bfdd: implement passive mode

The passive mode is briefly described in the RFC 5880 Bidirectional
Forwarding Detection (BFD), Section 6.1. Overview:

> A system may take either an Active role or a Passive role in session
> initialization.  A system taking the Active role MUST send BFD
> Control packets for a particular session, regardless of whether it
> has received any BFD packets for that session.  A system taking the
> Passive role MUST NOT begin sending BFD packets for a particular
> session until it has received a BFD packet for that session, and thus
> has learned the remote system's discriminator value.  At least one
> system MUST take the Active role (possibly both).  The role that a
> system takes is specific to the application of BFD, and is outside
> the scope of this specification.

Signed-off-by: Rafael Zalamena <rzalamena@opensourcerouting.org>

bfdd/bfd.c

@@ -88,6 +88,7 @@ static void bfd_profile_set_default(struct bfd_profile *bp)
 	bp->admin_shutdown = true;
 	bp->detection_multiplier = BFD_DEFDETECTMULT;
 	bp->echo_mode = false;
+	bp->passive = false;
 	bp->min_echo_rx = BFD_DEF_REQ_MIN_ECHO;
 	bp->min_rx = BFD_DEFREQUIREDMINRX;
 	bp->min_tx = BFD_DEFDESIREDMINTX;
@@ -159,8 +160,10 @@ static void _bfd_profile_remove(struct bfd_session *bs, bool apply)
 			bfd_set_echo(bs, bs->peer_profile.echo_mode);
 	}
 
-	if (apply)
+	if (apply) {
+		bfd_set_passive_mode(bs, bs->peer_profile.passive);
 		bfd_set_shutdown(bs, bs->peer_profile.admin_shutdown);
+	}
 }
 
 void bfd_profile_apply(const char *profname, struct bfd_session *bs)
@@ -221,6 +224,12 @@ void bfd_profile_apply(const char *profname, struct bfd_session *bs)
 			bfd_set_echo(bs, bs->peer_profile.echo_mode);
 	}
 
+	/* Toggle 'passive-mode' if default value. */
+	if (bs->peer_profile.passive == false)
+		bfd_set_passive_mode(bs, bp->passive);
+	else
+		bfd_set_passive_mode(bs, bs->peer_profile.passive);
+
 	/* Toggle 'no shutdown' if default value. */
 	if (bs->peer_profile.admin_shutdown)
 		bfd_set_shutdown(bs, bp->admin_shutdown);
@@ -374,8 +383,12 @@ int bfd_session_enable(struct bfd_session *bs)
 	 * protocol.
 	 */
 	bs->sock = psock;
-	bfd_recvtimer_update(bs);
+
-	ptm_bfd_start_xmt_timer(bs, false);
+	/* Only start timers if we are using active mode. */
+	if (CHECK_FLAG(bs->flags, BFD_SESS_FLAG_PASSIVE) == 0) {
+		bfd_recvtimer_update(bs);
+		ptm_bfd_start_xmt_timer(bs, false);
+	}
 
 	return 0;
 }
@@ -536,6 +549,12 @@ void ptm_bfd_sess_dn(struct bfd_session *bfd, uint8_t diag)
 	if (CHECK_FLAG(bfd->flags, BFD_SESS_FLAG_ECHO_ACTIVE))
 		ptm_bfd_echo_stop(bfd);
 
+	/* Stop attempting to transmit or expect control packets if passive. */
+	if (CHECK_FLAG(bfd->flags, BFD_SESS_FLAG_PASSIVE)) {
+		bfd_recvtimer_delete(bfd);
+		bfd_xmttimer_delete(bfd);
+	}
+
 	if (old_state != bfd->ses_state) {
 		bfd->stats.session_down++;
 		if (bglobal.debug_peer_event)
@@ -766,6 +785,7 @@ static void _bfd_session_update(struct bfd_session *bs,
 	 * the session is disabled.
 	 */
 	bs->peer_profile.admin_shutdown = bpc->bpc_shutdown;
+	bfd_set_passive_mode(bs, bpc->bpc_passive);
 	bfd_set_shutdown(bs, bpc->bpc_shutdown);
 
 	/*
@@ -986,6 +1006,10 @@ static void bs_down_handler(struct bfd_session *bs, int nstate)
 		 * bring it up.
 		 */
 		bs->ses_state = PTM_BFD_INIT;
+
+		/* Answer peer with INIT immediately in passive mode. */
+		if (CHECK_FLAG(bs->flags, BFD_SESS_FLAG_PASSIVE))
+			ptm_bfd_snd(bs, 0);
 		break;
 
 	case PTM_BFD_INIT:
@@ -1312,9 +1336,39 @@ void bfd_set_shutdown(struct bfd_session *bs, bool shutdown)
 		bs->ses_state = PTM_BFD_DOWN;
 		control_notify(bs, bs->ses_state);
 
-		/* Enable all timers. */
+		/* Enable timers if non passive, otherwise stop them. */
-		bfd_recvtimer_update(bs);
+		if (CHECK_FLAG(bs->flags, BFD_SESS_FLAG_PASSIVE)) {
+			bfd_recvtimer_delete(bs);
+			bfd_xmttimer_delete(bs);
+		} else {
+			bfd_recvtimer_update(bs);
+			bfd_xmttimer_update(bs, bs->xmt_TO);
+		}
+	}
+}
+
+void bfd_set_passive_mode(struct bfd_session *bs, bool passive)
+{
+	if (passive) {
+		SET_FLAG(bs->flags, BFD_SESS_FLAG_PASSIVE);
+
+		/* Session is already up and running, nothing to do now. */
+		if (bs->ses_state != PTM_BFD_DOWN)
+			return;
+
+		/* Lets disable the timers since we are now passive. */
+		bfd_recvtimer_delete(bs);
+		bfd_xmttimer_delete(bs);
+	} else {
+		UNSET_FLAG(bs->flags, BFD_SESS_FLAG_PASSIVE);
+
+		/* Session is already up and running, nothing to do now. */
+		if (bs->ses_state != PTM_BFD_DOWN)
+			return;
+
+		/* Session is down, let it attempt to start the connection. */
 		bfd_xmttimer_update(bs, bs->xmt_TO);
+		bfd_recvtimer_update(bs);
 	}
 }
 

bfdd/bfd.h

@@ -170,6 +170,7 @@ enum bfd_session_flags {
 	BFD_SESS_FLAG_SHUTDOWN = 1 << 7,	/* disable BGP peer function */
 	BFD_SESS_FLAG_CONFIG = 1 << 8,	/* Session configured with bfd NB API */
 	BFD_SESS_FLAG_CBIT = 1 << 9,	/* CBIT is set */
+	BFD_SESS_FLAG_PASSIVE = 1 << 10, /* Passive mode */
 };
 
 /* BFD session hash keys */
@@ -207,6 +208,8 @@ struct bfd_profile {
 	uint32_t min_rx;
 	/** Administrative state. */
 	bool admin_shutdown;
+	/** Passive mode. */
+	bool passive;
 
 	/** Echo mode (only applies to single hop). */
 	bool echo_mode;
@@ -607,6 +610,14 @@ void bfd_set_echo(struct bfd_session *bs, bool echo);
  */
 void bfd_set_shutdown(struct bfd_session *bs, bool shutdown);
 
+/**
+ * Set the BFD session passive mode.
+ *
+ * \param bs the BFD session.
+ * \param passive the passive mode.
+ */
+void bfd_set_passive_mode(struct bfd_session *bs, bool passive);
+
 /* BFD hash data structures interface */
 void bfd_initialize(void);
 void bfd_shutdown(void);

bfdd/bfdctl.h

@@ -89,6 +89,7 @@ struct bfd_peer_cfg {
 	bool bpc_shutdown;
 
 	bool bpc_cbit;
+	bool bpc_passive;
 
 	bool bpc_has_profile;
 	char bpc_profile[64];

bfdd/bfdd_cli.c

@@ -265,6 +265,27 @@ void bfd_cli_show_shutdown(struct vty *vty, struct lyd_node *dnode,
 			yang_dnode_get_bool(dnode, NULL) ? "" : "no ");
 }
 
+DEFPY_YANG(
+	bfd_peer_passive, bfd_peer_passive_cmd,
+	"[no] passive-mode",
+	NO_STR
+	"Don't attempt to start sessions\n")
+{
+	nb_cli_enqueue_change(vty, "./passive-mode", NB_OP_MODIFY,
+			      no ? "false" : "true");
+	return nb_cli_apply_changes(vty, NULL);
+}
+
+void bfd_cli_show_passive(struct vty *vty, struct lyd_node *dnode,
+			  bool show_defaults)
+{
+	if (show_defaults)
+		vty_out(vty, "  no passive-mode\n");
+	else
+		vty_out(vty, "  %spassive-mode\n",
+			yang_dnode_get_bool(dnode, NULL) ? "" : "no ");
+}
+
 DEFPY_YANG(
 	bfd_peer_mult, bfd_peer_mult_cmd,
 	"detect-multiplier (2-255)$multiplier",
@@ -462,6 +483,11 @@ ALIAS_YANG(bfd_peer_shutdown, bfd_profile_shutdown_cmd,
       NO_STR
       "Disable BFD peer\n")
 
+ALIAS_YANG(bfd_peer_passive, bfd_profile_passive_cmd,
+      "[no] passive-mode",
+      NO_STR
+      "Don't attempt to start sessions\n")
+
 ALIAS_YANG(bfd_peer_echo, bfd_profile_echo_cmd,
       "[no] echo-mode",
       NO_STR
@@ -530,6 +556,7 @@ bfdd_cli_init(void)
 	install_element(BFD_PEER_NODE, &bfd_peer_echo_cmd);
 	install_element(BFD_PEER_NODE, &bfd_peer_echo_interval_cmd);
 	install_element(BFD_PEER_NODE, &bfd_peer_profile_cmd);
+	install_element(BFD_PEER_NODE, &bfd_peer_passive_cmd);
 
 	/* Profile commands. */
 	cmd_variable_handler_register(bfd_vars);
@@ -546,4 +573,5 @@ bfdd_cli_init(void)
 	install_element(BFD_PROFILE_NODE, &bfd_profile_shutdown_cmd);
 	install_element(BFD_PROFILE_NODE, &bfd_profile_echo_cmd);
 	install_element(BFD_PROFILE_NODE, &bfd_profile_echo_interval_cmd);
+	install_element(BFD_PROFILE_NODE, &bfd_profile_passive_cmd);
 }

bfdd/bfdd_nb.c

@@ -77,6 +77,13 @@ const struct frr_yang_module_info frr_bfdd_info = {
 				.cli_show = bfd_cli_show_shutdown,
                         }
                 },
+                {
+                        .xpath = "/frr-bfdd:bfdd/bfd/profile/passive-mode",
+                        .cbs = {
+                                .modify = bfdd_bfd_profile_passive_mode_modify,
+				.cli_show = bfd_cli_show_passive,
+                        }
+                },
                 {
                         .xpath = "/frr-bfdd:bfdd/bfd/profile/echo-mode",
                         .cbs = {
@@ -146,6 +153,13 @@ const struct frr_yang_module_info frr_bfdd_info = {
 				.cli_show = bfd_cli_show_shutdown,
 			}
 		},
+		{
+			.xpath = "/frr-bfdd:bfdd/bfd/sessions/single-hop/passive-mode",
+			.cbs = {
+				.modify = bfdd_bfd_sessions_single_hop_passive_mode_modify,
+				.cli_show = bfd_cli_show_passive,
+			}
+		},
 		{
 			.xpath = "/frr-bfdd:bfdd/bfd/sessions/single-hop/echo-mode",
 			.cbs = {
@@ -328,6 +342,13 @@ const struct frr_yang_module_info frr_bfdd_info = {
 				.cli_show = bfd_cli_show_shutdown,
 			}
 		},
+		{
+			.xpath = "/frr-bfdd:bfdd/bfd/sessions/multi-hop/passive-mode",
+			.cbs = {
+				.modify = bfdd_bfd_sessions_single_hop_passive_mode_modify,
+				.cli_show = bfd_cli_show_passive,
+			}
+		},
 		{
 			.xpath = "/frr-bfdd:bfdd/bfd/sessions/multi-hop/stats/local-discriminator",
 			.cbs = {

bfdd/bfdd_nb.h

@@ -37,6 +37,7 @@ int bfdd_bfd_profile_desired_transmission_interval_modify(
 int bfdd_bfd_profile_required_receive_interval_modify(
 	struct nb_cb_modify_args *args);
 int bfdd_bfd_profile_administrative_down_modify(struct nb_cb_modify_args *args);
+int bfdd_bfd_profile_passive_mode_modify(struct nb_cb_modify_args *args);
 int bfdd_bfd_profile_echo_mode_modify(struct nb_cb_modify_args *args);
 int bfdd_bfd_profile_desired_echo_transmission_interval_modify(
 	struct nb_cb_modify_args *args);
@@ -62,6 +63,8 @@ int bfdd_bfd_sessions_single_hop_required_receive_interval_modify(
 	struct nb_cb_modify_args *args);
 int bfdd_bfd_sessions_single_hop_administrative_down_modify(
 	struct nb_cb_modify_args *args);
+int bfdd_bfd_sessions_single_hop_passive_mode_modify(
+	struct nb_cb_modify_args *args);
 int bfdd_bfd_sessions_single_hop_echo_mode_modify(
 	struct nb_cb_modify_args *args);
 int bfdd_bfd_sessions_single_hop_desired_echo_transmission_interval_modify(
@@ -206,5 +209,7 @@ void bfd_cli_show_profile(struct vty *vty, struct lyd_node *dnode,
 			  bool show_defaults);
 void bfd_cli_peer_profile_show(struct vty *vty, struct lyd_node *dnode,
 			       bool show_defaults);
+void bfd_cli_show_passive(struct vty *vty, struct lyd_node *dnode,
+			  bool show_defaults);
 
 #endif /* _FRR_BFDD_NB_H_ */

bfdd/bfdd_nb_config.c

@@ -359,6 +359,28 @@ int bfdd_bfd_profile_administrative_down_modify(struct nb_cb_modify_args *args)
 	return NB_OK;
 }
 
+/*
+ * XPath: /frr-bfdd:bfdd/bfd/profile/passive-mode
+ */
+int bfdd_bfd_profile_passive_mode_modify(struct nb_cb_modify_args *args)
+{
+	struct bfd_profile *bp;
+	bool passive;
+
+	if (args->event != NB_EV_APPLY)
+		return NB_OK;
+
+	passive = yang_dnode_get_bool(args->dnode, NULL);
+	bp = nb_running_get_entry(args->dnode, NULL, true);
+	if (bp->passive == passive)
+		return NB_OK;
+
+	bp->passive = passive;
+	bfd_profile_update(bp);
+
+	return NB_OK;
+}
+
 /*
  * XPath: /frr-bfdd:bfdd/bfd/profile/echo-mode
  */
@@ -611,6 +633,36 @@ int bfdd_bfd_sessions_single_hop_administrative_down_modify(
 	return NB_OK;
 }
 
+/*
+ * XPath: /frr-bfdd:bfdd/bfd/sessions/single-hop/passive-mode
+ */
+int bfdd_bfd_sessions_single_hop_passive_mode_modify(
+	struct nb_cb_modify_args *args)
+{
+	struct bfd_session *bs;
+	bool passive;
+
+	switch (args->event) {
+	case NB_EV_VALIDATE:
+	case NB_EV_PREPARE:
+		return NB_OK;
+
+	case NB_EV_APPLY:
+		break;
+
+	case NB_EV_ABORT:
+		return NB_OK;
+	}
+
+	passive = yang_dnode_get_bool(args->dnode, NULL);
+
+	bs = nb_running_get_entry(args->dnode, NULL, true);
+	bs->peer_profile.passive = passive;
+	bfd_set_passive_mode(bs, passive);
+
+	return NB_OK;
+}
+
 /*
  * XPath: /frr-bfdd:bfdd/bfd/sessions/single-hop/echo-mode
  */

bfdd/bfdd_vty.c

@@ -111,6 +111,10 @@ static void _display_peer(struct vty *vty, struct bfd_session *bs)
 
 	vty_out(vty, "\t\tID: %u\n", bs->discrs.my_discr);
 	vty_out(vty, "\t\tRemote ID: %u\n", bs->discrs.remote_discr);
+	if (CHECK_FLAG(bs->flags, BFD_SESS_FLAG_PASSIVE))
+		vty_out(vty, "\t\tPassive mode\n");
+	else
+		vty_out(vty, "\t\tActive mode\n");
 
 	vty_out(vty, "\t\tStatus: ");
 	switch (bs->ses_state) {
@@ -203,6 +207,8 @@ static struct json_object *__display_peer_json(struct bfd_session *bs)
 
 	json_object_int_add(jo, "id", bs->discrs.my_discr);
 	json_object_int_add(jo, "remote-id", bs->discrs.remote_discr);
+	json_object_boolean_add(jo, "passive-mode",
+				CHECK_FLAG(bs->flags, BFD_SESS_FLAG_PASSIVE));
 
 	switch (bs->ses_state) {
 	case PTM_BFD_ADM_DOWN: