raspberry pi captive portal

Question

I have created a python flask script that runs on my raspberry pi, I have also configured rpi to switch to access point so when my laptop/mobile gets connected to the AP, I can navigate to the IP '192.168.4.1' to access the python flask web page. Now I want to do is set up a captive portal so that whenever I get connected to the AP, I get redirected to the IP of my pi and can access the flask web page. Can anyone give me an example/url to follow and understand what to do?

I have tried the following steps: Enable IP Forwarding:

nano /etc/sysctl.conf  

Uncomment:

net.ipv4.ip_forward=1 

Add these commands for the firewall and packet forwarding:

sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE  
sudo iptables -A FORWARD -i eth0 -o wlan0 -m state --state RELATED,ESTABLISHED -j ACCEPT
sudo iptables -A FORWARD -i wlan0 -o eth0 -j ACCEPT  

sh -c "iptables-save > /etc/iptables.ipv4.nat"  



sudo nano /etc/rc.local  

add these lines before Exit 0:

iptables-restore < /etc/iptables.ipv4.nat  
ifconfig wlan0 192.168.4.1

Answer 1

I do not understand the problem. If you have switched on your access point, then there is a web server running on it. You simply connect to it by entering the name or ip address in the browser of a remote client (e.g. laptop). Any web server presents a start web page. That can be the page of your app.

To connect to the web server just use the network name of the RasPi and not its ip address. Try first http://raspberrypi.local. But name resolution is not a problem of the RasPi. It is a problem of the network configuration. The Raspberry Pi OS uses mDNS (multicast DNS) by default that resolves the name raspberrypi.local to its ip address. It may be required that you have to setup a local DNS server to have normal internet DNS name resolution available. Or you can map the ip address to the name in the /etc/hosts file on every client.

To call direct the home page of the web app when starting the browser on the client you can define its start page.