INFA 630
Lab Assignment
Our third and final lab assignment builds on the “unacceptable site” detection we worked on in
assignment #2. In this lab we will attempt to accomplish the same goal using the new reputation
preprocessor in Snort. The documentation on the reputation preprocessor and the available
configuration options are in section 2.2.19 (starting on p. 119) of the Snort Manual, which is
posted under General Information under Course Content for your reference. The basic function
of the reputation preprocessor is similar in many ways to basic firewall operation: the
preprocessor evaluates source and destination IP addresses in network packets to see if they
appear on either a “whitelist” of approved/acceptable addresses or a “blacklist” of prohibited
addresses. Packets containing IP addresses on the blacklist are dropped. The overall intent for
this assignment is to block access to the “bad” site you selected for Lab #2 by adding the site to a
blacklist and enabling the reputation preprocessor in snort.conf.
To complete this assignment successfully, you will need to first edit the snort.conf file as
follows:
 At the end of Step #1, either set the path to the reputation preprocessor file location or
comment out these two lines (you can declare the blacklist file directly in the
preprocessor configuration settings if you don’t want to use a variable reference).
 At the end of Step #5, configure the reputation preprocessor. Look at the first
configuration example on page 119 of the Snort Manual as a guide, which simply
includes the preprocessor declaration and the specification of the blacklist and whitelist
files. You can run the preprocessor with either or both of these files, so for our purposes
you might just specify a blacklist file. The configuration could be as simple as:
“preprocessor reputation: blacklist /etc/snort/black.list”
 Save the snort.conf file.
Now, create a blacklist file and put it in the proper directory (such as /etc/snort/rules on Linux or
C:Snortetcrules on Windows). A blacklist file is just a plain text file with one IP address (or
address range, using CIDR notation) per line. The blacklist file name and file location should of
course match what you specified in the preprocessor configuration in snort.conf. Then startup
Snort as you would normally, open a browser, and visit the site corresponding to the IP
address(es) in the blacklist file.
For this assignment, compose a short writeup for submission to your Assignments folder that
includes the following:
1. The “unacceptable” site you selected in Lab #2 (you can pick a new one for this assignment if you prefer).
2. The IP address (individual, multiple, or a range) associated with that site. If you don’t know the IP address, you can either open a command shell and ping the site (e.g. “ping
www.facebook.com”), which will return the primary IP address on screen, or you can
look up the site on Netcraft.com to find one or more IP addresses used by the site.
http://www.netcraft.com/
3. The contents of the blacklist file the reputation preprocessor references. 4. A brief summary comparing the rule-based and preprocessor-based approaches used in
Lab #2 and #3, with an emphasis on identifying any strengths or weaknesses associated
with each approach.
5. If you are able to get Snort to run successfully with the reputation preprocessor active, include the output produced (a copy of the ASCII log file is sufficient).
As in Lab Assignment #2, the successful completion of this exercise does not require you to use
an actual inappropriate site. The primary purpose of this exercise is not to make you an expert in
the reputation preprocessor, but to illustrate the point that there are often multiple viable
approaches to accomplishing the same intrusion detection objectives.