From mboxrd@z Thu Jan 1 00:00:00 1970 From: Curt Sampson Subject: Re: Problems Receiving UDP Broadcasts on Some Versions of Linux Date: Wed, 27 Jan 2010 14:14:06 +0900 Message-ID: <20100127051405.GA5316@analytic.cynic.net> References: <20100125072749.GG21419@analytic.cynic.net> <4B5D51E6.5090601@gmail.com> <20100127003744.GA16322@analytic.cynic.net> <1264564565.2810.11.camel@edumazet-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-kernel@vger.kernel.org, Linux Netdev List To: Eric Dumazet Return-path: Received: from static-122-103-239-153.ng-fam.svips.gol.ne.jp ([122.103.239.153]:62154 "EHLO priv.dyadic.cynic.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750993Ab0A0FOL (ORCPT ); Wed, 27 Jan 2010 00:14:11 -0500 Content-Disposition: inline In-Reply-To: <1264564565.2810.11.camel@edumazet-laptop> Sender: netdev-owner@vger.kernel.org List-ID: On 2010-01-27 04:56 +0100 (Wed), Eric Dumazet wrote: > And you receive a frame on eth1 with src ip address = 192.166.1.120 > > I suspect your kernel drops this frame because of asymetric routing > > Check "ip route get 192.166.1.120" and if answer is directed to another interface, > this may explain the problem. Indeed, you are absolutely correct. I've further verified that this is the issue by having the 8.04 host generate broadcast packets on eth0 and eth1, and the "malfunctioning" 9.04 host receives them correctly in both cases. I ought to have known, looking at that patently bogus source address (there's no way I should be seeing anything to 255.255.255.255 that has a source address from a different network), to start looking at these sorts > Solution : tweak rp_filter settings. And indeed, that worked. (I've added the old settings to the StackOverflow page.) Thank you very much! Let me know (by private e-mail) if you're going to add an answer to my question on StackOverflow, so I can give you the reputation points. Otherwise I'll add the answer myself. The URL, again, is: http://stackoverflow.com/questions/2130563/udp-broadcast-reception-problems-with-ubuntu-9-04-but-not-8-04 cjs -- Curt Sampson +81 90 7737 2974 http://www.starling-software.com The power of accurate observation is commonly called cynicism by those who have not got it. --George Bernard Shaw