From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Re: Bug#625914: linux-image-2.6.38-2-amd64: bridging is not interacting well with multicast in 2.6.38-4 Date: Mon, 9 May 2011 20:15:28 -0700 Message-ID: <20110509201528.52d87ec4@nehalam> References: <20110506201234.6297.70279.reportbug@ip6-localhost> <1304995124.4065.157.camel@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Noah Meyerhans , 625914@bugs.debian.org, netdev , bridge@lists.linux-foundation.org To: Ben Hutchings Return-path: Received: from mail.vyatta.com ([76.74.103.46]:58508 "EHLO mail.vyatta.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753243Ab1EJDPa (ORCPT ); Mon, 9 May 2011 23:15:30 -0400 In-Reply-To: <1304995124.4065.157.camel@localhost> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, 10 May 2011 03:38:44 +0100 Ben Hutchings wrote: > On Fri, 2011-05-06 at 13:12 -0700, Noah Meyerhans wrote: > > Package: linux-2.6 > > Version: 2.6.38-3 > > Severity: normal > > > > Hi. I've got a system that hosts several kvm virtual hosts. The VMs > > access the network via tap devices bridged with a physical interface. > > After upgrading to linux-image-2.6.38-2-amd64_2.6.38-4, I noticed that > > the virtualhosts were not autoconfiguring their IPv6 interfaces. > > Debugging revealed that no multicast was passing over the bridge. > > > > The bridge configuration is: > > bridge name bridge id STP enabled interfaces > > br0 8000.0002e3080eb5 no eth1 > > tap0 > > tap1 > > tap2 > > > > If I attach tcpdump to br0, I can see multicast (e.g. IPv6 Neighbor > > Solicitation) packets. However, if I attach tcpdump to eth1, I do not > > see multicast packets sourced from one of the VMs. > > > > Downgrading to 2.6.38-3 solves the problem. > > This is pretty weird. Debian version 2.6.38-3 has a few bridging > changes from stable 2.6.38.3 and 2.6.38.4, but they don't look like they > would cause this. > > Ben. There are two possible explainations: 1. In 2.6.37 and kernels the bridge uses IGMP snooping, there were several fixes to that in the stable kernel; especially related to IPv6. 2. There was also a recent change to block link local multicast address. But that should impact what you are doing.