
    { 0x15, 0, 1, 0x00001388 },
    { 0x6, 0, 0, 0x00000044 },
    { 0x6, 0, 0, 0x00000000 }
  };                           
  struct sock_fprog Filter;
     
  Filter.len = 15;
  Filter.filter = BPF_code;
   
  if ( (sock=socket(PF_PACKET, SOCK_RAW, htons(ETH_P_IP)))<0) {
    perror("socket");
    return -1;
  }
 
  /* Set the network card in promiscuous mode 設置網卡為混雜模式*/
  strncpy(ethreq.ifr_name,"eth3",IFNAMSIZ); //hardcode, please check your computer: $ifconfig
  if (ioctl(sock,SIOCGIFFLAGS,&ethreq)==-1) {
    perror("ioctl");
    close(sock);
    return -1;
  }
  ethreq.ifr_flags|=IFF_PROMISC;
  if (ioctl(sock,SIOCSIFFLAGS,&ethreq)==-1) {
    perror("ioctl");
    close(sock);
    return -1;
  }
 
  /* Attach the filter to the socket */
  if(setsockopt(sock, SOL_SOCKET, SO_ATTACH_FILTER, &Filter, sizeof(Filter))<0){
    perror("setsockopt");
    close(sock);
    return -1;
  }
 
  while (1) {
    printf("----------\n");
    n = recvfrom(sock,buffer,2048,0,NULL,NULL);
    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<42) {
      perror("recvfrom():");
      printf("Incomplete packet (errno is %d)\n", errno);
      close(sock);
      return 0;
    }
 
    ethhead = buffer;
    printf("Source MAC address: %02x:%02x:%02x:%02x:%02x:%02x\n",
           ethhead[0],ethhead[1],ethhead[2],ethhead[3],ethhead[4],ethhead[5]);
    printf("Destination MAC address: %02x:%02x:%02x:%02x:%02x:%02x\n",
           ethhead[6],ethhead[7],ethhead[8],ethhead[9],ethhead[10],ethhead[11]);
 
    iphead = buffer+14; /* Skip Ethernet  header */
    if (*iphead==0x45) { /* Double check for IPv4 and no options present */
      printf("Source host %d.%d.%d.%d\n", iphead[12],iphead[13],iphead[14],iphead[15]);
      printf("Dest host %d.%d.%d.%d\n", iphead[16],iphead[17], iphead[18],iphead[19]);
      printf("Source,Dest ports %d,%d\n", (iphead[20]<<8)+iphead[21], (iphead[22]<<8)+iphead[23]);
      printf("Layer-4 protocol %d\n",iphead[9]);
    }
  }
   
}

Linux下sniffer實現(轉)