Cisco IPS-4255-K9 Installation Guide - Page 46

Time Sources and the Sensor Chapter 1 Introducing the Sensor Synchronizing IPS Module System Clocks with the Parent Device System Clock All IPS modules (AIM IPS, AIP SSM, IDSM2, and NME IPS) synchronize their system clocks to the parent chassis clock (switch, router, or security appliance) each time the module boots up and any time the parent chassis clock is set. The module clock and parent chassis clock tend to drift apart over time. The difference can be as much as several seconds per day. To avoid this problem, make sure that both the module clock and the parent clock are synchronized to an external NTP server. If only the module clock or only the parent chassis clock is synchronized to an NTP server, the time drift occurs. Verifying the Sensor is Synchronized with the NTP Server In Cisco IPS, you cannot apply an incorrect NTP configuration, such as an invalid NTP key value or ID, to the sensor. If you try to apply an incorrect configuration, you receive an error message. To verify the NTP configuration, use the show statistics host command to gather sensor statistics. The NTP statistics section provides NTP statistics including feedback on sensor synchronization with the NTP server. To verify the NTP configuration, follow these steps: Step 1 Step 2 Step 3 Step 4 Log in to the sensor. Generate the host statistics: sensor# show statistics host ... NTP Statistics remote refid st t when poll reach delay 11.22.33.44 CHU_AUDIO(1) 8 u 36 64 1 0.536 LOCAL(0) 73.78.73.84 5 l 35 64 1 0.000 ind assID status conf reach auth condition last_event cnt 1 10372 f014 yes yes ok reject reachable 1 2 10373 9014 yes yes none reject reachable 1 status = Not Synchronized ... Generate the hosts statistics again after a few minutes: sensor# show statistics host ... NTP Statistics remote refid st t when poll reach delay *11.22.33.44 CHU_AUDIO(1) 8 u 22 64 377 0.518 LOCAL(0) 73.78.73.84 5 l 22 64 377 0.000 ind assID status conf reach auth condition last_event cnt 1 10372 f624 yes yes ok sys.peer reachable 2 2 10373 9024 yes yes none reject reachable 2 status = Synchronized offset jitter 0.069 0.001 0.000 0.001 offset jitter 37.975 33.465 0.000 0.001 If the status continues to read Not Synchronized, check with the NTP server administrator to make sure the NTP server is configured correctly. 1-28 Cisco Intrusion Prevention System Appliance and Module Installation Guide for IPS 7.0 OL-18504-01