在C中使用icmp实现traceroute

Question

我正在尝试使用icmp原始套接字通过构造适当的ip头和icmp头来实现traceroute。我使用的端口号是7，我已经计算了校验和。每次都会增加跳跃限制并发送数据包直到回复message包含类型0的echo回复。

#include "libsock"
#include<netinet/ip.h>
#include<netinet/ip_icmp.h>


unsigned short
csum (unsigned short *buf, int nwords)
{
  unsigned long sum;
  for (sum = 0; nwords > 0; nwords--)
    sum += *buf++;
  sum = (sum >> 16) + (sum & 0xffff);
  sum += (sum >> 16);
  return ~sum;
}

int
main (int argc, char *argv[])
{
  if (argc != 2)
    {
      printf ("need destination for tracert\n");
      exit (0);
    }
  int sfd = socket (AF_INET, SOCK_RAW, IPPROTO_ICMP);
  char buf[4096] = { 0 };
  struct ip *ip_hdr = (struct ip *) buf;
  int hop = 0;

  int one = 1;
  const int *val = &one;
  if (setsockopt (sfd, IPPROTO_IP, IP_HDRINCL, val, sizeof (one)) < 0)
    printf ("Cannot set HDRINCL!\n");

  struct sockaddr_in addr;
  addr.sin_port = htons (7);
  addr.sin_family = AF_INET;
  inet_pton (AF_INET, argv[1], &(addr.sin_addr));


  while (1)
    {
      ip_hdr->ip_hl = 5;
      ip_hdr->ip_v = 4;
      ip_hdr->ip_tos = 0;
      ip_hdr->ip_len = 20 + 8;
      ip_hdr->ip_id = 10000;
      ip_hdr->ip_off = 0;
      ip_hdr->ip_ttl = hop;
      ip_hdr->ip_p = IPPROTO_ICMP;
      inet_pton (AF_INET, "172.30.104.59", &(ip_hdr->ip_src));
      inet_pton (AF_INET, argv[1], &(ip_hdr->ip_dst));
      ip_hdr->ip_sum = csum ((unsigned short *) buf, 9);

      struct icmphdr *icmphd = (struct icmphdr *) (buf + 20);
      icmphd->type = ICMP_ECHO;
      icmphd->code = 0;
      icmphd->checksum = 0;
      icmphd->un.echo.id = 0;
      icmphd->un.echo.sequence = hop + 1;
      icmphd->checksum = csum ((unsigned short *) (buf + 20), 4);
      sendto (sfd, buf, 28, 0, SA & addr, sizeof addr);
      char buff[4096] = { 0 };
      struct sockaddr_in addr2;
      socklen_t len = sizeof (struct sockaddr_in);
      recvfrom (sfd, buff, 28, 0, SA & addr2, &len);
      struct icmphdr *icmphd2 = (struct icmphdr *) (buff + 20);
      if (icmphd2->type != 0)
    printf ("hop limit:%d Address:%s\n", hop, inet_ntoa (addr2.sin_addr));
      else
    {
      printf ("Reached destination:%s with hop limit:%d\n",
          inet_ntoa (addr2.sin_addr), hop);
      exit (0);
    }

      hop++;
    }

  return 0;
}

当输入即argv[1]为"127.0.0.1" ，o / p为

hop limit:0 Address:127.0.0.1

Reached destination:127.0.0.1 with hop limit:1

但是对于我的局域网中存在的其他地址，tracepath可以在recvfrom阻止我的程序块。

你能指出原因吗？

谢谢。

这是libsock： -

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<arpa/inet.h>
#include<sys/types.h>
#include<netinet/in.h>
#include<sys/socket.h>
#include<unistd.h>
#include<pthread.h>
#include<poll.h>
#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/ipc.h>
#include<fcntl.h>
#include<sys/stat.h>
#include<signal.h>
#include<sys/sem.h>
#include<poll.h>
#include<pthread.h>
#include<sys/select.h>
#include<sys/un.h>
#define SA (struct sockaddr*)

Answer 1

如果要手动构建IP标头，则必须将源地址设置为IP，该IP具有可作为目标的IP地址的可路由性。 例如，对于localhost，您可以将源设置为127.0.0.1，因为localhost“可以ping”localhost（即具有可路由性）。

你给发送和接收的尺寸看起来真的太小了。 我在家用计算机上进行了以下更改（它位于NAT设备后面，因此是192.168.1.0/24地址）。

inet_pton (AF_INET, "192.168.1.168", &(ip_hdr->ip_src));
....
sendto (sfd, buf, sizeof(struct ip) + sizeof(struct icmphdr), 0, SA & addr, sizeof addr);
....
recvfrom (sfd, buff, sizeof(buff), 0, SA & addr2, &len);

示例输出：

thuovila@glx:~/src/so$ sudo ./a.out 128.214.248.132
hop limit:0 Address:192.168.1.1
hop limit:1 Address:192.168.1.1
hop limit:2 Address:91.156.128.1
hop limit:3 Address:139.97.9.58
hop limit:4 Address:139.97.6.209
hop limit:5 Address:139.97.6.250
hop limit:6 Address:193.110.224.14
hop limit:7 Address:193.166.255.93
Reached destination:128.214.248.132 with hop limit:8