The specificity of my setup, is that the Raspberry won’t be a router but a bridge. DHCP is thus delegated to the main ADSL router and all devices connected to the AP will appear on the same network than other devices. The instructions below are based on a fresh Raspbian lite install so that it can be reproduced easily.
$ sudo apt-get install -y bridge-utils hostapd
To create a bridge, we need to enable ip_forward in the kernel, for that, edit /etc/sysctl.conf and remove comment (#) from the following line :
net.ipv4.ip_forward=1
Then configure your network to create a bridge with eth0, in /etc/network/interfaces :
auto lo
iface lo inet loopback
# Disable eth0 / wlan0 config, handled by bridge
auto eth0
iface eth0 inet manual
allow-hotplug wlan0
iface wlan0 inet manual
# Create a bridge with static IP
auto br0
iface br0 inet dhcp
bridge_ports eth0
You may have noticed that wlan0 is not configured in bridge br0. This is because hostapd will handle this once the access point is ready.
So, next step is to configure the access point. For this, edit the file /etc/hostapd/hostapd.conf :
# First part is about configuring the access point and is copied from reference 1
interface=wlan0
driver=nl80211
hw_mode=g
channel=6
ieee80211n=1
wmm_enabled=1
ht_capab=[HT40][SHORT-GI-20][DSSS_CCK-40]
macaddr_acl=0
auth_algs=1
ignore_broadcast_ssid=0
wpa=2
wpa_key_mgmt=WPA-PSK
rsn_pairwise=CCMP
# This part is about setting SSID and WPA2 password
ssid=wifi_ssid
wpa_passphrase=wifi_password
# This line ask hostapd to add wlan0 to the bridge br0
bridge=br0
Now we need to tell hostapd to use our config. For that, edit /etc/default/hostapd and set:
DAEMON_CONF="/etc/hostapd/hostapd.conf"
Ok, here we go, just reboot the Pi and waaaw!
sudo reboot
Works great on RPI5 and RPI4!