Merge pull request #3177 from authmillenon/ng_ndp/doc/nbr_adv_timer

ng_ndp: expand documentation on ng_ipv6_nc_t::nbr_adv_timer

sys/include/net/ng_ipv6/nc.h

@@ -134,6 +134,12 @@ typedef struct {
 
     /**
      * @brief Delay timer for neighbor advertisements of this entry.
+     *
+     * @note Only needed for delayed anycast neighbor advertisements
+     *
+     * @see <a href="https://tools.ietf.org/html/rfc4861#section-7.2.7">
+     *          RFC 4861, section 7.2.7
+     *      </a>
      */
     vtimer_t nbr_adv_timer;
 

sys/net/network_layer/ng_ndp/ng_ndp.c

@@ -764,7 +764,8 @@ static void _send_nbr_adv(kernel_pid_t iface, ng_ipv6_addr_t *tgt,
     ((ng_netif_hdr_t *)hdr->data)->if_pid = iface;
 
     if (ng_ipv6_netif_addr_is_non_unicast(tgt)) {
-        /* avoid collision for anycast addresses */
+        /* avoid collision for anycast addresses
+         * (see https://tools.ietf.org/html/rfc4861#section-7.2.7) */
         timex_t delay = { _rand(0, NG_NDP_MAX_AC_TGT_DELAY), 0 };
         ng_ipv6_nc_t *nc_entry = ng_ipv6_nc_get(iface, tgt);