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

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Message-ID: <1317070616.2773.46.camel@bwh-desktop>
Date:	Mon, 26 Sep 2011 21:56:56 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Stephen Hemminger <shemminger@...tta.com>
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 Mon, 2011-09-26 at 13:05 -0700, Stephen Hemminger wrote:
> On Mon, 26 Sep 2011 22:02:21 +0200
> Nicolas de Pesloüan <nicolas.2p.debian@...il.com> wrote:
[...]
> > 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.
> 
> Has anyone looked at this issue in relation to systemd which does early
> opportunistic binding of services?

I think it is recommended to use the IP_FREEBIND socket option.  Which
of course is not available for IPv6.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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