[182419] in North American Network Operators' Group
RE: Speaking of NTP...
daemon@ATHENA.MIT.EDU (Tony Hain)
Thu Jul 16 15:24:26 2015
X-Original-To: nanog@nanog.org
From: "Tony Hain" <alh-ietf@tndh.net>
To: "'Rafael Possamai'" <rafael@gav.ufsc.br>, "'Matthew Huff'" <mhuff@ox.com>
In-Reply-To: <CAJB2g-EpzwhJ=zLKEvNsOxkSnyFrH73Nf4SO2xB13z0WY1LYEQ@mail.gmail.com>
Date: Thu, 16 Jul 2015 12:24:11 -0700
X-SA-Exim-Mail-From: alh-ietf@tndh.net
Cc: nanog@nanog.org
Errors-To: nanog-bounces@nanog.org
I have had a consistent 10ms offset on a set of servers for the last 5 =
years. After extensive one-way tracing, it turns out there is a 20ms =
asymmetry "within" the Seattle Westin colo between HE & Comcast, causing =
all the IPv6 peers appearing over the HE tunnel to be 10ms offset from =
everything else. There may be other instances of indirect peering =
causing a static asymmetric path delay, and NTP will report that as an =
offset of half of the difference.=20
Tony
> -----Original Message-----
> From: NANOG [mailto:nanog-bounces+alh-ietf=3Dtndh.net@nanog.org] On
> Behalf Of Rafael Possamai
> Sent: Thursday, July 16, 2015 8:53 AM
> To: Matthew Huff
> Cc: nanog@nanog.org
> Subject: Re: Speaking of NTP...
>=20
> Depending on how exactly you have these servers configured with =
relation
> to one another, small variations from one single source can be =
augmented
> down the line.
>=20
> https://en.wikipedia.org/wiki/Propagation_of_uncertainty
>=20
>=20
>=20
> On Mon, Jul 13, 2015 at 8:17 AM, Matthew Huff <mhuff@ox.com> wrote:
>=20
> > We have 5 NTP server: 2 x stratum 1 rubidium oscillator time =
servers
> > with GPS sync, and 3 servers running NTP 4.2.6p5-3 synced to =
external
> > internet based NTP stratum 1 servers. We monitor our NTP environment
> > closely, and over the last 10+ years, normally all of our NTP =
servers
> > are sync'ed within
> > +/- 2 msec. Starting last Friday, we started seeing some remote NTP
> > +servers
> > with GPS reference consistently offset by 10 msec.
> >
> > Any one else seeing this?
> >
> > ----
> > Matthew Huff | 1 Manhattanville Rd
> > Director of Operations | Purchase, NY 10577
> > OTA Management LLC | Phone: 914-460-4039
> > aim: matthewbhuff | Fax: 914-694-5669
> >
> >
