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C-18
Cisco Intrusion Prevention System CLI Sensor Configuration Guide for IPS 7.1
OL-19892-01
Appendix C Troubleshooting
Time Sources and the Sensor
The ASA IPS Modules
• The ASA 5500 AIP SSM, ASA 5500-X IPS SSP, and ASA 5585-X IPS SSP automatically
synchronize their clocks with the clock in the adaptive security appliance in which they are installed.
This is the default.
• Configure them to get their time from an NTP time synchronization source, such as a Cisco router
other than the parent router.
For More Information
For the procedure for configuring NTP, see Configuring NTP, page 4-41.
Synchronizing IPS Clocks with Parent Device Clocks
The ASA IPS modules (ASA 5500 AIP SSM, ASA 5500-X IPS SSP, and ASA 5585-X IPS SSP)
synchronize their clocks to the parent chassis clock (switch, router, or adaptive security appliance) each
time the IPS boots up and any time the parent chassis clock is set. The IPS 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 IPS clock and the parent clock are synchronized to an external NTP
server. If only the IPS 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 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 Log in to the sensor.
Step 2 Generate the host statistics.
sensor# show statistics host
...
NTP Statistics
remote refid st t when poll reach delay offset jitter
11.22.33.44 CHU_AUDIO(1) 8 u 36 64 1 0.536 0.069 0.001
LOCAL(0) 73.78.73.84 5 l 35 64 1 0.000 0.000 0.001
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
...
Step 3 Generate the hosts statistics again after a few minutes.
sensor# show statistics host
...
NTP Statistics
remote refid st t when poll reach delay offset jitter
*11.22.33.44 CHU_AUDIO(1) 8 u 22 64 377 0.518 37.975 33.465
LOCAL(0) 73.78.73.84 5 l 22 64 377 0.000 0.000 0.001
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