New ntp deployment replaces old ntp server

[ziqex]

Hi,

There was new ntp gps clock deployed on the network. We use dns entry to point to it. (ntp server ntp.clock.corp)

The communication to it is allowed.

The devices that already have ntp server configured that points to the ntp.clock.corp do not sync with the new clock unless you remove and re-add the entry or you re-enter the command ntp server ntp.clock.corp

DNS entry was updated a few ago and resolves to the new address.

Switches have correct dns servers and are resolving the ntp.clock.corp correctly.

In the ntp association I can still see the old address and not the new one.

Will the switch ever pick the new ip for the ntp server and sync with it or it is cached and need to be manually removed and re-added?

Initially I thought that maybe it is matter of time but have already waited over 24 hours and the clock still did not sync.

However when you re-run the command with  #ntp server ntp.clock.corp it syncs immediately. 

Any suggestions? 

Thank you.

Regards,

Daniel

[Reza Sharifi]

Hi,

Do both NTP servers (the old one and the new one) provide the same clock stratum? Maybe the old server is providing better timing and that is why the switches keep referring to that. As a test, what happens if you apply the new name and delete the old one?

HTH

[ziqex]

Old NTP server is down since January. If you remove and re-add the config the clock is syncing fine.

[Leo Laohoo]

---

@ziqex wrote:

We use dns entry to point to it. (ntp server ntp.clock.corp)

---

Use DHCP Option 42.

[paul driver]

Helllo
re-entering the ntp server name is required so it realigns the switch to the remaining ntp server ip

Another possible alternative is to clear the ntp table as/when you made the change

clear ntp server xxx

[ziqex]

Hi,

Thanks for the suggestion, unfortunately there is no command: clear ntp server 

#clear ntp ?
% Unrecognized command

Thanks

[ziqex · Accepted solution]

The only way is to re-enter the ntp server command or removing no ntp server and re-adding it.

There is no clear ntp server command on the L3 switches.

Thank you.