Thanks for the help with this. My colleague and I are trying to setup a RPI 4 as a router not connected to the internet. It is just for the purposes of connecting multiple wifi controllers together. The controllers are wifi but the main computer we want to control them with would be plugged into the ethernet port. The problem is all the examples online NAT and we can't figure out how to make the ethernet port just another DHCP addressable interface to the router.
To date the closest recipe we have used is below. It makes routing over the wifi great but we can't talk to anything through the ethernet port.
sudo systemctl unmask hostapd.service
Sudo systemctl enable hostapd.service
Sudo vim /etc/dhcpcd.conf
Go to the bottom and add the following
Interface wlan0
static ip_address=10.20.1.1/24
nohook wpa_supplicant
Sudo vim /etc/sysctl.d/routed-ap.conf
Add the following
net.ipv4.ip_forward=1
Then run sysctl -p
Sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
Sudo rm /etc/dnsmasq.conf
Sudo vim /etc/dnsmasq.conf
Add the following
interface=wlan0
interface=eth0
dhcp-range=10.20.1.100,10.20.1.200,255.255.255.0,365d
domain=wlan
address=/rt.wlan/10.20.1.1
Sudo vim /etc/hostapd/hostapd.conf
Write the following
country_code=US
interface=wlan0
ssid=switchblade_SN#
hw_mode=g
channel=7
macaddr_acl=0
auth_algs=1
ignore_broadcast_ssid=0
wpa=2
wpa_passphrase=switchblade123
wpa_key_mgmt=WPA-PSK
wpa_pairwise=TKIP
rsn_pairwise=CCMP
Needless to say this isn't the only way we have tried. Mostly we have monkeyed with the iptables and the dnsmasq.conf. Pretty much we are just trying to find a way to do LAN/Wifi without internet access. Any help would be appreciated.