CORC 1312
Lab #2: URLs, IP addresses, DNS names, tracert

"Show and Tell"

  1. You can't judge a domain by its name
    1. Open a Web browser and go to http://www.whitehouse.com. Look at some of the items on the page, and then compare the site with http://www.whitehouse.gov.
    2. Yahoo is pretty smart about similar DNS names -- check out http://www.yahoo.org

  2. DNS names <-> IP addresses

    1. We will use a utility called nslookup to obtain IP addresses corresponding to DNS names. Here is a link to an online nslookup tool and an alternative site.

      Use nslookup to find the IP addresses for these DNS names:

      1. www.cuny.edu
      2. www.yahoo.com

    2. What happens if you type in a DNS name incorrectly? Try linking to http://www.brooklyn.cuny.e or http://www.brklyn.cuny.edu
      Try to use nslookup for those DNS names - try entering www.brooklyn.cuny.e and www.brklyn.cuny.edu on the nslookup page.

    3. What happens if you type in an IP address directly, instead of a DNS name? Try linking to http://146.245.252.76.

    4. What if you type the IP address in incorrectly? Try linking to http://146.245.252.16 (click the stop icon at the top of the browser window if there is no response.)
      Try using nslookup with 146.245.252.16

    5. When you use a browser and type in a URL as a domain name, what service translates that name into an IP address? Your internet service provider(ISP) has a domain name server that does the translation. In the exercises above, we have used alternative servers to do the translation. A computer user can choose which company, their ISP, Google, etc., to employ for all their browsing needs. A recent article on this topic describes the OpenDNS company. What advantages are listed to using OpenDNS rather than your ISP company?

    3. The following section will not work in some of the computer labs because of the proxy server. If it does not work in your Brooklyn College Lab room, try it at home.

  3. Tracing a route through the Internet

    We will use tracert to trace the route from your machine to other computers on the Internet. To use tracert, you will also need to use the DOS window. To use tracert to a site called www.whatever.com, type tracert www.whatever.com.

    1. Use tracert to track a route to these sites.
      1. www.yahoo.com
      2. www.cuny.edu
      3. home.netscape.com

    2. The next few sites are outside the USA - can you tell which countries they are in?
      1. www.unimelb.edu.au
      2. www.insee.fr

    In each case, note the IP address of the destination, and the number of hops it took to reach the destination. Can you say anything about the setup of the Brooklyn College LAN? Can you tell how messages get routed out of Brooklyn College?

  4. Visualizing a route

    1. Open this page in another window (right-click on it, then select "Open in New Window").  This site allows you to visually follow the transfer of packets of information from one router to the next as the packets travel from the source computer to the destination computer. You can perform a trace from the host computer of the website or a proxy trace from your computer through the website's host computer. Using the Host Trace, look up www.mta.info.
      1. In what state did the trace begin?
      2. How many routers does information travel through between the host computer and the MTA website?
      3. Can you identify the companies who own the routers?  List some of the companies.

    2. Now try tracing to a server in a different country. Try looking up www.insee.fr.  How many routers does information travel through between the host computer and the INSEE website?