On Mon, May 13, 2024 at 9:00 AM Dumitru Ceara <[email protected]> wrote: > > On 5/4/24 11:38, Vasyl Saienko wrote: > > Hello Numan > > > > Thanks for review and feedback. > > > > On Fri, May 3, 2024 at 7:14 PM Numan Siddique <[email protected]> wrote: > > > >> On Mon, Apr 22, 2024 at 2:54 AM Vasyl Saienko <[email protected]> > >> wrote: > >>> > >>> Reply only if target ethernet address is broadcast, if > >>> address is specified explicitly do noting to let target > >>> reply by itself. This technique allows to monitor target > >>> aliveness with arping. > >> > >> Thanks for the patch. > >> > >> This patch does change the behavior of OVN. Having ARP responder > >> flows avoids tunnelling the request packet if the destination is on a > >> different compute node. > >> But I don't think its a big deal. > >> > >> You are totally correct that the ARP responder allows limiting ARP > > broadcast traffic between nodes. Normally ARP requests are sent to > > broadcast ff:ff:ff:ff:ff:ff ethernet, as the protocol is designed to > > identify ethernet addresses for known IP addresses. In this case since > > traffic is broadcast it will be flooded among all nodes if ARP responder is > > not applied. At the same time the client may specify the target > > ethernet address as unicast (in this case a broadcast storm will not > > happen, as the destination ethernet address is unicast). > > > > In OpenStack we use unicast ARP requests as a way to monitor VM aliveness > > from remote locations to make sure there are no issues with > > flows/underlying networking infra between nodes. We use ARPs due to several > > reasons: > > 1. This protocol is mandatory and can't be disabled on the target machine > > (which guarantees that the target VM will always reply to ARPs if it is > > alive) > > 2. This protocol is not filtered by firewalls/security groups as it is > > mandatory for network workability > > 3. We can't use upper layers protocols such as ICMP as they will require > > specific firewall rules inside VMs, and we do not control VMs in cloud > > cases, but still need to monitor infrastructure aliveness. > > > > If ARP responder replies to requests with broadcast and unicast target > > ethernet address, we can't use this technique for monitoring, as even if > > target VM is down (not necessary that ovn port is down, the VM may stuck or > > be in kernel panic for example, or datapath between monitoring tool and VM > > is broken) the ARP responder will do reply to our request so we can't > > identify if VM is really accessible or not as we will always got replies > > from local ARP responder. At the same time there is no need to set up ARP > > responder for requests with a unicast ethernet address, as they will not > > generate broadcast storms by design (they are unicasts). > > > > Right, this sounds acceptable to me too. > > > > >> 1. Accept your patch > >> 2. Use the NB Global option - "ignore_lsp_down" and set it to false, > >> so that ovn-northd will install the ARP responder flows only if the > >> logical port is up. > >> > > This option will not allow catching a situation when there is an issue in > > datapath between monitoring software and VM located on another node, for > > example issues with flows or some underlying networking problems. > > > > Have you considered this approach for your use case ? > >> 3. Add another global option - "disable_arp_responder" which when set > >> to true, ovn-northd will not install ARP responder flows. > >> > >> Disabling ARP responder for ports completely will allow broadcast storms > > for ARP requests. Which we would like to avoid, but enable the possibility > > to monitor infrastructure aliveness. > > > > > >> Given that OpenStack neutron ml2ovs uses ARP responder flows only for > >> broad cast my preference would be (1). > >> > >> I'd like to know other's opinion on this. > >> > > I'd accept the patch too so I'd go for (1). > > Regards, > Dumitru > > >> Thanks > >> Numan > >> > >>> > >>> Closes #239 > >>> > >>> Signed-off-by: Vasyl Saienko <[email protected]> > >>> --- > >>> northd/northd.c | 11 +++++++++-- > >>> tests/ovn-northd.at | 4 ++-- > >>> 2 files changed, 11 insertions(+), 4 deletions(-) > >>> > >>> diff --git a/northd/northd.c b/northd/northd.c > >>> index 37f443e70..e80e1885d 100644 > >>> --- a/northd/northd.c > >>> +++ b/northd/northd.c > >>> @@ -8832,8 +8832,15 @@ build_lswitch_arp_nd_responder_known_ips(struct > >> ovn_port *op, > >>> for (size_t i = 0; i < op->n_lsp_addrs; i++) { > >>> for (size_t j = 0; j < op->lsp_addrs[i].n_ipv4_addrs; j++) { > >>> ds_clear(match); > >>> - ds_put_format(match, "arp.tpa == %s && arp.op == 1", > >>> - op->lsp_addrs[i].ipv4_addrs[j].addr_s); > >>> + /* NOTE(vsaienko): Do not reply on unicast ARPs, forward > >>> + * them to the target to have ability to monitor target > >>> + * aliveness via ARPs. > >>> + */ > >>> + ds_put_format(match, > >>> + "arp.tpa == %s && " > >>> + "arp.op == 1 && " > >>> + "eth.dst == ff:ff:ff:ff:ff:ff", > >>> + op->lsp_addrs[i].ipv4_addrs[j].addr_s); > >>> ds_clear(actions); > >>> ds_put_format(actions, > >>> "eth.dst = eth.src; " > >>> diff --git a/tests/ovn-northd.at b/tests/ovn-northd.at > >>> index be006fb32..4162196f4 100644 > >>> --- a/tests/ovn-northd.at > >>> +++ b/tests/ovn-northd.at > >>> @@ -9283,9 +9283,9 @@ AT_CAPTURE_FILE([S1flows]) > >>> > >>> AT_CHECK([grep -e "ls_in_arp_rsp" S1flows | ovn_strip_lflows], [0], [dnl > >>> table=??(ls_in_arp_rsp ), priority=0 , match=(1), > >> action=(next;) > >>> - table=??(ls_in_arp_rsp ), priority=100 , match=(arp.tpa == > >> 192.168.0.10 && arp.op == 1 && inport == "S1-vm1"), action=(next;) > >>> + table=??(ls_in_arp_rsp ), priority=100 , match=(arp.tpa == > >> 192.168.0.10 && arp.op == 1 && eth.dst == ff:ff:ff:ff:ff:ff && inport == > >> "S1-vm1"), action=(next;) > >>> table=??(ls_in_arp_rsp ), priority=100 , match=(nd_ns && > >> ip6.dst == {fd00::10, ff02::1:ff00:10} && nd.target == fd00::10 && inport > >> == "S1-vm1"), action=(next;) > >>> - table=??(ls_in_arp_rsp ), priority=50 , match=(arp.tpa == > >> 192.168.0.10 && arp.op == 1), action=(eth.dst = eth.src; eth.src = > >> 50:54:00:00:00:10; arp.op = 2; /* ARP reply */ arp.tha = arp.sha; arp.sha = > >> 50:54:00:00:00:10; arp.tpa = arp.spa; arp.spa = 192.168.0.10; outport = > >> inport; flags.loopback = 1; output;) > >>> + table=??(ls_in_arp_rsp ), priority=50 , match=(arp.tpa == > >> 192.168.0.10 && arp.op == 1 && eth.dst == ff:ff:ff:ff:ff:ff), > >> action=(eth.dst = eth.src; eth.src = 50:54:00:00:00:10; arp.op = 2; /* ARP > >> reply */ arp.tha = arp.sha; arp.sha = 50:54:00:00:00:10; arp.tpa = arp.spa; > >> arp.spa = 192.168.0.10; outport = inport; flags.loopback = 1; output;) > >>> table=??(ls_in_arp_rsp ), priority=50 , match=(nd_ns && > >> ip6.dst == {fd00::10, ff02::1:ff00:10} && nd.target == fd00::10), > >> action=(nd_na { eth.src = 50:54:00:00:00:10; ip6.src = fd00::10; nd.target > >> = fd00::10; nd.tll = 50:54:00:00:00:10; outport = inport; flags.loopback = > >> 1; output; };)
I took a look at this patch. There's one problem with this patch. If you see the test case changes, this patch now replaces the below logical flow table=??(ls_in_arp_rsp ), priority=100 , match=(arp.tpa == 192.168.0.10 && arp.op == 1 && inport == "S1-vm1"), action=(next;) with table=??(ls_in_arp_rsp ), priority=100 , match=(arp.tpa == 192.168.0.10 && arp.op == 1 && eth.dst == ff:ff:ff:ff:ff:ff && inport == "S1-vm1"), action=(next;) This is wrong. If there is an ARP request packet entering from a router port to the switch, we were advancing this packet to the next stage. But now, we only advance if it's a broadcast pkt. Please correct this. Also please update the logical flow documentation in ovn-northd.8.xml for the "ls_in_arp_rsp" stage. I think its also worth mentioning this change in the NEWS file. Thanks Numan > >>> ]) > >>> > >>> -- > >>> 2.40.1 > >>> > >>> _______________________________________________ > >>> dev mailing list > >>> [email protected] > >>> https://mail.openvswitch.org/mailman/listinfo/ovs-dev > >>> > >> > > > > > > _______________________________________________ > dev mailing list > [email protected] > https://mail.openvswitch.org/mailman/listinfo/ovs-dev _______________________________________________ dev mailing list [email protected] https://mail.openvswitch.org/mailman/listinfo/ovs-dev
