[ntp:questions] Re: ntpd, boot time, and hot plugging
David L. Mills
mills at udel.edu
Thu Feb 3 03:16:46 UTC 2005
Kenneth,
This is the single most persistent issue in the engineering design of
NTP. There must be tradeoffs between security, robustenss, accuracy and
initial delay. In the current design compromise, a server is acceptable
only after three/four rounds of messages and the ensemble time is
acceptable with at least one of possibly several acceptable servers.
With IBURST mode, takes takes 6-8 seconds.
For better robustness use "tos minclock N", where the at least N
(default 1) servers must be acceptable to set the clock. Tonight I put
in a "tos maxdist M", where M is the distance threshold below which the
server is acceptable. Set "tos maxdist 16" and the first sample received
from any server will set the clock likety-split. Of course, essentially
all the mitigation algorithms using multiple-sample redundancy and
multiple-server diversity are systematically defeated. You might as well
use SNTP.
Dave
Kenneth Porter wrote:
> There's been some discussion on the Fedora-devel list about ways to speed
> up booting for workstations. One of the things that slows down the boot
> process is waiting for an initial network time sync. I'd like to solicit
> opinions on how to organize the interaction between ntpd, the OS, the boot
> scripts, the network interfaces (which may come and go; think mobile
> devices), and possible hot-plugged local time sources. There was also
> discussion a few months ago about getting NTP server addresses from DHCP,
> so that should be considered.
More information about the questions
mailing list