Re: IPv6 route to gateway on fe80::1%eth0 when I have fe80::1%br0 locally

From: Marc Haber <mh+netdev@zugschlus.de>
To: Hannes Frederic Sowa <hannes@stressinduktion.org>
Cc: netdev@vger.kernel.org
Subject: Re: IPv6 route to gateway on fe80::1%eth0 when I have fe80::1%br0 locally
Date: Mon, 22 Feb 2016 16:47:58 +0100	[thread overview]
Message-ID: <20160222154758.GW26042@torres.zugschlus.de> (raw)
In-Reply-To: <56CB2564.9030003@stressinduktion.org>

On Mon, Feb 22, 2016 at 04:12:36PM +0100, Hannes Frederic Sowa wrote:
> On 22.02.2016 16:04, Marc Haber wrote:
> >In prose:
> >
> >The host is a host for KVM VMs. It receives IPv6 connectivity via RA
> >on eth0, where the default gateway announces its address as fe80::1.
> >It also provides IPv6 connectivity to the VMs via the br0 interface.
> >It is running radvd on br0, and for statically configured VMs it has
> >also fe80::1 on br0.
> >
> >If accept_ra_from_local on eth0 were 0, the system would not accept
> >the RA from the default gateway and and up with no IPv6 since fe80::1
> >is locally configured with br0.
> 
> Isn't this behavior fixed with
> 
> commit c1a9a291cee0890eb0f435243f3fb84fefb04348
> Author: Hannes Frederic Sowa <hannes@stressinduktion.org>
> Date:   Wed Dec 23 22:44:37 2015 +0100
> 
>     ipv6: honor ifindex in case we receive ll addresses in router
> advertisements
> 
> $ git describe --contains c1a9a291cee0890eb0f435243f3fb84fefb04348
> v4.4-rc8~5^2~10
> 
> ?
> 
> If you don't have fe80::1%br0 bound on exactly that interface, it should
> work, no? So, no need for accept_ra_from_local, which has dubious semantics
> anyway.

I have accept_ra_from_local set to 0 on all interfaces now, and I
still get the dubious default route on eth0.

> >If accept_ra_from_local on eth0 is 1, the system accepts both the RA
> >from the default gateway on eth0 _AND_ its own RA sent out and
> >received on br0, and, making things worse, is setting the IP address
> >and default route not on br0, but on eth0.
> 
> Understood. Thanks, I was just able to easily reproduce it. Was already
> wondering why someone would enable accept_ra_from_local besides only
> testing. I check it out, thanks!

Can you reproduce the behavior with accept_ra_from_local =0 as well?
Unfortunately, the debugging VM I build works fine, it's just the
physical host showing this behavior. This is really strange.

Greetings
Marc

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