NTP on CISCO 3850 16.6.1

[netmask127]

Hi,

I have two CISCO 3850 routers setup as stratum 3 NTP servers. I have the servers pointing to each other as peer associations and also two other servers (server associations).

I would like the CISCO switches to maintain their clocks when the external time source is not avaliable. And when the external time source comes back I would like the CISCO ntp to jump to the correct time.

The problem is that the cisco routers don't seem to like jumping to external ntp server time if there is a large time difference. I have not set the ntp panic update command so shouldn't the cisco clocks jump to the external time?

Also when both CISCOs are out of sync they don't seem to get back in sync.

Server X <---------------CISCO A <------> CISCO B ---------------------> Server X

On CISCO A

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ntp orphan 5

ntp master 3

ntp peer ciscoB*

ntp server serverX* prefer

On CISCO B

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ntp orphan 5

ntp master 3

ntp peer ciscoA* prefer

ntp server serverX* prefer

*actual IPs not displayed.

Anyone here got some experience with NTP on cisco devices and would like to share some knowledge??

[Leo Laohoo]

ntp orphan 5 

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Don't use that command.

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ntp master 3 

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Don't use that command.

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ntp peer ciscoB* 

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Don't use that command. 

Look, keep it simple.  The only important command to use is "ntp server <IP address> prefer".  That's it.  Nothing more, nothing less.  

Another thing, Windows-based "NTP" servers only talk to Windows-based system.  Microsoft's implementation of NTP/SNTP is subject to Microsoft's own (mis)interpretation.  

[netmask127]

Thanks for your comment.

Can you please explain why I shouldn't use the commands?

I need ntp master 3 as A and B switches are NTP servers to other clients. I thought I needed peer associate to keep A/B times in synchronise so the clients don't jump between the servers.

I used orphan mode because I thought this was needed in case external sources are not available (which may happen in this network)

Have you had any issues with the switch not stepping to the server time?

Thanks for the reminder about windows. Lucky for me there is no windows client in the network and its not a requirement I have to consider :-)

[Leo Laohoo]

Cisco appliances do not have clock batteries and cannot hold time and date. NTP Master command lets the appliance tells downstream devices to "trust me, I know what I'm doing" and jumps off an aeroplane, with a parachute, when the plane is still on the tarmac. *Splat!*