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POImplementing traceroute using icmp in C
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2013-03-17T07:14:25.097
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2013-03-17T12:16:29.983
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I am trying to implement traceroute using icmp raw sockets by constructing the appropriate ip header and icmp header.The port number i am using is 7 and i have calculated the checksums.The hop limit is incremented each time and a packet is sent till the reply message contains the echo reply of type 0. <pre><code>#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; } </code></pre> When the input ie <code>argv[1]</code> is <code>"127.0.0.1"</code> the o/p is <pre><code>hop limit:0 Address:127.0.0.1 Reached destination:127.0.0.1 with hop limit:1 </code></pre> but for other addresses present in my lan for whom tracepath works my program blocks at <code>recvfrom</code>. Can you please point out the reasons? Thank you. Here's libsock:- <pre><code>#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*) </code></pre>
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<c><sockets><icmp>
Title
Implementing traceroute using icmp in C
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