oberman at es.net
Mon Jun 21 22:13:28 UTC 2010
> From: Joe Abley <jabley at hopcount.ca>
> Date: Mon, 21 Jun 2010 17:55:40 -0400
> I'm interested in the idea of anycasting one of the pool.ntp.org
> herd-members. Every time I've suggested such a thing I've been told
> (paraphrasing) that a good (server, client) NTP session exhibits
> reasonable RTT stability, this constitutes, in effect, a long-lived
> transaction, and hence anycast is not a good answer unless you have
> confidence that the potential for oscillations is low, or that the
> frequency of the oscillations is very low (i.e. in a private network
> this might be a good answer, but across the public Internet it's a
> poor answer).
> Has the thinking changed, or did I just misunderstand?
This would be better asked on the NTP list, but I'd say it depends on
the accuracy you want to achieve. For the NTP pool, the idea is to try
for good accuracy and very good long-term stability are the goals. That
does not work well of the actual source of the data changes very often.
Aside from losing the advantages of long-term PLL filtering of the time,
you also will see substantial changes in delay (i.e. RTT) and, almost
Unless you are confident that the source of the anycast at any point in
the network will remain stable over a very long term, it really does not
sound like a good solution to me. Then again, with GPS time source
available for <75 USD, anyone who is really trying for really good time
should just buy one and run a local stratum 1 server.
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net Phone: +1 510 486-8634
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