I recently had the need to create a backup internet solution for my network.  The only option I had was a mobile hotspot that I wanted to share with my network.  To accomplish this I turned a raspberry pi into a pseudo hotspot gateway for the network, basically replacing a cable modem.

These steps work as of Feb 2024, using Raspbian based on Debian bookworm.

First, download Raspberry Pi OS Lite 64bit at https://www.raspberrypi.com/software/operating-systems/ and install it onto your Pi.  Boot it up, and update it:

Next, go into the raspi-config tool, and set up the wifi connection to your hotspot:

When you set up the wifi connection for the first time, it'll ask you for the Wifi country.  After you set it, you'll attempt to connect to the wifi hotspot, but if it fails, simply exit the installer, reboot and try again.  Also, double check that predictable network interface names is disabled.  You want to see your interfaces as eth0 and wlan0.

Next, configure the ethernet adapter to be a static IP address, so that I can act like a DHCP server.  To do that, use the network-manager cli tool:

For the purpose of this tutorial, we're going to use the network segment 192.168.32.0/24 and a static ip of 192.168.32.1.  In nmtui, set the ip address to static and set it to 192.168.32.1/24.  Disable ipv6 and no need to set a router.

Next, install dnsmasq:

After, edit the config file:

Add:

After, edit dhcpd's config file:

Add:

Lastly, install iptables:

Run these 2 commands, and restart:

You're done!