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

[Danny Mayer <[e-mail]>]

On 8/30/22 4:51 PM, Hal Murray wrote:
> [e-mail] said:
>> 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, 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.
> That brings up an interesting point.
>
> What does loop mean?
>
> The draft for NTPv5 is only the wire protocol.  It doesn't cover what goes on
> inside a server.  If a server latches on to the best upstream server and only
> uses any others for checking, then the topology is simple and loop would be
> easy to define.
>
> Is that a reasonable assumption?  Do we need a section in the draft to collect
> assumptions about the internals of servers?
NTP is not just about the on-wire protocol. The analysis and the 
algorithms within the server are integral parts of NTP. I have no idea 
what you think are the assumptions in the internals of servers.
> Consider the alternative where a server does some sort of weighting on the use
> of its upstream servers.  What does stratum mean?  Is loop well defined?
>
> ------
>
> Do we want 2 different client/server packet modes/formats?  One for
> leaf-clients (SNTP) and another for the client side of servers?  Or maybe the
> same packet format but different descriptions of the way fields are used.
>
> Or maybe even 2 separate RFCs.  The idea being that SNTP will be much easier
> to understand and we can target it for a longer lifetime.  In particular, it
> wouldn't have to say anything about loop detection.
>
The only real difference between NTP and SNTP is that a SNTP client is 
not a server and does not provide NTP packets to another system.

Danny