Re: IPv6 socket behaviour different to IPv4?

[Darren Reed <darrenr%netbsd.org@localhost>]

So the issue appears to be with how IPv6 determines what addresses
are ok to use on a network interface. In particular, it always wants to
use DAD before an interface is deemed ok to use. Of course when a NIC
is down, it is not possible for DAD to start so non-link local addresses
are never marked safe for use.

When autoconfiguration of addresses is active, I can't see a problem
with this, nor even automatic address selection where a full /128 is
not configured, only the portion of the IPv6 address that doesn't have
an EID in it.

But when I configure "fd00::1" or "1::1" as an IPv6 address, I would
expect that the system should be able to recognise that there is no
desire on my part to change the address should a conflict arise but
I can't see any way for the kernel to divine that when it is just given
an IP address.

To change the behaviour, it would be necessary to add a new flag to
ifa_flags (IFA_NOAUTOSEL?) that could only be set when the address
was assigned to the interface.

Darren