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| 关键词： ICMP include 字节 unsigned int struct 报头 short sum timeval |
ping的原理就是首先建立通道，然后发送包，对方接受后返回信息，这个包至少包括以下内容，发送的时候，包的内容包括对方的ip地址和自己的地址，还有序列数，回送的时候包括双方地址，还有时间等，主要是接受方在都是在操作系统内核里做好的，时刻在监听，提供一段c程序的代码，希望对大家有用。 #include #include #include #include #include #include #include #include #include #include #include #include #define PACKET_SIZE 4096 #define MAX_WAIT_TIME 5 #define MAX_NO_PACKETS 3 char sendpacket[PACKET_SIZE]; char recvpacket[PACKET_SIZE]; int sockfd,datalen=56; int nsend=0,nreceived=0; struct sockaddr_in dest_addr; pid_t pid; struct sockaddr_in from; struct timeval tvrecv; void statistics(int signo); unsigned short cal_chksum(unsigned short *addr,int len); int pack(int pack_no); void send_packet(void); void recv_packet(void); int unpack(char *buf,int len); void tv_sub(struct timeval *out,struct timeval *in); void statistics(int signo) { printf("\n--------------------PING statistics-------------------\n"); printf("%d packets transmitted, %d received , %%%d lost\n",nsend,nreceived, (nsend-nreceived)/nsend*100); close(sockfd); exit(1); } /*校验和算法*/ unsigned short cal_chksum(unsigned short *addr,int len) { int nleft=len; int sum=0; unsigned short *w=addr; unsigned short answer=0; /*把ICMP报头二进制数据以2字节为单位累加起来*/ while(nleft>1) { sum+=*w++; nleft-=2; } /*若ICMP报头为奇数个字节，会剩下最后一字节。把最后一个字节视为一个2字节数据的高字节，这个2字节数据的低字节为0，继续累加*/ if( nleft==1) { *(unsigned char *)(&answer)=*(unsigned char *)w; sum+=answer; } sum=(sum>>16)+(sum&0xffff); sum+=(sum>>16); answer=~sum; return answer; } /*设置ICMP报头*/ int pack(int pack_no) { int i,packsize; struct icmp *icmp; struct timeval *tval; icmp=(struct icmp*)sendpacket; icmp->icmp_type=ICMP_ECHO; icmp->icmp_code=0; icmp->icmp_cksum=0; icmp->icmp_seq=pack_no; icmp->icmp_id=pid; packsize=8+datalen; tval= (struct timeval *)icmp->icmp_data; gettimeofday(tval,NULL); /*记录发送时间*/ icmp->icmp_cksum=cal_chksum( (unsigned short *)icmp,packsize); /*校验算法*/ return packsize; } |
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