I'll try my best to keep this simple and easy to understand. If you see a UDP port translation message, there is a separate thread about port forwarding you can look at here: https://forum.fopnu.com/support/305

Background / Info
IPv4 addresses are 32 bits and this limits them to approximately 4 billion (2^32) unique addresses in total. The reason for this limitation is due to design. If the bits/length part is confusing just remember that it is related to how many addresses are available. When IPv4 was first designed, nobody at that time envisioned a future where every single device a person owns would get connected to the internet. IPv4 is still being used on the internet but the increasing scarcity and price is making it more and more difficult. There are some solutions to more efficiently use a limited amount of IPv4 addresses but none of them are perfect. Most of these "solutions" aren't ideal for P2P applications. Fopnu can still function fine but it always does help to port forward if you can. The real solution to this problem is a new version of IP addresses. And it's called IPv6. IPv6 provides users with 128 bit addresses and so the maximum number of addresses is approximately 2^128 or 3.4*10^38 or 340,282,366,920,938,463,463,374,607,431,768,211,456 in total. That's a really really long number! While IPv6 support is fairly common these days, not every single ISP, website or program supports it. Fopnu has already had support for IPv6! :)

Here is an example of what an IPv4 address looks like: 10.23.48.94 (Private address example. Doesn't belong to anyone on the public internet.)
And here is an example of what an IPv6 address looks like: 2001:db8:1234:abcd:9876::1 (From documentation prefix example. Doesn't belong to anyone on the public internet.)

Do I already have IPv6?
There are a few different ways you can check. I'll be listing two methods.
1) Use a website such as: https://ipv6-test.com/
2) Windows users: open command prompt or powershell (search for either) and run the following command: "ipconfig". If you see "IPv6 Address" and/or "Temporary IPv6 Address", you have IPv6. Linux users: open a terminal and run "ip -6 addr" (This command will only display IPv6 address.)

Key points
1) Ask your ISP to support IPv6. (If they do not already.)
2) Check your router and if needed, enable IPv6 from there. (For me, it's a simple checkbox I enable on my router's webUI.)
3) Your OS most likely already has IPv6 enabled. It's not getting an IPv6 address because either: a) your ISP doesn't support IPv6 or b) it's disabled on your router
4) If you have confirmed that you have IPv6, you do not need to do anything else. Fopnu can use IPv6 unless you disabled it from its networking section in settings.
5) By also using IPv6 on Fopnu you are bettering your connectivity to the network. Unlike IPv4, you do not need to setup any port forwarding for IPv6. (The reason for this is because all of your devices can get their own public IPv6 address unlike IPv4.)
6) Currently, most VPN providers seem to not support IPv6. (Just like with your ISP, you should also ask them to support it.)

Questions?
Comment below and I'll try my best to answer any questions you might have. Here is an example screenshot of "ipconfig" on a computer that has an IPv6 address: https://ibb.co/CbxXzmc