The computing profession has a long and honored tradition of
high ethical behavior with regard to the possession of
information. At a company for which I once worked programmers
had easy access to confidential medical records. For one
project I had access to a decade of such information. In spite
of this the track record of the profession in honoring the
trust given to it is a good one.
The assignments in this chapter are in many ways foundational.
Their completion will help you in so many ways, yet the very
process of collecting the needed information is fraught with
problems. Most likely, your ability to sniff packets at your
school will be severely limited for obvious reasons. Assuming
you have access to an off-campus network, you may decide to
generate your own data. Please, think about the ethical
implications.
Assuming that you are able to capture packets you need to know
how to get the ones you need for the assignments.
To generate ARP packets ping a non-existent host from a
special machine. ICMP packets can be obtained by pinging
a special machine from another machine. To get UDP packets
run rusers on a special machine. TCP packets would be
generated by running telnet or ssh on another machine to one
of the special machines.
One major problem you may have with this assignment is due
a lack of compatibility among packet sniffers. The
tcpdump that comes with most versions of Linux
is not even consistent. Here is a table that lists the
variations that I have encountered. As you encounter further
variations through your own experience, please help me add to the
table.
| Packet Sniffer |
Machine |
OS |
Version |
File Header |
Packet Header |
Position of Length in PH |
Header included in Packet Length |
Extra Bytes |
Source |
| snoop |
SunBlade 100 |
Solaris |
8 |
16 |
24 |
0-3 |
No |
Align to 8 byte boundary |
WDL |
| tcpdump |
COMPAQ PC |
Mandrake Linux |
8.1 |
16 |
24 |
16-19 |
Yes |
16 |
WDL |
| tcpdump |
COMPAQ PC |
Red Hat Linux |
7.1 |
24 |
24 |
8-11 |
No |
None |
WDL |
| tcpdump |
Powerbook G4 550 |
MacOS X |
10.2.1 |
24 |
16 |
8-11 |
No |
None |
CPSC370 |
This site is maintained by W. David Laverell
of the Computer Science Department
at Calvin College. For assistance or corrections,
please contact him at .
