nanog mailing list archives
Re: Speaking of NTP...
From: Matthew Huff <mhuff () ox com>
Date: Thu, 16 Jul 2015 19:43:41 +0000
Thanks. We have always had a few outliers, but we have never had a large number of external NTP have a consistent offset, and not one as big as 10ms. Something changed last Friday, probably at some peering point that caused the issue. Maybe a symmetric path got created to route around some outage. Maybe some MPLS circuit got introduced into the mix that hides the underlying path/latency. Glad to know someone else has seen something like this. Our 3 NTP servers that sync from external sources have at least 5 upstream stratum 1 servers and are peered to each other . They have settled on a sense of time that is good within +/i 1 msec of our strata 1 clocks, so all is good, but it was a stage occurrence after we had been good for so long. Each of our servers are clients of our 2 x strata 1 servers and 3 x strata 2 NTP servers. They all look good now.
On Jul 16, 2015, at 3:24 PM, Tony Hain <alh-ietf () tndh net> wrote: 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. Tony-----Original Message----- From: NANOG [mailto:nanog-bounces+alh-ietf=tndh.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... 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. https://en.wikipedia.org/wiki/Propagation_of_uncertainty On Mon, Jul 13, 2015 at 8:17 AM, Matthew Huff <mhuff () ox com> wrote: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
Current thread:
- Speaking of NTP... Matthew Huff (Jul 13)
- Re: Speaking of NTP... Stephane Bortzmeyer (Jul 13)
- Re: Speaking of NTP... Rafael Possamai (Jul 16)
- RE: Speaking of NTP... Tony Hain (Jul 16)
- Re: Speaking of NTP... Matthew Huff (Jul 16)
- RE: Speaking of NTP... Tony Hain (Jul 16)