netdev - Re: IGMP joins come from the wrong SA/interface

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Message-ID: <20140204233206.GA16198@order.stressinduktion.org>
Date:	Wed, 5 Feb 2014 00:32:06 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	"Steinar H. Gunderson" <sgunderson@...foot.com>
Cc:	netdev@...r.kernel.org
Subject: Re: IGMP joins come from the wrong SA/interface

On Tue, Feb 04, 2014 at 11:08:09PM +0100, Steinar H. Gunderson wrote:
> On Thu, Jan 30, 2014 at 11:44:11PM +0100, Hannes Frederic Sowa wrote:
> > The routing lookup is done at IP_ADD_MEMBERSHIP time. I really wonder why you
> > have routed the 239.0.0.0/8 range to eth0.11. It seems to me that the kernel
> > does what you told it to do. ;)
> > 
> > multicast flag on ip route is just used for multicast forwarding and does not
> > matter for local multicast. Also if we find unicast route first (more
> > specific) kernel does not do backtracking if destination is in multicast
> > scope.
> 
> Hah, you're right. The issue was a combination of:

Thanks for letting me know!

>  1. mediatomb's initscript on Debian at some point started to add a bogus
>     239.0.0.0/8 route (and I didn't notice this because I earlier tested with
>     addresses outside this range).
>  2. I didn't properly understand that the multicast flag on the route did not
>     matter (although it really should!).

Hmm, maybe that would be good but I am not sure if that could break existing
setups if we change that now. It seems it is handled like that since Alexey
implemented it in that way.

Greetings,

  Hannes

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