The work is based on discussion at stackoverflow http://stackoverflow.com/questions/15458438/implementing-traceroute-using-icmp-in-c. Additional information comes from Unix Network Programming by W. Richard Stevens, and from the website that discusses the various data structures for IP addresses, https://beej.us/guide/bgnet/output/html/multipage/sockaddr_inman.html.
ICMP, or the Internet Control Message Protocol, is a message exchange protocol. It is widely used for various message exchange and information probing at the network layer. Popular tools such as traceroute and ping are examples of ICMP applications. The protocol logically resides within the IP protocol, though in reality it works on top of the IP layer.
This website illustrates the relation between IP and ICMP, as well ICMP header format, the type, and the code that ICMP packet carries.
Traceroute is a program that is available on Linux hosts. One can use this tool to examine the path between the current host and the destination host. For example, the following is a screen capture of using traceroute to see the path from the local host to the host www.example.org
% traceroute www.example.org traceroute to www.example.org (18.104.22.168), 30 hops max, 60 byte packets 1 22.214.171.124 (126.96.36.199) 1.132 ms 1.179 ms 1.236 ms 2 172.30.254.41 (172.30.254.41) 0.364 ms 0.432 ms 0.496 ms 3 188.8.131.52 (184.108.40.206) 0.912 ms 0.902 ms 0.860 ms 4 ncc-1701.bucknell.edu (220.127.116.11) 1.203 ms 1.299 ms 1.225 ms 5 ae-0.590.rtr01.nbrd.net.pennren.net (18.104.22.168) 7.857 ms 7.874 ms 7.850 ms 6 22.214.171.124 (126.96.36.199) 8.035 ms 7.977 ms 8.036 ms 7 188.8.131.52 (184.108.40.206) 12.120 ms 12.165 ms 12.172 ms 8 220.127.116.11 (18.104.22.168) 12.140 ms 12.191 ms 12.190 ms 9 198-7-25-16.edgecastcdn.net (22.214.171.124) 20.444 ms 20.417 ms 20.449 ms 10 126.96.36.199 (188.8.131.52) 20.145 ms 20.242 ms 20.354 ms
Similarly, one can ping a remote host to see if the remote host is alive and how long would it take to get to the remote host.
% ping www.example.org PING www.example.org (184.108.40.206) 56(84) bytes of data. 64 bytes from 220.127.116.11: icmp_seq=1 ttl=53 time=20.2 ms 64 bytes from 18.104.22.168: icmp_seq=2 ttl=53 time=20.2 ms 64 bytes from 22.214.171.124: icmp_seq=3 ttl=53 time=20.1 ms 64 bytes from 126.96.36.199: icmp_seq=4 ttl=53 time=20.0 ms ^C --- www.example.org ping statistics --- 4 packets transmitted, 4 received, 0% packet loss, time 3772ms rtt min/avg/max/mdev = 20.042/20.176/20.262/0.132 ms
Your tasks in this lab is to implement the traceroute program from a program example found on stackoverflow.
You man find many different traceroute implementations on the internet. You are going to use a particular one as a starting point for your work, download the program, understand what and how it does its work, revise it to fulfill our goals.
Create a working directory: Create directory
lab07 in your
csci363/labs/ directory. Your work will be saved in the
Read the post : Read the stackoverflow post at http://stackoverflow.com/questions/15458438/implementing-traceroute-using-icmp-in-c. Understand what is discussed.
Download the program : The stackoverflow post contains a complete set of code that works after the suggested revision in the Answer section. Copy and paste the code segments into your text editor and save them in two separate files, the header file, and the implementation file. Name the header file as
icmp_exp.h and the implementation file as
traceroute.c. Note that the original post named the header file
libsock. We want to change it to be
icmp_exp.h. You'd also change the implementation file to reflect the name change of the header file. Make sure you revise the program from the original post as the Answer suggests.
Compile and run the program : Create a proper
Makefile that will compile the source code and create an executable called
mytraceroute. Because traceroute is an existing Linux program, we don't want the names to be confused. The syntax of the program should be now correct and you can create an executable by simply doing a
make. The program won't run as it is because the local host IP is listed as the author's host IP (172.30.104.59). Search for the pattern and locate where this address is. You need to change this address to your VM's IP address. Once you make this change, you should be able to run on the program on your VM (not on your regular Linux machine as portion of the program requires root privilege.) Give it a try!
% make % ./mytraceroute 188.8.131.52 % ./mytraceroute 184.108.40.206
The first IP belongs to www.bucknell.edu, the second IP belongs to www.example.org. You can find a few other hosts to trace if you'd like. In particular, try to compare the behavior of this program with that of Linux traceroute. Make sure to try a few sites that are far away.
Once the program is working, you are asked to do a sequence of revisions to make the program better and easier to use. Along the way, you are asked to read some Linux manual pages and pages from the web to answer some technical questions.
Answer some questions : Create an answers.txt file. Record your answers to the following questions in that file. These questions are related to your current version of the program traceroute.c. Label the answers as traceroute questions.
IPPROTO_ICMPare used. What do these two parameters mean? What is the key difference between
SOCK_RAWand the ones we used to use such as
SOCK_DGRAM? You probably will need to read manual page section 7 for the subject of raw and for the subject of ip.
struct ip *ip_hdr = (struct ip *) buf;What does it mean? What is the memory address of the variable
ip_hdrafter this statement?
IP_HDRINCLin the call
setsockopt()mean? (Manual page section 7 for ip should give you answers.) The manual page would say that the application program can supply the IP header, do you see which part of the traceroute.c program builds an IP header? Where?
inet_pton()is used a number of times in traceroute.c. Read the manual page about this call and briefly explain what it does.
csum(). What does it do? What is the key difference between this function and the internet checksum function you wrote? What is the data for which this checksum is computed in this line?
ip_hdr->ip_sum = csum ((unsigned short *) buf, 9);
struct icmphdr *icmphd = (struct icmphdr *) (buf + 20);What does it mean? Why
(buf + 20)?
icmphd->type = ICMP_ECHO; icmphd->code = 0;What is the numerical value of
ICMP_ECHO? You may have to look for it in the file
/usr/include/netinet/ip_icmp.h. What does ICMP code zero (0) mean?
if (icmphd2->type != 0)What does
(icmphd2->type == 0)mean here? Find out what is the actual numerical value of the
typereturned here (other than 0) using either a debugging tool or a print statement. Then find out what that type means by searching for it in ICMP type and code list.
inet_ntoa()is used. Briefly describe what it does. What is the difference between the value that this library function return and its parameter (in our case
Now you have a working version of the program that can do the work of a regular Linux application traceroute, you are asked to revise the program to make it more user-friendly, and provide other desired features.
#ifndef _TRACEROUTE_ ...#endifsection in the header file.
while (1), change this loop condition so that the loop will stop if the hop count reaches a constant named
HOPLIMIT. You should define this consntat, give a value of 30 or 40, which means if the program can't reach the destination in
HOPLIMIThops, it should stop.
get_host_ip()that can retrieve the host IP in its dot-format. There are different ways of doing it. You can use a combination of gethostname() and getaddrinfo(), or getifaddr(). Use the function get_host_ip() to replace the hard-coded IP address in the traceroute.c program.
17 * * * 18 * * *You are asked to modify the program to have the same behavior. You need to set the socket receiving timer option so when the timer expires, the
recvfrom()call returns a negative value. You need to use the call
setsockopt(). Read manual page section 7 for the subject socket for more specific information.
In the above exercise, we discussed a method of creating customized IP packet (ICMP packet in this case) to accomplish some functionality. The method used there is to provide a valid IP header and packet ICMP packet as the data segment of the IP packet. Another approach is to create the socket using the ICMP as the protocol option as we did before, then provide the ICMP packet information including the ICMP header and the data, and let the TCP/IP software stack build the IP packet using this ICMP packet as its data. This is the approach BSD Unix used.
Copy the source code. Copy the source code of BSD Unix ping program from
~cs363/Spring16/student/labs/lab07 by recursively copying the entire directory to your directory. Among the files you copied, you should a directory named ping. This is a complete working program along with a Makefile. You can ftp this collection of files to your VM, compile and run the program there. The program should work as expected.
Read and explain how the program works. Answer the following questions after reading the program. Label the questions as ping questions. Explain the following:
Revise the program using the pattern in the first part of the lab, that is, build your own IP packet using the ICMP packet as the data for the IP packet.
Congratulations! You just finished this lab.