Hi DNSOP,

A few months ago, Puneet Sood, John Todd, and I proposed "probe.resolver.arpa" 
as the standard name for DNS resolver reachability probes [1].  Since then, my 
team has done a sizeable test deployment (several thousand clients), in a 
situation where we were probing the reachability of Google Public DNS using 
IPv4 and IPv6.

In the old configuration, clients were probing reachability by querying for "A" 
records at "www.google.com".  In the new configuration, clients were querying 
for "A" records at "probe.resolver.arpa".

The results show that the new reachability probes behave exactly as expected, 
or perhaps even better:

* The success/fail rates and error distributions are identical.
* The response latency is highly correlated, but 8 milliseconds faster on 
average.  We believe this is due to a "fast path" in Google Public DNS when 
synthesizing  NXDOMAIN responses under "resolver.arpa".

I would like to see this draft progress to RFC in order to formally reserve the 
target domain.  Otherwise, probers that expect NXDOMAIN could be confounded 
when records are added.  Given the rather trivial scope of this draft, I think 
AD sponsorship could be appropriate, but DNSOP adoption would also be welcome.

--Ben Schwartz

[1] https://datatracker.ietf.org/doc/draft-sst-dnsop-probe-name/
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