From: Jay Hennigan (jay@west.net)
Date: Sun May 11 2003 - 00:28:36 GMT-3
On Sun, 11 May 2003, Tom Young wrote:
> In the ntp master command , there is a parameter named
> stratum, what the function of this word? What can it do?
> In what environment I have to use this parameter?
It is an indication of precision and generations removed from a reference
source. Lower numbers are more precise. A reference standard of great
precision (atomic clock, GPS, etc.) would be a stratum 1 clock. An NTP
server that is synced to a stratum 1 clock is a stratum 2 clock. An NTP
server synced to a stratum 2 is a stratum 3, and so on.
Where you could use this within the NTP master command would be to set
the priority of multiple NTP masters. If you have two masters set to
strata 1 and 3, a client/peer that references both of them will choose
the stratum 1 source and become stratum 2, ignoring the stratum 3 source
(or feeding it if so configured). If the stratum 1 source becomes
unreachable, it would sync from the stratum 3 source and become stratum
4.
As with RIP, 16 hops is considered unreachable.
In the real world, unless you have a large enterprise it is considered
impolite to source your time from a public stratum 1 source. This is to
minimize the load on stratum 1 public time servers. Sourcing from a
stratum 2 public source is generally precise enough for most practical
purposes. Most stratum 1 sources request that you ask before sourcing
from them. Much good info here:
http://www.eecis.udel.edu/~mills/ntp/
http://www.faqs.org/rfcs/rfc1305.html
-- Jay Hennigan - CCIE #7880 - Network Administration - jay@west.net NetLojix Communications, Inc. - http://www.netlojix.com/ WestNet: Connecting you to the planet. 805 884-6323
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