Re: [gentoo-user] NTP problem

["Boyd Stephen Smith Jr." <bss03@volumehost.com>]

On Wednesday 22 February 2006 12:38, "Anthony E. Caudel" 
<acaudel@gt.rr.com> wrote about 'Re: [gentoo-user] NTP problem':
> Brandon Enright wrote:
> Well, overnight it only reset twice; - some improvement!
>
> Here is my complete ntp.conf:
> # Name of the servers ntpd should sync with
> # Please respect the access policy as stated by the responsible person.
> #server         ntp.example.tld         iburst
>
> server pool.ntp.org

This chooses a single random server from the pool to sync with, which is 
probably not /exactly/ what you want.

You have a few alternatives:
1) Change "server" to "servers".  Then, ntpd will use all the IPs 
associated with the domain name.  As part of the process of syncing it 
will invalidate peers that have long or volatile round-trip times.  It 
will, however, try to connect to 100s (IIRC) of IPs initially.

2) Use:
server 0.pool.ntp.org
server 1.pool.ntp.org
server 2.pool.ntp.org

In this case, the daemon will only use the first address from each domain 
name.  <n>.pool.ntp.org (for n = 0-9, IIRC) resolves to the same addresses 
as pool.ntp.org, but the primary address you get back is different each 
time.  (I believe the <n>. prefix is an attempt to prevent local caching, 
which would be a problem if you just repeated your server line 3 times.)

You'll get better times syncing off multiple servers because the daemon can 
use some statistics to remove some of the network latency issues.  
However, you could still get a "bad draw" and get 3 servers far away from 
you.

3) Follow this comment from *your* .conf file:
> # A good way to get servers for your machine is:
> # netselect -s 3 pool.ntp.org

netselect is available from portage, and I think it's generally installed 
during your gentoo install as a dependency of mirrorselect.  In any case, 
you can use it to find 3 (or however many you want to use) servers close 
to you.

Unfortunately, with this method, if better peers are added to the pool, the 
network topology changes, or anything else to invalidate the quality of 
the peers you pick, ntpd won't be able to automagically pick better ones.

Also, for any of these options, you should note the geographic sub-pools 
that are available.  I use us.pool.ntp.org.  For (1) this will reduce the 
number of IPs initially connected to, for (2) it will increase the chance 
that you don't get a bad draw (because, generally, geographically closer 
is closer on the network), for (3) ... Well, actually for 3 you might as 
well pick the best ones from the entire pool.

-- 
Boyd Stephen Smith Jr.
bss03@volumehost.com
ICQ: 514984 YM/AIM: DaTwinkDaddy
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