netdev - Re: Unexpected source address selection in routing

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Message-ID: <BAY103-DAV12061EF45C1BD09C570A4B2670@phx.gbl>
Date:	Mon, 25 Aug 2008 08:37:50 +0200
From:	"Marco Berizzi" <pupilla@...mail.com>
To:	"Jan Engelhardt" <jengelh@...ozas.de>
Cc:	<netdev@...r.kernel.org>, <netfilter-devel@...r.kernel.org>
Subject: Re: Unexpected source address selection in routing

Jan Engelhardt wrote:

>
> On Sunday 2008-08-24 20:31, David Miller wrote:
> >
> >> It appears that the routing code selects the outgoing source
address to
> >> use for packets is chosen when the socket is established instead of
> >> at routing time.
> >>
> >> The following presents a test case for "unexpected" (from a user's
> >> perspective) behavior.
> >>
> >> Is there any way to make it behave as a user would expect?
> >
> >No matter when we had made the routing lookup, we would have ended
> >up with what you see the kernel doing.
> >
> >The route is looked up long before netfilter even sees the packets.
> >
> >The source address selection at the socket level can only "see" the
> >original destination address and therefore makes the source address
> >selection using that original destination address.
>
> That's what I thought. With IPv4, one can cheat and use
> SNAT/MASQUERADE, but what about IPv6? (Other than using the RAWNAT
> extension, which bypasses netfilter connection tracking.)

Just for records, I opened a bug report (a feature request) about
this at http://bugzilla.kernel.org/show_bug.cgi?id=9767


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