[131454] in North American Network Operators' Group
Re: NTP Server
daemon@ATHENA.MIT.EDU (Cutler James R)
Sun Oct 24 20:44:11 2010
From: Cutler James R <james.cutler@consultant.com>
In-Reply-To: <SNT119-W189AD0AFF7AD29FA84AC0ADC410@phx.gbl>
Date: Sun, 24 Oct 2010 20:43:50 -0400
To: nanog group <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
Regarding leap seconds:
A modern OS kernel using the NTP daemon to control time will always =
experience monotonic time. Negative leap seconds should result in the =
local clock slowing slightly until the local time matches the =
NTP-derived time.
This is in strong contrast to what can happen when ntpdate or similar =
queries are used to adjust system time, as in the following example from =
a popular CPE log where the local CPU clock tended to run fast:
Oct 24 04:27:59 192.168.1.1 HomeN ntp: Clock synchronized to network =
time server time.apple.com (adjusted +0 seconds).
Oct 24 05:28:00 192.168.1.1 HomeN ntp: Clock synchronized to network =
time server time.apple.com (adjusted +0 seconds).
Oct 24 06:28:00 192.168.1.1 HomeN ntp: Clock synchronized to network =
time server time.apple.com (adjusted -1 seconds).
Oct 24 07:28:01 192.168.1.1 HomeN ntp: Clock synchronized to network =
time server time.apple.com (adjusted +0 seconds).
Oct 24 08:28:01 192.168.1.1 HomeN ntp: Clock synchronized to network =
time server time.apple.com (adjusted -1 seconds).
Oct 24 09:28:02 192.168.1.1 HomeN ntp: Clock synchronized to network =
time server time.apple.com (adjusted -1 seconds).
Oct 24 10:28:03 192.168.1.1 HomeN ntp: Clock synchronized to network =
time server time.apple.com (adjusted +0 seconds).
Oct 24 11:28:04 192.168.1.1 HomeN ntp: Clock synchronized to network =
time server time.apple.com (adjusted +0 seconds).
Oct 24 12:28:04 192.168.1.1 HomeN ntp: Clock synchronized to network =
time server time.apple.com (adjusted +0 seconds).
Oct 24 13:28:05 192.168.1.1 HomeN ntp: Clock synchronized to network =
time server time.apple.com (adjusted +0 seconds).
Oct 24 14:28:05 192.168.1.1 HomeN ntp: Clock synchronized to network =
time server time.apple.com (adjusted +0 seconds).
Oct 24 15:28:05 192.168.1.1 HomeN ntp: Clock synchronized to network =
time server time.apple.com (adjusted -1 seconds).
Oct 24 16:28:06 192.168.1.1 HomeN ntp: Clock synchronized to network =
time server time.apple.com (adjusted -1 seconds).
Oct 24 17:28:07 192.168.1.1 HomeN ntp: Clock synchronized to network =
time server time.apple.com (adjusted +0 seconds).
Oct 24 18:28:08 192.168.1.1 HomeN ntp: Clock synchronized to network =
time server time.apple.com (adjusted -1 seconds).
Oct 24 19:28:08 192.168.1.1 HomeN ntp: Clock synchronized to network =
time server time.apple.com (adjusted +0 seconds).
Oct 24 20:28:09 192.168.1.1 HomeN ntp: Clock synchronized to network =
time server time.apple.com (adjusted -1 seconds).
Regarding local time servers:
This is the situation in which local clients, at least those with UNIX =
or UNIX-like OS can take advantage of ntpd and local time servers to =
have consistent and monotonic time across your network with a measure of =
insulation from external vagaries. Yes, I have run ntpd on Windows =
systems, but have no quotable experience with the current Windows =
version (Windows 7).
James R. Cutler
james.cutler@consultant.com
