ospfd: An OSPF Ack should be sent when P2MP reflooding is delayed.

When "ip ospf network point-to-multipoint delayed-reflooding" is configured,
LSAs received on an OSPF P2MP network are not reflooded. Since LSA reflooding
would normally serve as an implied LSA acknowledgment, an explicit OSPF ack
should be sent to avoid retransmission by the neighbor which orginally flooded
the LSA on the P2MP network.

Signed-off-by: Acee Lindem <acee@lindem.com>

ospfd/ospf_flood.c

@@ -797,7 +797,7 @@ int ospf_flood_through_interface(struct ospf_interface *oi,
 				ospf_ls_upd_send_lsa(nbr, lsa,
 						     OSPF_SEND_PACKET_DIRECT);
 		}
-	} else
+	} else {
 		/* If P2MP delayed reflooding is configured and the LSA was
 		   received from a neighbor on the P2MP interface, do not flood
 		   if back out on the interface. The LSA will be  retransmitted
@@ -815,9 +815,17 @@ int ospf_flood_through_interface(struct ospf_interface *oi,
 					inbr ? &(inbr->router_id)
 					     : &(oi->ospf->router_id),
 					IF_NAME(oi));
-		} else
-			ospf_ls_upd_send_lsa(oi->nbr_self, lsa,
-					     OSPF_SEND_PACKET_INDIRECT);
+			/*
+			 * If reflooding is delayed, a delayed acknowledge
+			 * should be sent since the LSA will not be immediately
+			 * reflooded and interpreted as an implied
+			 * acknowledgment by the sender.
+			 */
+			return 1;
+		}
+		ospf_ls_upd_send_lsa(oi->nbr_self, lsa,
+				     OSPF_SEND_PACKET_INDIRECT);
+	}
 
 	return 0;
 }