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esp_slip_router

A SLIP to WiFi router

This is an implementation of a SLIP (Serial Line IP - RFC1055) router on the ESP8266. It can be used as simple (and slow) network interface to get WiFi connectivity. The ESP can act as STA or as AP. It transparently forwards any IP traffic through it. As it uses NAT no routing entries are required on the other side.

UPDATE: If you are experiencing DNS-issues or if you are looking for a dockerized build-environment have a look here: https://github.com/e1z0/esp_slip_router

Usage as STA

In this mode the ESP connects to the internet via an AP with ssid, password and offers at UART0 a SLIP interface with IP address 192.168.240.1. This default can be changed in the file user_config.h.

To connect a Linux-based host, start the firmware on the ESP, connect it via serial to USB, and use the following commands on the host:

sudo slattach -L -p slip -s 115200 /dev/ttyUSB0&
sudo ifconfig sl0 192.168.240.2 pointopoint 192.168.240.1 up mtu 1500

now

telnet 192.168.240.1 7777

gives you terminal access to the esp as router. On the ESP you then enter:

CMD>set ssid <your_ssid> 
CMD>set password <your_pw> 
CMD>set use_ap 0
CMD>save
CMD>reset

To get full internet access you will need aditionally a route:

sudo route add default gw 192.168.240.1

and a DNS server - add an appropriate entry (e.g. public DNS server) in /etc/resolv.conf, eg. by (as root):

echo "nameserver 9.9.9.9" > /etc/resolv.conf

A script may help to automize this process.

The status LED (default: GPIO2) indicates:

The default config of the router can be overwritten and persistenly saved to flash by using a console interface. This console is available via tcp port 7777 (e.g. from the host attached to the serial line - see above).

The console understands the following command:

If you want to enter non-ASCII or special characters you can use HTTP-style hex encoding (e.g. "My%20AccessPoint") or, only on the CLI, as shortcut C-style quotes with backslash (e.g. "My\ AccessPoint"). Both methods will result in a string "My AccessPoint".

Usage as AP

You can also turn the sides and make the ESP to work as AP - useful e.g. if you want to connect other devices to a RasPi that has no WiFi interface:

With a Linux-based host start the firmware on the esp, connect it via serial to USB, and use the following commands on the host:

sudo slattach -L -p slip -s 115200 /dev/ttyUSB0&
sudo ifconfig sl0 192.168.240.2 pointopoint 192.168.240.1 up mtu 1500
sudo route add -net 192.168.4.0/24 gw 192.168.240.1

again

telnet 192.168.240.1 7777

gives you terminal access to the ESP as router. On the ESP you then enter:

CMD>set ap_ssid <your_ssid> 
CMD>set ap_password <your_pw> 
CMD>set use_ap 1
CMD>save
CMD>reset

Now STAs of this AP get IP adresses in the 192.168.4.0/24 network and can reach the Linux machine as "192.168.240.2". The AP interface is NATed, i.e. you cannot set up connections from the Linux machine to the STAs, but from STAs to Linux works. Useful e.g. if you want to reach an MQTT server on the Linux.

The console understands the following command for the AP mode:

Hayes-compatible Modem Mode

There is an option to have the SLIP router act as a Hayes-compatible modem, enabling you to use it as a modem on, for example, early Windows releases as a serial modem (with an appropriate transciever).

To use this, simply uncomment #define ENABLE_HAYES 1 in the user/user_config.h file. The modem can be configured to boot up into an already-dialled state by uncommenting #define HAYES_CMD_MODE_AT_BOOT true and changing true to false.

Building and Flashing

To build this binary you download and install the esp-open-sdk (https://github.com/pfalcon/esp-open-sdk). The software was developed and tested usinfg NONOS SDK v2.2. Make sure, you can compile and download the included "blinky" example.

Then download this source tree in a separate directory and adjust the BUILD_AREA variable in the Makefile and any desired options in user/user_config.h. Build the esp_wifi_repeater firmware with "make". "make flash" flashes it onto an esp8266.

The source tree includes a binary version of the liblwip_open plus the required additional includes from my fork of esp-open-lwip. No additional install action is required for that. Only if you don't want to use the precompiled library, checkout the sources from https://github.com/martin-ger/esp-open-lwip . Use it to replace the directory "esp-open-lwip" in the esp-open-sdk tree. "make clean" in the esp_open_lwip dir and once again a "make" in the upper esp_open_sdk directory. This will compile a liblwip_open.a that contains the NAT-features. Replace liblwip_open_napt.a with that binary.

If you want to use the precompiled binaries you can flash them with "esptool.py --port /dev/ttyUSB0 write_flash -fs 32m 0x00000 firmware/0x00000.bin 0x10000 firmware/0x10000.bin" (use -fs 8m for an ESP-01)

Softuart UART

As UART0, the HW UART of the esp8266 is busy with the SLIP protocoll, it cannot be used simultaniuosly as debugging output. This is highly uncomfortable especially during development. If you define DEBUG_SOFTUART in user_config.h, a second UART will be simulated in software (Rx GPIO 14, Tx GPIO 12, 19200 baud). All debug output (os_printf) will then be redirectd to this port.

Known Issues