Christopher Fitzgerald
Comments
Apologies for the lack of updates lately.
I've just had a chance to test out the last few versions to see if there was any change. As before, the problem lies with the launcher. I've updated the summary to point out my previous comment regarding its cause.
Good to see confirmation regarding the launcher.
Speaking of which, I had a chance to do a cursory look over its classes and the problem is with LauncherFrame.class. It sets the "java.net.preferIPv4Stack" property to true and the "java.net.preferIPv6Addresses" property to false, which prohibits the use of IPv6 on systems configured as we've described.
Sorry for the lack of updates. I've been having some trouble using this site. When I try to browse issues or even a specific issue, it puts me in some kind of redirect loop. I had to enable NoScript so I could start this reply.
The IPv6 problem still persists. As I mentioned previously, the launcher appears to be the culprit. It works fine when I run it in MultiMC. I think the launcher may be setting a Java property that causes it to prefer using the IPv4 stack. Unfortunately, I haven't yet had the time to run it in a debugger to find out exactly what's going on.
I recently discovered that the problem I've been having appears to be caused by the Minecraft.exe launcher. If I run Minecraft from one of the third party launchers or straight from the minecraft.jar file (albeit without logging in) the problem vanishes.
It looks to me like the launcher may be setting some Java network property that interferes with the use of IPv6 addresses when IPv4 is also present.
Let me know if there is anything I can do to further help determine why this occurs. It would really be nice to use my IPv6 server again.
This problem still persists in Minecraft 1.4.6.
I've not had the time to test (or inspect the bytecode) of versions past 1.6.4 myself. As of those tests, I can for certain state that (at least on Windows) the problem definitely is the launcher (whether that be .exe or .jar). Given you (Hugo) state that Linux appears to suffer a similar problem, I'd bet the same for it. Try running the game from a 3rd party launcher (IPv6 worked with both MultiMC and MagicLauncher last I checked).
At this point, given Grum's statement (as pointed out by Omar) I don't feel the need to keep updating this report, since the bug will remain by design. Perhaps they'll fix it when IPv6 becomes more prevalent. At the very least it wouldn't hurt to add an IPv6 option (with an appropriate warning) to the launcher. In the meantime, to use IPv6 we're forced to use a 3rd party launcher or a modified version of the official one.
I'll update the topic version (to 1.7.9) and modify the summary to clarify that the launcher's extension is irrelevant and that this affects Linux users as well.