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

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Message-ID: <20150113150048.GA28371@oracle.com>
Date:	Tue, 13 Jan 2015 10:00:48 -0500
From:	Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:	David Ahern <dsahern@...il.com>
Cc:	Hannes Frederic Sowa <hannes@...hat.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 (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.

--Sowmini
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