🛠 Se connecter au Wi-Fi (et comprendre les limites 2,4 GHz / WPA2)

Objectives

Configure and diagnose the Wi-Fi connection on the Zero 2 W: the onboard radio combo (Cypress/Infineon class 43430 chip) is limited to 2.4 GHz 802.11n (35 Mb/s max) and WPA2 — no 5 GHz, no WPA3 (upstream bug open since 2021, raspberrypi/linux#4718). Knowing how to read link quality is the foundation of any reliable IoT project.

Hardware

• 1 Raspberry Pi Zero 2 W already booted in headless mode (see the installation tutorial)
• A 2.4 GHz access point using WPA2 (if your router is WPA3-only, create a guest network with WPA2/2.4 GHz — the Zero 2 W will not be able to join the main network)
• Onboard antenna under the metal shielding: no external antenna connector (the u.FL footprint on the board is for certification only) — the placement of the board therefore matters a lot.

Complete code

# Avec wpa_cli (Raspberry Pi OS Lite) :
sudo wpa_cli -i wlan0 scan
sudo wpa_cli -i wlan0 scan_results | grep -i "mon_reseau"
sudo wpa_cli -i wlan0 add_network
sudo wpa_cli -i wlan0 set_network 0 ssid '"mon_reseau"'
sudo wpa_cli -i wlan0 set_network 0 psk '"motdepassewifi"'
sudo wpa_cli -i wlan0 select_network 0

# Diagnostic du lien :
iw dev wlan0 link          # état + signal en dBm
iw dev wlan0 info          # canal, bitrate
ip -4 addr show wlan0      # adresse IP obtenue (DHCP ?)
ping -c 4 1.1.1.1          # connectivité hors DNS

Expected verification

iw dev wlan0 link displays Connected to with a signal: above -70 dBm is comfortable, below -85 dBm is marginal on 2.4 GHz. The ping to 1.1.1.1 succeeds. If the target network is WPA3, the scan sees it but the association fails indefinitely — this is the documented hardware limitation, not your password.

Common errors

• Router in WPA3-only mode: the chip cannot handle it; stick to WPA2 or WPA2/WPA3 mixed mode.
• Enterprise network 802.1X: wpa_cli with PSK is not enough, you need a dedicated wpa_supplicant file (EAP-PEAP + identity).
• Connecting only to 5 GHz: the Zero 2 W is blind to 5 GHz; if the router broadcasts only a 5 GHz SSID, it will never see it.
• 2.4 GHz interference (neighbors, microwaves): throughput and latency collapse without visible disconnection — compare the bitrate with iw dev wlan0 info.
• Errors brcmfmac ... failed: -5 and disconnections after upgrading to Bookworm: known bug (raspberrypi/firmware#1962); test an earlier kernel/firmware or log the output with dmesg before suspecting the antenna.