# ifnow
A Linux network interface device for communication over the ESP-Now wireless broadcast protocol.

NOTE: This is EXTREMELY work in progress and as it requires root permissions is not recommended to be run unmonitored.

This code would not be possible without the groundwork done by the [Linux-ESPNOW](https://hackaday.io/project/161896-linux-espnow)[[github](https://github.com/thomasfla/Linux-ESPNOW)] project. They put in a huge amount of work to reverse engineer the ESP-Now protocol and provided some [example code](https://github.com/thomasfla/Linux-ESPNOW) that this was heavily based on.

Additionally [this article by John Millikin](https://john-millikin.com/creating-tun-tap-interfaces-in-linux)
was an extremely helpful refresher on working with a Tun/Tap interface.

# Build
```
git clone https://git.oit.cloud/morgan/ifnow.git
cd ifnow
mkdir build
cd build
cmake ../
make
```

This should result in the `ifnow` binary in the build directory.

# Usage
This is two steps, first setting up monitoring mode (using aircrack-ng in this method). You will need to determine
your wireless interface name and replace if different from `wlp2s0` in the example. You will also want to set the
channel to match the ESP32 configuration. 

```
sudo airmon-ng start wlp2s0
sudo iw wlp2s0 set channel 1
./ifnow wlp2s0mon now1 10.10.0.13
```

The interface is now up as `now1` and you should be able to write to this interface. In theory `pcap` can
be used to intercept raw packets but if used with LwIP on the ESP32 end, which can be accomplished with
[esp_netif_now](https://git.oit.cloud/morgan/esp_netif_now), any IP stack should work. Has been testing
with UDP and some [CoAP](https://libcoap.net). There are definitely still issues with parsing some incoming
packets.

# Reference Material
These are resources I relied on during development to help me better understand the
Linux network interface stack. Unfortunately there is not a lot of reference material on ESP-Now,
Espressif only ships a binary blob and header file.

### UDP/IP Stack
* [IPv4 Header](https://en.wikipedia.org/wiki/Internet_Protocol_version_4)
* [UDP Datagram structure](https://en.wikipedia.org/wiki/User_Datagram_Protocol#UDP_datagram_structure)
* [Universal TUN/TAP device driver](https://www.kernel.org/doc/html/latest/networking/tuntap.html)

### Radiotap
* [radiotap.org](https://www.radiotap.org/)