Re: [Ntp] NTPv5 Loop Detection without Stratum

[Miroslav Lichvar <[e-mail]>]

On Tue, Aug 23, 2022 at 12:21:19PM +0200, Heiko Gerstung wrote:
> 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
> - a stratum two server would add its own ID to the ID of its upstream server, responding with a sync trace of two IDs
> - a stratum 1+n server would respond with the sync trace of its upstream source(s) plus its own ID 
> - if you use more than one upstream source, you can respond with a list of all IDs from the sync trace of all your upstream sources (removing duplicates)
> - by checking if your own ID is in the sync trace of your upstream source(s), you can find out if there is a loop

That was the original idea before Daniel Franke suggested to use a
bloom filter instead of a simple list. This makes the amount of
exchanged data constant and it can contain a very large number of
reference IDs before collisions can be expected.

-- 
Miroslav Lichvar