Another benefit to using NTP on Cisco PIX firewalls is found in a dynamic LAN to LAN VPN tunnel where the NTP request and response generates enough traffic to avoid the sometimes troublesome inactivity timeout.

Assuming that your NTP server (10.0.0.1) is accessible through the inside interface:

clock timezone EST -5
clock summer-time EDT recurring first Sunday April 2:00 last Sunday October 2:00 60
ntp server 10.0.0.1 source inside

You can then verify the NTP association with:

• CST -6
• CST -6
• CST -6

You can then verify the NTP association with:
show ntp association detail

You can also verify the PIX clock with:
show clock detail