Week 4 discussion
In snyder chapter 3, it mentioned your data or message are actually chopped into smaller packets and relayed by computers on the Internet. To help you understand that, go to DNSstuff.com. There is a tool called Tracert that can help you trace where your data packets go. For example, if I want to see what happened when my computer communicates with the website www.pitt.edu. I just type in www.pitt.edu into the textbox under tracert (second one at the right side), a list of computers on the route and their ip addresses will be shown up in the table. Try some websites yourself, tell me how many machines the data packet goes through before hit the destination. Try it several times, see whether the machines are the same ones. Why or why not? It is really interesting to try some foreign websites such as www.bbc.com. Feel free to try other tools. For example, find out what is the ip address of the ECU web server.
posted by Dr. Z @ ECU at 1:39 PM
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The mechanism behind the traceroute program is that it sent out 32kb packet to the destination machine using a method call "ping". Ever heard a hacker attack call "Ping to death". Some machines with firewall (a server protection software) installed will reject any ping to them. Which means you can not see the the packet get relayed. Regular packet is not a ping packet. However, there is no tool available to trace the regular packet.
Alan, Thank you for sharing the virtual map program.
Emmanuel, I am not sure whether I understand your questions correctly. Let's think hops as the number of connections you have to make when you fly from greenville to Bali, Indonesia. TCP/IP protocol will decide which router is the next stop for the data packet. First several hops are mostly the same since that is from an end machine to its ISP. After the packet get on the Internet backbone (You can see lots AT&T router there), the packet is free to take whichever route. The reason you can trace the packet using traceroute is that whenver a packet arrives a rounter or a computer, that machine will send an information back to the original machine telling it the packet is received (and sent out again). Sometimes some machines are configured to turn off the function, that's why sometimees you can not get DNS or IP address of certain intermediate machine. Also, firewall can reject ping or traceroute data packet. However, regular data packets can be passed on.
Hope this answers your question.
Amy, each machine on the route is not obligated to send a reverse DNS to the original machine. For security reason, they can turn that function off. The packet will still get relayed to the destination machine. Also tracert packets are different from regular packets. Some machine refuse them for avoiding potential hacker attack.
Dianne, sometimes a computer filewall (protection program running on a server) refuse to relay tracert packet to prevent potential hacker attacks. There are not many machines between U.S. and UK does not mean the distance is the shortest. It only means number of servers. That make sence. There is no server at the bottom of the atlantic ocean.
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