Traceroute

My computer -> www.sfc.keio.ac.jp

My computer ---> router in studio art building closet ---> router at edge of Reed network ---> router at network provider...

• Routers
  
  
  
• Scope:
  • Routers know a lot about its own network. (eg. router in the Reed network knows where every computer is in its own network).
  • Routers have limited knowledge outside of its network. (eg. if a packet is going east coast forward it to network B, if it is going to the west coast forward it to network C).
  
  
  
• Best-effort:
  • If one network is down, it will try another route.
  • If a particular network is congested, routers may forward your packet to another network.
  • Routers are allowed to drop (give up on) your packets if it's too busy.

Looking up routing table using a UNIX command
%netstat -r

To prevent infinite loops, limit the lifespan of packets

• TTL (time to live. aka hop limit) value in packet header. Set to a number (eg. 64)
• Everytime a router forwards a packet, it decrements the TTL value by one.
• When the TTL value has reached 0, the packet is dropped.
• A report (an ICMP error message "hey I killed your packet") is often sent back to the sender).

Traceroute

• Traceroute sends out a packet to the desitination starting with the TTL value of 1, and subsequently increasing the TTL value by one.

On the Terminal.app

% traceroute www.sfc.keio.ac.jp
     traceroute to www.sfc.keio.ac.jp (133.27.4.221), 64 hops max, 52 byte packets
 1  clarkacad (134.10.2.44)  1.214 ms  0.926 ms  1.340 ms
 2  borderrouter (134.10.64.2)  0.909 ms  0.863 ms  0.731 ms
 3  206-169-234-117.static.twtelecom.net (206.169.234.117)  0.943 ms  0.914 ms  0.863 ms
 4  64-129-238-138.static.twtelecom.net (64.129.238.138)  15.637 ms  15.664 ms  15.670 ms
 5  te-9-4.car1.sanjose2.level3.net (4.59.0.229)  15.884 ms  15.819 ms  15.853 ms
 6  vlan80.csw3.sanjose1.level3.net (4.69.152.190)  16.005 ms  18.096 ms  24.721 ms
 7  ae-81-81.ebr1.sanjose1.level3.net (4.69.153.9)  16.337 ms  16.031 ms  15.975 ms
 8  ae-2-2.ebr3.losangeles1.level3.net (4.69.132.10)  23.428 ms  23.507 ms  24.543 ms
 9  ae-93-93.csw4.losangeles1.level3.net (4.69.137.46)  23.420 ms
    ae-73-73.csw2.losangeles1.level3.net (4.69.137.38)  32.388 ms
    ae-83-83.csw3.losangeles1.level3.net (4.69.137.42)  28.521 ms
10  ae-1-60.edge5.losangeles1.level3.net (4.69.144.11)  23.699 ms
    ae-3-80.edge5.losangeles1.level3.net (4.69.144.139)  23.449 ms
    ae-4-90.edge5.losangeles1.level3.net (4.69.144.203)  23.646 ms
11  japan-telec.edge5.losangeles1.level3.net (4.59.48.2)  23.209 ms  23.487 ms  23.497 ms
12  tokyo-dc-gm2-xe5-3-2-vlan10.s4.sinet.ad.jp (150.99.2.81)  136.906 ms  136.761 ms
    tokyo-dc-gm2-xe4-3-0-vlan10.s4.sinet.ad.jp (150.99.2.77)  164.841 ms
13  tokyo-dc-rm-ae4-vlan10.s4.sinet.ad.jp (150.99.2.53)  151.746 ms  137.422 ms  137.273 ms
14  keio.gw.sinet.ad.jp (150.99.188.18)  153.990 ms  141.243 ms  141.152 ms
15  bb-sfc-core0-hc.bb.keio.ac.jp (131.113.1.166)  151.238 ms  151.232 ms  151.367 ms
16  fw1-entry-sfc.bb.keio.ac.jp (131.113.255.78)  126.761 ms  139.489 ms  139.620 ms
17  gw2.sfc.keio.ac.jp (133.27.3.1)  140.368 ms  152.952 ms  139.885 ms
18  www.sfc.keio.ac.jp (133.27.4.221)  140.742 ms  153.864 ms  140.836 ms
    

Hit Ctrl-C to stop.

If a packet is not acknowledged within the expected timeout, an asterisk is displayed.

traceroute to www.amazon.com (72.21.211.176), 64 hops max, 52 byte packets
 1  clarkacad (134.10.2.44)  1.196 ms  1.059 ms  1.013 ms
 2  borderrouter (134.10.64.2)  0.801 ms  0.947 ms  0.854 ms
 3  206-169-234-117.static.twtelecom.net (206.169.234.117)  0.884 ms  5.872 ms  1.154 ms
 4  sea2-pr2-xe-1-3-0-0.us.twtelecom.net (66.192.253.122)  4.654 ms  4.574 ms  4.556 ms
 5  64.132.69.202 (64.132.69.202)  4.502 ms  4.342 ms  4.388 ms
 6  dca2-edge-01.inet.qwest.net (67.14.28.110)  77.527 ms  78.077 ms  77.656 ms
 7  72.165.86.74 (72.165.86.74)  78.548 ms  78.287 ms  78.247 ms
 8  72.21.220.157 (72.21.220.157)  79.836 ms  87.652 ms
    72.21.220.125 (72.21.220.125)  80.156 ms
 9  72.21.222.147 (72.21.222.147)  84.281 ms  114.044 ms  78.168 ms
10  72.21.218.13 (72.21.218.13)  80.088 ms  79.859 ms  79.559 ms
11  * * *
12  * * *
13  * * *
14  * * *
15  * * *
16  * * *
17  * * *
18  * * *
19  * * *

    

basic convention used in many UNIX commands:

Ctrl-C            // quit program

man : getting help (manual)

% man man 
% man traceroute


   Space key         // continue scrolling when viewing "man" or using "less"
   b                 // go backward when viewing "man" or using "less"
   q                 // go backward when viewing "man" or using "less"

ls : list files

  % ls
  % ls -l
  % ls -a

cd : change directory (folder)

  % cd
  % cd ..               // move up one directory (.. means up)
  % cd ~                // move to home ~ means home
  % cd ~/Documents/     // move to Documents folder under home
  % cd ~/Documents/Processing    
  % cd ~/Documents/Processing/   // the final "/" makes it explicit that it is a directory    
  % cd ../../../        // move three directory up
  % cd .                // . means "here" 

pwd : display present working directory


cp : copy file

% cp file1 file2      // copy file1 to file 2
% cp ~/Desktop/test.txt foo.txt
% cp ~/Desktop/test.txt ~/Documents/

mv : move file

% mv file1 file2           // move file1 to file 2
% mv file1 html/lecture/   // move file1 to directory lecture

Other UNIX commands you might want to take a look at

Traceroute assignment: ping, dig, traceroute, whois, and an open-ended question