GTP: GPRS Tunneling Protocol

Introduction

This tutorial discusses the plugin gtpDecode.

Preparation

First, restore T2 into a pristine state by removing all unnecessary or older plugins from the plugin folder ~/.tranalyzer/plugins:

Are you sure you want to empty the plugin folder '/home/wurst/.tranalyzer/plugins' (y/N)? yes
Plugin folder emptied

Then compile the core (tranalyzer2) and the following plugins:

• basicFlow
• gtpDecode
• txtSink

...
BUILD SUCCESSFUL

If you did not create a separate data and results directory yet, please do it now in another bash window, that facilitates your workflow:

mkdir ~/data ~/results

The sample PCAP used in this tutorial can be downloaded here: gtp.pcap.

Please save it in your ~/data folder.

Now you are all set for analyzing GTP traffic!

gtpDecode

Let’s look at the plugin configuration first:

gtpDecode

vi src/gtpDecode.h

...
/* ========================================================================== */
/* ------------------------ USER CONFIGURATION FLAGS ------------------------ */
/* ========================================================================== */

/*              No configuration flags available for gtpDecode                */

/* ========================================================================== */
/* ------------------------- DO NOT EDIT BELOW HERE ------------------------- */
/* ========================================================================== */
...

Run t2 on the supplied pcap.

t2 -r ~/data/ -w ~/results/ -s

So the aggregated gtpStat currently has only one bit which states, there is GTP.

The gtpStat column with value 0x01 is to be interpreted as follows:

   bit | gtpStat | Description
   =============================================================================
     0 | 0x01    | Flow is GTP

tcol ~/results/gtp_flows.txt

Conclusion

Don’t forget to reset the plugin configuration for the next tutorial.

t2conf gtpDecode --reset && t2build gtpDecode

Have fun analyzing GTP traffic!