diff --git a/doc/user/ospf6d.rst b/doc/user/ospf6d.rst
index 8dacb9c9dc..e4da6d71e0 100644
--- a/doc/user/ospf6d.rst
+++ b/doc/user/ospf6d.rst
@@ -343,6 +343,10 @@ Graceful Restart
    To perform a graceful shutdown, the "graceful-restart prepare ipv6 ospf"
    EXEC-level command needs to be issued before restarting the ospf6d daemon.
 
+   When Graceful Restart is enabled and the ospf6d daemon crashes or is killed
+   abruptely (e.g. SIGKILL), it will attempt an unplanned Graceful Restart once
+   it restarts.
+
 .. clicmd:: graceful-restart helper enable [A.B.C.D]
 
 
diff --git a/ospf6d/ospf6_gr.c b/ospf6d/ospf6_gr.c
index 976eb529d7..18f36abda0 100644
--- a/ospf6d/ospf6_gr.c
+++ b/ospf6d/ospf6_gr.c
@@ -14,6 +14,7 @@
 #include "log.h"
 #include "hook.h"
 #include "printfrr.h"
+#include "lib_errors.h"
 
 #include "ospf6d/ospf6_lsa.h"
 #include "ospf6d/ospf6_lsdb.h"
@@ -25,21 +26,25 @@
 #include "ospf6d/ospf6_zebra.h"
 #include "ospf6d/ospf6_message.h"
 #include "ospf6d/ospf6_neighbor.h"
+#include "ospf6d/ospf6_network.h"
 #include "ospf6d/ospf6_flood.h"
 #include "ospf6d/ospf6_intra.h"
 #include "ospf6d/ospf6_spf.h"
 #include "ospf6d/ospf6_gr.h"
 #include "ospf6d/ospf6_gr_clippy.c"
 
-static void ospf6_gr_nvm_delete(struct ospf6 *ospf6);
+static void ospf6_gr_grace_period_expired(struct event *thread);
 
 /* Originate and install Grace-LSA for a given interface. */
-static int ospf6_gr_lsa_originate(struct ospf6_interface *oi)
+static int ospf6_gr_lsa_originate(struct ospf6_interface *oi,
+				  enum ospf6_gr_restart_reason reason)
 {
-	struct ospf6_gr_info *gr_info = &oi->area->ospf6->gr_info;
+	struct ospf6 *ospf6 = oi->area->ospf6;
+	struct ospf6_gr_info *gr_info = &ospf6->gr_info;
 	struct ospf6_lsa_header *lsa_header;
 	struct ospf6_grace_lsa *grace_lsa;
 	struct ospf6_lsa *lsa;
+	uint16_t lsa_length;
 	char buffer[OSPF6_MAX_LSASIZE];
 
 	if (IS_OSPF6_DEBUG_ORIGINATE(LINK))
@@ -61,29 +66,59 @@ static int ospf6_gr_lsa_originate(struct ospf6_interface *oi)
 	/* Put restart reason. */
 	grace_lsa->tlv_reason.header.type = htons(RESTART_REASON_TYPE);
 	grace_lsa->tlv_reason.header.length = htons(RESTART_REASON_LENGTH);
-	if (gr_info->restart_support)
-		grace_lsa->tlv_reason.reason = OSPF6_GR_SW_RESTART;
-	else
-		grace_lsa->tlv_reason.reason = OSPF6_GR_UNKNOWN_RESTART;
+	grace_lsa->tlv_reason.reason = reason;
 
 	/* Fill LSA Header */
+	lsa_length = sizeof(*lsa_header) + sizeof(*grace_lsa);
 	lsa_header->age = 0;
 	lsa_header->type = htons(OSPF6_LSTYPE_GRACE_LSA);
 	lsa_header->id = htonl(oi->interface->ifindex);
-	lsa_header->adv_router = oi->area->ospf6->router_id;
+	lsa_header->adv_router = ospf6->router_id;
 	lsa_header->seqnum =
 		ospf6_new_ls_seqnum(lsa_header->type, lsa_header->id,
 				    lsa_header->adv_router, oi->lsdb);
-	lsa_header->length = htons(sizeof(*lsa_header) + sizeof(*grace_lsa));
+	lsa_header->length = htons(lsa_length);
 
 	/* LSA checksum */
 	ospf6_lsa_checksum(lsa_header);
 
-	/* create LSA */
-	lsa = ospf6_lsa_create(lsa_header);
+	if (reason == OSPF6_GR_UNKNOWN_RESTART) {
+		struct ospf6_header *oh;
+		uint32_t *uv32;
+		int n;
+		uint16_t length = OSPF6_HEADER_SIZE + 4 + lsa_length;
+		struct iovec iovector[2] = {};
 
-	/* Originate */
-	ospf6_lsa_originate_interface(lsa, oi);
+		/* Reserve space for OSPFv3 header. */
+		memmove(&buffer[OSPF6_HEADER_SIZE + 4], buffer, lsa_length);
+
+		/* Fill in the OSPFv3 header. */
+		oh = (struct ospf6_header *)buffer;
+		oh->version = OSPFV3_VERSION;
+		oh->type = OSPF6_MESSAGE_TYPE_LSUPDATE;
+		oh->router_id = oi->area->ospf6->router_id;
+		oh->area_id = oi->area->area_id;
+		oh->instance_id = oi->instance_id;
+		oh->reserved = 0;
+		oh->length = htons(length);
+
+		/* Fill LSA header. */
+		uv32 = (uint32_t *)&buffer[sizeof(*oh)];
+		*uv32 = htonl(1);
+
+		/* Send packet. */
+		iovector[0].iov_base = lsa_header;
+		iovector[0].iov_len = length;
+		n = ospf6_sendmsg(oi->linklocal_addr, &allspfrouters6,
+				  oi->interface->ifindex, iovector, ospf6->fd);
+		if (n != length)
+			flog_err(EC_LIB_DEVELOPMENT,
+				 "%s: could not send entire message", __func__);
+	} else {
+		/* Create and install LSA. */
+		lsa = ospf6_lsa_create(lsa_header);
+		ospf6_lsa_originate_interface(lsa, oi);
+	}
 
 	return 0;
 }
@@ -134,11 +169,10 @@ static void ospf6_gr_restart_exit(struct ospf6 *ospf6, const char *reason)
 
 	ospf6->gr_info.restart_in_progress = false;
 	ospf6->gr_info.finishing_restart = true;
+	XFREE(MTYPE_TMP, ospf6->gr_info.exit_reason);
+	ospf6->gr_info.exit_reason = XSTRDUP(MTYPE_TMP, reason);
 	EVENT_OFF(ospf6->gr_info.t_grace_period);
 
-	/* Record in non-volatile memory that the restart is complete. */
-	ospf6_gr_nvm_delete(ospf6);
-
 	for (ALL_LIST_ELEMENTS_RO(ospf6->area_list, onode, area)) {
 		struct ospf6_interface *oi;
 
@@ -195,6 +229,26 @@ static void ospf6_gr_restart_exit(struct ospf6 *ospf6, const char *reason)
 	ospf6_gr_flush_grace_lsas(ospf6);
 }
 
+/* Enter the Graceful Restart mode. */
+void ospf6_gr_restart_enter(struct ospf6 *ospf6,
+			    enum ospf6_gr_restart_reason reason, int timestamp)
+{
+	unsigned long remaining_time;
+
+	ospf6->gr_info.restart_in_progress = true;
+	ospf6->gr_info.reason = reason;
+
+	/* Schedule grace period timeout. */
+	remaining_time = timestamp - time(NULL);
+	if (IS_DEBUG_OSPF6_GR)
+		zlog_debug(
+			"GR: remaining time until grace period expires: %lu(s)",
+			remaining_time);
+
+	event_add_timer(master, ospf6_gr_grace_period_expired, ospf6,
+			remaining_time, &ospf6->gr_info.t_grace_period);
+}
+
 #define RTR_LSA_MISSING 0
 #define RTR_LSA_ADJ_FOUND 1
 #define RTR_LSA_ADJ_NOT_FOUND 2
@@ -470,7 +524,7 @@ static void ospf6_gr_grace_period_expired(struct event *thread)
  * Record in non-volatile memory that the given OSPF instance is attempting to
  * perform a graceful restart.
  */
-static void ospf6_gr_nvm_update(struct ospf6 *ospf6)
+static void ospf6_gr_nvm_update(struct ospf6 *ospf6, bool prepare)
 {
 	const char *inst_name;
 	json_object *json;
@@ -496,16 +550,18 @@ static void ospf6_gr_nvm_update(struct ospf6 *ospf6)
 				       json_instance);
 	}
 
+	json_object_int_add(json_instance, "gracePeriod",
+			    ospf6->gr_info.grace_period);
+
 	/*
 	 * Record not only the grace period, but also a UNIX timestamp
 	 * corresponding to the end of that period. That way, once ospf6d is
 	 * restarted, it will be possible to take into account the time that
 	 * passed while ospf6d wasn't running.
 	 */
-	json_object_int_add(json_instance, "gracePeriod",
-			    ospf6->gr_info.grace_period);
-	json_object_int_add(json_instance, "timestamp",
-			    time(NULL) + ospf6->gr_info.grace_period);
+	if (prepare)
+		json_object_int_add(json_instance, "timestamp",
+				    time(NULL) + ospf6->gr_info.grace_period);
 
 	json_object_to_file_ext((char *)OSPF6D_GR_STATE, json,
 				JSON_C_TO_STRING_PRETTY);
@@ -516,7 +572,7 @@ static void ospf6_gr_nvm_update(struct ospf6 *ospf6)
  * Delete GR status information about the given OSPF instance from non-volatile
  * memory.
  */
-static void ospf6_gr_nvm_delete(struct ospf6 *ospf6)
+void ospf6_gr_nvm_delete(struct ospf6 *ospf6)
 {
 	const char *inst_name;
 	json_object *json;
@@ -552,6 +608,7 @@ void ospf6_gr_nvm_read(struct ospf6 *ospf6)
 	json_object *json_instances;
 	json_object *json_instance;
 	json_object *json_timestamp;
+	json_object *json_grace_period;
 	time_t timestamp = 0;
 
 	inst_name = ospf6->name ? ospf6->name : VRF_DEFAULT_NAME;
@@ -573,29 +630,33 @@ void ospf6_gr_nvm_read(struct ospf6 *ospf6)
 				       json_instance);
 	}
 
+	json_object_object_get_ex(json_instance, "gracePeriod",
+				  &json_grace_period);
 	json_object_object_get_ex(json_instance, "timestamp", &json_timestamp);
 	if (json_timestamp) {
 		time_t now;
-		unsigned long remaining_time;
 
-		/* Check if the grace period has already expired. */
+		/* Planned GR: check if the grace period has already expired. */
 		now = time(NULL);
 		timestamp = json_object_get_int(json_timestamp);
 		if (now > timestamp) {
 			ospf6_gr_restart_exit(
 				ospf6, "grace period has expired already");
-		} else {
-			/* Schedule grace period timeout. */
-			ospf6->gr_info.restart_in_progress = true;
-			remaining_time = timestamp - time(NULL);
-			if (IS_DEBUG_OSPF6_GR)
-				zlog_debug(
-					"GR: remaining time until grace period expires: %lu(s)",
-					remaining_time);
-			event_add_timer(master, ospf6_gr_grace_period_expired,
-					ospf6, remaining_time,
-					&ospf6->gr_info.t_grace_period);
-		}
+		} else
+			ospf6_gr_restart_enter(ospf6, OSPF6_GR_SW_RESTART,
+					       timestamp);
+	} else if (json_grace_period) {
+		uint32_t grace_period;
+
+		/*
+		 * Unplanned GR: the Grace-LSAs will be sent later as soon as
+		 * the interfaces are operational.
+		 */
+		grace_period = json_object_get_int(json_grace_period);
+		ospf6->gr_info.grace_period = grace_period;
+		ospf6_gr_restart_enter(ospf6, OSPF6_GR_UNKNOWN_RESTART,
+				       time(NULL) +
+					       ospf6->gr_info.grace_period);
 	}
 
 	json_object_object_del(json_instances, inst_name);
@@ -605,6 +666,19 @@ void ospf6_gr_nvm_read(struct ospf6 *ospf6)
 	json_object_free(json);
 }
 
+void ospf6_gr_unplanned_start_interface(struct ospf6_interface *oi)
+{
+	/*
+	 * Can't check OSPF interface state as the OSPF instance might not be
+	 * enabled yet.
+	 */
+	if (!if_is_operative(oi->interface) || if_is_loopback(oi->interface))
+		return;
+
+	/* Send Grace-LSA. */
+	ospf6_gr_lsa_originate(oi, oi->area->ospf6->gr_info.reason);
+}
+
 /* Prepare to start a Graceful Restart. */
 static void ospf6_gr_prepare(void)
 {
@@ -625,25 +699,17 @@ static void ospf6_gr_prepare(void)
 				ospf6->gr_info.grace_period,
 				ospf6_vrf_id_to_name(ospf6->vrf_id));
 
-		/* Freeze OSPF routes in the RIB. */
-		if (ospf6_zebra_gr_enable(ospf6, ospf6->gr_info.grace_period)) {
-			zlog_warn(
-				"%s: failed to activate graceful restart: not connected to zebra",
-				__func__);
-			continue;
-		}
-
 		/* Send a Grace-LSA to all neighbors. */
 		for (ALL_LIST_ELEMENTS_RO(ospf6->area_list, anode, area)) {
 			for (ALL_LIST_ELEMENTS_RO(area->if_list, inode, oi)) {
 				if (oi->state < OSPF6_INTERFACE_POINTTOPOINT)
 					continue;
-				ospf6_gr_lsa_originate(oi);
+				ospf6_gr_lsa_originate(oi, OSPF6_GR_SW_RESTART);
 			}
 		}
 
 		/* Record end of the grace period in non-volatile memory. */
-		ospf6_gr_nvm_update(ospf6);
+		ospf6_gr_nvm_update(ospf6, true);
 
 		/*
 		 * Mark that a Graceful Restart preparation is in progress, to
@@ -714,6 +780,12 @@ DEFPY(ospf6_graceful_restart, ospf6_graceful_restart_cmd,
 	ospf6->gr_info.restart_support = true;
 	ospf6->gr_info.grace_period = grace_period;
 
+	/* Freeze OSPF routes in the RIB. */
+	(void)ospf6_zebra_gr_enable(ospf6, ospf6->gr_info.grace_period);
+
+	/* Record that GR is enabled in non-volatile memory. */
+	ospf6_gr_nvm_update(ospf6, false);
+
 	return CMD_SUCCESS;
 }
 
@@ -736,6 +808,8 @@ DEFPY(ospf6_no_graceful_restart, ospf6_no_graceful_restart_cmd,
 
 	ospf6->gr_info.restart_support = false;
 	ospf6->gr_info.grace_period = OSPF6_DFLT_GRACE_INTERVAL;
+	ospf6_gr_nvm_delete(ospf6);
+	ospf6_zebra_gr_disable(ospf6);
 
 	return CMD_SUCCESS;
 }
diff --git a/ospf6d/ospf6_gr.h b/ospf6d/ospf6_gr.h
index 2c7e8b341c..42c7bab61b 100644
--- a/ospf6d/ospf6_gr.h
+++ b/ospf6d/ospf6_gr.h
@@ -155,9 +155,14 @@ extern int config_write_ospf6_gr(struct vty *vty, struct ospf6 *ospf6);
 extern int config_write_ospf6_gr_helper(struct vty *vty, struct ospf6 *ospf6);
 extern int config_write_ospf6_debug_gr_helper(struct vty *vty);
 
+extern void ospf6_gr_restart_enter(struct ospf6 *ospf6,
+				   enum ospf6_gr_restart_reason reason,
+				   int timestamp);
 extern void ospf6_gr_check_lsdb_consistency(struct ospf6 *ospf,
 					    struct ospf6_area *area);
 extern void ospf6_gr_nvm_read(struct ospf6 *ospf);
+extern void ospf6_gr_nvm_delete(struct ospf6 *ospf6);
+extern void ospf6_gr_unplanned_start_interface(struct ospf6_interface *oi);
 extern void ospf6_gr_init(void);
 
 #endif /* OSPF6_GR_H */
diff --git a/ospf6d/ospf6_interface.c b/ospf6d/ospf6_interface.c
index e7148d66ba..0f6d9e10d2 100644
--- a/ospf6d/ospf6_interface.c
+++ b/ospf6d/ospf6_interface.c
@@ -772,6 +772,17 @@ void interface_up(struct event *thread)
 		return;
 	}
 
+	/*
+	 * RFC 3623 - Section 5 ("Unplanned Outages"):
+	 * "The grace-LSAs are encapsulated in Link State Update Packets
+	 * and sent out to all interfaces, even though the restarted
+	 * router has no adjacencies and no knowledge of previous
+	 * adjacencies".
+	 */
+	if (oi->area->ospf6->gr_info.restart_in_progress &&
+	    oi->area->ospf6->gr_info.reason == OSPF6_GR_UNKNOWN_RESTART)
+		ospf6_gr_unplanned_start_interface(oi);
+
 #ifdef __FreeBSD__
 	/*
 	 * There's a delay in FreeBSD between issuing a command to leave a
diff --git a/ospf6d/ospf6_spf.c b/ospf6d/ospf6_spf.c
index 0990b14307..e39ae504a2 100644
--- a/ospf6d/ospf6_spf.c
+++ b/ospf6d/ospf6_spf.c
@@ -1262,6 +1262,7 @@ static void ospf6_ase_calculate_timer(struct event *t)
 		 * no longer valid.
 		 */
 		ospf6_zebra_gr_disable(ospf6);
+		ospf6_zebra_gr_enable(ospf6, ospf6->gr_info.grace_period);
 		ospf6->gr_info.finishing_restart = false;
 	}
 }
diff --git a/ospf6d/ospf6_top.c b/ospf6d/ospf6_top.c
index c2aa3abeed..01c962194c 100644
--- a/ospf6d/ospf6_top.c
+++ b/ospf6d/ospf6_top.c
@@ -455,6 +455,13 @@ struct ospf6 *ospf6_instance_create(const char *name)
 	if (ospf6->router_id == 0)
 		ospf6_router_id_update(ospf6, true);
 	ospf6_add(ospf6);
+
+	/*
+	 * Read from non-volatile memory whether this instance is performing a
+	 * graceful restart or not.
+	 */
+	ospf6_gr_nvm_read(ospf6);
+
 	if (ospf6->vrf_id != VRF_UNKNOWN) {
 		vrf = vrf_lookup_by_id(ospf6->vrf_id);
 		FOR_ALL_INTERFACES (vrf, ifp) {
@@ -465,12 +472,6 @@ struct ospf6 *ospf6_instance_create(const char *name)
 	if (ospf6->fd < 0)
 		return ospf6;
 
-	/*
-	 * Read from non-volatile memory whether this instance is performing a
-	 * graceful restart or not.
-	 */
-	ospf6_gr_nvm_read(ospf6);
-
 	event_add_read(master, ospf6_receive, ospf6, ospf6->fd,
 		       &ospf6->t_ospf6_receive);
 
@@ -490,6 +491,7 @@ void ospf6_delete(struct ospf6 *o)
 	ospf6_gr_helper_deinit(o);
 	if (!o->gr_info.prepare_in_progress)
 		ospf6_flush_self_originated_lsas_now(o);
+	XFREE(MTYPE_TMP, o->gr_info.exit_reason);
 	ospf6_disable(o);
 	ospf6_del(o);
 
@@ -693,6 +695,9 @@ DEFUN(no_router_ospf6, no_router_ospf6_cmd, "no router ospf6 [vrf NAME]",
 	if (ospf6 == NULL)
 		vty_out(vty, "OSPFv3 is not configured\n");
 	else {
+		if (ospf6->gr_info.restart_support)
+			ospf6_gr_nvm_delete(ospf6);
+
 		ospf6_delete(ospf6);
 		ospf6 = NULL;
 	}
diff --git a/ospf6d/ospf6_top.h b/ospf6d/ospf6_top.h
index 8fdd291122..a38dad8fce 100644
--- a/ospf6d/ospf6_top.h
+++ b/ospf6d/ospf6_top.h
@@ -51,6 +51,8 @@ struct ospf6_gr_info {
 	bool prepare_in_progress;
 	bool finishing_restart;
 	uint32_t grace_period;
+	int reason;
+	char *exit_reason;
 	struct event *t_grace_period;
 };
 
diff --git a/ospf6d/ospf6_zebra.c b/ospf6d/ospf6_zebra.c
index 6b3d4955da..1132c0a801 100644
--- a/ospf6d/ospf6_zebra.c
+++ b/ospf6d/ospf6_zebra.c
@@ -735,10 +735,20 @@ uint8_t ospf6_distance_apply(struct prefix_ipv6 *p, struct ospf6_route * or,
 
 static void ospf6_zebra_connected(struct zclient *zclient)
 {
+	struct ospf6 *ospf6;
+	struct listnode *node;
+
 	/* Send the client registration */
 	bfd_client_sendmsg(zclient, ZEBRA_BFD_CLIENT_REGISTER, VRF_DEFAULT);
 
 	zclient_send_reg_requests(zclient, VRF_DEFAULT);
+
+	/* Activate graceful restart if configured. */
+	for (ALL_LIST_ELEMENTS_RO(om6->ospf6, node, ospf6)) {
+		if (!ospf6->gr_info.restart_support)
+			continue;
+		(void)ospf6_zebra_gr_enable(ospf6, ospf6->gr_info.grace_period);
+	}
 }
 
 static zclient_handler *const ospf6_handlers[] = {