Minecraft Version: 1.8-1.20.X

Forge Version: All (Tested on 49.0.27, 11.14.4.1577 and some others)

Steps to Reproduce:

Setup a server with IPV6 only

Setup a docker container with forge

Try to connect to the Forge Server

Description of issue:

Hello,

I am reaching out to seek your expertise within this forum to clarify a technical situation I am encountering, suspecting a potential issue related to Forge in a Docker environment, specifically in an IPv6 context.

Initial Configuration: Debian 12 server, configured exclusively for IPv6, with Docker installed. Using the Docker image ghcr.io/pterodactyl/yolks:java_17, launching a Minecraft Vanilla server version 1.20.4 proceeds without any issues.

Problem: The issue arises when deploying a Minecraft Forge server version 1.20.4 with the same Docker image (ghcr.io/pterodactyl/yolks:java_17), where connecting to the server becomes impossible. Notably, this issue does not occur when launching outside of Docker, where the server functions as expected.

Hypothesis: This situation leads me to question the interaction between Forge and Docker, particularly in an IPv6-only configuration, despite several resolution attempts (testing with different versions of Forge, adjusting container network configurations (0.0.0.0, ::/0, and the server's ipv6), trials with various network settings, and modifications of Java options).

Further testing was conducted with and without the use of the Pterodactyl game panel, unsuccessfully. The parameter

-Djava.net.preferIPv4Stack=false

also did not provide a solution.

I tried to do the same things on multiple Minecraft server (include vanilla,spigot,fabric,sponge) and this work fine. The problem only happend with Forge.
This issue seem to happend on all forge versions.

 

I appreciate your time and assistance in advance.

Forge doesn't do anything differently to Vanilla in terms of IPv6 on MC versions prior to 1.18.2. Therefore, if you are still having trouble including on those older versions, the problem is likely caused by Pterodactyl's docker image.

I may be wrong, but I vaguely remember their setup for Forge forcibly disabling IPv6 no matter what. You may want to ask them for help with this, or use another Java docker image such as Azul's Zulu

I don't think that the problem come from the docker image as the docker image is same for paper and for forge. If that work on paper this should work on forge no? Also I don't see any ipv6 problem in this image.

https://github.com/pterodactyl/yolks/blob/master/java/21/Dockerfile

 

I don't understand how the problem can come from the docker image here.