NTP : Network Time Protocol is a networking protocol for clock synchronization between computer systems over packet-switched, variable-latency data networks. In operation since before 1985, NTP is one of the oldest Internet protocols in current use. NTP was designed by David L. Mills of the University of Delaware.
How does NTP work?
The NTP client initiates a time-request exchange with the NTP server. As a result of this exchange, the client is able to calculate the link delay and its local offset, and adjust its local clock to match the clock at the server’s computer. As a rule, six exchanges over a period of about five to 10 minutes are required to initially set the clock.
Once synchronized, the client updates the clock about once every 10 minutes, usually requiring only a single message exchange. In addition to client-server synchronization. This transaction occurs via the User Datagram Protocol on port 123. NTP also supports broadcast synchronization of peer computer clocks.
Features of NTP
NTP servers, of which there are thousands around the world, have access to highly precise atomic clocks and GPS clocks. Specialized receivers are required to directly communicate with the NTP servers for these services. It is not practical or cost-effective to equip every computer with one of these receivers. Instead, computers designated as primary time servers are outfitted with the receivers, and they use protocols such as NTP to synchronize the clock times of networked computers.
NTP uses Coordinated Universal Time (UTC) to synchronize computer clock times with extreme precision, offering greater accuracy on smaller networks — down to a single millisecond in a local area network and within tens of milliseconds over the internet. NTP does not account for time zones, instead relying on the host to perform such computations.
Our Sample Scenario :
Server name –dlp.server.world
Server ip address – 192.168.0.100
Client name – http://www.server.world
Client IP address – 192.168.0.101
Required Package – NTP
Configure NTP server (NTPd) : The Network Time Protocol daemon (ntpd) is an operating system program that maintains the system time in synchronization with time servers using the Network Time Protocol (NTP).
Step 1 : Install the NTP package using the below command
# yum install ntp
Step 2 : Now open the ntp configuration file and edit and go to line 18 and add
# vi /etc/ntp.conf
Restrict 192.168.0.0 mask 255.255.255.0 nomodify nnotrap
Step 3 : Now go to line number 27 , comment the line 23,24,25,26 and add the below lines
server ntp1.jst.mfeed.ad.jp iburst
server ntp2.jst.mfeed.ad.jp iburst
server ntp3.jst.mfeed.ad.jp iburst
Step 4 : Start the NTP services and enable the service at the boot time
#systemctl start ntp
#systemtl enable ntp
Configure NTP server Chrony : chrony is a versatile implementation of the Network Time Protocol (NTP). It can synchronise the system clock with NTP servers, reference clocks (e.g. GPS receiver), and manual input using wristwatch and keyboard.
Step 1 : Install the chrony packages
# yum -y install chrony
Step 2 : Now open the configuration file and go to line number 3 and comment the line 3,4,5,6 and add the below lines
# vi /etc/chrony.conf
Server ntp1.jst.mfeed.ad.jp iburst
Server ntp2.jst.mfeed.ad.jp iburst
Server ntp3.jst.mfeed.ad.jp iburst
Now go to line number 25 and add
Step 3 : Start the chrony service and enable it on boot time
# systemctl start chronyd
#systemctl enable chronyd
#systemctl restart chronyd
# chronyc sources
Configure NTP client : The settings of NTP Client on CentOS are mostly the same with Server’s settings, so refer to NTPd Settings or Chrony Settings. For different settings from Server’s one, Clients don’t need to receive time synchronization requests from other computers, so it does not need to set access permission. If you don’t use NTP service daemon but use a command to sync time at once, use ntpdate like follows.
Step 1 : Install the required package using the below command
# yum -y install ntpdate
Step 2 : Run the command for the first time of synchronization
Step 3 : Now enable the service for boot time
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! NTP server configured Successfully!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!