netdev - Re: Bridge stays down until a port is added

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Date:	Mon, 26 Sep 2011 17:43:19 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Sven-Haegar Koch <haegar@...net.de>
Cc:	Nicolas de Pesloüan 
	<nicolas.2p.debian@...il.com>, Marc Haber <mh+netdev@...schlus.de>,
	netdev@...r.kernel.org
Subject: Re: Bridge stays down until a port is added

On Tue, 27 Sep 2011 02:28:42 +0200 (CEST)
Sven-Haegar Koch <haegar@...net.de> wrote:

> On Tue, 27 Sep 2011, Nicolas de Pesloüan wrote:
> 
> > Le 26/09/2011 22:05, Stephen Hemminger a écrit :
> > > On Mon, 26 Sep 2011 22:02:21 +0200
> > > Nicolas de Pesloüan<nicolas.2p.debian@...il.com>  wrote:
> > [...]
> > > > Stephen,
> > > > 
> > > > What do you think about a generic per-interface option that would cause
> > > > bind() to accept tentative
> > > > address hold by a particular interface? This of course violate IPv6
> > > > principle, but we are talking
> > > > about interfaces that are unable to do DAD, either permanently or until
> > > > something happens on the
> > > > underlying device.
> > > > 
> > > > echo 1>  /sys/class/net/br0/allow_bind_on_tentative_address
> > > > echo 1>  /sys/class/net/dummy0/allow_bind_on_tentative_address
> > > > echo 1>  /sys/class/net/wlan0/allow_bind_on_tentative_address
> > > > and so on...
> > > > 
> > > > And we may possibly automatically reset this option to 0 if DAD eventually
> > > > causes the address to be
> > > > considered duplicate.
> > > 
> > > The issue is that if DAD rejects a duplicate, the socket is dead and
> > > application is
> > > out of luck.
> > 
> > Yes, and this is by design. Setting the option would state "I want to allow
> > early bind(), prior to DAD and I assume the fact that a possible duplicate
> > address will cause the corresponding socket to be dead and so the using
> > application."
> 
> How about a setting just completely disabling this 
> duplicate-address-detection crap?
>

Already multiple ways to disable it:
  1. Set /proc/sys/net/ipv6/XXX/accept_dad to 0
  2. Set flag when assigning address with 'ip add add ... nodad' 
  3. Set IFF_NOARP on the interface (done by drivers)

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