netdev - Re: [RFC PATCH net-next 2/2] udp: add sk opt to allow sending pkt with src 0.0.0.0

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Date:	Thu, 14 Nov 2013 15:31:54 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	David Miller <davem@...emloft.net>
Cc:	nicolas.dichtel@...nd.com, netdev@...r.kernel.org,
	David.Laight@...LAB.COM, jiri@...nulli.us, vyasevich@...il.com,
	kuznet@....inr.ac.ru, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
	kaber@...sh.net, thaller@...hat.com, stephen@...workplumber.org
Subject: Re: [RFC PATCH net-next 2/2] udp: add sk opt to allow sending pkt with src 0.0.0.0

On Mon, Nov 11, 2013 at 12:18:03AM -0500, David Miller wrote:
> From: Nicolas Dichtel <nicolas.dichtel@...nd.com>
> Date: Sat,  9 Nov 2013 01:54:34 +0100
> 
> > This feature allows to a send packets with address source set to 0.0.0.0 even if
> > an ip address is available on another interface.
> > 
> > It's useful for DHCP client, to allow them to use UDP sockets and be compliant
> > with the RFC2131, Section 4.1:
> > 
> > 4.1 Constructing and sending DHCP messages
> > ...
> >    DHCP messages broadcast by a client prior to that client obtaining
> >    its IP address must have the source address field in the IP header
> >    set to 0.
> > 
> > Based on a previous work from
> > Guillaume Gaudonville <guillaume.gaudonville@...nd.com>.
> > 
> > Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>
> 
> This requirement of the RFC is inconsistent with a host based
> addressing model, that which Linux employs, it assumes an interface
> based one.
> 
> The wording here is also very ambiguous.
> 
> This RFC fails to even remotely consider what the right behavior
> should be in a host based addressing environment at all, and anyone
> reading this RFC should just accept that.
> 
> Furthermore, the fact that you're implementing _addressing_ policy in
> the UDP code makes this change even more unreasonable.

I agree on this and will check how other operating systems which only
use sockets do deal with that.

Do you have an idea how to deal with the rp_filter issue if no ip address is
set? Should we relax it in such cases?

Greetings,

  Hannes

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