If dynamic routing was enabled on a logical router port with no
explicit IPs configured, then when the BGP control plane was learning
a route in the VRF monitored by that logical router port, ovn-northd
was generating syntactically incorrect logical flows (with
reg5 = (null) action) causing that route to never actually be
installed.

Reported-at: https://redhat.atlassian.net/browse/FDP-3583a
Fixes: 966ca1c919ce ("northd: Handle learned routes.")
Assisted-by: Claude Opus 4.6, Claude Code
Signed-off-by: Xavier Simonart <[email protected]>
---
 northd/northd.c     | 37 +++++++++++++++++++------------
 tests/ovn-northd.at | 53 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 76 insertions(+), 14 deletions(-)

diff --git a/northd/northd.c b/northd/northd.c
index 4162143de..0fdf6db42 100644
--- a/northd/northd.c
+++ b/northd/northd.c
@@ -12748,10 +12748,15 @@ add_ecmp_symmetric_reply_flows(struct lflow_table 
*lflows,
                   ds_cstr(route_match));
     ds_clear(&actions);
     ds_put_format(&actions, "ip.ttl--; flags.loopback = 1; "
-                  "eth.src = %s; %s = %s; outport = %s; next;",
-                  out_port->lrp_networks.ea_s,
-                  is_ipv4_nexthop ? REG_SRC_IPV4 : REG_SRC_IPV6,
-                  port_ip, out_port->json_key);
+                  "eth.src = %s; ",
+                  out_port->lrp_networks.ea_s);
+    if (port_ip) {
+        ds_put_format(&actions, "%s = %s; ",
+                      is_ipv4_nexthop ? REG_SRC_IPV4 : REG_SRC_IPV6,
+                      port_ip);
+    }
+    ds_put_format(&actions, "outport = %s; next;",
+                  out_port->json_key);
     ovn_lflow_add(lflows, od, S_ROUTER_IN_IP_ROUTING, 10300, ds_cstr(&match),
                   ds_cstr(&actions), lflow_ref, WITH_HINT(route->source_hint));
 
@@ -12891,13 +12896,15 @@ build_ecmp_route_flow(struct lflow_table *lflows,
         ds_put_format(&actions, "%s = ",
                       is_ipv4_nexthop ? REG_NEXT_HOP_IPV4 : REG_NEXT_HOP_IPV6);
         ipv6_format_mapped(route->nexthop, &actions);
-        ds_put_format(&actions, "; "
-                      "%s = %s; "
-                      "eth.src = %s; "
+        if (route->lrp_addr_s) {
+            ds_put_format(&actions, "; %s = %s",
+                          is_ipv4_nexthop ? REG_SRC_IPV4 : REG_SRC_IPV6,
+                          route->lrp_addr_s);
+        }
+        ds_put_format(&actions,
+                      "; eth.src = %s; "
                       "outport = %s; "
                       REGBIT_NEXTHOP_IS_IPV4" = %d; ",
-                      is_ipv4_nexthop ? REG_SRC_IPV4 : REG_SRC_IPV6,
-                      route->lrp_addr_s,
                       route->out_port->lrp_networks.ea_s,
                       route->out_port->json_key,
                       is_ipv4_nexthop);
@@ -12957,15 +12964,17 @@ add_route(struct lflow_table *lflows, const struct 
ovn_datapath *od,
                                            REG_NEXT_HOP_IPV6,
                           is_ipv4_prefix ? "4" : "6");
         }
-        ds_put_format(&common_actions, "; "
-                      "%s = %s; "
-                      "eth.src = %s; "
+        if (lrp_addr_s) {
+            ds_put_format(&common_actions, "; %s = %s",
+                          is_ipv4_nexthop ? REG_SRC_IPV4 : REG_SRC_IPV6,
+                          lrp_addr_s);
+        }
+        ds_put_format(&common_actions,
+                      "; eth.src = %s; "
                       "outport = %s; "
                       "flags.loopback = 1; "
                       REGBIT_NEXTHOP_IS_IPV4" = %d; "
                       "next;",
-                      is_ipv4_nexthop ? REG_SRC_IPV4 : REG_SRC_IPV6,
-                      lrp_addr_s,
                       op->lrp_networks.ea_s,
                       op->json_key,
                       is_ipv4_nexthop);
diff --git a/tests/ovn-northd.at b/tests/ovn-northd.at
index 501f78b67..6f8c1d30e 100644
--- a/tests/ovn-northd.at
+++ b/tests/ovn-northd.at
@@ -16317,6 +16317,59 @@ OVN_CLEANUP_NORTHD
 AT_CLEANUP
 ])
 
+OVN_FOR_EACH_NORTHD_NO_HV([
+AT_SETUP([dynamic-routing - learned routes on unnumbered LRP])
+AT_KEYWORDS([dynamic-routing])
+ovn_start
+
+check ovn-nbctl lr-add lr0
+check ovn-nbctl set Logical_Router lr0 option:dynamic-routing=true
+check ovn-nbctl lrp-add lr0 lrp1 00:00:00:00:ff:01 10.0.0.1/24
+check ovn-nbctl lrp-add lr0 lrp2 00:00:00:00:ff:02
+check ovn-nbctl --wait=sb lrp-add lr0 lrp3 00:00:00:00:ff:03
+datapath=$(fetch_column datapath_binding _uuid external_ids:name=lr0)
+lrp2=$(fetch_column port_binding _uuid logical_port=lrp2)
+lrp3=$(fetch_column port_binding _uuid logical_port=lrp3)
+
+check_uuid ovn-sbctl create Learned_Route \
+    datapath=$datapath                    \
+    logical_port=$lrp2                      \
+    ip_prefix=42.42.42.42/32              \
+    nexthop=192.168.2.42
+check ovn-nbctl --wait=sb sync
+
+ovn-sbctl dump-flows lr0 > lr0flows
+AT_CHECK([grep -F "42.42.42.42" lr0flows | grep -c '(null)'], [1], [0
+])
+
+AT_CHECK([grep -F "42.42.42.42" lr0flows | ovn_strip_lflows], [0], [dnl
+  table=??(lr_in_ip_routing   ), priority=258  , match=(reg7 == 0 && ip4.dst 
== 42.42.42.42/32), action=(ip.ttl--; reg8[[0..15]] = 0; reg0 = 192.168.2.42; 
eth.src = 00:00:00:00:ff:02; outport = "lrp2"; flags.loopback = 1; reg9[[9]] = 
1; next;)
+])
+
+check_uuid ovn-sbctl create Learned_Route \
+    datapath=$datapath                    \
+    logical_port=$lrp3                    \
+    ip_prefix=42.42.42.42/32              \
+    nexthop=192.168.3.42
+check ovn-nbctl --wait=sb sync
+
+ovn-sbctl dump-flows lr0 > lr0flows
+AT_CHECK([grep -c '(null)' lr0flows], [1], [0
+])
+
+AT_CHECK([grep -w "lr_in_ip_routing" lr0flows | grep -F "42.42.42.42" | 
ovn_strip_lflows], [0], [dnl
+  table=??(lr_in_ip_routing   ), priority=258  , match=(reg7 == 0 && ip4.dst 
== 42.42.42.42/32), action=(ip.ttl--; flags.loopback = 1; reg8[[0..15]] = 1; 
reg8[[16..31]] = select(1, 2);)
+])
+
+AT_CHECK([grep "lr_in_ip_routing_ecmp" lr0flows | grep "42" | sed -e 
's/reg8\[[16..31\]] == [[12]]/reg8\[[16..31\]] == ??/g' | ovn_strip_lflows | 
sort], [0], [dnl
+  table=??(lr_in_ip_routing_ecmp), priority=100  , match=(reg8[[0..15]] == 1 
&& reg8[[16..31]] == ??), action=(reg0 = 192.168.2.42; eth.src = 
00:00:00:00:ff:02; outport = "lrp2"; reg9[[9]] = 1; next;)
+  table=??(lr_in_ip_routing_ecmp), priority=100  , match=(reg8[[0..15]] == 1 
&& reg8[[16..31]] == ??), action=(reg0 = 192.168.3.42; eth.src = 
00:00:00:00:ff:03; outport = "lrp3"; reg9[[9]] = 1; next;)
+])
+
+OVN_CLEANUP_NORTHD
+AT_CLEANUP
+])
+
 OVN_FOR_EACH_NORTHD_NO_HV([
 AT_SETUP([dynamic-routing - route learning cleanup - router recreation])
 AT_KEYWORDS([dynamic-routing])
-- 
2.47.1

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