diff --git a/lib/isc/Makefile.in b/lib/isc/Makefile.in
index b10c99b7b1..4ca051c8f6 100644
--- a/lib/isc/Makefile.in
+++ b/lib/isc/Makefile.in
@@ -47,7 +47,8 @@ OBJS =		@ISC_EXTRA_OBJS@ \
 		assertions.@O@ base64.@O@ bitstring.@O@ buffer.@O@ \
 		bufferlist.@O@ commandline.@O@ error.@O@ event.@O@ heap.@O@ \
 		lex.@O@ lib.@O@ log.@O@ \
-		mem.@O@ mutexblock.@O@ random.@O@ result.@O@ rwlock.@O@ \
+		mem.@O@ mutexblock.@O@ random.@O@ \
+		ratelimiter.@O@ result.@O@ rwlock.@O@ \
 		serial.@O@ sockaddr.@O@ str.@O@ symtab.@O@ \
 		task.@O@ taskpool.@O@ timer.@O@ version.@O@ \
 		${UNIXOBJS} ${NLSOBJS} ${PTHREADOBJS}
@@ -57,7 +58,8 @@ SRCS =		@ISC_EXTRA_SRCS@ \
 		assertions.c base64.c bitstring.c buffer.c \
 		bufferlist.c commandline.c error.c event.c heap.c \
 		lex.c lib.c log.c \
-		mem.c mutexblock.c random.c result.c rwlock.c \
+		mem.c mutexblock.c random.c \
+		ratelimiter.c result.c rwlock.c \
 		serial.c sockaddr.c str.c symtab.c \
 		task.c taskpool.c timer.c version.c
 
diff --git a/lib/isc/include/isc/ratelimiter.h b/lib/isc/include/isc/ratelimiter.h
new file mode 100644
index 0000000000..e31de77f91
--- /dev/null
+++ b/lib/isc/include/isc/ratelimiter.h
@@ -0,0 +1,87 @@
+/*
+ * Copyright (C) 1999  Internet Software Consortium.
+ * 
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
+ * ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
+ * CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
+ * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
+ * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
+ * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
+ * SOFTWARE.
+ */
+
+#ifndef ISC_RATELIMITER_H
+#define ISC_RATELIMITER_H 1
+
+/*****
+ ***** Module Info
+ *****/
+
+/*
+ * A rate limiter is a mechanism for dispatching events at a limited
+ * rate.  This is intended to be used when sending zone maintenance 
+ * SOA queries, NOTIFY messages, etc.
+ */
+
+/***
+ *** Imports.
+ ***/
+
+#include <isc/task.h>
+#include <isc/timer.h>
+
+ISC_LANG_BEGINDECLS
+
+/*****
+ ***** Types.
+ *****/
+
+typedef struct isc_ratelimiter isc_ratelimiter_t;
+
+typedef enum {
+	isc_ratelimiter_ratelimited,
+	isc_ratelimiter_worklimited
+} isc_ratelimiter_state_t;
+
+/*****
+ ***** Functions.
+ *****/
+
+isc_result_t
+isc_ratelimiter_create(isc_mem_t *mctx, isc_timermgr_t *timermgr,
+		       isc_task_t *task, isc_ratelimiter_t **ratelimiterp);
+/*
+ * Create a rate limiter.  It will execute events in the context
+ * of 'task' with a guaranteed minimum interval, initially zero.
+ */
+
+isc_result_t
+isc_ratelimiter_setinterval(isc_ratelimiter_t *rl, isc_interval_t *interval);
+/*
+ * Set the mininum interval between event executions.
+ * The interval value is copied, so the caller need not preserve it.
+ */
+
+isc_result_t
+isc_ratelimiter_enqueue(isc_ratelimiter_t *rl, isc_event_t **eventp);
+/*
+ * Queue an event for rate-limited execution.  This is similar
+ * to doing an isc_task_send() to the rate limiter's task, except
+ * that the execution may be delayed to achieve the desired rate
+ * of execution.
+ */
+
+void
+isc_ratelimiter_destroy(isc_ratelimiter_t **ratelimiterp);
+/*
+ * Destroy a rate limiter.  All events that have not yet been
+ * dispatched to the task are freed immedately.
+ * Does not destroy the task or events already queued on it.
+ */
+
+#endif /* ISC_RATELIMITER_H */
diff --git a/lib/isc/ratelimiter.c b/lib/isc/ratelimiter.c
new file mode 100644
index 0000000000..5890f74e3d
--- /dev/null
+++ b/lib/isc/ratelimiter.c
@@ -0,0 +1,168 @@
+/*
+ * Copyright (C) 1999  Internet Software Consortium.
+ * 
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
+ * ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
+ * CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
+ * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
+ * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
+ * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
+ * SOFTWARE.
+ */
+
+#include <config.h>
+
+#include <isc/assertions.h>
+#include <isc/boolean.h>
+#include <isc/error.h>
+#include <isc/ratelimiter.h>
+
+#include "util.h"
+
+struct isc_ratelimiter {
+	isc_mem_t *		mctx;
+	isc_mutex_t		lock;
+	isc_task_t *		task;
+	isc_timer_t *		timer;
+	isc_interval_t		interval;
+	isc_ratelimiter_state_t	state;
+	ISC_LIST(isc_event_t)	pending;
+};
+
+static void ratelimiter_tick(isc_task_t *task, isc_event_t *event);
+
+isc_result_t
+isc_ratelimiter_create(isc_mem_t *mctx, isc_timermgr_t *timermgr,
+		       isc_task_t *task, isc_ratelimiter_t **ratelimiterp)
+{
+	isc_result_t result;
+	isc_ratelimiter_t *rl;
+	INSIST(ratelimiterp != NULL && *ratelimiterp == NULL);
+	
+	rl = isc_mem_get(mctx, sizeof(*rl));
+	if (rl == NULL)
+		return ISC_R_NOMEMORY;
+	rl->mctx = mctx;
+	rl->task = task;
+	isc_interval_set(&rl->interval, 0, 0);
+	rl->timer = NULL;
+	rl->state = isc_ratelimiter_worklimited;
+	ISC_LIST_INIT(rl->pending);
+
+	result = isc_mutex_init(&rl->lock);
+	if (result != ISC_R_SUCCESS)
+		goto free_mem;
+	result = isc_timer_create(timermgr, isc_timertype_inactive,
+				  NULL, NULL, rl->task, ratelimiter_tick,
+				  rl, &rl->timer);
+	if (result != ISC_R_SUCCESS)
+		goto free_mutex;
+
+	*ratelimiterp = rl;
+	return (ISC_R_SUCCESS);
+
+free_mutex:
+	isc_mutex_destroy(&rl->lock);
+free_mem:
+	isc_mem_put(mctx, rl, sizeof(*rl));
+	return (result);
+}
+
+isc_result_t
+isc_ratelimiter_setinterval(isc_ratelimiter_t *rl, isc_interval_t *interval)
+{
+	isc_result_t result = ISC_R_SUCCESS;
+	LOCK(&rl->lock);
+	rl->interval = *interval;
+	/*
+	 * If the timer is currently running, change its rate.
+	 */
+        if (rl->state == isc_ratelimiter_ratelimited) {
+		result = isc_timer_reset(rl->timer, isc_timertype_ticker, NULL,
+					 &rl->interval, ISC_FALSE);
+	}
+	UNLOCK(&rl->lock);
+	return (result);
+}
+			    
+			
+isc_result_t
+isc_ratelimiter_enqueue(isc_ratelimiter_t *rl, isc_event_t **eventp)
+{
+	isc_result_t result = ISC_R_SUCCESS;
+	INSIST(eventp != NULL && *eventp != NULL);
+	LOCK(&rl->lock);
+        if (rl->state == isc_ratelimiter_ratelimited) {
+		isc_event_t *ev = *eventp;
+                ISC_LIST_APPEND(rl->pending, ev, link);
+		*eventp = NULL;
+        } else {
+		result = isc_timer_reset(rl->timer, isc_timertype_ticker, NULL,
+					 &rl->interval, ISC_FALSE);
+		if (result == ISC_R_SUCCESS)
+			rl->state = isc_ratelimiter_ratelimited;
+	}
+	UNLOCK(&rl->lock);
+	if (*eventp != NULL)
+		isc_task_send(rl->task, eventp);
+	ENSURE(*eventp == NULL);
+	return (result);
+}
+
+static void
+ratelimiter_tick(isc_task_t *task, isc_event_t *event)
+{
+	isc_result_t result = ISC_R_SUCCESS;
+	isc_ratelimiter_t *rl = (isc_ratelimiter_t *) event->arg;
+	isc_event_t *p;
+	(void) task; /* Unused */
+	LOCK(&rl->lock);
+        p = ISC_LIST_HEAD(rl->pending);
+        if (p != NULL) {
+		/*
+		 * There is work to do.  Let's do it after unlocking.
+		 */
+                ISC_LIST_UNLINK(rl->pending, p, link);
+	} else {
+		/*
+		 * No work left to do.  Stop the timer so that we don't
+		 * waste resources by having it fire periodically.
+		 */
+		result = isc_timer_reset(rl->timer, isc_timertype_inactive,
+					 NULL, NULL, ISC_FALSE);
+		RUNTIME_CHECK(result == ISC_R_SUCCESS);
+		rl->state = isc_ratelimiter_worklimited;
+	}
+        UNLOCK(&rl->lock);
+	isc_event_free(&event);
+	/*
+	 * If we have an event, dispatch it.
+	 * There is potential for optimization here since
+	 * we are already executing in the context of "task".
+	 */
+	if (p != NULL)
+		isc_task_send(rl->task, &p);
+	INSIST(p == NULL);
+}
+
+void
+isc_ratelimiter_destroy(isc_ratelimiter_t **ratelimiterp) 
+{
+	isc_ratelimiter_t *rl = *ratelimiterp;
+	isc_event_t *p;
+	(void) isc_timer_reset(rl->timer, isc_timertype_inactive,
+			       NULL, NULL, ISC_FALSE);
+	isc_timer_detach(&rl->timer);
+	while ((p = ISC_LIST_HEAD(rl->pending)) != NULL) {
+		ISC_LIST_UNLINK(rl->pending, p, link);
+		isc_event_free(&p);
+	}
+	isc_mutex_destroy(&rl->lock);
+	isc_mem_put(rl->mctx, rl, sizeof(*rl));
+	*ratelimiterp = NULL;
+}