DatagramChannel::disconnect appears to rebind socket to the wildcard address

[Alan Bateman]

On 26/09/2019 13:15, Kurt Miller wrote:
> :
> Hi Alan,
>
> This one I don't have any insight into. OpenBSD is like Windows
> where it does not support IPv4-mapped IPv6 address at all. There
> is no way to enable it with a knob (sysctl). Since the networking
> implementation in the JVM on the Unix side of things depends on
> this, OpenBSD can't support both IPv4 and IPv6 at the same time.
>
> Ideally the dual socket implementation on the Windows side would
> be utilized on the Unix side as well. The would allow for avoiding
> the (perhaps debatable) security issues associated IPv4-mapped
> IPv6 addresses that were raised by one of the initial pioneers of
> IPv6, Itojun (Jun-ichiro Hagino) [1].
>
> I believe both FreeBSD and NetBSD have sysctl's to enable IPv4-mapped
> IPv6 address support, but is a system wide setting and puts an
> administrator in the position of having to enable a less secure
> setting to gain simultaneous IPv4 and IPv6 support in the JVM.
>
> Sorry I've gone off on a tangent here, but I felt it was related
> and perhaps could point out that the dual socket approach
> on the Windows side of the JVM networking implementation would
> likely be helpful for the Unix side as well.
>
Thanks anyway. As you brought up Windows, I should mention that 
Microsoft added support for dual stack sockets in Windows Vista and the 
JDK uses on that platform too (one only outlier is legacy 
MulticastSocket where it uses the two stack implementation but that 
should eventually be replaced). This allows the JDK to use IPv4-mapped 
IPv6 addresses when interfacing with the operating system (not on the 
wire of course).

-Alan