[ovs-dev] [RFC ovn 1/6] ovn-northd: Support optionally avoid static neighbor flows in routers.

[Han Zhou]

Support option:dynamic_neigh_routers for logical routers, so that in
particular use cases static neighbor flows are not prepopulated IP
addresses belonging to neighbor router ports, to avoid flow exploding
problem reported for ovn-kubernetes large scale setup.

Reported-by: Girish Moodalbail <gmoodalbail at gmail.com>
Reported-at: https://mail.openvswitch.org/pipermail/ovs-discuss/2020-May/049995.html
Signed-off-by: Han Zhou <hzhou at ovn.org>
---
 northd/ovn-northd.8.xml |  5 ++++-
 northd/ovn-northd.c     |  6 ++++++
 ovn-nb.xml              | 13 +++++++++++++
 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/northd/ovn-northd.8.xml b/northd/ovn-northd.8.xml
index dc56de2..87e90d1 100644
--- a/northd/ovn-northd.8.xml
+++ b/northd/ovn-northd.8.xml
@@ -2659,7 +2659,10 @@ outport = <var>P</var>;
           <code>Logical_Switch_Port</code> table.  For router ports
           connected to other logical routers, MAC bindings can be known
           statically from the <code>mac</code> and <code>networks</code>
-          column in the <code>Logical_Router_Port</code> table.
+          column in the <code>Logical_Router_Port</code> table.  (Note: the
+          flow is NOT installed for the IP addresses that belong to a neighbor
+          logical router port if the current router has the
+          <code>options:dynamic_neigh_routers</code> set to <code>true</code>)
         </p>
 
         <p>
diff --git a/northd/ovn-northd.c b/northd/ovn-northd.c
index eb78f31..d8197ab 100644
--- a/northd/ovn-northd.c
+++ b/northd/ovn-northd.c
@@ -9971,6 +9971,12 @@ build_lrouter_flows(struct hmap *datapaths, struct hmap *ports,
                 continue;
             }
 
+            if (peer->od->nbr &&
+                smap_get_bool(&peer->od->nbr->options,
+                              "dynamic_neigh_routers", false)) {
+                continue;
+            }
+
             for (size_t i = 0; i < op->od->n_router_ports; i++) {
                 const char *router_port_name = smap_get(
                                     &op->od->router_ports[i]->nbsp->options,
diff --git a/ovn-nb.xml b/ovn-nb.xml
index acf5648..c0222ca 100644
--- a/ovn-nb.xml
+++ b/ovn-nb.xml
@@ -1845,6 +1845,19 @@
           connected to the logical router. Default: False.
         </p>
       </column>
+      <column name="options" key="dynamic_neigh_routers" type='{"type": "boolean"}'>
+        <p>
+          If set to <code>true</code>, the router will resolve neighbor
+          routers' MAC addresses only by dynamic ARP/ND, instead of
+          prepopulating static mappings for all neighbor routers in the ARP/ND
+          Resolution stage.  This reduces number of flows, but requires ARP/ND
+          messages to resolve the IP-MAC bindings when needed.  It is
+          <code>false</code> by default.  It is recommended to set to
+          <code>true</code> when a large number of logical routers are
+          connected to the same logical switch but most of them never need to
+          send traffic between each other.
+        </p>
+      </column>
     </group>
 
     <group title="Common Columns">
-- 
2.1.0