I have a VPS that I was scanning to make sure everything is in check. A regular SYN scan reports that ports 25 and 80 are open (which they should be). When I run an idle scan however, I get back that all 1000 ports scanned are closed|filtered. I have tried the SYN scan and the idle scan on a few other servers and also have tried different zombies when doing an idle scan.
On another server I was testing this against, it had about 9 ports open but, again, the idle scan showed that all 1000 ports were closed|filtered.
Any ideas on why this is happening? I've read over the documentation about the idle scan and understand that it cannot determine the difference between a closed and filtered port due to the way it works, but since these servers have ports open I don't understand why the idle scan is picking them up as either closed or filtered.