Laboratory: Networks and Browsers
| CSC 105 |
The Digital Age |
Spring 2009 |
Part I: Browser Information
Whenever you request a Web page, your browser sends the Web server
data about itself. The program
http://www.cs.grinnell.edu/~walker/fluency-book/web-info.php
displays some of this information.
Exercise 1
Click on the above link, scan through the information that it presents, and
record the IP address of the computer you are working on.
Exercise 2
Since Internet communication requires an Internet Protocol Number
(sometimes called an IP number or an IP address), it is hardly
surprising that the server knows this information. Specifically,
the American Registry for Internet
Numbers (ARIN) is a nonprofit organization chartered to manage
Internet numbers for North America, a portion of the Caribbean, and
sub-equatorial Africa; and ARIN maintains a database of which IP
addresses are allocated to whom.
-
Go to the WHOIS service
that ARIN maintains for its database of IP addresses. In the
upper-let corner of the page, you should find a textbox you can
use to search the WHOIS database.
-
Type in the IP address given in step 1 for your computer. To what
extent can a Web server identify you based on an IP address?
Exercise 3
Various other groups build upon ARIN's database and other network
services to provide further information regarding IP addresses. Two
typical sources follow. In each case, try the tool, and describe what
information the Web server can locate about your browser and computer.
-
Geobytes maintains
an IP Address Locator
tool.
-
Hexa Software Development Center, based in Penang, Malaysia, runs
"IP2Location" locator services and maintains
an demo page
that includes a geographic display. Enter your machine's IP
address into the box and click "Find Location." When the result
appears, click "Map It".
-
To what extent do these additional groups provide information
beyond that available from ARIN?
Part II: Packet Routing
As we discussed in lecture, messages that are sent over the internet
make several "hops" from router to router before reaching their
destination. Linux provides a command traceroute that can be
used to determine the IP address of each router that the message
visits along the way.
For example, the command "traceroute cs.smith.edu"
will send an (essentially empty) message to the domain
cs.smith.edu and then output information about each router
that passes the message along. This information usually includes the
router's name and IP address; however, the owners of some routers block
this information from being reported, in which case the output will include
a string of asterisks instead.
Exercise 1
Open a terminal window and try the traceroute command given
above. It should provide a list of routers visited by the query
packet, perhaps 20 or so.
Exercise 2
Now determine the geographic path followed by your traceroute message
by searching the ARIN database and recording the organization name and
city of the routers visited. (Note that if a sequence of IP addresses
along the path begin with the same first two numbers, they likely
belong to the same organization and are located in the same city, so
you really only need to look up one of them.)
If you are interested in tracing the route of packets as they travel
to a domain you frequently communicate with, you can do that
too. Based on my experience, you may be more successful tracing the
path to small domains (such as email addresses) than large ones (such
as hugely successful websites). There are likely to be routers along
the way to hugely successful websites that do not
allow traceroute to display their IP addresses.
Part III: Cookies
When a browser accesses a Web page, the Web server can request that
your browser store a small piece of information, called
a cookie, on your machine. When you go to this Web page again,
the Web server can ask for the cookie and can use the cookie in
processing.
Exercise 1
-
Check whether your browser is set to accept cookies. (In the MathLAN,
we use IceWeasel, but you can follow the directions below for
Mozilla. The directions for other computers may be useful if you would
like to do this at home also.)
-
If you use the Mozilla browser, this information can
be found by looking under "Preferences" in the "Edit" menu,
and then going to "Privacy & Security" and "Cookies".
-
If you use Internet Explorer under Windows, this
information can be found by looking under select "Internet
Options" from the "Tools" menu, then look under "General" and
"Settings" in the "Temporary Internet Files" section.)
-
If you use Internet Explorer on a Macintosh, this
information can be found by looking under "Preferences" under
the "Explorer" menu, and then looking under "Cookies" in the
"Receiving Files" section.
-
If your browser does not usually accept cookies, change the setting so
that it does for this lab. You can change the settings back at the
end of the lab.
-
Locate and browse through the list of cookies that are stored on your
machine. (In IceWeasel, you can do this by clicking on the "Cookie
Manager" button, located on the same dialog box where you just
found your other cookie settings.)
-
Use your web browser to delete the cookies that are currently
stored. You should be able to do this in the same "Cookie
Manager" dialog window.
Exercise 2
-
Return to the page,
http://www.cs.grinnell.edu/~walker/fluency-book/web-info.php,
and find the "History Information" section (about in the middle of
the page, before a rather long table).
-
Reload the page a few times, and notice what changes. In
Mozilla/Iceweasel this can be done by clicking "Reload" to the left of
the URL near the top of the window.
-
The Web page web-info.php tries to save a cookie to keep
track of whether or not you have visited this page previously. Return
to your browser and locate the cookie(s) saved for this Web page, as
described in Steps (a),(c), and (d) above.
-
Describe what information is set by web-info.php.
-
Use your browser to delete the cookie associated with
web-info.php, and access that page again. Describe what appears
now in the "History Information" section of that page.
Part IV: Privacy Statements
This lab has highlighted some information transmitted to a Web
server from you browser whenever you access a Web page. Also, when
cookies are enabled, the Web server can record some data about you for
future reference. Of course, if you provide additional information
about yourself through a Web form (perhaps when you are making a
purchase over the Web), then a Web server will be able to link that
personal data with your browser and computer information. The use of
that data is left to the discretion of those running the Web server.
Many institutions and companies state their privacy policies regarding any
data they collect.
Exercise 1
Find and read the privacy policy for one or two websites that you
frequent, which you also give information to. Examples could include
sites from which you make purchases (perhaps www.amazon.com)
and social networking sites (perhaps www.facebook.com).
You might want to consider reading the privacy policy for any Web
site before filling out forms on that site.