gnrc/rpl: float DODAG during local repair

If the parent set of a router is empty and a local repair initiated, don't immediately poison all routes. Instead configure node as root of a new floating DODAG to maintain connectivity in the sub-tree.
Once a different, grounded DODAG is found the node will join the new DODAG.
If no other DODAG is found the floating DODAG will timeout after `CONFIG_GNRC_RPL_DODAG_FLOAT_TIMEOUT` and cleaned up..

Author: elenaf9

sys/include/net/gnrc/rpl.h

@@ -151,6 +151,7 @@
 #include "net/gnrc/rpl/dodag.h"
 #include "net/gnrc/rpl/of_manager.h"
 #include "net/fib.h"
+#include "time_units.h"
 #include "trickle.h"
 
 #ifdef MODULE_NETSTATS_RPL
@@ -627,6 +628,13 @@ extern netstats_rpl_t gnrc_rpl_netstats;
 #define CONFIG_GNRC_RPL_PARENT_TIMEOUT_DIS_RETRIES (3)
 #endif
 
+/**
+ * @brief Timeout for floating DODAGs in milliseconds.
+ */
+#ifndef CONFIG_GNRC_RPL_DODAG_FLOAT_TIMEOUT
+#  define CONFIG_GNRC_RPL_DODAG_FLOAT_TIMEOUT (15 * MS_PER_SEC * SEC_PER_MIN)
+#endif
+
 /**
  * @brief Default network interface for GNRC RPL
  */

sys/include/net/gnrc/rpl/dodag.h

@@ -166,6 +166,15 @@ void gnrc_rpl_parent_update(gnrc_rpl_dodag_t *dodag, gnrc_rpl_parent_t *parent);
  */
 void gnrc_rpl_cleanup_start(gnrc_rpl_dodag_t *dodag);
 
+/**
+ * @brief Poison all routes of @p dodag by setting an infinite rank, and schedule
+ * a cleanup for the @p dodag.
+ *
+ * @param[in] dodag     Pointer to the DODAG
+ *
+ */
+void gnrc_rpl_poison_routes(gnrc_rpl_dodag_t *dodag);
+
 /**
  * @brief   Start a local repair.
  *

sys/include/net/gnrc/rpl/structs.h

@@ -330,6 +330,10 @@ struct gnrc_rpl_dodag {
     uint8_t dio_opts;               /**< options in the next DIO
                                          (see @ref GNRC_RPL_REQ_DIO_OPTS "DIO Options") */
     evtimer_msg_event_t dao_event;  /**< DAO TX events (see @ref GNRC_RPL_MSG_TYPE_DODAG_DAO_TX) */
+    /**
+     * floating dodag timeout events (see @ref GNRC_RPL_MSG_TYPE_DODAG_FLOAT_TIMEOUT)
+     */
+    evtimer_msg_event_t float_timeout_event;
     trickle_t trickle;              /**< trickle representation */
 };
 

sys/net/gnrc/routing/rpl/gnrc_rpl.c

@@ -250,6 +250,15 @@ static void _parent_timeout(gnrc_rpl_parent_t *parent)
     evtimer_add_msg(&gnrc_rpl_evtimer, &parent->timeout_event, gnrc_rpl_pid);
 }
 
+/* Handle timeout for floating DODAG by poisoning all routes. */
+static void _dodag_float_timeout(gnrc_rpl_dodag_t *dodag)
+{
+    if (dodag->grounded != GNRC_RPL_GROUNDED) {
+        gnrc_rpl_poison_routes(dodag);
+    }
+    evtimer_del(&gnrc_rpl_evtimer, (evtimer_event_t *)&dodag->float_timeout_event);
+}
+
 static void *_event_loop(void *args)
 {
     msg_t msg, reply;
@@ -300,6 +309,11 @@ static void *_event_loop(void *args)
                     gnrc_rpl_instance_remove(instance);
                 }
                 break;
+            case GNRC_RPL_MSG_TYPE_DODAG_FLOAT_TIMEOUT:
+                DEBUG("RPL: GNRC_RPL_MSG_TYPE_DODAG_FLOAT_TIMEOUT received\n");
+                instance = msg.content.ptr;
+                _dodag_float_timeout(&instance->dodag);
+                break;
             case GNRC_RPL_MSG_TYPE_TRICKLE_MSG:
                 DEBUG("RPL: GNRC_RPL_MSG_TYPE_TRICKLE_MSG received\n");
                 trickle = msg.content.ptr;

sys/net/gnrc/routing/rpl/gnrc_rpl_dodag.c

@@ -77,6 +77,18 @@ static uint16_t _dflt_route_lifetime_sec(gnrc_rpl_dodag_t *dodag)
             (GNRC_RPL_PARENT_PROBE_INTERVAL / MS_PER_SEC));
 }
 
+void gnrc_rpl_poison_routes(gnrc_rpl_dodag_t *dodag)
+{
+    if (dodag->my_rank != GNRC_RPL_INFINITE_RANK) {
+        DEBUG("RPL: Poison all children routes in DODAG.\n");
+
+        /* Poison routes by advertising infinity rank */
+        dodag->my_rank = GNRC_RPL_INFINITE_RANK;
+        trickle_reset_timer(&dodag->trickle);
+        gnrc_rpl_cleanup_start(dodag);
+    }
+}
+
 bool gnrc_rpl_instance_add(uint8_t instance_id, gnrc_rpl_instance_t **inst)
 {
     *inst = NULL;
@@ -130,8 +142,9 @@ void gnrc_rpl_dodag_remove(gnrc_rpl_dodag_t *dodag)
     gnrc_rpl_dodag_remove_all_parents(dodag);
     trickle_stop(&dodag->trickle);
     evtimer_del(&gnrc_rpl_evtimer, (evtimer_event_t *)&dodag->dao_event);
+    evtimer_del(&gnrc_rpl_evtimer, (evtimer_event_t *)&dodag->float_timeout_event);
     evtimer_del(&gnrc_rpl_evtimer, (evtimer_event_t *)&dodag->instance->cleanup_event);
-
+    memset(dodag, 0, sizeof(gnrc_rpl_dodag_t));
 }
 
 void gnrc_rpl_instance_remove(gnrc_rpl_instance_t *inst)
@@ -200,6 +213,8 @@ bool gnrc_rpl_dodag_init(gnrc_rpl_instance_t *instance, const ipv6_addr_t *dodag
     dodag->iface = iface;
     dodag->dao_event.msg.content.ptr = instance;
     dodag->dao_event.msg.type = GNRC_RPL_MSG_TYPE_DODAG_DAO_TX;
+    dodag->float_timeout_event.msg.content.ptr = instance;
+    dodag->float_timeout_event.msg.type = GNRC_RPL_MSG_TYPE_DODAG_FLOAT_TIMEOUT;
 
     if ((netif != NULL) && !(netif->flags & GNRC_NETIF_FLAGS_IPV6_FORWARDING)) {
         gnrc_rpl_leaf_operation(dodag);
@@ -215,6 +230,32 @@ bool gnrc_rpl_dodag_init(gnrc_rpl_instance_t *instance, const ipv6_addr_t *dodag
     return true;
 }
 
+bool _float_dodag(gnrc_rpl_dodag_t *dodag)
+{
+    evtimer_event_t *float_event = (evtimer_event_t *)&dodag->float_timeout_event;
+
+    DEBUG("RPL: Set node as root for floating DODAG.\n");
+
+    evtimer_del(&gnrc_rpl_evtimer, float_event);
+
+    /* find address on interface that matches the prefix of the old dodag */
+    gnrc_netif_t *netif = gnrc_netif_get_by_pid(dodag->iface);
+    int idx = gnrc_netif_ipv6_addr_match(netif, &dodag->dodag_id);
+    if (idx < 0) {
+        DEBUG("RPL: could not find address to use as DODAGID.");
+        return false;
+    }
+    dodag->dodag_id = netif->ipv6.addrs[idx];
+    gnrc_rpl_dodag_root_init(dodag);
+    dodag->grounded &= !GNRC_RPL_GROUNDED;
+
+    /* floating dodag should timeout eventually if no new grounded dodag is found */
+    float_event->offset = CONFIG_GNRC_RPL_DODAG_FLOAT_TIMEOUT;
+    evtimer_add_msg(&gnrc_rpl_evtimer, &dodag->float_timeout_event, gnrc_rpl_pid);
+
+    return true;
+}
+
 void gnrc_rpl_dodag_remove_all_parents(gnrc_rpl_dodag_t *dodag)
 {
     gnrc_rpl_parent_t *elt = NULL;
@@ -300,10 +341,8 @@ void gnrc_rpl_local_repair(gnrc_rpl_dodag_t *dodag)
 
     dodag->dtsn++;
 
-    if (dodag->my_rank != GNRC_RPL_INFINITE_RANK) {
-        dodag->my_rank = GNRC_RPL_INFINITE_RANK;
-        trickle_reset_timer(&dodag->trickle);
-        gnrc_rpl_cleanup_start(dodag);
+    if ((CONFIG_GNRC_RPL_DODAG_FLOAT_TIMEOUT <= 0) || !_float_dodag(dodag)) {
+        gnrc_rpl_poison_routes(dodag);
     }
 
     if (dodag->parents) {

sys/net/gnrc/routing/rpl/gnrc_rpl_internal/globals.h

@@ -45,6 +45,10 @@ extern evtimer_msg_t gnrc_rpl_evtimer;
  * @brief   Message type for DAO transmissions.
  */
 #define GNRC_RPL_MSG_TYPE_DODAG_DAO_TX        (0x0906)
+/**
+ * @brief   Message type for floating DODAG timeouts.
+ */
+#define GNRC_RPL_MSG_TYPE_DODAG_FLOAT_TIMEOUT  (0x0907)
 /** @} */
 
 /**