bgpd: Implement Paths-Limit capability

https://datatracker.ietf.org/doc/html/draft-abraitis-idr-addpath-paths-limit

Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>

bgpd/bgp_addpath.h

@@ -21,6 +21,12 @@ struct bgp_addpath_capability {
 	uint8_t flags;
 };
 
+struct bgp_paths_limit_capability {
+	uint16_t afi;
+	uint8_t safi;
+	uint16_t paths_limit;
+};
+
 #define BGP_ADDPATH_TX_ID_FOR_DEFAULT_ORIGINATE 1
 
 void bgp_addpath_init_bgp_data(struct bgp_addpath_bgp_data *d);

bgpd/bgp_fsm.c

@@ -260,6 +260,8 @@ static struct peer *peer_xfer_conn(struct peer *from_peer)
 		peer->afc_recv[afi][safi] = from_peer->afc_recv[afi][safi];
 		peer->orf_plist[afi][safi] = from_peer->orf_plist[afi][safi];
 		peer->llgr[afi][safi] = from_peer->llgr[afi][safi];
+		peer->addpath_paths_limit[afi][safi] =
+			from_peer->addpath_paths_limit[afi][safi];
 	}
 
 	if (bgp_getsockname(peer) < 0) {

bgpd/bgp_open.c

@@ -42,6 +42,7 @@ const struct message capcode_str[] = {
 	{ CAPABILITY_CODE_LLGR, "Long-lived BGP Graceful Restart" },
 	{ CAPABILITY_CODE_ROLE, "Role" },
 	{ CAPABILITY_CODE_SOFT_VERSION, "Software Version" },
+	{ CAPABILITY_CODE_PATHS_LIMIT, "Paths-Limit" },
 	{ 0 }
 };
 
@@ -61,6 +62,7 @@ static const size_t cap_minsizes[] = {
 		[CAPABILITY_CODE_LLGR] = CAPABILITY_CODE_LLGR_LEN,
 		[CAPABILITY_CODE_ROLE] = CAPABILITY_CODE_ROLE_LEN,
 		[CAPABILITY_CODE_SOFT_VERSION] = CAPABILITY_CODE_SOFT_VERSION_LEN,
+		[CAPABILITY_CODE_PATHS_LIMIT] = CAPABILITY_CODE_PATHS_LIMIT_LEN,
 };
 
 /* value the capability must be a multiple of.
@@ -83,6 +85,7 @@ static const size_t cap_modsizes[] = {
 		[CAPABILITY_CODE_LLGR] = 1,
 		[CAPABILITY_CODE_ROLE] = 1,
 		[CAPABILITY_CODE_SOFT_VERSION] = 1,
+		[CAPABILITY_CODE_PATHS_LIMIT] = 5,
 };
 
 /* BGP-4 Multiprotocol Extentions lead us to the complex world. We can
@@ -739,6 +742,62 @@ static int bgp_capability_addpath(struct peer *peer,
 	return 0;
 }
 
+static int bgp_capability_paths_limit(struct peer *peer,
+				      struct capability_header *hdr)
+{
+	struct stream *s = BGP_INPUT(peer);
+	size_t end = stream_get_getp(s) + hdr->length;
+
+	if (hdr->length % CAPABILITY_CODE_PATHS_LIMIT_LEN) {
+		flog_warn(EC_BGP_CAPABILITY_INVALID_LENGTH,
+			  "Paths-Limit: Received invalid length %d, non-multiple of %d",
+			  hdr->length, CAPABILITY_CODE_PATHS_LIMIT_LEN);
+		return -1;
+	}
+
+	if (!CHECK_FLAG(peer->cap, PEER_CAP_ADDPATH_RCV)) {
+		flog_warn(EC_BGP_CAPABILITY_INVALID_DATA,
+			  "Paths-Limit: Received Paths-Limit capability without Add-Path capability");
+		return -1;
+	}
+
+	SET_FLAG(peer->cap, PEER_CAP_PATHS_LIMIT_RCV);
+
+	while (stream_get_getp(s) + CAPABILITY_CODE_PATHS_LIMIT_LEN <= end) {
+		afi_t afi;
+		safi_t safi;
+		iana_afi_t pkt_afi = stream_getw(s);
+		iana_safi_t pkt_safi = stream_getc(s);
+		uint16_t paths_limit = stream_getw(s);
+
+		if (bgp_debug_neighbor_events(peer))
+			zlog_debug("%s OPEN has %s capability for afi/safi: %s/%s limit: %u",
+				   peer->host,
+				   lookup_msg(capcode_str, hdr->code, NULL),
+				   iana_afi2str(pkt_afi),
+				   iana_safi2str(pkt_safi), paths_limit);
+
+		if (bgp_map_afi_safi_iana2int(pkt_afi, pkt_safi, &afi, &safi)) {
+			if (bgp_debug_neighbor_events(peer))
+				zlog_debug("%s Addr-family %s/%s(afi/safi) not supported. Ignore the Paths-Limit capability for this AFI/SAFI",
+					   peer->host, iana_afi2str(pkt_afi),
+					   iana_safi2str(pkt_safi));
+			continue;
+		} else if (!peer->afc[afi][safi]) {
+			if (bgp_debug_neighbor_events(peer))
+				zlog_debug("%s Addr-family %s/%s(afi/safi) not enabled. Ignore the Paths-Limit capability for this AFI/SAFI",
+					   peer->host, iana_afi2str(pkt_afi),
+					   iana_safi2str(pkt_safi));
+			continue;
+		}
+
+		SET_FLAG(peer->af_cap[afi][safi], PEER_CAP_PATHS_LIMIT_AF_RCV);
+		peer->addpath_paths_limit[afi][safi].receive = paths_limit;
+	}
+
+	return 0;
+}
+
 static int bgp_capability_enhe(struct peer *peer, struct capability_header *hdr)
 {
 	struct stream *s = BGP_INPUT(peer);
@@ -1012,6 +1071,7 @@ static int bgp_capability_parse(struct peer *peer, size_t length,
 		case CAPABILITY_CODE_EXT_MESSAGE:
 		case CAPABILITY_CODE_ROLE:
 		case CAPABILITY_CODE_SOFT_VERSION:
+		case CAPABILITY_CODE_PATHS_LIMIT:
 			/* Check length. */
 			if (caphdr.length < cap_minsizes[caphdr.code]) {
 				zlog_info(
@@ -1113,6 +1173,9 @@ static int bgp_capability_parse(struct peer *peer, size_t length,
 		case CAPABILITY_CODE_SOFT_VERSION:
 			ret = bgp_capability_software_version(peer, &caphdr);
 			break;
+		case CAPABILITY_CODE_PATHS_LIMIT:
+			ret = bgp_capability_paths_limit(peer, &caphdr);
+			break;
 		default:
 			if (caphdr.code > 128) {
 				/* We don't send Notification for unknown vendor
@@ -1874,6 +1937,31 @@ uint16_t bgp_open_capability(struct stream *s, struct peer *peer,
 		}
 	}
 
+	/* Paths-Limit capability */
+	SET_FLAG(peer->cap, PEER_CAP_PATHS_LIMIT_ADV);
+	stream_putc(s, BGP_OPEN_OPT_CAP);
+	ext_opt_params ? stream_putw(s, (CAPABILITY_CODE_PATHS_LIMIT_LEN *
+					 afi_safi_count) +
+						2)
+		       : stream_putc(s, (CAPABILITY_CODE_PATHS_LIMIT_LEN *
+					 afi_safi_count) +
+						2);
+	stream_putc(s, CAPABILITY_CODE_PATHS_LIMIT);
+	stream_putc(s, CAPABILITY_CODE_PATHS_LIMIT_LEN * afi_safi_count);
+
+	FOREACH_AFI_SAFI (afi, safi) {
+		if (!peer->afc[afi][safi])
+			continue;
+
+		bgp_map_afi_safi_int2iana(afi, safi, &pkt_afi, &pkt_safi);
+
+		stream_putw(s, pkt_afi);
+		stream_putc(s, pkt_safi);
+		stream_putw(s, peer->addpath_paths_limit[afi][safi].send);
+
+		SET_FLAG(peer->af_cap[afi][safi], PEER_CAP_PATHS_LIMIT_AF_ADV);
+	}
+
 	/* ORF capability. */
 	FOREACH_AFI_SAFI (afi, safi) {
 		if (CHECK_FLAG(peer->af_flags[afi][safi],

bgpd/bgp_open.h

@@ -53,6 +53,7 @@ struct graceful_restart_af {
 #define CAPABILITY_CODE_ENHE            5 /* Extended Next Hop Encoding */
 #define CAPABILITY_CODE_EXT_MESSAGE     6 /* Extended Message Support */
 #define CAPABILITY_CODE_ROLE            9 /* Role Capability */
+#define CAPABILITY_CODE_PATHS_LIMIT    76 /* Paths Limit Capability */
 
 /* Capability Length */
 #define CAPABILITY_CODE_MP_LEN          4
@@ -61,6 +62,7 @@ struct graceful_restart_af {
 #define CAPABILITY_CODE_RESTART_LEN     2 /* Receiving only case */
 #define CAPABILITY_CODE_AS4_LEN         4
 #define CAPABILITY_CODE_ADDPATH_LEN     4
+#define CAPABILITY_CODE_PATHS_LIMIT_LEN 5
 #define CAPABILITY_CODE_ENHE_LEN        6 /* NRLI AFI = 2, SAFI = 2, Nexthop AFI = 2 */
 #define CAPABILITY_CODE_MIN_FQDN_LEN    2
 #define CAPABILITY_CODE_ENHANCED_LEN    0

bgpd/bgp_packet.c

@@ -1461,6 +1461,49 @@ void bgp_capability_send(struct peer *peer, afi_t afi, safi_t safi,
 				   capability, iana_afi2str(pkt_afi),
 				   iana_safi2str(pkt_safi));
 
+		break;
+	case CAPABILITY_CODE_PATHS_LIMIT:
+		SET_FLAG(peer->cap, PEER_CAP_PATHS_LIMIT_ADV);
+
+		FOREACH_AFI_SAFI (afi, safi) {
+			if (!peer->afc[afi][safi])
+				continue;
+
+			addpath_afi_safi_count++;
+		}
+
+		stream_putc(s, action);
+		stream_putc(s, CAPABILITY_CODE_PATHS_LIMIT);
+		stream_putc(s, CAPABILITY_CODE_PATHS_LIMIT_LEN *
+				       addpath_afi_safi_count);
+
+		FOREACH_AFI_SAFI (afi, safi) {
+			if (!peer->afc[afi][safi])
+				continue;
+
+			bgp_map_afi_safi_int2iana(afi, safi, &pkt_afi,
+						  &pkt_safi);
+
+			stream_putw(s, pkt_afi);
+			stream_putc(s, pkt_safi);
+			stream_putw(s,
+				    peer->addpath_paths_limit[afi][safi].send);
+
+			SET_FLAG(peer->af_cap[afi][safi],
+				 PEER_CAP_PATHS_LIMIT_AF_ADV);
+
+			if (bgp_debug_neighbor_events(peer))
+				zlog_debug("%pBP sending CAPABILITY has %s %s for afi/safi: %s/%s, limit: %u",
+					   peer,
+					   action == CAPABILITY_ACTION_SET
+						   ? "Advertising"
+						   : "Removing",
+					   capability, iana_afi2str(pkt_afi),
+					   iana_safi2str(pkt_safi),
+					   peer->addpath_paths_limit[afi][safi]
+						   .send);
+		}
+
 		break;
 	case CAPABILITY_CODE_ORF:
 		/* Convert AFI, SAFI to values for packet. */
@@ -3170,6 +3213,85 @@ ignore:
 	}
 }
 
+static void bgp_dynamic_capability_paths_limit(uint8_t *pnt, int action,
+					       struct capability_header *hdr,
+					       struct peer *peer)
+{
+	uint8_t *data = pnt + 3;
+	uint8_t *end = data + hdr->length;
+	size_t len = end - data;
+	afi_t afi;
+	safi_t safi;
+
+	if (action == CAPABILITY_ACTION_SET) {
+		if (len % CAPABILITY_CODE_PATHS_LIMIT_LEN) {
+			flog_warn(EC_BGP_CAPABILITY_INVALID_LENGTH,
+				  "Paths-Limit: Received invalid length %zu, non-multiple of %d",
+				  len, CAPABILITY_CODE_PATHS_LIMIT_LEN);
+			return;
+		}
+
+		if (!CHECK_FLAG(peer->cap, PEER_CAP_ADDPATH_RCV)) {
+			flog_warn(EC_BGP_CAPABILITY_INVALID_DATA,
+				  "Paths-Limit: Received Paths-Limit capability without Add-Path capability");
+			goto ignore;
+		}
+
+		SET_FLAG(peer->cap, PEER_CAP_PATHS_LIMIT_RCV);
+
+		while (data + CAPABILITY_CODE_PATHS_LIMIT_LEN <= end) {
+			afi_t afi;
+			safi_t safi;
+			iana_afi_t pkt_afi;
+			iana_safi_t pkt_safi;
+			struct bgp_paths_limit_capability bpl = {};
+
+			memcpy(&bpl, data, sizeof(bpl));
+			pkt_afi = ntohs(bpl.afi);
+			pkt_safi = safi_int2iana(bpl.safi);
+
+			if (bgp_debug_neighbor_events(peer))
+				zlog_debug("%s OPEN has %s capability for afi/safi: %s/%s limit: %u",
+					   peer->host,
+					   lookup_msg(capcode_str, hdr->code,
+						      NULL),
+					   iana_afi2str(pkt_afi),
+					   iana_safi2str(pkt_safi),
+					   bpl.paths_limit);
+
+			if (bgp_map_afi_safi_iana2int(pkt_afi, pkt_safi, &afi,
+						      &safi)) {
+				if (bgp_debug_neighbor_events(peer))
+					zlog_debug("%s Addr-family %s/%s(afi/safi) not supported. Ignore the Paths-Limit capability for this AFI/SAFI",
+						   peer->host,
+						   iana_afi2str(pkt_afi),
+						   iana_safi2str(pkt_safi));
+				goto ignore;
+			} else if (!peer->afc[afi][safi]) {
+				if (bgp_debug_neighbor_events(peer))
+					zlog_debug("%s Addr-family %s/%s(afi/safi) not enabled. Ignore the Paths-Limit capability for this AFI/SAFI",
+						   peer->host,
+						   iana_afi2str(pkt_afi),
+						   iana_safi2str(pkt_safi));
+				goto ignore;
+			}
+
+			SET_FLAG(peer->af_cap[afi][safi],
+				 PEER_CAP_PATHS_LIMIT_AF_RCV);
+			peer->addpath_paths_limit[afi][safi].receive =
+				bpl.paths_limit;
+ignore:
+			data += CAPABILITY_CODE_PATHS_LIMIT_LEN;
+		}
+	} else {
+		FOREACH_AFI_SAFI (afi, safi)
+			UNSET_FLAG(peer->af_cap[afi][safi],
+				   PEER_CAP_PATHS_LIMIT_AF_RCV);
+
+		UNSET_FLAG(peer->cap, PEER_CAP_PATHS_LIMIT_RCV);
+	}
+}
+
 static void bgp_dynamic_capability_orf(uint8_t *pnt, int action,
 				       struct capability_header *hdr,
 				       struct peer *peer)
@@ -3723,6 +3845,10 @@ static int bgp_capability_msg_parse(struct peer *peer, uint8_t *pnt,
 		case CAPABILITY_CODE_ADDPATH:
 			bgp_dynamic_capability_addpath(pnt, action, hdr, peer);
 			break;
+		case CAPABILITY_CODE_PATHS_LIMIT:
+			bgp_dynamic_capability_paths_limit(pnt, action, hdr,
+							   peer);
+			break;
 		case CAPABILITY_CODE_ORF:
 			bgp_dynamic_capability_orf(pnt, action, hdr, peer);
 			break;

bgpd/bgp_updgrp.c

@@ -145,6 +145,8 @@ static void conf_copy(struct peer *dst, struct peer *src, afi_t afi,
 	dst->addpath_type[afi][safi] = src->addpath_type[afi][safi];
 	dst->addpath_best_selected[afi][safi] =
 		src->addpath_best_selected[afi][safi];
+	dst->addpath_paths_limit[afi][safi] =
+		src->addpath_paths_limit[afi][safi];
 	dst->local_as = src->local_as;
 	dst->change_local_as = src->change_local_as;
 	dst->shared_network = src->shared_network;
@@ -348,6 +350,8 @@ static unsigned int updgrp_hash_key_make(const void *p)
 	key = jhash_1word((flags & PEER_UPDGRP_AF_FLAGS), key);
 	key = jhash_1word((uint32_t)peer->addpath_type[afi][safi], key);
 	key = jhash_1word(peer->addpath_best_selected[afi][safi], key);
+	key = jhash_1word(peer->addpath_paths_limit[afi][safi].receive, key);
+	key = jhash_1word(peer->addpath_paths_limit[afi][safi].send, key);
 	key = jhash_1word((peer->cap & PEER_UPDGRP_CAP_FLAGS), key);
 	key = jhash_1word((peer->af_cap[afi][safi] & PEER_UPDGRP_AF_CAP_FLAGS),
 			  key);
@@ -461,6 +465,9 @@ static unsigned int updgrp_hash_key_make(const void *p)
 				      PEER_UPDGRP_AF_CAP_FLAGS),
 			   peer->v_routeadv, peer->change_local_as,
 			   peer->as_path_loop_detection);
+		zlog_debug("%pBP Update Group Hash: addpath paths-limit: (send %u, receive %u)",
+			   peer, peer->addpath_paths_limit[afi][safi].send,
+			   peer->addpath_paths_limit[afi][safi].receive);
 		zlog_debug(
 			"%pBP Update Group Hash: max packet size: %u pmax_out: %u Peer Group: %s rmap out: %s",
 			peer, peer->max_packet_size, peer->pmax_out[afi][safi],

bgpd/bgp_updgrp_adv.c

@@ -97,13 +97,19 @@ subgrp_announce_addpath_best_selected(struct bgp_dest *dest,
 	enum bgp_path_selection_reason reason;
 	char pfx_buf[PREFIX2STR_BUFFER] = {};
 	int paths_eq = 0;
-	int best_path_count = 0;
 	struct list *list = list_new();
 	struct bgp_path_info *pi = NULL;
+	uint16_t paths_count = 0;
+	uint16_t paths_limit = peer->addpath_paths_limit[afi][safi].receive;
 
 	if (peer->addpath_type[afi][safi] == BGP_ADDPATH_BEST_SELECTED) {
-		while (best_path_count++ <
+		paths_limit =
-		       peer->addpath_best_selected[afi][safi]) {
+			paths_limit
+				? MIN(paths_limit,
+				      peer->addpath_best_selected[afi][safi])
+				: peer->addpath_best_selected[afi][safi];
+
+		while (paths_count++ < paths_limit) {
 			struct bgp_path_info *exist = NULL;
 
 			for (pi = bgp_dest_get_bgp_path_info(dest); pi;
@@ -139,8 +145,26 @@ subgrp_announce_addpath_best_selected(struct bgp_dest *dest,
 				subgroup_process_announce_selected(
 					subgrp, NULL, dest, afi, safi, id);
 		} else {
-			subgroup_process_announce_selected(subgrp, pi, dest,
+			/* No Paths-Limit involved */
-							   afi, safi, id);
+			if (!paths_limit) {
+				subgroup_process_announce_selected(subgrp, pi,
+								   dest, afi,
+								   safi, id);
+				continue;
+			}
+
+			/* If we have Paths-Limit capability, we MUST
+			 * not send more than the number of paths expected
+			 * by the peer.
+			 */
+			if (paths_count++ < paths_limit)
+				subgroup_process_announce_selected(subgrp, pi,
+								   dest, afi,
+								   safi, id);
+			else
+				subgroup_process_announce_selected(subgrp, NULL,
+								   dest, afi,
+								   safi, id);
 		}
 	}
 

bgpd/bgp_vty.c

@@ -9198,6 +9198,63 @@ DEFPY(
 	return CMD_SUCCESS;
 }
 
+DEFPY (neighbor_addpath_paths_limit,
+       neighbor_addpath_paths_limit_cmd,
+       "neighbor <A.B.C.D|X:X::X:X|WORD>$neighbor addpath-rx-paths-limit (1-65535)$paths_limit",
+       NEIGHBOR_STR
+       NEIGHBOR_ADDR_STR2
+       "Paths Limit for Addpath to receive from the peer\n"
+       "Maximum number of paths\n")
+{
+	struct peer *peer;
+	afi_t afi = bgp_node_afi(vty);
+	safi_t safi = bgp_node_safi(vty);
+	int ret;
+
+	peer = peer_and_group_lookup_vty(vty, neighbor);
+	if (!peer)
+		return CMD_WARNING_CONFIG_FAILED;
+
+	ret = peer_af_flag_set_vty(vty, neighbor, afi, safi,
+				   PEER_FLAG_ADDPATH_RX_PATHS_LIMIT);
+
+	peer->addpath_paths_limit[afi][safi].send = paths_limit;
+
+	bgp_capability_send(peer, afi, safi, CAPABILITY_CODE_PATHS_LIMIT,
+			    CAPABILITY_ACTION_SET);
+
+	return ret;
+}
+
+DEFPY (no_neighbor_addpath_paths_limit,
+       no_neighbor_addpath_paths_limit_cmd,
+       "no neighbor <A.B.C.D|X:X::X:X|WORD>$neighbor addpath-rx-paths-limit [(1-65535)]",
+       NO_STR
+       NEIGHBOR_STR
+       NEIGHBOR_ADDR_STR2
+       "Paths Limit for Addpath to receive from the peer\n"
+       "Maximum number of paths\n")
+{
+	struct peer *peer;
+	afi_t afi = bgp_node_afi(vty);
+	safi_t safi = bgp_node_safi(vty);
+	int ret;
+
+	peer = peer_and_group_lookup_vty(vty, neighbor);
+	if (!peer)
+		return CMD_WARNING_CONFIG_FAILED;
+
+	ret = peer_af_flag_unset_vty(vty, neighbor, afi, safi,
+				     PEER_FLAG_ADDPATH_RX_PATHS_LIMIT);
+
+	peer->addpath_paths_limit[afi][safi].send = 0;
+
+	bgp_capability_send(peer, afi, safi, CAPABILITY_CODE_PATHS_LIMIT,
+			    CAPABILITY_ACTION_UNSET);
+
+	return ret;
+}
+
 DEFPY(
 	no_neighbor_aspath_loop_detection,
 	no_neighbor_aspath_loop_detection_cmd,
@@ -14146,6 +14203,86 @@ static void bgp_show_peer(struct vty *vty, struct peer *p, bool use_json,
 						       json_add);
 			}
 
+			/* Paths-Limit */
+			if (CHECK_FLAG(p->cap, PEER_CAP_PATHS_LIMIT_RCV) ||
+			    CHECK_FLAG(p->cap, PEER_CAP_PATHS_LIMIT_ADV)) {
+				json_object *json_add = NULL;
+				const char *print_store;
+
+				json_add = json_object_new_object();
+
+				FOREACH_AFI_SAFI (afi, safi) {
+					json_object *json_sub = NULL;
+
+					json_sub = json_object_new_object();
+					print_store = get_afi_safi_str(afi, safi,
+								       true);
+
+					if (CHECK_FLAG(p->af_cap[afi][safi],
+						       PEER_CAP_PATHS_LIMIT_AF_ADV) ||
+					    CHECK_FLAG(p->af_cap[afi][safi],
+						       PEER_CAP_PATHS_LIMIT_AF_RCV)) {
+						if (CHECK_FLAG(p->af_cap[afi][safi],
+							       PEER_CAP_PATHS_LIMIT_AF_ADV) &&
+						    CHECK_FLAG(p->af_cap[afi][safi],
+							       PEER_CAP_PATHS_LIMIT_AF_RCV)) {
+							json_object_boolean_true_add(
+								json_sub,
+								"advertisedAndReceived");
+							json_object_int_add(
+								json_sub,
+								"advertisedPathsLimit",
+								p->addpath_paths_limit
+									[afi][safi]
+										.send);
+							json_object_int_add(
+								json_sub,
+								"receivedPathsLimit",
+								p->addpath_paths_limit
+									[afi][safi]
+										.receive);
+						} else if (CHECK_FLAG(p->af_cap[afi]
+									       [safi],
+								      PEER_CAP_PATHS_LIMIT_AF_ADV)) {
+							json_object_boolean_true_add(
+								json_sub,
+								"advertised");
+							json_object_int_add(
+								json_sub,
+								"advertisedPathsLimit",
+								p->addpath_paths_limit
+									[afi][safi]
+										.send);
+						} else if (CHECK_FLAG(p->af_cap[afi]
+									       [safi],
+								      PEER_CAP_PATHS_LIMIT_AF_RCV)) {
+							json_object_boolean_true_add(
+								json_sub,
+								"received");
+							json_object_int_add(
+								json_sub,
+								"receivedPathsLimit",
+								p->addpath_paths_limit
+									[afi][safi]
+										.receive);
+						}
+					}
+
+					if (CHECK_FLAG(p->af_cap[afi][safi],
+						       PEER_CAP_PATHS_LIMIT_AF_ADV) ||
+					    CHECK_FLAG(p->af_cap[afi][safi],
+						       PEER_CAP_PATHS_LIMIT_AF_RCV))
+						json_object_object_add(json_add,
+								       print_store,
+								       json_sub);
+					else
+						json_object_free(json_sub);
+				}
+
+				json_object_object_add(json_cap, "pathsLimit",
+						       json_add);
+			}
+
 			/* Dynamic */
 			if (CHECK_FLAG(p->cap, PEER_CAP_DYNAMIC_RCV) ||
 			    CHECK_FLAG(p->cap, PEER_CAP_DYNAMIC_ADV)) {
@@ -14599,6 +14736,47 @@ static void bgp_show_peer(struct vty *vty, struct peer *p, bool use_json,
 				}
 			}
 
+			/* Paths-Limit */
+			if (CHECK_FLAG(p->cap, PEER_CAP_PATHS_LIMIT_RCV) ||
+			    CHECK_FLAG(p->cap, PEER_CAP_PATHS_LIMIT_ADV)) {
+				vty_out(vty, "    Paths-Limit:\n");
+
+				FOREACH_AFI_SAFI (afi, safi) {
+					if (CHECK_FLAG(p->af_cap[afi][safi],
+						       PEER_CAP_PATHS_LIMIT_AF_ADV) ||
+					    CHECK_FLAG(p->af_cap[afi][safi],
+						       PEER_CAP_PATHS_LIMIT_AF_RCV)) {
+						vty_out(vty, "      %s: ",
+							get_afi_safi_str(afi,
+									 safi,
+									 false));
+
+						if (CHECK_FLAG(p->af_cap[afi][safi],
+							       PEER_CAP_PATHS_LIMIT_AF_ADV))
+							vty_out(vty,
+								"advertised (%u)",
+								p->addpath_paths_limit
+									[afi][safi]
+										.send);
+
+						if (CHECK_FLAG(p->af_cap[afi][safi],
+							       PEER_CAP_PATHS_LIMIT_AF_RCV))
+							vty_out(vty,
+								"%sreceived (%u)",
+								CHECK_FLAG(p->af_cap[afi]
+										    [safi],
+									   PEER_CAP_PATHS_LIMIT_AF_ADV)
+									? " and "
+									: "",
+								p->addpath_paths_limit
+									[afi][safi]
+										.receive);
+
+						vty_out(vty, "\n");
+					}
+				}
+			}
+
 			/* Dynamic */
 			if (CHECK_FLAG(p->cap, PEER_CAP_DYNAMIC_RCV) ||
 			    CHECK_FLAG(p->cap, PEER_CAP_DYNAMIC_ADV)) {
@@ -18383,6 +18561,11 @@ static void bgp_config_write_peer_af(struct vty *vty, struct bgp *bgp,
 	if (CHECK_FLAG(peer->af_flags[afi][safi], PEER_FLAG_DISABLE_ADDPATH_RX))
 		vty_out(vty, "  neighbor %s disable-addpath-rx\n", addr);
 
+	if (CHECK_FLAG(peer->af_flags[afi][safi],
+		       PEER_FLAG_ADDPATH_RX_PATHS_LIMIT))
+		vty_out(vty, "  neighbor %s addpath-rx-paths-limit %u\n", addr,
+			peer->addpath_paths_limit[afi][safi].send);
+
 	/* ORF capability.  */
 	if (peergroup_af_flag_check(peer, afi, safi, PEER_FLAG_ORF_PREFIX_SM)
 	    || peergroup_af_flag_check(peer, afi, safi,
@@ -20544,6 +20727,26 @@ void bgp_vty_init(void)
 	install_element(BGP_VPNV6_NODE,
 			&no_neighbor_addpath_tx_bestpath_per_as_cmd);
 
+	/* "neighbor addpath-rx-paths-limit" commands.*/
+	install_element(BGP_NODE, &neighbor_addpath_paths_limit_cmd);
+	install_element(BGP_NODE, &no_neighbor_addpath_paths_limit_cmd);
+	install_element(BGP_IPV4_NODE, &neighbor_addpath_paths_limit_cmd);
+	install_element(BGP_IPV4_NODE, &no_neighbor_addpath_paths_limit_cmd);
+	install_element(BGP_IPV4M_NODE, &neighbor_addpath_paths_limit_cmd);
+	install_element(BGP_IPV4M_NODE, &no_neighbor_addpath_paths_limit_cmd);
+	install_element(BGP_IPV4L_NODE, &neighbor_addpath_paths_limit_cmd);
+	install_element(BGP_IPV4L_NODE, &no_neighbor_addpath_paths_limit_cmd);
+	install_element(BGP_IPV6_NODE, &neighbor_addpath_paths_limit_cmd);
+	install_element(BGP_IPV6_NODE, &no_neighbor_addpath_paths_limit_cmd);
+	install_element(BGP_IPV6M_NODE, &neighbor_addpath_paths_limit_cmd);
+	install_element(BGP_IPV6M_NODE, &no_neighbor_addpath_paths_limit_cmd);
+	install_element(BGP_IPV6L_NODE, &neighbor_addpath_paths_limit_cmd);
+	install_element(BGP_IPV6L_NODE, &no_neighbor_addpath_paths_limit_cmd);
+	install_element(BGP_VPNV4_NODE, &neighbor_addpath_paths_limit_cmd);
+	install_element(BGP_VPNV4_NODE, &no_neighbor_addpath_paths_limit_cmd);
+	install_element(BGP_VPNV6_NODE, &neighbor_addpath_paths_limit_cmd);
+	install_element(BGP_VPNV6_NODE, &no_neighbor_addpath_paths_limit_cmd);
+
 	/* "neighbor sender-as-path-loop-detection" commands. */
 	install_element(BGP_NODE, &neighbor_aspath_loop_detection_cmd);
 	install_element(BGP_NODE, &no_neighbor_aspath_loop_detection_cmd);

bgpd/bgpd.c

@@ -1527,6 +1527,8 @@ struct peer *peer_new(struct bgp *bgp)
 			 PEER_FLAG_SEND_LARGE_COMMUNITY);
 		peer->addpath_type[afi][safi] = BGP_ADDPATH_NONE;
 		peer->addpath_best_selected[afi][safi] = 0;
+		peer->addpath_paths_limit[afi][safi].receive = 0;
+		peer->addpath_paths_limit[afi][safi].send = 0;
 		peer->soo[afi][safi] = NULL;
 	}
 
@@ -1620,6 +1622,8 @@ void peer_xfer_config(struct peer *peer_dst, struct peer *peer_src)
 		peer_dst->weight[afi][safi] = peer_src->weight[afi][safi];
 		peer_dst->addpath_type[afi][safi] =
 			peer_src->addpath_type[afi][safi];
+		peer_dst->addpath_paths_limit[afi][safi] =
+			peer_src->addpath_paths_limit[afi][safi];
 	}
 
 	for (afidx = BGP_AF_START; afidx < BGP_AF_MAX; afidx++) {
@@ -4614,6 +4618,7 @@ static const struct peer_flag_action peer_af_flag_action_list[] = {
 	{PEER_FLAG_SOO, 0, peer_change_reset},
 	{PEER_FLAG_ACCEPT_OWN, 0, peer_change_reset},
 	{PEER_FLAG_SEND_EXT_COMMUNITY_RPKI, 1, peer_change_reset_out},
+	{PEER_FLAG_ADDPATH_RX_PATHS_LIMIT, 0, peer_change_none},
 	{0, 0, 0}};
 
 /* Proper action set. */

bgpd/bgpd.h

@@ -1140,6 +1140,11 @@ struct llgr_info {
 	uint8_t flags;
 };
 
+struct addpath_paths_limit {
+	uint16_t send;
+	uint16_t receive;
+};
+
 struct peer_connection {
 	struct peer *peer;
 
@@ -1333,6 +1338,8 @@ struct peer {
 #define PEER_CAP_ROLE_RCV		    (1ULL << 26) /* role received */
 #define PEER_CAP_SOFT_VERSION_ADV	    (1ULL << 27)
 #define PEER_CAP_SOFT_VERSION_RCV	    (1ULL << 28)
+#define PEER_CAP_PATHS_LIMIT_ADV (1U << 29)
+#define PEER_CAP_PATHS_LIMIT_RCV (1U << 30)
 
 	/* Capability flags (reset in bgp_stop) */
 	uint32_t af_cap[AFI_MAX][SAFI_MAX];
@@ -1351,6 +1358,8 @@ struct peer {
 #define PEER_CAP_ENHE_AF_NEGO               (1U << 14) /* Extended nexthop afi/safi negotiated */
 #define PEER_CAP_LLGR_AF_ADV                (1U << 15)
 #define PEER_CAP_LLGR_AF_RCV                (1U << 16)
+#define PEER_CAP_PATHS_LIMIT_AF_ADV         (1U << 17)
+#define PEER_CAP_PATHS_LIMIT_AF_RCV         (1U << 18)
 
 	/* Global configuration flags. */
 	/*
@@ -1528,6 +1537,7 @@ struct peer {
 #define PEER_FLAG_DISABLE_ADDPATH_RX (1ULL << 27)
 #define PEER_FLAG_SOO (1ULL << 28)
 #define PEER_FLAG_SEND_EXT_COMMUNITY_RPKI (1ULL << 29)
+#define PEER_FLAG_ADDPATH_RX_PATHS_LIMIT (1ULL << 30)
 #define PEER_FLAG_ACCEPT_OWN (1ULL << 63)
 
 	enum bgp_addpath_strat addpath_type[AFI_MAX][SAFI_MAX];
@@ -1845,6 +1855,9 @@ struct peer {
 	/* Add-Path Best selected paths number to advertise */
 	uint8_t addpath_best_selected[AFI_MAX][SAFI_MAX];
 
+	/* Add-Path Paths-Limit */
+	struct addpath_paths_limit addpath_paths_limit[AFI_MAX][SAFI_MAX];
+
 	QOBJ_FIELDS;
 };
 DECLARE_QOBJ_TYPE(peer);