diff --git a/core/net/ipv6/uip-ds6-nbr.c b/core/net/ipv6/uip-ds6-nbr.c
index b8666a14a..e5c6167e5 100644
--- a/core/net/ipv6/uip-ds6-nbr.c
+++ b/core/net/ipv6/uip-ds6-nbr.c
@@ -83,7 +83,7 @@ uip_ds6_nbr_add(const uip_ipaddr_t *ipaddr, const uip_lladdr_t *lladdr,
                 void *data)
 {
   uip_ds6_nbr_t *nbr = nbr_table_add_lladdr(ds6_neighbors, (linkaddr_t*)lladdr
-                                            ,reason, data);
+                                            , reason, data);
   if(nbr) {
     uip_ipaddr_copy(&nbr->ipaddr, ipaddr);
 #if UIP_ND6_SEND_NA || UIP_ND6_SEND_RA || !UIP_CONF_ROUTER
diff --git a/core/net/ipv6/uip-ds6-route.c b/core/net/ipv6/uip-ds6-route.c
index 21ce38f64..043ca78d4 100644
--- a/core/net/ipv6/uip-ds6-route.c
+++ b/core/net/ipv6/uip-ds6-route.c
@@ -207,8 +207,15 @@ uip_ds6_route_next(uip_ds6_route_t *r)
 }
 /*---------------------------------------------------------------------------*/
 int
-uip_ds6_route_is_nexthop(const uip_lladdr_t *lladdr)
+uip_ds6_route_is_nexthop(const uip_ipaddr_t *ipaddr)
 {
+  const uip_lladdr_t *lladdr;
+  lladdr = uip_ds6_nbr_lladdr_from_ipaddr(ipaddr);
+
+  if(lladdr == NULL) {
+    return 0;
+  }
+
   return nbr_table_get_from_lladdr(nbr_routes, (linkaddr_t *)lladdr) != NULL;
 }
 /*---------------------------------------------------------------------------*/
diff --git a/core/net/ipv6/uip-ds6-route.h b/core/net/ipv6/uip-ds6-route.h
index 7a5d805f0..6ca533c9b 100644
--- a/core/net/ipv6/uip-ds6-route.h
+++ b/core/net/ipv6/uip-ds6-route.h
@@ -124,6 +124,9 @@ void uip_ds6_notification_rm(struct uip_ds6_notification *n);
 #define RPL_ROUTE_SET_DAO_NACKED(route) do {                            \
     (route)->state.state_flags |= RPL_ROUTE_ENTRY_DAO_NACK;             \
   } while(0)
+#define RPL_ROUTE_CLEAR_DAO_NACKED(route) do {                          \
+    (route)->state.state_flags &= ~RPL_ROUTE_ENTRY_DAO_NACK;            \
+  } while(0)
 
 #define RPL_ROUTE_CLEAR_DAO(route) do {                                 \
     (route)->state.state_flags &= ~(RPL_ROUTE_ENTRY_DAO_NACK|RPL_ROUTE_ENTRY_DAO_PENDING); \
@@ -200,7 +203,7 @@ uip_ipaddr_t *uip_ds6_route_nexthop(uip_ds6_route_t *);
 int uip_ds6_route_num_routes(void);
 uip_ds6_route_t *uip_ds6_route_head(void);
 uip_ds6_route_t *uip_ds6_route_next(uip_ds6_route_t *);
-int uip_ds6_route_is_nexthop(const uip_lladdr_t *lladdr);
+int uip_ds6_route_is_nexthop(const uip_ipaddr_t *ipaddr);
 /** @} */
 
 #endif /* UIP_DS6_ROUTE_H */
diff --git a/core/net/nbr-table.h b/core/net/nbr-table.h
index cc58c2f80..88a90a46c 100644
--- a/core/net/nbr-table.h
+++ b/core/net/nbr-table.h
@@ -83,7 +83,7 @@ typedef enum {
 	NBR_TABLE_REASON_ROUTE,
 	NBR_TABLE_REASON_IPV6_ND,
 	NBR_TABLE_REASON_MAC,
-        NBR_TABLE_REASON_LLSEC
+	NBR_TABLE_REASON_LLSEC
 } nbr_table_reason_t;
 
 /** \name Neighbor tables: register and loop through table elements */
diff --git a/core/net/rpl/rpl-dag.c b/core/net/rpl/rpl-dag.c
index 034678ff5..27f781bdf 100644
--- a/core/net/rpl/rpl-dag.c
+++ b/core/net/rpl/rpl-dag.c
@@ -899,6 +899,18 @@ rpl_move_parent(rpl_dag_t *dag_src, rpl_dag_t *dag_dst, rpl_parent_t *parent)
   parent->dag = dag_dst;
 }
 /*---------------------------------------------------------------------------*/
+int
+rpl_has_downward_route(void)
+{
+  int i;
+  for(i = 0; i < RPL_MAX_INSTANCES; ++i) {
+    if(instance_table[i].used && instance_table[i].has_downward_route) {
+      return 1;
+    }
+  }
+  return 0;
+}
+/*---------------------------------------------------------------------------*/
 rpl_dag_t *
 rpl_get_any_dag(void)
 {
@@ -1157,8 +1169,6 @@ global_repair(uip_ipaddr_t *from, rpl_dag_t *dag, rpl_dio_t *dio)
   RPL_STAT(rpl_stats.global_repairs++);
 }
 
-void rpl_set_downward_link(uint8_t link);
-
 /*---------------------------------------------------------------------------*/
 void
 rpl_local_repair(rpl_instance_t *instance)
@@ -1177,8 +1187,8 @@ rpl_local_repair(rpl_instance_t *instance)
     }
   }
 
-  /* no downward link anymore */
-  rpl_set_downward_link(0);
+  /* no downward route anymore */
+  instance->has_downward_route = 0;
 
   rpl_reset_dio_timer(instance);
   /* Request refresh of DAO registrations next DIO */
diff --git a/core/net/rpl/rpl-icmp6.c b/core/net/rpl/rpl-icmp6.c
index 2296f0d97..0f20ddb67 100644
--- a/core/net/rpl/rpl-icmp6.c
+++ b/core/net/rpl/rpl-icmp6.c
@@ -90,7 +90,6 @@ void RPL_DEBUG_DAO_OUTPUT(rpl_parent_t *);
 #endif
 
 static uint8_t dao_sequence = RPL_LOLLIPOP_INIT;
-static uint8_t downward = 0;
 
 extern rpl_of_t RPL_OF;
 
@@ -105,18 +104,6 @@ UIP_ICMP6_HANDLER(dao_handler, ICMP6_RPL, RPL_CODE_DAO, dao_input);
 UIP_ICMP6_HANDLER(dao_ack_handler, ICMP6_RPL, RPL_CODE_DAO_ACK, dao_ack_input);
 /*---------------------------------------------------------------------------*/
 
-void
-rpl_set_downward_link(uint8_t link)
-{
-  downward = link;
-}
-
-int
-rpl_has_downward_link()
-{
-  return downward;
-}
-
 #if RPL_WITH_DAO_ACK
 static uip_ds6_route_t *
 find_route_entry_by_dao_ack(uint8_t seq)
@@ -215,8 +202,10 @@ rpl_icmp6_update_nbr_table(uip_ipaddr_t *from, nbr_table_reason_t reason, void *
 
   if(nbr != NULL) {
 #if UIP_ND6_SEND_NA
-    /* set reachable timer if we added or found the nbr entry */
+    /* set reachable timer if we added or found the nbr entry - and update
+       neighbor entry to reachable to avoid sending NS/NA, etc.  */
     stimer_set(&nbr->reachable, UIP_ND6_REACHABLE_TIME / 1000);
+    nbr->state = NBR_REACHABLE;
 #endif /* UIP_ND6_SEND_NA */
   }
   return nbr;
@@ -833,7 +822,7 @@ dao_input(void)
     if(flags & RPL_DAO_K_FLAG) {
       /* signal the failure to add the node */
       dao_ack_output(instance, &dao_sender_addr, sequence,
-		     is_root ? RPL_DAO_ACK_UNABLE_TO_ACCEPT_ROOT :
+		     is_root ? RPL_DAO_ACK_UNABLE_TO_ADD_ROUTE_AT_ROOT :
 		     RPL_DAO_ACK_UNABLE_TO_ACCEPT);
     }
     goto discard;
@@ -846,7 +835,7 @@ dao_input(void)
     if(flags & RPL_DAO_K_FLAG) {
       /* signal the failure to add the node */
       dao_ack_output(instance, &dao_sender_addr, sequence,
-		     is_root ? RPL_DAO_ACK_UNABLE_TO_ACCEPT_ROOT :
+		     is_root ? RPL_DAO_ACK_UNABLE_TO_ADD_ROUTE_AT_ROOT :
 		     RPL_DAO_ACK_UNABLE_TO_ACCEPT);
     }
     goto discard;
@@ -864,8 +853,12 @@ fwd_dao:
     int should_ack = 0;
 
     if(flags & RPL_DAO_K_FLAG) {
-      /* check if this route is already installed and we can ack now! */
-      /* not pending - and same seq-no means that we can ack.         */
+      /*
+       * check if this route is already installed and we can ack now!
+       * not pending - and same seq-no means that we can ack.
+       * (e.g. the route is installed already so it will not take any
+       * more room that it already takes - so should be ok!)
+       */
       if((!RPL_ROUTE_IS_DAO_PENDING(rep) &&
           rep->state.dao_seqno_in == sequence) ||
           dag->rank == ROOT_RANK(instance)) {
@@ -992,7 +985,7 @@ dao_output(rpl_parent_t *parent, uint8_t lifetime)
 #else
    /* We know that we have tried to register so now we are assuming
       that we have a down-link - unless this is a zero lifetime one */
-  rpl_set_downward_link(lifetime != RPL_ZERO_LIFETIME);
+  parent->dag->instance->has_downward_route = lifetime != RPL_ZERO_LIFETIME;
 #endif /* RPL_WITH_DAO_ACK */
 
   /* Sending a DAO with own prefix as target */
@@ -1122,9 +1115,7 @@ dao_ack_input(void)
 
   parent = rpl_find_parent(instance->current_dag, &UIP_IP_BUF->srcipaddr);
   if(parent == NULL) {
-    /* not a known instance - did we switch?? */
-    //    PRINTF("RPL: Received a DAO ACK from a not joined instance: %d",
-    //	   instance_id);
+    /* not a known instance - drop the packet and ignore */
     uip_clear_buf();
     return;
   }
@@ -1136,7 +1127,7 @@ dao_ack_input(void)
   PRINTF("\n");
 
   if(sequence == instance->my_dao_seqno) {
-    rpl_set_downward_link(status < 128);
+    instance->has_downward_route = status < 128;
 
     /* always stop the retransmit timer when the ACK arrived */
     ctimer_stop(&instance->dao_retransmit_timer);
@@ -1148,8 +1139,10 @@ dao_ack_input(void)
 
 #if RPL_REPAIR_ON_DAO_NACK
     if(status >= RPL_DAO_ACK_UNABLE_TO_ACCEPT) {
-      /* failed the DAO transmission - need to remove the default route. */
-      /* Trigger a local repair since we can not get our DAO in... */
+      /*
+       * Failed the DAO transmission - need to remove the default route.
+       * Trigger a local repair since we can not get our DAO in.
+       */
       rpl_local_repair(instance);
     }
 #endif
diff --git a/core/net/rpl/rpl-mrhof.c b/core/net/rpl/rpl-mrhof.c
index 6da2ec304..f9ea76080 100644
--- a/core/net/rpl/rpl-mrhof.c
+++ b/core/net/rpl/rpl-mrhof.c
@@ -54,7 +54,9 @@
 
 static void reset(rpl_dag_t *);
 static void neighbor_link_callback(rpl_parent_t *, int, int);
+#if RPL_WITH_DAO_ACK
 static void dao_ack_callback(rpl_parent_t *, int);
+#endif
 static rpl_parent_t *best_parent(rpl_parent_t *, rpl_parent_t *);
 static rpl_dag_t *best_dag(rpl_dag_t *, rpl_dag_t *);
 static rpl_rank_t calculate_rank(rpl_parent_t *, rpl_rank_t);
@@ -63,7 +65,9 @@ static void update_metric_container(rpl_instance_t *);
 rpl_of_t rpl_mrhof = {
   reset,
   neighbor_link_callback,
+#if RPL_WITH_DAO_ACK
   dao_ack_callback,
+#endif
   best_parent,
   best_dag,
   calculate_rank,
@@ -119,10 +123,11 @@ reset(rpl_dag_t *dag)
   PRINTF("RPL: Reset MRHOF\n");
 }
 
+#if RPL_WITH_DAO_ACK
 static void
 dao_ack_callback(rpl_parent_t *p, int status)
 {
-  if(status == RPL_DAO_ACK_UNABLE_TO_ACCEPT_ROOT) {
+  if(status == RPL_DAO_ACK_UNABLE_TO_ADD_ROUTE_AT_ROOT) {
     return;
   }
   /* here we need to handle failed DAO's and other stuff */
@@ -135,6 +140,7 @@ dao_ack_callback(rpl_parent_t *p, int status)
     neighbor_link_callback(p, MAC_TX_OK, 10);
   }
 }
+#endif /* RPL_WITH_DAO_ACK */
 
 static void
 neighbor_link_callback(rpl_parent_t *p, int status, int numtx)
diff --git a/core/net/rpl/rpl-nbr-policy.c b/core/net/rpl/rpl-nbr-policy.c
index 6f0dd9ca3..87849af40 100644
--- a/core/net/rpl/rpl-nbr-policy.c
+++ b/core/net/rpl/rpl-nbr-policy.c
@@ -72,6 +72,10 @@ static linkaddr_t *worst_rank_nbr; /* the parent that has the worst rank */
 static rpl_rank_t worst_rank;
 /*---------------------------------------------------------------------------*/
 #if DEBUG == DEBUG_FULL
+/*
+ * This create a periodic call of the update_nbr function that will print
+ * useful debugging information when in DEBUG_FULL mode
+ */
 static void update_nbr(void);
 static struct ctimer periodic_timer;
 static int timer_init = 0;
@@ -111,9 +115,12 @@ update_nbr(void)
     linkaddr_t *lladdr = nbr_table_get_lladdr(ds6_neighbors, nbr);
     is_used = 0;
 
-    /* Check if this neighbor is used as nexthop and therefor being a
-       RPL child. */
-    if(uip_ds6_route_is_nexthop((uip_lladdr_t *)lladdr) != 0) {
+    /*
+     * Check if this neighbor is used as nexthop and therefor being a
+     * RPL child.
+    */
+
+    if(uip_ds6_route_is_nexthop(&nbr->ipaddr) != 0) {
       is_used++;
       num_children++;
     }
@@ -123,10 +130,10 @@ update_nbr(void)
       num_parents++;
 
       if(parent->dag != NULL && parent->dag->preferred_parent == parent) {
-        /* This is the preferred parent for the DAG and must not be removed */
-
-        /* Note: this assumes that only RPL adds default routes. */
-
+        /*
+         * This is the preferred parent for the DAG and must not be removed
+         * Note: this assumes that only RPL adds default routes.
+         */
       } else if(is_used == 0 && worst_rank < INFINITE_RANK &&
                 parent->rank > 0 &&
                 parent->dag != NULL &&
@@ -168,9 +175,10 @@ find_removable_dis(uip_ipaddr_t *from)
 
   update_nbr();
   if(num_free > 0) {
-    printf("num-free > 0 = %d", num_free);
-    printf("**** Should remove unused elements but can not... \n");
-    /*    return 1; */
+    /* there are free entries (e.g. unsused by RPL and ND6) but since it is
+       used by other modules we can not pick these entries for removal. */
+    PRINTF("Num-free > 0 = %d - Other for RPL/ND6 unused NBR entry exists .",
+           num_free);
   }
   if(num_children < MAX_CHILDREN) {
     return worst_rank_nbr;
@@ -192,7 +200,7 @@ find_removable_dio(uip_ipaddr_t *from, rpl_dio_t *dio)
     return NULL;
   }
 
-  /* Add the new neighbor only if it is better than the preferred parent. */
+  /* Add the new neighbor only if it is better than the worst parent. */
   rank = instance->of->calculate_rank(NULL, dio->rank);
   if(rank < worst_rank - instance->min_hoprankinc / 2) {
     /* Found *great* neighbor - add! */
@@ -231,7 +239,8 @@ find_removable_dao(uip_ipaddr_t *from, rpl_instance_t *instance)
 }
 /*---------------------------------------------------------------------------*/
 const linkaddr_t *
-rpl_nbr_policy_find_removable(nbr_table_reason_t reason,void * data) {
+rpl_nbr_policy_find_removable(nbr_table_reason_t reason,void * data)
+{
   /* When we get the DIO/DAO/DIS we know that UIP contains the
      incoming packet */
   switch(reason) {
diff --git a/core/net/rpl/rpl-of0.c b/core/net/rpl/rpl-of0.c
index ed76bac4b..b0a909a4d 100644
--- a/core/net/rpl/rpl-of0.c
+++ b/core/net/rpl/rpl-of0.c
@@ -55,7 +55,9 @@ static void update_metric_container(rpl_instance_t *);
 rpl_of_t rpl_of0 = {
   reset,
   NULL,
+#if RPL_WITH_DAO_ACK
   NULL,
+#endif
   best_parent,
   best_dag,
   calculate_rank,
diff --git a/core/net/rpl/rpl-private.h b/core/net/rpl/rpl-private.h
index 161cdc532..ec885eaea 100644
--- a/core/net/rpl/rpl-private.h
+++ b/core/net/rpl/rpl-private.h
@@ -94,7 +94,7 @@
 #define RPL_DAO_ACK_UNCONDITIONAL_ACCEPT 0
 #define RPL_DAO_ACK_ACCEPT               1   /* 1 - 127 is OK but not good */
 #define RPL_DAO_ACK_UNABLE_TO_ACCEPT     128 /* >127 is fail */
-#define RPL_DAO_ACK_UNABLE_TO_ACCEPT_ROOT 255 /* root can not accept */
+#define RPL_DAO_ACK_UNABLE_TO_ADD_ROUTE_AT_ROOT 255 /* root can not accept */
 
 #define RPL_DAO_ACK_TIMEOUT              -1
 
diff --git a/core/net/rpl/rpl.h b/core/net/rpl/rpl.h
index dfc081d4b..532df4b3a 100644
--- a/core/net/rpl/rpl.h
+++ b/core/net/rpl/rpl.h
@@ -181,11 +181,19 @@ typedef struct rpl_instance rpl_instance_t;
  *  Updates the metric container for outgoing DIOs in a certain DAG.
  *  If the objective function of the DAG does not use metric containers,
  *  the function should set the object type to RPL_DAG_MC_NONE.
+ *
+ * dao_ack_callback(parent, status)
+ *
+ * A callback on the result of the DAO ACK. Similar to the neighbor link
+ * callback. A failed DAO_ACK (NACK) can be used for switching to another
+ * parent via changed link metric or other mechanisms.
  */
 struct rpl_of {
   void (*reset)(struct rpl_dag *);
   void (*neighbor_link_callback)(rpl_parent_t *, int, int);
+#if RPL_WITH_DAO_ACK
   void (*dao_ack_callback)(rpl_parent_t *, int status);
+#endif
   rpl_parent_t *(*best_parent)(rpl_parent_t *, rpl_parent_t *);
   rpl_dag_t *(*best_dag)(rpl_dag_t *, rpl_dag_t *);
   rpl_rank_t (*calculate_rank)(rpl_parent_t *, rpl_rank_t);
@@ -220,6 +228,8 @@ struct rpl_instance {
   /* my last registered DAO that I might be waiting for ACK on */
   uint8_t my_dao_seqno;
   uint8_t my_dao_transmissions;
+  /* this is intended to keep track if this instance have a route downward */
+  uint8_t has_downward_route;
   rpl_rank_t max_rankinc;
   rpl_rank_t min_hoprankinc;
   uint16_t lifetime_unit; /* lifetime in seconds = l_u * d_l */
@@ -302,11 +312,11 @@ enum rpl_mode rpl_get_mode(void);
 
 
 /**
- * Get the RPL's best guess on if we have downward link or not.
+ * Get the RPL's best guess on if we have downward route or not.
  *
- * \retval 1 if we have a downward link, 0 if not.
+ * \retval 1 if we have a downward route from RPL Root, 0 if not.
  */
-int rpl_has_downward_link(void);
+int rpl_has_downward_route(void);
 
 /*---------------------------------------------------------------------------*/
 #endif /* RPL_H */
diff --git a/regression-tests/21-large-rpl/code/node/client.c b/regression-tests/21-large-rpl/code/node/client.c
index 36dc40923..1e82e2df0 100644
--- a/regression-tests/21-large-rpl/code/node/client.c
+++ b/regression-tests/21-large-rpl/code/node/client.c
@@ -100,7 +100,7 @@ PROCESS_THREAD(http_example_process, ev, data)
   while(1) {
     PROCESS_WAIT_EVENT_UNTIL(etimer_expired(&et));
     etimer_reset(&et);
-    if(connect && rpl_has_downward_link()) {
+    if(connect && rpl_has_downward_route()) {
       printf("#A color=green\n");
       http_socket_get(&s, "http://www.contiki-os.org/", 0, 0,
 		      callback, NULL);