OpenWrt: route/NAT all traffic coming from the LAN to a WiFI station

openwrt-lan-wifi-repeater.uci

# this conf allows to connect an OpenWrt device to any WiFi WPA2/3 network which has internet connection
# then allows to connect other routers / devices to the LAN switch of the OpenWrt router or to its WiFi AP.
# The traffic is NATted.

# /etc/config/network

config interface 'lan'
        option type 'bridge'
        option ifname '<INTERFACES OF BR-LAN HERE>'
        option ip6assign '60'
        option proto 'static'
        # the ip network of the LAN must be different
        # than wireless AP we connect to
        option ipaddr '192.168.10.1'
        option netmask '255.255.255.0'

config interface 'wwan'
        option ifname 'wwan'
        option proto 'dhcp'

# /etc/config/wireless

# the radio must be on the same channel of AP
config wifi-iface 'wwan'
        option device 'radio0'
        option mode 'sta'
        option encryption 'psk2'
        option network 'wwan'
        option ifname 'wwan' 
        option ssid '<SSID>'
        option key '<WPA2_KEY>'
        option bssid '<MAC_OF_AP>'

# /etc/config/dhcp

config dnsmasq 'dnsmasq1'
        option authoritative '1'
        option boguspriv '1'
        option domain 'lan'
        option domainneeded '1'
        option ednspacket_max '1232'
        option expandhosts '1'
        option filterwin2k '0'
        option leasefile '/tmp/dhcp.leases'
        option local '/lan/'
        option localise_queries '1'
        option localservice '1'
        option nonegcache '0'
        option nonwildcard '1'
        option readethers '1'
        option rebind_localhost '1'
        option rebind_protection '1'
        option resolvfile '/tmp/resolv.conf.d/resolv.conf.auto'

config dhcp 'lan'
        option interface 'lan'
        option start '100'
        option limit '150'
        option leasetime '12h'
        option ra_slaac '1'
        list ra_flags 'managed-config'
        list ra_flags 'other-config'
        option ra 'disabled'
        option dhcpv6 'disabled'

config dhcp 'wan'
        option interface 'wan'
        option ignore '1'

config odhcpd 'odhcpd'
        option maindhcp '0'
        option leasefile '/tmp/hosts/odhcpd'
        option leasetrigger '/usr/sbin/odhcpd-update'
        option loglevel '4'

# /etc/rc.local

# it should be doable also with the OpenWrt firewall configuration
# but plain iptables is easier.
/etc/init.d/firewall stop
/etc/init.d/firewall disable

iptables -A FORWARD -i lan -o wwan -j ACCEPT
iptables -A FORWARD -i wwan -o lan -j ACCEPT
iptables -t nat -A POSTROUTING -o wwan -j MASQUERADE