CORC 1312
Lab #2: URLs, IP addresses, DNS names, tracert
"Show and Tell"
- You can't judge a domain by its name
- 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.
- Yahoo is pretty
smart about similar DNS names
-- check out http://www.yahoo.org
- DNS names <-> IP addresses
- 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:
- www.cuny.edu
- www.yahoo.com
- 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.
- What happens if you type in an IP address directly, instead of a DNS name? Try linking to http://146.245.252.76.
- 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
- 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?
- Visualizing a route
- 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.
- In what state did the trace begin?
- How many routers does information travel through between the host
computer and the MTA website?
- Can you identify the companies who own the routers? List some of
the companies.
- 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?