bgpd: Do not delete BGP dynamic peers if graceful restart kicks in

```
~# vtysh -c 'show bgp ipv4 unicast summary' | grep 192.168.10.17
*donatas-pc(192.168.10.17)           4      65002         8        12        0    0    0 00:01:35            2       14 N/A
```

Before shutting down 192.168.10.17:

```
~# vtysh -c 'show bgp ipv4 unicast 100.100.100.100/32'
BGP routing table entry for 100.100.100.100/32, version 7
Paths: (2 available, best #2, table default)
  Advertised to non peer-group peers:
  home-spine1.donatas.net(192.168.0.2)
  65002, (stale)
    192.168.10.17 from donatas-pc(192.168.10.17) (0.0.0.0)
      Origin incomplete, valid, external
      Last update: Sat Jan 15 21:45:47 2022
  65001
    192.168.0.2 from home-spine1.donatas.net(192.168.0.2) (2.2.2.2)
      Origin incomplete, metric 0, valid, external, best (Older Path)
      Last update: Sat Jan 15 21:25:19 2022
```

After 192.168.10.17 is down:

```
~# vtysh -c 'show bgp ipv4 unicast summary' | grep 192.168.10.17
donatas-pc(192.168.10.17)            4      65002         5         9        0    0    0 00:00:12       Active        0 N/A

~# vtysh -c 'show bgp ipv4 unicast 100.100.100.100/32'
BGP routing table entry for 100.100.100.100/32, version 7
Paths: (2 available, best #2, table default)
  Advertised to non peer-group peers:
  home-spine1.donatas.net(192.168.0.2)
  65002, (stale)
    192.168.10.17 from donatas-pc(192.168.10.17) (0.0.0.0)
      Origin incomplete, valid, external
      Community: llgr-stale
      Last update: Sat Jan 15 21:49:01 2022
      Time until Long-lived stale route deleted: 16
  65001
    192.168.0.2 from home-spine1.donatas.net(192.168.0.2) (2.2.2.2)
      Origin incomplete, metric 0, valid, external, best (First path received)
      Last update: Sat Jan 15 21:25:19 2022
```

Signed-off-by: Donatas Abraitis <donatas.abraitis@gmail.com>

2 files changed, 21 insertions, 7 deletions

diff --git a/bgpd/bgp_fsm.c b/bgpd/bgp_fsm.c
index 45e9aad1ba..c2e3d02230 100644
--- a/bgpd/bgp_fsm.c
+++ b/bgpd/bgp_fsm.c
@@ -662,6 +662,14 @@ static void bgp_graceful_restart_timer_off(struct peer *peer)
 
 	UNSET_FLAG(peer->sflags, PEER_STATUS_NSF_WAIT);
 	BGP_TIMER_OFF(peer->t_gr_stale);
+
+	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);
+	}
+
 	bgp_timer_set(peer);
 }
 
@@ -1380,8 +1388,8 @@ int bgp_stop(struct peer *peer)
 	    && peer->last_reset == PEER_DOWN_UPDATE_SOURCE_CHANGE)
 		bfd_sess_uninstall(peer->bfd_config->session);
 
-	if (peer_dynamic_neighbor(peer)
-	    && !(CHECK_FLAG(peer->flags, PEER_FLAG_DELETE))) {
+	if (peer_dynamic_neighbor_no_nsf(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);
@@ -1602,7 +1610,7 @@ static int bgp_stop_with_error(struct peer *peer)
 	if (peer->v_start >= (60 * 2))
 		peer->v_start = (60 * 2);
 
-	if (peer_dynamic_neighbor(peer)) {
+	if (peer_dynamic_neighbor_no_nsf(peer)) {
 		if (bgp_debug_neighbor_events(peer))
 			zlog_debug("%s (dynamic neighbor) deleted", peer->host);
 		peer_delete(peer);
@@ -1620,7 +1628,7 @@ static int bgp_stop_with_notify(struct peer *peer, uint8_t code,
 	/* Send notify to remote peer */
 	bgp_notify_send(peer, code, sub_code);
 
-	if (peer_dynamic_neighbor(peer)) {
+	if (peer_dynamic_neighbor_no_nsf(peer)) {
 		if (bgp_debug_neighbor_events(peer))
 			zlog_debug("%s (dynamic neighbor) deleted", peer->host);
 		peer_delete(peer);
@@ -1781,7 +1789,7 @@ static int bgp_connect_success_w_delayopen(struct peer *peer)
 /* TCP connect fail */
 static int bgp_connect_fail(struct peer *peer)
 {
-	if (peer_dynamic_neighbor(peer)) {
+	if (peer_dynamic_neighbor_no_nsf(peer)) {
 		if (bgp_debug_neighbor_events(peer))
 			zlog_debug("%s (dynamic neighbor) deleted", peer->host);
 		peer_delete(peer);
diff --git a/bgpd/bgpd.h b/bgpd/bgpd.h
index 747c185e39..57d135e781 100644
--- a/bgpd/bgpd.h
+++ b/bgpd/bgpd.h
@@ -2380,9 +2380,15 @@ static inline bool peer_established(struct peer *peer)
 	return peer->status == Established;
 }
 
-static inline int peer_dynamic_neighbor(struct peer *peer)
+static inline bool peer_dynamic_neighbor(struct peer *peer)
 {
-	return (CHECK_FLAG(peer->flags, PEER_FLAG_DYNAMIC_NEIGHBOR)) ? 1 : 0;
+	return CHECK_FLAG(peer->flags, PEER_FLAG_DYNAMIC_NEIGHBOR);
+}
+
+static inline bool peer_dynamic_neighbor_no_nsf(struct peer *peer)
+{
+	return (peer_dynamic_neighbor(peer) &&
+		!CHECK_FLAG(peer->sflags, PEER_STATUS_NSF_WAIT));
 }
 
 static inline int peer_cap_enhe(struct peer *peer, afi_t afi, safi_t safi)