Setting up a Raspberry Pi 3B plus as a routed wireless access point

raspberry pi wireless AP

## set up the raspberry pi 3B+ as a wifi AP ( a wireless router )
## suppose etho is your wan interface name, and wlan0 is your lan interface name
# https://www.raspberrypi.org/documentation/configuration/wireless/access-point-routed.md
# https://thepi.io/how-to-use-your-raspberry-pi-as-a-wireless-access-point/
# https://www.shellvoide.com/wifi/setup-wireless-access-point-hostapd-dnsmasq-linux/
## install softwares
apt install -y hostapd
apt install -y dnsmasq
DEBIAN_FRONTEND=noninteractive apt install -y netfilter-persistent iptables-persistent
# testing   ps -ef | grep hostapd
## define wlan0 IP configuration
cat >> /etc/dhcpcd.conf <<EOF 
interface wlan0
    static ip_address=192.168.7.1/24
    nohook wpa_supplicant
EOF
## enable routing between interfaces( eth0, wlan0)
cat >> /etc/sysctl.d/routed-ap.conf <<EOF 
# https://www.raspberrypi.org/documentation/configuration/wireless/access-point-routed.md
# Enable IPv4 routing
net.ipv4.ip_forward=1
EOF
## enable IP masquerading and save rules
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
netfilter-persistent save   # Rules will be saved to /etc/iptables/
## configure the DHCP and DNS services for the wireless network
mv /etc/dnsmasq.conf /etc/dnsmasq.conf.orig
cat >> /etc/dnsmasq.conf <<EOF 
interface=wlan0 # Listening interface
dhcp-range=192.168.7.2,192.168.7.200,255.255.255.0,24h
                # Pool of IP addresses served via DHCP
domain=wlan     # Local wireless DNS domain
address=/gw.wlan/192.168.7.1
                # Alias for this router
EOF
## configure the access point
echo 'DAEMON_CONF="/etc/hostapd/hostapd.conf"' >> /etc/default/hostapd
cat >> /etc/hostapd/hostapd.conf <<EOF 
interface=wlan0
ssid=pi-ap
hw_mode=g
channel=7
macaddr_acl=0
auth_algs=1
ignore_broadcast_ssid=0
wpa=2
wpa_passphrase=11112222
wpa_key_mgmt=WPA-PSK
wpa_pairwise=TKIP
rsn_pairwise=CCMP
EOF
## reboot and find the AP created to test, the password of the wifi is 11112222
systemctl reboot