gnrc_ipv6_nib: do not try to re-register to an unreachable router

sys/net/gnrc/network_layer/ipv6/nib/_nib-6ln.c

@@ -206,8 +206,10 @@ void _handle_rereg_address(const ipv6_addr_t *addr)
 {
     gnrc_netif_t *netif = gnrc_netif_get_by_ipv6_addr(addr);
     _nib_dr_entry_t *router = _nib_drl_get_dr();
+    const bool router_reachable = (router != NULL) &&
+                                  _is_reachable(router->next_hop);
 
-    if ((netif != NULL) && (router != NULL)) {
+    if (router_reachable && (netif != NULL)) {
         assert((unsigned)netif->pid == _nib_onl_get_if(router->next_hop));
         DEBUG("nib: Re-registering %s",
               ipv6_addr_to_str(addr_str, addr, sizeof(addr_str)));
@@ -224,9 +226,10 @@ void _handle_rereg_address(const ipv6_addr_t *addr)
     if (netif != NULL) {
         int idx = gnrc_netif_ipv6_addr_idx(netif, addr);
 
-        if (_is_valid(netif, idx) || (_is_tentative(netif, idx) &&
+        if (router_reachable &&
+            (_is_valid(netif, idx) || (_is_tentative(netif, idx) &&
              (gnrc_netif_ipv6_addr_dad_trans(netif, idx) <
-              SIXLOWPAN_ND_REG_TRANSMIT_NUMOF))) {
+              SIXLOWPAN_ND_REG_TRANSMIT_NUMOF)))) {
             uint32_t retrans_time;
 
             if (_is_valid(netif, idx)) {

sys/net/gnrc/network_layer/ipv6/nib/_nib-arsm.c

@@ -495,6 +495,17 @@ void _set_nud_state(gnrc_netif_t *netif, _nib_onl_entry_t *nce,
 #endif  /* GNRC_IPV6_NIB_CONF_ROUTER */
 }
 
+bool _is_reachable(_nib_onl_entry_t *entry)
+{
+    switch (_get_nud_state(entry)) {
+        case GNRC_IPV6_NIB_NC_INFO_NUD_STATE_UNREACHABLE:
+        case GNRC_IPV6_NIB_NC_INFO_NUD_STATE_INCOMPLETE:
+            return false;
+        default:
+            return true;
+    }
+}
+
 /* internal functions */
 static inline uint32_t _exp_backoff_retrans_timer(uint8_t ns_sent,
                                                   uint32_t retrans_timer)
@@ -547,7 +558,6 @@ static inline bool _rflag_set(const ndp_nbr_adv_t *nbr_adv)
     return (nbr_adv->type == ICMPV6_NBR_ADV) &&
            (nbr_adv->flags & NDP_NBR_ADV_FLAGS_R);
 }
-
 #endif /* GNRC_IPV6_NIB_CONF_ARSM */
 
 /** @} */

sys/net/gnrc/network_layer/ipv6/nib/_nib-arsm.h

@@ -178,6 +178,17 @@ static inline uint16_t _get_nud_state(_nib_onl_entry_t *nbr)
 void _set_nud_state(gnrc_netif_t *netif, _nib_onl_entry_t *nbr,
                     uint16_t state);
 
+/**
+ * @brief   Checks if a node is in a reachable state
+ *
+ * A node is reachable if it is not in NUD state UNREACHABLE or INCOMPLETE
+ *
+ * @param[in] entry A node.
+ *
+ * @return  true, if @p entry is in a reachable state.
+ * @return  false, if @p entry is not in a reachable state.
+ */
+bool _is_reachable(_nib_onl_entry_t *entry);
 #else   /* GNRC_IPV6_NIB_CONF_ARSM || defined(DOXYGEN) */
 #define _handle_snd_ns(ctx)                         (void)ctx
 #define _handle_state_timeout(ctx)                  (void)ctx
@@ -191,6 +202,7 @@ void _set_nud_state(gnrc_netif_t *netif, _nib_onl_entry_t *nbr,
 
 #define _get_nud_state(nbr)                 (GNRC_IPV6_NIB_NC_INFO_NUD_STATE_UNMANAGED)
 #define _set_nud_state(netif, nce, state)   (void)netif; (void)nbr; (void)state
+#define _is_reachable(entry)                (true)
 #endif  /* GNRC_IPV6_NIB_CONF_ARSM || defined(DOXYGEN) */
 
 #ifdef __cplusplus

sys/net/gnrc/network_layer/ipv6/nib/nib.c

@@ -983,20 +983,6 @@ static void _handle_nbr_adv(gnrc_netif_t *netif, const ipv6_hdr_t *ipv6,
     }
 }
 
-#if GNRC_IPV6_NIB_CONF_ARSM
-static inline bool _is_reachable(_nib_onl_entry_t *entry)
-{
-    (void)entry; /* _get_nud_state() might just resolved to UNMANAGED as macro */
-    switch (_get_nud_state(entry)) {
-        case GNRC_IPV6_NIB_NC_INFO_NUD_STATE_UNREACHABLE:
-        case GNRC_IPV6_NIB_NC_INFO_NUD_STATE_INCOMPLETE:
-            return false;
-        default:
-            return true;
-    }
-}
-#endif  /* GNRC_IPV6_NIB_CONF_ARSM */
-
 #if GNRC_IPV6_NIB_CONF_QUEUE_PKT
 static gnrc_pktqueue_t *_alloc_queue_entry(gnrc_pktsnip_t *pkt)
 {