Re:Ask HN: How did internet discover my subdomain?
by dspillett on Friday March 07, 2025 @07:53AM
(#43289769)
That is when there is an explicit PTR record, for instance one of my assigned addresses can be named that way due to:
74.231.187.81.in-addr.arpa. 3600 IN PTR ns2.nogoodnamesareleft.com.
in the zone file for that IPv4, but unless they've explicitly configured, or are using a hosting service that does it without asking, this it won't be what is happening.
It isn't practical to do a reverse lookup from “normal” name-to-address records like
ns2.nogoodnamesareleft.com. IN A 81.187.231.74
(it is possible to build a partial reverse mapping by collecting a huge number of DNS query results, but not really practical unless you are someone like Google or Cloudflare running a popular resolution service)
It isn't practical to do a reverse lookup from “normal” name-to-address records like
(it is possible to build a partial reverse mapping by collecting a huge number of DNS query results, but not really practical unless you are someone like Google or Cloudflare running a popular resolution service)