Merge pull request #12949 from opensourcerouting/ospf-unplanned-gr

OSPF GR for unplanned outages

28 files changed, 879 insertions, 122 deletions

diff --git a/doc/user/ospf6d.rst b/doc/user/ospf6d.rst
index 8dacb9c9d..2f4c956ff 100644
--- a/doc/user/ospf6d.rst
+++ b/doc/user/ospf6d.rst
@@ -287,6 +287,19 @@ OSPF6 interface
 
    Sets interface's Router Dead Interval. Default value is 40.
 
+.. clicmd:: ipv6 ospf6 graceful-restart hello-delay HELLODELAYINTERVAL
+
+   Set the length of time during which Grace-LSAs are sent at 1-second intervals
+   while coming back up after an unplanned outage. During this time, no hello
+   packets are sent.
+
+   A higher hello delay will increase the chance that all neighbors are notified
+   about the ongoing graceful restart before receiving a hello packet (which is
+   crucial for the graceful restart to succeed). The hello delay shouldn't be set
+   too high, however, otherwise the adjacencies might time out. As a best practice,
+   it's recommended to set the hello delay and hello interval with the same values.
+   The default value is 10 seconds.
+
 .. clicmd:: ipv6 ospf6 retransmit-interval RETRANSMITINTERVAL
 
    Sets interface's Rxmt Interval. Default value is 5.
@@ -343,6 +356,10 @@ 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/doc/user/ospfd.rst b/doc/user/ospfd.rst
index 517183260..effad0fd0 100644
--- a/doc/user/ospfd.rst
+++ b/doc/user/ospfd.rst
@@ -635,6 +635,19 @@ Interfaces
    :clicmd:`ip ospf dead-interval minimal hello-multiplier (2-20)` is also
    specified for the interface.
 
+.. clicmd:: ip ospf graceful-restart hello-delay (1-1800)
+
+   Set the length of time during which Grace-LSAs are sent at 1-second intervals
+   while coming back up after an unplanned outage. During this time, no hello
+   packets are sent.
+
+   A higher hello delay will increase the chance that all neighbors are notified
+   about the ongoing graceful restart before receiving a hello packet (which is
+   crucial for the graceful restart to succeed). The hello delay shouldn't be set
+   too high, however, otherwise the adjacencies might time out. As a best practice,
+   it's recommended to set the hello delay and hello interval with the same values.
+   The default value is 10 seconds.
+
 .. clicmd:: ip ospf network (broadcast|non-broadcast|point-to-multipoint|point-to-point [dmvpn])
 
    When configuring a point-to-point network on an interface and the interface
@@ -770,6 +783,10 @@ Graceful Restart
    To perform a graceful shutdown, the "graceful-restart prepare ip ospf"
    EXEC-level command needs to be issued before restarting the ospfd daemon.
 
+   When Graceful Restart is enabled and the ospfd 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/lib/libospf.h b/lib/libospf.h
index 3262534de..676b563ff 100644
--- a/lib/libospf.h
+++ b/lib/libospf.h
@@ -55,6 +55,7 @@ extern "C" {
 #define OSPF_ROUTER_DEAD_INTERVAL_DEFAULT  40
 #define OSPF_ROUTER_DEAD_INTERVAL_MINIMAL   1
 #define OSPF_HELLO_INTERVAL_DEFAULT        10
+#define OSPF_HELLO_DELAY_DEFAULT           10
 #define OSPF_ROUTER_PRIORITY_DEFAULT        1
 #define OSPF_RETRANSMIT_INTERVAL_DEFAULT    5
 #define OSPF_TRANSMIT_DELAY_DEFAULT         1
diff --git a/ospf6d/ospf6_gr.c b/ospf6d/ospf6_gr.c
index 976eb529d..3d5d4d259 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);
-
-	/* Originate */
-	ospf6_lsa_originate_interface(lsa, oi);
+	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] = {};
+
+		/* 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;
 
@@ -156,6 +190,14 @@ static void ospf6_gr_restart_exit(struct ospf6 *ospf6, const char *reason)
 		OSPF6_INTRA_PREFIX_LSA_SCHEDULE_STUB(area);
 
 		for (ALL_LIST_ELEMENTS_RO(area->if_list, anode, oi)) {
+			/* Disable hello delay. */
+			if (oi->gr.hello_delay.t_grace_send) {
+				oi->gr.hello_delay.elapsed_seconds = 0;
+				EVENT_OFF(oi->gr.hello_delay.t_grace_send);
+				event_add_event(master, ospf6_hello_send, oi, 0,
+						&oi->thread_send_hello);
+			}
+
 			/* Reoriginate Link-LSA. */
 			if (oi->type != OSPF_IFTYPE_VIRTUALLINK)
 				OSPF6_LINK_LSA_EXECUTE(oi);
@@ -195,6 +237,26 @@ 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
@@ -466,11 +528,26 @@ static void ospf6_gr_grace_period_expired(struct event *thread)
 	ospf6_gr_restart_exit(ospf6, "grace period has expired");
 }
 
+/* Send extra Grace-LSA out the interface (unplanned outages only). */
+void ospf6_gr_iface_send_grace_lsa(struct event *thread)
+{
+	struct ospf6_interface *oi = EVENT_ARG(thread);
+
+	ospf6_gr_lsa_originate(oi, oi->area->ospf6->gr_info.reason);
+
+	if (++oi->gr.hello_delay.elapsed_seconds < oi->gr.hello_delay.interval)
+		event_add_timer(master, ospf6_gr_iface_send_grace_lsa, oi, 1,
+				&oi->gr.hello_delay.t_grace_send);
+	else
+		event_add_event(master, ospf6_hello_send, oi, 0,
+				&oi->thread_send_hello);
+}
+
 /*
  * 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 +573,18 @@ 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 +595,7 @@ 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 +631,7 @@ 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 +653,33 @@ 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 +689,24 @@ 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);
+
+	/* Start GR hello-delay interval. */
+	oi->gr.hello_delay.elapsed_seconds = 0;
+	event_add_timer(master, ospf6_gr_iface_send_grace_lsa, oi, 1,
+			&oi->gr.hello_delay.t_grace_send);
+}
+
 /* Prepare to start a Graceful Restart. */
 static void ospf6_gr_prepare(void)
 {
@@ -625,25 +727,17 @@ 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 +808,12 @@ 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 +836,8 @@ 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 2c7e8b341..e6566a609 100644
--- a/ospf6d/ospf6_gr.h
+++ b/ospf6d/ospf6_gr.h
@@ -155,9 +155,15 @@ 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_iface_send_grace_lsa(struct event *thread);
+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 e7148d66b..ea059c4be 100644
--- a/ospf6d/ospf6_interface.c
+++ b/ospf6d/ospf6_interface.c
@@ -35,6 +35,7 @@
 #include "ospf6_proto.h"
 #include "lib/keychain.h"
 #include "ospf6_auth_trailer.h"
+#include "ospf6d/ospf6_interface_clippy.c"
 
 DEFINE_MTYPE_STATIC(OSPF6D, OSPF6_IF, "OSPF6 interface");
 DEFINE_MTYPE(OSPF6D, OSPF6_AUTH_KEYCHAIN, "OSPF6 auth keychain");
@@ -202,6 +203,7 @@ struct ospf6_interface *ospf6_interface_create(struct interface *ifp)
 	oi->priority = OSPF6_INTERFACE_PRIORITY;
 
 	oi->hello_interval = OSPF_HELLO_INTERVAL_DEFAULT;
+	oi->gr.hello_delay.interval = OSPF_HELLO_DELAY_DEFAULT;
 	oi->dead_interval = OSPF_ROUTER_DEAD_INTERVAL_DEFAULT;
 	oi->rxmt_interval = OSPF_RETRANSMIT_INTERVAL_DEFAULT;
 	oi->type = ospf6_default_iftype(ifp);
@@ -324,6 +326,9 @@ void ospf6_interface_disable(struct ospf6_interface *oi)
 	EVENT_OFF(oi->thread_intra_prefix_lsa);
 	EVENT_OFF(oi->thread_as_extern_lsa);
 	EVENT_OFF(oi->thread_wait_timer);
+
+	oi->gr.hello_delay.elapsed_seconds = 0;
+	EVENT_OFF(oi->gr.hello_delay.t_grace_send);
 }
 
 static struct in6_addr *
@@ -772,6 +777,17 @@ 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
@@ -1180,6 +1196,9 @@ static int ospf6_interface_show(struct vty *vty, struct interface *ifp,
 				json_arr, json_object_new_string(lsa->name));
 		json_object_object_add(json_obj, "pendingLsaLsAck", json_arr);
 
+		if (oi->gr.hello_delay.interval != 0)
+			json_object_int_add(json_obj, "grHelloDelaySecs",
+					    oi->gr.hello_delay.interval);
 	} else {
 		timerclear(&res);
 		if (event_is_scheduled(oi->thread_send_lsupdate))
@@ -1205,6 +1224,10 @@ static int ospf6_interface_show(struct vty *vty, struct interface *ifp,
 								   : "off"));
 		for (ALL_LSDB(oi->lsack_list, lsa, lsanext))
 			vty_out(vty, "      %s\n", lsa->name);
+
+		if (oi->gr.hello_delay.interval != 0)
+			vty_out(vty, "  Graceful Restart hello delay: %us\n",
+				oi->gr.hello_delay.interval);
 	}
 
 	/* BFD specific. */
@@ -2157,6 +2180,50 @@ ALIAS (ipv6_ospf6_deadinterval,
        "Interval time after which a neighbor is declared down\n"
        SECONDS_STR)
 
+DEFPY(ipv6_ospf6_gr_hdelay, ipv6_ospf6_gr_hdelay_cmd,
+      "ipv6 ospf6 graceful-restart hello-delay (1-1800)",
+      IP6_STR
+      OSPF6_STR
+      "Graceful Restart parameters\n"
+      "Delay the sending of the first hello packets.\n"
+      "Delay in seconds\n")
+{
+	VTY_DECLVAR_CONTEXT(interface, ifp);
+	struct ospf6_interface *oi;
+
+	oi = ifp->info;
+	if (oi == NULL)
+		oi = ospf6_interface_create(ifp);
+
+	/* Note: new or updated value won't affect ongoing graceful restart. */
+	oi->gr.hello_delay.interval = hello_delay;
+
+	return CMD_SUCCESS;
+}
+
+DEFPY(no_ipv6_ospf6_gr_hdelay, no_ipv6_ospf6_gr_hdelay_cmd,
+      "no ipv6 ospf6 graceful-restart hello-delay [(1-1800)]",
+      NO_STR
+      IP6_STR
+      OSPF6_STR
+      "Graceful Restart parameters\n"
+      "Delay the sending of the first hello packets.\n"
+      "Delay in seconds\n")
+{
+	VTY_DECLVAR_CONTEXT(interface, ifp);
+	struct ospf6_interface *oi;
+
+	oi = ifp->info;
+	if (oi == NULL)
+		oi = ospf6_interface_create(ifp);
+
+	oi->gr.hello_delay.interval = OSPF_HELLO_DELAY_DEFAULT;
+	oi->gr.hello_delay.elapsed_seconds = 0;
+	EVENT_OFF(oi->gr.hello_delay.t_grace_send);
+
+	return CMD_SUCCESS;
+}
+
 /* interface variable set command */
 DEFUN (ipv6_ospf6_transmitdelay,
        ipv6_ospf6_transmitdelay_cmd,
@@ -2624,6 +2691,11 @@ static int config_write_ospf6_interface(struct vty *vty, struct vrf *vrf)
 		else if (oi->type_cfg && oi->type == OSPF_IFTYPE_BROADCAST)
 			vty_out(vty, " ipv6 ospf6 network broadcast\n");
 
+		if (oi->gr.hello_delay.interval != OSPF_HELLO_DELAY_DEFAULT)
+			vty_out(vty,
+				" ipv6 ospf6 graceful-restart hello-delay %u\n",
+				oi->gr.hello_delay.interval);
+
 		ospf6_bfd_write_config(vty, oi);
 
 		ospf6_auth_write_config(vty, &oi->at_data);
@@ -2722,12 +2794,14 @@ void ospf6_interface_init(void)
 
 	install_element(INTERFACE_NODE, &ipv6_ospf6_deadinterval_cmd);
 	install_element(INTERFACE_NODE, &ipv6_ospf6_hellointerval_cmd);
+	install_element(INTERFACE_NODE, &ipv6_ospf6_gr_hdelay_cmd);
 	install_element(INTERFACE_NODE, &ipv6_ospf6_priority_cmd);
 	install_element(INTERFACE_NODE, &ipv6_ospf6_retransmitinterval_cmd);
 	install_element(INTERFACE_NODE, &ipv6_ospf6_transmitdelay_cmd);
 	install_element(INTERFACE_NODE, &ipv6_ospf6_instance_cmd);
 	install_element(INTERFACE_NODE, &no_ipv6_ospf6_deadinterval_cmd);
 	install_element(INTERFACE_NODE, &no_ipv6_ospf6_hellointerval_cmd);
+	install_element(INTERFACE_NODE, &no_ipv6_ospf6_gr_hdelay_cmd);
 	install_element(INTERFACE_NODE, &no_ipv6_ospf6_priority_cmd);
 	install_element(INTERFACE_NODE, &no_ipv6_ospf6_retransmitinterval_cmd);
 	install_element(INTERFACE_NODE, &no_ipv6_ospf6_transmitdelay_cmd);
diff --git a/ospf6d/ospf6_interface.h b/ospf6d/ospf6_interface.h
index ae0744b25..5942df0ab 100644
--- a/ospf6d/ospf6_interface.h
+++ b/ospf6d/ospf6_interface.h
@@ -74,6 +74,15 @@ struct ospf6_interface {
 	uint16_t dead_interval;
 	uint32_t rxmt_interval;
 
+	/* Graceful-Restart data. */
+	struct {
+		struct {
+			uint16_t interval;
+			uint16_t elapsed_seconds;
+			struct event *t_grace_send;
+		} hello_delay;
+	} gr;
+
 	uint32_t state_change;
 
 	/* Cost */
diff --git a/ospf6d/ospf6_message.c b/ospf6d/ospf6_message.c
index 14b02dac7..032988a91 100644
--- a/ospf6d/ospf6_message.c
+++ b/ospf6d/ospf6_message.c
@@ -2244,6 +2244,10 @@ void ospf6_hello_send(struct event *thread)
 
 	oi = (struct ospf6_interface *)EVENT_ARG(thread);
 
+	/* Check if the GR hello-delay is active. */
+	if (oi->gr.hello_delay.t_grace_send)
+		return;
+
 	if (oi->state <= OSPF6_INTERFACE_DOWN) {
 		if (IS_OSPF6_DEBUG_MESSAGE(OSPF6_MESSAGE_TYPE_HELLO, SEND_HDR))
 			zlog_debug("Unable to send Hello on down interface %s",
diff --git a/ospf6d/ospf6_spf.c b/ospf6d/ospf6_spf.c
index 0990b1430..e39ae504a 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 c2aa3abee..01c962194 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 8fdd29112..a38dad8fc 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 6b3d4955d..0f631c4d0 100644
--- a/ospf6d/ospf6_zebra.c
+++ b/ospf6d/ospf6_zebra.c
@@ -239,12 +239,18 @@ static int ospf6_zebra_gr_update(struct ospf6 *ospf6, int command,
 
 int ospf6_zebra_gr_enable(struct ospf6 *ospf6, uint32_t stale_time)
 {
+	if (IS_DEBUG_OSPF6_GR)
+		zlog_debug("Zebra enable GR [stale time %u]", stale_time);
+
 	return ospf6_zebra_gr_update(ospf6, ZEBRA_CLIENT_GR_CAPABILITIES,
 				     stale_time);
 }
 
 int ospf6_zebra_gr_disable(struct ospf6 *ospf6)
 {
+	if (IS_DEBUG_OSPF6_GR)
+		zlog_debug("Zebra disable GR");
+
 	return ospf6_zebra_gr_update(ospf6, ZEBRA_CLIENT_GR_DISABLE, 0);
 }
 
@@ -735,10 +741,20 @@ 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[] = {
diff --git a/ospf6d/subdir.am b/ospf6d/subdir.am
index 3dff03956..c34db3012 100644
--- a/ospf6d/subdir.am
+++ b/ospf6d/subdir.am
@@ -78,6 +78,7 @@ clippy_scan += \
 	ospf6d/ospf6_top.c \
 	ospf6d/ospf6_area.c \
 	ospf6d/ospf6_asbr.c \
+	ospf6d/ospf6_interface.c \
 	ospf6d/ospf6_lsa.c \
 	ospf6d/ospf6_gr_helper.c \
 	ospf6d/ospf6_gr.c \
diff --git a/ospfd/ospf_ase.c b/ospfd/ospf_ase.c
index cc2110d43..610b5fc08 100644
--- a/ospfd/ospf_ase.c
+++ b/ospfd/ospf_ase.c
@@ -615,6 +615,7 @@ static void ospf_ase_calculate_timer(struct event *t)
 	 */
 	if (ospf->gr_info.finishing_restart) {
 		ospf_zebra_gr_disable(ospf);
+		ospf_zebra_gr_enable(ospf, ospf->gr_info.grace_period);
 		ospf->gr_info.finishing_restart = false;
 	}
 }
diff --git a/ospfd/ospf_gr.c b/ospfd/ospf_gr.c
index f60f0e863..6999b3f62 100644
--- a/ospfd/ospf_gr.c
+++ b/ospfd/ospf_gr.c
@@ -33,7 +33,7 @@
 #include "ospfd/ospf_dump.h"
 #include "ospfd/ospf_gr_clippy.c"
 
-static void ospf_gr_nvm_delete(struct ospf *ospf);
+static void ospf_gr_grace_period_expired(struct event *thread);
 
 /* Lookup self-originated Grace-LSA in the LSDB. */
 static struct ospf_lsa *ospf_gr_lsa_lookup(struct ospf *ospf,
@@ -53,7 +53,9 @@ static struct ospf_lsa *ospf_gr_lsa_lookup(struct ospf *ospf,
 
 /* Fill in fields of the Grace-LSA that is being originated. */
 static void ospf_gr_lsa_body_set(struct ospf_gr_info *gr_info,
-				 struct ospf_interface *oi, struct stream *s)
+				 struct ospf_interface *oi,
+				 enum ospf_gr_restart_reason reason,
+				 struct stream *s)
 {
 	struct grace_tlv_graceperiod tlv_period = {};
 	struct grace_tlv_restart_reason tlv_reason = {};
@@ -68,10 +70,7 @@ static void ospf_gr_lsa_body_set(struct ospf_gr_info *gr_info,
 	/* Put restart reason. */
 	tlv_reason.header.type = htons(RESTART_REASON_TYPE);
 	tlv_reason.header.length = htons(RESTART_REASON_LENGTH);
-	if (gr_info->restart_support)
-		tlv_reason.reason = OSPF_GR_SW_RESTART;
-	else
-		tlv_reason.reason = OSPF_GR_UNKNOWN_RESTART;
+	tlv_reason.reason = reason;
 	stream_put(s, &tlv_reason, sizeof(tlv_reason));
 
 	/* Put IP address. */
@@ -85,7 +84,8 @@ static void ospf_gr_lsa_body_set(struct ospf_gr_info *gr_info,
 }
 
 /* Generate Grace-LSA for a given interface. */
-static struct ospf_lsa *ospf_gr_lsa_new(struct ospf_interface *oi)
+static struct ospf_lsa *ospf_gr_lsa_new(struct ospf_interface *oi,
+					enum ospf_gr_restart_reason reason)
 {
 	struct stream *s;
 	struct lsa_header *lsah;
@@ -112,7 +112,7 @@ static struct ospf_lsa *ospf_gr_lsa_new(struct ospf_interface *oi)
 	lsa_header_set(s, options, lsa_type, lsa_id, oi->ospf->router_id);
 
 	/* Set opaque-LSA body fields. */
-	ospf_gr_lsa_body_set(&oi->ospf->gr_info, oi, s);
+	ospf_gr_lsa_body_set(&oi->ospf->gr_info, oi, reason, s);
 
 	/* Set length. */
 	length = stream_get_endp(s);
@@ -135,15 +135,20 @@ static struct ospf_lsa *ospf_gr_lsa_new(struct ospf_interface *oi)
 }
 
 /* Originate and install Grace-LSA for a given interface. */
-static void ospf_gr_lsa_originate(struct ospf_interface *oi, bool maxage)
+static void ospf_gr_lsa_originate(struct ospf_interface *oi,
+				  enum ospf_gr_restart_reason reason,
+				  bool maxage)
 {
 	struct ospf_lsa *lsa, *old;
 
-	if (ospf_interface_neighbor_count(oi) == 0)
+	/* Skip originating a Grace-LSA when not necessary. */
+	if (!if_is_operative(oi->ifp) || if_is_loopback(oi->ifp) ||
+	    (reason != OSPF_GR_UNKNOWN_RESTART &&
+	     ospf_interface_neighbor_count(oi) == 0))
 		return;
 
 	/* Create new Grace-LSA. */
-	lsa = ospf_gr_lsa_new(oi);
+	lsa = ospf_gr_lsa_new(oi, reason);
 	if (!lsa) {
 		zlog_warn("%s: ospf_gr_lsa_new() failed", __func__);
 		return;
@@ -157,18 +162,36 @@ static void ospf_gr_lsa_originate(struct ospf_interface *oi, bool maxage)
 	if (old)
 		lsa->data->ls_seqnum = lsa_seqnum_increment(old);
 
-	/* Install this LSA into LSDB. */
-	if (ospf_lsa_install(oi->ospf, oi, lsa) == NULL) {
-		zlog_warn("%s: ospf_lsa_install() failed", __func__);
-		ospf_lsa_unlock(&lsa);
-		return;
+	if (!maxage && reason == OSPF_GR_UNKNOWN_RESTART) {
+		struct list *update;
+		struct in_addr addr;
+
+		/*
+		 * When performing an unplanned restart, send a handcrafted
+		 * Grace-LSA since the interface isn't fully initialized yet.
+		 */
+		ospf_lsa_checksum(lsa->data);
+		ospf_lsa_lock(lsa);
+		update = list_new();
+		listnode_add(update, lsa);
+		addr.s_addr = htonl(OSPF_ALLSPFROUTERS);
+		ospf_ls_upd_queue_send(oi, update, addr, true);
+		list_delete(&update);
+		ospf_lsa_discard(lsa);
+	} else {
+		/* Install this LSA into LSDB. */
+		if (ospf_lsa_install(oi->ospf, oi, lsa) == NULL) {
+			zlog_warn("%s: ospf_lsa_install() failed", __func__);
+			ospf_lsa_unlock(&lsa);
+			return;
+		}
+
+		/* Flood the LSA through out the interface */
+		ospf_flood_through_interface(oi, NULL, lsa);
 	}
 
 	/* Update new LSA origination count. */
 	oi->ospf->lsa_originate_count++;
-
-	/* Flood the LSA through out the interface */
-	ospf_flood_through_interface(oi, NULL, lsa);
 }
 
 /* Flush all self-originated Grace-LSAs. */
@@ -181,13 +204,14 @@ static void ospf_gr_flush_grace_lsas(struct ospf *ospf)
 		struct ospf_interface *oi;
 		struct listnode *inode;
 
-		if (IS_DEBUG_OSPF_GR)
-			zlog_debug(
-				"GR: flushing self-originated Grace-LSAs [area %pI4]",
-				&area->area_id);
+		for (ALL_LIST_ELEMENTS_RO(area->oiflist, inode, oi)) {
+			if (IS_DEBUG_OSPF_GR)
+				zlog_debug(
+					"GR: flushing self-originated Grace-LSA [area %pI4] [interface %s]",
+					&area->area_id, oi->ifp->name);
 
-		for (ALL_LIST_ELEMENTS_RO(area->oiflist, inode, oi))
-			ospf_gr_lsa_originate(oi, true);
+			ospf_gr_lsa_originate(oi, ospf->gr_info.reason, true);
+		}
 	}
 }
 
@@ -203,9 +227,6 @@ static void ospf_gr_restart_exit(struct ospf *ospf, const char *reason)
 	ospf->gr_info.restart_in_progress = false;
 	EVENT_OFF(ospf->gr_info.t_grace_period);
 
-	/* Record in non-volatile memory that the restart is complete. */
-	ospf_gr_nvm_delete(ospf);
-
 	for (ALL_LIST_ELEMENTS_RO(ospf->areas, onode, area)) {
 		struct ospf_interface *oi;
 
@@ -216,13 +237,22 @@ static void ospf_gr_restart_exit(struct ospf *ospf, const char *reason)
 		 */
 		ospf_router_lsa_update_area(area);
 
-		/*
-		 * 2) The router should reoriginate network-LSAs on all segments
-		 *    where it is the Designated Router.
-		 */
-		for (ALL_LIST_ELEMENTS_RO(area->oiflist, anode, oi))
+		for (ALL_LIST_ELEMENTS_RO(area->oiflist, anode, oi)) {
+			/* Disable hello delay. */
+			if (oi->gr.hello_delay.t_grace_send) {
+				oi->gr.hello_delay.elapsed_seconds = 0;
+				EVENT_OFF(oi->gr.hello_delay.t_grace_send);
+				OSPF_ISM_TIMER_MSEC_ON(oi->t_hello,
+						       ospf_hello_timer, 1);
+			}
+
+			/*
+			 * 2) The router should reoriginate network-LSAs on all
+			 * segments where it is the Designated Router.
+			 */
 			if (oi->state == ISM_DR)
 				ospf_network_lsa_update(oi);
+		}
 	}
 
 	/*
@@ -242,12 +272,34 @@ static void ospf_gr_restart_exit(struct ospf *ospf, const char *reason)
 	 *    should be removed.
 	 */
 	ospf->gr_info.finishing_restart = true;
+	XFREE(MTYPE_TMP, ospf->gr_info.exit_reason);
+	ospf->gr_info.exit_reason = XSTRDUP(MTYPE_TMP, reason);
 	ospf_spf_calculate_schedule(ospf, SPF_FLAG_GR_FINISH);
 
 	/* 6) Any grace-LSAs that the router originated should be flushed. */
 	ospf_gr_flush_grace_lsas(ospf);
 }
 
+/* Enter the Graceful Restart mode. */
+void ospf_gr_restart_enter(struct ospf *ospf,
+			   enum ospf_gr_restart_reason reason, int timestamp)
+{
+	unsigned long remaining_time;
+
+	ospf->gr_info.restart_in_progress = true;
+	ospf->gr_info.reason = reason;
+
+	/* Schedule grace period timeout. */
+	remaining_time = timestamp - time(NULL);
+	if (IS_DEBUG_OSPF_GR)
+		zlog_debug(
+			"GR: remaining time until grace period expires: %lu(s)",
+			remaining_time);
+
+	event_add_timer(master, ospf_gr_grace_period_expired, ospf,
+			remaining_time, &ospf->gr_info.t_grace_period);
+}
+
 /* Check if a Router-LSA contains a given link. */
 static bool ospf_router_lsa_contains_adj(struct ospf_lsa *lsa,
 					 struct in_addr *id)
@@ -518,11 +570,26 @@ static char *ospf_gr_nvm_filepath(struct ospf *ospf)
 	return filepath;
 }
 
+/* Send extra Grace-LSA out the interface (unplanned outages only). */
+void ospf_gr_iface_send_grace_lsa(struct event *thread)
+{
+	struct ospf_interface *oi = EVENT_ARG(thread);
+	struct ospf_if_params *params = IF_DEF_PARAMS(oi->ifp);
+
+	ospf_gr_lsa_originate(oi, oi->ospf->gr_info.reason, false);
+
+	if (++oi->gr.hello_delay.elapsed_seconds < params->v_gr_hello_delay)
+		event_add_timer(master, ospf_gr_iface_send_grace_lsa, oi, 1,
+				&oi->gr.hello_delay.t_grace_send);
+	else
+		OSPF_ISM_TIMER_MSEC_ON(oi->t_hello, ospf_hello_timer, 1);
+}
+
 /*
  * Record in non-volatile memory that the given OSPF instance is attempting to
  * perform a graceful restart.
  */
-static void ospf_gr_nvm_update(struct ospf *ospf)
+static void ospf_gr_nvm_update(struct ospf *ospf, bool prepare)
 {
 	char *filepath;
 	const char *inst_name;
@@ -550,16 +617,18 @@ static void ospf_gr_nvm_update(struct ospf *ospf)
 				       json_instance);
 	}
 
+	json_object_int_add(json_instance, "gracePeriod",
+			    ospf->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 ospfd is
 	 * restarted, it will be possible to take into account the time that
 	 * passed while ospfd wasn't running.
 	 */
-	json_object_int_add(json_instance, "gracePeriod",
-			    ospf->gr_info.grace_period);
-	json_object_int_add(json_instance, "timestamp",
-			    time(NULL) + ospf->gr_info.grace_period);
+	if (prepare)
+		json_object_int_add(json_instance, "timestamp",
+				    time(NULL) + ospf->gr_info.grace_period);
 
 	json_object_to_file_ext(filepath, json, JSON_C_TO_STRING_PRETTY);
 	json_object_free(json);
@@ -569,7 +638,7 @@ static void ospf_gr_nvm_update(struct ospf *ospf)
  * Delete GR status information about the given OSPF instance from non-volatile
  * memory.
  */
-static void ospf_gr_nvm_delete(struct ospf *ospf)
+void ospf_gr_nvm_delete(struct ospf *ospf)
 {
 	char *filepath;
 	const char *inst_name;
@@ -607,6 +676,7 @@ void ospf_gr_nvm_read(struct ospf *ospf)
 	json_object *json_instances;
 	json_object *json_instance;
 	json_object *json_timestamp;
+	json_object *json_grace_period;
 	time_t timestamp = 0;
 
 	filepath = ospf_gr_nvm_filepath(ospf);
@@ -629,29 +699,33 @@ void ospf_gr_nvm_read(struct ospf *ospf)
 				       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) {
 			ospf_gr_restart_exit(
 				ospf, "grace period has expired already");
-		} else {
-			/* Schedule grace period timeout. */
-			ospf->gr_info.restart_in_progress = true;
-			remaining_time = timestamp - time(NULL);
-			if (IS_DEBUG_OSPF_GR)
-				zlog_debug(
-					"GR: remaining time until grace period expires: %lu(s)",
-					remaining_time);
-			event_add_timer(master, ospf_gr_grace_period_expired,
-					ospf, remaining_time,
-					&ospf->gr_info.t_grace_period);
-		}
+		} else
+			ospf_gr_restart_enter(ospf, OSPF_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);
+		ospf->gr_info.grace_period = grace_period;
+		ospf_gr_restart_enter(ospf, OSPF_GR_UNKNOWN_RESTART,
+				      time(NULL) + ospf->gr_info.grace_period);
 	}
 
 	json_object_object_del(json_instances, inst_name);
@@ -660,6 +734,17 @@ void ospf_gr_nvm_read(struct ospf *ospf)
 	json_object_free(json);
 }
 
+void ospf_gr_unplanned_start_interface(struct ospf_interface *oi)
+{
+	/* Send Grace-LSA. */
+	ospf_gr_lsa_originate(oi, oi->ospf->gr_info.reason, false);
+
+	/* Start GR hello-delay interval. */
+	oi->gr.hello_delay.elapsed_seconds = 0;
+	event_add_timer(master, ospf_gr_iface_send_grace_lsa, oi, 1,
+			&oi->gr.hello_delay.t_grace_send);
+}
+
 /* Prepare to start a Graceful Restart. */
 static void ospf_gr_prepare(void)
 {
@@ -687,20 +772,12 @@ static void ospf_gr_prepare(void)
 			continue;
 		}
 
-		/* Freeze OSPF routes in the RIB. */
-		if (ospf_zebra_gr_enable(ospf, ospf->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(ospf->oiflist, inode, oi))
-			ospf_gr_lsa_originate(oi, false);
+			ospf_gr_lsa_originate(oi, OSPF_GR_SW_RESTART, false);
 
 		/* Record end of the grace period in non-volatile memory. */
-		ospf_gr_nvm_update(ospf);
+		ospf_gr_nvm_update(ospf, true);
 
 		/*
 		 * Mark that a Graceful Restart preparation is in progress, to
@@ -749,6 +826,12 @@ DEFPY(graceful_restart, graceful_restart_cmd,
 	ospf->gr_info.restart_support = true;
 	ospf->gr_info.grace_period = grace_period;
 
+	/* Freeze OSPF routes in the RIB. */
+	(void)ospf_zebra_gr_enable(ospf, ospf->gr_info.grace_period);
+
+	/* Record that GR is enabled in non-volatile memory. */
+	ospf_gr_nvm_update(ospf, false);
+
 	return CMD_SUCCESS;
 }
 
@@ -771,6 +854,8 @@ DEFPY(no_graceful_restart, no_graceful_restart_cmd,
 
 	ospf->gr_info.restart_support = false;
 	ospf->gr_info.grace_period = OSPF_DFLT_GRACE_INTERVAL;
+	ospf_gr_nvm_delete(ospf);
+	ospf_zebra_gr_disable(ospf);
 
 	return CMD_SUCCESS;
 }
diff --git a/ospfd/ospf_gr.h b/ospfd/ospf_gr.h
index 9760bb172..750d77381 100644
--- a/ospfd/ospf_gr.h
+++ b/ospfd/ospf_gr.h
@@ -166,11 +166,16 @@ extern void ospf_gr_helper_supported_gracetime_set(struct ospf *ospf,
 						   uint32_t interval);
 extern void ospf_gr_helper_set_supported_planned_only_restart(struct ospf *ospf,
 							     bool planned_only);
-
+extern void ospf_gr_iface_send_grace_lsa(struct event *thread);
+extern void ospf_gr_restart_enter(struct ospf *ospf,
+				  enum ospf_gr_restart_reason reason,
+				  int timestamp);
 extern void ospf_gr_check_lsdb_consistency(struct ospf *ospf,
 						  struct ospf_area *area);
 extern void ospf_gr_check_adjs(struct ospf *ospf);
 extern void ospf_gr_nvm_read(struct ospf *ospf);
+extern void ospf_gr_nvm_delete(struct ospf *ospf);
+extern void ospf_gr_unplanned_start_interface(struct ospf_interface *oi);
 extern void ospf_gr_init(void);
 
 #endif /* _ZEBRA_OSPF_GR_H */
diff --git a/ospfd/ospf_interface.c b/ospfd/ospf_interface.c
index f18aa399a..8da982aed 100644
--- a/ospfd/ospf_interface.c
+++ b/ospfd/ospf_interface.c
@@ -530,6 +530,7 @@ static struct ospf_if_params *ospf_new_if_params(void)
 	UNSET_IF_PARAM(oip, passive_interface);
 	UNSET_IF_PARAM(oip, v_hello);
 	UNSET_IF_PARAM(oip, fast_hello);
+	UNSET_IF_PARAM(oip, v_gr_hello_delay);
 	UNSET_IF_PARAM(oip, v_wait);
 	UNSET_IF_PARAM(oip, priority);
 	UNSET_IF_PARAM(oip, type);
@@ -679,6 +680,9 @@ int ospf_if_new_hook(struct interface *ifp)
 	SET_IF_PARAM(IF_DEF_PARAMS(ifp), fast_hello);
 	IF_DEF_PARAMS(ifp)->fast_hello = OSPF_FAST_HELLO_DEFAULT;
 
+	SET_IF_PARAM(IF_DEF_PARAMS(ifp), v_gr_hello_delay);
+	IF_DEF_PARAMS(ifp)->v_gr_hello_delay = OSPF_HELLO_DELAY_DEFAULT;
+
 	SET_IF_PARAM(IF_DEF_PARAMS(ifp), v_wait);
 	IF_DEF_PARAMS(ifp)->v_wait = OSPF_ROUTER_DEAD_INTERVAL_DEFAULT;
 
diff --git a/ospfd/ospf_interface.h b/ospfd/ospf_interface.h
index 649df437a..24768b9ab 100644
--- a/ospfd/ospf_interface.h
+++ b/ospfd/ospf_interface.h
@@ -72,6 +72,9 @@ struct ospf_if_params {
 	DECLARE_IF_PARAM(uint32_t, v_wait);  /* Router Dead Interval */
 	bool is_v_wait_set;                  /* Check for Dead Interval set */
 
+	/* GR Hello Delay Interval */
+	DECLARE_IF_PARAM(uint16_t, v_gr_hello_delay);
+
 	/* MTU mismatch check (see RFC2328, chap 10.6) */
 	DECLARE_IF_PARAM(uint8_t, mtu_ignore);
 
@@ -214,6 +217,14 @@ struct ospf_interface {
 	/* List of configured NBMA neighbor. */
 	struct list *nbr_nbma;
 
+	/* Graceful-Restart data. */
+	struct {
+		struct {
+			uint16_t elapsed_seconds;
+			struct event *t_grace_send;
+		} hello_delay;
+	} gr;
+
 	/* self-originated LSAs. */
 	struct ospf_lsa *network_lsa_self; /* network-LSA. */
 	struct list *opaque_lsa_self;      /* Type-9 Opaque-LSAs */
diff --git a/ospfd/ospf_ism.c b/ospfd/ospf_ism.c
index 9f795ea91..2516fa75d 100644
--- a/ospfd/ospf_ism.c
+++ b/ospfd/ospf_ism.c
@@ -244,6 +244,10 @@ void ospf_hello_timer(struct event *thread)
 	oi = EVENT_ARG(thread);
 	oi->t_hello = NULL;
 
+	/* Check if the GR hello-delay is active. */
+	if (oi->gr.hello_delay.t_grace_send)
+		return;
+
 	if (IS_DEBUG_OSPF(ism, ISM_TIMERS))
 		zlog_debug("ISM[%s]: Timer (Hello timer expire)", IF_NAME(oi));
 
@@ -282,6 +286,7 @@ static void ism_timer_set(struct ospf_interface *oi)
 		EVENT_OFF(oi->t_hello);
 		EVENT_OFF(oi->t_wait);
 		EVENT_OFF(oi->t_ls_ack);
+		EVENT_OFF(oi->gr.hello_delay.t_grace_send);
 		break;
 	case ISM_Loopback:
 		/* In this state, the interface may be looped back and will be
@@ -289,6 +294,7 @@ static void ism_timer_set(struct ospf_interface *oi)
 		EVENT_OFF(oi->t_hello);
 		EVENT_OFF(oi->t_wait);
 		EVENT_OFF(oi->t_ls_ack);
+		EVENT_OFF(oi->gr.hello_delay.t_grace_send);
 		break;
 	case ISM_Waiting:
 		/* The router is trying to determine the identity of DRouter and
diff --git a/ospfd/ospf_packet.c b/ospfd/ospf_packet.c
index fe94c34e4..d010b8b6e 100644
--- a/ospfd/ospf_packet.c
+++ b/ospfd/ospf_packet.c
@@ -4040,9 +4040,8 @@ static struct ospf_packet *ospf_ls_upd_packet_new(struct list *update,
 	return ospf_packet_new(size - sizeof(struct ip));
 }
 
-static void ospf_ls_upd_queue_send(struct ospf_interface *oi,
-				   struct list *update, struct in_addr addr,
-				   int send_lsupd_now)
+void ospf_ls_upd_queue_send(struct ospf_interface *oi, struct list *update,
+			    struct in_addr addr, int send_lsupd_now)
 {
 	struct ospf_packet *op;
 	uint16_t length = OSPF_HEADER_SIZE;
diff --git a/ospfd/ospf_packet.h b/ospfd/ospf_packet.h
index 4003e2add..234738979 100644
--- a/ospfd/ospf_packet.h
+++ b/ospfd/ospf_packet.h
@@ -132,6 +132,9 @@ extern void ospf_ls_req_send(struct ospf_neighbor *);
 extern void ospf_ls_upd_send_lsa(struct ospf_neighbor *, struct ospf_lsa *,
 				 int);
 extern void ospf_ls_upd_send(struct ospf_neighbor *, struct list *, int, int);
+extern void ospf_ls_upd_queue_send(struct ospf_interface *oi,
+				   struct list *update, struct in_addr addr,
+				   int send_lsupd_now);
 extern void ospf_ls_ack_send(struct ospf_neighbor *, struct ospf_lsa *);
 extern void ospf_ls_ack_send_delayed(struct ospf_interface *);
 extern void ospf_ls_retransmit(struct ospf_interface *, struct ospf_lsa *);
diff --git a/ospfd/ospf_vty.c b/ospfd/ospf_vty.c
index 1b4d26ef3..f92be3fca 100644
--- a/ospfd/ospf_vty.c
+++ b/ospfd/ospf_vty.c
@@ -232,9 +232,12 @@ DEFUN (no_router_ospf,
 		return CMD_NOT_MY_INSTANCE;
 
 	ospf = ospf_lookup(instance, vrf_name);
-	if (ospf)
+	if (ospf) {
+		if (ospf->gr_info.restart_support)
+			ospf_gr_nvm_delete(ospf);
+
 		ospf_finish(ospf);
-	else
+	} else
 		ret = CMD_WARNING_CONFIG_FAILED;
 
 	return ret;
@@ -3617,6 +3620,7 @@ static void show_ip_ospf_interface_sub(struct vty *vty, struct ospf *ospf,
 	struct ospf_neighbor *nbr;
 	struct route_node *rn;
 	uint32_t bandwidth = ifp->bandwidth ? ifp->bandwidth : ifp->speed;
+	struct ospf_if_params *params;
 
 	/* Is interface up? */
 	if (use_json) {
@@ -3936,6 +3940,20 @@ static void show_ip_ospf_interface_sub(struct vty *vty, struct ospf *ospf,
 				ospf_nbr_count(oi, 0),
 				ospf_nbr_count(oi, NSM_Full));
 
+
+		params = IF_DEF_PARAMS(ifp);
+		if (params &&
+		    OSPF_IF_PARAM_CONFIGURED(params, v_gr_hello_delay)) {
+			if (use_json) {
+				json_object_int_add(json_interface_sub,
+						    "grHelloDelaySecs",
+						    params->v_gr_hello_delay);
+			} else
+				vty_out(vty,
+					"  Graceful Restart hello delay: %us\n",
+					params->v_gr_hello_delay);
+		}
+
 		ospf_interface_bfd_show(vty, ifp, json_interface_sub);
 
 		/* OSPF Authentication information */
@@ -8639,6 +8657,59 @@ DEFUN_HIDDEN (no_ospf_retransmit_interval,
 	return no_ip_ospf_retransmit_interval(self, vty, argc, argv);
 }
 
+DEFPY (ip_ospf_gr_hdelay,
+       ip_ospf_gr_hdelay_cmd,
+       "ip ospf graceful-restart hello-delay (1-1800)",
+       IP_STR
+       "OSPF interface commands\n"
+       "Graceful Restart parameters\n"
+       "Delay the sending of the first hello packets.\n"
+       "Delay in seconds\n")
+{
+	VTY_DECLVAR_CONTEXT(interface, ifp);
+	struct ospf_if_params *params;
+
+	params = IF_DEF_PARAMS(ifp);
+
+	/* Note: new or updated value won't affect ongoing graceful restart. */
+	SET_IF_PARAM(params, v_gr_hello_delay);
+	params->v_gr_hello_delay = hello_delay;
+
+	return CMD_SUCCESS;
+}
+
+DEFPY (no_ip_ospf_gr_hdelay,
+       no_ip_ospf_gr_hdelay_cmd,
+       "no ip ospf graceful-restart hello-delay [(1-1800)]",
+       NO_STR
+       IP_STR
+       "OSPF interface commands\n"
+       "Graceful Restart parameters\n"
+       "Delay the sending of the first hello packets.\n"
+       "Delay in seconds\n")
+{
+	VTY_DECLVAR_CONTEXT(interface, ifp);
+	struct ospf_if_params *params;
+	struct route_node *rn;
+
+	params = IF_DEF_PARAMS(ifp);
+	UNSET_IF_PARAM(params, v_gr_hello_delay);
+	params->v_gr_hello_delay = OSPF_HELLO_DELAY_DEFAULT;
+
+	for (rn = route_top(IF_OIFS(ifp)); rn; rn = route_next(rn)) {
+		struct ospf_interface *oi;
+
+		oi = rn->info;
+		if (!oi)
+			continue;
+
+		oi->gr.hello_delay.elapsed_seconds = 0;
+		EVENT_OFF(oi->gr.hello_delay.t_grace_send);
+	}
+
+	return CMD_SUCCESS;
+}
+
 DEFUN (ip_ospf_transmit_delay,
        ip_ospf_transmit_delay_addr_cmd,
        "ip ospf transmit-delay (1-65535) [A.B.C.D]",
@@ -11831,6 +11902,15 @@ static int config_write_interface_one(struct vty *vty, struct vrf *vrf)
 				vty_out(vty, "\n");
 			}
 
+			/* Hello Graceful-Restart Delay print. */
+			if (OSPF_IF_PARAM_CONFIGURED(params,
+						     v_gr_hello_delay) &&
+			    params->v_gr_hello_delay !=
+				    OSPF_HELLO_DELAY_DEFAULT)
+				vty_out(vty,
+					" ip ospf graceful-restart hello-delay %u\n",
+					params->v_gr_hello_delay);
+
 			/* Router Priority print. */
 			if (OSPF_IF_PARAM_CONFIGURED(params, priority)
 			    && params->priority
diff --git a/ospfd/ospf_zebra.c b/ospfd/ospf_zebra.c
index 0b770a836..27d74cd4f 100644
--- a/ospfd/ospf_zebra.c
+++ b/ospfd/ospf_zebra.c
@@ -1252,12 +1252,18 @@ static int ospf_zebra_gr_update(struct ospf *ospf, int command,
 
 int ospf_zebra_gr_enable(struct ospf *ospf, uint32_t stale_time)
 {
+	if (IS_DEBUG_OSPF_GR)
+		zlog_debug("Zebra enable GR [stale time %u]", stale_time);
+
 	return ospf_zebra_gr_update(ospf, ZEBRA_CLIENT_GR_CAPABILITIES,
 				    stale_time);
 }
 
 int ospf_zebra_gr_disable(struct ospf *ospf)
 {
+	if (IS_DEBUG_OSPF_GR)
+		zlog_debug("Zebra disable GR");
+
 	return ospf_zebra_gr_update(ospf, ZEBRA_CLIENT_GR_DISABLE, 0);
 }
 
@@ -2120,10 +2126,20 @@ int ospf_zebra_label_manager_connect(void)
 
 static void ospf_zebra_connected(struct zclient *zclient)
 {
+	struct ospf *ospf;
+	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(om->ospf, node, ospf)) {
+		if (!ospf->gr_info.restart_support)
+			continue;
+		(void)ospf_zebra_gr_enable(ospf, ospf->gr_info.grace_period);
+	}
 }
 
 /*
diff --git a/ospfd/ospfd.c b/ospfd/ospfd.c
index 7e83714c0..eae1f301a 100644
--- a/ospfd/ospfd.c
+++ b/ospfd/ospfd.c
@@ -720,6 +720,7 @@ static void ospf_finish_final(struct ospf *ospf)
 
 	if (!ospf->gr_info.prepare_in_progress)
 		ospf_flush_self_originated_lsas_now(ospf);
+	XFREE(MTYPE_TMP, ospf->gr_info.exit_reason);
 
 	/* Unregister redistribution */
 	for (i = 0; i < ZEBRA_ROUTE_MAX; i++) {
@@ -1131,6 +1132,17 @@ struct ospf_interface *add_ospf_interface(struct connected *co,
 	    && if_is_operative(co->ifp))
 		ospf_if_up(oi);
 
+	/*
+	 * 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->ospf->gr_info.restart_in_progress &&
+	    oi->ospf->gr_info.reason == OSPF_GR_UNKNOWN_RESTART)
+		ospf_gr_unplanned_start_interface(oi);
+
 	return oi;
 }
 
diff --git a/ospfd/ospfd.h b/ospfd/ospfd.h
index 1f8d1a32e..36936b16f 100644
--- a/ospfd/ospfd.h
+++ b/ospfd/ospfd.h
@@ -148,6 +148,8 @@ struct ospf_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/tests/topotests/all_protocol_startup/r1/show_ip_ospf_interface.ref b/tests/topotests/all_protocol_startup/r1/show_ip_ospf_interface.ref
index cb63da471..7e28f04e1 100644
--- a/tests/topotests/all_protocol_startup/r1/show_ip_ospf_interface.ref
+++ b/tests/topotests/all_protocol_startup/r1/show_ip_ospf_interface.ref
@@ -10,6 +10,7 @@ r1-eth0 is up
   Timer intervals configured, Hello 1s, Dead 5s, Wait 5s, Retransmit 5
     Hello due in XX.XXXs
   Neighbor Count is 0, Adjacent neighbor count is 0
+  Graceful Restart hello delay: 10s
 r1-eth3 is up
   ifindex X, MTU 1500 bytes, BW XX Mbit <UP,BROADCAST,RUNNING,MULTICAST>
   Internet Address 192.168.3.1/26, Broadcast 192.168.3.63, Area 0.0.0.0
@@ -22,3 +23,4 @@ r1-eth3 is up
   Timer intervals configured, Hello 1s, Dead 5s, Wait 5s, Retransmit 5
     Hello due in XX.XXXs
   Neighbor Count is 0, Adjacent neighbor count is 0
+  Graceful Restart hello delay: 10s
diff --git a/tests/topotests/ospf6_gr_topo1/test_ospf6_gr_topo1.py b/tests/topotests/ospf6_gr_topo1/test_ospf6_gr_topo1.py
index aa43b977b..45e1bc8db 100755
--- a/tests/topotests/ospf6_gr_topo1/test_ospf6_gr_topo1.py
+++ b/tests/topotests/ospf6_gr_topo1/test_ospf6_gr_topo1.py
@@ -430,6 +430,144 @@ def test_gr_rt7():
     check_routers(restarting="rt7")
 
 
+#
+# Test rt1 performing an unplanned graceful restart
+#
+def test_unplanned_gr_rt1():
+    logger.info("Test: verify rt1 performing an unplanned graceful restart")
+    tgen = get_topogen()
+
+    # Skip if previous fatal error condition is raised
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    kill_router_daemons(tgen, "rt1", ["ospf6d"], save_config=False)
+    start_router_daemons(tgen, "rt1", ["ospf6d"])
+
+    expect_grace_lsa(restarting="1.1.1.1", helper="rt2")
+    ensure_gr_is_in_zebra("rt1")
+    check_routers(restarting="rt1")
+
+
+#
+# Test rt2 performing an unplanned graceful restart
+#
+def test_unplanned_gr_rt2():
+    logger.info("Test: verify rt2 performing an unplanned graceful restart")
+    tgen = get_topogen()
+
+    # Skip if previous fatal error condition is raised
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    kill_router_daemons(tgen, "rt2", ["ospf6d"], save_config=False)
+    start_router_daemons(tgen, "rt2", ["ospf6d"])
+
+    expect_grace_lsa(restarting="2.2.2.2", helper="rt1")
+    expect_grace_lsa(restarting="2.2.2.2", helper="rt3")
+    ensure_gr_is_in_zebra("rt2")
+    check_routers(restarting="rt2")
+
+
+#
+# Test rt3 performing an unplanned graceful restart
+#
+def test_unplanned_gr_rt3():
+    logger.info("Test: verify rt3 performing an unplanned graceful restart")
+    tgen = get_topogen()
+
+    # Skip if previous fatal error condition is raised
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    kill_router_daemons(tgen, "rt3", ["ospf6d"], save_config=False)
+    start_router_daemons(tgen, "rt3", ["ospf6d"])
+
+    expect_grace_lsa(restarting="3.3.3.3", helper="rt2")
+    expect_grace_lsa(restarting="3.3.3.3", helper="rt4")
+    expect_grace_lsa(restarting="3.3.3.3", helper="rt6")
+    ensure_gr_is_in_zebra("rt3")
+    check_routers(restarting="rt3")
+
+
+#
+# Test rt4 performing an unplanned graceful restart
+#
+def test_unplanned_gr_rt4():
+    logger.info("Test: verify rt4 performing an unplanned graceful restart")
+    tgen = get_topogen()
+
+    # Skip if previous fatal error condition is raised
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    kill_router_daemons(tgen, "rt4", ["ospf6d"], save_config=False)
+    start_router_daemons(tgen, "rt4", ["ospf6d"])
+
+    expect_grace_lsa(restarting="4.4.4.4", helper="rt3")
+    expect_grace_lsa(restarting="4.4.4.4", helper="rt5")
+    ensure_gr_is_in_zebra("rt4")
+    check_routers(restarting="rt4")
+
+
+#
+# Test rt5 performing an unplanned graceful restart
+#
+def test_unplanned_gr_rt5():
+    logger.info("Test: verify rt5 performing an unplanned graceful restart")
+    tgen = get_topogen()
+
+    # Skip if previous fatal error condition is raised
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    kill_router_daemons(tgen, "rt5", ["ospf6d"], save_config=False)
+    start_router_daemons(tgen, "rt5", ["ospf6d"])
+
+    expect_grace_lsa(restarting="5.5.5.5", helper="rt4")
+    ensure_gr_is_in_zebra("rt5")
+    check_routers(restarting="rt5")
+
+
+#
+# Test rt6 performing an unplanned graceful restart
+#
+def test_unplanned_gr_rt6():
+    logger.info("Test: verify rt6 performing an unplanned graceful restart")
+    tgen = get_topogen()
+
+    # Skip if previous fatal error condition is raised
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    kill_router_daemons(tgen, "rt6", ["ospf6d"], save_config=False)
+    start_router_daemons(tgen, "rt6", ["ospf6d"])
+
+    expect_grace_lsa(restarting="6.6.6.6", helper="rt3")
+    expect_grace_lsa(restarting="6.6.6.6", helper="rt7")
+    ensure_gr_is_in_zebra("rt6")
+    check_routers(restarting="rt6")
+
+
+#
+# Test rt7 performing an unplanned graceful restart
+#
+def test_unplanned_gr_rt7():
+    logger.info("Test: verify rt7 performing an unplanned graceful restart")
+    tgen = get_topogen()
+
+    # Skip if previous fatal error condition is raised
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    kill_router_daemons(tgen, "rt7", ["ospf6d"], save_config=False)
+    start_router_daemons(tgen, "rt7", ["ospf6d"])
+
+    expect_grace_lsa(restarting="6.6.6.6", helper="rt6")
+    ensure_gr_is_in_zebra("rt7")
+    check_routers(restarting="rt7")
+
+
 # Memory leak test template
 def test_memory_leak():
     "Run the memory leak test and report results."
diff --git a/tests/topotests/ospf_gr_topo1/test_ospf_gr_topo1.py b/tests/topotests/ospf_gr_topo1/test_ospf_gr_topo1.py
index ca2a3b287..73185d501 100755
--- a/tests/topotests/ospf_gr_topo1/test_ospf_gr_topo1.py
+++ b/tests/topotests/ospf_gr_topo1/test_ospf_gr_topo1.py
@@ -434,6 +434,144 @@ def test_gr_rt7():
     check_routers(restarting="rt7")
 
 
+#
+# Test rt1 performing an unplanned graceful restart
+#
+def test_unplanned_gr_rt1():
+    logger.info("Test: verify rt1 performing an unplanned graceful restart")
+    tgen = get_topogen()
+
+    # Skip if previous fatal error condition is raised
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    kill_router_daemons(tgen, "rt1", ["ospfd"], save_config=False)
+    start_router_daemons(tgen, "rt1", ["ospfd"])
+
+    expect_grace_lsa(restarting="1.1.1.1", area="0.0.0.1", helper="rt2")
+    ensure_gr_is_in_zebra("rt1")
+    check_routers(restarting="rt1")
+
+
+#
+# Test rt2 performing an unplanned graceful restart
+#
+def test_unplanned_gr_rt2():
+    logger.info("Test: verify rt2 performing an unplanned graceful restart")
+    tgen = get_topogen()
+
+    # Skip if previous fatal error condition is raised
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    kill_router_daemons(tgen, "rt2", ["ospfd"], save_config=False)
+    start_router_daemons(tgen, "rt2", ["ospfd"])
+
+    expect_grace_lsa(restarting="2.2.2.2", area="0.0.0.1", helper="rt1")
+    expect_grace_lsa(restarting="2.2.2.2", area="0.0.0.0", helper="rt3")
+    ensure_gr_is_in_zebra("rt2")
+    check_routers(restarting="rt2")
+
+
+#
+# Test rt3 performing an unplanned graceful restart
+#
+def test_unplanned_gr_rt3():
+    logger.info("Test: verify rt3 performing an unplanned graceful restart")
+    tgen = get_topogen()
+
+    # Skip if previous fatal error condition is raised
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    kill_router_daemons(tgen, "rt3", ["ospfd"], save_config=False)
+    start_router_daemons(tgen, "rt3", ["ospfd"])
+
+    expect_grace_lsa(restarting="3.3.3.3", area="0.0.0.0", helper="rt2")
+    expect_grace_lsa(restarting="3.3.3.3", area="0.0.0.0", helper="rt4")
+    expect_grace_lsa(restarting="3.3.3.3", area="0.0.0.0", helper="rt6")
+    ensure_gr_is_in_zebra("rt3")
+    check_routers(restarting="rt3")
+
+
+#
+# Test rt4 performing an unplanned graceful restart
+#
+def test_unplanned_gr_rt4():
+    logger.info("Test: verify rt4 performing an unplanned graceful restart")
+    tgen = get_topogen()
+
+    # Skip if previous fatal error condition is raised
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    kill_router_daemons(tgen, "rt4", ["ospfd"], save_config=False)
+    start_router_daemons(tgen, "rt4", ["ospfd"])
+
+    expect_grace_lsa(restarting="4.4.4.4", area="0.0.0.0", helper="rt3")
+    expect_grace_lsa(restarting="4.4.4.4", area="0.0.0.2", helper="rt5")
+    ensure_gr_is_in_zebra("rt4")
+    check_routers(restarting="rt4")
+
+
+#
+# Test rt5 performing an unplanned graceful restart
+#
+def test_unplanned_gr_rt5():
+    logger.info("Test: verify rt5 performing an unplanned graceful restart")
+    tgen = get_topogen()
+
+    # Skip if previous fatal error condition is raised
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    kill_router_daemons(tgen, "rt5", ["ospfd"], save_config=False)
+    start_router_daemons(tgen, "rt5", ["ospfd"])
+
+    expect_grace_lsa(restarting="5.5.5.5", area="0.0.0.2", helper="rt4")
+    ensure_gr_is_in_zebra("rt5")
+    check_routers(restarting="rt5")
+
+
+#
+# Test rt6 performing an unplanned graceful restart
+#
+def test_unplanned_gr_rt6():
+    logger.info("Test: verify rt6 performing an unplanned graceful restart")
+    tgen = get_topogen()
+
+    # Skip if previous fatal error condition is raised
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    kill_router_daemons(tgen, "rt6", ["ospfd"], save_config=False)
+    start_router_daemons(tgen, "rt6", ["ospfd"])
+
+    expect_grace_lsa(restarting="6.6.6.6", area="0.0.0.0", helper="rt3")
+    expect_grace_lsa(restarting="6.6.6.6", area="0.0.0.3", helper="rt7")
+    ensure_gr_is_in_zebra("rt6")
+    check_routers(restarting="rt6")
+
+
+#
+# Test rt7 performing an unplanned graceful restart
+#
+def test_unplanned_gr_rt7():
+    logger.info("Test: verify rt7 performing a graceful restart")
+    tgen = get_topogen()
+
+    # Skip if previous fatal error condition is raised
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    kill_router_daemons(tgen, "rt7", ["ospfd"], save_config=False)
+    start_router_daemons(tgen, "rt7", ["ospfd"])
+
+    expect_grace_lsa(restarting="7.7.7.7", area="0.0.0.3", helper="rt6")
+    ensure_gr_is_in_zebra("rt7")
+    check_routers(restarting="rt7")
+
+
 # Memory leak test template
 def test_memory_leak():
     "Run the memory leak test and report results."