Why is it not possible to join the Minecraft Multiplayer Server Local?

The question sounds strange but to describe it more precisely.

Before I explain the problem here, you have to know that I have a Telekom router W724 V, which I use for the Vanilla Minecraft server.

First I created a Minecraft multiplayer server for my friends and my brother (a little older) who are not on my local network to join. The port was activated and joining with the Ipv4 address was not a problem, but my brother could not join on this address. No matter what you do when you unlock the port in the Telekom router, the connection remains undetectable as before. It should read (No further information).

I've tried everything possible. E.g. Localhost or firewall deactivated, tries to open ports for him, etc.

Once it worked with the Ipv6 address. So far I'm wondering what the difference is between an Ipv4 and an Ipv6 address.

The IPv6 address does not work until the next day. Unfortunately, I don't know exactly what the problem is.

I would also like to go a little deeper into this matter in order to understand and to later solve this similar case. So if you have information then always bring it to me.

So you have a Minecraft server.
What a?
Which host?
Do you have a domain?

So if it doesn't work for you with ipv4, but you are of the opinion that the port sharing is correct, then you probably have DS-Lite, which is an Internet connection that can't be reached from the outside - why> google…

others can connect to ipv6, which is a good thing - the next day, as is customary at Telekom, the IP probably changed, why you have to change IPv6 is not conclusive to me, but that's Telekom…

so if your friends want to reconnect, you just have to tell them the new IPv6, or you can organize a service like Dyn.com, which always turns your changing IP into a host name that you can remember…

this service is now also available for IPv6:

https://dynv6.com/

there you can have your IPv6 converted into an easy-to-remember host name for free…

The way it reads, he hosts from home…

Jup is its own server

So all other players outside our local network can log in with no matter which IP they use. Only my brother who is in the local network can't be connected to "localhost" or IPv4 addresses.

Thanks for the tip!

Localhost ONLY works on the computer on which the server is running, so local…

otherwise the internal IP should work (192.168.xxx.xxx) …

the 127.0.0.1 = localhost, ONLY works on the server PC…

Ah ok. Unfortunately, I've never dealt with that before, sorry

Local normal is unfortunately not possible either.

I can't do anything with the statement… Which IP does he use? You can list the internal ones here, nobody can do anything with them…

Which IP do you mean the IP address or the IPv4? (Sorry stupid question)

I asked which IP it connects to… I wanted to see the numbers… - you don't need to be afraid to enter an IP that starts with 192.xxx.xxx.xxx… But if it doesn't start with 192.168.xxx.xxx, I would be interested…

So that he can connect (my brother) needed the IPv6 address. The IPv4 didn't work for some reason.
From me:

IPv4: 192.168.2.106
----> IPv6: 2003: f6: f16: 35a: a986: 3cca: bae9: 42c5 (needed to join the server)

My brother's IP:

IPv4: 192.168.2.107

IPv6: 2003: f6: f16: 35a: 782b: 9010: b2a1: 8db3

If I'm too stupid again or have misunderstood. I'm really sorry. I'm still a beginner, so it's best to explain where you can find this information under the calculator.