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

>>> Miroslav Lichvar <mlichvar@redhat.com> schrieb am 26.03.2020 um 15:01 in
Nachricht
<5022_1585231330_5E7CB5E2_5022_507_1_20200326140143.GD9039@localhost>:
> On Thu, Mar 26, 2020 at 02:01:16PM +0100, Ragnar Sundblad wrote:
>> Oh, so you think there is a risk that both the KE negotiation works
>> and at least one NTP requests works, and soon thereafter the
>> connection breaks, frequently?
>> I am not sure why that would happen very often, but if it did, there
>> Should at least be 8 NTP requests (until the client has exhausted its
>> cookies) until it contacts the KE server again.
> 
> Rate limiting of NTP packets in some networks is a major issue, which

Maybe the next NTP specification should talk about the QoS bits.

> was discussed on this list. I sometimes see over 90% packet loss. The
> client would need to reuse cookies to operate reasonably well in such
> conditions. I agree the 8 polling intervals from NTP helps here
> (assuming the interval is not reset to the minimum after NTS-KE and
> it's not using a burst).
> 
>> > 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.

Specifically Manycast and Pool configurations work like that.

> 
>> > Well, as I said above, there are many reasons why NTS-KE or NTS-NTP
>> > may be consistently failing. For example, an ISP may have a firewall
>> > that blocks large NTP packets. NTS-KE will work as expected, but
>> > no NTS-NTP reply will be ever received, so the clients will be
>> > constantly restarting NTS-KE. If the clients were restarted once per
>> > day and used the 1024*2^(n - 1) retry interval I suggested, the number
>> > of NTS-KE requests would drop to 30%.
>> 
>> Ok - in this case too, there should be 8 NTP requests before it contacts
>> the KE server again, and it will increase the retry interval each time
>> since it has not completed a full cycle of getting cookies and succeeded
>> in using them.
> 
> You are right. Good point. Maybe a bug or incompatibility between
> different implementations would be a better example.
> 
> -- 
> Miroslav Lichvar
> 
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