nx.dnsp.co
A name that is guaranteed not to exist.
What it does
nx.dnsp.co and everything under it answer NXDOMAIN, which is what a non-existent name is supposed to give. nxdomain.dnsp.co is the same test under a longer name, in case something in your path treats the short one specially. Providers that monetise typos replace that failure with an address pointing at a search or advertising page.
Example
$ dig nx.dnsp.co
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN
;; ANSWER SECTION: empty
Reading the answer
NXDOMAIN, no answer section
Failures are being passed through honestly.
an IP address
Your provider is overloading failed lookups with a landing page.
NXDOMAIN with a long lifetime
Harmless, but it means the failure will be cached for a while.
Notes
- Any label works: random123.nx.dnsp.co behaves the same.
- Browsers hide this behaviour, so test from the command line.