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?
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