[ntp:questions] Re: Freeware for NTP time synchronization under Windows?

Tapio Sokura oh2kku at iki.fi
Tue Oct 19 05:58:21 UTC 2004


David Woolley wrote:
> In article <MPG.1bdd1a06cc169f4b9896df at news.individual.net>,
> "Chaos Master <spammers.****@spam.com.INVALID>" <> wrote:
>>I am looking for a freeware Windows program to synchronize PC' clock over the 
>>Internet, using the NTP (Network Time Protocol) protocol

> What do you mean by Windows?  For any Windows system bought new in the
> last two or three years, you should use the reference NTP implementation,

There is at least one problem with using ntpd (as in www.ntp.org) 
especially in laptops and other computers that are not always connected 
to an IP-network and/or change IP-addresses frequently. Because ntpd 
expects to always have network connectivity and it doesn't handle IP 
addresses changing under it while it is running, it is not rare to have 
ntpd fail in circumstances where a simple(r) client achieves 
synchronization.

With simpler I mean an SNTP client that uses DNS to resolve the server 
IP address, opens a socket, sends a query & receives a response, closes 
the socket, steps the clock and then goes to sleep for x minutes after 
which the cycle is repeated. Naturally the result is not as accurate as 
can be achieved with ntpd, but often in the case of workstations 
(sub)second time accuracy is not that essential anyway.

I included DNS lookup in the loop above because I have noticed that some 
(S)NTP clients never use DNS for looking up the server address, unless 
the user specifically requests to do so. In my opinion if the user 
enters a DNS name for the NTP server address, the client should 
automatically re-resolve the name every time the client software is 
started/first queries a server. Resolving the server name before sending 
each individual query could result in needless clockhopping. Perhaps a 
good compromise would be to do a DNS lookup at every client software 
startup and after that periodically, like after running continuously for 
a week, as well after a server is unreachable for a certain period of 
time. But I'm getting sidetracked here..

What I meant to say is this: ntpd is excellent for servers and 
workstations that are always connected to an IP network with a stable IP 
address, but not optimal for "road warriors".

   Tapio



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