From f9ffa252f67b9d557641c0aa76399ea83f7007ab Mon Sep 17 00:00:00 2001
From: Laurent Deru <laurent.deru@cetic.be>
Date: Wed, 16 Mar 2016 13:12:20 +0100
Subject: [PATCH] Reject parents with invalid rank

---
 core/net/rpl/rpl-dag.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/core/net/rpl/rpl-dag.c b/core/net/rpl/rpl-dag.c
index 1eb6775c1..c4f3be14f 100644
--- a/core/net/rpl/rpl-dag.c
+++ b/core/net/rpl/rpl-dag.c
@@ -865,7 +865,10 @@ best_parent(rpl_dag_t *dag, int fresh_only)
   for(p = nbr_table_head(rpl_parents); p != NULL; p = nbr_table_next(rpl_parents, p)) {
 
     /* Exclude parents from other DAGs or announcing an infinite rank */
-    if(p->dag != dag || p->rank == INFINITE_RANK) {
+    if(p->dag != dag || p->rank == INFINITE_RANK || p->rank < ROOT_RANK(dag->instance)) {
+      if(p->rank < ROOT_RANK(dag->instance)) {
+        PRINTF("RPL: Parent has invalid rank\n");
+      }
       continue;
     }