How to organize the distribution of the Internet to the local network from the Raspberry USB modem with port forwarding?

Question

Arduino

There is an RPI with internet connection via modem. An Arduino with an Ethernet shield is connected to it, on which there is a server at 192.168.0.103 on port 3521. You need to distribute the Internet from raspberry to arduino and make a forwarding to access the server via the Internet. How to do it? I read articles about DNS, iptables, but somehow I got stuck and nothing came out.

Answer 1

Firstly, most likely you will run into the provider's NAT, because of which you will not be able to get access from the outside.
Secondly, using a raspberry as a router is like a shitty idea.
In your case, it will be easier to buy the most deshmanic router with a USB port, flash DD-WRT/OpenWRT/TomatoUSB/etc into it and stir it up already on it.
At least you will avoid glitches due to connecting network interfaces via USB, like on raspberries.

Answer 2

It will probably be faster if you put some kind of webadmin on the raspberry that is suitable for dummies and does all sorts of forwarding in 2 clicks.
And a lot also depends on the provider, since many (for example, tele2) do not want to give a white address, and without it, forwarding does not make sense.