При настройке NTP по рекомендациям Cisco SAFE появляется в логах большое число сообщений вида

000600: Sep 13 11:16:21.106 TSD: %SEC-6-IPACCESSLOGNP: list 10 denied 0 192.168.13.246 -> 0.0.0.0, 1 packet
000601: Sep 13 11:19:21.108 TSD: %SEC-6-IPACCESSLOGNP: list 10 denied 0 192.168.13.247 -> 0.0.0.0, 5 packets
000602: Sep 13 11:19:21.108 TSD: %SEC-6-IPACCESSLOGNP: list 10 denied 0 192.168.13.253 -> 0.0.0.0, 4 packets
000603: Sep 13 11:19:21.108 TSD: %SEC-6-IPACCESSLOGNP: list 10 denied 0 192.168.13.250 -> 0.0.0.0, 4 packets
000604: Sep 13 11:19:21.108 TSD: %SEC-6-IPACCESSLOGNP: list 10 denied 0 192.168.13.252 -> 0.0.0.0, 4 packets
000605: Sep 13 11:19:21.108 TSD: %SEC-6-IPACCESSLOGNP: list 10 denied 0 192.168.13.249 -> 0.0.0.0, 4 packets
000606: Sep 13 11:19:21.108 TSD: %SEC-6-IPACCESSLOGNP: list 10 denied 0 192.168.13.251 -> 0.0.0.0, 4 packets
000607: Sep 13 11:22:21.110 TSD: %SEC-6-IPACCESSLOGNP: list 10 denied 0 192.168.13.246 -> 0.0.0.0, 6 packets

Конфиг NTP на рутере такой:
ntp logging
ntp authentication-key 11 md5 test
ntp authenticate
ntp trusted-key 11
ntp clock-period 17180200
ntp source Loopback0
ntp access-group peer 10
ntp access-group serve-only 11
ntp master 6
ntp update-calendar
ntp server 192.168.100.1 key 11 prefer

access-list 10 remark ACL of allowed NTP peers
access-list 10 permit 192.168.100.1
access-list 10 permit 127.127.7.1
access-list 10 deny any log
!
access-list 11 remark ACL of allowed NTP clients
access-list 11 permit 192.168.13.0 0.0.0.255
access-list 11 deny any


Что это за обращения на 0.0.0.0 и как это убрать?