Minecraft authentication not working, can not play on server

Technical Support
1

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OS Name/Version:Linux

Product Name/Version: AMP Release “Phobos”

v2.6.0.12, built 24/02/2025 17:12

Problem Description:

I'm having trouble connecting to my modded minecraft server. I was using vanilla yesterday, and it worked perfectly fine. Heres the error I'm getting:
Authentication servers are down. Please try again later, sorry!
User Authenticator #3/ERROR21:08:27
Couldn't verify username because servers are unavailable

Steps to reproduce:

Open minecraft
Copy Ip
attempt to join

Actions taken to resolve so far:
disabled firewall rules
reset insatnce
made new instance

2

Are you self-hosting from home, or did you set up AMP in some datacenter?
Most likely either a DNS or IPv6 issue

3

Im self hosting from home, but using tunneling instead of port forwarding

4

Do you run into the same issue if you join locally? Does the issue still occur with the tunnel temporarily disabled?

5

Yes, I run into the same issue. I tested the sever on vanilla yesterday, and switched to modded and now am running into issues

6

If you create another local vanilla instance to test, does that work?

7

yes, just tested it again, worked perfectly, but as soon as I use neoforge it breaks

8

It might be an IPv6 issue due to Neo’s networking changes. You could either fix your IPv6 setup, or disable it entirely on that machine

9

Following up with another thing I blanked on earlier, you could try adding this argument under Java and Memory:

-Djava.net.preferIPv4Stack=true

10

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