Jan Stancek
2014-Mar-04 08:02 UTC
[Bridge] bridge is not forwaring ICMP6 neighbor solicitation to KVM guest
----- Original Message -----> From: "Linus L?ssing" <linus.luessing at web.de> > To: "Jan Stancek" <jstancek at redhat.com> > Cc: netdev at vger.kernel.org, "Florian Westphal" <fwestpha at redhat.com>, bridge at lists.linux-foundation.org > Sent: Tuesday, 4 March, 2014 1:00:41 AM > Subject: Re: bridge is not forwaring ICMP6 neighbor solicitation to KVM guest > > Hi Jan, > > 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. > > It can matter, but in this case it doesn't :). > > > > 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. > > > > I'm no expert in this area, but shouldn't neigh. solicit packets > > be forwarded to all ports regardless of any/no MLD reports? > > 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. > > In this case, MLD is not working properly, the main issue is the > following: > > 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"). > > 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. > > > 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. > > I'm going to make a patch for the bridge code adding this sanity > check. > > > 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> > Cheers, Linus >
Linus Lüssing
2014-Mar-04 10:52 UTC
[Bridge] bridge is not forwaring ICMP6 neighbor solicitation to KVM guest
Hi Jan, On Tue, Mar 04, 2014 at 03:02:36AM -0500, Jan Stancek wrote:> > 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. >Ah, okay. Can you check whether it maybe came from the querier code in the Linux bridge on host B? Is "cat /sys/class/net/br0/bridge/multicast_querier" 1? Can you isolate host B and disable any multicast router daemon on it? Then check again, if you still see these queries. What kernel version is running on host B? Cheers, Linus -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 819 bytes Desc: Digital signature URL: <http://lists.linuxfoundation.org/pipermail/bridge/attachments/20140304/09a91b47/attachment.sig>
Jan Stancek
2014-Mar-04 11:06 UTC
[Bridge] bridge is not forwaring ICMP6 neighbor solicitation to KVM guest
----- Original Message -----> From: "Linus L?ssing" <linus.luessing at web.de> > To: "Jan Stancek" <jstancek at redhat.com> > Cc: netdev at vger.kernel.org, "Florian Westphal" <fwestpha at redhat.com>, bridge at lists.linux-foundation.org > Sent: Tuesday, 4 March, 2014 11:52:54 AM > Subject: Re: bridge is not forwaring ICMP6 neighbor solicitation to KVM guest > > Hi Jan, > > On Tue, Mar 04, 2014 at 03:02:36AM -0500, Jan Stancek wrote: > > > 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. > > > > Ah, okay. Can you check whether it maybe came from the querier > code in the Linux bridge on host B? Is > "cat /sys/class/net/br0/bridge/multicast_querier" 1?# cat /sys/class/net/br0/bridge/multicast_querier cat: /sys/class/net/br0/bridge/multicast_querier: No such file or directory> Can you isolate host B and disable any multicast router daemon on it? Then > check again, if you still see these queries.Besides those cases where I sent it by myself, I haven't seen host B send that query for couple days now.> What kernel version is running on host B?2.6.32-279.42.1.el6.x86_64 It's a RHEL6.3.z kernel.> Where does Linux use :: for queries?I'm not sure if it's Linux (I'm trying to locate that system by MAC), but I see packets like these on my network every ~125 seconds: No. Time Source Destination Protocol Length Info 22675 1334.751135 :: ff02::1 ICMPv6 86 Multicast Listener Query Internet Control Message Protocol v6 Type: Multicast Listener Query (130) Code: 0 Checksum: 0x7ac1 [correct] Maximum Response Delay [ms]: 1000 Reserved: 0000 Multicast Address: :: (::) Regards, Jan
Jan Stancek
2014-Mar-04 11:06 UTC
Re: bridge is not forwaring ICMP6 neighbor solicitation to KVM guest
----- Original Message -----> From: "Linus Lüssing" <linus.luessing@web.de> > To: "Jan Stancek" <jstancek@redhat.com> > Cc: netdev@vger.kernel.org, "Florian Westphal" <fwestpha@redhat.com>, bridge@lists.linux-foundation.org > Sent: Tuesday, 4 March, 2014 11:52:54 AM > Subject: Re: bridge is not forwaring ICMP6 neighbor solicitation to KVM guest > > Hi Jan, > > On Tue, Mar 04, 2014 at 03:02:36AM -0500, Jan Stancek wrote: > > > 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. > > > > Ah, okay. Can you check whether it maybe came from the querier > code in the Linux bridge on host B? Is > "cat /sys/class/net/br0/bridge/multicast_querier" 1?# cat /sys/class/net/br0/bridge/multicast_querier cat: /sys/class/net/br0/bridge/multicast_querier: No such file or directory> Can you isolate host B and disable any multicast router daemon on it? Then > check again, if you still see these queries.Besides those cases where I sent it by myself, I haven't seen host B send that query for couple days now.> What kernel version is running on host B?2.6.32-279.42.1.el6.x86_64 It's a RHEL6.3.z kernel.> Where does Linux use :: for queries?I'm not sure if it's Linux (I'm trying to locate that system by MAC), but I see packets like these on my network every ~125 seconds: No. Time Source Destination Protocol Length Info 22675 1334.751135 :: ff02::1 ICMPv6 86 Multicast Listener Query Internet Control Message Protocol v6 Type: Multicast Listener Query (130) Code: 0 Checksum: 0x7ac1 [correct] Maximum Response Delay [ms]: 1000 Reserved: 0000 Multicast Address: :: (::) Regards, Jan