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 14:05:00 +0100
From:	Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:	David Miller <davem@...emloft.net>
CC:	hannes@...essinduktion.org, 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

Le 11/11/2013 06:18, David Miller a écrit :
> 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.
There are some exceptions, for example when user tunes arp_ignore sysctl ;-)

>
> 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.
I agree that this is ambiguous. And it's a 'must', not a 'MUST', which
is not the same for an RFC ;-)

>
> Furthermore, the fact that you're implementing _addressing_ policy in
> the UDP code makes this change even more unreasonable.
>
I made this choice because using 0.0.0.0, for TCP for example, seems a
non-sense.

But fair enough, let's drop this patch.


Thank you,
Nicolas
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