[Ntp] Antw: Re: Antw: Re: Antw: [EXT] NTPv5 Loop Detection without Stratum

>>> David Venhoek <david@venhoek.nl> schrieb am 30.08.2022 um 16:13 in Nachricht
<CAPz_-SVPE-Fd1vFWnbu+GAPc=y2bkJMW4pyu98bBwDfcm+R2rg@mail.gmail.com>:
> On Tue, Aug 30, 2022 at 3:22 PM Ulrich Windl
> <Ulrich.Windl@rz.uni-regensburg.de> wrote:
>>
>> >>> Danny Mayer <mayer@pdmconsulting.net> schrieb am 30.08.2022 um 00:37 in
>> Nachricht <69f413e8-793e-fc9d-849f-6c5971bd2e90@pdmconsulting.net>:
>>
>> > On 8/24/22 1:54 AM, Ulrich Windl wrote:
>> >>>>> Heiko Gerstung <heiko.gerstung@meinberg.de> schrieb am 23.08.2022 um 12:21
>> >> in
>> >> Nachricht <DA1F1664-8A84-4197-844A-CA7E8DAA36B8@meinberg.de>:
>> >>> One way of avoiding/detecting loops:
>> >>> - upon startup, an NTPv5 instance creates a random 64bit ID
>> >>> - we add a loop detection EF that can include n IDs (or we use n EFs)
>> >>> - a stratum one server, when ask for his "sync trace", responds with only
>> >>> his ID
>> >> Considering that a stratum-1 server may have more than one reference clock
>> >> (say m) to pick, I think a stratum-1 server should actually prepare one ID
>> > per
>> >> reference clock. It's a design issue whether to return one ID that is
>> > different
>> >> for each clock (see below), or two IDs (server's + clock's).
>> >
>> > No need. When it's a stratum-1 server the referenceID in the packet
>> > indicates the clock being used. See RFC5905 Figure 12.
>>
>> But if the Reference ID for all GPS clocks would be "GPS ", wouldn't he new 
> "loop avoidance" algorithm consider all those to be the same source, thus a 
> loop? So we could not have redundant GPS sources any more???
>>
>> Regards,
>> Ulrich
>> ...
> 
> No, the loop avoidance algorithm only rejects a source if that source
> depends on the node itself. So, when having 4 servers A B C and D, if
> server A is a stratum 1 server, and servers B and C sync to server A,
> server D can still use all of A,B and C to synchronize. However,

My point was a bit different: Assume a to D are stratum-1 servers fed by one GPS clock.
If you configure E to get time from a to D, would E accept more than one of those servers as they are seemingly all fed from the same source, namely GPS? If I understood the rules corretcly, and if there is no exception for Reference-IDs that specify a clock, only one source should be used.

> suppose it uses all 3, then at that point, it will no longer be
> accepted as a potential time source by node B or C, because these then
> see they were part of the source of D, and therefore reject.
> 
> Kind regards,
> David Venhoek
> 
> 
>>
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