The direction of the query. A normal lookup goes from a name to an address through
A and
AAAA records, and the site owner controls it. A reverse lookup goes
from an address to a name through
PTR records, and the
network owner controls
it, not the website owner. That single difference explains most of what looks strange here: a name
under a hoster's pattern such as
srv12.hoster.example says who runs the machine, and
says nothing about which website is on it.
No PTR answer is a normal result. Nobody is obliged to create a reverse name, and
most address blocks never do. An empty answer means the owner left it blank or that the answer was
removed, not that the address is unused or doing something wrong. It also travels through the normal
cache, so a recently added name can take a while to appear everywhere.
Why the neighbours are interesting. Address blocks are handed out in ranges, and the
smallest range a customer usually holds is a
/24 — 256 addresses. Hosters name
those addresses in a scheme, so reading a handful of names around one address often shows the pattern
and the provider behind the whole block. This page asks about the addresses nearest to yours first,
inside the same
/24, and never goes looking for names that are not addresses.
What it does not mean. A reverse name is not a website name: the name in the answer
may belong to a router, a mail relay or a load balancer rather than to any site. One address can serve
hundreds of unrelated sites, and one large site can spread over dozens of addresses, so a shared name
is a hint about hosting, never proof that two things are related. Treat the neighbours as a naming
pattern, not as a list of owners.
Cost, and why the neighbour list is slow. Every address in the list is a separate
query against the same resolver allowance the other pages use, and the list runs one address at a time
with a gap between items to stay inside what public resolvers accept. A full list therefore takes a
while, and you can cancel it: the remaining addresses are dropped without leaving anything running.
What this page does not do. No dictionary brute force, no range scanning, no port
probing and no registration data lookup. If an address has no reverse name and you want to know whose
network it sits in, the honest next step is the
IP Lookup page, which reads
the network and location fields that public services do publish, and the
Subnet Calculator, which shows the block boundaries of that
address without sending anything anywhere.
Public sources you can read yourself. The authoritative record of who holds an address
range is kept by the regional registries: the
IANA IPv4 address space
and
IANA IPv6 unicast assignments
files list which registry received each block, and each registry then publishes its own delegation
records. This page deliberately does not query those files: they are a separate, heavier kind of
query, and reading them by hand from the links above is the honest way to answer “whose network is
this”.
