ovn-controller: Fix conntrack zone in gateway routers.

The gateway router was using the ct_next action to
reassemble packets.  But ct_next action by default would
use the zone allocated for a logical port and in case of
gateway routers that value was zero.  This would make
the flow use the default zone of zero.  This had some
unintended consequences as the zone used to track packets
and the zone used to eventually commit it (DNAT zone)
was different.  As a result, a packet would never have ct.est set.

With this commit, when ct_next action is used in a gateway
router, we use the DNAT zone.  This is similar to the
strategy used in commit c2e954a (ovn-controller: Datapath
based conntrack zone for load-balancing.)

Signed-off-by: Gurucharan Shetty <[email protected]>
Acked-by: Ben Pfaff <[email protected]>

ovn/lib/actions.c

@@ -551,7 +551,8 @@ encode_CT_NEXT(const struct ovnact_next *next,
 {
     struct ofpact_conntrack *ct = ofpact_put_CT(ofpacts);
     ct->recirc_table = ep->first_ptable + next->ltable;
-    ct->zone_src.field = mf_from_id(MFF_LOG_CT_ZONE);
+    ct->zone_src.field = ep->is_switch ? mf_from_id(MFF_LOG_CT_ZONE)
+                            : mf_from_id(MFF_LOG_DNAT_ZONE);
     ct->zone_src.ofs = 0;
     ct->zone_src.n_bits = 16;
     ofpact_finish(ofpacts, &ct->ofpact);

ovn/ovn-sb.xml

@@ -1037,9 +1037,11 @@
             As a side effect, IP fragments will be reassembled for matching.
             If a fragmented packet is output, then it will be sent with any
             overlapping fragments squashed.  The connection tracking state is
-            scoped by the logical port, so overlapping addresses may be used.
-            To allow traffic related to the matched flow, execute
-            <code>ct_commit</code>.
+            scoped by the logical port when the action is used in a flow for
+            a logical switch, so overlapping addresses may be used.  To allow
+            traffic related to the matched flow, execute <code>ct_commit
+            </code>.  Connection tracking state is scoped by the logical
+            topology when the action is used in a flow for a router.
           </p>
 
           <p>