NTP conflates broadcast and multicast when opening sockets. The broadcast
address does not need to be opened for multicast clients. This has been
reported as NTP community bug 2990 (http://bugs.ntp.org/show_bug.cgi?id=2990)
and this patch may be removed after upgrading to a version of NTP which has
bug 2990 fixed.

--- include/ntpd.h
+++ include/ntpd.h
@@ -480,6 +480,7 @@ extern struct peer *sys_peer;		/* curren
  * Nonspecified system state variables.
  */
 extern int	sys_bclient;		/* we set our time to broadcasts */
+extern int	sys_mclient;		/* we set our time to multicast */
 extern double	sys_bdelay; 		/* broadcast client default delay */
 extern int	sys_authenticate;	/* requre authentication for config */
 extern l_fp	sys_authdelay;		/* authentication delay */
--- ntpd/ntp_io.c
+++ ntpd/ntp_io.c
@@ -2017,9 +2017,6 @@ update_interfaces(
 	 */
 	refresh_all_peerinterfaces();
 
-	if (broadcast_client_enabled)
-		io_setbclient();
-
 	if (sys_bclient)
 		io_setbclient();
 
--- ntpd/ntp_proto.c
+++ ntpd/ntp_proto.c
@@ -105,6 +105,7 @@ int leap_sec_in_progress;
  * Nonspecified system state variables
  */
 int	sys_bclient;		/* broadcast client enable */
+int	sys_mclient;		/* multicast client enable */
 double	sys_bdelay;		/* broadcast client default delay */
 int	sys_authenticate;	/* requre authentication for config */
 l_fp	sys_authdelay;		/* authentication delay */
@@ -1083,7 +1084,7 @@ receive(
 			return;
 		}
 #endif /* AUTOKEY */
-		if (sys_bclient == 0) {
+		if (sys_bclient == 0 && sys_mclient == 0) {
 			sys_restricted++;
 			return;			/* not enabled */
 		}
@@ -4209,6 +4210,7 @@ init_proto(void)
 	sys_survivors = 0;
 	sys_manycastserver = 0;
 	sys_bclient = 0;
+	sys_mclient = 0;
 	sys_bdelay = BDELAY_DEFAULT;	/*[Bug 3031] delay cutoff */
 	sys_authenticate = 1;
 	sys_stattime = current_time;
@@ -4356,7 +4358,7 @@ proto_config(
 	case PROTO_MULTICAST_ADD: /* add group address */
 		if (svalue != NULL)
 			io_multicast_add(svalue);
-		sys_bclient = 1;
+		sys_mclient = 1;
 		break;
 
 	case PROTO_MULTICAST_DEL: /* delete group address */
--- ntpd/ntp_request.c
+++ ntpd/ntp_request.c
@@ -1117,7 +1117,7 @@ sys_info(
 	is->flags = 0;
 	if (sys_authenticate)
 		is->flags |= INFO_FLAG_AUTHENTICATE;
-	if (sys_bclient)
+	if (sys_bclient || sys_mclient)
 		is->flags |= INFO_FLAG_BCLIENT;
 #ifdef REFCLOCK
 	if (cal_enable)