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Wireless Monitor

A Linux C program for capturing and parsing 802.11 WiFi frame headers in monitor mode. This tool is designed to verify and cross-check the ESP32 monitor code by comparing what a Linux machine sees vs what the ESP32 sees when monitoring the same WiFi traffic.

Purpose

This program captures 802.11 frames and displays:

RA (Receiver Address) and TA (Transmitter Address) - same fields ESP32 extracts
Frame type, size, duration (NAV)
RSSI, MCS, spatial streams (when available from radiotap)
Retry flag

This allows you to verify that the ESP32's frame parsing matches what Linux sees, helping debug issues like:

Missing frames
Incorrect MAC address extraction
Duration/NAV mismatches
Frame type classification

Requirements

Linux kernel with nl80211 support
libpcap development files
libnl3 development files
GNU autotools (autoconf, automake, libtool)

Install Dependencies

Ubuntu/Debian:

sudo apt-get install build-essential autoconf automake libtool \
    libpcap-dev libnl-genl-3-dev libnl-3-dev pkg-config

Fedora/RHEL:

sudo dnf install gcc autoconf automake libtool \
    libpcap-devel libnl3-devel pkgconfig

Building

# Generate configure script
./autogen.sh

# Configure build
./configure

# Build
make

# Install (optional)
sudo make install

Usage

# Run as root (required for monitor mode)
sudo ./src/wireless_monitor wlan0 11

# Or after installation
sudo wireless_monitor wlan1 36

# Example output (comparable to ESP32 debug logs):
# [1770775602.813] DATA: TA=80:84:89:93:c4:b6, RA=e0:46:ee:07:df:e1, Size=228 bytes, Dur=25038 us, RSSI=-94 dBm, Retry=YES

Comparison with ESP32

The output format is designed to match ESP32's debug output format:

TA = Transmitter Address (same as ESP32's addr2)
RA = Receiver Address (same as ESP32's addr1)
Frame type, size, duration, RSSI, retry flag

You can run both simultaneously on the same channel and compare:

Are the same frames seen?
Do RA/TA match?
Do durations match?
Are retry flags consistent?

Project Structure

wireless-monitor/
├── configure.ac          # Autoconf configuration
├── Makefile.am            # Top-level automake file
├── autogen.sh             # Script to generate configure
├── README.md
└── src/
    ├── Makefile.am        # Source automake file
    ├── main.c             # Main program
    ├── monitor.c          # Monitor mode setup (libnl3)
    ├── monitor.h
    ├── capture.c          # Packet capture (libpcap)
    ├── capture.h
    ├── frame_parser.c     # 802.11 frame parsing
    └── frame_parser.h     # Frame structures (matches ESP32)

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