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HORST - Highly Optimized Radio Scanning Tool

or "Horsts OLSR Radio Scanning Tool"

Overview

horst is a small, lightweight IEEE802.11 WLAN analyzer with a text interface. Its basic function is similar to tcpdump, Wireshark or Kismet, but it's much smaller and shows different, aggregated information which is not easily available from other tools. It is made for debugging wireless LANs with a focus on getting a quick overview instead of deep packet inspection and has special features for Ad-hoc (IBSS) mode and mesh networks. It can be useful to get a quick overview of what's going on all wireless LAN channels and to identify problems.

Shows signal (RSSI) values per station, something hard to get, especially in IBSS mode
Calculates channel utilization (“usage”) by adding up the amount of time the packets actually occupy the medium
“Spectrum Analyzer” shows signal levels and usage per channel
Graphical packet history, with signal, packet type and physical rate
Shows all stations per ESSID and the live TSF per node as it is counting
Detects IBSS “splits” (same ESSID but different BSSID – this is/was a common driver problem on IBSS mode)
Statistics of packets/bytes per physical rate and per packet type
Has some support for mesh protocols (OLSR and batman)
Can filter specific packet types, operating modes, source addresses or BSSIDs
Client/server support for monitoring on remote nodes
Automatically adds and removes monitor interface

horst is a Linux program and can be used on any wireless LAN interface which supports monitor mode.

Checkout

If you just want to use horst, the recommended way is to download the latest stable version from https://github.com/br101/horst/releases or to use the stable branch:

git clone -b stable https://github.com/br101/horst

Note: The master branch is in heavy restructuring mode right now, as it is switching to use libuwifi (https://github.com/br101/libuwifi).

The master branch of horst builds on libuwifi as a git submodule and libuwifi in turn includes radiotap as a submodule. With newer versions of git the easiest way to check out is:

git clone --recursive https://github.com/br101/horst

For older versions of git, or if you have already cloned horst before, you can use:

git submodule update --init --recursive

Dependencies

horst is just a simple tool, and libncurses and header files is the only hard requirement as well as the pkg-config tool. Recently we have added support for nl80211 via libnl, so on Linux normally you need libnl3 + header files as well. On Debian/Ubuntu based distros you can install them with:

sudo apt-get install libncurses5-dev libnl-3-dev libnl-genl-3-dev pkg-config

Building

Building is normally done with "make" (optional V=1 or DEBUG=1). This checks out libuwifi as a submodule if necessary:

make

If you want to maintain libuwifi not as a submodule but in a directory outside of horst you can specify it with:

make LIBUWIFI=../my/path/to/libuwifi

Should you expect on libuwifi in the system path (/usr/local/include/ and /usr/local/lib/ or similar) you can do:

make LIBUWIFI=

To install (with optional DESTDIR=/path):

sudo make install

Config and other files

By default horst reads a config file /etc/horst.conf. The location of the file can be changed with the -c file command line option. See the file itself or man horst.conf for a description of the options.

You can use -Mfilename to define a MAC address to host name mapping file which can either be a dhcp.leases file or simply contain MAC-Address<whitesspace>Name one each line.

-o outfile can write the packets to a comma separated list file.

-X[filename] is not a real file, but allows a control socket named pipe which can later be used with -x command to send commands in the same format as the options in the config file.

Usage notes

Starting with version 5.0 horst can automatically set the WLAN interface into monitor mode or add a monitor interface. But you can still set the interface into monitor mode manually before you start horst as well. With most standard Linux (mac80211) drivers you can use the iw command to add an additional monitor interface while you can continue to use the existing interface.

iw wlan0 interface add mon0 type monitor

Please note that while the main interface (wlan0) is in use, either as a client to an AP, in Ad-hoc mode, or creating an AP, the wifi driver does not allow horst to change the channel because that would disrupt connectivity. If you want horst to be able to change channels (horst -s or channel_scan option, or setting a channel manually in the horst UI) you need to set the main interface to monitor mode. This is how it is usually done:

ifconfig wlan0 down
iw wlan0 set type monitor

Optionally you could also set an initial channel, and it sometimes may be necessary to unblock the interface first:

rfkill unblock all
ifconfig wlan0 up
iw wlan0 set channel 6

If you still have to use the deprecated WEXT interface can put the interface into monitor mode with iwconfig wlan0 mode monitor channel X).

Usually you have to start horst as root:

sudo horst -i wlan0

To do remote monitoring over the network you can start a server (-q without a user interface), usually on your AP or device with

horst -i wlan0 -N -q

and connect a client (only one client is allowed at a time), usually from your PC with

horst -n IP

Please read the man page for more details about the options, output and abbreviations. It should be be part of your distribution package, but you can read it in the source code locally with:

man -l horst.8
man -l horst.conf.5

Please contact me if you have any problems or questions. New feature ideas, patches and feedback are always welcome. Please create GitHub issues at https://github.com/br101/horst/issues for problem reports and support.

Background and history

horst was created in 2005 to fill a need in the Wireless Mesh networking and Freifunk community of Berlin but has since grown to be a useful tool for debugging any kind of wireless network.

A notorious Berlin Freifunk community member known as "Offline Horst" had enough persistence to convince me that such a tool is necessary and thus started the development and gave the name to the horst tool.

With the usual wireless tools like iw, iwconfig and iwspy and even kismet or WireShark it is hard to measure the received signal strength (RSSI) of all available access points, stations and ad-hoc networks in a given location. It's especially difficult to differentiate the different nodes which form an ad-hoc network. This information however is very important for setting up, debugging and optimizing wireless mesh networks and antenna positions.

horst aims to fill this gap and lists each single node of an ad-hoc network separately, showing the signal strength (RSSI) of the last received packet. This way you can see which nodes are part of a specific ad-hoc cell (BSSID), discover problems with ad-hoc cell merging ("cell splitting", a problem of many WLAN drivers) and get a general overview of what's going on in the "air".

To do this, horst uses the monitor mode including radiotap headers (or before prism2 headers) for the signal strength information of the wlan cards and listens to all packets which come in the wireless interface. The packets are summarized by the MAC address of the sending node, analyzed and aggregated and displayed in a simple text (ncurses) interface.

Contributors

Thanks to the following persons for contributions:

Horst Krause
Sven-Ola Tuecke
Robert Schuster
Jonathan Guerin
David Rowe
Antoine Beaupré
Rami Refaeli
Joerg Albert
Tuomas Räsänen
Jiantao Fu