From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Stancek Subject: Re: bridge is not forwaring ICMP6 neighbor solicitation to KVM guest Date: Tue, 4 Mar 2014 03:02:36 -0500 (EST) Message-ID: <624414844.12834668.1393920156458.JavaMail.zimbra@redhat.com> References: <1566805413.12693479.1393872931017.JavaMail.zimbra@redhat.com> <2107636851.12713862.1393876035292.JavaMail.zimbra@redhat.com> <20140303212759.GW5090@Linus-Debian> <1808019554.12748658.1393886749190.JavaMail.zimbra@redhat.com> <20140304000041.GY5090@Linus-Debian> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: netdev@vger.kernel.org, Florian Westphal , bridge@lists.linux-foundation.org To: Linus =?utf-8?Q?L=C3=BCssing?= Return-path: Received: from mx3-phx2.redhat.com ([209.132.183.24]:52282 "EHLO mx3-phx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756262AbaCDICi convert rfc822-to-8bit (ORCPT ); Tue, 4 Mar 2014 03:02:38 -0500 In-Reply-To: <20140304000041.GY5090@Linus-Debian> Sender: netdev-owner@vger.kernel.org List-ID: ----- Original Message ----- > From: "Linus L=C3=BCssing" > To: "Jan Stancek" > Cc: netdev@vger.kernel.org, "Florian Westphal" ,= bridge@lists.linux-foundation.org > Sent: Tuesday, 4 March, 2014 1:00:41 AM > Subject: Re: bridge is not forwaring ICMP6 neighbor solicitation to K= VM guest >=20 > Hi Jan, >=20 > On Mon, Mar 03, 2014 at 05:45:49PM -0500, Jan Stancek wrote: > > There is also bridge on host B. I assume that doesn't matter > > but I could set up host B without bridge if needed. >=20 > It can matter, but in this case it doesn't :). >=20 > > > What I'm curious about is, whether the guest receives > > > the MLD query and responds with an MLD report. I suspect that > > > either the bridge doesn't get an MLD report and therefore is > > > shutting down the according port or there's a bug in parsing the > > > MLD report in the bridge code. > >=20 > > I'm no expert in this area, but shouldn't neigh. solicit packets > > be forwarded to all ports regardless of any/no MLD reports? >=20 > That's the beauty of IPv6 Neighbor Discovery using these neat > solicited-node multicast addresses :). With IPv4 and ARP > requests there's no other way than flooding. But for IPv6 we know > in advance behind which bridge port someone interested in the > neighbor solicitation message might be (assuming MLD is working, > properly), allowing us to save bandwidth. >=20 > In this case, MLD is not working properly, the main issue is the > following: >=20 > Host B sends broken MLD queries, the source address should be an > IPv6 link-local one, not "100:0:600:0:78fb:100::". MLDv2 mandates > this (see RFC3810, section 5.1.14.: "Source Addresses for > Queries"). >=20 > Though I couldn't find that requirement for MLDv1, Linux ignores > MLDv1 queries with a non-link-local source address, too (see > net/ipv6/mcast.c, igmp6_event_query() ). So Linux never sends an > MLD report in reply to these broken queries. >=20 >=20 > The second "minor" but in this case fatal issue is, that the > bridge code doesn't have this link-local-src check, therefore > kicking the snooping into gear even though it shouldn't because we > don't have a _working_ querier. >=20 > I'm going to make a patch for the bridge code adding this sanity > check. >=20 >=20 > For the broken query, ok, it's your manually crafted query. But > did you see a query with such a bogus source address "in the > wild", too? (I'm curious how urgent this sanity check is) It's real packet I managed to capture during one such occurrence. I'm sending it with small C program over raw socket, but it's byte by byte exact copy of what I captured with tcpdump previously. I'm not sure how that packet came to existence. Based on IPv6 address it came from host B, but all host B was doing at the time was running RHEL6 with couple qemu-kvm instances. KVM guests were set up to use bridge, so I'm assuming if any of them crafted this packet, source IPv6 address would be different. Regards, Jan >=20 > Cheers, Linus >=20