FRRouting · sougatahitcs · Nov 29, 2025
diff --git a/bfdd/bfd.c b/bfdd/bfd.c
@@ -444,7 +444,7 @@ void bfd_session_disable(struct bfd_session *bs)
 	bs->ifp = NULL;
 
 	/* Set session down so it doesn't report UP and disabled. */
-	ptm_bfd_sess_dn(bs, BD_PATH_DOWN);
+	ptm_bfd_sess_dn(bs, BD_PATH_DOWN, false);
 }
 
 static uint32_t ptm_bfd_gen_ID(void)
@@ -601,7 +601,17 @@ void ptm_bfd_sess_up(struct bfd_session *bfd)
 	}
 }
 
-void ptm_bfd_sess_dn(struct bfd_session *bfd, uint8_t diag)
+/*
+ * Transition BFD session to DOWN state.
+ *
+ * @param bfd BFD session
+ * @param diag Diagnostic code explaining reason for transition
+ * @param notify_admin_down If true, notify clients with ADMIN_DOWN status
+ *                          instead of DOWN. This is used when remote peer
+ *                          sends Admin Down - local state goes to DOWN but
+ *                          clients should not tear down protocol sessions.
+ */
+void ptm_bfd_sess_dn(struct bfd_session *bfd, uint8_t diag, bool notify_admin_down)
 {
 	int old_state = bfd->ses_state;
 
@@ -625,8 +635,17 @@ void ptm_bfd_sess_dn(struct bfd_session *bfd, uint8_t diag)
 	bs_set_slow_timers(bfd);
 
 	/* only signal clients when going from up->down state */
-	if (old_state == PTM_BFD_UP)
-		ptm_bfd_notify(bfd, PTM_BFD_DOWN);
+	if (old_state == PTM_BFD_UP) {
+		/*
+		 * If remote peer sent Admin Down, notify clients with
+		 * ADMIN_DOWN status so they don't tear down protocol sessions.
+		 * Otherwise, notify with DOWN status as usual.
+		 */
+		if (notify_admin_down)
+			ptm_bfd_notify(bfd, PTM_BFD_ADM_DOWN);
+		else
+			ptm_bfd_notify(bfd, PTM_BFD_DOWN);
+	}
 
 	/* Stop echo packet transmission if they are active */
 	if (CHECK_FLAG(bfd->flags, BFD_SESS_FLAG_ECHO_ACTIVE))
@@ -834,7 +853,7 @@ void bfd_recvtimer_cb(struct event *t)
 	switch (bs->ses_state) {
 	case PTM_BFD_INIT:
 	case PTM_BFD_UP:
-		ptm_bfd_sess_dn(bs, BD_CONTROL_EXPIRED);
+		ptm_bfd_sess_dn(bs, BD_CONTROL_EXPIRED, false);
 		break;
 	}
 }
@@ -852,7 +871,7 @@ void bfd_echo_recvtimer_cb(struct event *t)
 	switch (bs->ses_state) {
 	case PTM_BFD_INIT:
 	case PTM_BFD_UP:
-		ptm_bfd_sess_dn(bs, BD_ECHO_FAILED);
+		ptm_bfd_sess_dn(bs, BD_ECHO_FAILED, false);
 		break;
 	}
 }
@@ -1253,10 +1272,11 @@ static void bs_init_handler(struct bfd_session *bs, int nstate)
 	switch (nstate) {
 	case PTM_BFD_ADM_DOWN:
 		/*
-		 * Remote peer doesn't want to talk, so lets make the
-		 * connection down.
+		 * Remote peer sent Admin Down.
+		 * Go to DOWN state but notify clients with ADMIN_DOWN
+		 * so they don't tear down their protocol sessions.
 		 */
-		ptm_bfd_sess_dn(bs, BD_NEIGHBOR_DOWN);
+		ptm_bfd_sess_dn(bs, BD_NEIGHBOR_DOWN, true);
 		break;
 
 	case PTM_BFD_DOWN:
@@ -1281,9 +1301,16 @@ static void bs_up_handler(struct bfd_session *bs, int nstate)
 {
 	switch (nstate) {
 	case PTM_BFD_ADM_DOWN:
+		/*
+		 * Remote peer sent Admin Down.
+		 * Go to DOWN state but notify clients with ADMIN_DOWN
+		 * so they don't tear down their protocol sessions.
+		 */
+		ptm_bfd_sess_dn(bs, BD_NEIGHBOR_DOWN, true);
+		break;
 	case PTM_BFD_DOWN:
-		/* Peer lost or asked to shutdown connection. */
-		ptm_bfd_sess_dn(bs, BD_NEIGHBOR_DOWN);
+		/* Peer lost connection - bring session down normally. */
+		ptm_bfd_sess_dn(bs, BD_NEIGHBOR_DOWN, false);
 		break;
 
 	case PTM_BFD_INIT:

diff --git a/bfdd/bfd.h b/bfdd/bfd.h
@@ -605,7 +605,7 @@ int bfd_session_enable(struct bfd_session *bs);
 void bfd_session_disable(struct bfd_session *bs);
 struct bfd_session *ptm_bfd_sess_new(struct bfd_peer_cfg *bpc);
 int ptm_bfd_sess_del(struct bfd_peer_cfg *bpc);
-void ptm_bfd_sess_dn(struct bfd_session *bfd, uint8_t diag);
+void ptm_bfd_sess_dn(struct bfd_session *bfd, uint8_t diag, bool notify_admin_down);
 void ptm_bfd_sess_up(struct bfd_session *bfd);
 void ptm_bfd_echo_stop(struct bfd_session *bfd);
 void ptm_bfd_echo_start(struct bfd_session *bfd);

diff --git a/bgpd/bgp_bfd.c b/bgpd/bgp_bfd.c
@@ -67,6 +67,20 @@ static void bfd_session_status_update(struct bfd_session_params *bsp,
 			   bfd_get_status_str(bss->previous_state),
 			   bfd_get_status_str(bss->state));
 
+	/*
+	 * Handle Admin Down from peer separately.
+	 * When BFD receives Admin Down from peer, we should NOT tear down
+	 * the BGP session. The peer is administratively shutting down BFD,
+	 * but the BGP session should remain up.
+	 */
+	if (bss->state == BSS_ADMIN_DOWN && bss->previous_state == BSS_UP) {
+		if (BGP_DEBUG(bfd, BFD_LIB))
+			zlog_debug("%s: BFD received Admin Down from peer %s - BGP session maintained",
+				   __func__, peer->host);
+		/* Don't tear down BGP session, just log the event */
+		return;
+	}
+
 	if (bss->state == BSS_DOWN && bss->previous_state == BSS_UP) {
 		if (CHECK_FLAG(peer->sflags, PEER_STATUS_NSF_MODE)
 		    && bfd_sess_cbit(bsp) && !bss->remote_cbit) {

diff --git a/ospf6d/ospf6_bfd.c b/ospf6d/ospf6_bfd.c
@@ -101,6 +101,19 @@ static void ospf6_bfd_callback(struct bfd_session_params *bsp,
 {
 	struct ospf6_neighbor *on = arg;
 
+	/*
+	 * Handle Admin Down from peer separately.
+	 * When BFD receives Admin Down from peer, we should NOT tear down
+	 * the OSPFv6 neighbor. The peer is administratively shutting down BFD,
+	 * but the OSPFv6 adjacency should remain up.
+	 */
+	if (bss->state == BSS_ADMIN_DOWN && bss->previous_state == BSS_UP) {
+		/* Don't tear down OSPFv6 neighbor, just log the event */
+		zlog_info("OSPFv6 BFD: Neighbor %pI6: Received Admin Down from peer - adjacency maintained",
+			  &on->linklocal_addr);
+		return;
+	}
+
 	if (bss->state == BFD_STATUS_DOWN
 	    && bss->previous_state == BFD_STATUS_UP) {
 		event_cancel(&on->inactivity_timer);

diff --git a/ospfd/ospf_bfd.c b/ospfd/ospf_bfd.c
@@ -50,6 +50,20 @@ static void ospf_bfd_session_change(struct bfd_session_params *bsp,
 {
 	struct ospf_neighbor *nbr = arg;
 
+	/*
+	 * Handle Admin Down from peer separately.
+	 * When BFD receives Admin Down from peer, we should NOT tear down
+	 * the OSPF neighbor. The peer is administratively shutting down BFD,
+	 * but the OSPF adjacency should remain up.
+	 */
+	if (bss->state == BSS_ADMIN_DOWN && bss->previous_state == BSS_UP) {
+		if (IS_DEBUG_OSPF(bfd, BFD_LIB))
+			zlog_debug("%s: NSM[%s:%pI4]: BFD received Admin Down from peer - OSPF adjacency maintained",
+				   __func__, IF_NAME(nbr->oi), &nbr->address.u.prefix4);
+		/* Don't tear down OSPF neighbor, just log the event */
+		return;
+	}
+
 	/* BFD peer went down. */
 	if (bss->state == BFD_STATUS_DOWN
 	    && bss->previous_state == BFD_STATUS_UP) {

diff --git a/pimd/pim_bfd.c b/pimd/pim_bfd.c
@@ -59,6 +59,20 @@ static void pim_neighbor_bfd_cb(struct bfd_session_params *bsp,
 			   bfd_get_status_str(bss->previous_state));
 	}
 
+	/*
+	 * Handle Admin Down from peer separately.
+	 * When BFD receives Admin Down from peer, we should NOT tear down
+	 * the PIM neighbor. The peer is administratively shutting down BFD,
+	 * but the PIM adjacency should remain up.
+	 */
+	if (bss->state == BSS_ADMIN_DOWN && bss->previous_state == BSS_UP) {
+		if (PIM_DEBUG_PIM_TRACE)
+			zlog_debug("%s: BFD received Admin Down from peer - PIM neighbor maintained",
+				   __func__);
+		/* Don't delete PIM neighbor, just log the event */
+		return;
+	}
+
 	if (bss->state == BFD_STATUS_DOWN
 	    && bss->previous_state == BFD_STATUS_UP)
 		pim_neighbor_delete(nbr->interface, nbr, "BFD Session Expired");

diff --git a/tests/topotests/bfd_admin_down_no_impact/README.md b/tests/topotests/bfd_admin_down_no_impact/README.md
@@ -0,0 +1,75 @@
+# BFD Admin Down No Impact Test
+
+## Purpose
+
+This test verifies that when BFD receives an Admin Down message from a peer,
+it does NOT tear down protocol sessions (BGP, OSPF, PIM). This is the expected
+behavior because Admin Down indicates an administrative action (e.g., manual
+shutdown of BFD), not an actual connectivity failure.
+
+## Test Scenario
+
+1. Two routers (r1 and r2) are connected via a single link
+2. BGP (eBGP), OSPF, and PIM are configured on both routers
+3. BFD is enabled for BGP and OSPF neighbors
+4. All protocols converge and BFD sessions come UP
+5. r1 administratively shuts down its BFD peer (sending Admin Down to r2)
+6. r2 receives the Admin Down notification
+7. **Expected behavior**: r2's BFD state goes to DOWN, but BGP/OSPF/PIM sessions remain UP
+8. r1 re-enables BFD and the session comes back up
+
+## Topology
+
+```
+    r1 ----------- r2
+      .1   s1    .2
+   10.0.1.0/24
+
+r1: AS 65001, Router-ID 1.1.1.1, Loopback 1.1.1.1/32
+r2: AS 65002, Router-ID 2.2.2.2, Loopback 2.2.2.2/32
+```
+
+## Test Coverage
+
+### Direct Peer Shutdown Test
+- **BGP with BFD**: Verifies BGP session remains Established after BFD Admin Down
+- **OSPF with BFD**: Verifies OSPF neighbor remains in Full state after BFD Admin Down
+- **PIM with BFD**: Verifies PIM neighbor remains UP after BFD Admin Down
+- **BFD state transition**: Verifies BFD correctly moves to DOWN state on Admin Down
+- **BFD re-enable**: Verifies BFD can be re-enabled and session comes back UP
+
+### Profile-Based Shutdown Test
+- **BFD Profile Configuration**: Creates and applies BFD profiles to peers
+- **Profile Shutdown**: Shuts down BFD profile (affects all peers using that profile)
+- **Protocol Stability**: Verifies BGP/OSPF/PIM remain UP when profile is shut down
+- **Profile Re-enable**: Verifies BFD recovers when profile is re-enabled
+
+## Implementation Details
+
+The test validates the changes made to handle BFD Admin Down:
+
+1. **bfdd/bfd.c**: Added `notify_admin_down` parameter to `ptm_bfd_sess_dn()`
+2. **bfdd/bfd.c**: When receiving Admin Down from peer, BFD notifies clients with `PTM_BFD_ADM_DOWN` status instead of `PTM_BFD_DOWN`
+3. **bgpd/bgp_bfd.c**: BGP client checks for `BSS_ADMIN_DOWN` and doesn't tear down session
+4. **ospfd/ospf_bfd.c**: OSPF client checks for `BSS_ADMIN_DOWN` and doesn't tear down adjacency
+5. **ospf6d/ospf6_bfd.c**: OSPFv6 client checks for `BSS_ADMIN_DOWN` and doesn't tear down adjacency
+6. **pimd/pim_bfd.c**: PIM client checks for `BSS_ADMIN_DOWN` and doesn't delete neighbor
+
+## Running the Test
+
+```bash
+cd tests/topotests/bfd_admin_down_no_impact
+sudo -E pytest test_bfd_admin_down_no_impact.py -s -vv
+```
+
+## Expected Output
+
+All tests should pass:
+- `test_wait_protocols_convergence`: Verifies initial convergence
+- `test_bfd_peers_up`: Verifies BFD sessions come UP
+- `test_bfd_admin_down_no_protocol_impact`: **Main test** - verifies protocols remain UP after direct peer shutdown
+- `test_bfd_reenable`: Verifies BFD can be re-enabled after peer shutdown
+- `test_bfd_profile_shutdown_no_protocol_impact`: **Profile test** - verifies protocols remain UP after profile shutdown
+- `test_memory_leak`: Checks for memory leaks
+
+