From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: Bug with IPv6-UDP address binding
Date: Thu, 09 Aug 2012 13:37:50 +0200
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Cc: netdev <netdev@vger.kernel.org>, Thomas Graf <tgraf@suug.ch>
To: Jesper Dangaard Brouer <brouer@redhat.com>
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On Thu, 2012-08-09 at 11:40 +0200, Jesper Dangaard Brouer wrote:

> Yes, I guess its an application bug, because Berkely-derived
> implementations don't handle multihomeing well for UDP.
> 
> Why are we keeping this, counter-intuitive behavior? 
> 

Because the BSD api has no other choice.

> What about changing the implementation to act like Solaris, which IMHO
> makes much more sense?
> 
> (BTW, iperf also have this "bug")
> 

Please describe how connect() is able to correctly chose for you a
source address, if you have say 256 addresses.

connect() API only requires the destination.

If you want a precise source, you must use bind() before the connect()

Any UDP application wanting to correctly reflect "correct source IP"
must say so to the kernel.

I dont think kernel could magically help here, really.