[mirror_frr.git] / bgpd / bgp_fsm.c

/* BGP-4 Finite State Machine
 * From RFC1771 [A Border Gateway Protocol 4 (BGP-4)]
 * Copyright (C) 1996, 97, 98 Kunihiro Ishiguro
 *
 * This file is part of GNU Zebra.
 *
 * GNU Zebra is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 2, or (at your option) any
 * later version.
 *
 * GNU Zebra is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; see the file COPYING; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include <zebra.h>

#include "linklist.h"
#include "prefix.h"
#include "sockunion.h"
#include "thread.h"
#include "log.h"
#include "stream.h"
#include "ringbuf.h"
#include "memory.h"
#include "plist.h"
#include "workqueue.h"
#include "queue.h"
#include "filter.h"
#include "command.h"
#include "lib_errors.h"
#include "zclient.h"
#include "lib/json.h"
#include "bgpd/bgpd.h"
#include "bgpd/bgp_attr.h"
#include "bgpd/bgp_debug.h"
#include "bgpd/bgp_errors.h"
#include "bgpd/bgp_fsm.h"
#include "bgpd/bgp_packet.h"
#include "bgpd/bgp_network.h"
#include "bgpd/bgp_route.h"
#include "bgpd/bgp_dump.h"
#include "bgpd/bgp_open.h"
#include "bgpd/bgp_advertise.h"
#include "bgpd/bgp_updgrp.h"
#include "bgpd/bgp_nht.h"
#include "bgpd/bgp_bfd.h"
#include "bgpd/bgp_memory.h"
#include "bgpd/bgp_keepalives.h"
#include "bgpd/bgp_io.h"
#include "bgpd/bgp_zebra.h"

DEFINE_HOOK(peer_backward_transition, (struct peer * peer), (peer))
DEFINE_HOOK(peer_status_changed, (struct peer * peer), (peer))
extern const char *get_afi_safi_str(afi_t afi, safi_t safi, bool for_json);
/* Definition of display strings corresponding to FSM events. This should be
 * kept consistent with the events defined in bgpd.h
 */
static const char *const bgp_event_str[] = {
	NULL,
	"BGP_Start",
	"BGP_Stop",
	"TCP_connection_open",
	"TCP_connection_closed",
	"TCP_connection_open_failed",
	"TCP_fatal_error",
	"ConnectRetry_timer_expired",
	"Hold_Timer_expired",
	"KeepAlive_timer_expired",
	"Receive_OPEN_message",
	"Receive_KEEPALIVE_message",
	"Receive_UPDATE_message",
	"Receive_NOTIFICATION_message",
	"Clearing_Completed",
};

/* BGP FSM (finite state machine) has three types of functions.  Type
   one is thread functions.  Type two is event functions.  Type three
   is FSM functions.  Timer functions are set by bgp_timer_set
   function. */

/* BGP event function. */
int bgp_event(struct thread *);

/* BGP thread functions. */
static int bgp_start_timer(struct thread *);
static int bgp_connect_timer(struct thread *);
static int bgp_holdtime_timer(struct thread *);

/* BGP FSM functions. */
static int bgp_start(struct peer *);

/* Register peer with NHT */
static int bgp_peer_reg_with_nht(struct peer *peer)
{
	int connected = 0;

	if (peer->sort == BGP_PEER_EBGP && peer->ttl == BGP_DEFAULT_TTL
	    && !CHECK_FLAG(peer->flags, PEER_FLAG_DISABLE_CONNECTED_CHECK)
	    && !bgp_flag_check(peer->bgp, BGP_FLAG_DISABLE_NH_CONNECTED_CHK))
		connected = 1;

	return bgp_find_or_add_nexthop(
		peer->bgp, peer->bgp, family2afi(peer->su.sa.sa_family),
		NULL, peer, connected);
}

static void peer_xfer_stats(struct peer *peer_dst, struct peer *peer_src)
{
	/* Copy stats over. These are only the pre-established state stats */
	peer_dst->open_in += peer_src->open_in;
	peer_dst->open_out += peer_src->open_out;
	peer_dst->keepalive_in += peer_src->keepalive_in;
	peer_dst->keepalive_out += peer_src->keepalive_out;
	peer_dst->notify_in += peer_src->notify_in;
	peer_dst->notify_out += peer_src->notify_out;
	peer_dst->dynamic_cap_in += peer_src->dynamic_cap_in;
	peer_dst->dynamic_cap_out += peer_src->dynamic_cap_out;
}

static struct peer *peer_xfer_conn(struct peer *from_peer)
{
	struct peer *peer;
	afi_t afi;
	safi_t safi;
	int fd;
	int status, pstatus;
	unsigned char last_evt, last_maj_evt;

	assert(from_peer != NULL);

	peer = from_peer->doppelganger;

	if (!peer || !CHECK_FLAG(peer->flags, PEER_FLAG_CONFIG_NODE))
		return from_peer;

	/*
	 * Let's check that we are not going to loose known configuration
	 * state based upon doppelganger rules.
	 */
	FOREACH_AFI_SAFI (afi, safi) {
		if (from_peer->afc[afi][safi] != peer->afc[afi][safi]) {
			flog_err(
				EC_BGP_DOPPELGANGER_CONFIG,
				"from_peer->afc[%d][%d] is not the same as what we are overwriting",
				afi, safi);
			return NULL;
		}
	}

	if (bgp_debug_neighbor_events(peer))
		zlog_debug("%s: peer transfer %p fd %d -> %p fd %d)",
			   from_peer->host, from_peer, from_peer->fd, peer,
			   peer->fd);

	bgp_writes_off(peer);
	bgp_reads_off(peer);
	bgp_writes_off(from_peer);
	bgp_reads_off(from_peer);

	/*
	 * Before exchanging FD remove doppelganger from
	 * keepalive peer hash. It could be possible conf peer
	 * fd is set to -1. If blocked on lock then keepalive
	 * thread can access peer pointer with fd -1.
	 */
	bgp_keepalives_off(from_peer);

	BGP_TIMER_OFF(peer->t_routeadv);
	BGP_TIMER_OFF(peer->t_connect);
	BGP_TIMER_OFF(peer->t_connect_check_r);
	BGP_TIMER_OFF(peer->t_connect_check_w);
	BGP_TIMER_OFF(from_peer->t_routeadv);
	BGP_TIMER_OFF(from_peer->t_connect);
	BGP_TIMER_OFF(from_peer->t_connect_check_r);
	BGP_TIMER_OFF(from_peer->t_connect_check_w);
	BGP_TIMER_OFF(from_peer->t_process_packet);

	/*
	 * At this point in time, it is possible that there are packets pending
	 * on various buffers. Those need to be transferred or dropped,
	 * otherwise we'll get spurious failures during session establishment.
	 */
	frr_with_mutex(&peer->io_mtx, &from_peer->io_mtx) {
		fd = peer->fd;
		peer->fd = from_peer->fd;
		from_peer->fd = fd;

		stream_fifo_clean(peer->ibuf);
		stream_fifo_clean(peer->obuf);

		/*
		 * this should never happen, since bgp_process_packet() is the
		 * only task that sets and unsets the current packet and it
		 * runs in our pthread.
		 */
		if (peer->curr) {
			flog_err(
				EC_BGP_PKT_PROCESS,
				"[%s] Dropping pending packet on connection transfer:",
				peer->host);
			/* there used to be a bgp_packet_dump call here, but
			 * that's extremely confusing since there's no way to
			 * identify the packet in MRT dumps or BMP as dropped
			 * due to connection transfer.
			 */
			stream_free(peer->curr);
			peer->curr = NULL;
		}

		// copy each packet from old peer's output queue to new peer
		while (from_peer->obuf->head)
			stream_fifo_push(peer->obuf,
					 stream_fifo_pop(from_peer->obuf));

		// copy each packet from old peer's input queue to new peer
		while (from_peer->ibuf->head)
			stream_fifo_push(peer->ibuf,
					 stream_fifo_pop(from_peer->ibuf));

		ringbuf_wipe(peer->ibuf_work);
		ringbuf_copy(peer->ibuf_work, from_peer->ibuf_work,
			     ringbuf_remain(from_peer->ibuf_work));
	}

	peer->as = from_peer->as;
	peer->v_holdtime = from_peer->v_holdtime;
	peer->v_keepalive = from_peer->v_keepalive;
	peer->v_routeadv = from_peer->v_routeadv;
	peer->v_gr_restart = from_peer->v_gr_restart;
	peer->cap = from_peer->cap;
	status = peer->status;
	pstatus = peer->ostatus;
	last_evt = peer->last_event;
	last_maj_evt = peer->last_major_event;
	peer->status = from_peer->status;
	peer->ostatus = from_peer->ostatus;
	peer->last_event = from_peer->last_event;
	peer->last_major_event = from_peer->last_major_event;
	from_peer->status = status;
	from_peer->ostatus = pstatus;
	from_peer->last_event = last_evt;
	from_peer->last_major_event = last_maj_evt;
	peer->remote_id = from_peer->remote_id;
	peer->last_reset = from_peer->last_reset;

	peer->peer_gr_present_state = from_peer->peer_gr_present_state;
	peer->peer_gr_new_status_flag = from_peer->peer_gr_new_status_flag;
	bgp_peer_gr_flags_update(peer);

	BGP_GR_ROUTER_DETECT_AND_SEND_CAPABILITY_TO_ZEBRA(peer->bgp,
							  peer->bgp->peer);

	if (bgp_peer_gr_mode_get(peer) == PEER_DISABLE) {

		UNSET_FLAG(peer->sflags, PEER_STATUS_NSF_MODE);

		if (CHECK_FLAG(peer->sflags, PEER_STATUS_NSF_WAIT)) {
			peer_nsf_stop(peer);
		}
	}

	if (from_peer->hostname != NULL) {
		if (peer->hostname) {
			XFREE(MTYPE_BGP_PEER_HOST, peer->hostname);
			peer->hostname = NULL;
		}

		peer->hostname = from_peer->hostname;
		from_peer->hostname = NULL;
	}

	if (from_peer->domainname != NULL) {
		if (peer->domainname) {
			XFREE(MTYPE_BGP_PEER_HOST, peer->domainname);
			peer->domainname = NULL;
		}

		peer->domainname = from_peer->domainname;
		from_peer->domainname = NULL;
	}

	FOREACH_AFI_SAFI (afi, safi) {
		peer->af_flags[afi][safi] = from_peer->af_flags[afi][safi];
		peer->af_sflags[afi][safi] = from_peer->af_sflags[afi][safi];
		peer->af_cap[afi][safi] = from_peer->af_cap[afi][safi];
		peer->afc_nego[afi][safi] = from_peer->afc_nego[afi][safi];
		peer->afc_adv[afi][safi] = from_peer->afc_adv[afi][safi];
		peer->afc_recv[afi][safi] = from_peer->afc_recv[afi][safi];
		peer->orf_plist[afi][safi] = from_peer->orf_plist[afi][safi];
	}

	if (bgp_getsockname(peer) < 0) {
		flog_err(
			EC_LIB_SOCKET,
			"%%bgp_getsockname() failed for %s peer %s fd %d (from_peer fd %d)",
			(CHECK_FLAG(peer->sflags, PEER_STATUS_ACCEPT_PEER)
				 ? "accept"
				 : ""),
			peer->host, peer->fd, from_peer->fd);
		bgp_stop(peer);
		bgp_stop(from_peer);
		return NULL;
	}
	if (from_peer->status > Active) {
		if (bgp_getsockname(from_peer) < 0) {
			flog_err(
				EC_LIB_SOCKET,
				"%%bgp_getsockname() failed for %s from_peer %s fd %d (peer fd %d)",

				(CHECK_FLAG(from_peer->sflags,
					    PEER_STATUS_ACCEPT_PEER)
					 ? "accept"
					 : ""),
				from_peer->host, from_peer->fd, peer->fd);
			bgp_stop(from_peer);
			from_peer = NULL;
		}
	}


	// Note: peer_xfer_stats() must be called with I/O turned OFF
	if (from_peer)
		peer_xfer_stats(peer, from_peer);

	/* Register peer for NHT. This is to allow RAs to be enabled when
	 * needed, even on a passive connection.
	 */
	bgp_peer_reg_with_nht(peer);

	bgp_reads_on(peer);
	bgp_writes_on(peer);
	thread_add_timer_msec(bm->master, bgp_process_packet, peer, 0,
			      &peer->t_process_packet);

	return (peer);
}

/* Hook function called after bgp event is occered.  And vty's
   neighbor command invoke this function after making neighbor
   structure. */
void bgp_timer_set(struct peer *peer)
{
	switch (peer->status) {
	case Idle:
		/* First entry point of peer's finite state machine.  In Idle
		   status start timer is on unless peer is shutdown or peer is
		   inactive.  All other timer must be turned off */
		if (BGP_PEER_START_SUPPRESSED(peer) || !peer_active(peer)
		    || (peer->bgp->inst_type != BGP_INSTANCE_TYPE_VIEW &&
			peer->bgp->vrf_id == VRF_UNKNOWN)) {
			BGP_TIMER_OFF(peer->t_start);
		} else {
			BGP_TIMER_ON(peer->t_start, bgp_start_timer,
				     peer->v_start);
		}
		BGP_TIMER_OFF(peer->t_connect);
		BGP_TIMER_OFF(peer->t_holdtime);
		bgp_keepalives_off(peer);
		BGP_TIMER_OFF(peer->t_routeadv);
		break;

	case Connect:
		/* After start timer is expired, the peer moves to Connect
		   status.  Make sure start timer is off and connect timer is
		   on. */
		BGP_TIMER_OFF(peer->t_start);
		BGP_TIMER_ON(peer->t_connect, bgp_connect_timer,
			     peer->v_connect);
		BGP_TIMER_OFF(peer->t_holdtime);
		bgp_keepalives_off(peer);
		BGP_TIMER_OFF(peer->t_routeadv);
		break;

	case Active:
		/* Active is waiting connection from remote peer.  And if
		   connect timer is expired, change status to Connect. */
		BGP_TIMER_OFF(peer->t_start);
		/* If peer is passive mode, do not set connect timer. */
		if (CHECK_FLAG(peer->flags, PEER_FLAG_PASSIVE)
		    || CHECK_FLAG(peer->sflags, PEER_STATUS_NSF_WAIT)) {
			BGP_TIMER_OFF(peer->t_connect);
		} else {
			BGP_TIMER_ON(peer->t_connect, bgp_connect_timer,
				     peer->v_connect);
		}
		BGP_TIMER_OFF(peer->t_holdtime);
		bgp_keepalives_off(peer);
		BGP_TIMER_OFF(peer->t_routeadv);
		break;

	case OpenSent:
		/* OpenSent status. */
		BGP_TIMER_OFF(peer->t_start);
		BGP_TIMER_OFF(peer->t_connect);
		if (peer->v_holdtime != 0) {
			BGP_TIMER_ON(peer->t_holdtime, bgp_holdtime_timer,
				     peer->v_holdtime);
		} else {
			BGP_TIMER_OFF(peer->t_holdtime);
		}
		bgp_keepalives_off(peer);
		BGP_TIMER_OFF(peer->t_routeadv);
		break;

	case OpenConfirm:
		/* OpenConfirm status. */
		BGP_TIMER_OFF(peer->t_start);
		BGP_TIMER_OFF(peer->t_connect);

		/* If the negotiated Hold Time value is zero, then the Hold Time
		   timer and KeepAlive timers are not started. */
		if (peer->v_holdtime == 0) {
			BGP_TIMER_OFF(peer->t_holdtime);
			bgp_keepalives_off(peer);
		} else {
			BGP_TIMER_ON(peer->t_holdtime, bgp_holdtime_timer,
				     peer->v_holdtime);
			bgp_keepalives_on(peer);
		}
		BGP_TIMER_OFF(peer->t_routeadv);
		break;

	case Established:
		/* In Established status start and connect timer is turned
		   off. */
		BGP_TIMER_OFF(peer->t_start);
		BGP_TIMER_OFF(peer->t_connect);

		/* Same as OpenConfirm, if holdtime is zero then both holdtime
		   and keepalive must be turned off. */
		if (peer->v_holdtime == 0) {
			BGP_TIMER_OFF(peer->t_holdtime);
			bgp_keepalives_off(peer);
		} else {
			BGP_TIMER_ON(peer->t_holdtime, bgp_holdtime_timer,
				     peer->v_holdtime);
			bgp_keepalives_on(peer);
		}
		break;
	case Deleted:
		BGP_TIMER_OFF(peer->t_gr_restart);
		BGP_TIMER_OFF(peer->t_gr_stale);
		BGP_TIMER_OFF(peer->t_pmax_restart);
	/* fallthru */
	case Clearing:
		BGP_TIMER_OFF(peer->t_start);
		BGP_TIMER_OFF(peer->t_connect);
		BGP_TIMER_OFF(peer->t_holdtime);
		bgp_keepalives_off(peer);
		BGP_TIMER_OFF(peer->t_routeadv);
		break;
	}
}

/* BGP start timer.  This function set BGP_Start event to thread value
   and process event. */
static int bgp_start_timer(struct thread *thread)
{
	struct peer *peer;

	peer = THREAD_ARG(thread);
	peer->t_start = NULL;

	if (bgp_debug_neighbor_events(peer))
		zlog_debug("%s [FSM] Timer (start timer expire).", peer->host);

	THREAD_VAL(thread) = BGP_Start;
	bgp_event(thread); /* bgp_event unlocks peer */

	return 0;
}

/* BGP connect retry timer. */
static int bgp_connect_timer(struct thread *thread)
{
	struct peer *peer;
	int ret;

	peer = THREAD_ARG(thread);

	assert(!peer->t_write);
	assert(!peer->t_read);

	peer->t_connect = NULL;

	if (bgp_debug_neighbor_events(peer))
		zlog_debug("%s [FSM] Timer (connect timer expire)", peer->host);

	if (CHECK_FLAG(peer->sflags, PEER_STATUS_ACCEPT_PEER)) {
		bgp_stop(peer);
		ret = -1;
	} else {
		THREAD_VAL(thread) = ConnectRetry_timer_expired;
		bgp_event(thread); /* bgp_event unlocks peer */
		ret = 0;
	}

	return ret;
}

/* BGP holdtime timer. */
static int bgp_holdtime_timer(struct thread *thread)
{
	struct peer *peer;

	peer = THREAD_ARG(thread);
	peer->t_holdtime = NULL;

	if (bgp_debug_neighbor_events(peer))
		zlog_debug("%s [FSM] Timer (holdtime timer expire)",
			   peer->host);

	THREAD_VAL(thread) = Hold_Timer_expired;
	bgp_event(thread); /* bgp_event unlocks peer */

	return 0;
}

int bgp_routeadv_timer(struct thread *thread)
{
	struct peer *peer;

	peer = THREAD_ARG(thread);
	peer->t_routeadv = NULL;

	if (bgp_debug_neighbor_events(peer))
		zlog_debug("%s [FSM] Timer (routeadv timer expire)",
			   peer->host);

	peer->synctime = bgp_clock();

	thread_add_timer_msec(bm->master, bgp_generate_updgrp_packets, peer, 0,
			      &peer->t_generate_updgrp_packets);

	/* MRAI timer will be started again when FIFO is built, no need to
	 * do it here.
	 */
	return 0;
}

/* BGP Peer Down Cause */
const char *const peer_down_str[] = {"",
			       "Router ID changed",
			       "Remote AS changed",
			       "Local AS change",
			       "Cluster ID changed",
			       "Confederation identifier changed",
			       "Confederation peer changed",
			       "RR client config change",
			       "RS client config change",
			       "Update source change",
			       "Address family activated",
			       "Admin. shutdown",
			       "User reset",
			       "BGP Notification received",
			       "BGP Notification send",
			       "Peer closed the session",
			       "Neighbor deleted",
			       "Peer-group add member",
			       "Peer-group delete member",
			       "Capability changed",
			       "Passive config change",
			       "Multihop config change",
			       "NSF peer closed the session",
			       "Intf peering v6only config change",
			       "BFD down received",
			       "Interface down",
			       "Neighbor address lost",
			       "Waiting for NHT",
			       "Waiting for Peer IPv6 LLA",
			       "Waiting for VRF to be initialized",
			       "No AFI/SAFI activated for peer"};

static int bgp_graceful_restart_timer_expire(struct thread *thread)
{
	struct peer *peer;
	afi_t afi;
	safi_t safi;

	peer = THREAD_ARG(thread);
	peer->t_gr_restart = NULL;

	/* NSF delete stale route */
	for (afi = AFI_IP; afi < AFI_MAX; afi++)
		for (safi = SAFI_UNICAST; safi <= SAFI_MPLS_VPN; safi++)
			if (peer->nsf[afi][safi])
				bgp_clear_stale_route(peer, afi, safi);

	UNSET_FLAG(peer->sflags, PEER_STATUS_NSF_WAIT);
	BGP_TIMER_OFF(peer->t_gr_stale);

	if (bgp_debug_neighbor_events(peer)) {
		zlog_debug("%s graceful restart timer expired", peer->host);
		zlog_debug("%s graceful restart stalepath timer stopped",
			   peer->host);
	}

	bgp_timer_set(peer);

	return 0;
}

static int bgp_graceful_stale_timer_expire(struct thread *thread)
{
	struct peer *peer;
	afi_t afi;
	safi_t safi;

	peer = THREAD_ARG(thread);
	peer->t_gr_stale = NULL;

	if (bgp_debug_neighbor_events(peer))
		zlog_debug("%s graceful restart stalepath timer expired",
			   peer->host);

	/* NSF delete stale route */
	for (afi = AFI_IP; afi < AFI_MAX; afi++)
		for (safi = SAFI_UNICAST; safi <= SAFI_MPLS_VPN; safi++)
			if (peer->nsf[afi][safi])
				bgp_clear_stale_route(peer, afi, safi);

	return 0;
}

/* Selection deferral timer processing function */
static int bgp_graceful_deferral_timer_expire(struct thread *thread)
{
	struct afi_safi_info *info;
	afi_t afi;
	safi_t safi;
	struct bgp *bgp;

	info = THREAD_ARG(thread);
	afi = info->afi;
	safi = info->safi;
	bgp = info->bgp;

	if (BGP_DEBUG(update, UPDATE_OUT))
		zlog_debug(
			"afi %d, safi %d : graceful restart deferral timer expired",
			afi, safi);

	bgp->gr_info[afi][safi].t_select_deferral = NULL;

	bgp->gr_info[afi][safi].eor_required = 0;
	bgp->gr_info[afi][safi].eor_received = 0;
	XFREE(MTYPE_TMP, info);

	/* Best path selection */
	return bgp_best_path_select_defer(bgp, afi, safi);
}

static int bgp_update_delay_applicable(struct bgp *bgp)
{
	/* update_delay_over flag should be reset (set to 0) for any new
	   applicability of the update-delay during BGP process lifetime.
	   And it should be set after an occurence of the update-delay is
	   over)*/
	if (!bgp->update_delay_over)
		return 1;

	return 0;
}

int bgp_update_delay_active(struct bgp *bgp)
{
	if (bgp->t_update_delay)
		return 1;

	return 0;
}

int bgp_update_delay_configured(struct bgp *bgp)
{
	if (bgp->v_update_delay)
		return 1;

	return 0;
}

/* Do the post-processing needed when bgp comes out of the read-only mode
   on ending the update delay. */
void bgp_update_delay_end(struct bgp *bgp)
{
	THREAD_TIMER_OFF(bgp->t_update_delay);
	THREAD_TIMER_OFF(bgp->t_establish_wait);

	/* Reset update-delay related state */
	bgp->update_delay_over = 1;
	bgp->established = 0;
	bgp->restarted_peers = 0;
	bgp->implicit_eors = 0;
	bgp->explicit_eors = 0;

	quagga_timestamp(3, bgp->update_delay_end_time,
			 sizeof(bgp->update_delay_end_time));

	/*
	 * Add an end-of-initial-update marker to the main process queues so
	 * that
	 * the route advertisement timer for the peers can be started. Also set
	 * the zebra and peer update hold flags. These flags are used to achieve
	 * three stages in the update-delay post processing:
	 *  1. Finish best-path selection for all the prefixes held on the
	 * queues.
	 *     (routes in BGP are updated, and peers sync queues are populated
	 * too)
	 *  2. As the eoiu mark is reached in the bgp process routine, ship all
	 * the
	 *     routes to zebra. With that zebra should see updates from BGP
	 * close
	 *     to each other.
	 *  3. Unblock the peer update writes. With that peer update packing
	 * with
	 *     the prefixes should be at its maximum.
	 */
	bgp_add_eoiu_mark(bgp);
	bgp->main_zebra_update_hold = 1;
	bgp->main_peers_update_hold = 1;

	/* Resume the queue processing. This should trigger the event that would
	   take
	   care of processing any work that was queued during the read-only
	   mode. */
	work_queue_unplug(bm->process_main_queue);
}

/**
 * see bgp_fsm.h
 */
void bgp_start_routeadv(struct bgp *bgp)
{
	struct listnode *node, *nnode;
	struct peer *peer;

	zlog_info("bgp_start_routeadv(), update hold status %d",
		  bgp->main_peers_update_hold);

	if (bgp->main_peers_update_hold)
		return;

	quagga_timestamp(3, bgp->update_delay_peers_resume_time,
			 sizeof(bgp->update_delay_peers_resume_time));

	for (ALL_LIST_ELEMENTS(bgp->peer, node, nnode, peer)) {
		if (peer->status != Established)
			continue;
		BGP_TIMER_OFF(peer->t_routeadv);
		BGP_TIMER_ON(peer->t_routeadv, bgp_routeadv_timer, 0);
	}
}

/**
 * see bgp_fsm.h
 */
void bgp_adjust_routeadv(struct peer *peer)
{
	time_t nowtime = bgp_clock();
	double diff;
	unsigned long remain;

	/* Bypass checks for special case of MRAI being 0 */
	if (peer->v_routeadv == 0) {
		/* Stop existing timer, just in case it is running for a
		 * different
		 * duration and schedule write thread immediately.
		 */
		if (peer->t_routeadv)
			BGP_TIMER_OFF(peer->t_routeadv);

		peer->synctime = bgp_clock();
		thread_add_timer_msec(bm->master, bgp_generate_updgrp_packets,
				      peer, 0,
				      &peer->t_generate_updgrp_packets);
		return;
	}


	/*
	 * CASE I:
	 * If the last update was written more than MRAI back, expire the timer
	 * instantly so that we can send the update out sooner.
	 *
	 *                           <-------  MRAI --------->
	 *         |-----------------|-----------------------|
	 *         <------------- m ------------>
	 *         ^                 ^          ^
	 *         |                 |          |
	 *         |                 |     current time
	 *         |            timer start
	 *      last write
	 *
	 *                     m > MRAI
	 */
	diff = difftime(nowtime, peer->last_update);
	if (diff > (double)peer->v_routeadv) {
		BGP_TIMER_OFF(peer->t_routeadv);
		BGP_TIMER_ON(peer->t_routeadv, bgp_routeadv_timer, 0);
		return;
	}

	/*
	 * CASE II:
	 * - Find when to expire the MRAI timer.
	 *   If MRAI timer is not active, assume we can start it now.
	 *
	 *                      <-------  MRAI --------->
	 *         |------------|-----------------------|
	 *         <-------- m ----------><----- r ----->
	 *         ^            ^        ^
	 *         |            |        |
	 *         |            |   current time
	 *         |       timer start
	 *      last write
	 *
	 *                     (MRAI - m) < r
	 */
	if (peer->t_routeadv)
		remain = thread_timer_remain_second(peer->t_routeadv);
	else
		remain = peer->v_routeadv;
	diff = peer->v_routeadv - diff;
	if (diff <= (double)remain) {
		BGP_TIMER_OFF(peer->t_routeadv);
		BGP_TIMER_ON(peer->t_routeadv, bgp_routeadv_timer, diff);
	}
}

static int bgp_maxmed_onstartup_applicable(struct bgp *bgp)
{
	if (!bgp->maxmed_onstartup_over)
		return 1;

	return 0;
}

int bgp_maxmed_onstartup_configured(struct bgp *bgp)
{
	if (bgp->v_maxmed_onstartup != BGP_MAXMED_ONSTARTUP_UNCONFIGURED)
		return 1;

	return 0;
}

int bgp_maxmed_onstartup_active(struct bgp *bgp)
{
	if (bgp->t_maxmed_onstartup)
		return 1;

	return 0;
}

void bgp_maxmed_update(struct bgp *bgp)
{
	uint8_t maxmed_active;
	uint32_t maxmed_value;

	if (bgp->v_maxmed_admin) {
		maxmed_active = 1;
		maxmed_value = bgp->maxmed_admin_value;
	} else if (bgp->t_maxmed_onstartup) {
		maxmed_active = 1;
		maxmed_value = bgp->maxmed_onstartup_value;
	} else {
		maxmed_active = 0;
		maxmed_value = BGP_MAXMED_VALUE_DEFAULT;
	}

	if (bgp->maxmed_active != maxmed_active
	    || bgp->maxmed_value != maxmed_value) {
		bgp->maxmed_active = maxmed_active;
		bgp->maxmed_value = maxmed_value;

		update_group_announce(bgp);
	}
}

/* The maxmed onstartup timer expiry callback. */
static int bgp_maxmed_onstartup_timer(struct thread *thread)
{
	struct bgp *bgp;

	zlog_info("Max med on startup ended - timer expired.");

	bgp = THREAD_ARG(thread);
	THREAD_TIMER_OFF(bgp->t_maxmed_onstartup);
	bgp->maxmed_onstartup_over = 1;

	bgp_maxmed_update(bgp);

	return 0;
}

static void bgp_maxmed_onstartup_begin(struct bgp *bgp)
{
	/* Applicable only once in the process lifetime on the startup */
	if (bgp->maxmed_onstartup_over)
		return;

	zlog_info("Begin maxmed onstartup mode - timer %d seconds",
		  bgp->v_maxmed_onstartup);

	thread_add_timer(bm->master, bgp_maxmed_onstartup_timer, bgp,
			 bgp->v_maxmed_onstartup, &bgp->t_maxmed_onstartup);

	if (!bgp->v_maxmed_admin) {
		bgp->maxmed_active = 1;
		bgp->maxmed_value = bgp->maxmed_onstartup_value;
	}

	/* Route announce to all peers should happen after this in
	 * bgp_establish() */
}

static void bgp_maxmed_onstartup_process_status_change(struct peer *peer)
{
	if (peer->status == Established && !peer->bgp->established) {
		bgp_maxmed_onstartup_begin(peer->bgp);
	}
}

/* The update delay timer expiry callback. */
static int bgp_update_delay_timer(struct thread *thread)
{
	struct bgp *bgp;

	zlog_info("Update delay ended - timer expired.");

	bgp = THREAD_ARG(thread);
	THREAD_TIMER_OFF(bgp->t_update_delay);
	bgp_update_delay_end(bgp);

	return 0;
}

/* The establish wait timer expiry callback. */
static int bgp_establish_wait_timer(struct thread *thread)
{
	struct bgp *bgp;

	zlog_info("Establish wait - timer expired.");

	bgp = THREAD_ARG(thread);
	THREAD_TIMER_OFF(bgp->t_establish_wait);
	bgp_check_update_delay(bgp);

	return 0;
}

/* Steps to begin the update delay:
     - initialize queues if needed
     - stop the queue processing
     - start the timer */
static void bgp_update_delay_begin(struct bgp *bgp)
{
	struct listnode *node, *nnode;
	struct peer *peer;

	/* Stop the processing of queued work. Enqueue shall continue */
	work_queue_plug(bm->process_main_queue);

	for (ALL_LIST_ELEMENTS(bgp->peer, node, nnode, peer))
		peer->update_delay_over = 0;

	/* Start the update-delay timer */
	thread_add_timer(bm->master, bgp_update_delay_timer, bgp,
			 bgp->v_update_delay, &bgp->t_update_delay);

	if (bgp->v_establish_wait != bgp->v_update_delay)
		thread_add_timer(bm->master, bgp_establish_wait_timer, bgp,
				 bgp->v_establish_wait, &bgp->t_establish_wait);

	quagga_timestamp(3, bgp->update_delay_begin_time,
			 sizeof(bgp->update_delay_begin_time));
}

static void bgp_update_delay_process_status_change(struct peer *peer)
{
	if (peer->status == Established) {
		if (!peer->bgp->established++) {
			bgp_update_delay_begin(peer->bgp);
			zlog_info(
				"Begin read-only mode - update-delay timer %d seconds",
				peer->bgp->v_update_delay);
		}
		if (CHECK_FLAG(peer->cap, PEER_CAP_RESTART_BIT_RCV))
			bgp_update_restarted_peers(peer);
	}
	if (peer->ostatus == Established
	    && bgp_update_delay_active(peer->bgp)) {
		/* Adjust the update-delay state to account for this flap.
		   NOTE: Intentionally skipping adjusting implicit_eors or
		   explicit_eors
		   counters. Extra sanity check in bgp_check_update_delay()
		   should
		   be enough to take care of any additive discrepancy in bgp eor
		   counters */
		peer->bgp->established--;
		peer->update_delay_over = 0;
	}
}

/* Called after event occurred, this function change status and reset
   read/write and timer thread. */
void bgp_fsm_change_status(struct peer *peer, int status)
{
	struct bgp *bgp;
	uint32_t peer_count;

	bgp = peer->bgp;
	peer_count = bgp->established_peers;

	if (status == Established)
		bgp->established_peers++;
	else if ((peer->status == Established) && (status != Established))
		bgp->established_peers--;

	if (bgp_debug_neighbor_events(peer)) {
		struct vrf *vrf = vrf_lookup_by_id(bgp->vrf_id);

		zlog_debug("%s : vrf %s(%u), Status: %s established_peers %u", __func__,
			   vrf ? vrf->name : "Unknown", bgp->vrf_id,
			   lookup_msg(bgp_status_msg, status, NULL),
			   bgp->established_peers);
	}

	/* Set to router ID to the value provided by RIB if there are no peers
	 * in the established state and peer count did not change
	 */
	if ((peer_count != bgp->established_peers) &&
	    (bgp->established_peers == 0))
		bgp_router_id_zebra_bump(bgp->vrf_id, NULL);

	/* Transition into Clearing or Deleted must /always/ clear all routes..
	 * (and must do so before actually changing into Deleted..
	 */
	if (status >= Clearing) {
		bgp_clear_route_all(peer);

		/* If no route was queued for the clear-node processing,
		 * generate the
		 * completion event here. This is needed because if there are no
		 * routes
		 * to trigger the background clear-node thread, the event won't
		 * get
		 * generated and the peer would be stuck in Clearing. Note that
		 * this
		 * event is for the peer and helps the peer transition out of
		 * Clearing
		 * state; it should not be generated per (AFI,SAFI). The event
		 * is
		 * directly posted here without calling clear_node_complete() as
		 * we
		 * shouldn't do an extra unlock. This event will get processed
		 * after
		 * the state change that happens below, so peer will be in
		 * Clearing
		 * (or Deleted).
		 */
		if (!work_queue_is_scheduled(peer->clear_node_queue))
			BGP_EVENT_ADD(peer, Clearing_Completed);
	}

	/* Preserve old status and change into new status. */
	peer->ostatus = peer->status;
	peer->status = status;

	/* Save event that caused status change. */
	peer->last_major_event = peer->cur_event;

	/* Operations after status change */
	hook_call(peer_status_changed, peer);

	if (status == Established)
		UNSET_FLAG(peer->sflags, PEER_STATUS_ACCEPT_PEER);

	/* If max-med processing is applicable, do the necessary. */
	if (status == Established) {
		if (bgp_maxmed_onstartup_configured(peer->bgp)
		    && bgp_maxmed_onstartup_applicable(peer->bgp))
			bgp_maxmed_onstartup_process_status_change(peer);
		else
			peer->bgp->maxmed_onstartup_over = 1;
	}

	/* If update-delay processing is applicable, do the necessary. */
	if (bgp_update_delay_configured(peer->bgp)
	    && bgp_update_delay_applicable(peer->bgp))
		bgp_update_delay_process_status_change(peer);

	if (bgp_debug_neighbor_events(peer))
		zlog_debug("%s went from %s to %s", peer->host,
			   lookup_msg(bgp_status_msg, peer->ostatus, NULL),
			   lookup_msg(bgp_status_msg, peer->status, NULL));
}

/* Flush the event queue and ensure the peer is shut down */
static int bgp_clearing_completed(struct peer *peer)
{
	int rc = bgp_stop(peer);

	if (rc >= 0)
		BGP_EVENT_FLUSH(peer);

	return rc;
}

/* Administrative BGP peer stop event. */
/* May be called multiple times for the same peer */
int bgp_stop(struct peer *peer)
{
	afi_t afi;
	safi_t safi;
	char orf_name[BUFSIZ];
	int ret = 0;
	struct bgp *bgp = peer->bgp;
	struct graceful_restart_info *gr_info = NULL;

	peer->nsf_af_count = 0;

	if (peer_dynamic_neighbor(peer)
	    && !(CHECK_FLAG(peer->flags, PEER_FLAG_DELETE))) {
		if (bgp_debug_neighbor_events(peer))
			zlog_debug("%s (dynamic neighbor) deleted", peer->host);
		peer_delete(peer);
		return -1;
	}

	/* Can't do this in Clearing; events are used for state transitions */
	if (peer->status != Clearing) {
		/* Delete all existing events of the peer */
		BGP_EVENT_FLUSH(peer);
	}

	/* Increment Dropped count. */
	if (peer->status == Established) {
		peer->dropped++;

		/* bgp log-neighbor-changes of neighbor Down */
		if (bgp_flag_check(peer->bgp, BGP_FLAG_LOG_NEIGHBOR_CHANGES)) {
			struct vrf *vrf = vrf_lookup_by_id(peer->bgp->vrf_id);

			zlog_info(
				"%%ADJCHANGE: neighbor %s(%s) in vrf %s Down %s",
				peer->host,
				(peer->hostname) ? peer->hostname : "Unknown",
				vrf ? ((vrf->vrf_id != VRF_DEFAULT)
						? vrf->name
						: VRF_DEFAULT_NAME)
				    : "",
				peer_down_str[(int)peer->last_reset]);
		}

		/* graceful restart */
		if (peer->t_gr_stale) {
			BGP_TIMER_OFF(peer->t_gr_stale);
			if (bgp_debug_neighbor_events(peer))
				zlog_debug(
					"%s graceful restart stalepath timer stopped",
					peer->host);
		}
		if (CHECK_FLAG(peer->sflags, PEER_STATUS_NSF_WAIT)) {
			if (bgp_debug_neighbor_events(peer)) {
				zlog_debug(
					"%s graceful restart timer started for %d sec",
					peer->host, peer->v_gr_restart);
				zlog_debug(
					"%s graceful restart stalepath timer started for %d sec",
					peer->host, peer->bgp->stalepath_time);
			}
			BGP_TIMER_ON(peer->t_gr_restart,
				     bgp_graceful_restart_timer_expire,
				     peer->v_gr_restart);
			BGP_TIMER_ON(peer->t_gr_stale,
				     bgp_graceful_stale_timer_expire,
				     peer->bgp->stalepath_time);
		} else {
			UNSET_FLAG(peer->sflags, PEER_STATUS_NSF_MODE);

			for (afi = AFI_IP; afi < AFI_MAX; afi++)
				for (safi = SAFI_UNICAST; safi <= SAFI_MPLS_VPN;
				     safi++)
					peer->nsf[afi][safi] = 0;
		}

		/* If peer reset before receiving EOR, decrement EOR count and
		 * cancel the selection deferral timer if there are no
		 * pending EOR messages to be received
		 */
		if (BGP_PEER_GRACEFUL_RESTART_CAPABLE(peer)) {
			FOREACH_AFI_SAFI (afi, safi) {
				if (!peer->afc_nego[afi][safi]
				    || CHECK_FLAG(peer->af_sflags[afi][safi],
						  PEER_STATUS_EOR_RECEIVED))
					continue;

				gr_info = &bgp->gr_info[afi][safi];
				if (!gr_info)
					continue;

				if (gr_info->eor_required)
					gr_info->eor_required--;

				if (BGP_DEBUG(update, UPDATE_OUT))
					zlog_debug("peer %s, EOR_required %d",
						   peer->host,
						   gr_info->eor_required);

				/* There is no pending EOR message */
				if (gr_info->eor_required == 0) {
					BGP_TIMER_OFF(
						gr_info->t_select_deferral);
					gr_info->eor_received = 0;
				}
			}
		}

		/* set last reset time */
		peer->resettime = peer->uptime = bgp_clock();

		if (BGP_DEBUG(update_groups, UPDATE_GROUPS))
			zlog_debug("%s remove from all update group",
				   peer->host);
		update_group_remove_peer_afs(peer);

		hook_call(peer_backward_transition, peer);

		/* Reset peer synctime */
		peer->synctime = 0;
	}

	/* stop keepalives */
	bgp_keepalives_off(peer);

	/* Stop read and write threads. */
	bgp_writes_off(peer);
	bgp_reads_off(peer);

	THREAD_OFF(peer->t_connect_check_r);
	THREAD_OFF(peer->t_connect_check_w);

	/* Stop all timers. */
	BGP_TIMER_OFF(peer->t_start);
	BGP_TIMER_OFF(peer->t_connect);
	BGP_TIMER_OFF(peer->t_holdtime);
	BGP_TIMER_OFF(peer->t_routeadv);

	/* Clear input and output buffer.  */
	frr_with_mutex(&peer->io_mtx) {
		if (peer->ibuf)
			stream_fifo_clean(peer->ibuf);
		if (peer->obuf)
			stream_fifo_clean(peer->obuf);

		if (peer->ibuf_work)
			ringbuf_wipe(peer->ibuf_work);
		if (peer->obuf_work)
			stream_reset(peer->obuf_work);

		if (peer->curr) {
			stream_free(peer->curr);
			peer->curr = NULL;
		}
	}

	/* Close of file descriptor. */
	if (peer->fd >= 0) {
		close(peer->fd);
		peer->fd = -1;
	}

	FOREACH_AFI_SAFI (afi, safi) {
		/* Reset all negotiated variables */
		peer->afc_nego[afi][safi] = 0;
		peer->afc_adv[afi][safi] = 0;
		peer->afc_recv[afi][safi] = 0;

		/* peer address family capability flags*/
		peer->af_cap[afi][safi] = 0;

		/* peer address family status flags*/
		peer->af_sflags[afi][safi] = 0;

		/* Received ORF prefix-filter */
		peer->orf_plist[afi][safi] = NULL;

		if ((peer->status == OpenConfirm)
		    || (peer->status == Established)) {
			/* ORF received prefix-filter pnt */
			sprintf(orf_name, "%s.%d.%d", peer->host, afi, safi);
			prefix_bgp_orf_remove_all(afi, orf_name);
		}
	}

	/* Reset keepalive and holdtime */
	if (CHECK_FLAG(peer->flags, PEER_FLAG_TIMER)) {
		peer->v_keepalive = peer->keepalive;
		peer->v_holdtime = peer->holdtime;
	} else {
		peer->v_keepalive = peer->bgp->default_keepalive;
		peer->v_holdtime = peer->bgp->default_holdtime;
	}

	peer->update_time = 0;

/* Until we are sure that there is no problem about prefix count
   this should be commented out.*/
#if 0
  /* Reset prefix count */
  peer->pcount[AFI_IP][SAFI_UNICAST] = 0;
  peer->pcount[AFI_IP][SAFI_MULTICAST] = 0;
  peer->pcount[AFI_IP][SAFI_LABELED_UNICAST] = 0;
  peer->pcount[AFI_IP][SAFI_MPLS_VPN] = 0;
  peer->pcount[AFI_IP6][SAFI_UNICAST] = 0;
  peer->pcount[AFI_IP6][SAFI_MULTICAST] = 0;
  peer->pcount[AFI_IP6][SAFI_LABELED_UNICAST] = 0;
#endif /* 0 */

	if (!CHECK_FLAG(peer->flags, PEER_FLAG_CONFIG_NODE)
	    && !(CHECK_FLAG(peer->flags, PEER_FLAG_DELETE))) {
		peer_delete(peer);
		ret = -1;
	} else {
		bgp_peer_conf_if_to_su_update(peer);
	}
	return ret;
}

/* BGP peer is stoped by the error. */
static int bgp_stop_with_error(struct peer *peer)
{
	/* Double start timer. */
	peer->v_start *= 2;

	/* Overflow check. */
	if (peer->v_start >= (60 * 2))
		peer->v_start = (60 * 2);

	if (peer_dynamic_neighbor(peer)) {
		if (bgp_debug_neighbor_events(peer))
			zlog_debug("%s (dynamic neighbor) deleted", peer->host);
		peer_delete(peer);
		return -1;
	}

	return (bgp_stop(peer));
}


/* something went wrong, send notify and tear down */
static int bgp_stop_with_notify(struct peer *peer, uint8_t code,
				uint8_t sub_code)
{
	/* Send notify to remote peer */
	bgp_notify_send(peer, code, sub_code);

	if (peer_dynamic_neighbor(peer)) {
		if (bgp_debug_neighbor_events(peer))
			zlog_debug("%s (dynamic neighbor) deleted", peer->host);
		peer_delete(peer);
		return -1;
	}

	/* Clear start timer value to default. */
	peer->v_start = BGP_INIT_START_TIMER;

	return (bgp_stop(peer));
}

/**
 * Determines whether a TCP session has successfully established for a peer and
 * events as appropriate.
 *
 * This function is called when setting up a new session. After connect() is
 * called on the peer's socket (in bgp_start()), the fd is passed to poll()
 * to wait for connection success or failure. When poll() returns, this
 * function is called to evaluate the result.
 *
 * Due to differences in behavior of poll() on Linux and BSD - specifically,
 * the value of .revents in the case of a closed connection - this function is
 * scheduled both for a read and a write event. The write event is triggered
 * when the connection is established. A read event is triggered when the
 * connection is closed. Thus we need to cancel whichever one did not occur.
 */
static int bgp_connect_check(struct thread *thread)
{
	int status;
	socklen_t slen;
	int ret;
	struct peer *peer;

	peer = THREAD_ARG(thread);
	assert(!CHECK_FLAG(peer->thread_flags, PEER_THREAD_READS_ON));
	assert(!CHECK_FLAG(peer->thread_flags, PEER_THREAD_WRITES_ON));
	assert(!peer->t_read);
	assert(!peer->t_write);

	THREAD_OFF(peer->t_connect_check_r);
	THREAD_OFF(peer->t_connect_check_w);

	/* Check file descriptor. */
	slen = sizeof(status);
	ret = getsockopt(peer->fd, SOL_SOCKET, SO_ERROR, (void *)&status,
			 &slen);

	/* If getsockopt is fail, this is fatal error. */
	if (ret < 0) {
		zlog_err("can't get sockopt for nonblocking connect: %d(%s)",
			  errno, safe_strerror(errno));
		BGP_EVENT_ADD(peer, TCP_fatal_error);
		return -1;
	}

	/* When status is 0 then TCP connection is established. */
	if (status == 0) {
		BGP_EVENT_ADD(peer, TCP_connection_open);
		return 1;
	} else {
		if (bgp_debug_neighbor_events(peer))
			zlog_debug("%s [Event] Connect failed %d(%s)",
				   peer->host, status, safe_strerror(status));
		BGP_EVENT_ADD(peer, TCP_connection_open_failed);
		return 0;
	}
}

/* TCP connection open.  Next we send open message to remote peer. And
   add read thread for reading open message. */
static int bgp_connect_success(struct peer *peer)
{
	if (peer->fd < 0) {
		flog_err(EC_BGP_CONNECT,
			 "bgp_connect_success peer's fd is negative value %d",
			 peer->fd);
		bgp_stop(peer);
		return -1;
	}

	if (bgp_getsockname(peer) < 0) {
		flog_err_sys(EC_LIB_SOCKET,
			     "%s: bgp_getsockname(): failed for peer %s, fd %d",
			     __FUNCTION__, peer->host, peer->fd);
		bgp_notify_send(
			peer, BGP_NOTIFY_FSM_ERR,
			BGP_NOTIFY_SUBCODE_UNSPECIFIC); /* internal error */
		bgp_writes_on(peer);
		return -1;
	}

	bgp_reads_on(peer);

	if (bgp_debug_neighbor_events(peer)) {
		char buf1[SU_ADDRSTRLEN];

		if (!CHECK_FLAG(peer->sflags, PEER_STATUS_ACCEPT_PEER))
			zlog_debug("%s open active, local address %s",
				   peer->host,
				   sockunion2str(peer->su_local, buf1,
						 SU_ADDRSTRLEN));
		else
			zlog_debug("%s passive open", peer->host);
	}

	bgp_open_send(peer);

	return 0;
}

/* TCP connect fail */
static int bgp_connect_fail(struct peer *peer)
{
	if (peer_dynamic_neighbor(peer)) {
		if (bgp_debug_neighbor_events(peer))
			zlog_debug("%s (dynamic neighbor) deleted", peer->host);
		peer_delete(peer);
		return -1;
	}

	return (bgp_stop(peer));
}

/* This function is the first starting point of all BGP connection. It
   try to connect to remote peer with non-blocking IO. */
int bgp_start(struct peer *peer)
{
	int status;

	bgp_peer_conf_if_to_su_update(peer);

	if (peer->su.sa.sa_family == AF_UNSPEC) {
		if (bgp_debug_neighbor_events(peer))
			zlog_debug(
				"%s [FSM] Unable to get neighbor's IP address, waiting...",
				peer->host);
		peer->last_reset = PEER_DOWN_NBR_ADDR;
		return -1;
	}

	if (BGP_PEER_START_SUPPRESSED(peer)) {
		if (bgp_debug_neighbor_events(peer))
			flog_err(EC_BGP_FSM,
				 "%s [FSM] Trying to start suppressed peer"
				 " - this is never supposed to happen!",
				 peer->host);
		return -1;
	}

	/* Scrub some information that might be left over from a previous,
	 * session
	 */
	/* Connection information. */
	if (peer->su_local) {
		sockunion_free(peer->su_local);
		peer->su_local = NULL;
	}

	if (peer->su_remote) {
		sockunion_free(peer->su_remote);
		peer->su_remote = NULL;
	}

	/* Clear remote router-id. */
	peer->remote_id.s_addr = INADDR_ANY;

	/* Clear peer capability flag. */
	peer->cap = 0;

	/* If the peer is passive mode, force to move to Active mode. */
	if (CHECK_FLAG(peer->flags, PEER_FLAG_PASSIVE)) {
		BGP_EVENT_ADD(peer, TCP_connection_open_failed);
		return 0;
	}

	if (peer->bgp->inst_type != BGP_INSTANCE_TYPE_VIEW &&
	    peer->bgp->vrf_id == VRF_UNKNOWN) {
		if (bgp_debug_neighbor_events(peer))
			flog_err(
				EC_BGP_FSM,
				"%s [FSM] In a VRF that is not initialised yet",
				peer->host);
		peer->last_reset = PEER_DOWN_VRF_UNINIT;
		return -1;
	}

	/* Register peer for NHT. If next hop is already resolved, proceed
	 * with connection setup, else wait.
	 */
	if (!bgp_peer_reg_with_nht(peer)) {
		if (bgp_zebra_num_connects()) {
			if (bgp_debug_neighbor_events(peer))
				zlog_debug("%s [FSM] Waiting for NHT",
					   peer->host);
			peer->last_reset = PEER_DOWN_WAITING_NHT;
			BGP_EVENT_ADD(peer, TCP_connection_open_failed);
			return 0;
		}
	}

	assert(!peer->t_write);
	assert(!peer->t_read);
	assert(!CHECK_FLAG(peer->thread_flags, PEER_THREAD_WRITES_ON));
	assert(!CHECK_FLAG(peer->thread_flags, PEER_THREAD_READS_ON));
	status = bgp_connect(peer);

	switch (status) {
	case connect_error:
		if (bgp_debug_neighbor_events(peer))
			zlog_debug("%s [FSM] Connect error", peer->host);
		BGP_EVENT_ADD(peer, TCP_connection_open_failed);
		break;
	case connect_success:
		if (bgp_debug_neighbor_events(peer))
			zlog_debug(
				"%s [FSM] Connect immediately success, fd %d",
				peer->host, peer->fd);
		BGP_EVENT_ADD(peer, TCP_connection_open);
		break;
	case connect_in_progress:
		/* To check nonblocking connect, we wait until socket is
		   readable or writable. */
		if (bgp_debug_neighbor_events(peer))
			zlog_debug(
				"%s [FSM] Non blocking connect waiting result, fd %d",
				peer->host, peer->fd);
		if (peer->fd < 0) {
			flog_err(EC_BGP_FSM,
				 "bgp_start peer's fd is negative value %d",
				 peer->fd);
			return -1;
		}
		/*
		 * - when the socket becomes ready, poll() will signify POLLOUT
		 * - if it fails to connect, poll() will signify POLLHUP
		 * - POLLHUP is handled as a 'read' event by thread.c
		 *
		 * therefore, we schedule both a read and a write event with
		 * bgp_connect_check() as the handler for each and cancel the
		 * unused event in that function.
		 */
		thread_add_read(bm->master, bgp_connect_check, peer, peer->fd,
				&peer->t_connect_check_r);
		thread_add_write(bm->master, bgp_connect_check, peer, peer->fd,
				 &peer->t_connect_check_w);
		break;
	}
	return 0;
}

/* Connect retry timer is expired when the peer status is Connect. */
static int bgp_reconnect(struct peer *peer)
{
	if (bgp_stop(peer) < 0)
		return -1;

	/* Send graceful restart capabilty */
	BGP_GR_ROUTER_DETECT_AND_SEND_CAPABILITY_TO_ZEBRA(peer->bgp,
							  peer->bgp->peer);

	bgp_start(peer);
	return 0;
}

static int bgp_fsm_open(struct peer *peer)
{
	/* Send keepalive and make keepalive timer */
	bgp_keepalive_send(peer);

	/* Reset holdtimer value. */
	BGP_TIMER_OFF(peer->t_holdtime);

	return 0;
}

/* FSM error, unexpected event.  This is error of BGP connection. So cut the
   peer and change to Idle status. */
static int bgp_fsm_event_error(struct peer *peer)
{
	flog_err(EC_BGP_FSM, "%s [FSM] unexpected packet received in state %s",
		 peer->host, lookup_msg(bgp_status_msg, peer->status, NULL));

	return bgp_stop_with_notify(peer, BGP_NOTIFY_FSM_ERR, 0);
}

/* Hold timer expire.  This is error of BGP connection. So cut the
   peer and change to Idle status. */
static int bgp_fsm_holdtime_expire(struct peer *peer)
{
	if (bgp_debug_neighbor_events(peer))
		zlog_debug("%s [FSM] Hold timer expire", peer->host);

	return bgp_stop_with_notify(peer, BGP_NOTIFY_HOLD_ERR, 0);
}

/* Start the selection deferral timer thread for the specified AFI, SAFI */
static int bgp_start_deferral_timer(struct bgp *bgp, afi_t afi, safi_t safi,
				    struct graceful_restart_info *gr_info)
{
	struct afi_safi_info *thread_info;

	/* If the deferral timer is active, then increment eor count */
	if (gr_info->t_select_deferral) {
		gr_info->eor_required++;
		return 0;
	}

	/* Start the deferral timer when the first peer enabled for the graceful
	 * restart is established
	 */
	if (gr_info->eor_required == 0) {
		thread_info = XMALLOC(MTYPE_TMP, sizeof(struct afi_safi_info));

		thread_info->afi = afi;
		thread_info->safi = safi;
		thread_info->bgp = bgp;

		thread_add_timer(bm->master, bgp_graceful_deferral_timer_expire,
				 thread_info, bgp->select_defer_time,
				 &gr_info->t_select_deferral);
	}
	gr_info->eor_required++;
	/* Send message to RIB indicating route update pending */
	if (gr_info->af_enabled[afi][safi] == false) {
		gr_info->af_enabled[afi][safi] = true;
		/* Send message to RIB */
		bgp_zebra_update(afi, safi, bgp->vrf_id,
				 ZEBRA_CLIENT_ROUTE_UPDATE_PENDING);
	}
	if (BGP_DEBUG(update, UPDATE_OUT))
		zlog_debug("Started the deferral timer for %s eor_required %d",
			   get_afi_safi_str(afi, safi, false),
			   gr_info->eor_required);
	return 0;
}

/* Update the graceful restart information for the specified AFI, SAFI */
static int bgp_update_gr_info(struct peer *peer, afi_t afi, safi_t safi)
{
	struct graceful_restart_info *gr_info;
	struct bgp *bgp = peer->bgp;
	int ret = 0;

	if ((afi < AFI_IP) || (afi >= AFI_MAX)) {
		if (BGP_DEBUG(update, UPDATE_OUT))
			zlog_debug("%s : invalid afi %d", __func__, afi);
		return -1;
	}

	if ((safi < SAFI_UNICAST) || (safi > SAFI_MPLS_VPN)) {
		if (BGP_DEBUG(update, UPDATE_OUT))
			zlog_debug("%s : invalid safi %d", __func__, safi);
		return -1;
	}

	/* Restarting router */
	if (BGP_PEER_GRACEFUL_RESTART_CAPABLE(peer)
	    && BGP_PEER_RESTARTING_MODE(peer)) {
		/* Check if the forwarding state is preserved */
		if (bgp_flag_check(bgp, BGP_FLAG_GR_PRESERVE_FWD)) {
			gr_info = &(bgp->gr_info[afi][safi]);
			ret = bgp_start_deferral_timer(bgp, afi, safi, gr_info);
		}
	}
	return ret;
}

/**
 * Transition to Established state.
 *
 * Convert peer from stub to full fledged peer, set some timers, and generate
 * initial updates.
 */
static int bgp_establish(struct peer *peer)
{
	afi_t afi;
	safi_t safi;
	int nsf_af_count = 0;
	int ret = 0;
	struct peer *other;
	int status;

	other = peer->doppelganger;
	peer = peer_xfer_conn(peer);
	if (!peer) {
		flog_err(EC_BGP_CONNECT, "%%Neighbor failed in xfer_conn");
		return -1;
	}

	if (other == peer)
		ret = 1; /* bgp_establish specific code when xfer_conn
			    happens. */

	/* Reset capability open status flag. */
	if (!CHECK_FLAG(peer->sflags, PEER_STATUS_CAPABILITY_OPEN))
		SET_FLAG(peer->sflags, PEER_STATUS_CAPABILITY_OPEN);

	/* Clear start timer value to default. */
	peer->v_start = BGP_INIT_START_TIMER;

	/* Increment established count. */
	peer->established++;
	bgp_fsm_change_status(peer, Established);

	/* bgp log-neighbor-changes of neighbor Up */
	if (bgp_flag_check(peer->bgp, BGP_FLAG_LOG_NEIGHBOR_CHANGES)) {
		struct vrf *vrf = vrf_lookup_by_id(peer->bgp->vrf_id);
		zlog_info("%%ADJCHANGE: neighbor %s(%s) in vrf %s Up",
			  peer->host,
			  (peer->hostname) ? peer->hostname : "Unknown",
			  vrf ? ((vrf->vrf_id != VRF_DEFAULT)
					? vrf->name
					: VRF_DEFAULT_NAME)
			      : "");
	}
	/* assign update-group/subgroup */
	update_group_adjust_peer_afs(peer);

	/* graceful restart */
	UNSET_FLAG(peer->sflags, PEER_STATUS_NSF_WAIT);
	if (bgp_debug_neighbor_events(peer)) {
		if (BGP_PEER_RESTARTING_MODE(peer))
			zlog_debug("peer %s BGP_RESTARTING_MODE", peer->host);
		else if (BGP_PEER_HELPER_MODE(peer))
			zlog_debug("peer %s BGP_HELPER_MODE", peer->host);
	}
	for (afi = AFI_IP; afi < AFI_MAX; afi++)
		for (safi = SAFI_UNICAST; safi <= SAFI_MPLS_VPN; safi++) {
			if (peer->afc_nego[afi][safi]
			    && CHECK_FLAG(peer->cap, PEER_CAP_RESTART_ADV)
			    && CHECK_FLAG(peer->af_cap[afi][safi],
					  PEER_CAP_RESTART_AF_RCV)) {
				if (peer->nsf[afi][safi]
				    && !CHECK_FLAG(
					       peer->af_cap[afi][safi],
					       PEER_CAP_RESTART_AF_PRESERVE_RCV))
					bgp_clear_stale_route(peer, afi, safi);

				peer->nsf[afi][safi] = 1;
				nsf_af_count++;
			} else {
				if (peer->nsf[afi][safi])
					bgp_clear_stale_route(peer, afi, safi);
				peer->nsf[afi][safi] = 0;
			}
			/* Update the graceful restart information */
			if (peer->afc_nego[afi][safi]) {
				if (!BGP_SELECT_DEFER_DISABLE(peer->bgp)) {
					status = bgp_update_gr_info(peer, afi,
								    safi);
					if (status < 0)
						zlog_err(
							"Error in updating graceful restart for %s",
							get_afi_safi_str(
								afi, safi,
								false));
				} else {
					if (BGP_PEER_GRACEFUL_RESTART_CAPABLE(
						    peer)
					    && BGP_PEER_RESTARTING_MODE(peer)
					    && bgp_flag_check(
						    peer->bgp,
						    BGP_FLAG_GR_PRESERVE_FWD))
						peer->bgp->gr_info[afi][safi]
							.eor_required++;
				}
			}
		}

	peer->nsf_af_count = nsf_af_count;

	if (nsf_af_count)
		SET_FLAG(peer->sflags, PEER_STATUS_NSF_MODE);
	else {
		UNSET_FLAG(peer->sflags, PEER_STATUS_NSF_MODE);
		if (peer->t_gr_stale) {
			BGP_TIMER_OFF(peer->t_gr_stale);
			if (bgp_debug_neighbor_events(peer))
				zlog_debug(
					"%s graceful restart stalepath timer stopped",
					peer->host);
		}
	}

	if (peer->t_gr_restart) {
		BGP_TIMER_OFF(peer->t_gr_restart);
		if (bgp_debug_neighbor_events(peer))
			zlog_debug("%s graceful restart timer stopped",
				   peer->host);
	}

	/* Reset uptime, turn on keepalives, send current table. */
	if (!peer->v_holdtime)
		bgp_keepalives_on(peer);

	peer->uptime = bgp_clock();

	/* Send route-refresh when ORF is enabled */
	FOREACH_AFI_SAFI (afi, safi) {
		if (CHECK_FLAG(peer->af_cap[afi][safi],
			       PEER_CAP_ORF_PREFIX_SM_ADV)) {
			if (CHECK_FLAG(peer->af_cap[afi][safi],
				       PEER_CAP_ORF_PREFIX_RM_RCV))
				bgp_route_refresh_send(peer, afi, safi,
						       ORF_TYPE_PREFIX,
						       REFRESH_IMMEDIATE, 0);
			else if (CHECK_FLAG(peer->af_cap[afi][safi],
					    PEER_CAP_ORF_PREFIX_RM_OLD_RCV))
				bgp_route_refresh_send(peer, afi, safi,
						       ORF_TYPE_PREFIX_OLD,
						       REFRESH_IMMEDIATE, 0);
		}
	}

	/* First update is deferred until ORF or ROUTE-REFRESH is received */
	FOREACH_AFI_SAFI (afi, safi) {
		if (CHECK_FLAG(peer->af_cap[afi][safi],
			       PEER_CAP_ORF_PREFIX_RM_ADV))
			if (CHECK_FLAG(peer->af_cap[afi][safi],
				       PEER_CAP_ORF_PREFIX_SM_RCV)
			    || CHECK_FLAG(peer->af_cap[afi][safi],
					  PEER_CAP_ORF_PREFIX_SM_OLD_RCV))
				SET_FLAG(peer->af_sflags[afi][safi],
					 PEER_STATUS_ORF_WAIT_REFRESH);
	}

	bgp_announce_peer(peer);

	/* Start the route advertisement timer to send updates to the peer - if
	 * BGP
	 * is not in read-only mode. If it is, the timer will be started at the
	 * end
	 * of read-only mode.
	 */
	if (!bgp_update_delay_active(peer->bgp)) {
		BGP_TIMER_OFF(peer->t_routeadv);
		BGP_TIMER_ON(peer->t_routeadv, bgp_routeadv_timer, 0);
	}

	if (peer->doppelganger && (peer->doppelganger->status != Deleted)) {
		if (bgp_debug_neighbor_events(peer))
			zlog_debug(
				"[Event] Deleting stub connection for peer %s",
				peer->host);

		if (peer->doppelganger->status > Active)
			bgp_notify_send(peer->doppelganger, BGP_NOTIFY_CEASE,
					BGP_NOTIFY_CEASE_COLLISION_RESOLUTION);
		else
			peer_delete(peer->doppelganger);
	}

	/*
	 * If we are replacing the old peer for a doppelganger
	 * then switch it around in the bgp->peerhash
	 * the doppelgangers su and this peer's su are the same
	 * so the hash_release is the same for either.
	 */
	hash_release(peer->bgp->peerhash, peer);
	hash_get(peer->bgp->peerhash, peer, hash_alloc_intern);

	bgp_bfd_register_peer(peer);
	return ret;
}

/* Keepalive packet is received. */
static int bgp_fsm_keepalive(struct peer *peer)
{
	BGP_TIMER_OFF(peer->t_holdtime);
	return 0;
}

/* Update packet is received. */
static int bgp_fsm_update(struct peer *peer)
{
	BGP_TIMER_OFF(peer->t_holdtime);
	return 0;
}

/* This is empty event. */
static int bgp_ignore(struct peer *peer)
{
	flog_err(
		EC_BGP_FSM,
		"%s [FSM] Ignoring event %s in state %s, prior events %s, %s, fd %d",
		peer->host, bgp_event_str[peer->cur_event],
		lookup_msg(bgp_status_msg, peer->status, NULL),
		bgp_event_str[peer->last_event],
		bgp_event_str[peer->last_major_event], peer->fd);
	return 0;
}

/* This is to handle unexpected events.. */
static int bgp_fsm_exeption(struct peer *peer)
{
	flog_err(
		EC_BGP_FSM,
		"%s [FSM] Unexpected event %s in state %s, prior events %s, %s, fd %d",
		peer->host, bgp_event_str[peer->cur_event],
		lookup_msg(bgp_status_msg, peer->status, NULL),
		bgp_event_str[peer->last_event],
		bgp_event_str[peer->last_major_event], peer->fd);
	return (bgp_stop(peer));
}

void bgp_fsm_event_update(struct peer *peer, int valid)
{
	if (!peer)
		return;

	switch (peer->status) {
	case Idle:
		if (valid)
			BGP_EVENT_ADD(peer, BGP_Start);
		break;
	case Connect:
		if (!valid) {
			BGP_TIMER_OFF(peer->t_connect);
			BGP_EVENT_ADD(peer, TCP_fatal_error);
		}
		break;
	case Active:
		if (valid) {
			BGP_TIMER_OFF(peer->t_connect);
			BGP_EVENT_ADD(peer, ConnectRetry_timer_expired);
		}
		break;
	case OpenSent:
	case OpenConfirm:
	case Established:
		if (!valid && (peer->gtsm_hops == 1))
			BGP_EVENT_ADD(peer, TCP_fatal_error);
	case Clearing:
	case Deleted:
	default:
		break;
	}
}

/* Finite State Machine structure */
static const struct {
	int (*func)(struct peer *);
	int next_state;
} FSM[BGP_STATUS_MAX - 1][BGP_EVENTS_MAX - 1] = {
	{
		/* Idle state: In Idle state, all events other than BGP_Start is
		   ignored.  With BGP_Start event, finite state machine calls
		   bgp_start(). */
		{bgp_start, Connect}, /* BGP_Start                    */
		{bgp_stop, Idle},     /* BGP_Stop                     */
		{bgp_stop, Idle},     /* TCP_connection_open          */
		{bgp_stop, Idle},     /* TCP_connection_closed        */
		{bgp_ignore, Idle},   /* TCP_connection_open_failed   */
		{bgp_stop, Idle},     /* TCP_fatal_error              */
		{bgp_ignore, Idle},   /* ConnectRetry_timer_expired   */
		{bgp_ignore, Idle},   /* Hold_Timer_expired           */
		{bgp_ignore, Idle},   /* KeepAlive_timer_expired      */
		{bgp_ignore, Idle},   /* Receive_OPEN_message         */
		{bgp_ignore, Idle},   /* Receive_KEEPALIVE_message    */
		{bgp_ignore, Idle},   /* Receive_UPDATE_message       */
		{bgp_ignore, Idle},   /* Receive_NOTIFICATION_message */
		{bgp_ignore, Idle},   /* Clearing_Completed           */
	},
	{
		/* Connect */
		{bgp_ignore, Connect}, /* BGP_Start                    */
		{bgp_stop, Idle},      /* BGP_Stop                     */
		{bgp_connect_success, OpenSent}, /* TCP_connection_open */
		{bgp_stop, Idle},	   /* TCP_connection_closed        */
		{bgp_connect_fail, Active}, /* TCP_connection_open_failed   */
		{bgp_connect_fail, Idle},   /* TCP_fatal_error              */
		{bgp_reconnect, Connect},   /* ConnectRetry_timer_expired   */
		{bgp_fsm_exeption, Idle},   /* Hold_Timer_expired           */
		{bgp_fsm_exeption, Idle},   /* KeepAlive_timer_expired      */
		{bgp_fsm_exeption, Idle},   /* Receive_OPEN_message         */
		{bgp_fsm_exeption, Idle},   /* Receive_KEEPALIVE_message    */
		{bgp_fsm_exeption, Idle},   /* Receive_UPDATE_message       */
		{bgp_stop, Idle},	   /* Receive_NOTIFICATION_message */
		{bgp_fsm_exeption, Idle},   /* Clearing_Completed           */
	},
	{
		/* Active, */
		{bgp_ignore, Active}, /* BGP_Start                    */
		{bgp_stop, Idle},     /* BGP_Stop                     */
		{bgp_connect_success, OpenSent}, /* TCP_connection_open */
		{bgp_stop, Idle},	 /* TCP_connection_closed        */
		{bgp_ignore, Active},     /* TCP_connection_open_failed   */
		{bgp_fsm_exeption, Idle}, /* TCP_fatal_error              */
		{bgp_start, Connect},     /* ConnectRetry_timer_expired   */
		{bgp_fsm_exeption, Idle}, /* Hold_Timer_expired           */
		{bgp_fsm_exeption, Idle}, /* KeepAlive_timer_expired      */
		{bgp_fsm_exeption, Idle}, /* Receive_OPEN_message         */
		{bgp_fsm_exeption, Idle}, /* Receive_KEEPALIVE_message    */
		{bgp_fsm_exeption, Idle}, /* Receive_UPDATE_message       */
		{bgp_fsm_exeption, Idle}, /* Receive_NOTIFICATION_message */
		{bgp_fsm_exeption, Idle}, /* Clearing_Completed           */
	},
	{
		/* OpenSent, */
		{bgp_ignore, OpenSent},   /* BGP_Start                    */
		{bgp_stop, Idle},	 /* BGP_Stop                     */
		{bgp_stop, Active},       /* TCP_connection_open          */
		{bgp_stop, Active},       /* TCP_connection_closed        */
		{bgp_stop, Active},       /* TCP_connection_open_failed   */
		{bgp_stop, Active},       /* TCP_fatal_error              */
		{bgp_fsm_exeption, Idle}, /* ConnectRetry_timer_expired   */
		{bgp_fsm_holdtime_expire, Idle}, /* Hold_Timer_expired */
		{bgp_fsm_exeption, Idle},    /* KeepAlive_timer_expired      */
		{bgp_fsm_open, OpenConfirm}, /* Receive_OPEN_message         */
		{bgp_fsm_event_error, Idle}, /* Receive_KEEPALIVE_message    */
		{bgp_fsm_event_error, Idle}, /* Receive_UPDATE_message       */
		{bgp_fsm_event_error, Idle}, /* Receive_NOTIFICATION_message */
		{bgp_fsm_exeption, Idle},    /* Clearing_Completed           */
	},
	{
		/* OpenConfirm, */
		{bgp_ignore, OpenConfirm}, /* BGP_Start                    */
		{bgp_stop, Idle},	  /* BGP_Stop                     */
		{bgp_stop, Idle},	  /* TCP_connection_open          */
		{bgp_stop, Idle},	  /* TCP_connection_closed        */
		{bgp_stop, Idle},	  /* TCP_connection_open_failed   */
		{bgp_stop, Idle},	  /* TCP_fatal_error              */
		{bgp_fsm_exeption, Idle},  /* ConnectRetry_timer_expired   */
		{bgp_fsm_holdtime_expire, Idle}, /* Hold_Timer_expired */
		{bgp_ignore, OpenConfirm},    /* KeepAlive_timer_expired      */
		{bgp_fsm_exeption, Idle},     /* Receive_OPEN_message         */
		{bgp_establish, Established}, /* Receive_KEEPALIVE_message    */
		{bgp_fsm_exeption, Idle},     /* Receive_UPDATE_message       */
		{bgp_stop_with_error, Idle},  /* Receive_NOTIFICATION_message */
		{bgp_fsm_exeption, Idle},     /* Clearing_Completed           */
	},
	{
		/* Established, */
		{bgp_ignore, Established}, /* BGP_Start                    */
		{bgp_stop, Clearing},      /* BGP_Stop                     */
		{bgp_stop, Clearing},      /* TCP_connection_open          */
		{bgp_stop, Clearing},      /* TCP_connection_closed        */
		{bgp_stop, Clearing},      /* TCP_connection_open_failed   */
		{bgp_stop, Clearing},      /* TCP_fatal_error              */
		{bgp_stop, Clearing},      /* ConnectRetry_timer_expired   */
		{bgp_fsm_holdtime_expire, Clearing}, /* Hold_Timer_expired */
		{bgp_ignore, Established}, /* KeepAlive_timer_expired      */
		{bgp_stop, Clearing},      /* Receive_OPEN_message         */
		{bgp_fsm_keepalive,
		 Established}, /* Receive_KEEPALIVE_message    */
		{bgp_fsm_update, Established}, /* Receive_UPDATE_message */
		{bgp_stop_with_error,
		 Clearing},		  /* Receive_NOTIFICATION_message */
		{bgp_fsm_exeption, Idle}, /* Clearing_Completed           */
	},
	{
		/* Clearing, */
		{bgp_ignore, Clearing}, /* BGP_Start                    */
		{bgp_stop, Clearing},   /* BGP_Stop                     */
		{bgp_stop, Clearing},   /* TCP_connection_open          */
		{bgp_stop, Clearing},   /* TCP_connection_closed        */
		{bgp_stop, Clearing},   /* TCP_connection_open_failed   */
		{bgp_stop, Clearing},   /* TCP_fatal_error              */
		{bgp_stop, Clearing},   /* ConnectRetry_timer_expired   */
		{bgp_stop, Clearing},   /* Hold_Timer_expired           */
		{bgp_stop, Clearing},   /* KeepAlive_timer_expired      */
		{bgp_stop, Clearing},   /* Receive_OPEN_message         */
		{bgp_stop, Clearing},   /* Receive_KEEPALIVE_message    */
		{bgp_stop, Clearing},   /* Receive_UPDATE_message       */
		{bgp_stop, Clearing},   /* Receive_NOTIFICATION_message */
		{bgp_clearing_completed, Idle}, /* Clearing_Completed */
	},
	{
		/* Deleted, */
		{bgp_ignore, Deleted}, /* BGP_Start                    */
		{bgp_ignore, Deleted}, /* BGP_Stop                     */
		{bgp_ignore, Deleted}, /* TCP_connection_open          */
		{bgp_ignore, Deleted}, /* TCP_connection_closed        */
		{bgp_ignore, Deleted}, /* TCP_connection_open_failed   */
		{bgp_ignore, Deleted}, /* TCP_fatal_error              */
		{bgp_ignore, Deleted}, /* ConnectRetry_timer_expired   */
		{bgp_ignore, Deleted}, /* Hold_Timer_expired           */
		{bgp_ignore, Deleted}, /* KeepAlive_timer_expired      */
		{bgp_ignore, Deleted}, /* Receive_OPEN_message         */
		{bgp_ignore, Deleted}, /* Receive_KEEPALIVE_message    */
		{bgp_ignore, Deleted}, /* Receive_UPDATE_message       */
		{bgp_ignore, Deleted}, /* Receive_NOTIFICATION_message */
		{bgp_ignore, Deleted}, /* Clearing_Completed           */
	},
};

/* Execute event process. */
int bgp_event(struct thread *thread)
{
	int event;
	struct peer *peer;
	int ret;

	peer = THREAD_ARG(thread);
	event = THREAD_VAL(thread);

	ret = bgp_event_update(peer, event);

	return (ret);
}

int bgp_event_update(struct peer *peer, int event)
{
	int next;
	int ret = 0;
	struct peer *other;
	int passive_conn = 0;
	int dyn_nbr;

	/* default return code */
	ret = FSM_PEER_NOOP;

	other = peer->doppelganger;
	passive_conn =
		(CHECK_FLAG(peer->sflags, PEER_STATUS_ACCEPT_PEER)) ? 1 : 0;
	dyn_nbr = peer_dynamic_neighbor(peer);

	/* Logging this event. */
	next = FSM[peer->status - 1][event - 1].next_state;

	if (bgp_debug_neighbor_events(peer) && peer->status != next)
		zlog_debug("%s [FSM] %s (%s->%s), fd %d", peer->host,
			   bgp_event_str[event],
			   lookup_msg(bgp_status_msg, peer->status, NULL),
			   lookup_msg(bgp_status_msg, next, NULL), peer->fd);

	peer->last_event = peer->cur_event;
	peer->cur_event = event;

	/* Call function. */
	if (FSM[peer->status - 1][event - 1].func)
		ret = (*(FSM[peer->status - 1][event - 1].func))(peer);

	if (ret >= 0) {
		if (ret == 1 && next == Established) {
			/* The case when doppelganger swap accurred in
			   bgp_establish.
			   Update the peer pointer accordingly */
			ret = FSM_PEER_TRANSFERRED;
			peer = other;
		}

		/* If status is changed. */
		if (next != peer->status) {
			bgp_fsm_change_status(peer, next);

			/*
			 * If we're going to ESTABLISHED then we executed a
			 * peer transfer. In this case we can either return
			 * FSM_PEER_TRANSITIONED or FSM_PEER_TRANSFERRED.
			 * Opting for TRANSFERRED since transfer implies
			 * session establishment.
			 */
			if (ret != FSM_PEER_TRANSFERRED)
				ret = FSM_PEER_TRANSITIONED;
		}

		/* Make sure timer is set. */
		bgp_timer_set(peer);

	} else {
		/*
		 * If we got a return value of -1, that means there was an
		 * error, restart the FSM. Since bgp_stop() was called on the
		 * peer. only a few fields are safe to access here. In any case
		 * we need to indicate that the peer was stopped in the return
		 * code.
		 */
		if (!dyn_nbr && !passive_conn && peer->bgp) {
			flog_err(
				EC_BGP_FSM,
				"%s [FSM] Failure handling event %s in state %s, "
				"prior events %s, %s, fd %d",
				peer->host, bgp_event_str[peer->cur_event],
				lookup_msg(bgp_status_msg, peer->status, NULL),
				bgp_event_str[peer->last_event],
				bgp_event_str[peer->last_major_event],
				peer->fd);
			bgp_stop(peer);
			bgp_fsm_change_status(peer, Idle);
			bgp_timer_set(peer);
		}
		ret = FSM_PEER_STOPPED;
	}

	return ret;
}
/* BGP GR Code */

int bgp_gr_lookup_n_update_all_peer(struct bgp *bgp,
				    enum global_mode global_new_state,
				    enum global_mode global_old_state)
{
	struct peer *peer = {0};
	struct listnode *node = {0};
	struct listnode *nnode = {0};
	enum peer_mode peer_old_state = PEER_INVALID;

	for (ALL_LIST_ELEMENTS(bgp->peer, node, nnode, peer)) {

		if (BGP_DEBUG(graceful_restart, GRACEFUL_RESTART))
			zlog_debug("%s [BGP_GR] Peer: (%s) :", __func__,
				   peer->host);

		peer_old_state = bgp_peer_gr_mode_get(peer);

		if (peer_old_state == PEER_GLOBAL_INHERIT) {

			/*
			 *Reset only these peers and send a
			 *new open message with the change capabilities.
			 *Considering the mode to be "global_new_state" and
			 *do all operation accordingly
			 */

			switch (global_new_state) {
			case GLOBAL_HELPER:
				BGP_PEER_GR_HELPER_ENABLE(peer);
				break;
			case GLOBAL_GR:
				BGP_PEER_GR_ENABLE(peer);
				break;
			case GLOBAL_DISABLE:
				BGP_PEER_GR_DISABLE(peer);
				break;
			case GLOBAL_INVALID:
				zlog_debug("%s [BGP_GR] GLOBAL_INVALID",
					   __func__);
				return BGP_ERR_GR_OPERATION_FAILED;
			}
		}
	}

	bgp->global_gr_present_state = global_new_state;

	return BGP_GR_SUCCESS;
}

int bgp_gr_update_all(struct bgp *bgp, int global_gr_cmd)
{
	enum global_mode global_new_state = GLOBAL_INVALID;
	enum global_mode global_old_state = GLOBAL_INVALID;

	if (BGP_DEBUG(graceful_restart, GRACEFUL_RESTART))
		zlog_debug("%s [BGP_GR]START: global_gr_cmd :%s:", __func__,
			   print_global_gr_cmd(global_gr_cmd));

	global_old_state = bgp_global_gr_mode_get(bgp);

	if (BGP_DEBUG(graceful_restart, GRACEFUL_RESTART))
		zlog_debug("[BGP_GR] global_old_gr_state :%s:",
			   print_global_gr_mode(global_old_state));

	if (global_old_state != GLOBAL_INVALID) {
		global_new_state =
			bgp->GLOBAL_GR_FSM[global_old_state][global_gr_cmd];

		if (BGP_DEBUG(graceful_restart, GRACEFUL_RESTART))
			zlog_debug("[BGP_GR] global_new_gr_state :%s:",
				   print_global_gr_mode(global_new_state));
	} else {
		zlog_err("%s [BGP_GR] global_old_state == GLOBAL_INVALID",
			 __func__);
		return BGP_ERR_GR_OPERATION_FAILED;
	}

	if (global_new_state == GLOBAL_INVALID) {
		zlog_err("%s [BGP_GR] global_new_state == GLOBAL_INVALID",
			 __func__);
		return BGP_ERR_GR_INVALID_CMD;
	}
	if (global_new_state == global_old_state) {
		/* Trace msg */
		if (BGP_DEBUG(graceful_restart, GRACEFUL_RESTART))
			zlog_debug(
				"%s [BGP_GR] global_new_state == global_old_state :%s",
				__func__,
				print_global_gr_mode(global_new_state));
		return BGP_GR_NO_OPERATION;
	}

	return bgp_gr_lookup_n_update_all_peer(bgp, global_new_state,
					       global_old_state);
}

const char *print_peer_gr_mode(enum peer_mode pr_mode)
{
	const char *peer_gr_mode = NULL;

	switch (pr_mode) {
	case PEER_HELPER:
		peer_gr_mode = "PEER_HELPER";
		break;
	case PEER_GR:
		peer_gr_mode = "PEER_GR";
		break;
	case PEER_DISABLE:
		peer_gr_mode = "PEER_DISABLE";
		break;
	case PEER_INVALID:
		peer_gr_mode = "PEER_INVALID";
		break;
	case PEER_GLOBAL_INHERIT:
		peer_gr_mode = "PEER_GLOBAL_INHERIT";
		break;
	}

	return peer_gr_mode;
}

const char *print_peer_gr_cmd(enum peer_gr_command pr_gr_cmd)
{
	const char *peer_gr_cmd = NULL;

	switch (pr_gr_cmd) {
	case PEER_GR_CMD:
		peer_gr_cmd = "PEER_GR_CMD";
		break;
	case NO_PEER_GR_CMD:
		peer_gr_cmd = "NO_PEER_GR_CMD";
		break;
	case PEER_DISABLE_CMD:
		peer_gr_cmd = "PEER_GR_CMD";
		break;
	case NO_PEER_DISABLE_CMD:
		peer_gr_cmd = "NO_PEER_GR_CMD";
		break;
	case PEER_HELPER_CMD:
		peer_gr_cmd = "PEER_HELPER_CMD";
		break;
	case NO_PEER_HELPER_CMD:
		peer_gr_cmd = "NO_PEER_HELPER_CMD";
		break;
	}

	return peer_gr_cmd;
}

const char *print_global_gr_mode(enum global_mode gl_mode)
{
	const char *global_gr_mode = NULL;

	switch (gl_mode) {
	case GLOBAL_HELPER:
		global_gr_mode = "GLOBAL_HELPER";
		break;
	case GLOBAL_GR:
		global_gr_mode = "GLOBAL_GR";
		break;
	case GLOBAL_DISABLE:
		global_gr_mode = "GLOBAL_DISABLE";
		break;
	case GLOBAL_INVALID:
		global_gr_mode = "GLOBAL_INVALID";
		break;
	}

	return global_gr_mode;
}

const char *print_global_gr_cmd(enum global_gr_command gl_gr_cmd)
{
	const char *global_gr_cmd = NULL;

	switch (gl_gr_cmd) {
	case GLOBAL_GR_CMD:
		global_gr_cmd = "GLOBAL_GR_CMD";
		break;
	case NO_GLOBAL_GR_CMD:
		global_gr_cmd = "NO_GLOBAL_GR_CMD";
		break;
	case GLOBAL_DISABLE_CMD:
		global_gr_cmd = "GLOBAL_DISABLE_CMD";
		break;
	case NO_GLOBAL_DISABLE_CMD:
		global_gr_cmd = "NO_GLOBAL_DISABLE_CMD";
		break;
	}

	return global_gr_cmd;
}

enum global_mode bgp_global_gr_mode_get(struct bgp *bgp)
{
	return bgp->global_gr_present_state;
}

enum peer_mode bgp_peer_gr_mode_get(struct peer *peer)
{
	return peer->peer_gr_present_state;
}

int bgp_neighbor_graceful_restart(struct peer *peer, int peer_gr_cmd)
{
	enum peer_mode peer_new_state = PEER_INVALID;
	enum peer_mode peer_old_state = PEER_INVALID;
	struct bgp_peer_gr peer_state;
	int result = BGP_GR_FAILURE;

	/*
	 * fetch peer_old_state from peer structure also
	 * fetch global_old_state from bgp structure,
	 * peer had a back pointer to bgpo struct ;
	 */

	if (BGP_DEBUG(graceful_restart, GRACEFUL_RESTART))
		zlog_debug("%s [BGP_GR] START:Peer: (%s) : peer_gr_cmd :%s:",
			   __func__, peer->host,
			   print_peer_gr_cmd(peer_gr_cmd));

	peer_old_state = bgp_peer_gr_mode_get(peer);

	if (peer_old_state == PEER_INVALID) {
		zlog_debug("[BGP_GR] peer_old_state == Invalid state !");
		return BGP_ERR_GR_OPERATION_FAILED;
	}

	peer_state = peer->PEER_GR_FSM[peer_old_state][peer_gr_cmd];
	peer_new_state = peer_state.next_state;

	if (peer_new_state == PEER_INVALID) {
		zlog_debug(
			"[BGP_GR] Invalid bgp graceful restart command used !");
		return BGP_ERR_GR_INVALID_CMD;
	}

	if (peer_new_state != peer_old_state) {
		result = peer_state.action_fun(peer, peer_old_state,
					       peer_new_state);
	} else {
		if (BGP_DEBUG(graceful_restart, GRACEFUL_RESTART))
			zlog_debug(
				"[BGP_GR] peer_old_state == peer_new_state !");
		return BGP_GR_NO_OPERATION;
	}

	if (result == BGP_GR_SUCCESS) {

		/* Update the mode i.e peer_new_state into the peer structure */
		peer->peer_gr_present_state = peer_new_state;
		if (BGP_DEBUG(graceful_restart, GRACEFUL_RESTART))
			zlog_debug(
				"[BGP_GR] Succesfully change the state of the peer to : %s : !",
				print_peer_gr_mode(peer_new_state));

		return BGP_GR_SUCCESS;
	}

	return result;
}

unsigned int bgp_peer_gr_action(struct peer *peer, int old_peer_state,
				int new_peer_state)
{
	if (BGP_DEBUG(graceful_restart, GRACEFUL_RESTART))
		zlog_debug(
			"%s [BGP_GR] Move peer from old_peer_state :%s: to new_peer_state :%s: !!!!",
			__func__, print_peer_gr_mode(old_peer_state),
			print_peer_gr_mode(new_peer_state));

	int bgp_gr_global_mode = GLOBAL_INVALID;
	unsigned int ret = BGP_GR_FAILURE;

	if (old_peer_state == new_peer_state) {
		/* Nothing to do over here as the present and old state is the
		 * same */
		return BGP_GR_NO_OPERATION;
	}
	if ((old_peer_state == PEER_INVALID)
	    || (new_peer_state == PEER_INVALID)) {
		/* something bad happend , print error message */
		return BGP_ERR_GR_INVALID_CMD;
	}

	bgp_gr_global_mode = bgp_global_gr_mode_get(peer->bgp);

	if ((old_peer_state == PEER_GLOBAL_INHERIT)
	    && (new_peer_state != PEER_GLOBAL_INHERIT)) {

		/* fetch the Mode running in the Global state machine
		 *from the bgp structure into a variable called
		 *bgp_gr_global_mode
		 */

		/* Here we are checking if the
		 *1. peer_new_state == global_mode == helper_mode
		 *2. peer_new_state == global_mode == GR_mode
		 *3. peer_new_state == global_mode == disabled_mode
		 */

		BGP_PEER_GR_GLOBAL_INHERIT_UNSET(peer);

		if (new_peer_state == bgp_gr_global_mode) {
			/*This is incremental updates i.e no tear down
			 *of the existing session
			 *as the peer is already working in the same mode.
			 */
			ret = BGP_GR_SUCCESS;
		} else {
			if (BGP_DEBUG(graceful_restart, GRACEFUL_RESTART))
				zlog_debug(
					"[BGP_GR] Peer state changed from :%s ",
					print_peer_gr_mode(old_peer_state));

			bgp_peer_move_to_gr_mode(peer, new_peer_state);

			ret = BGP_GR_SUCCESS;
		}
	}
	/* In the case below peer is going into Global inherit mode i.e.
	 * the peer would work as the mode configured at the global level
	 */
	else if ((new_peer_state == PEER_GLOBAL_INHERIT)
		 && (old_peer_state != PEER_GLOBAL_INHERIT)) {
		/* Here in this case it would be destructive
		 * in all the cases except one case when,
		 * Global GR is configured Disabled
		 * and present_peer_state is not disable
		 */

		BGP_PEER_GR_GLOBAL_INHERIT_SET(peer);

		if (old_peer_state == bgp_gr_global_mode) {

			/* This is incremental updates
			 *i.e no tear down of the existing session
			 *as the peer is already working in the same mode.
			 */
			ret = BGP_GR_SUCCESS;
		} else {
			/*  Destructive always */
			/*  Tear down the old session
			 *  and send the new capability
			 *  as per the bgp_gr_global_mode
			 */

			if (BGP_DEBUG(graceful_restart, GRACEFUL_RESTART))
				zlog_debug(
					"[BGP_GR] Peer state changed from :%s",
					print_peer_gr_mode(old_peer_state));

			bgp_peer_move_to_gr_mode(peer, bgp_gr_global_mode);

			ret = BGP_GR_SUCCESS;
		}
	} else {
		/*
		 *This else case, it include all the cases except -->
		 *(new_peer_state != Peer_Global) &&
		 *( old_peer_state != Peer_Global )
		 */
		if (BGP_DEBUG(graceful_restart, GRACEFUL_RESTART))
			zlog_debug("[BGP_GR] Peer state changed from :%s",
				   print_peer_gr_mode(old_peer_state));

		bgp_peer_move_to_gr_mode(peer, new_peer_state);

		ret = BGP_GR_SUCCESS;
	}

	return ret;
}

inline void bgp_peer_move_to_gr_mode(struct peer *peer, int new_state)

{
	int bgp_global_gr_mode = bgp_global_gr_mode_get(peer->bgp);

	switch (new_state) {
	case PEER_HELPER:
		BGP_PEER_GR_HELPER_ENABLE(peer);
		break;
	case PEER_GR:
		BGP_PEER_GR_ENABLE(peer);
		break;
	case PEER_DISABLE:
		BGP_PEER_GR_DISABLE(peer);
		break;
	case PEER_GLOBAL_INHERIT:
		BGP_PEER_GR_GLOBAL_INHERIT_SET(peer);

		if (bgp_global_gr_mode == GLOBAL_HELPER) {
			BGP_PEER_GR_HELPER_ENABLE(peer);
		} else if (bgp_global_gr_mode == GLOBAL_GR) {
			BGP_PEER_GR_ENABLE(peer);
		} else if (bgp_global_gr_mode == GLOBAL_DISABLE) {
			BGP_PEER_GR_DISABLE(peer);
		} else {
			zlog_err(
				"[BGP_GR] Default switch inherit mode ::: SOMETHING IS WRONG !!!");
		}
		break;
	default:
		zlog_err(
			"[BGP_GR] Default switch mode ::: SOMETHING IS WRONG !!!");
		break;
	}
	if (BGP_DEBUG(graceful_restart, GRACEFUL_RESTART))
		zlog_debug("[BGP_GR] Peer state changed  --to-->  : %d : !",
			   new_state);
}

void bgp_peer_gr_flags_update(struct peer *peer)
{
	if (BGP_DEBUG(graceful_restart, GRACEFUL_RESTART))
		zlog_debug("%s [BGP_GR] called !", __func__);
	if (CHECK_FLAG(peer->peer_gr_new_status_flag,
		       PEER_GRACEFUL_RESTART_NEW_STATE_HELPER))
		SET_FLAG(peer->flags, PEER_FLAG_GRACEFUL_RESTART_HELPER);
	else
		UNSET_FLAG(peer->flags, PEER_FLAG_GRACEFUL_RESTART_HELPER);
	if (BGP_DEBUG(graceful_restart, GRACEFUL_RESTART))
		zlog_debug(
			"[BGP_GR] Peer %s Flag PEER_FLAG_GRACEFUL_RESTART_HELPER : %s : !",
			peer->host,
			(CHECK_FLAG(peer->flags,
				    PEER_FLAG_GRACEFUL_RESTART_HELPER)
				 ? "Set"
				 : "UnSet"));
	if (CHECK_FLAG(peer->peer_gr_new_status_flag,
		       PEER_GRACEFUL_RESTART_NEW_STATE_RESTART))
		SET_FLAG(peer->flags, PEER_FLAG_GRACEFUL_RESTART);
	else
		UNSET_FLAG(peer->flags, PEER_FLAG_GRACEFUL_RESTART);
	if (BGP_DEBUG(graceful_restart, GRACEFUL_RESTART))
		zlog_debug(
			"[BGP_GR] Peer %s Flag PEER_FLAG_GRACEFUL_RESTART : %s : !",
			peer->host,
			(CHECK_FLAG(peer->flags, PEER_FLAG_GRACEFUL_RESTART)
				 ? "Set"
				 : "UnSet"));
	if (CHECK_FLAG(peer->peer_gr_new_status_flag,
		       PEER_GRACEFUL_RESTART_NEW_STATE_INHERIT))
		SET_FLAG(peer->flags,
			 PEER_FLAG_GRACEFUL_RESTART_GLOBAL_INHERIT);
	else
		UNSET_FLAG(peer->flags,
			   PEER_FLAG_GRACEFUL_RESTART_GLOBAL_INHERIT);
	if (BGP_DEBUG(graceful_restart, GRACEFUL_RESTART))
		zlog_debug(
			"[BGP_GR] Peer %s Flag PEER_FLAG_GRACEFUL_RESTART_GLOBAL_INHERIT : %s : !",
			peer->host,
			(CHECK_FLAG(peer->flags,
				    PEER_FLAG_GRACEFUL_RESTART_GLOBAL_INHERIT)
				 ? "Set"
				 : "UnSet"));

	if (!CHECK_FLAG(peer->flags, PEER_FLAG_GRACEFUL_RESTART)
	    && !CHECK_FLAG(peer->flags, PEER_FLAG_GRACEFUL_RESTART_HELPER)) {
		zlog_debug("[BGP_GR] Peer %s UNSET PEER_STATUS_NSF_MODE!",
			   peer->host);

		UNSET_FLAG(peer->sflags, PEER_STATUS_NSF_MODE);

		if (CHECK_FLAG(peer->sflags, PEER_STATUS_NSF_WAIT)) {

			peer_nsf_stop(peer);
			zlog_debug(
				"[BGP_GR] Peer %s UNSET PEER_STATUS_NSF_WAIT!",
				peer->host);
		}
	}
}