Re: NTP Sync Issue Across Tata (Europe)

["Forrest Christian (List Account)" <lists () packetflux com>]

The recommendation tends to be the following:

1) Run your GPS-derived NTP appliances, but DO NOT point end-user clients
at it.
2) Run a set of internal NTPd servers, and configure them to pull time from
all of your GPS-derived NTP servers, AND trusted public NTP servers
3) Point your clients at the internal NTPd servers.

Note that it's not entirely unreasonable to go out and buy numerous GPS
appliances, deploy them at multiple locations, and point your NTPd servers
at those.   With enough sites, your NTPd server will skip over any
defective NTP appliance.    At some point, using publicly available NTP
sources is redundant unless one wants to mitigate away the risks behind
failure of the GPS system itself.

What I'm advocating against is the seemingly common practice to go buy an
off-the-shelf lower-cost GPS-NTP appliance (under $1K or so), stick an
antenna in a window or maybe on the rooftop, and point all your devices at
that device.    This is asking for a failure for reasons I've covered
previously.   Robust time needs multiple time sources in order to mitigate
against any one source being spoofed or jammed.   The more time sources you
incorporate into your solution, the less likely it is that any one of them
going haywire would cause a timing failure.

On Wed, Aug 9, 2023 at 6:12 PM Mel Beckman <mel () beckman org> wrote:

> Seth,
>
> My point exactly. Use GPS as primary, and have anti-PS back up, and if you
> want automatic fail over, do that in an intermediate server on your site
> that makes a conscious test and decision to fail over to regular NTP
>
> -mel via cell
>
> > On Aug 9, 2023, at 5:01 PM, Seth Mattinen via NANOG <nanog () nanog org>
> wrote:
> > On 8/9/23 3:25 PM, Forrest Christian (List Account) wrote:
> > > Note that NIST operates a pool of 24 time servers for public use.
> These are spread across four different locations in two different states.
> My understanding is that they all get their time directly from the official
> NIST clocks without GPS or NTP being involved.
> > I used to jump through all the hoops for that but honestly I like the
> appliances better (they are also PTP grandmaster clocks). I can always
> disable the GPS inputs if any of the doom and gloom actually comes to pass.
> > ~Seth


-- 
- Forrest