netdev - Re: sysctls below net.ipv[46].conf.all not working as expected

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Message-Id: <20101230.123023.226775556.davem@davemloft.net>
Date:	Thu, 30 Dec 2010 12:30:23 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	u.kleine-koenig@...gutronix.de
Cc:	netdev@...r.kernel.org
Subject: Re: sysctls below net.ipv[46].conf.all not working as expected

From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Date: Wed, 29 Dec 2010 17:06:07 +0100

> I did the following:
> 
> 	cassiopeia:~# sysctl net.ipv6.conf.all.use_tempaddr
> 	net.ipv6.conf.all.use_tempaddr = 0
> 
> 	cassiopeia:~# sysctl net.ipv6.conf.eth0.use_tempaddr
> 	net.ipv6.conf.eth0.use_tempaddr = 0
> 
> 	cassiopeia:~# sysctl -w net.ipv6.conf.all.use_tempaddr=1
> 	net.ipv6.conf.all.use_tempaddr = 1
> 
> 	cassiopeia:~# sysctl net.ipv6.conf.all.use_tempaddr
> 	net.ipv6.conf.all.use_tempaddr = 1
> 
> 	cassiopeia:~# sysctl net.ipv6.conf.eth0.use_tempaddr
> 	net.ipv6.conf.eth0.use_tempaddr = 0
> 
> Here I would have expected that eth0's use_tempaddr is 1, too.  The
> problem is not that this entry isn't writeable:

The "all" value is propagated at the first moment that the ipv6 device
private is created, usually that is when the device is first brought up
which means it can happen as early as the exact moment the device is
registered.

Therefore, if you want "all" to apply to "eth0", you must make sure
the sysctl is set properly before the device is registered.
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