Re: IPv6 socket behaviour different to IPv4?

[Roy Marples <roy%marples.name@localhost>]

On 04/06/2014 17:20, 神明達哉 wrote:
> Does this mean this address was once usable when the host is connected
> (after performing DAD), but disconnecting it makes it unusable
> somehow for a reason related to DAD?  I'm not familiar with very
> latest NetBSD kernel code, but IIRC the original DAD implementation of
> the KAME project didn't behave that way.  If you reboot a system while
> it's disconnected, though, the kernel may try to perform DAD, making
> the address tentative, noticing the interface is down, and keeping the
> address tentative (thus unusable).  Perhaps this is the problem
> currently discussed?
>
> If so, again IIRC, the tentative flag should be able to be cleared
> manually.  We might also consider changing the kernel behavior so it
> only initiates DAD when the interface becomes up.

So what used to happen is this
Tentative address assigned, DAD performed, tentative flag cleared and 
optionally duplicated flag set.

What happens now is this
Tentative address assigned
    IF link != DOWN then
      DAD performed, tentative flag cleared and optionally duplicated 
flag set.
    else
      detached flag is set

Link goes from != DOWN to DOWN then all IPv6 addresses are marked as 
detached (this is what Darren is complaining about)

Link goes from DOWN to != DOWN then all IPv6 addresses are marked as 
tentative, detached flag is cleared and DAD is performed again

The rationale for this is simple, DAD must be performed on link change 
as we may have moved to a different network.
This is also stated in RFC6509 Section 5.4

5.4. Link-Layer Indication

   In order to start detection of network attachment procedures, a host
   typically requires a link-layer indication that the medium has become
   available [RFC4957].

   After the indication is received, the host MUST mark all currently
   configured (non-tentative) IP addresses as inoperable until the
   change detection process completes.

I chose to mark them as non tentative (ie detached) at link down, 
because we're fractionally to late at link up.

I did experiment with just marking the addresses as tentative instead of 
detached, but this had the side effect of an active link taking over in 
a timely manner.
My use case is my laptop with wired and wireless connections, unplug one 
then the other takes over.

Roy