[ntp:questions] Re: ntpd, boot time, and hot plugging

David L. Mills mills at udel.edu
Thu Feb 3 03:16:46 UTC 2005


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.


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.

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