[ntp:questions] Routers and NTP Timing loops

unruh unruh at wormhole.physics.ubc.ca
Thu Jun 17 09:51:24 UTC 2010

On 2010-06-16, Jacobs, Kevin J. <kjacobs at mitre.org> wrote:
> I  had an interesting experience with a Cisco router as "ntp master 9" using itself as an NTP source and it's neighboring switch as the only other  NTP source.
> The switch had the exact same configuration right back at the router!. So what happens? Is NTP smart enough to know that this is a bad idea? If not, what goofy things happen if you establish an NTP timing loop? I know that if this were frequency references and stratum 3 clocks,  they would ultimately peg at the end of their frequency range (not good) but I don't know what happens from a time perspective. I had some interesting date-time issues and this is a potential root cause. Just looking to see if anyone has had similar experience and have done some in-depth research in this area.

That is what the stratum is supposed to guard against. At each reference
the stratum is increased by 1. In your case the stratum should ratchet
itself up by 1 each time is referes to the toehr, until both are at
stratum 15 and are ignored. They they use themselves only which is
useless. YOu would be better off not using ntp at all. 

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