ping.c

很好用的ping程序

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
/*

* If your kernel doesn't muck with raw packets, #define REALLY_RAW.

* This is probably only Linux.

*/
#ifdef REALLY_RAW
#define FIX(x) htons(x)
#else
#define FIX(x) (x)

#endif
int main(int argc, char **argv)
{
	int s;//define a socket
	char buf[1500];
	struct ip *ip = (struct ip *)buf;
	struct icmp *icmp = (struct icmp *)(ip + 1);
	struct hostent *hp;
	struct sockaddr_in dst;
	int offset;
	int on = 1;
	bzero(buf, sizeof buf);
	if ((s = socket(AF_INET, SOCK_RAW, IPPROTO_IP)) < 0) {
		perror("socket");
		exit(1);
	}
	if (setsockopt(s, IPPROTO_IP, IP_HDRINCL, &on, sizeof(on)) < 0) {
		perror("IP_HDRINCL");//contain the data and may be only used with the scok_RAW type
		exit(1);
	}
	if (argc != 2) {
		fprintf(stderr, "usage: %s hostname\n", argv[0]);
		exit(1);
	}
	if ((hp = gethostbyname(argv[1])) == NULL) {
		if ((ip->ip_dst.s_addr = inet_addr(argv[1])) == -1) {//change a host(char*) to a ip addr
			fprintf(stderr, "%s: unknown host", argv[1]);
		}
	}
    else {
		bcopy(hp->h_addr_list[0], &ip->ip_dst.s_addr, hp->h_length);
	}
	printf("Sending to %s\n", inet_ntoa(ip->ip_dst));
	//takes an Internet address and returns an ASCII 
	//string representing the address in '.' notation.
	ip->ip_v = 4;//version
	ip->ip_hl = sizeof *ip >> 2;
	ip->ip_tos = 0;//type of service 
	ip->ip_len = FIX(sizeof buf);//ip length
	ip->ip_id = htons(4321);//if o that means kernal to set approviate value.
	ip->ip_off = FIX(0);//offset
	ip->ip_ttl = 255;//time to live
	ip->ip_p = 1;
	ip->ip_sum = 0; /* kernel fills in */
	ip->ip_src.s_addr = 0; /* kernel fills in */
	dst.sin_addr = ip->ip_dst;
	dst.sin_family = AF_INET;
	icmp->icmp_type = ICMP_ECHO;
	icmp->icmp_code = 0;
	icmp->icmp_cksum = htons(~(ICMP_ECHO << 8));
	/* the checksum of all 0's is easy to compute */
	for (offset = 0; offset < 65536; offset += (sizeof buf - sizeof *ip)) {
		ip->ip_off = FIX(offset >> 3);
		if (offset < 65120)
			ip->ip_off |= FIX(IP_MF);
		else
			ip->ip_len = FIX(418); /* make total 65538 */
		if (sendto(s, buf, sizeof buf, 0, (struct sockaddr *)&dst,
			sizeof dst) < 0) {
			fprintf(stderr, "offset %d: ", offset);
			perror("sendto");
		}
		if (offset == 0) {
			icmp->icmp_type = 0;
			icmp->icmp_code = 0;
			icmp->icmp_cksum = 0;
		}
	}
}