How to Analyze a Firewall Ruleset with Hadoop

Ruleset Analysis is a tool for analyzing firewall log files to determine what firewall rules are in use and by what kind of traffic. The first release supports the Cisco ASA and FWSM firewalls. The analysis is built as Hadoop Streaming jobs since the log volume to analyze easily can reach hundreds of gigabytes or even terabytes for very active firewalls. To make useful results the logs analyzed must span a time period of at least a couple months, preferably six or twelve months. The analysis will tell you exactly what traffic was allowed by each of the firewall rules and when that traffic occurred.

A common use case for Ruleset Analysis is to use the insight produced to reduce the size of large firewall rulesets. Armed with knowledge about when a rule was last in use and by what traffic, it becomes easier to determine if the rule can be removed. Rules with no hits in the analyzed time span are also likely candidates for removal. In addition, Ruleset Analysis can be used to replace a generic rule with more specific rules. Traffic counters are often used to check what rules are in use, but I explained some of their shortcomings in my previous post.

Sample results

Here is an example of the output for each firewall rule:

fw01: access-list inside-in, rule 123: permit tcp ->[8080]
access-list inside-in extended permit tcp object-group inside-subnets any object-group Web
Total number of hits: 7
 COUNT PROTO  FROM IP       TO IP          PORT  FIRST SEEN           LAST SEEN          
     6  TCP   8080  2014-06-06 14:47:35  2014-06-06 15:17:01
     1  TCP  8080  2014-09-27 08:15:34  2014-09-27 08:15:34

This says that outbound access to websites on port 8080 got seven hits during the last year, but only from two distinct sources. An internal machine initiated six of those connections to one external server on port 8080 in half an hour on June 6th. All in all, this tells us that the rule is rarely in use and may be a candidate for removal.

The second line of the output shows the access-list entry in the original Cisco syntax. Note that Ruleset Analysis supports object-groups and will expand the list of objects in the object-group to create distinct rules. For instance, here it has expanded the object-group Web to the TCP port 8080 (and other ports not shown here). For each object in an object-group the preprocessor creates a distinct rule object, effectively expanding the object-group to separate objects. The benefit of this is that Ruleset Analysis is able to find out which objects in an object-group are in use and which are not, so objects not in use can be removed from the object-group (and therefore from the ruleset).

How to run the analysis on Hadoop

To be able to run the analysis you need the firewall config, log files and access to a Hadoop cluster.

Clone the repository from Github:

git clone
cd ruleset-analysis

Preprocess the config file to extract access-lists and generate ACL objects:

./ -f FW.CONF

Submit the job to the Hadoop cluster with the path to the firewall log files in the Hadoop filesystem HDFS (wildcards allowed):


The output from Hadoop Streaming is shown on the console:

arnes@hadoop01:~/ruleset-analysis$ ./ /data/fw01/*2014*
arnes@hadoop01:~/ruleset-analysis$ packageJobJar: [.//, .//, .//input/accesslists.db, .//name-number-mappings.db, .//, .//, /tmp/hadoop-arnes/hadoop-unjar8081511066204186990/] [] /tmp/streamjob7183564462078091113.jar tmpDir=null
15/01/04 11:24:56 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
15/01/04 11:24:56 WARN snappy.LoadSnappy: Snappy native library not loaded
15/01/04 11:24:57 INFO mapred.FileInputFormat: Total input paths to process : 365
15/01/04 11:24:57 INFO streaming.StreamJob: getLocalDirs(): [/data/1/mapred/local, /data/2/mapred/local, /data/3/mapred/local]
15/01/04 11:24:57 INFO streaming.StreamJob: Running job: job_201411291614_1372
15/01/04 11:24:57 INFO streaming.StreamJob: To kill this job, run:
15/01/04 11:24:57 INFO streaming.StreamJob: /usr/libexec/../bin/hadoop job  -Dmapred.job.tracker=hadoop01:8021 -kill job_201411291614_1372
15/01/04 11:24:57 INFO streaming.StreamJob: Tracking URL: http://hadoop01:50030/jobdetails.jsp?jobid=job_201411291614_1372
15/01/04 11:24:58 INFO streaming.StreamJob:  map 0%  reduce 0%
15/01/04 11:25:07 INFO streaming.StreamJob:  map 1%  reduce 0%
15/01/04 11:25:08 INFO streaming.StreamJob:  map 13%  reduce 0%
15/01/04 11:25:09 INFO streaming.StreamJob:  map 16%  reduce 0%
15/01/04 11:25:11 INFO streaming.StreamJob:  map 24%  reduce 0%
15/01/04 11:26:39 INFO streaming.StreamJob:  map 98%  reduce 29%
15/01/04 11:26:41 INFO streaming.StreamJob:  map 99%  reduce 30%
15/01/04 11:26:42 INFO streaming.StreamJob:  map 100%  reduce 30%
15/01/04 11:26:47 INFO streaming.StreamJob:  map 100%  reduce 33%
15/01/04 11:26:49 INFO streaming.StreamJob:  map 100%  reduce 67%
15/01/04 11:26:50 INFO streaming.StreamJob:  map 100%  reduce 100%
15/01/04 11:26:52 INFO streaming.StreamJob: Job complete: job_201411291614_1372
15/01/04 11:26:52 INFO streaming.StreamJob: Output: output-20150104-1124_RulesetAnalysis

Note the name of the output directory on the last line of output, “output-20150104-1124_RulesetAnalysis” in this example. You’ll use that to fetch the results from HDFS. Insert the name of the output directory in the variable below:

mkdir output; outputdir="OUTPUT_PATH_FROM_JOB_OUTPUT"
hadoop dfs -getmerge $outputdir output/$outputdir

With the job results now on disk, the last step is to run postprocessing to generate the final report and view it:

./ -f output/$outputdir > output/$outputdir-report.log
less output/$outputdir-report.log

Manually test the analysis on a small log volume

For small log volumes and trial runs, the analysis can be run with no Hadoop cluster (no parallellization), like this:

Clone the repository from Github, if you haven’t already:

git clone
cd ruleset-analysis

Preprocess the config file to extract access-lists and generate ACL objects:

./ -f FW.CONF

Pipe the firewall log through the Python mapper and reducer manually:

cat FW.LOG | ./ | sort | ./ > results

Postprocess the results to generate the final ruleset report and take a look at it:

./ -f results > final_report
less final_report

How to get help and answers

If you encounter problems when running Ruleset Analysis, please register it at Github as an Issue. Pull requests are also very welcome.

For instructions on how to install the prerequisites required for the analysis to work (mostly Python modules), see the README at Github.

For generic questions about the analysis, leave a comment here or contact me on Twitter: @A_r_n_e.

Reducing the Size of Large Firewall Rulesets

After operating a set of firewalls for some years, the rulesets have grown to thousands of rules, each fulfilling a specific application need or some user demand. Firewalls don’t live forever, and the time came to replace the current firewall with a new, more powerful appliance from a different vendor. Changing vendors made migrating rules more difficult since the syntax was different. In addition, the conversion tool provided by the new vendor failed to utilize the powerful features of the new syntax. So it was decided to implement all the rules on the new firewall manually.

When faced with a big, manual task, my first question is How can we simplify this? One way to reduce the workload is to reduce the scope of work. In this case reduce the number of firewall rules that must be re-implemented. However, it is not easy to determine if a rule can be removed. Traffic counters give some information, but are typically reset on reboots. Before you go ahead and remove a rule you want to be sure no-one relied on that rule for, say, the last six or maybe twelve months. Any firmware upgrade in the last year could make traffic counters less valuable.

Among all the rules with positive counters there are almost certainly also rules that are no longer in use. The counters do not tell you when each hit occured in the period since last reset. However, the firewall logs contain that information. Configured for full audit logging, a firewall will tell you the exact pattern of the traffic that traversed the firewall. So parsing that information can potentially reveal what rules are in use and when.

A common issue with firewall rulesets is the generic rules. Those are the rules which are added when the application need is unclear or a deadline is rapidly approaching. The generic rules allow more than they should, and removing them requires in-depth knowledge and certainty about what the rule should have looked like. One way to get that knowledge is to inspect the audit logs in detail. Parsing all log entries it is possible to say with certainty what traffic was allowed by which rule. Armed with a list of all traffic matching a generic rule, it’s easier to replace that rule with specific rules or remove it entirely. How to parse logs to be able to do that is the topic of my next post.