netdev - Re: [patch net-next] ipv6: allow userspace to create address with IFLA_F

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Message-ID: <20131029124010.GA15762@order.stressinduktion.org>
Date:	Tue, 29 Oct 2013 13:40:10 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	David Miller <davem@...emloft.net>, jiri@...nulli.us,
	vyasevich@...il.com, netdev@...r.kernel.org, kuznet@....inr.ac.ru,
	jmorris@...ei.org, yoshfuji@...ux-ipv6.org, kaber@...sh.net,
	thaller@...hat.com, stephen@...workplumber.org
Subject: Re: [patch net-next] ipv6: allow userspace to create address with IFLA_F_TEMPORARY flag

On Tue, Oct 29, 2013 at 09:37:06AM -0000, David Laight wrote:
> > Note that you don't even need to put the DHCP protocol core into the
> > kernel to fix the promiscuous problem.  You just have to use the
> > current kernel interfaces correctly.
> > 
> > It used to be the case a very long time ago that you couldn't even
> > receive broadcast UDP datagrams on a socket until an address was
> > configured on it.
> > 
> > So everyone turns on promiscuous mode and uses RAW sockets or
> > AF_PACKET.
> > 
> > Stupid?  yes.
> 
> Not only that, but the dhcp client could use a normal UDP socket
> to keep the lease renewed - I suspect it has only ever needed
> to use the BPF interface (I didn't think it set promiscuous)
> when acquiring the initial lease.

Yes, this is a very unfortunate situation. From my experience it is not that
easy to get a patch merged into isc-dhcp.

It seems not that invasive to switch from af_packet to an udp socket with
SO_BROADCAST set.

Greetings,

  Hannes

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