Need trusted NTP Sources

Matthew Huff mhuff at
Fri Feb 7 15:56:35 UTC 2014

Working in the financial world, the best practices is to have 4 ntp servers (if not using PTP).

1) You need 3 to determine the correct time (and detect bad tickers)
2) If you lose 1 of the 3 above, then you no longer can determine the correct time
3) Therefore with 4, you have redundancy.

We have two Symmetricom Stratum 1 time servers synced via GPS  with Rubidium oscillators,  and two RHEL 6 servers running ntpd for our 4 servers.

Matthew Huff             | 1 Manhattanville Rd
Director of Operations   | Purchase, NY 10577
OTA Management LLC       | Phone: 914-460-4039

-----Original Message-----
From: Roy [mailto:r.engehausen at] 
Sent: Friday, February 7, 2014 10:23 AM
To: nanog at
Subject: Re: Need trusted NTP Sources

On 2/7/2014 3:35 AM, Saku Ytti wrote:
> On (2014-02-06 21:14 -0500), Jay Ashworth wrote:
>> My usual practice is to set up two in house servers, each of which 
>> talks to:
>> And then point everyone in house to both of them, assuming they 
>> accept multiple server names.
> Two is worst possible amount of NTP servers to have. Either one fails 
> and your timing is wrong, because you cannot vote false ticker. And 
> chance of either of two failing is higher than one specific of them.

"A man with a watch knows what time it is. A man with two watches is never sure."

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