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

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Date:	Mon, 05 Sep 2011 19:18:38 +0200
From:	Nicolas de Pesloüan 
	<nicolas.2p.debian@...il.com>
To:	Stephen Hemminger <shemminger@...tta.com>
CC:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] bridge: leave carrier on for empty bridge

Le 04/09/2011 18:36, Stephen Hemminger a écrit :
> On Sun, 04 Sep 2011 09:35:10 +0200
> Nicolas de Pesloüan<nicolas.2p.debian@...il.com>  wrote:
>
>> Le 04/09/2011 06:14, Stephen Hemminger a écrit :
>>
>>>> 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.
>>
>> Sorry, I missed to say that we should of course also assert carrier on if one port has carrier on.
>>
>> And rethinking about it, the delay is probably useless :
>>
>> bridge_carrier_on = at_least_one_port_has_carrier_on | (bridge_has_no_port&  bridge_has_at_least_one_ip)
>>
>> That way :
>> - for those using bridge without any port, manually setting the IP will assert carrier on. (By the
>> way, why don't they use a dummy device instead?)
>>
>> - for those using bridge with ports:
>> -- Using any kind of autoconfig will work as expected. Carrier will only be asserted at the time
>> first port get carrier.
>> -- Using static IP confifiguration, carrier will possibly be erroneously reported as on during the
>> small time gap between IP address configuration and first port is added to the bridge. This time gap
>> may be removed by simply configuring the IP after the first port is added. This is probably already
>> true for most distribs. And anyway, this time gap is probably not a problem.
>> -- Carrier will also be erroneously reported as on after removing the last port, if the bridge still
>> has an IP. (But we can arrange for this not to happen).
>>
>> And in order to ensure user really understand why carrier is on of off, we can simply issue an INFO
>> message for the non-natural case (bridge_has_no_port&  bridga_has_at_least_one_ip).
>>
>> I consider all this reasonable.
>>
>> 	Nicolas.
>
> Any bridge behaviour based on IP address configuration is a
> layering violation and won't work.  The problem is related to dynamic issues
> with IPv6 and DHCP and needs to be addressed at that level.

Well, this is not a bridge behavior, this is a behavior of the local (non physical) interface of the 
bridge. If this interface were physical, it would have been external to the bridge (on one of the 
hosts connected to the bridge).  As such, this behavior is not related to the layering of the 
bridge, so I don't consider it a layering violation.

My proposed change doesn't impact the way the bridge works (forwards packets) in any way.

And it really solves both issues.

	Nicolas.
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