netdev - Re: why are IPv6 addresses removed on link down

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Date:	Tue, 13 Jan 2015 16:09:51 +0100
From:	Hannes Frederic Sowa <hannes@...hat.com>
To:	Sowmini Varadhan <sowmini.varadhan@...cle.com>
Cc:	David Ahern <dsahern@...il.com>,
	YOSHIFUJI Hideaki <hideaki.yoshifuji@...aclelinux.com>,
	Stephen Hemminger <stephen@...workplumber.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: why are IPv6 addresses removed on link down

On Di, 2015-01-13 at 10:00 -0500, Sowmini Varadhan wrote:
> On (01/13/15 07:53), David Ahern wrote:
> > 
> > The current code seems inconsistent: I can put an IPv6 address on a
> > link in the down state. On a link up the address is retained. Only
> > on a subsequent link down is it removed. If DAD or anything else is
> > the reason for the current logic then why allow an address to be
> > assigned in the down state? Similarly that it currently seems to
> > work ok then it suggests the right thing is done on a link up in
> > which case a flush is not needed.
> > 
> > Bottom line is there a harm in removing the flush? If there is no
> > harm will mainline kernel take a patch to do that or is your
> > backward compatibility concern enough to block it?
> 
> Does some of this have to do with the manner in which this interacts
> with SLAAC? I recall that there were two schools of thought for doing
> DAD when SLAAC is present: one says it is sufficient to just do DAD
> on the interface-id, the other requies DAD on the whole 128-bit IPv6
> address. I'm not sure which choice linux makes.

Yes, it does have something to do with it. But I didn't understand what
you meant by doing DAD on the interface-id.

If you look at the patches I just posted, only addresses which are in
link-local and not in permanent state will be flushed.

I also need to do research on how to safely approach this, I don't know,
yet.

Bye,
Hannes


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