Index: src/plugins/rt_topo/crbs_route.c
===================================================================
--- src/plugins/rt_topo/crbs_route.c	(revision 1443)
+++ src/plugins/rt_topo/crbs_route.c	(revision 1444)
@@ -320,7 +320,6 @@
 
 		while(a->grbs_idx < 5) {
 			if (crbs_trace_ast) printf(" try from %s P%ld to P%ld", from_type, curr->pt->uid, pt->gpt->uid);
-
 			if (crbs->disable_vconcave) {
 				if (a->grbs_idx < 3)
 					a->grbs_idx = 3;
@@ -430,7 +429,7 @@
 	usrch_a_star_t ast = {0};
 	usrch_a_star_node_t *it;
 	grbs_detached_addr_t addr_tmp[2];
-	grbs_detached_addr_t *first, *da;
+	grbs_detached_addr_t *first, *da, *last;
 	grbs_addr_t *na, *pa, *firsta, *lasta;
 	crbs_2net_t *tn;
 	int res = -1;
@@ -451,6 +450,26 @@
 		htad_clear(&crbs->addrs);
 	}
 
+	crbs->first = first = addr_new_point(crbs, ctn->cstart, &addr_tmp[0]);
+	crbs->target = ast.target = last = addr_new_point(crbs, ctn->cend, &addr_tmp[1]);
+
+#warning TODO: per net wire thickness
+	if (ctn->gtn == NULL) {
+		crbs->routing_tn = ctn->gtn = grbs_2net_new(&crbs->grbs, rt_topo_cfg.wire_thick, rt_topo_cfg.wire_clr);
+		crbs->routing_tn->user_data = ctn;
+	}
+	else
+		crbs->routing_tn = ctn->gtn;
+
+	/* check if it is possible to start and end the twonet as incident line in
+	   start and end point */
+	if ((grbs_is_target_pt_routable(&crbs->grbs, crbs->routing_tn, first->pt) == 0) || (grbs_is_target_pt_routable(&crbs->grbs, crbs->routing_tn, last->pt) == 0)) {
+		printf("  Can not route from start or to end because of incident line end cap collision\n");
+		res = -1;
+		goto err;
+	}
+
+
 	ast.heuristic = crbs_ast_heuristic;
 	ast.cost = crbs_ast_cost;
 	ast.neighbor_pre = crbs_ast_neighbor_pre;
@@ -461,17 +480,6 @@
 
 	cnt_grbs++;
 
-	crbs->first = first = addr_new_point(crbs, ctn->cstart, &addr_tmp[0]);
-	crbs->target = ast.target = addr_new_point(crbs, ctn->cend, &addr_tmp[1]);
-
-#warning TODO: per net wire thickness
-	if (ctn->gtn == NULL) {
-		crbs->routing_tn = ctn->gtn = grbs_2net_new(&crbs->grbs, rt_topo_cfg.wire_thick, rt_topo_cfg.wire_clr);
-		crbs->routing_tn->user_data = ctn;
-	}
-	else
-		crbs->routing_tn = ctn->gtn;
-
 	printf(" route_net: from P%ld to P%ld (step 3_GRBS_routed_%d)\n",
 		((crbs_point_t *)(ctn->cstart->data))->gpt->uid,
 		((crbs_point_t *)(ctn->cend->data))->gpt->uid,