mismatch.dnsp.co
An answer of deliberately the wrong type.
What it does
This name answers an address query with a TXT record. Nothing should do that, so it is a clean way to see whether anything between you and us inspects and filters responses that do not match the question.
Example
$ dig @dnsp.co mismatch.dnsp.co A
;; ANSWER SECTION:
mismatch.dnsp.co. 0 IN TXT "TXT-ANSWER-TO-A-QUERY"
Reading the answer
the TXT record
Nothing filtered it, which is normal when asking us directly.
an empty answer
A recursive resolver stripped it. Most do, and that is correct behaviour.
Notes
- Compare against cname.dnsp.co, which every resolver passes through. If both are stripped, the path is rewriting heavily.