At 10:06 AM -0500 2005-09-11, wayne wrote:
Actually, network topology is only an approximation of what we want
because different links have different latencies and jitter.
Topology is the closest approximation of what we want before we
start actually measuring latencies and jitter, because topology
directly maps to the number of routers, bridges, switches, etc...
that are located between you and the machine at the other end, and
those are the factors that are most likely to impact things like
latency and jitter.
There is no closer approximation than network topology. To get
any closer, you have to start actually measuring things. Moreover,
NTP doesn't really care about latency and jitter directly. NTP cares
more about stratum and root dispersion, and things like latency and
jitter only indirectly affect the things that NTP really cares about.
But, in terms of approximations, the best we can do is to start
with network topology. From there, we have to start measuring things.
If you want to put a bunch of work into configuring your NTP clients,
you should get the complete NTP pool list, send NTP packets to each of
them and see what kind of latency/jitter you get, and use the best.
Actually, one of the things we're looking at is implementing a
"servers" directive. This won't make it into 4.2.1-RELEASE, and
probably won't make 4.2.2-RELEASE, but might make 4.2.3-RELEASE.
The idea being that you take all of the IP returned by the DNS
for a given label, and sets up unicast client/server relationships
with *all* of them. It would then automatically sort through the
list and eliminate the lower-quality servers and make use of the
higher-quality servers. Of course, ntpd would still only make use of
the top ten servers that it knows about, regardless of their source.
That would make it pretty trivial to configure your /etc/ntp.conf
-- all you'd need is a single "servers" directive for most clients.
Of course, this is something that can't be controlled by the
operators of the pool. That is precisely why I was talking about our
need to look at this situation from a wholistic point of view, and
not lose sight of the overall picture when we're down contemplating
the individual pixels.
--
Brad Knowles, <[EMAIL PROTECTED]>
"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."
-- Benjamin Franklin (1706-1790), reply of the Pennsylvania
Assembly to the Governor, November 11, 1755
SAGE member since 1995. See <http://www.sage.org/> for more info.
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