在網路上有不少ping命令的實現，但是要麼連執行都不行，要麼就是表層的僥倖的能成功一些例子。今我自己寫了個ping命令程式，自習研究了一下，原來問題頗多。。。。。。 很多還得看底層協議**才能搞清楚它的來龍去脈。。。 先將除錯版ping命令程式**貼上：
/***********************ping程式，completed by ben****************************/
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#define bufsize 1024
#define max_pack_num
char sendbuf[bufsize];
char recvbuf[bufsize];
//int buflen=128;
int datalen=56;
unsigned short pid;
struct sockaddr *sasend;
struct sockaddr *sarecv;
struct sockaddr_in *dst;
char abuf[inet_addrstrlen];
int sckadlen;
static unsigned short nsend=0;
int sockfd;
int recvnum=0;
int totaltime=0;
struct timeval sendtime,endtime;
//static int sendnum=0;
unsigned short cksum(unsigned short *addr ,int len)
if( nleft==1)
sum=(sum>>16)+(sum&0xffff);
sum+=(sum>>16);
answer=~sum;
return answer;
}void sendpkg()
struct icmp *icmp;
icmp=(struct icmp *)sendbuf;
icmp->icmp_type=icmp_echo;
icmp->icmp_code=0;
icmp->icmp_seq=htons(nsend++);
//icmp->icmp_seq=htons(0);
//printf("seq is %d/n",icmp->icmp_seq);
//printf("icmp_type is %x/n",&icmp->icmp_type);
//printf("icmp_seq is %x/n",&icmp->icmp_seq);
//printf("icmp->icmp_id is %x/n",&icmp->icmp_id);
//printf("icmp len is %d/n",sizeof(struct icmp));
//printf("icmp_data is %x/n",&icmp->icmp_data);
//printf("pid is %d/n",pid);
//icmp->icmp_id=htons(pid);
icmp->icmp_id=htons(pid);
//printf("icmp->icmp_id is %x/n",icmp->icmp_id);
//printf("sendbuf byte 4 is %d/n",sendbuf[4]);
//int n;
memset(icmp->icmp_data,0xa5,datalen);
gettimeofday((struct timeval *)icmp->icmp_data,null);
struct timeval *temptival=(struct timeval *)icmp->icmp_data;
temptival->tv_sec=ntohl(temptival->tv_sec);
temptival->tv_usec=ntohl(temptival->tv_usec);
if(nsend==1) gettimeofday(&sendtime,null);
//if(flag==0)
int len=8+datalen;
//printf("heheheheh/n");
icmp->icmp_cksum=htons(cksum((unsigned short *)icmp,len));
//icmp->icmp_cksum=cksum((unsigned short *)icmp,len);
//printf("sasend->sa_len is %d/n",sasend->sa_family);
//sleep(1);
unsigned char a=8;
//printf("a is %x/n",a);
//for(n=0;n<64;n++)
// if((n=sendto(sockfd,sendbuf,len,0,sasend,sckadlen))<0)
//printf("n is %d /n",n);
return;
}void sig_alrm(int signo)
void tv_sub(struct timeval *out,struct timeval *in)
out->tv_sec-=in->tv_sec;
}void catchint(int signo)
void recvpkg()
//printf("n is %d/n",n);
//printf("error when recv/n");
//exit(-1);
//gettimeofday(tval,null);
ip=(struct ip*)recvbuf;
iph_len=ip->ip_hl<<2;
//printf("hehe/n");
if(ip->ip_p!=ipproto_icmp)
return;
//printf("hododo/n");
icmp=(struct icmp*)(recvbuf+iph_len);
icmplen=n-iph_len;
if(icmplen<8) continue;
//printf("jkjk/n");
if(icmp->icmp_type==icmp_echoreply&&ntohs(icmp->icmp_id)==pid)
else
continue;
}free(sarecv);
printf("out of circle /n");
return;
}int main(int argc,char **argv)
struct addrinfo hints,*res;
struct sockaddr_in *dst;
bzero(&hints,sizeof(struct addrinfo));
hints.ai_flags=ai_canonname;
hints.ai_family=af_unspec;//0
hints.ai_socktype=0;
host=argv[1];
signal(sigalrm,sig_alrm);
signal(sigint,catchint);
pid=getpid();
printf("hi,pid is %d/n",pid);
if(getaddrinfo(host,null,&hints,&res)!=0)
sasend=res->ai_addr;
sckadlen=res->ai_addrlen;
//printf("sckadlen is %d/n",sckadlen);
dst=(struct sockaddr_in *)res->ai_addr;//dst=(sockaddr_in *)&res->ai_addr;
//sasend=dst
h=inet_ntop(af_inet,&dst->sin_addr,abuf,inet_addrstrlen);
if(h==null)
printf("h is %s/n",h);
printf("ping %s(%s):%d data bytes/n",res->ai_canonname?res->ai_canonname:h,h,datalen);
//int protocol;
struct protoent *protocol;
if( (protocol=getprotobyname("icmp") )==null)
sockfd=socket(af_inet,sock_raw,protocol->p_proto); //ipproto_icmp
int buflen=bufsize;
//printf("come to here:/n");
setsockopt(af_inet,sol_socket,so_rcvbuf,&buflen,sizeof(buflen));
sig_alrm(sigalrm);
//sendpkg();
recvpkg();
return 1;
} 對方接受到icmp資料報在ip層還會做處理：
當乙個i c m p報文到達時，i p層通過i n e t s w [ 4 ]的p r _ i n p u t
函式，間接呼叫i c m p _ i n p u t函式。
icmp_input->in_cksum():這個函式會重新計算校驗和，如果校驗和不對，接受到的包含icmp報文ip包將就不會被傳送。
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