[ntp:questions] UK report on GPS vulnerabilities seems to overlook NTP

Terje Mathisen "terje.mathisen at tmsw.no" at ntp.org
Tue Mar 8 17:15:48 UTC 2011

JohnAllen wrote:
> Maybe I read this too quickly, but the report published today by the
> UK Royal Academy of Engineering (see
> http://www.raeng.org.uk/news/publications/list/reports/RAoE_Global_Navigation_Systems_Report.pdf
> and also the BBC coverage at http://www.bbc.co.uk/news/science-environment-12668230)
> seems to be saying that many organisations are vulnerable to GPS
> failures because their IT systems rely on GPS for precise time.
> Can this be true? I would have thought that most systems are using
> NTP, and synchronising with diverse enough time sources that
> unavailable or incorrect GPS time would not cause short-term problems.

Most corporate ntp setups are probably using only network sources, and 
most of those lead to a gps as the S1 reference.

There are however alternative clock sources, and many of the pool 
servers use multiple references.

When GPS is temporarily unavailable, large parts of the ntp network will 
drop down one or two stratum levels, but we won't get too many orphaned 

My corporate setup with 3 Oncore gps clocks use both pool servers and 
configured internet sources, I know that a couple of these use radio 
clocks, so my internal network will drop from S2 to S4 or so.


- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"

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