Single Pair Ethernet Router with Raspberry Pi

Single Pair Ethernet (SPE) is a technology that enables the transmission of Ethernet data over a single twisted pair of wires, as opposed to the traditional Ethernet which typically uses four pairs of twisted wires. Today, a bridge Ethernet-SPE is an expensive item, but using a Raspberry Pi with a SPE Shield it is implement one with a small investment.

Prerequisite

Before to implement the router configuration proposed in this tutorial, it is mandatory to configure eth1 on Raspberry as described in ADIN1110 Linux kernel configuration and read Raspberry pi as wireless router of Yoganathan V.

Hardware setup

The hardware setup for this tutorial is very simple, we have a couple of Raspberry with SPE shield. The first works as router, the second as a connected device.

Software configuration for Raspberry as Router

Install the following packages

sudo apt install hostapd
sudo apt install dnsmasq

edit dhcpcd.conf

sudo nano /etc/dhcpcd.conf

add to the end of file the following configuration

interface eth1
static ip_address=192.168.2.1/24
static routers=192.168.2.1
static domain_name_servers=8.8.8.8

The address for single pair Ethernet interface eth1 of Raspberry Router is 192.168.2.1

Reload dhcpcd with

sudo systemctl daemon-reload && sudo systemctl restart dhcpcd

To allow traffic to flow from one network to the other in the Raspberry Pi, create a file using the following command

sudo nano /etc/sysctl.d/routed-ap.conf

add

# Enable IPv4 routing
net.ipv4.ip_forward=1

This process is configured by adding a single firewall rule in the Raspberry Pi

sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

Now save the current firewall rules for IPv4 (including the rule above) and IPv6 to be loaded at boot by the netfilter-persistent service using the below command

sudo netfilter-persistent save

Configure the DHCP and DNS services for the SPE network. The DHCP and DNS services are provided by dnsmasq. Rename the default configuration file and edit a new one

sudo mv /etc/dnsmasq.conf /etc/dnsmasq.conf.orig
sudo nano /etc/dnsmasq.conf

Add the following to the file and save it

interface=eth1
dhcp-range=192.168.2.2,192.168.2.20,255.255.255.0,24h
domain=wlan
address=/gw.wlan/192.168.2.1

Now restart systemctl

sudo systemctl reboot

If the configuration was executed correctly we can see the address 192.168.2.1 in eth1 with command ifconfig

Software configuration for Raspberry as Device

It is important to note that the eth1 MAC address is defined in overlay file, then is mandatory to edit adin1110-overlay.dts on Raspberry as Device and change it. In this example the MAC address of Router is CA 2F B7 10 23 63, instead on Raspberry as Device it is CA 2F B7 10 23 64. After that recompile adin1110-overlay.dts with

sudo dtc -@ -I dts -O dtb -o adin1110.dtbo adin1110-overlay.dts

Copy the adin1110.dtbo in /boot/overlays/. Add adint1110 in /boot/config.txt

dtoverlay=adin1110

Reboot the board

sudo reboot

After the boot phase enable eth1 with

sudo ifconfig eth1 up

If the configuration was executed correctly we can see the address 192.168.2.x in eth1 with command ifconfig.

Test communication

The first test is to check the link the communication with a simple pig from router to device

ping 192.168.2.19

Now we can ping the device to router with

sudo ping 192.168.2.1

If the link works correctly we can try to ping an external server from Raspberry as Device, with the following command

ping -I eth1 www.google.com

We can repeat the test with eth0 of Raspberry Router disconnected

We can see that ping command response is Destination Host Unreachable.

Final test

The final test consists on web browsing with chromium through SPE.

Conclusion

Single Pair Ethernet standard is very interesting, we hope in a fast diffusion on industrial environment.