on IIS gethostbyaddr take 4 seconds

Hello

with IIS, I have problem, that if IP address has none reverse dns record, it take 4.5 seconds until php can process it by GetHostByAddr($ip).
If IP has reverse hostname, answer is instant.

I do not understand why, because on another linux shared server I do not have this issue.

What is most curious, I tried that IP address via nslookup with all DNS in my network, and response is instant (response is of course that there is no hostname for that IP).

So question is, where or what is causing this delay? How can I configure php.ini to just ask DNS servers and nothing else?

many thanks