An odd IPv6 application issue

[George Bonser]

> Sent: Monday, December 13, 2010 5:45 PM
> To: George Bonser
> Cc: Francois Tigeot; ipv6-ops at lists.cluenet.de
> Subject: Re: An odd IPv6 application issue
> 
> George,
> 
> As well as java.net.preferIPv6Addresses, there is
> java.net.preferIPv4Stack.

Yeah, tried that too.  If you do that you cannot ever talk to a v6 host.

> I may be out of date but I understood that by playing with both of
> these you can get appropriate dual stack behaviour.

Oh, I can get dual stack behavior, except it wants to send with a mapped v4 address (say, ::ffff:10.1.69.200 ) which isn't going to mean much to someone on the other side of the Internet because an IPv6 mapped RFC1918 v4 address is useless.  That is the behavior that Java needs to get rid of.

> But if the underlying o/s stack does the wrong thing with
> IPv4-Mapped addresses you are definitely hosed. I suspect that
> is when you need java.net.preferIPv4Stack quite badly.

If you use that, you lose all capability to talk to a v6 host.