diff --git a/sys/net/route/route_ctl.c b/sys/net/route/route_ctl.c
--- a/sys/net/route/route_ctl.c
+++ b/sys/net/route/route_ctl.c
@@ -785,7 +785,7 @@
     int op_flags, struct rib_cmd_info *rc)
 {
 	struct route_nhop_data rnd_orig;
-	struct nhop_object *nh;
+	struct nhop_object *nh, *nh_orig;
 	struct rtentry *rt_orig;
 	int error = 0;
 
@@ -829,6 +829,23 @@
 		goto out;
 	}
 
+	nh_orig = rt_orig->rt_nhop;
+	/*
+	 * For append or create, if both rt have gateway flag and they gw addrs
+	 * are the same, they actually are the same route. We can either return
+	 * existing erro or change to do replace that can save the new property.
+	 * Here we prefer to return error and ignore the property change,
+	 * because it can inform the caller error, if he want to change the
+	 * existing route propery, he should select RTM_REPLACE op_flag
+	 */
+	if ((nh->nh_flags & NHF_GATEWAY) &&
+	    (nh_orig->nh_flags & NHF_GATEWAY) &&
+	    match_nhop_gw(nh, &rt_orig->rt_nhop->gw_sa)) {
+		RIB_WUNLOCK(rnh);
+		error = EEXIST;
+		goto out;
+	}
+
 	RIB_WUNLOCK(rnh);
 
 #ifdef ROUTE_MPATH