Index: sys/netinet/ip_carp.c
===================================================================
--- sys/netinet/ip_carp.c
+++ sys/netinet/ip_carp.c
@@ -212,11 +212,13 @@
 static VNET_DEFINE(int, carp_ifdown_adj) = CARP_MAXSKEW;
 #define	V_carp_ifdown_adj	VNET(carp_ifdown_adj)
 
+static int carp_allow_sysctl(SYSCTL_HANDLER_ARGS);
 static int carp_demote_adj_sysctl(SYSCTL_HANDLER_ARGS);
 
 SYSCTL_NODE(_net_inet, IPPROTO_CARP,	carp,	CTLFLAG_RW, 0,	"CARP");
-SYSCTL_INT(_net_inet_carp, OID_AUTO, allow, CTLFLAG_VNET | CTLFLAG_RW,
-    &VNET_NAME(carp_allow), 0, "Accept incoming CARP packets");
+SYSCTL_PROC(_net_inet_carp, OID_AUTO, allow,
+    CTLFLAG_VNET | CTLTYPE_INT | CTLFLAG_RW, 0, 0, carp_allow_sysctl, "I",
+    "Accept incoming CARP packets");
 SYSCTL_INT(_net_inet_carp, OID_AUTO, preempt, CTLFLAG_VNET | CTLFLAG_RW,
     &VNET_NAME(carp_preempt), 0, "High-priority backup preemption mode");
 SYSCTL_INT(_net_inet_carp, OID_AUTO, log, CTLFLAG_VNET | CTLFLAG_RW,
@@ -315,12 +317,15 @@
 static void	carp_ifa_addroute(struct ifaddr *);
 static void	carp_delroute(struct carp_softc *);
 static void	carp_ifa_delroute(struct ifaddr *);
+static void	carp_reset(void *, int);
 static void	carp_send_ad_all(void *, int);
 static void	carp_demote_adj(int, char *);
 
 static LIST_HEAD(, carp_softc) carp_list;
 static struct mtx carp_mtx;
 static struct sx carp_sx;
+static struct task carp_reset_task =
+    TASK_INITIALIZER(0, carp_reset, NULL);
 static struct task carp_sendall_task =
     TASK_INITIALIZER(0, carp_send_ad_all, NULL);
 
@@ -801,6 +806,27 @@
  * be called directly, but scheduled via taskqueue.
  */
 static void
+carp_reset(void *ctx __unused, int pending __unused)
+{
+	struct carp_softc *sc;
+
+	mtx_lock(&carp_mtx);
+	LIST_FOREACH(sc, &carp_list, sc_next) {
+		CARP_LOCK(sc);
+		CURVNET_SET(sc->sc_carpdev->if_vnet);
+		if ((V_carp_allow == 0) != (sc->sc_state == INIT))
+			carp_sc_state(sc);
+		CURVNET_RESTORE();
+		CARP_UNLOCK(sc);
+	}
+	mtx_unlock(&carp_mtx);
+}
+
+/*
+ * To avoid LORs and possible recursions this function shouldn't
+ * be called directly, but scheduled via taskqueue.
+ */
+static void
 carp_send_ad_all(void *ctx __unused, int pending __unused)
 {
 	struct carp_softc *sc;
@@ -1293,7 +1319,8 @@
 
 	if ((sc->sc_carpdev->if_flags & IFF_UP) == 0 ||
 	    sc->sc_carpdev->if_link_state != LINK_STATE_UP ||
-	    (sc->sc_naddrs == 0 && sc->sc_naddrs6 == 0))
+	    (sc->sc_naddrs == 0 && sc->sc_naddrs6 == 0) ||
+	    !V_carp_allow)
 		return;
 
 	switch (sc->sc_state) {
@@ -2066,7 +2093,8 @@
 	CARP_LOCK_ASSERT(sc);
 
 	if (sc->sc_carpdev->if_link_state != LINK_STATE_UP ||
-	    !(sc->sc_carpdev->if_flags & IFF_UP)) {
+	    !(sc->sc_carpdev->if_flags & IFF_UP) ||
+	    !V_carp_allow) {
 		callout_stop(&sc->sc_ad_tmo);
 #ifdef INET
 		callout_stop(&sc->sc_md_tmo);
@@ -2097,6 +2125,24 @@
 }
 
 static int
+carp_allow_sysctl(SYSCTL_HANDLER_ARGS)
+{
+	int new, error;
+
+	new = V_carp_allow;
+	error = sysctl_handle_int(oidp, &new, 0, req);
+	if (error || !req->newptr)
+		return (error);
+
+	if(V_carp_allow != new) {
+		V_carp_allow = new;
+		taskqueue_enqueue(taskqueue_swi, &carp_reset_task);
+	}
+
+	return (0);
+}
+
+static int
 carp_demote_adj_sysctl(SYSCTL_HANDLER_ARGS)
 {
 	int new, error;
@@ -2170,6 +2216,7 @@
 	carp_demote_adj_p = NULL;
 	carp_master_p = NULL;
 	mtx_unlock(&carp_mtx);
+	taskqueue_drain(taskqueue_swi, &carp_reset_task);
 	taskqueue_drain(taskqueue_swi, &carp_sendall_task);
 	mtx_destroy(&carp_mtx);
 	sx_destroy(&carp_sx);