I am seeing this very same issue on Solaris. Not only did I have to remove the if statement from Socket6.pm, I also had to explicitly import AF_INET6 in INET6.pm, to get everything working. This doesn't make much sense to me. With ActiveState Perl 5.10 everything works as I would expect, I don't have to do anything special, but with 5.8 I have issues. I compared the Socket.pm file between the two and as far as AF_INET6 is concerned they are the same.