NTP Server configuration in Ubuntu

Task:

We want to create a local NTP server so that our local devices like switches / routers / systems can syn time with it without requiring internet access. The NTP daemon allows a machine on your network (if you would like) to operate as an NTP time server. Doing so will allow other machines on your local network to synchronize with your LAN time server in a very quick and accurate manner, since network latency is minimized. In this way, the differences in clocks between machines on your network is kept as minimal as possible. Mac, and even Windows boxes are also able to synchronize with an NTP server.

Note: If your windows workstation is part of domain, you will not be able to see INTERNET TIME setup in DATE TIME because workstation will sync time with the Domain.

OS: Ubuntu 16.04.4 LTS with internet access

First, Install the NTP daemon

sudo aptitude remove ntpdate
sudo aptitude install ntpd

Note: Once you have found one good syncing peer,  add it to the list, putting ‘iburst’ after the most promising one. For instance:

server 91.189.91.157 iburst

This will cause ntpd to synchronize very quickly with this server after starting up.

Now restart NTPD daemon …

sudo /etc/init.d/ntp restart

It may take few seconds or up to 15-20 minutes for the initial time sync.

Next, monitor your system log to see if you synchronize with a time server:

tail -f /var/log/syslog

root@linux:~# ntpq -c lpeer
remote refid st t when poll reach delay offset jitter
==============================================================================
+alphyn.canonica 132.246.11.231 2 u 109 1024 377 195.030 -3.184 1.820
-jiro.paina.net 131.113.192.40 2 u 55 1024 377 285.680 55.800 15.483
*ntp5.mobinnet.n 85.199.214.98 2 u 1026 1024 377 208.593 -2.359 3.459
+118.140.184.98 223.255.185.2 2 u 1207 512 174 128.292 2.083 30.041
-103.47.76.177 193.0.0.229 2 u 757 1024 17 110.355 7.986 75.054

You can test if NTP Server is working or not, just download NTPTOOL and Query.
As showed in the image below …

Configure Cisco Switch to sync with ubuntu time server

enable
configure terminal
# Timezone for Asia/Karachi, you may adjust it according to your local TZ
clock timezone PST +5
service timestamps log datetime localtime
# change NTP Server IP Address
ntp server 192.168.100.1
end
show ntp associations

Before vs After (on cisco 3850 switch)

BEFORE

Switch#sh clock
*11:36:14.321 UTC Tue Jun 19 2018

enable
configure terminal
clock timezone PST +5
service timestamps log datetime localtime
ntp server 101.11.11.240
end

AFTER

Switch#sh clock
*16:37:16.103 PST Tue Jun 19 2018

Switch#show ntp associations

address ref clock st when poll reach delay offset disp
~101.11.11.240 91.189.91.157 3 11 64 1 1002.8 283436. 7937.9
* sys.peer, # selected, + candidate, - outlyer, x falseticker, ~ configured
Switch#

Done.