[atlas] Trying to measure Quad9 latency

Hi,

I think there may be some confusion here. Let me try to clarify a bit.

*  For RTT measurements, use DNS queries (ICMP may get lower priority).

> I think Quad9 uses round robin dns with server pools (3?) behind 9.9.9.9
> anycast address: 
> 
> My findigs: 
> 
> $ for i in $(seq 0 9); do echo -n "$i "; dig +short @9.9.9.9
> <http://9.9.9.9> hostname.bind txt CH; sleep 3; done
> 
>  0 "res300.ams.rrdns.pch.net <http://res300.ams.rrdns.pch.net>"
>  1 "res300.ams.rrdns.pch.net <http://res300.ams.rrdns.pch.net>"
>  2 "res100.ams.rrdns.pch.net <http://res100.ams.rrdns.pch.net>"
>  3 "res200.ams.rrdns.pch.net <http://res200.ams.rrdns.pch.net>"
>  4 "res200.ams.rrdns.pch.net <http://res200.ams.rrdns.pch.net>"
>  5 "res200.ams.rrdns.pch.net <http://res200.ams.rrdns.pch.net>"
>  6 "res300.ams.rrdns.pch.net <http://res300.ams.rrdns.pch.net>"
>  7 "res200.ams.rrdns.pch.net <http://res200.ams.rrdns.pch.net>"
>  8 "res300.ams.rrdns.pch.net <http://res300.ams.rrdns.pch.net>"
>  9 "res300.ams.rrdns.pch.net <http://res300.ams.rrdns.pch.net>"

Typically anycast services are build as  in Figure 1[1]: a anycast
service (such as Quad9) is distributed across sites. In your example,
the site is AMS. On each site, they may use a load balancer that sends
the queries (section 3.5 on [1]) to individual servers (res100, res200,
and res300 in this case).

How, from your measurements, you reach AMS all the time. You can not
control for that, because that is what BGP does: matches you the
"closest" site (closest meaning in terms of BGP distance between you and
quad9).

If you want to see other anycast sites from Quad9, you'll need to
measure from other vantage points (using Atlas for example).

And anycast is quite stable during normal operations[2]: once you reach
a site, you'll tend to stick to it -- unless there's a DDoS or routing
manipulations, as in [1].



> ... Quand9  dns server are not created equal:
> 
> $ for i in $(seq 0 9); do echo -n "$i "; dig +short @9.9.9.9
> <http://9.9.9.9> version.bind txt CH; sleep 3; done
> 

Diversity of version , maybe. For resiliency.

/giovane


[1] https://www.isi.edu/~johnh/PAPERS/Moura16b.pdf
[2] https://www.isi.edu/%7ejohnh/PAPERS/Wei17b.pdf