I have successfully setup a raspberry pi to function as an access point. I have a pi connected via ethernet to my router, and am able to connect to the pi's wifi network and access other devices on that wifi network, as well as the external internet (via cable to router). I did so by following this guide:
https://www.raspberrypi.com/documentation/computers/configuration.html#setting-up-a-routed-wireless-access-point
However, I am having trouble locking down this AP wifi network with iptables. What I want is a default deny policy for everything, with the exception of a static IP on this AP wifi which will have unrestricted access to connect to other machines on the AP network as well as to the internet.
Currently I have the following rules:
$ sudo iptables -L --line-numbers -v
Chain INPUT (policy DROP 579 packets, 78551 bytes)
num pkts bytes target prot opt in out source destination
1 190 14054 ACCEPT all -- lo any anywhere anywhere
2 3491 247K ACCEPT all -- any any Fruit.wlan anywhere
Chain FORWARD (policy DROP 4599 packets, 315K bytes)
num pkts bytes target prot opt in out source destination
1 7201 876K ACCEPT all -- any any Fruit.wlan anywhere
2 1 68 ACCEPT all -- any any anywhere Fruit.wlan
Chain OUTPUT (policy DROP 1437 packets, 103K bytes)
num pkts bytes target prot opt in out source destination
1 184 13544 ACCEPT all -- any lo anywhere anywhere
2 2357 231K ACCEPT all -- any any anywhere Fruit.wlan
$ sudo iptables -L --line-numbers -v -t nat
Chain PREROUTING (policy ACCEPT 3171 packets, 275K bytes)
num pkts bytes target prot opt in out source destination
Chain INPUT (policy ACCEPT 1631 packets, 122K bytes)
num pkts bytes target prot opt in out source destination
Chain OUTPUT (policy ACCEPT 1726 packets, 124K bytes)
num pkts bytes target prot opt in out source destination
Chain POSTROUTING (policy ACCEPT 86 packets, 6578 bytes)
num pkts bytes target prot opt in out source destination
1 1069 70865 MASQUERADE all -- any eth0 anywhere anywhere
With these rules, I can still ssh into the pi (Access Point) from the Fruit.wlan machine, however I cannot access the internet. I think it is an issue with my forwarding rules, but I can't figure out what is blocking me.
pi access point IP is 192.168.10.1
upstream router IP is 192.168.0.1
Fruit.wlan IP is 192.168.10.123