EXAMPLE 1
...
clock timezone CST -6
clock summer-time CDT recurring
ntp source eth 0
ntp peer
ntp peer
ntp peer
...
EXAMPLE 2
...
ntp source Ethernet0/0
ntp update-calendar
ntp peer
ntp peer prefer
...
EXAMPLE 3
...
service timestamps debug datetime localtime
service timestamps log datetime localtime
clock timezone PST -8
clock summer-time PDT recurring
interface Ethernet0
ip address
ntp broadcast
ntp clock-period 17180319
ntp source Ethernet0
ntp server
ntp server
ntp server