linux-kernel - Re: Strange UDP Issue on 2.6.20.8 - broadcasts not being received if socket bound to local ip

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Date:	Wed, 2 May 2007 12:14:53 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	"Dylan Taft" <d13f00l@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Strange UDP Issue on 2.6.20.8 - broadcasts not being received
 if socket bound to local ip

On Wed, 2 May 2007 05:55:28 -0400
"Dylan Taft" <d13f00l@...il.com> wrote:

> I've been pulling my hair out for the past several hours trying to
> debug a program in wine.  I'm currently on kernel 2.6.20.8.  The
> problem was that I was not getting any broadcasts to 255.255.255.255
> on a UDP socket bound to 192.168.0.8 with SO_BROADCAST enabled.
> 
> I was fiddling around a bit, broadcasts come in fine if the socket is
> bound to INADDR_ANY( 0.0.0.0), but if it's bound to 192.168.0.8
> nothing comes in.  I did a packet sniff, and indeed packets were being
> sent out to 255.255.255.255 via another machine on the network.  I
> wrote a quick test program that would bind a socket to the lan ip and
> wait for incoming data.  I tested it on a windows machine and linux.
> The windows machine could pick up packets fine, my linux machine could
> not.   Is this proper behavior?  It's fudging up several games and
> things in the wine project.
> 
> Does anyone else experience this?  Thanks!

It seems you are expecting too much of SO_BROADCAST option.

http://www.opengroup.org/onlinepubs/009695399/functions/xsh_chap02_10.html

SO_BROADCAST :

Non-zero requests permission to transmit broadcast datagrams (SOCK_DGRAM sockets only).

Note this only handles the transmission of packets, not receiving them.

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