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List:       busybox
Subject:    Re: [PATCH] The NTP client/server applet
From:       walter harms <wharms () bfs ! de>
Date:       2009-11-24 14:40:32
Message-ID: 4B0BF060.3030602 () bfs ! de
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Denys Vlasenko schrieb:
> On Mon, Nov 23, 2009 at 1:57 PM, Adam Tkac <vonsch@gmail.com> wrote:
>> I agree with all your changes except one piece below.
>>
>> Admins usually use "NTP pool" as the main time source (pool.ntp.org).
>> With your patch only one server is used. I know the old version of
>> add_peers consumes more space (+241B) but on the other hand it makes
>> ntpd more accurate.
> 
> They have a pool of machines with many IPs but one DNS name?
> Not one machine?
> 
> I see. Since for NTP it can be done, they decided that this
> setup would be is neat, and did it.
> But neatness not necessarily equals usefulness.
> 
> Think about how multi-IP hostnames work.
> 
> ping google.com  - which IP will ping select? It can't ping them all,
> that would be weird (and harder to implement).
> 
> ssh multihomed.org - which IP will ssh select? It can't use
> more than one at once for sure!
> 
> wget http://multihomed.org/  - which IP .... ?
> 
> See? Almost always, when you give a hostname, it does not make sense
> to "explode" it into *many* IPs, you want *one* IP.
> 
> Thus, it makes sense to just follow this model always.
> When you have a hostname -> IP translation, return *one* IP.
> 
> Either DNS servers or DNS resolver in libc may give
> this IP semi-randomly from the set of available IPs
> for that hostname, in order to load-balance it, but that's
> about it.
> 
> Getting fancy and hiding *several* servers (to be treated
> as separate servers, not a cluster) behind one hostname
> breaks this simple concept. So whoever is doing it
> did not think whether cool factor is worth resulting PITA.
> 
> I think this was a stupid idea.
> 
> For one, what if someone else has a *single* NTP server,
> which just happens to have 27 addresses? ntpd
> will erroneously think that there are 27 peers
> at that hostname!!!
> 
> If they want to have a pool of machines,
> srv1.pool.ntp.org, srv2.pool.ntp.org, srv3.pool.ntp.org
> would have worked just fine.
> 
> Having said that, we'd probably need to support that
> stupid thing now, it's out of our control to fix it...
> --



From:
http://www.pool.ntp.org/en/
http://www.pool.ntp.org/en/use.html

setup of ntpd is like:

server 0.pool.ntp.org
server 1.pool.ntp.org
server 2.pool.ntp.org
server 3.pool.ntp.org

"The 0, 1 and 2.pool.ntp.org names point to a random set of servers that will change every hour"

pool.ntp.org can be fine tuned:

  pool.ntp.org       -> world wide
europe.pool.ntp.org  -> europe only
    de.pool.ntp.org  -> germany only

hope that helps
re
 wh




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