how nmap can know my firewalled servers ?

Hi all !

I know that "nmap" can show open ports. But nmap also shows my
firewalled ports !

Since some servers (like apache) are firewalled with iptables, how can
nmap know wherever
my system run the service with open port, filtered port or doesn't run
it at all ?

Relevant Pages

  • FW: Nmap time-out issue.
    ... In this section is located the host-timeout condition and if the host reaches the timeout, nmap doesn't show the report of the open ports, even if in that moment nmap had detected open ports. ...
  • Re: nmap -S option
    ... nmap does not show open ports at end of scan. ... In many cases, this can be attributed to fact that in order to be able to distinguish a closed port from an open one, NMAP actually needs to see the replies from the scanned machine... ... The other cases include the packets being dropped by some device on their way to / from the scanned machine. ... Cenzic Hailstorm finds vulnerabilities fast. ...
  • Re: nmap -S option
    ... so the replies are going back to that spoffed address. ... Because when i use nmap with "nmap -sS targetaddress", nmap shows me open ports at the end of scan. ... Cenzic Hailstorm finds vulnerabilities fast. ...
  • Re: Installer inadequacies
    ... sometimes about someone trying to hack into it when I access the there some security measures I can ... use a portscanner like nmap to test for open ports and close them if not needed ...
  • Re: Pentest - ISA server
    ... of them have over 50000 open ports. ... What options did you use on NMAP? ... opened TCP sessions - but then again this will trigger connect messages ... Information Assurance Certification Review Board ...