【发布时间】：2012-03-13 17:21:59
【问题描述】：
我正在尝试用 C 创建一个 ICMP ping 测试程序，但在成功发送数据包时遇到了困难。 sendto 函数返回字节数，除了没有数据包之外的所有内容都被实际发送。我已经在目标计算机上使用 WireShark 验证了这一点。主机上的常规 ping 工作正常，但会显示在 WireShark 中。
这是我的代码：
#include <stdio.h>
#include <stdlib.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>
#include <string.h>
#include <arpa/inet.h>
#include <sys/select.h>
#include <sys/time.h>
unsigned short cksum(unsigned short *addr, int len);
int main(int argc, char *argv[])
{
int sock;
char send_buf[400], recv_buf[400], src_name[256], src_ip[15], dst_ip[15];
struct ip *ip = (struct ip *)send_buf;
struct icmp *icmp = (struct icmp *)(ip + 1);
struct hostent *src_hp, *dst_hp;
struct sockaddr_in src, dst;
struct timeval t;
int on;
int num = 10;
int failed_count = 0;
int bytes_sent, bytes_recv;
int dst_addr_len;
int result;
fd_set socks;
/* Initialize variables */
on = 1;
memset(send_buf, 0, sizeof(send_buf));
/* Check for valid args */
if(argc < 2)
{
printf("\nUsage: %s <dst_server>\n", argv[0]);
printf("- dst_server is the target\n");
exit(EXIT_FAILURE);
}
/* Check for root access */
if (getuid() != 0)
{
fprintf(stderr, "%s: This program requires root privileges!\n", argv[0]);
exit(EXIT_FAILURE);
}
/* Get source IP address */
if(gethostname(src_name, sizeof(src_name)) < 0)
{
perror("gethostname() error");
exit(EXIT_FAILURE);
}
else
{
if((src_hp = gethostbyname(src_name)) == NULL)
{
fprintf(stderr, "%s: Can't resolve, unknown source.\n", src_name);
exit(EXIT_FAILURE);
}
else
ip->ip_src = (*(struct in_addr *)src_hp->h_addr);
}
/* Get destination IP address */
if((dst_hp = gethostbyname(argv[1])) == NULL)
{
if((ip->ip_dst.s_addr = inet_addr(argv[1])) == -1)
{
fprintf(stderr, "%s: Can't resolve, unknown destination.\n", argv[1]);
exit(EXIT_FAILURE);
}
}
else
{
ip->ip_dst = (*(struct in_addr *)dst_hp->h_addr);
dst.sin_addr = (*(struct in_addr *)dst_hp->h_addr);
}
sprintf(src_ip, "%s", inet_ntoa(ip->ip_src));
sprintf(dst_ip, "%s", inet_ntoa(ip->ip_dst));
printf("Source IP: '%s' -- Destination IP: '%s'\n", src_ip, dst_ip);
/* Create RAW socket */
if((sock = socket(AF_INET, SOCK_RAW, IPPROTO_RAW)) < 0)
{
perror("socket() error");
/* If something wrong, just exit */
exit(EXIT_FAILURE);
}
/* Socket options, tell the kernel we provide the IP structure */
if(setsockopt(sock, IPPROTO_IP, IP_HDRINCL, &on, sizeof(on)) < 0)
{
perror("setsockopt() for IP_HDRINCL error");
exit(EXIT_FAILURE);
}
/* IP structure, check the ip.h */
ip->ip_v = 4;
ip->ip_hl = 5;
ip->ip_tos = 0;
ip->ip_len = htons(sizeof(send_buf));
ip->ip_id = htons(321);
ip->ip_off = htons(0);
ip->ip_ttl = 255;
ip->ip_p = IPPROTO_ICMP;
ip->ip_sum = 0;
/* ICMP structure, check ip_icmp.h */
icmp->icmp_type = ICMP_ECHO;
icmp->icmp_code = 0;
icmp->icmp_id = 123;
icmp->icmp_seq = 0;
/* Set up destination address family */
dst.sin_family = AF_INET;
/* Loop based on the packet number */
for(int i = 1; i <= num; i++)
{
/* Header checksums */
icmp->icmp_cksum = 0;
ip->ip_sum = cksum((unsigned short *)send_buf, ip->ip_hl);
icmp->icmp_cksum = cksum((unsigned short *)icmp,
sizeof(send_buf) - sizeof(struct icmp));
/* Get destination address length */
dst_addr_len = sizeof(dst);
/* Set listening timeout */
t.tv_sec = 5;
t.tv_usec = 0;
/* Set socket listening descriptors */
FD_ZERO(&socks);
FD_SET(sock, &socks);
/* Send packet */
if((bytes_sent = sendto(sock, send_buf, sizeof(send_buf), 0,
(struct sockaddr *)&dst, dst_addr_len)) < 0)
{
perror("sendto() error");
failed_count++;
printf("Failed to send packet.\n");
fflush(stdout);
}
else
{
printf("Sent %d byte packet... ", bytes_sent);
fflush(stdout);
/* Listen for the response or timeout */
if((result = select(sock + 1, &socks, NULL, NULL, &t)) < 0)
{
perror("select() error");
failed_count++;
printf("Error receiving packet!\n");
}
else if (result > 0)
{
printf("Waiting for packet... ");
fflush(stdout);
if((bytes_recv = recvfrom(sock, recv_buf,
sizeof(ip) + sizeof(icmp) + sizeof(recv_buf), 0,
(struct sockaddr *)&dst,
(socklen_t *)&dst_addr_len)) < 0)
{
perror("recvfrom() error");
failed_count++;
fflush(stdout);
}
else
printf("Received %d byte packet!\n", bytes_recv);
}
else
{
printf("Failed to receive packet!\n");
failed_count++;
}
fflush(stdout);
icmp->icmp_seq++;
}
}
/* Display success rate */
printf("Ping test completed with %d%% success rate.\n",
(((num - failed_count) / num) * 100));
/* close socket */
close(sock);
return 0;
}
/* One's Complement checksum algorithm */
unsigned short cksum(unsigned short *addr, int len)
{
int nleft = len;
int sum = 0;
unsigned short *w = addr;
unsigned short answer = 0;
while (nleft > 1)
{
sum += *w++;
nleft -= 2;
}
if (nleft == 1)
{
*(unsigned char *)(&answer) = *(unsigned char *)w;
sum += answer;
}
sum = (sum >> 16) + (sum & 0xffff);
sum += (sum >> 16);
answer = ~sum;
return (answer);
}
对我做错了什么有什么想法吗？另外，校验和好吗？两者都使用 0 可以吗？
编辑：好的，多亏了下面的人，我已经设法正确发送了数据包！并且目标计算机将发送回一个回显回复。但是，现在，我的程序没有收到回复。 select() 函数总是超时。我已经更新了上面的代码。
编辑 2： 好的，我搞定了！我需要将套接字协议设置为IPPROTO_ICMP 而不是IPPROTO_RAW，效果很好！再次感谢评论的各位！真的帮了大忙！看起来我只能将一个答案标记为正确，但你们都帮助解决了这个问题。 :)
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