Add network-extender blog post
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title = "How to use your Raspberry Pi as a WiFi extender!"
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date = "2022-08-04"
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The place where I program has the worst connection to my router throughout the whole house. Obviously, this isn't ideal for most programming workloads such as looking up documentation and especially for cloning the [crates.io index](https://github.com/rust-lang/crates.io-index).
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Luckily, I had Ethernet wired through the whole house, and I also had a Raspberry Pi and about 30 minutes.
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### Required materials
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For my setup, I used a [Raspberry Pi 0 W](https://www.raspberrypi.com/products/raspberry-pi-zero-w/) because it's dirt cheap and has WiFi built-in.
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You'll also need a [Ethernet-to-MicroUSB adapter](https://www.amazon.com/Smays-Micro-B-Ethernet-compatible-Raspberry/dp/B01AT4C3KQ/ref=sr_1_3?keywords=ethernet+to+micro+usb+adapter&qid=1659634388&sr=8-3) if you're on one of the Raspberry Pi 0 models (such as 02, 0W, and 0WH), like I am. If you're on a Pi 1-4, you can just use the onboard Ethernet port.
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Just in case, you might also want to keep around a USB keyboard and an HDMI monitor around in case anything goes wrong and you can't access the Pi using SSH.
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### Switch to systemd-networkd
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<p class="warning">This setup <em>will</em> break any DNS servers already running on your Pi, such as Pi-Hole, so make sure you know what you're getting into.</p>
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You need to be root for the whole guide, so either use `sudo -Es` or `sudo su` to switch to the root user.
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First, you have to remove the "classic" networking. You can do this while connected to SSH, so don't worry.
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```bash
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systemctl daemon-reload
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systemctl disable --now ifupdown dhcpcd dhcpcd5 isc-dhcp-client isc-dhcp-common rsyslog
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apt --autoremove purge ifupdown dhcpcd dhcpcd5 isc-dhcp-client isc-dhcp-common rsyslog
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rm -r /etc/network /etc/dhcp
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systemctl disable --now avahi-daemon libnss-mdns
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apt --autoremove purge avahi-daemon
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```
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Next, install and set up systemd-resolved and systemd-networkd.
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```bash
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apt install libnss-resolve
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ln -sf /run/systemd/resolve/stub-resolv.conf /etc/resolv.conf
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apt-mark hold avahi-daemon dhcpcd dhcpcd5 ifupdown isc-dhcp-client isc-dhcp-common libnss-mdns openresolv raspberrypi-net-mods rsyslog
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systemctl enable systemd-networkd.service systemd-resolved.service
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```
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### Set up wpa_supplicant as an access point.
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wpa_supplicant is what Raspbian uses for its WiFi configuration. We need to configure it to broadcast an access point that our devices can later connect to.
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First, create `/etc/wpa_supplicant/wpa_supplicant-wlan0.conf` and add the following contents:
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```conf
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# /etc/wpa_supplicant/wpa_supplicant-wlan0.conf
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country=US
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ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
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update_config=1
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network={
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ssid="..." # Set to your desired network name
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mode=2
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frequency=2437 # change this to 5000 if you want a 5GHz access point
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#key_mgmt=NONE # uncomment this if you don't want a password
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# delete next 3 lines if key_mgmt=NONE
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key_mgmt=WPA-PSK
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proto=RSN WPA
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psk="..." # set this to your desired password
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}
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```
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<p class="warning">Your password will be stored in <em>plain text</em> so make sure this file is not readable by anyone you don't want seeing the password.</p>
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### Setting up the bridge
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Now, we need to create a *bridge* network interface. This interface will bridge packets coming from the WiFi interface (`wlan0`) and send them over the Ethernet interface (`eth0`). This will allow devices connected to the Pi to appear on the same subnet as devices connected to the router itself.
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First, define the interface:
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```ini
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; /etc/systemd/network/02-br0.netdev
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[NetDev]
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Name=br0
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Kind=bridge
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```
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Then, tell `systemd-networkd` to bridge packets to `eth0`:
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```ini
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; /etc/systemd/network/04-br0_add-eth0.network
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[Match]
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Name=eth0
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[Network]
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Bridge=br0
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```
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Finally, configure network settings on the bridge:
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```ini
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; /etc/systemd/network/12-br0_up.network
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[Match]
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Name=br0
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[Network]
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MulticastDNS=yes
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DHCP=yes
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```
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### Tell wpa_supplicant to use a bridge
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Now we have our bridge configured, but we need to tell our WiFi interface to actually use it. To do this, edit the `.service` file:
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```bash
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systemctl edit wpa_supplicant@wlan0.service
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```
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This will open up your editor. In this editor add these lines:
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```ini
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[Service]
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ExecStartPre=/sbin/iw dev %i set type __ap
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ExecStartPre=/bin/ip link set %i master br0
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ExecStart=
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ExecStart=/sbin/wpa_supplicant -c/etc/wpa_supplicant/wpa_supplicant-%I.conf -Dnl80211,wext -i%I -bbr0
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ExecStopPost=-/bin/ip link set %i nomaster
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ExecStopPost=-/sbin/iw dev %i set type managed
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```
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### Epilogue
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Finally, reboot. That's it! Your shiny new network extender should appear in the list of local WiFi networks. Connect to it, and see the difference!
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If you have any questions, feel free to [shoot me an email](mailto:yash@karx.xyz)!
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