Snort rules | Computer Science homework help

Lab #3 

Our third lab builds on the “unacceptable site” detection we worked on in Lab #2. In this exercise, 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 2.2.20 (starting on p. 122) of the Snort Manual, which is posted under General Information under 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 “black list” 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 (or a different site chosen for this assignment) by adding the site to a blacklist and enabling the reputation preprocessor in snort.conf.

Please note: If you are using the Virtual Lab, the reputation preprocessor is already configured properly, and the supporting whitelist and blacklist files are stored in /etc/snort/rules. All you need to do is identify the IP address(es) to use and add them to the black.List file.

To complete this assignment successfully using Snort on Windows, you may need to first edit the “snort.conf” file as follows if you did not already configure these items when you first installed Snort:

  • 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. The default configuration should work fine for most students, as long as the file paths and names are accurate for the local installation. Look at the first configuration example on page 120 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. Where the configuration designates a file (such as “black.list” or “white.list”), the file must exist in the location specified, or Snort will generate an error at start-up.
  • 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:\Snort\etc\rules 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 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.


Vitual lab link


For this assignment, compose a short write-up 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 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“), which will return the primary IP address on screen, or you can look up the site on to find one or more IP addresses used by the site.
  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 Labs #2 and #3, with an emphasis on identifying any strengths or weaknesses associated with each approach.
  5. If you can get Snort to run successfully with the reputation preprocessor active, include the output produced (a copy of the ASCII log file is sufficient).


Not sure if this helps:


o to the rules folder where you downloaded the VRT certified rules during your Snort install (by default on Windows, this will be C:\Snort\rules). If you have not yet installed these rules, please do so. If you have any trouble downloading the current VRT rules release package, you can retrieve them from on my UMUC Polaris server. In the compressed (zipped) package, you are looking for the files that end in “.rules” extensions.

Pick one of the named rules files, open it, and choose a rule. If this is your first exposure to Snort rule syntax, please note that the rules are the sometimes-cryptic looking items starting with the word “alert”. Copy the rule you pick into your response and describe what the rule means in your own words.