netdev - Re: [PATCH 1/2] bridge: leave carrier on for empty bridge

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Message-ID: <20110903211438.2a43d2f2@nehalam.ftrdhcpuser.net>
Date:	Sat, 3 Sep 2011 21:14:38 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Nicolas de Pesloüan 
	<nicolas.2p.debian@...il.com>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] bridge: leave carrier on for empty bridge

On Sat, 03 Sep 2011 20:32:28 +0200
Nicolas de Pesloüan <nicolas.2p.debian@...il.com> wrote:

> Le 03/09/2011 00:11, Stephen Hemminger a écrit :
> > On Fri, 02 Sep 2011 23:39:03 +0200
> > Nicolas de Pesloüan<nicolas.2p.debian@...il.com>  wrote:
> >
> >> Le 02/09/2011 19:22, Stephen Hemminger a écrit :
> >>> This resolves a regression seen by some users of bridging.
> >>> Some users use the bridge like a dummy device.
> >>> They expect to be able to put an IPv6 address on the device
> >>> with no ports attached during boot.
> >>>
> >>> Note: the bridge still will reflect the state of ports in the
> >>> bridge if there are any added.
> >>
> >> Doesn't this jeopardize the behavior introduced in 1faa4356a3bd89ea11fb92752d897cff3a20ec0e
> >> "bridge: control carrier based on ports online"?
> >>
> >> If the user starts the DHCP client before adding the first port to the bridge, the DHCP client will
> >> have a carrier and start the autoconfiguration process. This was the old behavior, but you fixed it.
> >>
> >> 	Nicolas.
> >>
> >
> > There is no perfect solution.
> > If DHCP works then IPv6 breaks?
> 
> Instead of asserting carrier when the bridge have no port, can't we assert carrier when the three 
> following condition are true at the same time :
> 
> - The bridge have no port.
> - At least one IP address is setup on the bridge.
> - The two above conditions are true for more than a configurable amount of seconds, with a default 
> of 10, for example.
> 
> This would only delay carrier on for a few seconds for the regression and keep the current behavior 
> (carrier off until at least 1 port is on) for DHCP.

This fails on two counts:
1. Bridge's often run without IP addresses!
2. DHCP won't try and send out request until carrier is true.

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