default host detection

Hi
If I run the command

nmap -p 445 1.2.3.4

what host detection should nmap use to decide if the host is up before it
checks the ports? I would have assumed that one of the checks would be to
ping it but if you look at the attached screenshot, I ping the host and get
a reply, nmap then says that it is down, I ping again, still have replies,
I then scan with -P0 and I get the response I'm expecting, that the port is
open.

Why do I have to force the host to be up?

Robin

[image: nmap_no_ping.png]