netdev - Re: [PATCH net-next v2] ipv6: sysctl to restrict candidate source addresses

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Message-ID: <1436342988.2928.9.camel@stressinduktion.org>
Date:	Wed, 08 Jul 2015 10:09:48 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Lorenzo Colitti <lorenzo@...gle.com>, Erik Kline <ek@...gle.com>
Cc:	吉藤英明 
	<hideaki.yoshifuji@...aclelinux.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH net-next v2] ipv6: sysctl to restrict candidate source
 addresses

On Wed, 2015-07-08 at 10:29 +0900, Lorenzo Colitti wrote:
> On Mon, Jul 6, 2015 at 12:05 PM, Erik Kline <ek@...gle.com> wrote:
> > Per RFC 6724, section 4, "Candidate Source Addresses":
> > 
> >     It is RECOMMENDED that the candidate source addresses be the set
> >     of unicast addresses assigned to the interface that will be used
> >     to send to the destination (the "outgoing" interface).
> > 
> > Add a sysctl to enable this behaviour.
> > 
> > Signed-off-by: Erik Kline <ek@...gle.com>
> 
> I think this is useful, because it ensures that devices with a working
> IPv6 configuration on interface A, and a partial IPv6 configuration on
> interface B do not attempt to send packets on interface B using
> interface A's source address.
> 
> Example: there are home routers in the wild that send out an IPv6
> router advertisement that configures a default route but no IPv6
> address. This change makes it so that the host does not attempt to use
> an IPv6 address from another network (e.g., a cellular data
> connection) on the home network.
> 
> It is also what the RFC recommends.
> 
> Acked-by: Lorenzo Colitti <lorenzo@...gle.com>

I wonder a little bit, because addresses which match the outgoing
interface should get a higher score in saddr_eval, thus be automatically
preferred. Is this check not strong enough?

I really wonder if we can improve source address selection and make this
behavior a default without introducing a new sysctl.

Bye,
Hannes

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