1 int sockfd = socket(AF_INET,SOCK_PACKET,htons(0x0003));  

1 struct ifreq ifr;
2 strcpy(ifr.ifr_name,"eth0");
3 ioctl(sockfd,SIOCGIFFLAGS,&ifr);

1 ifr.ifr_flags| = IFR_PROMISC;
2 ioctl(sockfd,SIOCSIFFLAGS,&ifr);

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<iostream>
#include<unistd.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<sys/ioctl.h>
#include<net/if.h>
#include<arpa/inet.h>
#include<netinet/if_ether.h>
#include<netinet/in.h>
#include<netinet/ip.h>
#include<netinet/tcp.h>
#include<netinet/udp.h>using namespace std;char ethernet_frame[ETH_FRAME_LEN];//定义一个数据帧的长度
struct iphdr *ipheader;//定义ip头部指针int socketcreate()
{int sockfd = socket(AF_INET,SOCK_PACKET,htons(0x0003));    //构建了一个数据链路层的数据包；if(sockfd == -1){cout<<"Socket init error!"<<endl;    return -1;}/*下面设置接口结构*/char *ifname = "eth0";struct ifreq ifr;strcpy(ifr.ifr_name,ifname);int result = ioctl(sockfd,SIOCGIFFLAGS,&ifr);if(result == -1){cout<<"Can't get flags!"<<endl;close(sockfd);return -2;}ifr.ifr_flags|= IFF_PROMISC;/*一般而言，Linux系统截获数据包后，会通过协议栈，按照TCP/IP层次进行解析，那我们如何直接获得更为底层的数据报文呢，这里用到一个类型SOCK_PACKET类型。int sockfd = socket(AF_INET,SOCK_PACKET,htons(0x0003));通过上面这个函数可以获得一个特殊的套接字，其中：AF_INET：                              表示因特网协议族SOCK_PACKET：                   表示数据包截取在物理层0x0003：                                 表示数据帧类型不确定修改网络接口结构：struct ifreq ifr;strcpy(ifr.ifr_name,"eth0");ioctl(sockfd,SIOCGIFFLAGS,&ifr);设置混杂模式ifr.ifr_flags| = IFR_PROMISC;ioctl(sockfd,SIOCSIFFLAGS,&ifr);注意：进行标志位设定时，遵循以下步骤：（1）取出原标识位；（2）与待设定标志位进行位或运算（“|”）；（3）重新写入；*/result = ioctl(sockfd,SIOCSIFFLAGS,&ifr);if(result == -1){cout<<"Can't set flags!"<<endl;close(sockfd);return -3;}return sockfd;
}
int getframe(int sockfd,int num)
{struct ethhdr* fheader;fheader = (struct ethhdr*)ethernet_frame;memset(ethernet_frame,0,ETH_FRAME_LEN);int size = read(sockfd,ethernet_frame,ETH_FRAME_LEN);if(size <= 0){cout<<"No packet or packet error!"<<endl;    return -1;}cout<<"************************Packet"<<num<<"received from eth0 START!************************"<<endl;printf("DST MAC: ");for(int i=0;i<ETH_ALEN-1;i++){printf("%2x-",fheader->h_dest[i]);    }printf("%2x\n",fheader->h_dest[ETH_ALEN-1]);printf("SRC MAC: ");for(int i=0;i<ETH_ALEN-1;i++){printf("%2x-",fheader->h_source[i]);    }printf("%2x\n",fheader->h_source[ETH_ALEN-1]);if(ntohs(fheader->h_proto) == 0x0800){cout<<"Protocol: IP"<<endl;    }if(ntohs(fheader->h_proto) == 0x0806){cout<<"Protocol: RAP"<<endl;    }if(ntohs(fheader->h_proto) == 0x8035){cout<<"Protocol: RARP"<<endl;    }int ret = ntohs(fheader->h_proto);return ret;
}int getip(int protocol,int num)
{if(protocol != 0x0800){cout<<"NO IP Packet!"<<endl;cout<<"************************Packet"<<num<<"received from eth0 END!**************************"<<endl;return 0;    }ipheader = (struct iphdr*)(ethernet_frame+ETH_HLEN);printf("Version: 4");cout<<endl;in_addr *p,*q;p = (struct in_addr*)&ipheader->saddr;printf("SRC IP: %s",inet_ntoa(*p));cout<<endl;q = (struct in_addr*)&ipheader->daddr;printf("DST IP: %s",inet_ntoa(*q));cout<<endl;if(ipheader->protocol == 1){cout<<"PROTOCOL: ICMP"<<endl;    }if(ipheader->protocol == 6){cout<<"PROTOCOL: TCP"<<endl;    }if(ipheader->protocol == 17){cout<<"PROTOCOL: UDP"<<endl;    }return ipheader->protocol;
}int gettcp(int protocol)
{if(protocol != 6){return -1;    }struct tcphdr* tcph;tcph = (struct tcphdr*)(ipheader+((ipheader->ihl)*4));printf("SRC PORT: %d",ntohs(tcph->source));cout<<endl;printf("DST PORT: %d",ntohs(tcph->dest));cout<<endl;return 0;
}int getudp(int protocol)
{if(protocol != 17){return -1;    }struct udphdr* udph;udph = (struct udphdr*)(ipheader+((ipheader->ihl)*4));printf("SRC PORT: %d",ntohs(udph->source));cout<<endl;printf("DST PORT: %d",ntohs(udph->dest));cout<<endl;return 0;
}int main(int argc,char *argv[])
{        if(argc < 2){cout<<"Please input the nummber of packet that you want to catch!"<<endl;return 0;}int num = (int)argv[1][0];int sock = socketcreate();for(int i=1;i<num;i++){int ip_protocol = getframe(sock,i);int trasnport_protocol = getip(ip_protocol,i);gettcp(trasnport_protocol);getudp(trasnport_protocol);cout<<"************************Packet"<<num<<"received from eth0 END!**************************"<<endl;cout<<endl;cout<<endl;cout<<endl;cout<<endl;}return 0;
}