Hal Murray via devel writes: > devel@ntpsec.org said: >> Provided you somehow route the packets from different networks to different >> (virtual) interfaces, you could measure and eventually compensate the >> asymmetry associated with that particular network provided you have some >> trusted time server on each side of the asymmetry. > > There is a tangle between interface and routing info. An interface can be > asymmetric. But the asymmetry can also be one or more hops away. You might > be able to catch that case based on IP address.
That's what I'd do by routing said packets to different virtual interfaces. > This could turn into a bottomless pit. There could be a router on the far > end of an asymmetric link that routes to many CIDR blocks. Yes. The general case is _really_ complicated and ugly and would need some different protocol than NTP to solve properly. It's doable approximately if you have enough sources of "good enough" absolute time that feed NTP servers on many network nodes (a properly set up and maintained GPS-based stratum 1 chimer is "good enough" in that it should have a smaller error than the inevitable noise from other sources). I think there's one paper that calls this "network tomography", based on the deconvolution of sorts you'll have to do to figure out the delays. For instance, I see much larger temporal variability of these asymmetric delays to the PTB servers for some time now. It seems the packets are now going through some software defined routing mess from Telia for me (which is also almost twice as long as the shortest network path). I know it's the routing since I can see this from five GPS-backed servers which I can correlate to each other. That also shows me that there is some sort of round-robin load-balancing going on for the three public facing servers. Last but not least I can see when I'm using up the bandwidth fully on my connection. Regards, Achim. -- +<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+ Factory and User Sound Singles for Waldorf Blofeld: http://Synth.Stromeko.net/Downloads.html#WaldorfSounds _______________________________________________ devel mailing list devel@ntpsec.org http://lists.ntpsec.org/mailman/listinfo/devel
