[dns-operations] Ultra DNS responding with NXDOMAIN for "www.uber.com"

[Dave Lawrence]

I agree with Viktor that the parent should have delegation records for
the same-server child, but note that response with the rcode NXDOMAIN
for a CNAME chain shouldn't be causing a problem for a modern
resolver.  A resolver should restart query processing with the target
of each CNAME in the chain, and ultimately come to its own conclusion
about whether the target at the end of the chain exists.

I suspect that this issue existed for a while and the lack of
screaming about it hints to me that for the vast majority of clients
things continued to work fine.  FWIW, from my network vantage point,
when querying edns126.ultradns.com for type A directly I get a
response that has rcode NOERROR and terminates the chain with an
address record.

Shreyas, did you encounter a production resolver that was having a
problem with chain/NXDOMAIN response?