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

[Ragnar Sundblad <[e-mail]>]

> On 26 Mar 2020, at 21:10, Hal Murray <[e-mail]> wrote:
> 
> 
>>>>> No, clients may switch between servers when they become unreachable
>>>>> (e.g. due to rate limiting). I see this often with my mini-pool of NTS
>>>>> servers.
> 
>>>> Oh really, I didn’t know. So chrony does that? (Nice!)
>>> I think most NTP and SNTP clients do that.
> 
>> Right, SNTP most likely. But NTP? Oh well. 
> 
> In pool mode, yes.
> 
> With the current pool, there is no way to ask "Is this site still in the pool?"
> (There isn't a clean way to turn off traffic when you remove a site from the 
> pool.)
> 
> It makes sense when a site stops responding to go through the DNS step again 
> and try a new server.
> 
> 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!)

Ragnar