DOS Command Window
See Ping Lab for how to open a window for DOS commands.
tracert
Note: Traceroute is discussed on pp. 44-45 of the 2nd edition of the textbook.
We will use a special Internet probing program called "traceroute," which is truncated to tracert under DOS, but is traceroute under Unix and MacOSX. It attempts to trace the route an IP packet would follow to a specified Internet host by launching multiple probe packets with a small ttl field, which specifies "time to live." It then listens for a TIME_EXCEEDED reply from a gateway. If it hears no response within 3 seconds, it gives up and just prints a *.
- First trace the route to sophia:
> tracert sophia.smith.edu
- Next try the traceroute command with a nearby site:
> tracert cs.umass.edu
This can be a time-consuming, network-intensive command, so we will use it sparingly (it will be useful in Assignment 1 and perhaps Quiz 2). Just to show you, however, here is a traceroute (from Linux, which gives a bit more information) to New Zealand, which shows the packets went via San Francisco:
traceroute to cs.auckland.ac.nz (130.216.35.100), 30 hops max, 40 byte packets 1 131.229.222.100 (131.229.222.100) 1 ms (ttl=30!) 2 131.229.64.101 (131.229.64.101) 9 ms 3 fc-umass-rt-ser3.five-colleges.net (192.80.66.97) 16 ms 4 border1-rt-eth1-0-3.gw.umass.edu (192.80.66.146) 10 ms 5 bordercore1-hssi5-0-1.Boston.cw.net (166.48.60.5) 103 ms 6 corerouter1.SanFrancisco.cw.net (204.70.9.131) 147 ms 7 bordercore4.SanFrancisco.cw.net (166.48.18.1) 159 ms 8 concentric-network.SanFrancisco.cw.net (166.48.19.254) 164 ms 9 us-ca-scl-core1-a3-0-0d20.rtr.concentric.net (207.88.3.129) 152 ms 10 us-ca-la-core1-a12-0d6.rtr.concentric.net (207.88.0.6) 159 ms 11 * 12 203.167.249.218 (203.167.249.218) 329 ms 13 ba2-fe0-1-0-acld.Auckland.clix.net.nz (203.97.2.244) 296 ms 14 clix-uofauckland-nz-2.cpe.clix.net.nz (203.167.226.46) 347 ms 15 ccr4-e0.auckland.ac.nz (130.216.1.254) 340 ms 16 130.216.191.119 (130.216.191.119) 274 ms 17 * 18 data.cs.auckland.ac.nz (130.216.35.100) 307 ms (ttl=48!)
Incidentally, when the probing process times out, it displays an asterisk * in place of the data it could not find.
It is useful to know you can cancel a DOS (or Unix or MacOSX) command with control-c. Sometimes you need this to kill overly long searches.
There are more complicated tools available, built on the same principles as tracert. If you have time, try experimenting with this visual traceroute tool (one of several such services you can find via google). Unfortunately, this will show the route from the web site's host, not from the machine you are using.