diff --git a/lib/isc/include/isc/result.h b/lib/isc/include/isc/result.h

index 246aefb..0007543 100644

--- a/lib/isc/include/isc/result.h

+++ b/lib/isc/include/isc/result.h

@@ -83,9 +83,9 @@

 #define ISC_R_UNSET			61	/*%< unset */

 #define ISC_R_MULTIPLE			62	/*%< multiple */

 #define ISC_R_WOULDBLOCK		63	/*%< would block */

-

+#define ISC_R_TIMESHIFTED               64      /*%< system time changed */

 /*% Not a result code: the number of results. */

-#define ISC_R_NRESULTS 			64

+#define ISC_R_NRESULTS 			66

 ISC_LANG_BEGINDECLS

diff --git a/lib/isc/include/isc/util.h b/lib/isc/include/isc/util.h

index 332dc0c..f81967d 100644

--- a/lib/isc/include/isc/util.h

+++ b/lib/isc/include/isc/util.h

@@ -233,6 +233,10 @@

  * Time

  */

 #define TIME_NOW(tp) 	RUNTIME_CHECK(isc_time_now((tp)) == ISC_R_SUCCESS)

+#ifdef CLOCK_BOOTTIME

+#define TIME_MONOTONIC(tp) 	RUNTIME_CHECK(isc_time_boottime((tp)) == ISC_R_SUCCESS)

+#endif

+

 /*%

  * Misc

diff --git a/lib/isc/result.c b/lib/isc/result.c

index a707c32..6776fc6 100644

--- a/lib/isc/result.c

+++ b/lib/isc/result.c

@@ -99,6 +99,7 @@ static const char *description[ISC_R_NRESULTS] = {

 	"unset",				/*%< 61 */

 	"multiple",				/*%< 62 */

 	"would block",				/*%< 63 */

+        "time changed",                         /*%< 64 */

 };

 static const char *identifier[ISC_R_NRESULTS] = {

@@ -166,6 +167,7 @@ static const char *identifier[ISC_R_NRESULTS] = {

 	"ISC_R_UNSET",

 	"ISC_R_MULTIPLE",

 	"ISC_R_WOULDBLOCK",

+        "ISC_R_TIMESHIFTED",

 };

 #define ISC_RESULT_RESULTSET			2

diff --git a/lib/isc/unix/app.c b/lib/isc/unix/app.c

index bace2bd..e9814d2 100644

--- a/lib/isc/unix/app.c

+++ b/lib/isc/unix/app.c

@@ -441,15 +441,51 @@ isc__app_ctxonrun(isc_appctx_t *ctx0, isc_mem_t *mctx, isc_task_t *task,

 static isc_result_t

 evloop(isc__appctx_t *ctx) {

 	isc_result_t result;

+        isc_time_t now;

+#ifdef CLOCK_BOOTTIME

+        isc_time_t monotonic;

+        isc_uint64_t diff  = 0;

+#else

+        isc_time_t prev;

+        TIME_NOW(&prev;;

+#endif

+

+

+

 	while (!ctx->want_shutdown) {

 		int n;

-		isc_time_t when, now;

+		isc_time_t when;

+                

 		struct timeval tv, *tvp;

 		isc_socketwait_t *swait;

 		isc_boolean_t readytasks;

 		isc_boolean_t call_timer_dispatch = ISC_FALSE;

+                isc_uint64_t us; 

+

+#ifdef CLOCK_BOOTTIME

+                // TBD macros for following three lines

+                TIME_NOW(&now;;

+                TIME_MONOTONIC(&monotonic);

+                // INSIST(now.seconds > monotonic.seconds) 

+                us = isc_time_microdiff (&now, &monotonic);

+                if (us < diff){ 

+                  us = diff - us;

+                  if (us > 1000000){ // ignoring shifts less than one second

+                    return ISC_R_TIMESHIFTED;

+                  };

+                  diff = isc_time_microdiff (&now, &monotonic);

+                } else {

+                  diff = isc_time_microdiff (&now, &monotonic);

+                  // not implemented

+                }

+#else

+                TIME_NOW(&now;;

+                if (isc_time_compare (&now, &prev) < 0)

+                  return ISC_R_TIMESHIFTED;

+                TIME_NOW(&prev;;

+#endif                

 		/*

 		 * Check the reload (or suspend) case first for exiting the

 		 * loop as fast as possible in case:

@@ -474,9 +510,10 @@ evloop(isc__appctx_t *ctx) {

 			if (result != ISC_R_SUCCESS)

 				tvp = NULL;

 			else {

-				isc_uint64_t us;

+

 				TIME_NOW(&now;;

+

 				us = isc_time_microdiff(&when, &now;;

 				if (us == 0)

 					call_timer_dispatch = ISC_TRUE;

diff --git a/lib/isc/unix/include/isc/time.h b/lib/isc/unix/include/isc/time.h

index 75e24b9..de8b399 100644

--- a/lib/isc/unix/include/isc/time.h

+++ b/lib/isc/unix/include/isc/time.h

@@ -129,6 +129,26 @@ isc_time_isepoch(const isc_time_t *t);

  *\li	't' is a valid pointer.

  */

+#ifdef CLOCK_BOOTTIME

+isc_result_t

+isc_time_boottime(isc_time_t *t);

+/*%<

+ * Set 't' to monotonic time from previous boot

+ * it's not affected by system time change. It also

+ * includes the time system was suspended

+ *

+ * Requires:

+ *\li	't' is a valid pointer.

+ *

+ * Returns:

+ *

+ *\li	Success

+ *\li	Unexpected error

+ *		Getting the time from the system failed.

+ */

+#endif /* CLOCK_BOOTTIME */

+ 

+

 isc_result_t

 isc_time_now(isc_time_t *t);

 /*%<

diff --git a/lib/isc/unix/time.c b/lib/isc/unix/time.c

index 2210240..d7613b8 100644

--- a/lib/isc/unix/time.c

+++ b/lib/isc/unix/time.c

@@ -496,3 +496,25 @@ isc_time_formatISO8601ms(const isc_time_t *t, char *buf, unsigned int len) {

 			 t->nanoseconds / NS_PER_MS);

 	}

 }

+

+

+#ifdef CLOCK_BOOTTIME

+isc_result_t

+isc_time_boottime(isc_time_t *t) {

+  struct timespec ts;

+  

+  char strbuf[ISC_STRERRORSIZE];

+

+  if (clock_gettime (CLOCK_BOOTTIME, &ts) != 0){

+    isc__strerror(errno, strbuf, sizeof(strbuf));

+    UNEXPECTED_ERROR(__FILE__, __LINE__, "%s", strbuf);

+    return (ISC_R_UNEXPECTED);    

+  }

+

+  t->seconds = ts.tv_sec;

+  t->nanoseconds = ts.tv_nsec;

+

+  return (ISC_R_SUCCESS);

+  

+};

+#endif