How to support both IPv4 and IPv6 connections

Question

I\'m currently working on a UDP socket application and I need to build in support so that IPV4 and IPV6 connections can send packets to a server.

I was hoping that

Answer 1

The RFCs don't really specify the existence of the IPV6_V6ONLY socket option, but, if it is absent, the RFCs are pretty clear that the implementation should be as though that option is FALSE.

Where the option is present, I would argue that it should default FALSE, but, for reasons passing understanding, BSD and Windows implementations default to TRUE. There is a bizarre claim that this is a security concern because an unknowing IPv6 programmer could bind thinking they were binding only to IN6ADDR_ANY for only IPv6 and accidentally accept an IPv4 connection causing a security problem. I think this is both far-fetched and absurd in addition to a surprise to anyone expecting an RFC-compliant implementation.

In the case of Windows, non-compiance won't usually be a surprise. In the case of BSD, this is unfortunate at best.