Network Time Protocol

Network Time Protocol (NTP)

NTP is an internet protocol used to synchronize the clock of computer to some time reference. It developed by Professor David L. Mills at the University of Delaware.  

NTP uses co-ordinated universal Time to synchronize computer clock times to a millisecond. NTP is run over the User datagram protocol (UDP), using port No. 123 as both the source and destination. An NTP network usually gets its time from an authoritative time source, such as radio clock and an atomic clock attached to a time server.

Each cisco switch has an internal time clock that runs continuously without any intervention. However, do not assume that a switch already has its internal clock set to the correct date and time.  We can use the show clock command to find time:

Router# show clock

We can use the following commands as a guideline to define the  time zone and summer time and to set the clock:

Switch(config)# clock timezone <name,any> <offset-hours> <offset-minutes>

Offset-hours means if we can set offset -5 than it calculate time 19 means 7:00.

 Offset-minute same as but in minutes.

Switch(config)# clock summer-time <name> date <start date> <start-month> <start-year><hh:mm> <end-date> <end-month> <end-year> <hh:MM>

Or

Switch(config)#clock summer-time <name> recurring <start-week> <start-day> <start-month> <hh:mm> <end-week> <end-day> <end-month> <hh:mm>

If we want donn’t set any other parameters

Switch(config)# clock summer-time <name> recurring

NTP With Server Configuration

Router(config)# ntp server <server ip address>

 

Check NTP Server Status

Router# show ntp status  

Securing NTP

On NTP enable authentication key and password and on router

Router(config)# ntp authentication-key <key-no.> md5 <key-string>

Router(config)# ntp  authenticate

Router(config)# ntp trusted-key <key-no.>

Router(config)#ntp server <ip address> key <key-no>