[Ntp] Antw: [EXT] Re: I-D Action: draft-ietf-ntp-using-nts-for-ntp-27.txt

Ulrich Windl <Ulrich.Windl@rz.uni-regensburg.de> Tue, 31 March 2020 06:00 UTC

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Date: Tue, 31 Mar 2020 08:00:17 +0200
From: Ulrich Windl <Ulrich.Windl@rz.uni-regensburg.de>
To: "ntp@ietf.org" <ntp@ietf.org>, mlichvar@redhat.com
References: <20200326201030.397D340605C@ip-64-139-1-69.sjc.megapath.net> <9B282475-3DE0-46B9-9184-43351772E6F3@netnod.se> <00a66f26-a079-2650-9c7b-285b026269e3@nwtime.org> <24990_1585556439_5E81ABD7_24990_85_1_20200330081958.GB17158@localhost>
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Subject: [Ntp] Antw: [EXT] Re: I-D Action: draft-ietf-ntp-using-nts-for-ntp-27.txt
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>>> Miroslav Lichvar <mlichvar@redhat.com> schrieb am 30.03.2020 um 10:19 in
Nachricht
<24990_1585556439_5E81ABD7_24990_85_1_20200330081958.GB17158@localhost>:
> On Fri, Mar 27, 2020 at 12:47:06AM ‑0700, Harlan Stenn wrote:
>> On 3/27/2020 12:15 AM, Ragnar Sundblad wrote:
>> >> On 26 Mar 2020, at 21:10, Hal Murray <hmurray@megapathdsl.net> wrote:
>> >> It would also make sense for sites that are up 24/7 to do something like

> once 
>> >> a day, scan the list of pool servers currently in use and kick out the 
> worst 
>> >> one and try a new one.  The idea is to gradually pick servers that are 
> better, 
>> >> probably nearer, but distance measured in network performance rather
than 
>> >> kilometers.
>> > 
>> > Sounds like a very good idea!
>> > 
>> > (I suppose you should take into consideration especially jitter, but
also
>> > loss, and the larger the round trip, the higher the risk for large
>> > asymmetries = phase error and phase variations when routing change,
>> > and the current measured phase error should probably also take into
>> > account, and there are probably other things. Interesting problem!)
>> 
>> This has always been part of the 'pool' directive in the Reference
>> Implementation.
> 
> Are you sure it does that? If ntpd automatically replaced the worst
> performing servers (e.g. by root distance or jitter), it would break
> the load balancing of pool.ntp.org. It shouldn't be a default
> behavior of clients using the pool. (With other pools it might be ok.)

AFAIK, it work like this: ntpd picks a set of servers (say 6) and start using
them. Some of those may be flagged with '-' or may be unreachable. ntpd
replaces those with a new pool query to fill up the slots and the process
repeats.


I think the corresponding log messages (if loglevel macthes) are:
#sever pick a new host
21 Mar 10:40:14 ntpd[15087]: Soliciting pool server 172.20.16.4
#server drops a host
21 Mar 13:20:12 ntpd[15087]: 172.20.16.36 local addr 172.20.16.35 -> <null>

The example is manycast, but pools should be very similar.

Regards,
Ulrich

> 
> ‑‑ 
> Miroslav Lichvar
> 
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