NTP is a system which helps to synchronize time of day computer clocks across the Internet.
The NTP system is based on Internet time servers.These NTP servers run a software service that provides the clock's time of day to client computers over UDP port 123.
The FWSM gets its clock from the switch. There are no NTP settings.
Issue the show clock command on the FWSM and the Switch. You find the same time on both.
NTP traffic through the firewall can be allowed with the use of this access-list command.
access-list < allow_ntp > extended permit any host eq ntp
Note: In this command, allow_ntp is the name of the access-group, that can be replaced with the access-group name that exists applied in the configuration.