Why do I need java.net.preferIPv4Stack=true only on some windows 7 systems?

Question

I have used Java on Windows 7 (64bit) machines for quite some time and have never had problems with not being able to create a network connection. Now on the systems at the

Answer 1

Ok so we found out the reason.

This problem seemed to have occured on systems containing a special version of remote access software that our company used. This seems to have inserted some modified dlls into Windows network stack (We were told in order to auto-detect network connectivity). It seems this dll had some issues, causing all IPv6 traffic to be blocked. It also caused the affected Machines to have regular Bluescreens. Uninstalling that software got the system Bluescreen free and I no longer need the preferIPv4Stack setting.