I am trying to determine if hosts are up. For hosts where a ping fails, I run a Nmap (6.40) Regular and/or Quick Scan. For a subset of my hosts, the Nmap response is "Host seems down". As a follow up per the Nmap response, I run the no ping port scan -Pn.
For the -Pn scans, on the 10-15 different hosts I have tried, the response is always: Host is up. All 1000 scanned ports on x.y.z are filtered. Nmap was done: 1 IP address (1 host up) scanned in 205.37 seconds
My question is if the ports are in a filtered status, why is Nmap returning "Host is up"?. I would have guessed that the status returned would have been "Host seems up" or "Unknown". Has Nmap verified that the host is up, and if so, how does Nmap determine that the host is up?
These are the commands I executed:
nmap hostname => Regular Scan nmap -T4 -F hostname => Quick Scan nmap -Pn hostname => No Ping Scan