[131442] in North American Network Operators' Group
Re: NTP Server
daemon@ATHENA.MIT.EDU (David Andersen)
Sun Oct 24 14:18:32 2010
From: David Andersen <dga@cs.cmu.edu>
In-Reply-To: <m2vd4r5xh6.wl%randy@psg.com>
Date: Sun, 24 Oct 2010 14:18:18 -0400
To: Randy Bush <randy@psg.com>
Cc: North American Network Operators Group <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Oct 24, 2010, at 1:09 PM, Randy Bush wrote:
>> 1) How necessary do you believe in local NTP servers? Do you really
>> need the logs to be perfectly accurate?
>=20
> what is "perfectly accurate?" perfection is not very realistic. to
> what use do you put these logs? what precision and jitter are =
required
> for that use?
>=20
> imiho, if you are just comparing router and server log files, run off
> public. if you are trying to do fine-grained measurement, you are =
going
> to invest a lot in clock and propagation research.
As one of the aforementioned "time-nuts", I'd strongly second Randy's =
recommendation. It's hard to find a middle ground in timing: Most of =
the network-accessible stratum {1, 2} clocks are good enough for many =
uses. If you find yourself needing really precise time with good =
guarantees, you're not just talking about buying one GPS unit -- you can =
easily go down a rathole of finding multiple units with good holdover. =
(And if you don't need that, then ask yourself why public isn't good =
enough).
Possible very reasonable answers include needing to do one-way delay =
measurements; others include wanting to depend on time for =
authentication protocols or other protocols and not have an external =
dependency (assuming you're not high-value enough for someone to try to =
spoof GPS at you).
The problem is that once you have a timing device or two, you've added =
to the set of crap you have to manage and monitor. I use a lot of =
CDMA-based time receivers so that I can throw them in machine rooms with =
no sky access, and every year or two, I have to go upgrade a lot of =
firmware because some cellular company has changed their protocols. I =
find a lot of cellular base stations that keep the wrong time =
(suggesting that their GPS-based time sync is fubared in some way). =
Yadda, yadda. Nothing is free.
-Dave=20=
